What Is Beyond The Observable Universe?

[Silverbackman]

Is it just black space extending forever? Or perhaps black space for a finite distance until another universe?

I find it hard to believe our universe is just the only universe. I don't see how it wouldn't extend for eternity instead. What is so special about our universe and the space we are in?

What do you think?

[Chronos]

By logical necessity, there is literally 'nothing' beyond the observable universe. It is impossible to apply falsifiable predictions to something that is inherently unobservable.

[Silverbackman]

By logical necessity, there is literally 'nothing' beyond the observable universe. It is impossible to apply falsifiable predictions to something that is inherently unobservable.

In other words it is more in the realms of philosophy right now. But don't you think in the future we may be able to see beyond what is now considered the observable universe and find other universes? What do you think?

It just doesn't make any sense how this universe could be the only one. I always thought of the universe/multiverse/omniverse as infinite.

If there is 'nothing' outside the observable universe it would be just black space for eternity, right? Unless the universe is round (which all current evidence points to it being flat) then you can't arrive back in the universe in the other side. Plus most likelly space, like "time" is infinite.

[mathman]

According to the inflation model, the universe is much bigger than the observable universe. On the other hand, the total universe is is still finite, but there is no such thing as outside. The simplest analogy is what is outside the surface of a sphere (ingnoring the third dimension).

[Silverbackman]

But most evidence points to the universe being flat. In that case a what would happen if you reach the end of the universe? If it were a spherical universe then we would just reach the other side. But what would happen if you reach the end of the universe? Would their be like a giant hard barrier that you can hit but not explode? Sounds to mythical to me. The universe seems to complex for it to be just finite.

The universe isn't infinitely big and infinitely small?

[Chronos]

The 'edge' of our observable universe is receeding faster than the speed of light: which means you can't get there from here.

[Silverbackman]

The 'edge' of our observable universe is receeding faster than the speed of light: which means you can't get there from here.

Well yea of course we can't really see it. However is that proof there is nothing beyond there? What proof is there that 'nothing' exists at the edge of the observable universe? We just can't see it from our place in the cosmos. Perhaps if we were on another planet across the universe we may be able to observe more into what we cannot currently see, right?

[kant]

By logical necessity, there is literally 'nothing' beyond the observable universe. It is impossible to apply falsifiable predictions to something that is inherently unobservable.

What do you mean by "logical necessity"?

I think there is something that cannot be explain 'outside' space-time of own universe, but that is a different assertion of "nothing"?

[Chronos]

Let's focus on the definition of a 'universe'. It necessarily includes all things possible to observe. This allows the possibility we have not yet observed all things possible to observe. In that sense, anything that is truly external to our observable universe is literally 'nothing'. It is, and will forever be undefinable.

[Silverbackman]

Our guess the space and time in our universe is finite. However it is just hard to believe there was no time before the big bang and no content beyond our observable universe. It doesn't make sense how things can by finite. I mean what happened before the big bang and why are there boundaries at the ends of our universe?

By studying the universe and the physical world one can truly see things aren't orderly per se. They far beyond the realms of organized imagination and can only be understood with observation and empiricism. Limits on the universe would truly make things beyond confusing.

BTW, what do scientists think happened before the big bang. Since the universe is expanding according to most of the evidence today, the cyclical big crunch is unlikely. What do scientists think are the likely choices?

[kant]

Let's focus on the definition of a 'universe'. It necessarily includes all things possible to observe. This allows the possibility we have not yet observed all things possible to observe. In that sense, anything that is truly external to our observable universe is literally 'nothing'. It is, and will forever be undefinable.

You define 'everything' to be the observable universe( U ), and anything that is not U is nothing. Am i talking to a robot, or am i talking to a human being?

[Chronos]

Just dealing with the logical inconsistencies. 'U' includes the set of events possible to observe in this universe. 'Not U' includes the set of events impossible to observe. 'Not U', hence, is not causal in the chain of events that occur in this universe. 'Not U', therefore, is irrelevant [i.e., does not exist].

[kant]

Just dealing with the logical inconsistencies. 'U' includes the set of events possible to observe in this universe. 'Not U' includes the set of events impossible to observe. 'Not U' has no effect on the causal chain of events that occur in this universe. 'Not U' is therefore meaningless [i.e., does not exist].

So if an 'event' occur outside of our spacetime; its effect is incapabe of reaching us. In your opinion, it does not exist?

Why should existence need an observer?

[selfAdjoint]

So if an 'event' occur outside of our spacetime; its effect is incapabe of reaching us. In your opinion, it does not exist?

Why should existence need an observer?

Listen to yourself! Do events we can never know about exist or not? How the hell can you or I or anyone ever know? It's just a fantasy!

[kant]

Listen to yourself! Do events we can never know about exist or not? How the hell can you or I or anyone ever know? It's just a fantasy!


What is your point? Your last three sentence seems to be in agreement with me.

[SpaceTiger]

But most evidence points to the universe being flat. In that case a what would happen if you reach the end of the universe? The generic flat universe (with a trivial topology) is actually infinite in extent. Other topologies allow for a finite universe, in which one could (in theory) loop around it, given enough time.

[SpaceTiger]

...why are there boundaries at the ends of our universe?

The only boundaries are those set by the finite age of the universe (also known as "horizons"). For example, the "particle horizon" is the distance of the largest object whose light could have reached us since the beginning of time.


what do scientists think happened before the big bang. Since the universe is expanding according to most of the evidence today, the cyclical big crunch is unlikely. What do scientists think are the likely choices?

In the standard cosmological model, there is no "before" the Big Bang. Realistically, though, we can't say much of anything about the universe pre-inflation, so the best answer is that we don't know.

[heliocentricprose]

I believe that more stars, black holes, and galaxies lie beyond the observable universe. These unseen do not effect us because of the cosmic expansion. However, (I think this has been said before) I like to think of the observable as a line of sight. You can't see it over the horizon, yet you know China exists. Outside that 'sphere' of the universe, I believe, out of pure guesswork and fantasy (of course), that the other dimensions of the universe, come into play... this is the point where I start confusing myself and start watching Spongebob Square Pants. :) Good day.

[hejs]

If we travel infinitely far into the microcosmos then we will meet the astronaut who travel infinitely far out to the macrocosmos. Sound good at least :)

[Tojen]

Isn't space created by matter? If that's the case, there should be nothing past the boundaries of the Universe, at least nothing we can perceive or relate to in any way.

[kmarinas86]

Isn't space created by matter? If that's the case, there should be nothing past the boundaries of the Universe, at least nothing we can perceive or relate to in any way.

No, the majority of physicists think it is created by "dark energy", but its not really the creation of space, it's the expansion of it.

[kant]

So, i guess the robot is giving me the silent treatment.

[Tojen]

No, the majority of physicists think it is created by "dark energy", but its not really the creation of space, it's the expansion of it.

kmarinas86,

What I meant to say was that you can't have space without matter, and vice versa. At least that's my uneducated take on it. I didn't know dark energy was considered to be the cause of space, or its expansion. I learned something already. Thanks. :smile:

[matt.o]

dark energy is not the cause of space, nor is it the cause of the expansion of space. Dark energy is thought to cause the acceleration of the expansion of space.

[roland]

Beyond the observable universe is the unobserved universe that we have yet to see. It simply goes on forever. If it is not infinite, where does it end? Think about it. It cannot possibly end.

[Chronos]

Beyond the observable universe is irrelevant. It has no consequences in our observable universe. This is a philosophical, not scientific issue.

[roland]

Hi Chronos. Yes you are right. However I do feel that this is a very negative answer to the original question.

[Chronos]

Agreed. But, I am sticking by my guns: non-observables are irrelevant.

[Silverbackman]

Chronos you do have a point. However just because this question overlaps a bit with philosophy it doesn't mean it is totally not science. We have no observable evidence that aliens exist, but nearly all scientists know even without observation that there has to be other life in the galaxy (or at least the universe).

So what would happen if you were to go theoretically in a space ship beyond the observable universe? If space is more than empty space and you do keep going in black space, then I assume there definitely is something beyond this observable universe. I assume there maybe other universes perhaps billions of "light years" away.

I mean what else can explain the ends of the universe? It wouldn't make much sense to bump into a barrier would it? We see the ends of the universe as just black space, correct? There is no proof it is nothing more than just black space.

[Silverbackman]

The only boundaries are those set by the finite age of the universe (also known as "horizons"). For example, the "particle horizon" is the distance of the largest object whose light could have reached us since the beginning of time.




In the standard cosmological model, there is no "before" the Big Bang. Realistically, though, we can't say much of anything about the universe pre-inflation, so the best answer is that we don't know.

When we say "beginning of time" we really mean when this current manifest of particles arose, correct? We refer to time as light years traveling back to the big bang but I assume time in its broadest sense has existed for infinite and while the universe(s) may manifest have a finite time span (but in reality an infinite lifespan because of the perhaps cyclical constant flux). This also gets into philosophy as well.

[SpaceTiger]

When we say "beginning of time" we really mean when this current manifest of particles arose, correct?

We technically mean the time when the density of our cosmological model diverges (the initial singularity). On a linear timescale, this would appear coincident with the creation of matter, but we usually describe the evolution of the universe on a logarithmic scale.



We refer to time as light years traveling back to the big bang but I assume time in its broadest sense has existed for infinite and while the universe(s) may manifest have a finite time span (but in reality an infinite lifespan because of the perhaps cyclical constant flux). This also gets into philosophy as well.

In the standard model, there is a finite age to the universe if one uses the standard definition of time (a ticking clock, for example) for an observer with no velocity in comoving coordinates.

[kant]

Agreed. But, I am sticking by my guns: non-observables are irrelevant.


An apple falls from a tree, and there is no one to hear or observed the occurence. That does not negate the occurence of that event(apple falling) . I think you need to use your brain more, and stop pretending to be a robot.

[heliocentricprose]

An apple falls from a tree, and there is no one to hear or observed the occurence. That does not negate the occurence of that event(apple falling) . I think you need to use your brain more, and stop pretending to be a robot.

I agree. Cosmology is the study of the universe as a whole. Since the expansion of the universe is greater than the speed of light(the speed of information in the universe), we will gradually be able to observe less and less of the universe. I don't think that means we should abandon the unobservables and work only in our 'tiny' seemingly uniform patch of space. Who knows? Maybe someday there will be a way to 'see' past the horizon.

[Burnsys]

I think this link is usefull to the thread.. it talks about inflation

http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec28.html

http://abyss.uoregon.edu/~js/images/inflation.gif

Only the part of the universe that is inside the observable universe is "OUR universe".
Becouse space expanded faster that ligth we won't be able to "observe" anything beyon the age of the univers in light years (15 billons)

Anything else, exist or not, is irrelevant, becouse we will never be able to observe it.

In other universes with diferent rules, constants, dimensions etc (if they exists) the action of observe may doen't even make any sense.


http://abyss.uoregon.edu/~js/images/anthropic_bubbles.gif

[Burnsys]

I agree. Cosmology is the study of the universe as a whole. Since the expansion of the universe is greater than the speed of light(the speed of information in the universe), we will gradually be able to observe less and less of the universe. I don't think that means we should abandon the unobservables and work only in our 'tiny' seemingly uniform patch of space. Who knows? Maybe someday there will be a way to 'see' past the horizon.

How do you "Study" something you can't interact with????

[Silverbackman]

How do you "Study" something you can't interact with????

We may not be able to observe it at the moment but we need to make the assumption something is there. We have never seen life outside our planet but we assume it exists and create ways to seek out and prove it. A similar thing should be done in cosmology. We should be making insturments that can help us study the beyond.

I think this link is usefull to the thread.. it talks about inflation

http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec28.html

http://abyss.uoregon.edu/~js/images/inflation.gif

Only the part of the universe that is inside the observable universe is "OUR universe".
Becouse space expanded faster that ligth we won't be able to "observe" anything beyon the age of the univers in light years (15 billons)

Anything else, exist or not, is irrelevant, becouse we will never be able to observe it.

In other universes with diferent rules, constants, dimensions etc (if they exists) the action of observe may doen't even make any sense.


http://abyss.uoregon.edu/~js/images/anthropic_bubbles.gif

Yes it maybe irrevelent and these other universes may contian different laws of Nature. However like alien life, I do think we will be able to learn about it in the future. We shouldn't give up. No one has ever seen a quark (correct me if I'm wrong) but we assume the microverse goes further.

If we had a space ship that can do this, what do you think it will run into at the ends of the universe? Will the space ship keep going or is it constricted to this universe only? What do you think?

[Burnsys]

An apple falls from a tree, and there is no one to hear or observed the occurence. That does not negate the occurence of that event(apple falling) . I think you need to use your brain more, and stop pretending to be a robot.

An apple falls from a tree and there is no one to hear or observe...
You have absolutly no way of knowing what "Reality" is... You will never know if the apple felt, or not, or if it exploded or get rotten...
With the same criteria i can say that beyond the observable horizon dragons fly and spit fire..

[SpaceTiger]

Let's keep in mind here that the part of the universe outside our "observable universe" is not completely disconnected from us. We're causally connected to it prior to inflation, so we have some inkling that it exists. There are, however, events that may never be observable. If the universe continues accelerating indefinitely, then a supernova outside of our horizon will never be observable from earth (or what remains of it). We could, however, potentially observe a much younger version of the part of the universe where the supernova occurred. Without being able to see into the future, however, we can't say for sure whether or not the supernova itself will someday be observable.

[Burnsys]

We may not be able to observe it at the moment but we need to make the assumption something is there. We have never seen life outside our planet but we assume it exists and create ways to seek out and prove it. A similar thing should be done in cosmology. We should be making insturments that can help us study the beyond.
But you can't make an instrument to see beyond the observable universe, unless you can travel faster than the speed of light.



Yes it maybe irrevelent and these other universes may contian different laws of Nature. However like alien life, I do think we will be able to learn about it in the future. We shouldn't give up. No one has ever seen a quark (correct me if I'm wrong) but we assume the microverse goes further.

If i am not wrong, yes, we can see quarks in particle accelerators. But anyway if we can't "see" them directly we can see their trace becouse they interact with matter or energy we can observe...



If we had a space ship that can do this, what do you think it will run into at the ends of the universe? Will the space ship keep going or is it constricted to this universe only? What do you think?


i don't think there is a "Wall" at the end of the universe, i don't think it has a boundary. We live in a finite and unbounded universe. i guess if you start traveling lets say at. 0.99c for 15 billion years even if there is a boundary you will never be able to reach it. becouse the universe is expanding faster than c.

[kant]

An apple falls from a tree and there is no one to hear or observe...
You have absolutly no way of knowing what "Reality" is... You will never know if the apple felt, or not, or if it exploded or get rotten...
With the same criteria i can say that beyond the observable horizon dragons fly and spit fire..

i will play along with you, burnsys ( anyone can reply to me)

ok, we will use your analogy. Beyond the obversable universe, there is simply no way to confirm the existence of the dragon fly with a simple yes, or no answer. In otherword, the dragon fly ` s existence is uncertain. It is an unverifiable statment.The statement of the existence of the dragon fly is one that cannot be derived/answered/perdicted by the known axioms/"laws of nature". This doesn` t imply the non-existence of the dragon fly.

[Silverbackman]

But you can't make an instrument to see beyond the observable universe, unless you can travel faster than the speed of light.





If i am not wrong, yes, we can see quarks in particle accelerators. But anyway if we can't "see" them directly we can see their trace becouse they interact with matter or energy we can observe...




i don't think there is a "Wall" at the end of the universe, i don't think it has a boundary. We live in a finite and unbounded universe. i guess if you start traveling lets say at. 0.99c for 15 billion years even if there is a boundary you will never be able to reach it. becouse the universe is expanding faster than c.

Who knows, one day we may be able to make a tool that can travel more than the speed of light. Nothing is impossible. I'm sure if we were to go back in time back to when the Greeks tried to understand the universe, they probably would be quite blown away by the things we can do now and the information we have received from it. Back then it was thought that the Earth was one of the only worlds and that every other "light spheres" revolved around it. Similarly today we think that this universe maybe the only universe but I don't think we could ever know everything for sure. Science and learning is infinite and perhaps the goal of life in the end.

If the universe is unbounded I don't see how it can not be apart of a greater multiverse, don't you think? Ok perhaps our own universe is finite in terms of the extent of matter and particles, but apart of an absolute "omniverse" that may extend forever like the microverse perhaps.

So let us say you could theoretically travel beyond the speed of light, you do agree there wouldn't be a "barrier wall". Or universe will continue to expand forever and who knows, billions of years down the line it may expand into a different universe. What do you think?

[heliocentricprose]

An example of the relevance of the unobservable part of our universe is the total mass of universe. I think this and other characteristics of the universe need to be taken into account when studying cosmology. The fact remains, as already said, the observable universe IS affected by the unobservable universe. Gravity waves that have not yet reached us (because of the horizon), will affect us if inflation's acceleration ceases in the future.

Also, I have a question. The rate of expansion is accelerating, which implies that it is never constant. Is it plausible that it can slow down?

[kant]

Who knows, one day we may be able to make a tool that can travel more than the speed of light. Nothing is impossible.

In a irrational universe, everything is possible, there would be not laws of nature, and no science at all. The otherwise option is that universe is rational, and certains things is impossible.




I'm sure if we were to go back in time back to when the Greeks tried to understand the universe, they probably would be quite blown away by the things we can do now and the information we have received from it. Back then it was thought that the Earth was one of the only worlds and that every other "light spheres" revolved around it. Similarly today we think that this universe maybe the only universe but I don't think we could ever know everything for sure. Science and learning is infinite and perhaps the goal of life in the end.

Don t play drama with me. Science is very limited, because mainly sceinctist define the universe as being U. U = space+time+ energy. Physics as a science is limited by empirical observation, and to go beyond observation or U is not allowed.



If the universe is unbounded I don't see how it can not be apart of a greater multiverse, don't you think?

mutiverse is not physics.

Ok perhaps our own universe is finite in terms of the extent of matter and particles, but apart of an absolute "omniverse" that may extend forever like the microverse perhaps.

You ask your god. this cannot be answered by physic

[Chronos]

Nonsense. Your 'God' of logic appears to have feet of clay.

[kant]

^ what are you talking about now?

[Silverbackman]

In a irrational universe, everything is possible, there would be not laws of nature, and no science at all. The otherwise option is that universe is rational, and certains things is impossible.



You know there are ways around the speed of light like strings or wormholes. Science's is goal is to find the laws of nature yes. But finding ways to go around the laws of nature can be achieved. Gravity is a fundamental force that seems like we cannot overcome. However in the future anti-gravity maybe very possible. Seems like you’re dogmatic about science.

Don t play drama with me. Science is very limited, because mainly sceinctist define the universe as being U. U = space+time+ energy. Physics as a science is limited by empirical observation, and to go beyond observation or U is not allowed.


Don't know how what I said was "drama". But if you do know anything about science there are many concepts in the past that weren't observable at first but later became observable. Dark matter seems invisible, so should we give up looking for dark matter just because we don't have tools right now? Science changes from time to time and soon we will find a way to do this I'm sure.

mutiverse is not physics.

Yes "mutiverse" is not physics. Multiverse will become physics in time perhaps like black holes and perhaps even dark matter. M-theory, which is a theory in development definitely shows that their maybe other universes.


You ask your god. this cannot be answered by physic

In time it can be known. Who knows when but with negative attitudes toward it like your own will definitely delay things.

[kant]

You know there are ways around the speed of light like strings or wormholes. Science's is goal is to find the laws of nature yes. But finding ways to go around the laws of nature can be achieved. Gravity is a fundamental force that seems like we cannot overcome. However in the future anti-gravity maybe very possible. Seems like you’re dogmatic about science.

You cannot go around the "laws", because they form the foundation for the perdictive system in physics. The "laws" are determined empirical, generalized, and must be accepted on faith( based on those generalization). If you want an analogy, if the statement "1+1 is not to 2 " is false, math would not exist, because all other mathematics that based on it would no longer be ture.


Don't know how what I said was "drama". But if you do know anything about science there are many concepts in the past that weren't observable at first but later became observable. Dark matter seems invisible, so should we give up looking for dark matter just because we don't have tools right now? Science changes from time to time and soon we will find a way to do this I'm sure.

You miss my point: science is limited.

If science is based on the axoimatic/"laws of nature" generalization of
nature, all there is that comes with the word "science" is open to doubt, as the foundation( fundamental generalization: physical law) that supports it.

Yes "mutiverse" is not physics. Multiverse will become physics in time perhaps like black holes and perhaps even dark matter. M-theory, which is a theory in development definitely shows that their maybe other universes.

Physic is not math. Physics is limitated by its empirical, observational nature. If we can t observe/verify an assertions for things that has no effect on us, it can t be established. strings, m- thory, multiverse ...etc might have nice sounding names, but they are not rooted in empirical observation.


In time it can be known. Who knows when but with negative attitudes toward it like your own will definitely delay things.

my point: What is 'outside' the universe is not something that could be verified. It is not possible to answer such questions.

There are inherent limitations to reasoning itself in science.

[Rake]

forgive me if I am mistaken, however does the principle of entanglement not imply that there is some kind of unobservable physical system that connects particles and if so does this not also imply that causality is not the final say on what we can ultimately glean from "reality" (whatever that means)? I understand that presently this argument is more of a phylosophical rather than scientific one...

[ianthow]

What if:

1) We cannot comprehend what is beyond this universe and someONE or someTHING prevent us from seeing beyond this universe? The science and technology that we all believe in says that it is impossible to see and go beyond this universe (e.g: the universe is infinite, there is no beginning and end, etc), why are all this "rules" in place at the begining? Can we comprehend what we don't understand?

2) If we can see beyond this universe, will it do more harm than good?

3) We are all creatures on Discovery Channel and are being study or observe by someONE or THING? How do we know that we are living in a world created not by random but with a purpose? And what is that purpose?

Science is truly limited in explaining the world beyond this universe, science is based on reasoning, logic, emphirical, observation. IF you do a search on "what is beyond this universe" on Google, you will find that most answers say "more universe" or "there is no beyond as the universe is infinite" or "nothing".

To really answer the question of what's beyond this universe, we have to think beyond science but then what if we are by default unable to think beyond as the someONE or someTHING who created us prevent us from thinking beyond? The answer might lie beyond the logic, reasoning and science that we are all familiar with.

[jon_pan]

to my understanding from research:
(people who know what they're talking about, please correct me if im wrong)


Current Big Bang cosmology defines universe as "everything that exists anywhere" "Finite and Spherical."


the big-bang and the extent of our observable universe is finite and spherical, but not necesarrily everything that exists. Our universe as far as we can observe, is one of an infinite amount of finite sphere's of matter, in an infinte space where time is eternal and continuous.

so to answer your question, i would say probably the same sh.it you see around here. (around here in a cosmological sense of course)

[Tojen]

ianthow,

There's a distinct odour of New Age-ism in your post. New Age "ideas" denigrate, at the same time, science ("we have to think beyond science") and religion ("the someONE or someTHING who created us prevent us from thinking beyond") to pave the way for its own agenda ("The answer might lie beyond the logic, reasoning and science...").

[patrik75]

Could it be that it is not a relevant question to ask? I am thinking of entanglement and distance as an "illusion". Right or wrong?

[Soul Surfer]

We may not be able to see directly or measure the properties of anything outside our observable universe but we can predict potential properies based on the fact that is probably made of the same "stuff" that our observable universe is made of. Bearing in mind of course that conditions may well exist where the current physical constants we observe may be tweaked a bit.

Or actual universe may well extend a long way beyond our observable universe but there is strong evidence that it had some sort of beginning, is evolving and changing with time and will eventually have an end.

This suggests that our universe is likely to be a finite object in a "multiverse" of indefinite extent.

We also have strong evidence that there are seperate "universes" budding from our universe in the form of black holes. This tends to strengthen this feeling that multiple universes exist.

This makes me favour an overall fractal structure for the multiverse in which the laws of physics have evolved to produce maximum numbers of structures of maximum longevity following the general rules of "evolutionary metaphysics".

You can find a bit more about this on my website but the basic thinking behind "evolutionary metaphysics" is to look at the processes that would operate in any system with physical laws, to create complexity by exploiting metastable and recycling processes to extend the life of what would otherwise be only transient and random intereactions.

[SpaceTiger]

We also have strong evidence that there are seperate "universes" budding from our universe in the form of black holes. This tends to strengthen this feeling that multiple universes exist.

What evidence is that? Last I heard, that was only speculation.

[Soul Surfer]

The evidence is purely in the properties of the object. Any activities inside an independant universe can by definition never be observable from our universe. All that can be done is theoretical modelling which is not subject to such barriers.

A black hole is a construct into which mass may pass and we will not be able to observe it altough it does have still an effect in the form of a gravitational field in our universe.

It is true that once our universe has cooled down sufficiently (a long time from now) the black hole will start to evaporate very slowly and will eventually vanish but the time that even a stellar mass black hole will take to do this is very many orders of magnitude longer than the current age of our universe.

Anything inside the hole will not be able to see out and will be largely unaware of the size of the space because the gravitiational field will tend to distort things so it looks very much larger. OK there may be a certain amount of high energy inflow from outside in the form of things that look like cosmic rays. but their source will not be detectable.

If that isnt a specification for an independant universe I don't know what is!

OK I will concede that it may well be possible to measure that the space is finite and see a retreating set of echoes of one's self at greater and greater distances like looking into a set of parallel mirrors but since when has that been a bar to declaring a universe. I am aware of at least three occasions in cosmology over the last hundred years or so when there was serious consideration that we might be able to do something like this in our universe (one of them is around now)!

[SpaceTiger]

The evidence is purely in the properties of the object. Any activities inside an independant universe can by definition never be observable from our universe. All that can be done is theoretical modelling which is not subject to such barriers.

Anything for which there is no observational test falls into the realm of philosophy and using words like "evidence" here is deceptive.

Perhaps pervect can give more detail, but to the best of my knowledge, the standard model of the universe and the standard model of a black hole are not compatible with one another unless one invokes a wormhole connection, which is in itself a matter of pure speculation.


A black hole is a construct into which mass may pass and we will not be able to observe it altough it does have still an effect in the form of a gravitational field in our universe.

The standard definition of a black hole gives it only three properties: charge, mass, and spin. The only property we think we've been able to measure so far (for some black holes) is mass. These measurements don't tell us anything about whether or not the black hole has spawned a new universe.



It is true that once our universe has cooled down sufficiently (a long time from now) it will start to evaporate very slowly and will eventually vanish

Based on what? An extrapolation of \Lambda CDM? There's no reason to think that the current model of the universe will be good for all time.



If that isnt a specification for an independant universe I don't know what is!

You've granted black holes and our universe several rather arbitrary properties in the process of getting there.

Is it possible that the formation of a black hole spawns a new universe? Sure! Is there any evidence for it? No. At this point, it's pure speculation -- it doesn't come naturally from standard theory and it hasn't made any predictions that have been confirmed by experiment.

[Soul Surfer]

How then do YOU define the properites of an independant universe?

Of course this is pure speculation the original question posed here was one that could only be answered with pure speculation because it dealt only with unobservables.

Mathematical modelling is a perfectly acceptable approach to coping with unobservables our current cosmological understanding is strongly dependant on using the matematival modelling of galaxy strucures and clustering to "prove" that our theories about the composition of the universe fit what we observe

[Soul Surfer]

Note I tend to use the term our universe to mean everything that we can observe and strongly infer (like areas hidden by inflation) and the multiverse to mean everything there is.

I personally favour a multiverse that obeys the perfect cosmological principle it that on a large enough scale it is generally similar for all time and space and has evolved to be so. it contains very many evolving universes (like our own) at all stages of development and is probably fractally structured.

I would strongly prefer to end up with an aspect of scale invariance in which the space and time were a property of the universe and the inside of a budding univese was of indefinite size to those who were inside it.

[SpaceTiger]

How then do YOU define the properites of an independant universe?

I'm not bickering with your definition of "independent universe", I'm bickering with what seemed to be a claim that there is observational evidence for them. If you acknowledge it as speculation then I have no quarrel.

[Silverbackman]

How could a black hole "spawn" another universe? I would think it would lead to another universe perhaps? And who is to say black holes in other universes are like our own. Yes it is speculation at the moment.

[Arian]

You guys, here are a few points
1. Space is not Infinite.
2.There is a high, high high probabiltiy of life
THe point is, if we can't see it, somebody else probaby can.
The universe is also looped, this means that if you go infinitly in one direction you will come back to one place again and again.BUt this can never happen because the universe expands way faster then the speed of light, but you can't go faster then the speed of light.
Its like the Earth exapnding really fast to a point that you can't actually ever go around it.

[matt.o]

You guys, here are a few points
1. Space is not Infinite.


How do you know? Which measurements prove this?

2.There is a high, high high probabiltiy of life


Obviously, we are here. But what is the probability of life in other solar systems? Have you worked this out?

The universe is also looped, this means that if you go infinitly in one direction you will come back to one place again and again.BUt this can never happen because the universe expands way faster then the speed of light, but you can't go faster then the speed of light.
Its like the Earth exapnding really fast to a point that you can't actually ever go around it.

Again, how do you know the universe is "looped"?

You have stated things as fact that are far from fact.

[kmarinas86]

You guys, here are a few points
1. Space is not Infinite.
2.There is a high, high high probabiltiy of life
THe point is, if we can't see it, somebody else probaby can.
The universe is also looped, this means that if you go infinitly in one direction you will come back to one place again and again.BUt this can never happen because the universe expands way faster then the speed of light, but you can't go faster then the speed of light.
Its like the Earth exapnding really fast to a point that you can't actually ever go around it.

When you think like you finally know the truth, your research suffers.

[Garth]

Hi Arian and welcome to these Forums!

You may think your post has been replied to rather brusquely. If you had put your points of view as a series of questions then you would have received some thoughtful and helpful answers. They may have led to an interesting discusssion, however there are others here who do know the subject in depth and rash or false assertions are countered quickly.

Keep asking questions and you will learn. :smile:

Garth

[Silverbackman]

Regarding the shape of the universe, most evidence shows that it is flat (at least the curvature).

[CosmologyHobbyist]

Is there any chance that the big bang was a quantum event? If so, wouldn't that require quantum field to pre-exist the universe? If that is the case, doesn't quantum field provide possibility for pre-BB space and time? Is quantum-event BB still a valid theory, or is it gone for some reason?

[Garth]

Is there any chance that the big bang was a quantum event? If so, wouldn't that require quantum field to pre-exist the universe? If that is the case, doesn't quantum field provide possibility for pre-BB space and time? Is quantum-event BB still a valid theory, or is it gone for some reason?Yes! :smile:

[But we have to wait for a tested quantum gravity theory to be sure.]

Garth

[Flatland]

String Theory actually claims to explain what happened before the BB.

[Chronos]

String Theory actually claims to explain what happened before the BB.Re-review what matt.o had to say. I think you are hopelessly deluded. String theory predicts . . . not a damn thing. Feel free to to contradict that assertion with . . . a testable prediction. I love those things.

[wolram]

I think some one has just put a paper in about the (bouncing) universe,so
if he is correct there never was a begining, and it may be possible to see
beyond the BB, the paper may be in arxives by now.

[Balence]

Its impossible to know exactly. We can speculate their are more stars and galaxies out there, and other things we would expect to find in the known universe. Its possible that if you went so far into the universe that you may find a place that is a duplicate, seeing as odds make no difference when looking at infinity.

[callistoite]

I have a simple answer.

We dont know "yet"

[Tapeworm69]

Okay. There is obviously no answer to this question... YET!
I think philosophically we have to assume both that there is both, something "beyond" our universe and that there also is nothing. You must assume both, seeing as you know neither to be true or false. Get it?

[Sorry!]

Ok I have been trying to bend my mind around the whole there is nothing outside our universe (as in we can not know ever) But on the first page I read an analogy of a Sphere whats outside a sphere.. can anyone explain this to me?>

[squidsoft]

Suppose we lived in sum world:

\sum_{n=1}^{\infty} \frac{1}{n^s}

and we asked, "what is outside of sum world?". We know if we go far enough, sum world reaches a singularity (it diverges). But is there anything beyond that singularity? Is there something larger that encompasses sum world and reduces down to it when certain conditions are met? Of course the answer is yes: zeta world. How is zeta world different than sum world? We certainly can't use the same "methods" (convergent sums) of sum world to describe zeta world. The two worlds are qualitatively different but zeta world contains sum world and can completely describe sum world using zeta methods (a contour integral). How did we get to zeta methods? How can we get to those methods which can describe our Universe as well as the larger world for which ours is only a particular instantiation?

[callistoite]

Well.. c'mon guys. lets take it easy..
Forget about we being the tiny little human beings on this small planet that we call "earth".
Suppose we are BIG in size. about 10s of billions of times Bigger than the observable universe, that we even have to use microscopic equipments to actually see a galaxy floating in the empty space, it will take billions of light years for an earthling to travel from your toe to head. an earthling will be much much smaller than an "atom" - if we call it that way - on your body.

In that size, if you look around, what can you see?
Okay, just for a change, shall we not talk about philosophy and add a little bit of creative, sci-fiction like thought?

[DaveC426913]

If, instead of being here in the Milky Way, we are actually 11 billion light years away in a different galaxy, we're still going to see a universe that is homogenous in every direction. We're not going to look one way and see a giant black void. If we did, it would be because the universe is not homogenous at large scales, that there is and edge and there is a centre.

So, what's beyond our observable universe is more, similar universe.

We can't ever see it, but we can deduce it.

[_____A-L-E-X_____]

I wonder how the recent "discovery" of dark flow plays into all this-- what if whats just beyond the visible universe can gravitationally affect that which is just within?

[ray b]

there be dragons

at least thats what the old maps said
about the areas as yet unexplored

[Hal King]

That's the wonderful thing about cosmology -- fantastic possibilities and predictions -- most of which can never be proved wrong!

Just for the fun of it, I calculated -- using the current model I'm playing with -- how much the observable universe makes of the total amount that 'must' exist NOW due to the Cosmological Principle.

Answer was: 39.349307% meaning the other 60.650693% we can't see -- but by the Cosmological Principle should be more of the same. By this model it turns out that this percentage doesn't change -- but the universe just keeps getting bigger.

In order to get a limit I had to ASSUME that the photons did NOT travel backward in time on their way to us -- regrettable.

There were several other assumptions -- like ONLY considering matter as 'something to see' and a value for the expansion velocity for matter (0.8660254 of the speed of light). Nothing important.

Now I'm sure everyone feels much better knowing this.

[Chronos]

An interesting proposition, and unsupported. Do you have any papers in mind? Your calculations appear to be a naive solution to the Friedmann equation.

[keepitmoving]

more of the same.

[Onslaught]

I know that this is a physics forum but just because physics can't explain the proposed question in totality doesn't mean you can't have some insight into a possible solution.

I doubt that the questioner wanted an exact answer. You should let your imagination explore these ideas sometime. Who knows what someone with your knowledge in physics might come up with. I bet you could come up with better answers than were given in this thread.

Just because you don't have an answer doesn't mean you shouldn't try to answer.

[Cryptonic]

I know that this is a physics forum but just because physics can't explain the proposed question in totality doesn't mean you can't have some insight into a possible solution.

I doubt that the questioner wanted an exact answer. You should let your imagination explore these ideas sometime. Who knows what someone with your knowledge in physics might come up with. I bet you could come up with better answers than were given in this thread.

Just because you don't have an answer doesn't mean you shouldn't try to answer.

Nah they don't like that here, I have learned. Just another bastion of closed-minded reactionism, like the horrible bautforum.

[Onslaught]

I was also wondering what people thought about poincare dodecahedral space. I haven't found any papers refuting this theory about the shape of space. Especially with the recent WMAP data.

[Chronos]

The dodecahedral proposition is weak. See, for example:
Dodecahedral topology fails to explain quadrupole-octupole alignment
http://arxiv.org/abs/astro-ph/0611640

[Onslaught]

Thanks for the link, thought it sounded to good to be true.

I find it impossible to comprehend a universe that is infinite, because no matter how you try to explain it, it HAS to end somewhere. Even if you use the balloon analogy that's like saying walking on a straight path on earth will bring you back to where you started. However if you take a rocket at escape velocity you can go beyond this.

Should there be a way, no matter how inconceivable, to escape from this so called Universe. i.e. an escape velocity for our Universe?

[Chronos]

By most models, the speed of light is the escape velocity of this universe. That is obviously impossible to achieve. It is unclear if the universe is finite. I tend to think it is from a strictly observational standpoint - e.g.. Olber's paradox. There may be 'stuff' outside our universe but I see no possible way to confirm this by observation,

[danda22]

hmm. a very hard question to consider with no definite answers.

i tend to belive that there is nothing outside our universe. just... nothing

btw. even if youu were travelling at lightspeed you could never escape"" or even reach anywhere near the edge of our universe. (the furtherst particle away from the "middle")
simply because it is also expanding at the speed of light.

[DaveC426913]

hmm. a very hard question to consider with no definite answers.

i tend to belive that there is nothing outside our universe. just... nothing

btw. even if youu were travelling at lightspeed you could never escape"" or even reach anywhere near the edge of our universe. (the furtherst particle away from the "middle")
simply because it is also expanding at the speed of light.

The universe has no middle. The universe has no edge.

The best model that shows how this can be so is that the universe is curved and closed. A 4-spatial-dimensional sphere.

Travel in any direction long enough and you will arrive back at your starting point.

[cfung]

This is what I know about the structure of the universe.

In our universe there are 2 parts. The observable part, like many have said, is +/-13.7 billions light years long. Then outside the observable you've got the unobservable part of the universe.

It's unobservable simply because light isn't catching up with the speed at which the universe expands. The distance between the edge of the universe and the light that's trying to reach the edge of the universe is what we meant by unobservable universe.

In other words, the universe is being expanded and light is trying to fill in and cover the created space-time, but the space-time being created is faster than what light can cover, so there is always an unobservable part of the universe where light hasn't reach.

But even without light, this unilluminated space-time obeys the laws of physics, it's nothing more than space without light. With that said, the unobservable universe is existing and so it's relevant that we understand what it is.

However, what's outside the edge of our expanding universe? There could be something like a higher dimension or a turtleback, though as much as there is a possibility of something outside, there's an equal chance that there is non-existence (if existence involves space-time). But if you want a correct answer to the question, what's outside the edge of the universe, the answer would be: there is the edge of our universe.

Many who understands often label the question pointless to ask, since one is asked to describe an object that is non-existing in the world.
Likewise if there's a non-existing object called Mr.X, how would you describe Mr.X to me? Seriously, try answering that until you get a sense of impossibility.

To see how it's unanswerable, Steven Hawkings once rephrase such questions along the following: What is north of North Pole? North Pole, probably.

[Chronos]

Our universe could be embedded in an infinitely large 'void', but, I fail to see how that helps us understand the universe. It would also raise issues like why matter occupies just an infinitesimal volume in all that can be characterized as 'spacetime'. Creepy. Cosmology is hard enough as is. All we can say with any certainty at present is the universe is observationally finite. That may not be all there is to it, but, it is all we can hope to describe for now. Better theories may give us new perspectives, but, better observations would raise my comfort level more quickly.

[ray b]

The universe has no middle. The universe has no edge.

The best model that shows how this can be so is that the universe is curved and closed. A 4-spatial-dimensional sphere.

Travel in any direction long enough and you will arrive back at your starting point.

do you have any proof of that last statement ???????????

[DaveC426913]

do you have any proof of that last statement ???????????

No, I'm not stating it is so, I'm stating there exists a model of the universe with this geometry.

[diogenesNY]

The universe has no middle. ...[edit]...


But Dave, isn't it _all_ middle? :)

diogenesNY

[DaveC426913]

But Dave, isn't it _all_ middle? :)

diogenesNY
Sure, that too.

But of course, 'middle' is only meaningful inasmuch as it is distinguishable from every other point; it is unique.

If it is all middle, then it is not unique.


To modify your statement: it all was middle.

[diogenesNY]

Sure, that too.

[edit]

To modify your statement: it all was middle.

A point lucidly made, well taken, and appreciated.

diogenesNY

[Onslaught]

By most models, the speed of light is the escape velocity of this universe. That is obviously impossible to achieve. It is unclear if the universe is finite. I tend to think it is from a strictly observational standpoint - e.g.. Olber's paradox. There may be 'stuff' outside our universe but I see no possible way to confirm this by observation,


I would be careful in saying that it is impossible to achieve faster than light travel, it may be highly improbable but not impossible. These are theories for a reason. If scientists have learned anything in our short time in this universe it is that "universal truth is not measured in mass appeal."

I agree that the universe will most likely turn out to be finite, but what if the speed of light can be reached or even surpassed, imagine the implications. Now I am admittedly slightly ignorant when it comes to these matters but my understanding of Einstein's famous equation E=mc^2 is that the amount of energy it takes to move an object is that objects mass multiplied by the speed of light squared. Hypothetically if we were able to control this much or MORE energy and focus it we should be able to travel light speed.

One problem I can't explain is that the faster you go or more energy you use your mass seems to increase a lot, which would require more energy to move but maybe when your mass reaches a certain amount you tear through the fabric of space-time.

Just a thought I had, feel free to mathematically, logically, or theoretically tear my argument to shreds. :-)

[map19]

E = mc^2 is nothing to do with moving mass. It is the energy equivalence of mass.
To move mass the simple F = ma is all that is needed.
As you go faster your mass does NOT increase. It's the problem posed by Special Relativity that a "Stationary" observer appears to see your mass increase. Or putting it another way, if you are moving compared with another frame of reference, observers on that frame see your mass as increased, while you see their masses as increased.
In your own frame, and their own frame, there is no increase.

[Onslaught]

Thanks for the clarification, I guess that idea is DOA.

Is there any reason to believe that F=ma doesn't work or works differently towards the 'edge' of the Universe or do we assume that since it works here it must work everywhere?

[map19]

No. From astronomical observations it seems that the same rules of physics apply all over. And the same chemistry.
However, you can never say never.

[Anticitizen]

I think that to make a statement like "conceptualizing the nature of the universe's 'edge' is irrelevant because it's unobservable" and refusing to even consider the possibilities is rather unproductive, if not downright unscientific. Through simulation and modeling we can construct hypotheticals, and quite accidentally run across something useful or testable. Just because we can't fly a probe to the edge of the cosmos doesn't mean we won't construct a model that just so happens to explain, say, lambda/the cosmological constant/whatever as an added bonus. Many times, a theory been made to explain one thing - and then, quite accidentally, someone steps back and says 'hey! this also explains THIS wacky phenomenon!' They may never experimentally verify the thing they originally set out to explain, but those happy accidentals that end up getting explained as a result certainly can go a ways in supporting the theory.

I get sensitive about those sorts of statements because they half-seem to be actively trying to stifle progress. String theory, for instance, predicts nothing, and instead of simply being content to simply not believe it, some people go out of there way to call it useless, a waste of time, etc. Those people will be in for a surprise if ever some testable prediction does pop up at some point as a result of the work that's been put into it (Note, I'm not trying to turn this into a string theory discussion, I just used it as an example).

In any case, it's a fun question whether verifiable or not. Now, to get more on topic:

When I was 15, I was puzzing over this same question (or one similar enough). Assuming the universe is a finite bubble of spacetime, what happens to the traveller that sneaks up to the 'edge' and tries to push beyond? Is there a beyond?

I followed a few assumptions (and note they're only assumptions):

The universe is
- finite
- spherical
- spacetime is the 'medium' in which matter, energy, and measureable dimensions exist
- anything 'outside' of the bubble of spacetime must have zero measurable distance. There is no 'there' there

Okay. The universe obviously has a measurable diameter, and a volume. Here's where I ran into a puzzler: How can a universe have an edge, a perimeter, and outside surface area as it were, and be 'surrounded' by an area of zero distance? I figured that was impossible - that a traveller moving toward the outside edge would be getting closer and closer to an area of zero distance. There can be no such thing as a 'perimeter' or surface area to the bubble if it's rubbing elbows, or expanding into, with an 'area' of zero distance.

But the universe does have pockets of measurable area that 'rub up' against areas of (theoretically) zero distance: singularities.

Therefore, as one would travel to the 'edge' of the universe, he'd find that he's moving through space that curves into a singularity. That's the only way the universe can be 'surrounded' by an area of zero distance - no matter what direction you travel in, go far enough and you'll fall into a black hole, basically. This means the universe has a diameter and an area, but no perimeter.

It would also mean that the 'edge' of the universe is a massive gravity well. :)

I invented a word for this all-encompassing singularity; 'pangularity', from the latin pan meaning 'all'. (It was easier to pronounce than 'omnigularity'.)

This tied in to something else I was pontificating about at the same time: relativity in a spinning disc. If you take a disc and spin it so the outer edge accelerates near the speed of light, the measured perimeter would shrink, but the diameter and area remains the same. If it was a magical disc whose edge could spin at the speed of light, you'd have a perimeter of zero distance. Given the equivalence of acceleration and gravity, the relativistic spinning disc could serve (at least mathematically) as a two-dimensional model for the pangularity idea. This was good news for me, because I was failing Algebra at the time. :)

I ran into a problem. At the time, it was 'common knowledge' that the universe's expansion was slowing. According to my hypothesis, the further you travelled away from the center of the universe, you should start falling into the 4D curvature of space into the pangularity, and therefore start speeding up instead of slowing down. So I said 'well, so much for that', congratulated myself for having a neat idea and forgot all about it, until I read an article about a year later about the surprising new measurements that demonstrated the universe was accelerating in its expansion. I did a happy jig and congratulated myself for being the smartest human being on the planet.

I started getting silly and conjecturing completely baseless speculations, such as the existence of a white hole, a convex singularity, at the center of the universe serving as the 'other side' of the pangularity, and the universe constantly recycling its matter and energy... etc.

Of course, that was almost 15 years ago, and I've gotten a little wiser, if not smarter. I don't think it can be adapted to explain why everything is moving apart from everything else at an accelerating rate. As two objects get closer to the outer edge of the universe, they should actually come closer together as they fall into the pangularity. And if the gravity well's effects were to extend into our local observable area of the universe, movement of objects should seem biased in one direction, assuming we're not parked in the exact center of the universe, etc. Of course, the volume and diameter of the universe could still be expanding due to inflation in this model, but the perimeter is always zero.

I still suspect that if spacetime is expanding 'into nothing', then the perimeter must have zero distance.

But it was fun speculation, and speculation can lead to some very interesting ideas. I think that the culture of strict positivism ('the question is irrelevant!', etc) seems counterproductive.

[DaveC426913]

I think that to make a statement like "conceptualizing the nature of the universe's 'edge' is irrelevant because it's unobservable" and refusing to even consider the possibilities is rather unproductive, if not downright unscientific. Through simulation and modeling we can construct hypotheticals, and quite accidentally run across something useful or testable. Just because we can't fly a probe to the edge of the cosmos doesn't mean we won't construct a model that just so happens to explain, say, lambda/the cosmological constant/whatever as an added bonus. Many times, a theory been made to explain one thing - and then, quite accidentally, someone steps back and says 'hey! this also explains THIS wacky phenomenon!' They may never experimentally verify the thing they originally set out to explain, but those happy accidentals that end up getting explained as a result certainly can go a ways in supporting the theory.

I get sensitive about those sorts of statements because they half-seem to be actively trying to stifle progress. String theory, for instance, predicts nothing, and instead of simply being content to simply not believe it, some people go out of there way to call it useless, a waste of time, etc. Those people will be in for a surprise if ever some testable prediction does pop up at some point as a result of the work that's been put into it (Note, I'm not trying to turn this into a string theory discussion, I just used it as an example).

In any case, it's a fun question whether verifiable or not. Now, to get more on topic:

When I was 15, I was puzzing over this same question (or one similar enough). Assuming the universe is a finite bubble of spacetime, what happens to the traveller that sneaks up to the 'edge' and tries to push beyond? Is there a beyond?

I followed a few assumptions (and note they're only assumptions):

The universe is
- finite
- spherical
- spacetime is the 'medium' in which matter, energy, and measureable dimensions exist
- anything 'outside' of the bubble of spacetime must have zero measurable distance. There is no 'there' there

Okay. The universe obviously has a measurable diameter, and a volume. Here's where I ran into a puzzler: How can a universe have an edge, a perimeter, and outside surface area as it were, and be 'surrounded' by an area of zero distance? I figured that was impossible - that a traveller moving toward the outside edge would be getting closer and closer to an area of zero distance. There can be no such thing as a 'perimeter' or surface area to the bubble if it's rubbing elbows, or expanding into, with an 'area' of zero distance.

But the universe does have pockets of measurable area that 'rub up' against areas of (theoretically) zero distance: singularities.

Therefore, as one would travel to the 'edge' of the universe, he'd find that he's moving through space that curves into a singularity. That's the only way the universe can be 'surrounded' by an area of zero distance - no matter what direction you travel in, go far enough and you'll fall into a black hole, basically. This means the universe has a diameter and an area, but no perimeter.

It would also mean that the 'edge' of the universe is a massive gravity well. :)

I invented a word for this all-encompassing singularity; 'pangularity', from the latin pan meaning 'all'. (It was easier to pronounce than 'omnigularity'.)

This tied in to something else I was pontificating about at the same time: relativity in a spinning disc. If you take a disc and spin it so the outer edge accelerates near the speed of light, the measured perimeter would shrink, but the diameter and area remains the same. If it was a magical disc whose edge could spin at the speed of light, you'd have a perimeter of zero distance. Given the equivalence of acceleration and gravity, the relativistic spinning disc could serve (at least mathematically) as a two-dimensional model for the pangularity idea. This was good news for me, because I was failing Algebra at the time. :)

I ran into a problem. At the time, it was 'common knowledge' that the universe's expansion was slowing. According to my hypothesis, the further you travelled away from the center of the universe, you should start falling into the 4D curvature of space into the pangularity, and therefore start speeding up instead of slowing down. So I said 'well, so much for that', congratulated myself for having a neat idea and forgot all about it, until I read an article about a year later about the surprising new measurements that demonstrated the universe was accelerating in its expansion. I did a happy jig and congratulated myself for being the smartest human being on the planet.

I started getting silly and conjecturing completely baseless speculations, such as the existence of a white hole, a convex singularity, at the center of the universe serving as the 'other side' of the pangularity, and the universe constantly recycling its matter and energy... etc.

Of course, that was almost 15 years ago, and I've gotten a little wiser, if not smarter. I don't think it can be adapted to explain why everything is moving apart from everything else at an accelerating rate. As two objects get closer to the outer edge of the universe, they should actually come closer together as they fall into the pangularity. And if the gravity well's effects were to extend into our local observable area of the universe, movement of objects should seem biased in one direction, assuming we're not parked in the exact center of the universe, etc. Of course, the volume and diameter of the universe could still be expanding due to inflation in this model, but the perimeter is always zero.

I still suspect that if spacetime is expanding 'into nothing', then the perimeter must have zero distance.

But it was fun speculation, and speculation can lead to some very interesting ideas. I think that the culture of strict positivism ('the question is irrelevant!', etc) seems counterproductive.While speculation can be fun, it is a fine line you walk here. Overly-speculative discussion and personal theories are expressly forbidden. (Remember that PF is first and foremost a homework help forum, and thus concentrates on currently-accepted physics.)

[Anticitizen]

I understand and apologize - I went a little too deep into it. The purpose of the post wasn't really about the idea itself, though - the moral of the story was the point I made in the first two paragraphs about keeping an open mind. In this case, a wacky, arguably untestable idea I had made one prediction one I didn't intend to make - that the universe's expansion would accelerate. Turns out it is. I'm 99.9% sure it's for a completely different reason, of course, but I think my point stands that 'irrelevant' concepts may lead to real conclusions. I suppose I should've used a real-world example (that is, something established in physics).

[crzykila86]

Our guess the space and time in our universe is finite. However it is just hard to believe there was no time before the big bang and no content beyond our observable universe. It doesn't make sense how things can by finite. I mean what happened before the big bang and why are there boundaries at the ends of our universe?

By studying the universe and the physical world one can truly see things aren't orderly per se. They far beyond the realms of organized imagination and can only be understood with observation and empiricism. Limits on the universe would truly make things beyond confusing.

BTW, what do scientists think happened before the big bang. Since the universe is expanding according to most of the evidence today, the cyclical big crunch is unlikely. What do scientists think are the likely choices?
nobody can really say what was before the big bang or whats beyond the observable universe simply because it is beyond our comprehension(for now anyways). their are lots of different theories for those things but until we gain the technology to see beyond what we can see now and to go out their we will never really know. any thoughts on this?

[crzykila86]

we do not understand what is outside our universe because we live in existence, has anybody ever tried to imagine what it would be like to not exist? its the same thing if you think about it. we cannot comprehend what we are not physically capable of understanding

[DaveC426913]

crzykila, these are simply philosophical rationalizations.

[Chronos]

We live in a temporally finite universe where nothing can travel faster than light, according to the most widely accepted current theories. We should insist one or both of these assertions be overturned before becoming distracted by logic grenades, IMO.

[turkeyburgers]

So if the Sun sends out a photon and it is absorbed by plants and then those plants decay and that becomes coal and the coal is burned to power a power plant and the electricity is sent to my house to power my T.V that I am watching a movie of a sunset on am I just seeing that same photon that the sun put out? Or is it like a three to one special like put three coins into machine get one back where like 2 million photons of the sun gets converted into one photon from my t.v.?

[DaveC426913]

So if the Sun sends out a photon and it is absorbed by plants and then those plants decay and that becomes coal and the coal is burned to power a power plant and the electricity is sent to my house to power my T.V that I am watching a movie of a sunset on am I just seeing that same photon that the sun put out? Or is it like a three to one special like put three coins into machine get one back where like 2 million photons of the sun gets converted into one photon from my t.v.?

This is unrelated to the topic. Please start a new thread.

But here is the simple answer:

No, it is not the same photon exiting your TV that exited the sun.

Photons are not created equal. Yes, it is possible (in principle) that 2 million low-energy photons can be converted through chemical processes into a single high-energy photon.

Or whatever. Consider the amount of wastage in heat alone (more photons) that lead from the Sun to your TV.

[Constantin]

There's nothing beyond the observable universe. There's no such option in the initial poll so people had to vote "other" .

I also prefer the concept of "what you can't see doesn't exist". And this concept can never be proven wrong.

[DaveC426913]

There's nothing beyond the observable universe. There's no such option in the initial poll so people had to vote "other" .
No, people voted 'other' because the option that's missing is "just more of the same".

[Constantin]

The edge of the Observable Universe is moving away with the speed of light, so you can't get any closer to it. Furthermore, no matter how fast you're traveling, presumably very close to the speed of light, the edge will move away with the speed of light in all directions.
So no matter in what direction or at what speed you're traveling, you'll still be in the center of the visible universe, just an older universe. And you'll see nothing new, no new area, just the same edge, now further away.

[bapowell]

The edge of the Observable Universe is moving away with the speed of light, so you can't get any closer to it. Furthermore, no matter how fast you're traveling, presumably very close to the speed of light, the edge will move away with the speed of light in all directions.
So no matter in what direction or at what speed you're traveling, you'll still be in the center of the visible universe, just an older universe. And you'll see nothing new, no new area, just the same edge, now further away.

That's night quite true in a universe with accelerated expansion (and this is what current observations seem to be telling us about our universe). It's true that the particle horizon, the distance that particles (light) could have traveled since the big bang, is propagating outwards at the speed of light. However, this does not define the boundary of our observable universe. It's not the light going out that defines the boundary of the observable universe, but the light coming in. In a non-accelerating spacetime, these two boundary are equivalent. However, once we allow spacetime to accelerate, there is a boundary beyond which objects are not only receding from us at greater than light speed, but this boundary itself moves at less than light speed (in a universe with a pure cosmological constant, this boundary doesn't move at all -- the observable universe gets no bigger or smaller in size -- simply because distant objects are racing away from us too quickly for us to causally interact).

[Constantin]

My view is nothing has moved past the horizon. The light there comes from a time close to when the Universe was formed, from t -> 0 .
And I'm not considering technological barriers like how far our instruments can see.

And it doesn't matter how far or how fast you move in one direction, you won't see past that t -> 0 . Nor would any part of the Universe move out of the horizon, as the horizon moves away with the relativistic speed of light.

I'm also not trying to calculate the distance to the horizon right now. As it is moving away at the speed of light, one could consider the distance to the horizon as infinite.

[bapowell]

I guess you didn't read my post. The horizon -- the boundary of our observable universe -- is not moving away from us at the speed of light. Not in an accelerating universe, which is the one we live in. In an accelerating universe (for example, during inflation), things can and do cross outside our horizon.

The main point here is that the particle horizon and the Hubble radius are no longer equivalent in an accelerating universe.

[Phyisab****]

Why is there not an option "I have no @&*@!)U idea."

[Constantin]

I guess you didn't read my post. The horizon -- the boundary of our observable universe -- is not moving away from us at the speed of light. Not in an accelerating universe, which is the one we live in. In an accelerating universe (for example, during inflation), things can and do cross outside our horizon.
The main point here is that the particle horizon and the Hubble radius are no longer equivalent in an accelerating universe.

Leave the inflation aside, and let's start with the hot dense initial state. I'm also not trying to calculate any distance, radius etc. As I said before, as the horizon is moving away at the speed of light, one could consider the distance to the horizon as infinite.


That's night quite true in a universe with accelerated expansion (and this is what current observations seem to be telling us about our universe). It's true that the particle horizon, the distance that particles (light) could have traveled since the big bang, is propagating outwards at the speed of light. However, this does not define the boundary of our observable universe. It's not the light going out that defines the boundary of the observable universe, but the light coming in. In a non-accelerating spacetime, these two boundary are equivalent. However, once we allow spacetime to accelerate, there is a boundary beyond which objects are not only receding from us at greater than light speed, but this boundary itself moves at less than light speed (in a universe with a pure cosmological constant, this boundary doesn't move at all -- the observable universe gets no bigger or smaller in size -- simply because distant objects are racing away from us too quickly for us to causally interact).

I am considering the light coming in, not the light going out.
You say that objects are receding from us at greater than light speed, but in special relativistic coordinates the velocities are less than c.

[bapowell]

Leave the inflation aside, and let's start with the hot dense initial state. I'm also not trying to calculate any distance, radius etc. As I said before, as the horizon is moving away at the speed of light, one could consider the distance to the horizon as infinite.
In a decelerating universe, yes, the horizon is moving outward at the speed of light. But why bother considering it as infinite? How about r = ct, where t = age of the universe?




I am considering the light coming in, not the light going out.
You say that objects are receding from us at greater than light speed, but in special relativistic coordinates the velocities are less than c.

Indeed they are. When dealing with the universe, we consult general relativity, not special relativity. Look at Hubble's Law:

v = Hr (here v is the recession velocity of an object at a distance r, H is a constant).

From this expression (which is general relativistic, although approximate), we see that there is a point (r = c/H), at which distant objects are receding from us at greater than the speed of light. No contradiction here with SR: it's the space that is expanding -- all objects are at rest locally. And this is true for any expanding universe, not just inflation.

[marcus]

No, people voted 'other' because the option that's missing is "just more of the same".

I think that's right, and it's a good way to put it. At least that's why I said "other" and my guess is most people said that for the same reason. The standard model of cosmology is pretty widely accepted and "more of the same" is the standard assumption. We can't TELL but it is consistent with observation and it is the simplest thing to assume that is consistent with gen rel. and the data we have.

[marcus]

...When dealing with the universe, we consult general relativity, not special relativity. Look at Hubble's Law:

v = Hr (here v is the recession velocity of an object at a distance r, H is a constant).

From this expression (which is general relativistic, although approximate), we see that there is a point (r = c/H), at which distant objects are receding from us at greater than the speed of light. No contradiction here with SR: it's the space that is expanding -- all objects are at rest locally. And this is true for any expanding universe, not just inflation.

Powell I want to express support and appreciation. You've been giving Constantin the straight story about the standard cosmology model.
I'll add some detail (I hope it doesn't make things confusing to have extra detail. So far you and Dave have managed to be very clear.)

Constantin, you should understand what distance measure is used in the Hubble law
v = Hd.
A good way to think about it is to imagine freezing expansion right before you measure. So the distance doesn't change while you are measuring it.
You freeze at a certain moment, and measure by timing a light pulse or radio blip.* And then unfreeze so things are back to normal again.
Maybe we could call it "freeze-frame radar ranging".

The Hubble law applies to large distances like those separating independent clusters of galaxies and it says that a distance d, imagine it measured the way I described, expands at rate v = Hd.

The Hubble ratio H(t) changes over time, so I should specify a present moment t when we make the measurements and say v = H(t)d, but that too is a technicality. The standard cosmo model gives us past values of H as well as the present value.

Check this out:
http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html

To use it, put in .27 for matter density and .73 for cosmo constant, and 71 for present value of H(t). Then you can put in any redshift z and it will tell you the present (freeze) distance and the past (freeze) distance when the light was emitted and started traveling towards us. And it will tell the past value of H(t) when the light started its journey. And it will tell the distance expansion rates.

Personally I avoid saying "space itself expands". I say distances expand. I think of geometry as dynamic and geometry is about distances, angles, areas etc. I don't say "space" expands because I don't like to give the impression that it is a substance like rubber or bread-dough. I focus on geometry that rides on the material metaphor. But at this point, for Constantin and Powell and the rest of us, that technical distinction is not important. The main thing is picture Hubble law and picture the relevant distances.

Constantin, how about trying that calculator and getting distances for, say z = 1.4 and z = 1.7, and z = 1090. z=1090 is pretty close to the edge of the observable universe. The microwave background (CMB) comes in with redshift 1090 and it comes from the most distant matter we can see. Let us know if you have any trouble.

I keep the link to that calculator in my sig, to have it convenient, since it is very useful.

-----------------------------------footnote-----------------------------------------
*technically the CMB (the background of ancient light) helps in defining the moment when you freeze expansion.

[Constantin]

Recession velocities exceed the speed of light in all viable cosmological models for objects with redshifts greater than z ~ 1.5.
We routinely observe galaxies that have, and always have had, superluminal recession velocities.
The above is quoted from: http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf .

In my view, the light coming from the edge of the observable universe comes from a time when the age of the Universe was almost zero. And nothing can get further than that. So in this view nothing can ever get out of the observable universe.

The way I imagine the edge of the observable universe has similarities with a Milne universe, in that I imagine the objects near the edge as infinitely dense, either because of Lorentz contraction, or because we observe those objects as they were when the Universe was very young and dense.

That way we can already observe all the Universe, although it is infinite.

I must add that these ideas are very hard to imagine. This is not an easy subject.

[sylas]

Recession velocities exceed the speed of light in all viable cosmological models for objects with redshifts greater than z ~ 1.5.
We routinely observe galaxies that have, and always have had, superluminal recession velocities.
The above is quoted from: http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf .

In my view, the light coming from the edge of the observable universe comes from a time when the age of the Universe was almost zero. And nothing can get further than that. So in this view nothing can ever get out of the observable universe.


That doesn't follow. The observable universe is just that part of the universe which is sufficiently close that there's been enough time for the light to get from there to here. Nothing we see can be more distant than that; but plenty that we can't see may be more distant.

Think of it this way. The material from which we are made was emitting light 13.7 billion years ago, and that light will be seen now by alien astronomers who are formed from the stuff that WE now see with light that old (the cosmic background). So WE are at the edge of the observable universe for any astronomers who happen to be at the edge of our observable universe. And there's no extra density, or bound, or limit involved.

Furthermore, consider two regions, at opposite sides of the sky, which we can see with light coming in opposite directions since the origin of the universe. We only see those regions when they were very young, of course. Strictly, we see hot glowing gas with a redshift of about 1100; since then that gas has had 13.7 billion years to form into galaxies, just like out galaxy was formed from hot dense gas that long ago.

Both those regions are at the edge of our observable universe... and we are the edge of their observable universe as measured now. But those two regions at opposite sides of the sky are OUTSIDE the observable universe for each other.

Cheers -- sylas

[Calimero]

Check this out:
http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html

To use it, put in .27 for matter density and .73 for cosmo constant, and 71 for present value of H(t). Then you can put in any redshift z and it will tell you the present (freeze) distance and the past (freeze) distance when the light was emitted and started traveling towards us. And it will tell the past value of H(t) when the light started its journey. And it will tell the distance expansion rates.


Why at z=~2.5 'speed away from us now' becomes less then 'speed away from us then' ?

[Constantin]

Think of it this way. The material from which we are made was emitting light 13.7 billion years ago, and that light will be seen now by alien astronomers who are formed from the stuff that WE now see with light that old (the cosmic background). So WE are at the edge of the observable universe for any astronomers who happen to be at the edge of our observable universe. And there's no extra density, or bound, or limit involved.

There is extra density, that cosmic background represents the Universe as it was ~380,000 years after t=0 , as dense as it was then. And of course, not counting the technological limits we could see very close to t=0 . And if we could observe that cosmic background for a long enough period of time, like billions of years, we would see stars and galaxies forming out of it.

Furthermore, consider two regions, at opposite sides of the sky, which we can see with light coming in opposite directions since the origin of the universe. We only see those regions when they were very young, of course. Strictly, we see hot glowing gas with a redshift of about 1100; since then that gas has had 13.7 billion years to form into galaxies, just like out galaxy was formed from hot dense gas that long ago.

Both those regions are at the edge of our observable universe... and we are the edge of their observable universe as measured now. But those two regions at opposite sides of the sky are OUTSIDE the observable universe for each other.

That example can't be used. Two observers in those two regions can see the same Universe in a different way, because they're in a different frame of reference. In order for what observer A sees to have any meaning for observer B, observer A needs to send that information, presumably with the speed of light. Observer B would receive that information after a very long time, very many billions of years, and by then the way the Universe looks for observer B will match observer A's information well enough.

[marcus]

Why at z=~2.5 'speed away from us now' becomes less then 'speed away from us then' ?

This is a really perceptive question. You have been experimenting with the standard cosmo model (which is realized in this calculator in a concrete hands-on form.) It is so important to get hands-on numerical experience with the usual model of the universe! Thanks for the great question, Calimero!

Anyone interested in cosmology should do this, what you obviously have done.

Put successively z = 1, 2, 2.5, 3, 4, 1090* into the calculator and notice what happens to the "speed now", "speed then", and also the HUBBLE parameter, as z increases. These "speeds" should be thought of as the rate that the distance is increasing. (The distance used in the model here is the freeze-frame distance, and the recession rate is the rate that distance is increasing.)

The Hubble parameter gives the relation of distance to recession rate. For each distance it tells the rate at which that distance is growing. v = Hd

If H would not change, then since distance now is always bigger than distance then, we would have that recession rate now would always be bigger than recession rate then.

Indeed this is what happens for smaller redshift like z = 1 and 2, because over the fairly recent past the H has not changed very much.

But H has been much bigger in the past, and has been constantly decreasing during the whole history of expansion, and according to the model it will continue to decrease, but ever more slowly.

So this effect competes with what I said earlier. And if you go out to z = 2.5 it just balances. The two effects cancel!

* I added z = 1090 to the list of sample redshifts because 1090 is the redshift of the background of ancient light---the socalled CMB.

You, Calimero, probably know most of what I am saying but I hope some more newcomers will read this as well and be persuaded to try using the online model of the cosmos.

You should already be thinking of a followup question---how can H be always decreasing when we are told that expansion accelerates?---well, ask if you want that to be discussed. It's often good when one answer leads to a further question.

I assume you know what these numbers are. Anyone else reading this thread can guess:


1 .78 .66 120.7
2 1.24 1.17 201.1
2.5 1.40 1.40 301.3
3 1.53 1.62
4 173 2.03
1090 3.3 56.7 1.3 million

[Calimero]

Thanks, I have to digest this. What you wrote is clear, but now I am puzzled with other stuff. I'll be back for more.

[Calimero]

You should already be thinking of a followup question---how can H be always decreasing when we are told that expansion accelerates?---well, ask if you want that to be discussed. It's often good when one answer leads to a further question.


Exactly. That is what I am puzzled about. If something is receding slower now then it was receding then, it means it is slowing down !? Furthermore it would appear that at z=2.5 there is some kind of 'boundary' where expansion from acceleration goes to deacceleration? But I am guessing that it is not the case.

[marcus]

Then you should get acquainted with the scale-factor a(t). This is the most basic quantity in the standard cosmos model.

Sometimes it is intuitively described as a dimensionless number which increases with time, and which keeps track of "the average distance between galaxies".

(It is always the "freeze-frame" distance we are talking about. any question about that? you freeze expansion at some moment t and then do radar ranging.)

Mathematically, a(t) is a factor which plugs into the Friedman metric. The standard model IS the time-evolution of the Friedman metric, a solution to the Einst. equation which provides the best fit to the data. We do not need to speak so technically. a(t) is a handle on the size of the world, it is a numerical handle on the average distance between galaxies.

The Friedman equations (look Wiki for "Friedmann equations") are the simple differential equations that govern the increase in a(t). That is really all that the standard model amounts to, in essence---modeling the growth of a(t).

Because it is dimensionless a(t) can be normalized so that, at the present time, it equals anything you want. It is usual to normalize it so that a(t) = 1 at the present time.

Now their are two easy hurdles, two easy low fences for you to get over.

YOU MUST UNDERSTAND THAT the wavelength expansion factor is 1+z
(a 50% increase in wavelength is expressed as z = 0.5 and therefore the wavelength now is 1.5 times the wavelength then)
and you must understand that 1+z = a(now)/a(then)

We measure that the light from some galaxy has z = 2.5, therefore the wavelength now is 3.5 times what it was when the light was emitted. And also the average distance between galaxies is now 3.5 times what it was when the light began its journey to us.

And YOU MUST UNDERSTAND WHY the Hubble parameter at any time t is equal to a certain fraction H(t) = a'(t)/a(t).
This is a sort of non-trivial interesting fact, nice to think about. The time derivative of a(t) divided by a(t) itself. The Hubble parameter H(t) is the time derivative of the scalefactor divided by the scalefactor itself, at any given instant in time.

The first people on earth to discover interesting facts about the geometry of the world were the Ionians, and this is because the air on the Aegean coast of Anatolia is extremely clear and the outlines of the islands are very sharp. These facts about the scale factor and the Hubble ratio are essentially "Ionian" facts. heh heh :wink: That's just my private point of view. Carl Sagan said something like this.

[Calimero]

Ok, now I really have some work to do. But basically it would mean that nothing odd is happening to the scale factor, it is steadily increasing over time?

[marcus]

Ok, now I really have some work to do. But basically it would mean that nothing odd is happening to the scale factor, it is steadily increasing over time?

It is always increasing, but at first the increase slows because matter dominates over the effect of the cosmological constant (or "dark energy") and matter always slows the increase of a(t).

Saying that the cosmo constant is constant over time means the same thing as saying that the energy density of the "dark energy" is constant over time. Since it is a small density, it is at first dominated by the matter density. But as distances and volumes expand the matter density becomes small, and then the constant dark energy density becomes more important.

When you used the calculator you put .27 for matter and .73 for dark energy or cosmo constant.

So at first the increase in a(t) SLOWS and then after the cosmo constant term becomes dominant the increase in a(t) accelerates.

When they told you "expansion is accelerating" they were not talking about H(t). They were talking about a(t).

[marcus]

... a followup question---how can H be always decreasing when we are told that expansion accelerates?---well, ask if you want that to be discussed. It's often good when one answer leads to a further question.

I assume you know what these numbers are. Anyone else reading this thread can guess:


1 .78 .66 120.7
2 1.24 1.17 201.1
2.5 1.40 1.40 301.3
3 1.53 1.62
4 173 2.03
1090 3.3 56.7 1.3 million


When they say expansion accelerates they are not talking about the recession of some particular galaxy, they are talking about the behavior of a(t). Focus on a(t). It is the most important quantity in the cosmo model.

When they say expansion accelerates they are not talking about H(t) either. H(t) is just a convenience because it relates nicely to observational data, the plots of the distance-redshift relation. H(t) is always decreasing.

Why? because H(t) = a'(t)/a(t) and the denominator of that fraction dominates. The growth in the denominator swamps any diddly changes that might be happening to the numerator.

One can imagine universes where H(t) does not decrease. Like the extreme case where there is no matter at all but only pure dark energy and a(t) increases exponentially. Then H(t) will be constant, so it will at least not decrease, then.

But in any universe at all like ours, H(t) will always be decreasing---only more and more slowly as time goes on, so that it kind of levels out.

Our model tells us what H(t) will level out to. What the asymptotic value is.

Take your time and assimilate this stuff. Ask more questions when you want to. I thought your first question was really good because it showed you had been playing around with the Cosmos Calculator.
http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html

[bapowell]

That example can't be used. Two observers in those two regions can see the same Universe in a different way, because they're in a different frame of reference. In order for what observer A sees to have any meaning for observer B, observer A needs to send that information, presumably with the speed of light. Observer B would receive that information after a very long time, very many billions of years, and by then the way the Universe looks for observer B will match observer A's information well enough.

You're missing sylas's point. He's merely suggesting that there may be more to the universe than what we can observe -- he's not setting up some elaborate experiment that requires two observers to communicate.

I think it's great that you are interested in these questions about the universe. However, many of your views expressed so far in this thread are not factually correct. Myself and the others in this thread have tried to offer more correct views of the way the universe actually behaves, not how it ought to behave. I think you could benefit from thinking deeply about some of the things we've mentioned, and perhaps modifying your views to incorporate them. Perhaps you should pick up a good popular science treatment of the subject, eg, the books by Weinberg, Guth, or Harrison.

[Phyisab****]

I voted other because... wait for it... we can't observe it.

[sylas]

There is extra density, that cosmic background represents the Universe as it was ~380,000 years after t=0 , as dense as it was then. And of course, not counting the technological limits we could see very close to t=0 . And if we could observe that cosmic background for a long enough period of time, like billions of years, we would see stars and galaxies forming out of it.

I agree with all of this.

We may be talking at cross purposes. Much of what you say is fine, but I have a problem sorting out what you could have meant by this:
Recession velocities exceed the speed of light in all viable cosmological models for objects with redshifts greater than z ~ 1.5.
We routinely observe galaxies that have, and always have had, superluminal recession velocities.
The above is quoted from: http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf .

In my view, the light coming from the edge of the observable universe comes from a time when the age of the Universe was almost zero. And nothing can get further than that. So in this view nothing can ever get out of the observable universe.

I think I misunderstood you previously, so forget my last post. I was simply saying that there's stuff outside the observable universe which is the same as stuff inside the observable universe, but I see you agree with this. My fault for missing your point.

But I still think you may be mistaken, so let me try again. Your reference, Davis and Lineweaver 2003, is very good, IMO. Have a look at their figure 1. Here it is: click to enbiggen.
23848

The three diagrams in this figure are showing the same thing, but with different co-ordinates for the axes. The bottom diagram is the simplest, though the notions of co-moving distance and conformal time may be unfamiliar to many folks. The top diagram is the most intuitive for many readers, as it uses proper distance and proper time co-ordinates, which correspond to time and distance as we normally understand them.

What we usually mean by "observable universe" is everything within our present light cone. In a trivial sense, pretty much everything has "now" moved out of the observable universe, because the light leaving it "now" hasn't reached us yet. This only means that what we see at a distance is as things were in the past, and which is obvious.

But in an accelerating universe, something rather more strange can happen.

Figure 1 is showing the ΛCDM model, a flat universe with matter (0.3) and dark energy (0.7). In this case the expansion of the universe is accelerating, and will continue to accelerate. When this occurs you have an "event horizon", which is shown in the diagrams. This means everything which we can ever hope to observe now or at any time in the future. And look... in this case, all co-moving particle WILL eventually move past the event horizon!

What this means, in more practical terms, is that distant galaxies which are not gravitationally bound to us will eventually move out of the observable universe. What we can actually see, for such a galaxy, as time passes, is that the red shift of the galaxy will increase without limit. It is, in fact, red shifted to invisibility. We will never see the galaxy at any age beyond the age at which it crossed our event horizon. If we had the capacity to see infinitely redshifted signals, we would actually see the galaxy appear to be "frozen" in time, at the age at which it crosses the event horizon. We never ever see it older than that moment.

There is an intriguing implication of this for astronomers of the distant future!

The current models for the universe suggest that as time passes the universe will appear more and more "empty", as we see less and less of the universe, until at a time billions of years into the future astronomers will only ever be able to see a small number of galaxies that have become gravitationally bound with us. Our local group of galaxies. The rest of the sky will be dark, betraying no hint of the nature of the universe, or of the billions of galaxies which will have, by then, moved forever beyond any possibility of observation. It seems that such astronomers will have no available evidence to be able to identify the big bang, or dark energy, or expansion.

Cheers -- sylas

[Constantin]

I thank everyone for the replies.

This is the explanation that has helped me most:


What this means, in more practical terms, is that distant galaxies which are not gravitationally bound to us will eventually move out of the observable universe. What we can actually see, for such a galaxy, as time passes, is that the red shift of the galaxy will increase without limit. It is, in fact, red shifted to invisibility. We will never see the galaxy at any age beyond the age at which it crossed our event horizon. If we had the capacity to see infinitely redshifted signals, we would actually see the galaxy appear to be "frozen" in time, at the age at which it crosses the event horizon. We never ever see it older than that moment.

It explains the way objects can look while moving out of the observable universe, which is very hard to imagine without proper explanation. Naively one can imagine that they simply move out of sight and disappear, which is of course illogical.

[sylas]

It explains the way objects can look while moving out of the observable universe, which is very hard to imagine without proper explanation. Naively one can imagine that they simply move out of sight and disappear, which is of course illogical.

Thanks very much; I get a real buzz when something I've written manages to help like this.

You've hit the nail on the head about what is hard to imagine here; I also had a hard time figuring this one out, in another closely related situation. You have exactly the same thing occurring when a particle moves across the event horizon of a black hole!

For an outside observer, they can never see this occur. What they can see is a signal redshifted without limit, and (if you find a way to see an arbitrarily redshifted signal) this signal reveals the particle apparently frozen in time at the point of approaching the event horizon. The particle itself crosses the horizon just fine; but we can never see this occur, no matter how long we wait.

Cheers -- sylas

[Skolon]

You've hit the nail on the head about what is hard to imagine here; I also had a hard time figuring this one out, in another closely related situation. You have exactly the same thing occurring when a particle moves across the event horizon of a black hole!

For an outside observer, they can never see this occur. What they can see is a signal redshifted without limit, and (if you find a way to see an arbitrarily redshifted signal) this signal reveals the particle apparently frozen in time at the point of approaching the event horizon. The particle itself crosses the horizon just fine; but we can never see this occur, no matter how long we wait.
That mean we can study all history of a black hole after its born just observing more and more redshifted signals? Very interesting.

What this means, in more practical terms, is that distant galaxies which are not gravitationally bound to us will eventually move out of the observable universe. What we can actually see, for such a galaxy, as time passes, is that the red shift of the galaxy will increase without limit. It is, in fact, red shifted to invisibility. We will never see the galaxy at any age beyond the age at which it crossed our event horizon. If we had the capacity to see infinitely redshifted signals, we would actually see the galaxy appear to be "frozen" in time, at the age at which it crosses the event horizon. We never ever see it older than that moment.

There is an intriguing implication of this for astronomers of the distant future!
Why we don't observe that kind of "frozen" galaxies right now? I think right now must be a lot of galaxies beyond the current event horizon already. Or I'm wrong?

[Constantin]

The answers to Skolon's questions would be interesting.

Thing is very very few people can imagine these things properly: the way objects would look to an observer.
And you can look for an explanation on the internet for hours, days, weeks, but you won't find it. Or at least I didn't.

[Ich]

That mean we can study all history of a black hole after its born just observing more and more redshifted signals?
No. Redshift increases exponentially with time near the horizon, after a few seconds it is far in the millions. There is nothing to observe.
Why we don't observe that kind of "frozen" galaxies right now?
The universe is too young. The first galaxies have a redshift of about 8, which does not exactly qualify as "frozen", I think. If you wait for another ~50 billion years, their redshift will be ~280.
The CMB has a redshift of 1088. That's quite frozen.

[sylas]

That mean we can study all history of a black hole after its born just observing more and more redshifted signals? Very interesting.

I qualified my remarks to say IF we could actually see a signal redshifted arbitrarily far. But we can't.

If you think in terms of a classical wave, a red shifted signal is one in which the distance between successive wave crests becomes large. That is, wavelength increases as light is shifted into the infrared.

Light is also quantized... it is made up of photons. Another difference with a red shifted signal is that the distance between successive photons is increased... or in other words, you get less photons per unit time. As a signal is shifted arbitrarily far, in the limit there is an arbitrary distance between photons.

Another way of think about it. A particle crossing an event horizon emits only a finite number of photons before it has crossed the horizon. Hence there are only a finite number of photons available to an observer. There will be a last photon from an arbitrarily redshifted source, after which... nothing more, ever.


Why we don't observe that kind of "frozen" galaxies right now? I think right now must be a lot of galaxies beyond the current event horizon already. Or I'm wrong?

Well, yes, there are galaxies "now" beyond the event horizon, assuming a universe homogenous on large scales and a ΛCDM model. But have a look at the diagram from Davis and Lineweaver, attached above in message post #135. and read off the implications.

We can only ever see matter before it crosses the event horizon. In the current epoch, the oldest light we see is the cosmic background radiation. The galaxies formed from that material, given a (0.3,0.7) ΛCDM model, crossed the event horizon long ago. But what we see now is still only material from which they were made, redshifted with about about z=1088. Time is not quite frozen, but in the signal we perceive it appears to run about 1089 times more slowly than reality. We don't even see it formed into galaxies yet.

Given enormous lengths of time and the capacity to see extreme redshift signal, it will eventually be possible to see it formed into galaxies. That material will have crossed our event horizon (from the diagram) about a billion years after the Big Bang; which is comparable to the age of the most distant actual galaxies we can now see.

What about galaxies we see with z=9? That's a little bit more redshifted that the best we've observed so far, but its close. We would be seeing light emitted when the scale factor was a=0.1, and there's a vertical line in the diagrams to help pinpoint those galaxies. So this is a convenient example.

The z=9 galaxy will have crossed the event horizon about 4 billion years after the Big Bang; and what we see now is from less than a billion years after the Big Bang. So in principle, there are still three billion more years of their history potentially visible to future astronomers.

Now... hold on to your hat and think on this. Consider material from a=0.001 (which is very close to what we see in the CMBR) and material from a=0.1 (which is very close to the most distant galaxies detected). When in the future would we be potentially able to observe that CMBR material developed into galaxies at the same epoch as we now observe in the most distant galaxies? You can read that off the diagram; it will be hundreds of billions of years into the future.

I have not done the actual calculations for myself. Sometime I might try it, for fun.

Cheers -- sylas

[Calimero]

And YOU MUST UNDERSTAND WHY the Hubble parameter at any time t is equal to a certain fraction H(t) = a'(t)/a(t).
This is a sort of non-trivial interesting fact, nice to think about. The time derivative of a(t) divided by a(t) itself. The Hubble parameter H(t) is the time derivative of the scalefactor divided by the scalefactor itself, at any given instant in time.




I have two questions:

1. Is there any significance in fact that when we divide speed of light wit current H(t) we get 13.6 GLY?

2. How can we see something that is now and ever was (at least when light ventured towards us) receding from us faster then light?

[sylas]

1. Is there any significance in fact that when we divide speed of light wit current H(t) we get 13.6 GLY?

No. Current indications are that it is simply a co-incidence.


2. How can we see something that is now and ever was (at least when light ventured towards us) receding from us faster then light?

Because as the photon crosses space, it eventually moves into regions where co-moving observers are receding at less than the speed of light. The "proper distance" from us to a photon emitted from such a galaxy makes a kind of pear shape. Initially, when the photon is emitted, the proper distance from us to the photon is actually increasing. That is, the direction of motion of the photon is towards us, but the distance between us and the photon is increasing, at first, because of how the universe expands.

You can reasonably speak of a "recession velocity" for the approaching photon. Locally, the photon moves at c. But the rate of change of proper distance from us to the photon is another matter. Initially, it is receding; but as it crosses space it recedes more and more slowly. Eventually, it moves into a region where the co-moving recession velocity is equal to the speed of light. At that point, the "recession velocity" of the photon is zero. But the recession velocity continues to fall, so that the photon from this point actually starts to become closer to us.

Eventually, the photon comes into our own local region of space, and it is now approaching at the speed of light.

Cheers -- sylas

[marcus]

...2. How can we see something that is now and ever was (at least when light ventured towards us) receding from us faster then light?


Because as the photon crosses space, it eventually moves into regions where co-moving observers are receding at less than the speed of light. The "proper distance" from us to a photon emitted from such a galaxy makes a kind of pear shape. Initially, when the photon is emitted, the proper distance from us to the photon is actually increasing. That is, the direction of motion of the photon is towards us, but the distance between us and the photon is increasing, at first, because of how the universe expands.

You can reasonably speak of a "recession velocity" for the approaching photon. Locally, the photon moves at c. But the rate of change of proper distance from us to the photon is another matter. Initially, it is receding; but as it crosses space it recedes more and more slowly. Eventually, it moves into a region where the co-moving recession velocity is equal to the speed of light. At that point, the "recession velocity" of the photon is zero. But the recession velocity continues to fall, so that the photon from this point actually starts to become closer to us.

Eventually, the photon comes into our own local region of space, and it is now approaching at the speed of light.


Calimero, I agree with everything Sylas said here. He gave you a good answer. But left out an important reason why this happens. It has to do with H(t) decreasing.
In the past it has decreased very rapidly. H(t) used to be like 1.3 million (when the background was emitted) and is now only 71. A huge decrease. Playing with the calculator let's you track this decrease.

You showed that you know how to get the HUBBLE RADIUS c/H. Good, so when H was decreasing rapidly then c/H was increasing rapidly.

But notice this distance divides space into two regions: Anything outside that radius is receding faster than c and anything inside is receding slower than c.

So if a photon is aimed at us, it may at first be swept back by expansion of distance as long as it is outside the c/H radius. But if it hangs in there and keeps trying to reach us, then eventually it may happen that c/H reaches out and takes it in.

Once it is inside the region of slower than c recession then its own speed dominates and it will gradually reduce its distance to us. It will gradually get closer.

The key thing is that in the past the c/H radius has extended out very very fast.

This is the basic reason we can see a lot of stuff which, when it originally emitted the light, was receding several times faster than c.

You can see this happening graphically in an animation. Google "wright balloon model"

The wiggly things (cartoon photons) travel a fixed speed like 1 millimeter per second. The whirly things are galaxies

[Calimero]

Marcus and Sylas, thank you both.
So what is now receding at, say, 2 C will need much more time to reach to us (light from it) then it would need earlier in the history?
And what is 'proper distance' ? Distance measured if we freeze expansion, and then measure? Also, what is proper time?

[sylas]

And what is 'proper distance' ? Distance measured if we freeze expansion, and then measure? Also, what is proper time?

Proper time is simply time as measured by a conventional clock that is at rest with the Hubble flow. That is, there's no additional peculiar motions to worry about. You can also think of it as the time measured by co-moving clocks.

Your description of proper distance is fine. Another way to think of it... imagine all of space filled with co-moving observers equipped with conventional clocks and rulers. The proper distance between two co-moving observers at a designated proper time instant would be the instantaneous sum of distances given by all the co-moving rulers.

And thanks Marcus for adding the point about H changing over time!

[marcus]

So what is now receding at, say, 2 C will need much more time to reach to us (light from it) then it would need earlier in the history?
...

Indeed infinitely more, will never get there. Good intuition. Abs. on target!

In fact even 25% greater than c and the galaxy cannot send us a message that will reach us.
This is because H(t) is decreasing so much slower now than in the past. So the distance c/H is reaching out so much more slowly now.

The distance limit as of now is about 15 Gly. Somewhere between 15 and 16 as I recall.

If a galaxy is within that range, we could send a light signal to it today that would reach it eventually. And some event occurred there today, an explosion say, we would eventually see it. Even though the distance to the galaxy is increasing faster than c.

But if it is beyond that range today, say more than 16 Gly in "now" freezeframe distance, we can as of today send no signal that will get there. But of course there is plenty of information already on its way, we can look forward to watching her for a long long time. Just nothing she does from now on will ever reach us.

As a very very rough estimate (Sylas may be able to refine this) the breakpoint is redshift z = 1.6
You can refer to Morgan's cosmos calculator and see what that corresponds to in distance terms. It corresponds to distance just slightly less than 15 Gly, and a recession rate of around 1.1 c.

I haven't checked this but I think its roughly right.

It used to be that H was decreasing so fast that material could be receding at 3 c or faster and emit light and it would reach us. Now if a galaxy or other material is receding at even 1.15 c or so, it can't reach us
but if it is receding 1.05 c it can emit light that will still eventually reach us.
And borderline is around 1.1.

I'm overstating the precision because I want to talk concrete examples, but I don't actually know the breakpoint (and it depends on cosmo parameters like 0.73 and 0.27 and 71 which are themselves uncertain!)

I have to go do something realworld. Can't finish this post. Sylas mentioned something extremely interesting--observers at rest with respect to the expansion process itself.

In practical terms that means at rest with respect to the ancient light. the background. that means no doppler hotspot in any direction, when you measure the microwave sky temperature. Absolutely an all important concept.
The concept of a network of observers at rest is what the ideas of NOW and then rest on, the idea of being able to specify a moment when you freeze expansion in order to define the freeze distance. The time "t" that is really there in the Hubble law v = H t. That time depends on the concept of being at rest with respect to background, or with respect to the expansion process. It is so important, so basic. It is the "t" in the basic Friedman equations model that all cosmology rests on, and the "t" of the scalefactor a(t).

Have to go move the car, however, because tomorrow is street cleaning. Don't want to get a ticket.

[E=mc^84]

We may not be able to observe it at the moment but we need to make the assumption something is there. We have never seen life outside our planet but we assume it exists and create ways to seek out and prove it. A similar thing should be done in cosmology. We should be making insturments that can help us study the beyond.



Yes it maybe irrevelent and these other universes may contian different laws of Nature. However like alien life, I do think we will be able to learn about it in the future. We shouldn't give up. No one has ever seen a quark (correct me if I'm wrong) but we assume the microverse goes further.

If we had a space ship that can do this, what do you think it will run into at the ends of the universe? Will the space ship keep going or is it constricted to this universe only? What do you think?

What if we can observe it indirectly lke we do with blackholes?

[Calimero]

In fact even 25% greater than c and the galaxy cannot send us a message that will reach us.
This is because H(t) is decreasing so much slower now than in the past. So the distance c/H is reaching out so much more slowly now.

The distance limit as of now is about 15 Gly. Somewhere between 15 and 16 as I recall.

If a galaxy is within that range, we could send a light signal to it today that would reach it eventually. And some event occurred there today, an explosion say, we would eventually see it. Even though the distance to the galaxy is increasing faster than c.

But if it is beyond that range today, say more than 16 Gly in "now" freezeframe distance, we can as of today send no signal that will get there. But of course there is plenty of information already on its way, we can look forward to watching her for a long long time. Just nothing she does from now on will ever reach us.

As a very very rough estimate (Sylas may be able to refine this) the breakpoint is redshift z = 1.6
You can refer to Morgan's cosmos calculator and see what that corresponds to in distance terms. It corresponds to distance just slightly less than 15 Gly, and a recession rate of around 1.1 c.

I haven't checked this but I think its roughly right.

It used to be that H was decreasing so fast that material could be receding at 3 c or faster and emit light and it would reach us. Now if a galaxy or other material is receding at even 1.15 c or so, it can't reach us
but if it is receding 1.05 c it can emit light that will still eventually reach us.
And borderline is around 1.1.

I'm overstating the precision because I want to talk concrete examples, but I don't actually know the breakpoint (and it depends on cosmo parameters like 0.73 and 0.27 and 71 which are themselves uncertain!)


That numbers are just about right according to calculator. Does it mean that it tends to even at C at some distant future?

Let me ask you another question about calculator. I obviously lack math behind it, but for any redshift (z), you can put any value for H(t) above ~35 and speed away is not affected, just the distance is changing proportionally. Why is that? Can you even "go trough time" with changing just H(t), or you must change Omega too?

[Chronos]

So how are we able to observe the CMB at z ~ 1090? I perceive an ATM reply.

[sylas]

So how are we able to observe the CMB at z ~ 1090? I perceive an ATM reply.

What is the problem? At that redshift, the wavelength is in the microwave region, at about 2mm wavelength. You observe it with a microwave receiver; nothing ATM about it.

[marcus]

That numbers are just about right according to calculator. Does it mean that it tends to even at C at some distant future?

Let me ask you another question about calculator. I obviously lack math behind it, but for any redshift (z), you can put any value for H(t) above ~35 and speed away is not affected, just the distance is changing proportionally. Why is that? Can you even "go trough time" with changing just H(t), or you must change Omega too?

Calimero I just this moment saw your post :biggrin: it is after midnight here and I need to get some sleep. Other wise I'd answer!
I found a source with exact estimates of the cosmic event horizon.
A paper by Egan and Lineweaver (excellent guy)
I was saying something like 15 Gly and in fact that was close---actually 15.7 Gly. But it is shifting slightly and in the longterm limit it will be 16.4 Gly
Yes. Asymptotically the recession speed will be c at that distance. Your intuition was correct.

I can't answer your question about the calculator right now because sleep is more important. In case anyone wants to look at Egan Lineweaver I'll get the link.
http://lanl.arxiv.org/abs/0909.3983
It is a technical paper but it has some useful numbers in an appendix at the end.

So on Lineweaver's excellent authority, if a galaxy is 15.6 Gly from us right now, then we could send them a message today and it would eventually get there! But it would take a hell of a long time.
And if the galaxy is now 15.8 Gly from us there is no way, the message would never get to them. Even if we set off a supernova they would never see it. :biggrin:

[lambdaorionis]

May I try and simplify....

Observable = Baryonic matter
Outside this is the Vaccum -

The Big bang did not cause the baryonic matter to "spread out" but it is the reaction of the vacuum which is responsible.
The big bang did not start from a singularity.

Anyone like to add?

[qwe]

Is it just black space extending forever? Or perhaps black space for a finite distance until another universe?

I find it hard to believe our universe is just the only universe. I don't see how it wouldn't extend for eternity instead. What is so special about our universe and the space we are in?

What do you think?
By logical necessity, there is literally 'nothing' beyond the observable universe. It is impossible to apply falsifiable predictions to something that is inherently unobservable.
In other words it is more in the realms of philosophy right now. But don't you think in the future we may be able to see beyond what is now considered the observable universe and find other universes? What do you think?

It just doesn't make any sense how this universe could be the only one. I always thought of the universe/multiverse/omniverse as infinite.

If there is 'nothing' outside the observable universe it would be just black space for eternity, right? Unless the universe is round (which all current evidence points to it being flat) then you can't arrive back in the universe in the other side. Plus most likelly space, like "time" is infinite.
don't you all mean "universe"? the observable universe extends to the hubble sphere right, but there's no evidence that everything would just stop exactly at the line of earth's observable universe. that'd place us at the center, which is silly. things seem like they extend for quite some space beyond the sphere we can observe right?

[marcus]

... that'd place us at the center, which is silly. ...

You have the right idea. It would be quite silly to limit our idea of the U to an observable sphere around us. :biggrin: Because models which extend beyond that can be tested by what they predict that we can observe.

Restricting our models to the immediately observable range would make them unnecessarily and unreasonably complex. Nobody does it and there would be no justification for it. So you are right. Silly is the correct word.

But you need to check the definition of the Hubble sphere, and be sure what the different horizons mean.


the observable universe extends to the hubble sphere right,

Actually not Qwe, the observable extends way way beyond the Hubble sphere. The Hubble radius corresponds to redshift z = 1.4, ( BTW that is a proper distance of 13.7 Gly. Proper means freeze-frame, it would be what you would measure by conventional means if you could freeze the expansion process at this moment, and depends on estimated values of cosmo parameters).


Anyway we see way beyond z = 1.4. We see millions of galaxies with redshifts larger than 1.4, out to more than z = 7! And the Background has redshift about z = 1090!

When we observe the microwave background we are looking at matter which is now at a proper distance of over 45 Gly. If you could freeze expansion it would take 45 billion years for a flash of light to get from here to the matter that emitted the background radiation we are now receiving. Of course that matter used to be a thousand times closer but that is how far it is now.

By definition the Hubble radius is merely the distance that is expanding at rate exactly c. If a galaxy is right at z = 1.4 then (if it is stationary relative to background) the distance to it is increasing at rate c. If it is farther, with larger redshift, then of course the distance is increasing at more than c.

The Hubble law v = Hd is defined in terms of proper distances and the current rate they are increasing.

But anyway, just to be clear, the observable is way bigger than the Hubble.

but there's no evidence that everything would just stop exactly at the line of earth's observable universe.

That's right! It's an important point. It would be foolish to pretend the universe "stops" at a proper distance of 45 Gly (the distance today of the most distant matter we are observing.) In cosmology we work with a mathematical model and our view of the universe is inferred. The standard model certainly does not stop at 45 Gly! :biggrin:
It wouldn't work if it did.

The game in a math science like cosmo is to get the simplest model that fits the data. And nobody I know of uses a bounded model where the U "cuts off" at some observation limit like 45 Gly (proper).

A few (pretty clearly misguided) people might say we OUGHT to only consider the universe what we can see in real time----mathematical inference based on model-fitting should not be allowed, they imply.
Heh heh, but almost NOTHING is being eyeballed real-time. A dragon could have eaten everything out beyond redshift z = 0.1 yesterday and we wouldn't know it for a long time!
Almost everything we can say is based on inference using a model (which has been tested every way we can think using all the data we can scrape up!)

We infer how things are nowadays from light we are getting now that was mostly emitted long ago. Strictly speaking that is mathematical model based inference, and relies on the simplicity of the model. You could always postulate a dragon who has moved things around or eaten a bunch of stuff, so that the real U is different from what we infer, but putting in the dragon would complicate the model.

Same way with putting in a boundary with a cutoff at some distance like 45. It would just make things more complicated and there is no reason to do it.

[Flatland]

In other words it is more in the realms of philosophy right now. But don't you think in the future we may be able to see beyond what is now considered the observable universe and find other universes? What do you think?

It just doesn't make any sense how this universe could be the only one. I always thought of the universe/multiverse/omniverse as infinite.

If there is 'nothing' outside the observable universe it would be just black space for eternity, right? Unless the universe is round (which all current evidence points to it being flat) then you can't arrive back in the universe in the other side. Plus most likelly space, like "time" is infinite.

If the universe is infinite then there will just be more stars and galaxies beyond the observable universe.

[marcus]

If the universe is infinite then there will just be more stars and galaxies beyond the observable universe.

I agree, Flatland. The basic premise in cosmology is matter distributed uniformly. The so-called "Cosmological Principle" that Einstein stated in a 1917 paper on cosmology. Then restated in a paper in 1931. It was first called that in 1935, I believe

As long as we have no reason to think otherwise, we assume the Universe is just more of the same in every direction. And that makes the models simple, because no edges to worry about.

It's kind of a Copernican idea---that we aren't special and our location isn't special. But it's more important than just ideas, it makes the math simple and makes the model work right. And it continues to check out pretty well, at least to first order approximation. Can never be sure of course.
=========================
A good exercise in this connection is to use one of the online calculators to find the distance to the surface of last scattering. This is basically the location of the matter that emitted the radiation we detect as microwave background (the socalled CMB).

The CMB has an estimated redshift z = 1090. So for instance you google "cosmo calculator" and get Ned Wright's online calculator and put 1090 in the z box.
You get that the proper distance (the kind that goes into Hubble law) is 45.6 billion light years. The light travel time (a time, not a distance) comes out to be 13.7 billion years. That is sometimes called the "look-back time". Because of expansion, the lookback time is not readily convertible into the distance and shouldn't be confused with it.
Here's a quote from the calculator output:

=====quote Wright's cosmo calculator==

For Ho = 71, OmegaM = 0.270, Omegavac = 0.730, z = 1090.000

It is now 13.666 Gyr since the Big Bang.
The age at redshift z was 0.377 Myr.
The light travel time was 13.665 Gyr.
The comoving radial distance, which goes into Hubble's law, is 13995.7 Mpc or 45.648 Gly.
===endquote===

[Chronos]

Most modern cosmological models limit the extent of the observable universe to one that has an observed [and model dependent] limit of about 13.7 billion light years from earth. At that point your hit a wall called the surface of last scattering. We are currently unable to observe more ancient/distant entities. There are theories suggesting there may be more than we can currently observe, but, none have observational support to date. Marcus is better acquainted and frequently posts on this very interesting topic.

[jreelawg]

Let's rephrase the question. What is beyond the observable everything? That doesn't even make sense. There is no observable universe. The universe includes both observable and the unobservable. Taking all we see and calling it the universe is dumb. Lot's of cosmologists do this and it is annoying. Some of them have the decency to at least say observable universe which as I pointed out makes no sense also, but at least I can understand what they intend to say.

[marcus]

Let's rephrase the question. What is beyond the observable everything? That doesn't even make sense. There is no observable universe. The universe includes both observable and the unobservable. Taking all we see and calling it the universe is dumb. Lot's of cosmologists do this and it is annoying. Some of them have the decency to at least say observable universe which as I pointed out makes no sense also, but at least I can understand what they intend to say.

I agree that it is silly--or as you say, "dumb"--to say universe when what you mean is just the observable portion. My favorite cosmology prof at Berkeley was very careful about this---always said "observable universe" when he meant just the that limited portion. My impression is that most others, professionals, are equally careful but I couldn't swear to it.

It strikes me as either misleading or crackpot to insist on a nonstandard terminology, where only the directly visible portion is treated as the whole. Except when talking to journalists or to a lay audience I can't think of any working cosmologist who makes that mistake.
I could be wrong though, you may have encountered that more than I have.

We do get a small amount of it here at PF though. Most people are not confused, I hope.
A kind of mild ineffectual trolling---best thing could be to simply ignore.

[MotoH]

Wouldn't the non-observable universe be everything and nothing? Since electrons can take all paths to a given point, and only chooses a specific path once it is observed, shouldn't anything beyond our observations be either here nor their?

Am I out of line in believing this?

[marcus]

Wouldn't the non-observable universe be everything and nothing? Since electrons can take all paths to a given point, and only chooses a specific path once it is observed, shouldn't anything beyond our observations be either here nor their?

Am I out of line in believing this?

Well you could be getting quantum mechanics mixed up with classical concepts here :biggrin:

Words have different meanings in different contexts. The observable universe in cosmology is a CLASSICAL idea (not quantum mechanical). It is a big spherical region a ball with us at the center. Full of all the matter from which we could be currently getting light and other signals (neutrinos, gravity waves...)

Or in 4D you can think of it as contained in our backwards lightcone.

=======================

In Quantum Mechanics, what passes for observation does not need to involve humans, or even consciousness. It is a very general idea. A particle can be forced to choose simply by interacting with other particles---with its environment.

For us, the most distant matter that we get light from is at the socalled "surface of last scattering"---currently about 45 billion light years away.
That's the distance you would measure if you could stop the expansion process now and use conventional means. Sometimes called the now distance, or the current proper distance.

Don't think of the stuff that is out beyond 45 Gly as somehow "fuzzy" just because WE are not out there to see it :biggrin: We aren't that important.

[hurk4]

existence, whatever that is!
hurk4

[marcus]

existence, whatever that is!
hurk4

Heh heh, good to hear from you, Hurk!
Sounds like you hit the nail on the head.

Or how about this: "what is beyond the observable universe?"
"The unobservable universe."

[iflexit_1]

Perhaps an easier explanation is available, premised in GR. In General Relativity, space is dynamic. It can expand, shrink and curve without being embedded in a higher-dimensional space. In this sense, the universe is self-contained. It needs neither a center to expand away from nor empty space on the outside (whatever that is) to expand into. When it expands, it does not claim previously unoccupied space from its surroundings.

[Chronos]

If you see it, it is by definition part of the observable universe. The 'unseeable' parts of the universe are, and will always be observer dependent.

[aashay]

I think it makes no sense in thinking what is there beyond the observable universe as we cannot visualize it. It is like an ant on a surface of an expanding balloon who cannot imagine anything outside the surface of the balloon.

[DarkStar7]

The edge of the Universe is where all matter is expanding away from us at the speed of light. Any energies lost over this universes 'event horizon' is returned back into the quantum realm to drive microbangs that produces dark energy inflation along with all the other properties of the excepted standard
model.


I think if this were true dark energy and an excess cosmic microwave radiation should be more concentrated near large blackholes such as our Milkyways super massive one. Is there such evidence?

[bapowell]

Most of the accepted hypotheses regarding the origin of the universe (U) refer to it as if we could take a God's Eye view and see it from the perspective of an outsider. For instance, Alan Guth's Inflation postulates an inflaton particle that came into existence as a statistical necessity because it could do so in an extremely high energy state which could then decay into the U that we see. For this to happen, there must have been some sort of meta space and meta time, a metaspacetime.
What do you mean by metaspacetime? How does that follow from your previous point? Low energy inflation can certainly be implemented in the early universe, although many would argue that it's not as natural as high energy inflation.

[bapowell]

Where is (or was) the Inflaton particle? We are speaking of it as if it had an existence of its own before it decayed into our universe. If so, there was and is a whole set of dimensions beyond this universe that I call metaspacetime. don't let semantics get in the way. It doesn't matter what we call it. Pythagoras said "All is Number." If we can represent it mathematically, it is real. Somewhere, somewhen.
I think you're misunderstanding the premise of the inflationary universe. The inflaton didn't decay into our universe, rather, it is a field that lived in our universe. It is typically modeled as a quantum field, just like any other. Linde's early chaotic inflation model takes the stage soon after the standard hot big bang. It postulates that the inflaton field existed everywhere in space in the early universe (along with all the other matter and energy from the big bang), with an energy density stochastically distributed in space. Regions of high relative inflaton energy density underwent inflation. The small inflationary patch grew in size to a an empty, homogeneous, essentially flat region. The inflaton field then decays into radiation. This is now the hot big bang from the perspective of the inflated region. In other words, the inflationary patch that eventually grew to form our observable piece of the universe was itself just an ordinary region of space already existing in the universe soon after the big bang.

[bapowell]

Lots of physicists still resist the quantum concept as it may apply in the macroscopic world,
Isn't this what decoherence addresses?

[bapowell]

Decoherenc is another word for collapse of the quantum waveform upon observation. But, decoherence is just an interpretation according to the Copehagen convention. Wheeler and his students would opt for superposition and divergence of some of the "many worlds" upon any such observation. But is any of this testable?
I don't know if it's testable, that's not the point I was refuting. You claimed earlier that physicists resist the application of QM to the macroscopic world. I was pointing out the decoherence as it applies to the 'qauntum-to-classical' transition is an example of how quantum mechanics is applied to macroscopic objects. I agree that there are several competing interpretation of exactly what all this means, but that's a different matter entirely from whether or not QM, at least phenomenologically, is applied to the macroscopic world.

[hurk4]

Heh heh, good to hear from you, Hurk!
Sounds like you hit the nail on the head.

Or how about this: "what is beyond the observable universe?"
"The unobservable universe."
Dear Marcus, thank you for your kind remark.
My answer "Existence" was the most general I could imagine, but what can we do we this "non practical" remark, I guess almost nothing.
I could eventually fill in more details at the price being speculative.
So I could for instance add "coherence with our observable universe".
Glad to see that Martin Bojowald came with a book "before the big bang" in german language also translated in dutch language year 2009. This of course is his view on what is beyond.
I must also remark to you that the (our) unobservable universe is partly observable by a virtual observer near the edge of our observable universe and so on until there might eventally/(inevitably?!) be a real event horizon for our domein of the universe .
kind regards,
Hurk4

[ChrisHG23]

Hi,
This will be my first ever post. and I apologise of its wrong but,...

It seems to me the universe is only flat because like fish in water we are only able to perceive our realm, and not the whole universe in which our watery realm exists. Outside of the observable universe is the rest of time, either left behind, or yet to come. I see the universe as an infinite singularity in which our experiences are relative points formed from the balance between the infinite expansion and contraction of time, space and the universe as a whole. The Big Bang was also a Big Crunch and it's is still happening beyond the boundary of the 'Observable Universe'.

To me 'we' are still shrinking, why else would galaxies spin so fast and Black Holes get so small. This is a product of The BigBangBigCrunch. If THE infinite nothing that has no scale, then the primordial universe could not be limited to form or scale as it would have the infinite spectrum of form and scale to 'evolve', 'grow', 'expand' or 'contract', and it is this relative part of time and space we call home, our universe.

[bapowell]

Hi,
This will be my first ever post. and I apologise of its wrong but,...

It seems to me the universe is only flat because like fish in water we are only able to perceive our realm, and not the whole universe in which our watery realm exists. Outside of the observable universe is the rest of time, either left behind, or yet to come. I see the universe as an infinite singularity in which our experiences are relative points formed from the balance between the infinite expansion and contraction of time, space and the universe as a whole. The Big Bang was also a Big Crunch and it's is still happening beyond the boundary of the 'Observable Universe'.

To me 'we' are still shrinking, why else would galaxies spin so fast and Black Holes get so small. This is a product of The BigBangBigCrunch. If THE infinite nothing that has no scale, then the primordial universe could not be limited to form or scale as it would have the infinite spectrum of form and scale to 'evolve', 'grow', 'expand' or 'contract', and it is this relative part of time and space we call home, our universe.
I'm going to assume that this is a joke and that you aren't really looking for an intelligent response to this...

[DaveC426913]

I'm going to assume that this is a joke and that you aren't really looking for an intelligent response to this...

I do not think it is a joke (that's not very nice - he did say it was his first ever post), but Chris should review the PF rules on posting overly-speculative ideas.

Overly Speculative Posts:
One of the main goals of PF is to help students learn the current status of physics as practiced by the scientific community; accordingly, Physicsforums.com strives to maintain high standards of academic integrity. There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound. It is against our Posting Guidelines to discuss, in most of the PF forums or in blogs, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion. Personal theories/Independent Research may be submitted to our Independent Research Forum, provided they meet our Independent Research Guidelines; Personal theories posted elsewhere will be deleted. Poorly formulated personal theories, unfounded challenges of mainstream science, and overt crackpottery will not be tolerated anywhere on the site. Linking to obviously "crank" or "crackpot" sites is prohibited.
http://www.physicsforums.com/showthread.php?t=5374

[Ray Palmer]

New to forum - what lies beyond the stuff that lies beyond the edge of the universe? The recent "dark flow" observations are perhaps some circumstantial evidence for other branes. However, if we are just holographic projections then a richer reality lies beyond.

[hurk4]

Observable?
Observations on systems near the edge of the (our) observable universe could give information about the observable universes of those systems. Their OU's partly overlap with our unobservable universe (UOU). So IMO our UOU can be indirectly be observed?
regards,
hurk4

[SheldonCooper]

This is a fascinating question. I think the answer to the poll at the beginning of this thread has to be "C - Other", since we cannot possibly hypothesize what we have never observed, not just with our senses, but also with our math. Garrett Lisi, Steven Hawking, LHC, and the rest are all doing important work, but the real interesting questions may still remain even after Higgs is explained. How did this singularity with such enormous potential just appear in this infinite void in space/time? Think about it; really think about it. Things are going to get very interesting very soon I think. Right Rhody boy?

[marcus]

...since we cannot possibly hypothesize what we have never observed...

?

Like living dinosaurs? Like the formation of the solar system?

We use logical and mathematical models all the time to reconstruct the past, and to infer conditions in regions where we have no direct sensory knowledge.

There are no absolute certainties, but people can weigh the evidence in good faith and search for consistent economical explanations.

[DaveC426913]

?

Like living dinosaurs? Like the formation of the solar system?

We use logical and mathematical models all the time to reconstruct the past...

We have more than logical and mathematical models of dinosaurs and newborn solar systems. We have direct observation.


I think that the connection you are trying to draw between [living crocodiles + bones and soft-tissue samples of extinct animals, etc.] and [a part of the universe we can never observe, or any indirect evidence of it - even in principle] is very weak.

[marcus]

I think that the connection you are trying to draw

What connection do you imagine I am trying to draw?
In what I just said I was not talking about the early universe or whatever, I was responding to a general statement which the poster made:

"we cannot hypothesize about anything we have not directly observed"

I want to contradict that general proposition, and there are a million and one different examples. I chose living dinosaurs.

Fairies may have manufactured fossils and buried them where we would find them, to fool us. :biggrin: Or leprechauns. But it is simpler to assume that they lived and that the fossils are their remains.

My point there is simply that we CAN hypothesize and infer about (at least some things) that we have not observed!

You are putting words in my mouth if you think this is being equated to cosmology, or put on the same level of certainty, or something. That is your, Dave's, idea.

However we do use inference in cosmology, and pick simple economical explanations. What the level of certainty is, is another question that needs a separate discussion.

[bapowell]

Fairies may have manufactured fossils and buried them where we would find them, to fool us. :biggrin: Or leprechauns.
This is what I've been saying all along!!! At last, someone who shares my view! :smile:

[marcus]

:rofl:

I guess the point should be made, in case anyone hasn't followed the discussion, that from a standard cosmo viewpoint the correct "OTHER" in the poll was "more of same". Essentially because that is the simplest thing to assume.

The simplest mathematical model that fits the data (and conforms with fundamental physics like GR) does not have any boundary or discontinuity at our observational horizon. The most distant matter we see is what we see as it was 13.7 billion years ago as it was hot gas radiating the CMB light we now detect and use to map its temperature and density variations. We have no reason to suppose that that matter has not evolved just like ours has---cooling and condensing to form stars and galaxies.

It would complicate the model physically to try to introduce some sort of boundary out there, or some drop-off of density. So we assume that things look, out there, pretty much the same as they do here, in all directions.

This was the choice which the original poster Silverback, who set up the poll, should have included explicitly. But did not, causing many of us to either not vote, or choose "other".

[ComfortNumb]

Gonna be flippant on my very first post.

I reckon there is a big brick wall made out of dark matter encircling our universe. Then when a galaxy hits the wall the energy passes through it to create a big bang on the other side and therefore creating another universe!

Then I woke-up!!!

[DaveC426913]

What connection do you imagine I am trying to draw?
In what I just said I was not talking about the early universe or whatever, I was responding to a general statement which the poster made:

"we cannot hypothesize about anything we have not directly observed"

...which is a direct comment on hypothesizing about what is outside the observable universe.


Either you are suggesting that
- we can hypothesize about what is beyond our observable universe
analagous to the way
- we can hypothesize about dinosaurs and our own solar system
or you are not paying attention.

What I am saying is that yours is a faulty analogy. I refute that there are a million and one examples. I suggest the examples could be counted on one hand at the most. There are few, if any, things in all creation that are analagous to hypothesizing about outside the universe. It's just not the same thing as extrapolating from known bones to unknown dinosaurs.

[marcus]

*sigh*
We aren't communicating Dave.
I made no reference to the observable universe (in that statement).

What we have not directly observed (like live T. Rex walking around) is not the same as what a cosmologist means by "outside the observable universe."

You misinterpreted what I said, and you made a false imputation. I don't see how it benefits you to continue insisting. I don't see why I should discuss it with you until you acknowledge your mistake and stop telling me I said something that hadn't even crossed my mind :biggrin:

[marcus]

.
...Either you are suggesting that
- we can hypothesize about what is beyond our observable universe
analagous to the way
- we can hypothesize about dinosaurs and our own solar system
or you are not paying attention.
...

Dave, instead of your telling me all about what you think I said and what you think it implies, let's move the discussion in a more productive direction! Do you have anything substantive to say about the topic?

Would you like to summarize what you've said already? (about our knowledge/reasonable assumptions about what is beyond the limits of observation.)

Would you like to say briefly what you think those limits are?

[DaveC426913]

Dave, instead of your telling me all about what you think I said and what you think it implies, let's move the discussion in a more productive direction! Do you have anything substantive to say about the topic?

Would you like to summarize what you've said already? (about our knowledge/reasonable assumptions about what is beyond the limits of observation.)

Would you like to say briefly what you think those limits are?

No. I am unnecessarily interrupting the discussion. Carry on.

[Dav333]

So what could "other" be? lol something our primitive minds could never comprehend?

This topic makes me go a little crazy thinking about it.

[friend]

Dave, instead of your telling me all about what you think I said and what you think it implies, let's move the discussion in a more productive direction! Do you have anything substantive to say about the topic?

Would you like to summarize what you've said already? (about our knowledge/reasonable assumptions about what is beyond the limits of observation.)

Would you like to say briefly what you think those limits are?

I'd like to venture a possibility, maybe it's already been said in this thread. But each observer has a different observable horizon than any other observer by the distance that separates the two observers. The fact that both observers see the same interactions at the edge of their observability would suggest that what is unobservable to us is essentially the same as what we do observe.

[marcus]

So what could "other" be? lol something our primitive minds could never comprehend?
...

Not necessarily. For many of those who answered "other", the preferred choice would have been "more of the same". I gather this from several comments made already. Also it is the standard view of professional cosmologists.

It's just that the person who set up the poll overlooked that possibility and neglected to include "more of same" as one of the choices!

So those of us who go with the conventional view (as the simplest and most likely working hypothesis) had no choice but to select "other".

... would suggest that what is unobservable to us is essentially the same as what we do observe.

Friend, it sounds like you are searching for an argument to justify the "more of same" answer (which in this rather imperfect poll we have had to represent by choosing "other").

In other words if you and I could magically transport ourselves out 45 billion lightyears from here, to the matter which 13.7 billion years ago as a glowing hot gas emitted the background radiation which we are now receiving with the WMAP spacecraft, we would see that that matter had condensed into stars and galaxies similar to ours.

We would see that from that point at the edge of earth's observable, the universe looks pretty much the same in all directions as it does viewed from earth. Same types of galaxies, with the same types of stars in them, distributed in the same more or less random way. Without a detailed map one wouldn't expect to be able to tell the difference.

This is what is generally assumed because it is the simplest, and because nothing has been observed that suggests anything else. And probably also, I suppose, because it leads to a nice mathematically simple, manageable model.

[atyy]

This is what is generally assumed because it is the simplest, and because nothing has been observed that suggests anything else. And probably also, I suppose, because it leads to a nice mathematically simple, manageable model.

There's interesting commentary about this http://books.google.com/books?id=uG9sDiUZJ94C&printsec=frontcover&dq=plebanski+relativity&source=bl&ots=Y4Fj8Sujq_&sig=2CtlfguFEYxQMnw-0XVZEuCAzSU&hl=en&ei=6v_BS9G5A4H88AaGo4jPCA&sa=X&oi=book_result&ct=result&resnum=7&ved=0CCAQ6AEwBg#v=onepage&q&f=false , p236.

"Today the cosmological principle still has no direct observational verification, while models not obeying the principle ... are known ............. inertia in thinking and of emotional attachment to the, mathematically elegant .......... However, natural sciences, ..... are said to use the criterion of consistency with observation .... At the very least in order to verify the cosmological principle, alternatives have to be considered ....."

[friend]

We would see that from that point at the edge of earth's observable, the universe looks pretty much the same in all directions as it does viewed from earth. Same types of galaxies, with the same types of stars in them, distributed in the same more or less random way. Without a detailed map one wouldn't expect to be able to tell the difference.

The alternative would be that the constants of nature are not constant. If they don't change sharply at the edge of observability, then we would see them changing gradually. But we don't see them changing gradually, and we don't expect to see them change abruptly. So we conclude that they don't change from one patch of observability to the next.

[DevilsAvocado]

Since this question can’t be answered by current theories... I guess it’s 'Carte blanche' for some personal speculations...

Many have expressed a similar view – but I would take it to the next step and say: There must be more (observable) universe, much much more. I would claim the universe must (probably) be infinite.

Why!?

To start with "much more", as marcus mentioned – it’s the only logical path. Imagine a lot of observers at the edge of our observable universe, 45 billion lightyears from the Earth. They clearly must see the same as we do, in all directions. And so on, and so forth, etc...

http://i43.tinypic.com/10hlvv5.jpg

Any objections against this would put us back to the Middle Ages, where the Earth was the center of everything, and was flat. And the obvious question would remain – "Fall down into what?"

And WMAP has shown that our local universe is almost flat, meaning we are not looping around our local universe.

The "infinite question" is answered by the same logic. Why would we be in the center of something that looks like the cosmological principle? But in other very remote parts of the universe we would experience chaotic collisions with other (explosive) "stuff", or a strange "sharp edge", or "wall"??

The only problem with an infinite universe is the propagation of the cosmological principle (and physical laws). Some say inflation can fix this. But, as to my understanding, it must then be an "infinite inflation"...??

Well, that's my personal speculations, and nothing more.

[pixchips]

If I imagine that I am the center of the universe (my wife suggests that this is often the case), and everything extends only to the 45billion lyr radius, then density calculations of the universe make some sense. The total matter/energy in that sphere is pretty big, but finite. So the original singularity (or whatever) that started the BB may have been of infinite density, but finite mass. If, on the other hand, the universe is infinite, and no matter where I transport myself, I see the same thing out to 45billion lyrs, then the original singularity had infinite mass. And was doubly infinitely dense (Aleph1 ... or what?) I don't know how to think about this. Homogeneous and infinite sounds good from a modelling standpoint, but how can we ever imagine that it all started with an infinitely small spec of infinite mass? Or am I making a bogus assumption? Was the 'primordial egg' really infinitely big, and just really really dense, and just started expanding?

According to recent popular culture: "The whole universe was in a hot, dense state, when nearly 14billion years ago expansion started ..." So maybe it wasn't all scrunched into a point??????? It would be great if real physical insight came from the lyrics of a silly sitcom.

Dave

[bapowell]

Right. Noboby thinks that singularities are physical. It's most like a breakdown of classical gravity where quantum gravitational effects are likely to become important. The Big Bang model of cosmology is just what you said: it's a model of how the universe evolved from a nascent hot, dense state.

[pixchips]

Okay, so the notion that there was an infinitely dense, infinite mass singularity that effectively exploded is just a holdover from the popular notion that the BB was just a really big bomb. The actual model says that the whole extent of the universe was extremely hot and dense, and once the BB started, it was expanding and cooling, and transistioning through its various epochs. This prompts the question: what was 'the whole extent' of the universe as t ->0.

Is it accurate to say that the universe started with infinite extent (even as t->0), and then started expanding? This changes the view (in my head anyway) that when radiation decoupled from matter (universe become transparent) it: a) happened within a finite sphere the represents the extent of a finite universe at about 100k years, or, b) happened everywhere at once in an infinitely extended universe whose density had fallen sufficiently. If (a), then the universe is not infinite, but if (b) it has always been infinite.

How would we tell the difference?



Dave

[DevilsAvocado]

... that effectively exploded ... the BB was just a really big bomb ...
pixchips, this is a BIG question for a small event...

Some 'facts':

1) No, absolutely no "big bomb". It’s a very common erroneous assumption that the Big Bang clearly must derive from the BIG BOMB! BOOOM!! But that’s totally wrong. Expansion yes, bomb no.

2) We can’t tell if the (global) universe is finite or infinite (yet), and maybe we never can.

3) When cosmologists are talking about the "BB singularity" in the size of a few centimeters, they are talking about our local universe (the observable universe). (Don’t ask me where one 'buys' a ruler at BB, because I don’t know! :wink:)

4) If the universe turns out to be infinite, then (as far as I understand) the "BB singularity" must also be infinite in size. (Please, don’t ask how this 'works' because I have absolutely no idea... :uhh:)

Besides that, why don’t you start a new thread on this topic, this is a little "Beyond The Original Question"... :biggrin:

[bapowell]

Is it accurate to say that the universe started with infinite extent (even as t->0), and then started expanding?
As DevilsAvocado (do I really need to call you that...can I just call you Dave or something?) says, we don't know what the global extent of the universe is. However, it's perfectly OK to imagine things as you state, operationally anyway. If the observable universe is sufficiently small relative to the actual size of the universe (if it's closed then small relative to the radius of curvature).


This changes the view (in my head anyway) that when radiation decoupled from matter (universe become transparent) it: a) happened within a finite sphere the represents the extent of a finite universe at about 100k years, or, b) happened everywhere at once in an infinitely extended universe whose density had fallen sufficiently. If (a), then the universe is not infinite, but if (b) it has always been infinite.

How would we tell the difference?

I think the main difference here is not whether the universe is finite vs. infinite, but whether the whole universe is larger than our observable universe. Decoupling happened everywhere at once (roughly) in the universe, whether it was finite or infinite. If our observable universe is 'all there is', then yes, this would coincide with having occurred within a finite sphere. However, the fact that we still see the CMB means that the CMB photons that we observe today originated outside of our horizon at decoupling. That's one way we know the difference. But, there's no way at present to determine whether the universe is truly infinite or just really #*$&@ big.

[DevilsAvocado]

DevilsAvocado (do I really need to call you that...can I just call you Dave or something?)
bapowell, you can call me anything you like, as long I as understand you’re addressing me (and that it’s not the 'usual' name-calling :biggrin:). Dave is OK!

Anyhow, this is getting real interesting, so I think I’ll pop in for a sec...
Decoupling happened everywhere at once (roughly) in the universe, whether it was finite or infinite.
This is the magic (at least to me): happened + everywhere + infinite

I’ve been pondering 'some' over this. It’s not only a question of decoupling, it’s question of; how do we propagate the cosmological principle + the laws of physics + everything else, that’s needed for a "working universe" – (almost) simultaneously in an infinite universe – when we know that the word 'NOW' is already completely useless in our 'little' local universe...???? :confused:

I’m complete and utterly lost here. Some say a really #*$&@ big inflation could fix this... but I doubt it...

Any ideas... :uhh:


Edit: Maybe DAve or DA’ve is better... ;)

[pixchips]

Beyond The Original Question[/B]"... :biggrin:

Okay, I was thinking of that anyway. But it does seem that 'what's beyond the observable universe' has to have a lot to do with what actually happened when BB started. On the other hand, the eventual evolution of bunny rabbits hopping around pastural fields also has a lot to do with the BB, and I don't think you'd let me pursue that topic right here. So I'm off to a new thread as soon as I get my afternoon chores done.

...

I think the main difference here is not whether the universe is finite vs. infinite, but whether the whole universe is larger than our observable universe. Decoupling happened everywhere at once (roughly) in the universe, whether it was finite or infinite. If our observable universe is 'all there is', then yes, this would coincide with having occurred within a finite sphere. However, the fact that we still see the CMB means that the CMB photons that we observe today originated outside of our horizon at decoupling. That's one way we know the difference. But, there's no way at present to determine whether the universe is truly infinite or just really #*$&@ big.

Okay, I was afraid of this. The right answer is probably in the middle. If it is, then the universe isn't infinite, it's just really really big. And for us, that's practically the same as infinite. But when we ask, 'What's beyond the observable universe?', I still think there's a difference between 'more of the same forever' and 'more of the same, up to a point'. Seems like the latter is the best answer we can give, but may not actually be a scientific question if there's no way to test it.

Thanks much for your thoughts,
I'm off to other threads ....

Dave

[bapowell]

DA've,
Sorry to take so long in replying. Couple things:

Sure, there's always conceptual trouble with an infinite space. However, nothing prohibits us from defining a time slicing such that all comoving observers are inertial. Then, there's a common time that all such observers can use, and decoupling could in principle occur simultaneously everywhere (that this slicing is defined) simultaneously. In the absence of perturbations, one can argue that this decoupling could occur simultaneously in any patch that is sufficiently uniform. Inflation could be invoked to prepare such a patch. Of course, the real universe isn't that simple, which is why I said "roughly" in my original post. Perturbations cause some regions to decouple sooner than others, both for microphysical reasons and because of the good old time dilation associated with the overdensities.

[pixchips]

Thanks for the clarification, Bapowell. I'm interested in understanding more about the time slicing you mention. This may not be the place for such a discussion, but do you have a good reference or pointer? I will try some more googling.

Dave

[bapowell]

Sure pixchips. This just different language for choosing a coordinate system. It is also referred to as choosing a spacetime foliation, or foliating spacetime. There are several good reviews on the arXiv: I'm not sure what level of detail you're interested in. There have also been some discussions about foliation here on the forum -- I participated in one a while back: http://www.physicsforums.com/showthread.php?t=381521

[DevilsAvocado]

... But it does seem that 'what's beyond the observable universe' has to have a lot to do with what actually happened when BB started. On the other hand, the eventual evolution of bunny rabbits hopping around pastural fields also has a lot to do with the BB, and I don't think you'd let me pursue that topic right here. So I'm off to a new thread as soon as I get my afternoon chores done.
pixchips, don’t take this too seriously, it was more of a 'joke' than anything else. I for one, have done this 'hijacking' numerous times... sorry if I gave the wrong 'impression'. Let’s hope the mentors don’t notice us now... :wink:

[DevilsAvocado]

... I'm interested in understanding more about the time slicing you mention.
Maybe this will work:
Wikipedia - Inertial frame of reference (http://en.wikipedia.org/wiki/Inertial_frames)
Wikipedia - Comoving observer (http://en.wikipedia.org/wiki/Comoving_observer)

[DevilsAvocado]

DA've,
Sorry to take so long in replying.
No worries mate! :wink:
In the absence of perturbations, one can argue that this decoupling could occur simultaneously in any patch that is sufficiently uniform. Inflation could be invoked to prepare such a patch.
Okay, that’s what’s been running around in my head for awhile... to get the almost smooth initial conditions, we need inflation to "stretch the sheet out" almost perfectly, leaving just a few "wrinkles"... but then some argue that the pre-conditions needed for this inflation to ever occur, is even more 'remarkable' than the resulting smoothness...

And if we add 'infinite-factor' to this – I do get some kind of 'wooziness'... :bugeye:

Some "personal speculations" to maybe get this into my head:
Could we think of the 'propagation' as some kind of a 'symmetry breaking', in the quantum-fluctuations of the 'primordial soup'...?? Like a "giant infinite lake"... the temperature is getting lower, and lower, and lower, and suddenly the whole lake is frozen, roughly at once...? (= 'symmetry breaking') ...or...??

[DevilsAvocado]

This just different language for choosing a coordinate system. It is also referred to as choosing a spacetime foliation, or foliating spacetime.
Excellent explanation in your post #2!
bapowell post #2 (http://www.physicsforums.com/showpost.php?p=2597749&postcount=2)
As a simple analogy, allow a book to represent a 3D spacetime. Then, the 2D pages of the book are your hypersurfaces, and the page numbers define how you go from one to the next: the pages and page numbers make up your foliation.
I looked around for Foliation and found Wikipedia – Foliation (http://en.wikipedia.org/wiki/Foliation) and Wikipedia – Reeb foliation (http://en.wikipedia.org/wiki/Reeb_foliation), but it doesn’t explain it as well as you did.

Could this be considered as a picture of Foliation?
http://upload.wikimedia.org/wikipedia/commons/thumb/2/21/Saddle_pt.jpg/300px-Saddle_pt.jpg
An open surface with X-, Y-, and Z-contours shown.
(Looks like two eyes or a bra... :smile:)


Reeb foliation (foliation of the 3-sphere) is illustrated as this:
http://upload.wikimedia.org/wikipedia/commons/thumb/c/cb/Reebfoliation-ring-2d-2.svg/300px-Reebfoliation-ring-2d-2.svg.pnghttp://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Reeb_foliation_half-torus_POV-Ray.png/350px-Reeb_foliation_half-torus_POV-Ray.png
Looks nice for a 'torus universe'!

[qwe]

What Is Beyond The Observable Universe?

the unobservable universe, aka the rest of our universe, aka the galaxies we don't see but are right outside of our sight range so they are next to galaxies we do see

What is beyond the Universe Altogether?

the bulk, because the universe is a brane :P

What is beyond the bulk?

not sure if this question has any meaning yet

[Frame Dragger]

What Is Beyond The Observable Universe?

the unobservable universe, aka the rest of our universe, aka the galaxies we don't see but are right outside of our sight range so they are next to galaxies we do see

What is beyond the Universe Altogether?

the bulk, because the universe is a brane :P

What is beyond the bulk?

not sure if this question has any meaning yet

You're assuming that Brane Cosmology, which is highly speculative is a physical reality? that's purely ATM. The question, and your answers cease to be meaningful after "so they are next to galaxies we do see," and even that is deceptively simplified. What is beyond the observable universe?: more of what we see around us, as we're looking at "old" light. That said, if you're talking about those we can't see it's not an LOS issue, it's an issue of recession speeds.

I don't mean this as an insult, but you just killed one thread, please don't kill this one with the same speculation.

[pixchips]

pixchips, don’t take this too seriously...:wink:

No worries! I started another thread and got some interesting discussion. At some point I have to dig into the math, but at the moment I'd like to get some pictures in my head that are at least consistent with the math.

BTW: the folliation pixes are cool, but make my head spin. I will cogitate and try to grok these.

[DevilsAvocado]

Okay, cool!

[bapowell]

but then some argue that the pre-conditions needed for this inflation to ever occur, is even more 'remarkable' than the resulting smoothness...
Probably not more remarkable, but some argue that the initial conditions for inflation are hard to come by.

Some "personal speculations" to maybe get this into my head:
Could we think of the 'propagation' as some kind of a 'symmetry breaking', in the quantum-fluctuations of the 'primordial soup'...?? Like a "giant infinite lake"... the temperature is getting lower, and lower, and lower, and suddenly the whole lake is frozen, roughly at once...? (= 'symmetry breaking') ...or...??
Not sure what you mean by 'propagation'. But the quantum fluctuations amplified by inflation can certainly be thought of as 'breaking the symmetry' of the classical, smooth geometry. As far as the "giant infinite lake" goes, I think you're just about describing the early understanding of inflation. Guth perceived inflation as a phase transition, much like the kind we read about in thermodynamics. He suggested that as the universe cooled, parts of it were 'trapped' in a higher energy phase -- the universe is said to have undergone supercooling (just like when you lower the temperature of a liquid below its freezing point without it becoming frozen). These higher energy phases (the liquid) are the inflating regions. Finally, the phase transition completes -- the inflating regions decay to lower energy and the standard radiation dominated expansion commences (where does this radiation come from? From the phase transition perspective, it's the latent heat associated with the phase change!) Now you may also know that the scalar field that drives inflation is the order parameter of this phase change, and the shape of its potential can resemble those functions seen in the 1st or 2nd order phase transitions in thermodynamics. The truly exciting part, is that in the early days it was hoped that the inflaton was a GUT Higgs field, responsible for breaking the GUT symmetry. The idea that symmetry breaking in particle physics could manifest itself as a cosmological phase transition is beyond awesome. Unfortunately, today we know that it's unlikely that the inflaton is a GUT Higgs, and it's unclear what its identity is.

[George Jones]

Probably not more remarkable, but some argue that the initial conditions for inflation are hard to come by.

A few "radicals" think "More remarkable."

http://www.physicsforums.com/showthread.php?p=1355858#post1355858

[Flatland]

Re-review what matt.o had to say. I think you are hopelessly deluded. String theory predicts . . . not a damn thing. Feel free to to contradict that assertion with . . . a testable prediction. I love those things.

I never said string theory made any testable predictions. Reread what I said and get a clue. No one would suggest that string theory is anything more than a hypothesis. Who's the deluded one again?

[Frame Dragger]

I never said string theory made any testable predictions. Reread what I said and get a clue. No one would suggest that string theory is anything more than a hypothesis. Who's the deluded one again?

You said, String Theory actually claims to explain what happened before the BB.

If those predictions are not testable, and you don't believe in them... why bring that up as an answer to "what is beyond the observable universe"? I would conclude that by page 5 or 6, other more basic answers had been given, and you don't endorse string theory, but simply offered a fact... string theory DOES in fact, make that claim.

That said, for what I suspect is a simple misread on Chronos' part (something we've all done, probably) your response is rude as HELL. Is this how you want others to respond to your simple mistakes?

[qwe]

You're assuming that Brane Cosmology, which is highly speculative is a physical reality? that's purely ATM. The question, and your answers cease to be meaningful after "so they are next to galaxies we do see," and even that is deceptively simplified. What is beyond the observable universe?: more of what we see around us, as we're looking at "old" light. That said, if you're talking about those we can't see it's not an LOS issue, it's an issue of recession speeds.

I don't mean this as an insult, but you just killed one thread, please don't kill this one with the same speculation.
i know brane cosmology is not certain

we pretty much totally agree though. what's beyond the observable universe? more of the same. that's why i said a galaxy happening to be right outside of our visual range, would be close to galaxies we cannot see

[DevilsAvocado]

... Unfortunately, today we know that it's unlikely that the inflaton is a GUT Higgs, and it's unclear what its identity is.

Thanks bapowell. Sorry for being very late... I was 'ensnared' in an EPR discussion over at QM...

[Frame Dragger]

i know brane cosmology is not certain

we pretty much totally agree though. what's beyond the observable universe? more of the same. that's why i said a galaxy happening to be right outside of our visual range, would be close to galaxies we cannot see

That works for me! Don't get me wrong either, I find brane cosmology absolutely fascinating, and if it turns out to be on the right track it would be stunning. Then again, there is a bit of "stacks of turtles" going on there, so who knows. Either way, I take your point, and I think we agree on the physics.

[tohamas]

The 'edge' of our observable universe is receeding faster than the speed of light: which means you can't get there from here.

But surely the 'edge' of our universe can't be moving faster than the speed of light, relativity makes that impossible, unless the boundary of our universe is just light, moving outwards. But even so it's impossible for the edge of our universe to be moving faster than the speed of light.

[DaveC426913]

But surely the 'edge' of our universe can't be moving faster than the speed of light, relativity makes that impossible, unless the boundary of our universe is just light, moving outwards. But even so it's impossible for the edge of our universe to be moving faster than the speed of light.

Google superluminal recession. Your questions will be answered.

[AbsoluteChaos]

I think the answer is "I don't know." The observable universe is limited by our position in the universe and our limited understanding. There may be many universes inside this one, outside our dimension/understanding or this one maybe one of many within the description "universe" or all alone as "Uno-universe". I think the question of what is observable is slightly distracting because the observable universe is quite small by comparison to what is out there and is changing fast.

I think the comparison to the goldfish bowl is helpful in so far as we are the goldfish, the water our universe, the glass the limitation of our understanding and beyond the glass is beyond the observable universe. Maybe there is a little kid looking in wondering why we swim around in circles. Of cause the little kid would be a green alien with tentacles speaking with an Amercian accent.

[jackmell]

What do you think?

Critical points. They change things don't they. Do you know what I mean by critical points?

Take dropping the temp of water until it freezes. The critical point is the freezing point and something qualitatively different emerges when that point is reached. Many phenomena in nature are like that: smooth flowing until a critical point is reached and then suddenly something qualitatively different emerges. That's what I think about the Universe. A critical point started it, and if we could see beyond it, we'd reach another critical point which would change qualitatively, our understanding of it.

[DevilsAvocado]

... Of cause the little kid would be a green alien with tentacles speaking with an Amercian accent.

This must be Sarah Palin!? :rofl:

[Unit]

What do you think?

Beyond the observable universe is the not-yet-observed universe.

[map19]

jackmell. Wiki phase transitions.
In the early universe just after the BB the phase transitions were essential. for ex. taking the electroweak symmetry and giving us the electromagnetic stuff we have today.
last I heard Weinberg was investigating early transitions. I believe whether they are first order or second order is the question.

[map19]

The "observable universe" is a vague term.
There's our Hubble Sphere, which is the distance from earth that the recession velocity = c.
But red shift, recession, is measured by a factor that is frequency of emitted light divided by frequency of light received here minus 1. It is Z = (f0/fr)-1.
So you would expect light sources receding at c to have a Z of 1. That is; Vr = Zc.
This is not the case due to the general relativistic curvature of space.
Light sources with a recession velocity of c have a Z of about 1.5.
radio telescopes can, and do, receive signals with a Z of about 10.
That is a recession velocity about 4c.
I recommend the Davis and Lineweaver paper to anybody interested in further details.

[Jake4]

I swear this is a troll..

If your whole concievable world is a table, thus all that you can and ever will observe is on that table, then why waste your time wondering what's under the table?

That is what he's saying, there's no reason to contemplate its existance because you can't say anything about it, nor will you ever be able to say anything about it, rooted in certainty.


Someone who spends years trying to find out what lies beyond, is no more correct than someone simply saying its a space occupied solely by cotton candy.

And also, "black extending for eternity" isn't nothing, that's a very juvenile way of putting it.

[jackmell]

jackmell. Wiki phase transitions.
In the early universe just after the BB the phase transitions were essential. for ex. taking the electroweak symmetry and giving us the electromagnetic stuff we have today.
last I heard Weinberg was investigating early transitions. I believe whether they are first order or second order is the question.

Hello map. Thanks for that reference. The part about the early Universe was interesting. I suspect the onset of a phase-transition WAS the Big Bang and have every confidence we will one day learn what larger phenomenon we are part of and in so doing begin to model the creation of Universes.

[crawfs98]

If the universe is infinite, then an infinite number of all possible universes exist, so you are all correct (except those who say nothing exists that cannot be observed - or perhaps even that, the most absurd proposition of all, is infinitely possible too). And somewhere a slightly brighter version of me just came up with a better answer than this too, an infinite number of times.

[bapowell]

And somewhere a slightly brighter version of me just came up with a better answer than this too, an infinite number of times.
Aha! But only if there are an infinite number of ways of coming up with a better answer :tongue:

[f24u7]

by observing the extent of observable universe can't we predict structures outside the observable universe by ruling out the gravitational influence inside the observable universe?

[Dylan Roberts]

I think it's like in dangermouse with all weird hands and things. ;)

[Richard Haber]

When you leave the edge of our universe you will eventaully find another universe in the process of expansion and after that another etc, the result of successive so called "big bangs" proceeding the result of our current one,we just happen to be in the most recent as we ride it out into far space this expansion covers every direction possible. Far far beyond this unmeasurable ripple effect of successive explosions one will find the same effect coming from different locations. Big bangs happen repeatedly and in countless locations and the distaces apart are so great that by the time such forces meet each other they are virtually meaningless.

[brother time]

I think that if there was one "big bang" there must be others. I voted blank space until other Universes
BT

[shunyadragon]

Is it just black space extending forever? Or perhaps black space for a finite distance until another universe?

I find it hard to believe our universe is just the only universe. I don't see how it wouldn't extend for eternity instead. What is so special about our universe and the space we are in?

What do you think?

I put other, because to conclude either of the other options would make assumptions we at present cannot make. It is not unreasonable to conclude that we are one of many possible universes, based on our present knowledge. One of the concepts of the philosophy of science is the assumption of uniformity of the nature of our physical existence. To hold that our universe is in some way unique or singular would a violation of this concept. It may be possible be true, but so far we have never discovered anything that is unique and singular in our physical existence, and not related to a more universal and greater physical existence.

One problem with the choice of a black void, is we have never observed this as an option and it would not go well with all our present QM knowledge concerning the nature of our physical existence.

[DaveC426913]

When you leave the edge of our universe you will eventaully find another universe in the process of expansion and after that another etc, the result of successive so called "big bangs" proceeding the result of our current one,we just happen to be in the most recent as we ride it out into far space this expansion covers every direction possible. Far far beyond this unmeasurable ripple effect of successive explosions one will find the same effect coming from different locations. Big bangs happen repeatedly and in countless locations and the distaces apart are so great that by the time such forces meet each other they are virtually meaningless.
Stop! Please! You're killin' me!

This is worse than wild speculation; it's wild speculation based on ignorance of the facts.

[blandrew]

As a layperson allow me to throw in my two-penneth worth.

Where ever you find yourself in the universe, you are both at its centre and at its edge.

Looking in any direction from any point in the universe is merely an observation into the history of the universe.

Einsteins equations tell us that it would take infinite energy to accelerate mass beyond c, so your kinda stuck with the first two statements.

"What is beyond the observable universe?" ....tomorrow is.

[nismaratwork]

As a layperson allow me to throw in my two-penneth worth.

Where ever you find yourself in the universe, you are both at its centre and at its edge.

Looking in any direction from any point in the universe is merely an observation into the history of the universe.

Einsteins equations tell us that it would take infinite energy to accelerate mass beyond c, so your kinda stuck with the first two statements.

"What is beyond the observable universe?" ....tomorrow is.

That is without meaning. This is Cosmology, not religion.

[blandrew]

As a layperson allow me to throw in my two-penneth worth.

Where ever you find yourself in the universe, you are both at its centre and at its edge.

Looking in any direction from any point in the universe is merely an observation into the history of the universe.

Einsteins equations tell us that it would take infinite energy to accelerate mass beyond c, so your kinda stuck with the first two statements.

"What is beyond the observable universe?" ....tomorrow is.


That is without meaning. This is Cosmology, not religion.


Being unable to understand something does not equate to it being without meaning.

My observations are based on science and logic, not theology.

[DaveC426913]

That is without meaning. This is Cosmology, not religion.

I'm afraid I don't follow either. blandrew's comments are more in line with our current understanding of cosmology than anyone else's in this thread.

Not sure if you've noticed, but this thread is otherwise full of people thinking the universe is a sphere - of which we happen to be at the centre and, flying to the "edge", we could lay down traffic cones. Then fly past that and look around to see other Big Bangs off in the distance. This is just a complete lack of understanding of cosmology.

[brother time]

We are not in the center!! And it is more odd shaped, the expansion is not at a constant linear rate for all parts of it.


Thanks Dave, BT

[blandrew]

Where ever you find yourself in the universe, you are both at its centre and at its edge.

Looking in any direction from any point in the universe is merely an observation into the history of the universe.

Einsteins equations tell us that it would take infinite energy to accelerate mass beyond c, so your kinda stuck with the first two statements.

"What is beyond the observable universe?" ....tomorrow is.


We are not in the center!! And it is more odd shaped, the expansion is not at a constant linear rate for all parts of it.


Where ever you are in the universe, everything else is expanding away from you. So your always at the centre in that regard.

Suggesting that the universe has any shape at all is to suggest that the universe is expanding in to some other space.

[bapowell]

We are not in the center!! And it is more odd shaped, the expansion is not at a constant linear rate for all parts of it.

To the best of our knowledge, the expansion of the universe is isotropic about the earth's position.

Suggesting that the universe has any shape at all is to suggest that the universe is expanding in to some other space.
This is not so. The universe could be expanding anisotropically -- faster in one direction than another. Additionally, the universe could have some exotic shape to it -- like a donut or a sphere. The notion that such a universe would need a higher dimensional space within which to exist is false -- the geometry and topology of the universe are intrinsic properties of the (3+1)-dim surface, and do not require an embedding into a higher dimension space to be realized.

[blandrew]

To the best of our knowledge, the expansion of the universe is isotropic about the earth's position.


This is not so. The universe could be expanding anisotropically -- faster in one direction than another. Additionally, the universe could have some exotic shape to it -- like a donut or a sphere. The notion that such a universe would need a higher dimensional space within which to exist is false -- the geometry and topology of the universe are intrinsic properties of the (3+1)-dim surface, and do not require an embedding into a higher dimension space to be realized.

I believe there is stronger consensus for a "flat" infinite universe.

[bapowell]

I believe there is stronger consensus for a "flat" infinite universe.
Of course, current observations show the local geometry of the universe to be flat to within a few percent. This observation is not inconsistent with a closed universe (spherical geometry), just that such a closed universe would need to be sufficiently large to look locally flat (like the earth to us humans). Also, a torus is geometrically flat -- it is topologically nontrivial. There is no 'consensus' regarding whether the universe is infinite or finite. Current cosmological observations have nothing to say (yet) about the global properties of the universe.

[blandrew]

Of course, current observations show the local geometry of the universe to be flat to within a few percent. This observation is not inconsistent with a closed universe (spherical geometry), just that such a closed universe would need to be sufficiently large to look locally flat (like the earth to us humans). Also, a torus is geometrically flat -- it is topologically nontrivial. There is no 'consensus' regarding whether the universe is infinite or finite. Current cosmological observations have nothing to say (yet) about the global properties of the universe.

"global properties"? Unfortunate use of language :)

[nismaratwork]

I'm afraid I don't follow either. blandrew's comments are more in line with our current understanding of cosmology than anyone else's in this thread.

Not sure if you've noticed, but this thread is otherwise full of people thinking the universe is a sphere - of which we happen to be at the centre and, flying to the "edge", we could lay down traffic cones. Then fly past that and look around to see other Big Bangs off in the distance. This is just a complete lack of understanding of cosmology.

That may be, but the universe has a definite geometry, and we are somewhere within that. We cannot be at its edge and center simultaneously. There are better ways to describe a bounded universe and our observations of old light, than with borderline poetry. That the universe may be embedded in a membrane, or conform to the holographic principle, or a number of other options doesn't support such a fanciful description.

Speculating as to the geometry of our observable region is one thing, but conjecture as to its overall topology is part of the problem with M-Theory; it is probably not falsifiable or provable. That's not science, it's fancy.

[blandrew]

Where ever you find yourself in the universe, you are both at its centre and at its edge.

Looking in any direction from any point in the universe is merely an observation into the history of the universe.

Einsteins equations tell us that it would take infinite energy to accelerate mass beyond c, so your kinda stuck with the first two statements.

"What is beyond the observable universe?" ....tomorrow is.


That may be, but the universe has a definite geometry, and we are somewhere within that. We cannot be at its edge and center simultaneously. There are better ways to describe a bounded universe and our observations of old light, than with borderline poetry. That the universe may be embedded in a membrane, or conform to the holographic principle, or a number of other options doesn't support such a fanciful description.

Speculating as to the geometry of our observable region is one thing, but conjecture as to its overall topology is part of the problem with M-Theory; it is probably not falsifiable or provable. That's not science, it's fancy.


Thank you for describing my comments as poetry.

In a homogeneous and isotropic universe it could be said that, where ever you find yourself within it, your at it's centre.

Perhaps there is an assumption here that the universe is infinite and that Einsteins STR holds true.

Being at its edge and finding tomorrow beyond the observable is more cheeky i'll grant. But the universe has 4 dimensions (i'm sure someone will tell us it has more) and we live in its present, observe its past and wait for its future. So in that regard, we're at the edge.

[Tenny]

Where ever you find yourself in the universe, you are both at its centre and at its edge.

Looking in any direction from any point in the universe is merely an observation into the history of the universe.

Einsteins equations tell us that it would take infinite energy to accelerate mass beyond c, so your kinda stuck with the first two statements.

"What is beyond the observable universe?" ....tomorrow is.





Thank you for describing my comments as poetry.

In a homogeneous and isotropic universe it could be said that, where ever you find yourself within it, your at it's centre.

Perhaps there is an assumption here that the universe is infinite and that Einsteins STR holds true.

Being at its edge and finding tomorrow beyond the observable is more cheeky i'll grant. But the universe has 4 dimensions (i'm sure someone will tell us it has more) and we live in its present, observe its past and wait for its future. So in that regard, we're at the edge.

Hi. Accepting that it has 4D's, 1 of time and 3 of space, isn't it a dodge to equate the edge with time ? What is it's spatial rather than it's temporal edge?

[nismaratwork]

Where ever you find yourself in the universe, you are both at its centre and at its edge.

Looking in any direction from any point in the universe is merely an observation into the history of the universe.

Einsteins equations tell us that it would take infinite energy to accelerate mass beyond c, so your kinda stuck with the first two statements.

"What is beyond the observable universe?" ....tomorrow is.





Thank you for describing my comments as poetry.

In a homogeneous and isotropic universe it could be said that, where ever you find yourself within it, your at it's centre.

Perhaps there is an assumption here that the universe is infinite and that Einsteins STR holds true.

Being at its edge and finding tomorrow beyond the observable is more cheeky i'll grant. But the universe has 4 dimensions (i'm sure someone will tell us it has more) and we live in its present, observe its past and wait for its future. So in that regard, we're at the edge.

I see your point, but doesn't that really imply that the notion of being at a center or edge is meaningless? Maybe that's your point. Consider that the universe, according to Hawking, has (from our point of view), a singularity at a Big Bang, and crunch. I'm not saying that is the case, but for the sake of using his globe model, lets. Our present exists at a definite point along time axis from BB->BC, or infinite expansion, it doesn't matter. We're not at an edge, or a center, but definite coordinates within a system we can't properly define, somewhere in the history, and future of the universe.

If you take away the future portion, then I see your point, in that for us the present is the leading edge of our experience in spacetime. If you consider spacetime as a complete structure with a past and future, we exist at a point in that structure, defined by our "when" which also defines our "where".

Being in a homogeneous and isotropic universe means that we cannot distinguish at large scales where we are in absolute terms, but in the strictest sense the time coordinate should solve that. I don't claim that this means that you could reach an "edge" to the universe and punch through that edge into something else. It might be better to say that no matter where you go in a homogeneous and isotropic universe, in spacetime, you'd eventually return to where and when you left, if you could travel in such a fashion.

I suppose my point is that you're speaking from our point of view, that of something embedded in this universe. It is entirely possible that beyond the observable universe, is nothing, or other universes, or cream cheese if we're being cheeky. As ants on the apple we can only deal with traversing this structure of (at least, as you say) spacetime in a particular way, but in an absolute sense, that doesn't remove the orchard.

Oh hell, you've gotten to me with your cheek and poetry. :p

[blandrew]

Hi. Accepting that it has 4D's, 1 of time and 3 of space, isn't it a dodge to equate the edge with time ? What is it's spatial rather than it's temporal edge?

Time could be said to be geometrically fundamental in regard to the universe.

I see your point, but doesn't that really imply that the notion of being at a center or edge is meaningless? Maybe that's your point. Consider that the universe, according to Hawking, has (from our point of view), a singularity at a Big Bang, and crunch. I'm not saying that is the case, but for the sake of using his globe model, lets. Our present exists at a definite point along time axis from BB->BC, or infinite expansion, it doesn't matter. We're not at an edge, or a center, but definite coordinates within a system we can't properly define, somewhere in the history, and future of the universe.

If you take away the future portion, then I see your point, in that for us the present is the leading edge of our experience in spacetime. If you consider spacetime as a complete structure with a past and future, we exist at a point in that structure, defined by our "when" which also defines our "where".

Being in a homogeneous and isotropic universe means that we cannot distinguish at large scales where we are in absolute terms, but in the strictest sense the time coordinate should solve that. I don't claim that this means that you could reach an "edge" to the universe and punch through that edge into something else. It might be better to say that no matter where you go in a homogeneous and isotropic universe, in spacetime, you'd eventually return to where and when you left, if you could travel in such a fashion.

I suppose my point is that you're speaking from our point of view, that of something embedded in this universe. It is entirely possible that beyond the observable universe, is nothing, or other universes, or cream cheese if we're being cheeky. As ants on the apple we can only deal with traversing this structure of (at least, as you say) spacetime in a particular way, but in an absolute sense, that doesn't remove the orchard.

Oh hell, you've gotten to me with your cheek and poetry. :p


Well, the faster than c expansion of the universe would presumably mean one would not return to the point of origin even if there is curvature.

"cream cheese" oh I do hope not, hate the stuff

[nismaratwork]

Time could be said to be geometrically fundamental in regard to the universe.




Well, the faster than c expansion of the universe would presumably mean one would not return to the point of origin even if there is curvature.

"cream cheese" oh I do hope not, hate the stuff

The +c issue is why I added the codicil, "if you could travel in such a fashion". The point about the geometry is possibly valid however. For cream cheese, how do you eat bagels? Cheesecake?! Bagels need cream cheese, they cry for it, and you would deny them this sweet offshoot of Neufchatel Cheese? No sir, I reject that premise; it's "[cream cheese] all the way down." :)

[Tenny]

Time could be said to be geometrically fundamental in regard to the universe.



I still don't get it. And earlier you posted ;

we live in its present, observe its past and wait for its future. So in that regard, we're at the edge

That would seem to me to be in the middle of the temporal dimension, not at the edge.

But why mix space and time ? Surely the three spatial dimensions I see around me are just that - three spatial dimensions! I don't feel I'm on the edge of the universe, though.

How can be ? I can see in all directions and there is more space. Isn't it shifting the goalpost to say I'm on the edge, but it's the edge in relation to time (which I still feel is a dodge) ?

[nismaratwork]

I still don't get it. And earlier you posted ;

we live in its present, observe its past and wait for its future. So in that regard, we're at the edge

That would seem to me to be in the middle of the temporal dimension, not at the edge.

But why mix space and time ? Surely the three spatial dimensions I see around me are just that - three spatial dimensions! I don't feel I'm on the edge of the universe, though.

How can be ? I can see in all directions and there is more space. Isn't it shifting the goalpost to say I'm on the edge, but it's the edge in relation to time (which I still feel is a dodge) ?

You mix space and time because that is a fundamental principle of Relativity. If you existed only in a space-like manner, you could not do anything, never mind looking around. There is a reason it's called "spacetime" and not "space and time".

[blandrew]

I still don't get it. And earlier you posted ;

we live in its present, observe its past and wait for its future. So in that regard, we're at the edge

That would seem to me to be in the middle of the temporal dimension, not at the edge.

But why mix space and time ? Surely the three spatial dimensions I see around me are just that - three spatial dimensions! I don't feel I'm on the edge of the universe, though.

How can be ? I can see in all directions and there is more space. Isn't it shifting the goalpost to say I'm on the edge, but it's the edge in relation to time (which I still feel is a dodge) ?


I guess this is the point of the homogeneous isotropic universe. It's only with the fourth dimension, that of time, that one can place oneself within it. In this context, I would equate "present" with "edge".

[blandrew]

The +c issue is why I added the codicil, "if you could travel in such a fashion". The point about the geometry is possibly valid however. For cream cheese, how do you eat bagels? Cheesecake?! Bagels need cream cheese, they cry for it, and you would deny them this sweet offshoot of Neufchatel Cheese? No sir, I reject that premise; it's "[cream cheese] all the way down." :)

Sultan-ed, sliced, toasted and buttered .....you can keep your "cream cheese" .... philistine! :)

[nismaratwork]

Sultan-ed, sliced, toasted and buttered .....you can keep your "cream cheese" .... philistine! :)

You sir, may be an excellent cosmologist, but when it comes to baked goods you are an unlettered barbarian. Without cream cheese, the lox cannot be properly ensconced in creamy goodness, and the scallions or red onion are too sharp. I believe this was known in the Neolithic period, when cave etchings clearly show our ancestors smoking salmon for bagels. I believe they preferred Philadelphia cream cheese too, but it's hard to translate as there was no Philadelphia at the time.

:smile:

[Tenny]

I guess this is the point of the homogeneous isotropic universe. It's only with the fourth dimension, that of time, that one can place oneself within it. In this context, I would equate "present" with "edge".


I still don't get it. To equate the edge of the universe to time, seems to be just playing with language. To repeat once again, you said “we live in its present, observe its past and wait for its future. So in that regard, we're at the edge”

In what regard ? I am at the edge of the universe right now, according to earlier words here, including yours. But I certainly don’t feel like I’m at the edge of the universe. I can see the three dimensions around me, and I seem to be in the middle of them, not on some edge. And I can remember the past, and anticipate the future (to some degree). I certainly don’t feel like I’m at the edge of the universe in space, or in time, or in spacetime.

[Trenton]

It is highly probable our 'observable' universe is actually a black hole of radius 30, 40 or more billion light years (This is only the same as asking if it has enough mass to one day fall in on itself).

Outside this black hole will be yet more space with matter floating around and other black holes of course. (Purely my opionion, I can't prove it of course).

I don't buy this idea that outside the 'universe' is no time or space nor do I buy the multi-dimension idea

[DaveC426913]

It is highly probable our 'observable' universe is actually a black holeHighly probable. Care to back that up with some references?

[blandrew]

I still don't get it. To equate the edge of the universe to time, seems to be just playing with language. To repeat once again, you said “we live in its present, observe its past and wait for its future. So in that regard, we're at the edge”

In what regard ? I am at the edge of the universe right now, according to earlier words here, including yours. But I certainly don’t feel like I’m at the edge of the universe. I can see the three dimensions around me, and I seem to be in the middle of them, not on some edge. And I can remember the past, and anticipate the future (to some degree). I certainly don’t feel like I’m at the edge of the universe in space, or in time, or in spacetime.


You kind of answer this yourself.

If I were to use an analogy. Lets say you've been reading a novel of indeterminate length for an indeterminate length of time. Well, you could say you were in the centre of the book and at the edge of the story.

I hardly think that's semantics.

[nismaratwork]

You kind of answer this yourself.

If I were to use an analogy. Lets say you've been reading a novel of indeterminate length for an indeterminate length of time. Well, you could say you were in the centre of the book and at the edge of the story.

I hardly think that's semantics.

In fact, knowing what is to come in the novel would still place you at the leading edge of whatever you know. There might be a middle, but you can also appreciate that in retrospect. Only seeing it as a complete structure with boundaries can allow you to overcome the homogeneity and isotropy, and that is definitely NOT how we live.

[Trenton]

Dave,

References no but only coz I don't get enough time to browse. The idea though, that we are in a black hole of perhaps 30 billion light years radius, maybe a lot more - is not that difficult to support. Much is made of so called 'missing mass' but when you look at the rudimentry approach to how mass is calculated it leaves a lot of room for inacuracy. Even without exotic theories (which I largely do not support) I suspect there is a lot more intergelactic gas, a lot more WIMPS and probably large numbers of 'failed galaxies' (which did not have enough rotational enery to avoid the entire ediface collapsing to a black hole). I could go on and on ....

[Trenton]

Further to the issue of the (observable) universe being a black hole; Should this turn out to be the case it is more likely that the galaxies are falling in rather than flying out. You can forget the 'current bun' model, it just would not apply. Instead the (apparent) expansion would be expalained better by progressive time dilation. Black holes are not wormholes (unless one is both an idiot and a fantasist) - but they are larger on the inside than on the out. You could fall into one and while away what would seem like years observing other infalling objects before hitting the singularity. The distance to the center would thus appear to be very large. This distance amplification would be very small in a large black hole but would be about the cosmological constant for a black hole of 30bn light years.

[George Jones]

The idea though, that we are in a black hole of perhaps 30 billion light years radius, maybe a lot more - is not that difficult to support.

Then support this with peer-reviewed mainstream references. Physics Forums Rules,

http://www.physicsforums.com/showthread.php?t=5374

in part, say
Overly Speculative Posts: One of the main goals of PF is to help students learn the current status of physics as practiced by the scientific community; accordingly, Physicsforums.com strives to maintain high standards of academic integrity. There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound. It is against our Posting Guidelines to discuss, in most of the PF forums or in blogs, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion.


Personal theories are not allowed here.

[eha]

Some people still believes there is nothing beyond universe, and they don't even accept empty space or anything else. But they can't answer the question when you ask "How are you gonna fill up the rest of the infite volume?" They can't realize the truth of "Black space extend forever". I wonder how many intelligent people are there can't see this fact? Isn't that hard to understand, am I wrong?

[DaveC426913]

...am I wrong*

Well, yes.

[nismaratwork]

Well, yes.

I believe you meant to say, "really really wrong."

eha: What exactly do you mean, because I find your wording vague, and you don't seem to offer obvious alternatives.

[Tenny]

You kind of answer this yourself.

If I were to use an analogy. Lets say you've been reading a novel of indeterminate length for an indeterminate length of time. Well, you could say you were in the centre of the book and at the edge of the story.

I hardly think that's semantics.

Definitely sounds like semantics or more.

How did you deterimine the centre of the book if it's length was INdeterminate ?

Edge of the story ? What does that analogise ?

[nismaratwork]

Definitely sounds like semantics or more.

How did you deterimine the centre of the book if it's length was INdeterminate ?

Edge of the story ? What does that analogise ?

I don't think you understand what it means that the universe is homogeneous and isotropic. I recommend a googling of the terms, and what they mean. The book analogy is really quite apt in 3+1 dimensions.

[eha]

Okay! What I say is; We are within a space which extends forever in 3D. Our universe occupies a certain volume within this infinite black space. We can't find even a one single atom outside our universe. I don't think there are another universe or universes around or in deep distant space. Our universe itself is a biggest miracle within endless space. The chance for another miracle is so slim, so slim nearly zero. I strongly believe these facts due to my knowledge in astronomy for 50 years and my logic.
I prefer to receive very short and very plain answers.
Thanks, love you all!

[Trenton]

George,

Less of the rules of overly speculative posts. The question of if there is sufficient mass to eventually arrest the expansion and lead to a crunch is an old one and all I am doing is re-phrasing it. It is mathematically the same as asking if the observable universe has a swartzchild radius large enough to contain it - ie is a black hole.

The story on this has to date been one of astronomers discovering more and more mass so it is quite probable more will be discovered.

Beyond that it is just a question of applying the relevant relativistic equations - which I either have got right or wrong.

It is not my fault people don't like the consequences of these equations.

[nismaratwork]

George,

Less of the rules of overly speculative posts. The question of if there is sufficient mass to eventually arrest the expansion and lead to a crunch is an old one and all I am doing is re-phrasing it. It is mathematically the same as asking if the observable universe has a swartzchild radius large enough to contain it - ie is a black hole.

The story on this has to date been one of astronomers discovering more and more mass so it is quite probable more will be discovered.

Beyond that it is just a question of applying the relevant relativistic equations - which I either have got right or wrong.

It is not my fault people don't like the consequences of these equations.

You agreed to rules when you joined, it's that simple.

[DaveC426913]

Okay! What I say is; We are within a space which extends forever in 3D. Our universe occupies a certain volume within this infinite black space. We can't find even a one single atom outside our universe. I don't think there are another universe or universes around or in deep distant space. Our universe itself is a biggest miracle within endless space. The chance for another miracle is so slim, so slim nearly zero. I strongly believe these facts due to my knowledge in astronomy for 50 years and my logic.
I prefer to receive very short and very plain answers.
Thanks, love you all!

eha, we do not entertain personal theories here; this forum is first and foremost a homework help forum and is conscientious about discussing established and accepted theories.

If you wish to submit a paper with your theories, there is a specific section for that with its own rules.

All this you agreed to when you signed up.

There are other fora where you can put up your personal ideas about the universe. This is not one of them.

[nismaratwork]

Okay! What I say is; We are within a space which extends forever in 3D. Our universe occupies a certain volume within this infinite black space. We can't find even a one single atom outside our universe. I don't think there are another universe or universes around or in deep distant space. Our universe itself is a biggest miracle within endless space. The chance for another miracle is so slim, so slim nearly zero. I strongly believe these facts due to my knowledge in astronomy for 50 years and my logic.
I prefer to receive very short and very plain answers.
Thanks, love you all!

Your basis is not scientific, but anecdotal. In short, this is your faith, and has no place here unless you can in some way support this with more than your espoused expertise. Words such as "miracle" are fanciful, not meaningful in this context. The argument that the universe is commonplace has been made as well, and nothing you've said refutes that. Care to rise to the challenge?

[Ich]

Beyond that it is just a question of applying the relevant relativistic equations - which I either have got right or wrong.
...which you have not done at all. So please provide references or the relevant equations.
Btw., swartzchild is not relevant, you might want to look up the vreedman equations instead.

[Tenny]

I don't think you understand what it means that the universe is homogeneous and isotropic. I recommend a googling of the terms, and what they mean.

I have a reasonable idea of what they mean. There was a statement made earlier by blandview (?) that we live at the edge of the universe. I queried this and was given some analogy, which I need to understand .. equally vague, in order to understand the former .. kind of circular, that!

Either that, or I'm just plain stupid and your intellect far surpasses mine - a possibility I'm ready to admit if readily shown. But all I've seen so far is circular argument and semantics - and the subtle changing of the meaning of words to suit.

The book analogy is really quite apt in 3+1 dimensions.

I am at the edge of the universe, (according to others previous posts) right ?

But I don't feel like I'm at the edge of the universe. I can see for miles in each direction - millions.

"Ah, the simpleton" I hear you say"

.. but anyway, you (and blandview more to the point) haven't 'splained it proply so far. And to say that the edge is the 4th dimension, time, kind of shifts the goalpost merely.

The present, is the futures past !

[blandrew]

I have a reasonable idea of what they mean. There was a statement made earlier by blandview (?) that we live at the edge of the universe. I queried this and was given some analogy, which I need to understand .. equally vague, in order to understand the former .. kind of circular, that!

Either that, or I'm just plain stupid and your intellect far surpasses mine - a possibility I'm ready to admit if readily shown. But all I've seen so far is circular argument and semantics - and the subtle changing of the meaning of words to suit.



I am at the edge of the universe, (according to others previous posts) right ?

But I don't feel like I'm at the edge of the universe. I can see for miles in each direction - millions.

"Ah, the simpleton" I hear you say"

.. but anyway, you (and blandview more to the point) haven't 'splained it proply so far. And to say that the edge is the 4th dimension, time, kind of shifts the goalpost merely.

The present, is the futures past !

"Blandview" i see what you done there.

Ok, this is what I originally posted:

"Where ever you find yourself in the universe, you are both at its centre and at its edge.

Looking in any direction from any point in the universe is merely an observation into the history of the universe.

Einsteins equations tell us that it would take infinite energy to accelerate mass beyond c, so your kinda stuck with the first two statements.

"What is beyond the observable universe?" ....tomorrow is."

-------------------

I think I've answered to, and explained this to the best of my ability in subsequent posts, so I'll not hijack this thread any longer.

I'm glad that I've aroused debate to some degree. Perhaps the issue here is the counter intuitive nature of the universe and/or the inadequacy of the English language.

[nismaratwork]

I have a reasonable idea of what they mean. There was a statement made earlier by blandview (?) that we live at the edge of the universe. I queried this and was given some analogy, which I need to understand .. equally vague, in order to understand the former .. kind of circular, that!

Either that, or I'm just plain stupid and your intellect far surpasses mine - a possibility I'm ready to admit if readily shown. But all I've seen so far is circular argument and semantics - and the subtle changing of the meaning of words to suit.



I am at the edge of the universe, (according to others previous posts) right ?

But I don't feel like I'm at the edge of the universe. I can see for miles in each direction - millions.

"Ah, the simpleton" I hear you say"

.. but anyway, you (and blandview more to the point) haven't 'splained it proply so far. And to say that the edge is the 4th dimension, time, kind of shifts the goalpost merely.

The present, is the futures past !

Yes, insult the people who are trying to explain a basic concept that you fail to grasp, that's going to provide strong motivation for anyone to help you. You're on your own.

[DaveC426913]

Yes, insult the people who are trying to explain a basic concept that you fail to grasp, that's going to provide strong motivation for anyone to help you. You're on your own.nismar, I do not think he meant any insult (Note, by the way, that he did not actually make any insult). He is feeling frustration that he does not understand, though we seme to claim we are using simple words. It is most definitely not a "basic concept"!

See his frustration, don't take it as an attack.

[nismaratwork]

nismar, I do not think he meant any insult (Note, by the way, that he did not actually make any insult). He is feeling frustration that he does not understand, though we seme to claim we are using simple words. It is most definitely not a "basic concept"!

See his frustration, don't take it as an attack.

Generally manipulating a name (blandrew to blandview) is an insult, showing hostility. Frustration is understandable, but that doesn't mean this should degenerate into something hostile when the only reason the frustration exists at all is because the people he mentions are willing to engage at all.

If he doesn't understand, the best policy is to read, listen, research, and ask questions. Instead we get assertion after assertion, and pages of what appears to be a lack of independent inquiry.

I see his frusteration, and saw it earlier, but when that changed to something else I decided to walk away. I'm sorry, but "And to say that the edge is the 4th dimension, time, kind of shifts the goalpost merely..." is absurd, when that is in essence the point. He wants an answer that makes s certain kind of sense to him, rather than the correct answer, or best guess. How do you work with that, when there is no personal stake in his learning?

Out of respect for you Dave, Tenny: As far as you can see, and even beyond is a single time-like slice, and the next moment (t2) what is contained in that slice changes. Your place in the universe and your ability to see old light from a distance effects the range of space-like events you can observe in any moment. That is an edge in an indeterminant universe. To be in a center, you would have to define a beginning and end (to simplify), like the beginning and end of book. Then, with foreknowledge you say, "I'm at page 3 of 7"! In the universe, you can't tell how long the book is, and your position is bounded by your current position in spacetime.

[Trenton]

I did not mean to insult anyone and I appologise if I have done so. I conceed I lacked contrition when saying it was not my fault if people don't like the consequences of equations.

I am though baffled by the rules. No-one knows what lays beyond the observable universe and thus ANY thought we may have on the subject is speculative.

For the record I am not stating that the [observable] universe amounts to a black hole, meerly that it looks likely that it does - And if it does then there are other ways in which the cosmos can be viewed other than the presently entrenched version of the big bang.

On the subject in hand though, two things that are not speculative or a matter of opionion:-

1) The laws of physics and mathematics are valid regardless of weather or not there is anything to apply them too! For example 1+1=2 has always been and will always be true no matter if there is anything to count or an outside to the observable universe or not.

2) The radius of a black hole is proportional to it's mass.

One interpretation of (1) is that 'before and outside' are legal space-time coordinates.

And one interpretation of (2) is that black holes can be exceptionally large and have very low density and micro-gravity at the event horizon. It would still require light speed plus to escape to infinity.

I accept that this is a bit hard to get one's head round but unless it can be shown that gravity eventually departs from inverse-square, this interpretation is (at least mathematically) valid.

By contrast though, some of the solutions to the Einstein field equations are questionable because they yeild a singularity both at the center (valid) and at the event horizon (invalid). And yet some assertions about black holes seem to depend on the latter (eg an object falling into a black hole is seen to stop at the event horizon by an outside observer because time stops a this point). My interpretation of the horizon is that it is the point at which the escape velocity reaches C - which is not the same as saying an infalling object will reach C at this point (and anyway we all know it can't reach C). Any comments on this?

My interest in ultra-large black holes owes much to the fact that they illistrate quite clearly where these assertions are or seem to be faulty.

My best regards to eveyone - Trenton Maiers

[nismaratwork]

I did not mean to insult anyone and I appologise if I have done so. I conceed I lacked contrition when saying it was not my fault if people don't like the consequences of equations.

I am though baffled by the rules. No-one knows what lays beyond the observable universe and thus ANY thought we may have on the subject is speculative.

For the record I am not stating that the [observable] universe amounts to a black hole, meerly that it looks likely that it does - And if it does then there are other ways in which the cosmos can be viewed other than the presently entrenched version of the big bang.

On the subject in hand though, two things that are not speculative or a matter of opionion:-

1) The laws of physics and mathematics are valid regardless of weather or not there is anything to apply them too! For example 1+1=2 has always been and will always be true no matter if there is anything to count or an outside to the observable universe or not.

2) The radius of a black hole is proportional to it's mass.

One interpretation of (1) is that 'before and outside' are legal space-time coordinates.

And one interpretation of (2) is that black holes can be exceptionally large and have very low density and micro-gravity at the event horizon. It would still require light speed plus to escape to infinity.

I accept that this is a bit hard to get one's head round but unless it can be shown that gravity eventually departs from inverse-square, this interpretation is (at least mathematically) valid.

By contrast though, some of the solutions to the Einstein field equations are questionable because they yeild a singularity both at the center (valid) and at the event horizon (invalid). And yet some assertions about black holes seem to depend on the latter (eg an object falling into a black hole is seen to stop at the event horizon by an outside observer because time stops a this point). My interpretation of the horizon is that it is the point at which the escape velocity reaches C - which is not the same as saying an infalling object will reach C at this point (and anyway we all know it can't reach C). Any comments on this?

My interest in ultra-large black holes owes much to the fact that they illistrate quite clearly where these assertions are or seem to be faulty.

My best regards to eveyone - Trenton Maiers

4x5=10

How about quaternions?

[Trenton]

quaternions? Aren't they something to do with hamiltonians and complex numbers? Would you care to enlighten me as to where these might fit in? Hithertoo I was of the misapprehension that all one had to do was work out where to apply the Lorentz contraction.

[nismaratwork]

quaternions? Aren't they something to do with hamiltonians and complex numbers? Would you care to enlighten me as to where these might fit in? Hithertoo I was of the misapprehension that all one had to do was work out where to apply the Lorentz contraction.

My comment was in reference to your comment about the constancy of 1+1=2; it was meant to be a prod in the direction of the mutability of such things in different systems. You are correct that the relevance is in regards to commuting and non commuting operators.

[Tenny]

To mismaratwork, #281;

In post #279 I said ..

"There was a statement made earlier by blandview (?) that we live at the edge of the universe"

.. which you took as an insult, and said in post #283 ..

"Generally manipulating a name (blandrew to blandview) is an insult, showing hostility"

But "blandrew to blandview" was just a mistake on my part - as can be evidenced by the question mark (?) immediately following it. I was simply running on memory of what I had read earlier you see, and being relatively new, remembered the name wrongly. I was also on a dial up connection at that moment, (as I am right now) and you know how it is with dial up - to go back and forth, load several pages, etc, takes forever (just about).

Look - you even had some funnies in your #283 ..

“I see his frusteration”
(I hope not - I’m blushing, now)

“He wants an answer that makes s certain”
(not really - I see more certitude in ‘r’)

.. but I'm not too bothered. It's easy to make a mistake or two, isn‘t it ?

So you jumped the gun with YOUR hostility, but that's OK. Cheer up! You have no stake in my learning, nor did I ask for any from you. It is your choice however, to participate (or not) in an internet forum where many questions are bound to flow - even from dummies !

To blandrew #280

You said to me ..

"Blandview" i see what you done there"

I hope the above explains my error. No offence or hostility was intended on my part.


Thank you both for your responses. I'll have a good read of them and post later if I need to.

To Dave #282 - you said ..

“He is feeling frustration that he does not understand, though we seme to claim we are using simple words. It is most definitely not a "basic concept"!

Which really nails it, I think. Thanks.

[Trenton]

Good point nismar - I had not thought of that one. I shall mull that at length.

Another thing I am surprised I have not been pulled up on is event horizon disruption by neighboring black holes (and other outside mass). If the observable universe were a black hole among an infinite number of them randomly spaced, they would have to be very sparse to act as black holes.

Anyway in the meantime I am pondering a different matter. Hawkins radiation - Not at the event horizon but further in. Presumably the same mechanism would still apply. Of course the virtual particles would never escape but they would nonetheless mean that not all the mass of a black hole was concentrated at the center.

Has anyone else considered this or found any decent papers on it?

[nismaratwork]

Good point nismar - I had not thought of that one. I shall mull that at length.

Another thing I am surprised I have not been pulled up on is event horizon disruption by neighboring black holes (and other outside mass). If the observable universe were a black hole among an infinite number of them randomly spaced, they would have to be very sparse to act as black holes.

Anyway in the meantime I am pondering a different matter. Hawkins radiation - Not at the event horizon but further in. Presumably the same mechanism would still apply. Of course the virtual particles would never escape but they would nonetheless mean that not all the mass of a black hole was concentrated at the center.

Has anyone else considered this or found any decent papers on it?

Yes, but I also couldn't grasp the derivation, really HR is incredibly tough. I think the best way to think of the particle beyond the event horizon is the past of the particle which escapes. The math is really beyond me without sitting for specialized lectures, and even then I don't think I could grasp it.

[Max™]

http://news.nationalgeographic.com/news/2010/04/100409-black-holes-alternate-universe-multiverse-einstein-wormholes/

"What is new here is an actual wormhole solution in general relativity that acts as the passage from the exterior black hole to the new interior universe," said Easson, who was not involved in the new study.

"In our paper, we just speculated that such a solution could exist, but Poplawski has found an actual solution," said Easson, referring to Poplawski's equations.

Nevertheless, the idea is still very speculative, Easson said in an email.

"Is the idea possible? Yes. Is the scenario likely? I have no idea. But it is certainly an interesting possibility."

I'm not one to take exact EFE solutions lightly, it isn't proof, but it appears at least possible that this Universe is inside of a black hole in another Universe.

[Trenton]

Nismar,

I can't do the math either but before one even gets to that I can't properly picture the HR process in my mind.

Another example of my poor math is the above mentioned NAT GEOGRAPHIC article. It is obvious that time dilation gives rise to an 'inner universe' in black holes in that they are larger on the inside than the out - I was of this view more than 20 years ago but could not formulate a decent proof.

But back to HR - I have been contemplating something else though that may be HR related. The light emited from stars loses some of it's energy climbing away from the star's gravity. The star loses mass in producing the light of course but not all of that converted mass makes it out to infinity - part of it is lost to the redshift. Where does this missing mass end up? In the star in some other form than nuclear binding energy such a heat? And how?

Does anyone have a name for this conumdrum or know of any papers on it?

[Chronos]

The blackbody spectrum of the CMB is not a match to that expected from the interior of a black hole, Max.

[qmpash]

A big, nasty kid who is playing all kinds of jokes on us.

[ViewsofMars]

"What is Beyond The Observable Universe?" is the topic. Science only deals with the observable. We have The Big Bang Theory. It is extremely important to know what a theory means. Also, the following definition of a *theory* applies to every other scientific theory. Everyone should know this:


Theory
A scientifically testable general principle or body of principles offered to explain observed phenomena. In scientific usage, a theory is distinct from a hypothesis (or conjecture) that is proposed to explain previously observed phenomena. For a hypothesis to rise to the level of theory, it must predict the existence of new phenomena that are subsequently observed. A theory can be overturned if new phenomena are observed that directly contradict the theory.
http://map.gsfc.nasa.gov/site/glossary.html
:biggrin:

[ViewsofMars]

What CMB blackbody spectrum would match a quantum particle sea of universes?


There are no "observable sea of universes."

[ViewsofMars]

If the Universe originated from a quantum particle, what CMB spectrum would match that?

The question is 'what is beyond the observable universe'?

A quantum particle sea of universes.


Orion, I already answered the questions. You need to read again and attempt to understand what I have previously posted. Also, a theory doesn't deal with "ifs." You need to first understand what a theory means. There are no universes. Period. End of story.

[Tenny]

Hello. I've read through the last several pages again recently, in an attempt to resolve the issue I was wondering about earlier. I still haven't been able to resolve it, and could even say I'm even more confused and mystified as to what's been said by some.

I have a reasonable understanding of what homogenous and isotropic means. And I ask again, how can it be said that I am, (and we) are at the edge of the universe ? I can see for countless millions of miles in any direction, so it certainly doesn't seem that I'm on any edge.

The analogy ..

'Lets say you've been reading a novel of indeterminate length for an indeterminate length of time. Well, you could say you were in the centre of the book and at the edge of the story (blandrew #263).

.. was given, but this merely confuses further, as it seems to be more vague than that which it is attempting to analogise. Worse, it seems to shift the meaning of the word 'edge' from a literal to a metaphorical one. I could say 'I'm at my wits end', or 'this is cutting edge stuff' but in both cases, I'm using a metaphor only.

In further posts it was suggested (I think) that time is the edge. But even with that, I can't see how I'm on the edge there either. We flow from the past to the future - and both past and future have a length (whatever that might be) so again, I do not feel I'm on the edge of time. In any case, I feel it is somewhat of a dodge (no hostility intended) to say that time puts me at the edge of the universe. It seems to me to be merely shifting the goalposts.

Please tell me how I'm at the edge of the universe, bearing in mind;

If you can't explain it simply, you don't understand it well enough.
Albert Einstein

Most of the fundamental ideas of science are essentially simple, and may, as a rule, be expressed in a language comprehensible to everyone.
Albert Einstein

[DaveC426913]

Please tell me how I'm at the edge of the universe, bearing in mind;


Keep in mind this is merely a spurious analogy, designed to show that sometimes "what we see" is not the only way to see things.

An ant is crawling on the surface of an balloon. Every direction it looks it sees more balloon surface - there are no boundaries, no edges. If the ant is not at the centre of this universe, it is certainly not near any edge.

I look down upon the ant from my vantage point. I can see that it is at the surface of the balloon. In fact, it is at the boundary of a sphere that is defined by the balloon's skin. Moreso, as I inflate this balloon, I can even say that the ant is on the leading edge of an expanding sphere that is defined by the balloon's skin.


The 2D surface of the balloon is analagous to our 3D universe (with one dminesion ignored). The expansion of the balloon in a radial direction is analagous to the movement of our 3D universe through the 4th dimension of time. The ant cannot go "forward" any more than the balloon expands. Outward is the future, inward is the past.

[Tenny]

Keep in mind this is merely a spurious analogy, designed to show that sometimes "what we see" is not the only way to see things.

An ant is crawling on the surface of an balloon. Every direction it looks it sees more balloon surface - there are no boundaries, no edges. If the ant is not at the centre of this universe, it is certainly not near any edge.

I look down upon the ant from my vantage point. I can see that it is at the surface of the balloon. In fact, it is at the boundary of a sphere that is defined by the balloon's skin. Moreso, as I inflate this balloon, I can even say that the ant is on the leading edge of an expanding sphere that is defined by the balloon's skin.


The 2D surface of the balloon is analagous to our 3D universe (with one dminesion ignored). The expansion of the balloon in a radial direction is analagous to the movement of our 3D universe through the 4th dimension of time. The ant cannot go "forward" any more than the balloon expands. Outward is the future, inward is the past.

Hi Dave. Thanks. Yes, I am familiar with your analogies above - very 'Flatland'.

Interesting that you to refer the 'edge of the universe' thing as a spurious analogy - I thought it was an actual proposition by other posters, and that analogies were given to explain THAT !

Anyhow, I need to think more about your, yes, clearer analogies.

[sylas]

Hello. I've read through the last several pages again recently, in an attempt to resolve the issue I was wondering about earlier. I still haven't been able to resolve it, and could even say I'm even more confused and mystified as to what's been said by some.

I have a reasonable understanding of what homogenous and isotropic means. And I ask again, how can it be said that I am, (and we) are at the edge of the universe ? I can see for countless millions of miles in any direction, so it certainly doesn't seem that I'm on any edge.

Hi Tenny; I wrote this a while ago and then my network connection dropped out. Meanwhile Dave has answered. But with the network back I'll post mine as well...

There's no edge. The universe is (on large scales, as far as we can tell) homogeneous and isotropic, and that means there's no edge.

Blandrew was using some picturesque language which may have been misleading. The only sense in which there are edges is the sense of a limit to how far you can see from some position. Like a horizon on the ocean, there's a boundary beyond which you can't see; but at the horizon there's nothing special. You are at the center of your own field of view, and also on the horizon of certain other observers.

You can also think of a horizon in time. From here-and-now, we can see 2010; but you can't see 2011. You'll have to wait another six months. It's not that NOW is some special identifiable edge in time; merely the horizon of what we see from this point in time.

These kinds of "edges" are not something special about a location, but depend on an observer. They are better called "horizons".

Even better, just forget all that observer stuff and consider simply that the universe has no edge. (Unless the universe is really different from what we currently tend to think on the basis of available evidence.)

Cheers -- Sylas

[Sinker]

I can screw up a two car funeral, but here is my thoughts on subject:

I don't think we as a species have evolved enough yet to fathom infinity. However, I think we will get there eventually. We can guess, however: I think other big bangs occur from quantum fluctuations a great distance from our observable universe. It's got a whole new time frame and as such can never contact our observable universe for two reasons: i) expanding of space between observable universes, and ii) time differences.
Regards
Sinker

[ViewsofMars]

Orion1 deleted his/her contributions from this topic though I did quote (copy) Orion1 as noted in posts #296 and 297 prior to Orion1's action. Shame on you, Orion1! Beware people of Orion1's tricky nonsense. The person may do it again. You should know Orion1 that your message does appear in my mail box.:biggrin:


I can screw up a two car funeral, but here is my thoughts on subject:

I don't think we as a species have evolved enough yet to fathom infinity. However, I think we will get there eventually. We can guess, however: I think other big bangs occur from quantum fluctuations a great distance from our observable universe. It's got a whole new time frame and as such can never contact our observable universe for two reasons: i) expanding of space between observable universes, and ii) time differences.
Regards
Sinker

Hi Sinker. Welcome to Physics Forums. As a human being I like to deal with reality. Observations are based on evidence. There hasn't been any big bangs that have occured outside our observable universe. :biggrin: Science isn't based on speculations but rather observations.

[Sinker]

Orion1 deleted his/her contributions from this topic though I did quote (copy) Orion1 as noted in posts #296 and 297 prior to Orion1's action. Shame on you, Orion1! Beware people of Orion1's tricky nonsense. The person may do it again. You should know Orion1 that your message does appear in my mail box.:biggrin:




Hi Sinker. Welcome to Physics Forums. As a human being I like to deal with reality. Observations are based on evidence. There hasn't been any big bangs that have occured outside our observable universe. :biggrin: Science isn't based on speculations but rather observations.

Thanks for the welcome. Nice forum. Yep - observations are based on evidence. We can still use imagination to speculate and theorize to lay groundwork for observations.
Outside our observable universe is a lot of space. If it is expanding, we can never verify other bubble universes (observable universes to those inside). If we could understand dimensions beyond the known ones, it may be possible.
Humans some time will evolve to a state where we can understand the concept of more dimensions and their nature. Before the slow process of evolution, we may produce machines that will manufacture smarter machines that will do the job for us. (Singularity, I believe is the term.) Once we get a handle on quantum computers, I believe this will happen.
Regards
Sinker

[Flatland]

Blacks Space Until A Different Universe

That statement makes absolutely not sense whatsoever. If beyond the observable universe is "black space until a different universe" that "different universe" would still be part of our universe and not a different universe.

Get it?

[Sinker]

You don't get it. I said "observable universe"

Get it??

[marcus]

In conventional cosmology, do you know what "observable universe" means? It means the part of the whole universe that we have received light or some other signals from, so in principle we can see or have information about.

The observable portion of the universe is constantly increasing, as radiation comes in from farther and farther away.

There is no indication that anything is any different. So we assume that beyond the present range of observation there is just "more of same".

I never met anybody with as much as one introductory college course in Astro who thought that beyond the current observable range there was "black space". That wouldn't make dynamical (general rel.) sense and there is no evidence for it.
"Black space" surrounding the observable portion is a kind of extravagant fantasy without any observational or theoretical support.

Would suggest that anybody who thinks that beyond observable U is anything besides more of same should maybe just take a beginning Astro course.
The conventional model everybody uses could of course be wrong! there could be a large plexiglass sphere just outside the range of what we currently can see. But no reason to think that. So, by Occam's razor (the "keep it simple" principle) we assume more of same until evidence to contrary. If there is ever any evidence of something else you will hear about it! The pros would love a surprise like that and would immediately jump on it!
===================

Edit to reply to the post by NUTGEB that comes next:

Nutgeb, notice that I just said "more of same", not "infinite".

Space could be for example a very large 3D hypersphere, with matter more or less uniformly scattered all over, and a small patch of it what we can now observe. To do the usual analysis and modeling they don't have to assume that the "finite or infinite" question is answered.

I interpret the question of this thread in a modest limited way: what is just out beyond the limit of the observable portion?

I wouldn't encourage anybody to speculate about what the whole space looks like, what topology etc etc. We just don't know enough yet! (In my opinion.) Infinite is a logical possibility, so are various versions of finite. But what is gained by speculating?

But I think it is reasonable to assume "more of same" out past the present bound of what we are observing. (which of course we are observing not how it is at present but how it was way back in the past.)

So I will leave the speculating about infinite or not to you, for the time being.

[nutgeb]

There's no doubt that the idea of a finite universe surrounded by empty space is not accepted by cosmologists. Applying Occam's Razor makes sense. And the balloon analogy works very well if used properly. It makes sense to study cosmology before critisizing it.

Nevertheless, isn't it accurate to say that the infinite nature of the universe is a strong assumption, based on the Copernican Principle and CMB observations, rather than a demonstrated fact? It might be helpful for someone to describe specifically how the existence of an outer edge would contradict general relativity or current observations.

I am not aware of anything specific in GR or in the FRW metric that prohibits the existence of 'empty' space outside of a finite universe. GR math seems to work fine with a model with finite space and time, as long as everything external to that universe is ignored.

Consider a model universe that begins with an 'explosion' of mass energy away from a single point in otherwise empty space. It seems possible that, depending on the nature of the explosion, the fluid mass-energy distribution would arrange itself homogeneously (within the total expanding envelope of the exploding mass-energy), and all individual comoving observers (except those in a position to look beyond the outer edge) would observe the same isotropic Hubble's Law that we observe. For example, a homogeneous distribution might arise if the explosion resulted from a brief period of strong mutual repulsion among particles that previously were tightly packed together. Particles that originally were packed further from the 'center' would gain a proportionally higher recession rate relative to the center.

The original center of the explosion would immediately lose any local uniqueness and as a practical matter would become locally indistinguishable from any other location within the expanding envelope. Once the explosion occurred, gravity and later dark energy would begin to affect the expansion rate of the comoving stream.

One complication is that the positive pressure of free radiation, particularly in the dense, radiation-dominated early universe, would contribute a factor of acceleration to the expansion rate, because a finite universe would have a pressure gradient at its outer edge, giving the pressure something to push into. I don't think that would cause a problem for the FRW metric, but it would need to be factored into the expansion parameters. Perhaps that factor would be found to contradict observations in some way.

If our arbitrary location happened to be very, very far from the supposed edge of a very large but finite universe, the edge would be too far away for us to see, and could also be too far away to affect the homogeneity and isotropy of the CMB radiation we are currently receiving. The non-isotropic distribution of photons at the largest scale just wouldn't have arrived here yet. Then someday, perhaps billions of years in the future, we might detect a slowly growing cold spot in the CMB signalling the first indication of an outer edge.

[Tenny]

Keep in mind this is merely a spurious analogy, designed to show that sometimes "what we see" is not the only way to see things.

OK - I understand. One could end up a little nonplussed about the spurious nature of the analogy though.

An ant is crawling on the surface of an balloon. Every direction it looks it sees more balloon surface - there are no boundaries, no edges. If the ant is not at the centre of this universe, it is certainly not near any edge.

Yes, and we could extrapolate the analogy to apply to a human being on the surface of the earth.

I look down upon the ant from my vantage point. I can see that it is at the surface of the balloon. In fact, it is at the boundary of a sphere that is defined by the balloon's skin. Moreso, as I inflate this balloon, I can even say that the ant is on the leading edge of an expanding sphere that is defined by the balloon's skin.

OK ..

The 2D surface of the balloon is analagous to our 3D universe (with one dminesion ignored). The expansion of the balloon in a radial direction is analagous to the movement of our 3D universe through the 4th dimension of time. The ant cannot go "forward" any more than the balloon expands. Outward is the future, inward is the past.

OK. I thought at the outset, we were talking about an edge to the three spatial dimensions. If the universe is homogenous and isotropic as we say it is, then it should be the same for me here, as if I was gazzillion miles away. And I can see no end or edge in sight (or out of sight) to the three spatial dimensions, so I guess it's infinite in all directions - spatially.

Thanks for taking the time to explain this.

[Tenny]

Hi Tenny; I wrote this a while ago and then my network connection dropped out. Meanwhile Dave has answered. But with the network back I'll post mine as well...

There's no edge. The universe is (on large scales, as far as we can tell) homogeneous and isotropic, and that means there's no edge.

Blandrew was using some picturesque language which may have been misleading. The only sense in which there are edges is the sense of a limit to how far you can see from some position. Like a horizon on the ocean, there's a boundary beyond which you can't see; but at the horizon there's nothing special. You are at the center of your own field of view, and also on the horizon of certain other observers.

You can also think of a horizon in time. From here-and-now, we can see 2010; but you can't see 2011. You'll have to wait another six months. It's not that NOW is some special identifiable edge in time; merely the horizon of what we see from this point in time.

These kinds of "edges" are not something special about a location, but depend on an observer. They are better called "horizons".

Even better, just forget all that observer stuff and consider simply that the universe has no edge. (Unless the universe is really different from what we currently tend to think on the basis of available evidence.)

Cheers -- Sylas

Hi Sylas. Thanks. Your explaination is very clear and helpful.

The universe has no edge, but we can consider our present location in time, this moment, as a horizon to our limits of perception.

Can I then make the assumption that the universe is spatially infinite in all directions ? Given that;

- it is homogenous and isotropic
- I see no spatial end / edge to it for millions of miles - light years even
- if I were in a location a billion miles away, I would probably see the same as I do now


EDIT; I just saw marcus has answered this somewhat, but I would still appreciate your response.

[DaveC426913]

- I see no spatial end / edge to it for millions of miles - light years even
- if I were in a location a billion miles away, I would probably see the same as I do now


Not to put too fine a point on it but:
- "millions of miles" doesn't even get you to Mars
- "a billion miles away" doesn't even get you to Pluto

You want to be talking about billions of light years.

[Chiclayo guy]

I never met anybody with as much as one introductory college course in Astro who thought that beyond the current observable range there was "black space". That wouldn't make dynamical (general rel.) sense and there is no evidence for it.
"Black space" surrounding the observable portion is a kind of extravagant fantasy without any observational or theoretical support.

But wasn’t empty, black space the dominant condition prior to the big bang, and if so why couldn’t it exist now outside of the observable universe?

Tom

[DaveC426913]

But wasn’t empty, black space the dominant condition prior to the big bang, and if so why couldn’t it exist now outside of the observable universe?

Tom

No, the dominant condition pre-BB was no space at all.

The BB did not occur in space, the BB created space.

[nismaratwork]

No, the dominant condition pre-BB was no space at all.

The BB did not occur in space, the BB created space.

*Pipes up* and time!

[justwondering]

The 'edge' of our observable universe is receeding faster than the speed of light: which means you can't get there from here.

But NOT any Mass that may be near the 'edge', that can NOT be traveling away from us that fast?

[DaveC426913]

But NOT any Mass that may be near the 'edge', that can NOT be traveling away from us that fast?

Yes, galaxies are receding from us at speeds greater than the speed of light.

No, that does not violate SR.

[Max™]

They aren't traveling away from us through space, they're being dragged along with the expansion of the Universe.

Locally they aren't moving that rapidly, it is only when you examine scales approaching that of the observable horizon that you see this apparently forbidden motion.

Nothing can move THROUGH spacetime faster than light, spacetime itself is not moving through spacetime, it has different constraints.

[sylas]

They aren't traveling away from us through space, they're being dragged along with the expansion of the Universe.

This depends, I suggest, on what analogies or similes you like. But IMO the technical descriptions do not really correspond to anything "dragging" things. "Dragging" suggests some kind of force, which pulls objects along in some way. But there is no "force" corresponding to a drag that is forcing things apart. There's dark energy of course, which is a bit like a pressure that accelerates expansion; but you still get all the same superluminal proper recession velocities in a universe where there is no dark energy and the expansion is slowing down. You get superluminal expansions in a model where the expansion rates are linear, without any acceleration or deceleration. That is, no forces at all, just expansion of things with recession velocities for co-moving objects remaining constant.

That is -- you STILL get superluminal recessions whether the expansion is being pushed to increase or dragged to slow down, or if it is just coasting.

So for this reason, I feel that speaking of space "dragging" things is really misleading.

Personally, I think might be better to say that space is being dragged along by all the stuff that is expanding, if we speaking of anything being "dragged". Any sufficiently large volume withing boundaries that are locally not superluminal will be increasing in total volume. That is, there's more space between things as time goes by.

Locally they aren't moving that rapidly, it is only when you examine scales approaching that of the observable horizon that you see this apparently forbidden motion.

That's definitely incorrect on two counts.

The most unambiguous problem is with the suggestion that superluminal recession velocities have anything to do with being at boundaries of the observable universe. That just isn't true. You get superluminal proper recession velocities for galaxies that are "now" something like 14 billion light years away in proper distance, or only about a third of the way to the edge of the observable universe. Roughly speaking.

More subtly, I don't think it is really meaningful to say "locally they aren't moving that rapidly".

Of course, everything out at some distant location is all moving locally with respect to each other at small velocities, much like in our own neighbourhood. But that's simply not bothering to look at expansion of the universe at all. The expansion of the universe is not a local effect. It really means that density of things is falling as everything moves apart from everything else (on sufficiently large non-local scales).

The proper distance between things IS increasing that rapidly. Whether you speak of this as things moving apart, or as the space between things increasing; it still isn't any object being dragged.

The precise way to describe expansion of the universe is GR, of course. The rest is analogies or similes, and all too often they end up being actively misleading if you are not careful to remain consistent with the underlying GR account.

Cheers -- Sylas

[Max™]

I didn't mean to imply that it had to do with being at the edge of the observable Universe, as symmetrically we would expect our current position to appear the same from the perspective of an arbitrarily distant point.

I use the term dragging out of habit, as the space in which you are located itself is moving, you aren't going to observe forces relative to it, you would only notice red shift from everything else moving away from you.

I'm only speaking of the GR description, I take that for granted in such discussions.

[Mihael@@/&]

Things have changed since Mar8-06, 06:08 AM :)

http://en.wikipedia.org/wiki/Observable_universe

"No evidence exists to suggest that the boundary of the observable universe corresponds precisely to the physical boundary of the universe (if such a boundary exists); this is exceedingly unlikely in that it would imply that Earth is exactly at the center of the Universe, in violation of the Copernican principle. It is likely that the galaxies within our visible universe represent only a minuscule fraction of the galaxies in the Universe. According to the theory of cosmic inflation and its founder, Alan Guth, the lower bound for the diameter of the entire Universe could be at least in the range of 10^23 to 10^26 times as large as the observable universe."

[heusdens]

Is it just black space extending forever? Or perhaps black space for a finite distance until another universe?

I find it hard to believe our universe is just the only universe. I don't see how it wouldn't extend for eternity instead. What is so special about our universe and the space we are in?

What do you think?


You didn't mention this option in the poll, but the most serious candidate for the universe outside the horizon, since the horizon is just an arbitray limit, is that the universe outside of the horizon is simply more of the same, and in fact not anything different then we see here.

All other assumptions are speculations. Why would it be that the universe outside of the horizon (which used to be bigger in the past and will be smaller in the future) would be any different then the part we see?

That needs an explenation.

So the only serious option is that the universe outside of the horizon is the same (same homogeneity and isotropy) as the part we see.

[heusdens]

.. On the other hand, the total universe is is still finite, but there is no such thing as outside.

How do you know that?

[heusdens]

But most evidence points to the universe being flat. In that case a what would happen if you reach the end of the universe? If it were a spherical universe then we would just reach the other side. But what would happen if you reach the end of the universe? Would their be like a giant hard barrier that you can hit but not explode? Sounds to mythical to me. The universe seems to complex for it to be just finite.

The universe isn't infinitely big and infinitely small?

The current assumption or basic premise is that the universe has no edge or boundary.

You will never see a sign in space "end of universe, turn back now" there will simply be "more universe" after such a (fictional) sign.

For practical measurements, the universe we can observe only exists in finite parts and measurements, but this does not imply the universe must be finite and spatially closed (like a 2d surface on a 3D sphere, but then for the 3D analogous situation).

But from a more philosophical point of view I would think that by necessity the university (the totality of it) must be infinite, yet at the same time this infinity only exists in the form of finitudes. Indespite that this seems a contradiction, it is not as can be seen from this analogy: you can pick arbitraily any natural number, and you will always come up with a definite finite (and countable) quantity, yet the number set itself is infinite, you can always draw more numbers and larger numbers, no matter how long you draw a number.

Our measurements are like the numbers we can draw, the universe is like the complete set.

Notice also that the finitude and/or the infinitude of the world form a dialectical unity, you can not determine one without the other, they are like the two sides of the same coin, or the two poles of a magnet.

[heusdens]

...

Both those regions are at the edge of our observable universe... and we are the edge of their observable universe as measured now. But those two regions at opposite sides of the sky are OUTSIDE the observable universe for each other.

Cheers -- sylas

Good argument, and when we invoke the cosmological principle, that the universe looks (at sufficient large scale) the same in all parts of the universe, we arrive at the conclusion that beyond the horizon of observation there is just more universe that looks about the same as the stuff and structure we see.

[zahero_2007]

there is a multiverse

[TheTechNoir]

there is a multiverse

Care to elaborate?

And my answer is that what exists beyond the visible universe is the exact same as what exists here. I find it an unlikely possibility that somewhere far off the laws of physics change.

I believe that the universe has no boundary and therefore I also believe that outside the observable universe you see the same thing there as we see here (speaking on a large, far away view that is - obviously locally there are lots of differences but broadly speaking the universe is quite uniform). Because of no boundary, this means that a spatially flat universe with a finite size, a spatially flat universe with infinite size (seems to currently be a lot of people's prefered belief whereas flat/finite seems to be more fringe), the closed universe or 2d surface of sphere anology universe, the saddle, and all other known possibilities would all lead me to believe that in any given region of space outside of our observable universe you would observe roughly the same thing as we do here.

EDIT: Question: I understand it, but am I the only one who finds it a bit difficult to mentally visualize the step up from 2d analogue to full 3d closed universe?

EDIT 2: Lastly, I find it EXCEEDINGLY unlikely that just past the exact tip of our observable universe at any given time all matter disappears and space becomes utterly empty. Heck if from ANYONE'S perspective this were to be the case I would be beyond shocked. But for it to happen to be exactly/perfectly around us, no less? Me thinks the poll options are both completely crackpot.

[cristo]

EDIT: Question: I understand it, but am I the only one who finds it a bit difficult to mentally visualize the step up from 2d analogue to full 3d closed universe?


I think it's perfectly normal not to be able to visualise in 4D :biggrin:

[mistergrinch]

Beyond the observable universe it's turtles all the way down -- aka the "turtleverse". Turtleverse Theory is about to revolutionize the field of cosmology!

[harcel]

Beyond the observable universe there is lots and lots of unobservable universe,

[Radrook]

Beyond the observable universe there is lots and lots of unobservable universe,

Where is the universe located?

[Jake4]

Beyond the observable universe there is lots and lots of unobservable universe,


I like this answer the best.

[DevilsAvocado]

Where is the universe located?

Here.

[rinardman]

Is the universe infinite? If it isn't infinite, then how much bigger is it than the observable universe? How would humans ever be able to answer the second question?

I can't imagine the universe being finite, because that would mean besides there being a "here", there would have to be a "there". (At least in my mind)

And, I can't imagine a universe that is infinite, because my human brain, as magnificently constructed as it is, is woefully underpowered to do that job.

I pondered this a lot in my younger days, but now that I'm getting old I've decided to just be as happy as I can, in my little corner of whatever the universe really is. :biggrin:

*

[Gold333]

I don't understand this question.

If the poll asks what the change in structure is that the boundary of the observable universe represents (e.g. photon decoupling, looking back into the past up until close to the big bang, etc)

...that would put Earth at the centre of this sphere (at the "edges" of which something changes).

How can the Earth be at the centre of the universe? (or at the centre of the sphere at whose "edges" something changes?

[Radrook]

If indeed the universe is infinite then how can it grow? You cannot add to the inifinite because if you do then it wasn't infinite to begin with.

[Nabeshin]

If indeed the universe is infinite then how can it grow? You cannot add to the inifinite because if you do then it wasn't infinite to begin with.

This is a very fundamental misconception of what something means to be infinite. I do not really feel like writing a very long post explaining precisely why this is wrong (perhaps someone else will), so I suggest you google around for a short while and come to understand infinity a little better.

[periot123]

universe is not flat it has three and some say it has four dimentions philosophically we can call it infinite. No one can measure its boundary if we say that the universe is finite its like counting sand in the shore ^_^ in the end even if the universe is finite or infinite we cannot measure its boundary .................

[JaredJames]

universe is not flat it has three and some say it has four dimentions philosophically we can call it infinite. No one can measure its boundary if we say that the universe is finite its like counting sand in the shore ^_^ in the end even if the universe is finite or infinite we cannot measure its boundary .................

What does any of that mean?

There are four basic dimension of the universe, not three - don't know where you pulled that from.

The number of grains of sand on a shore line is a finite number and nothing to do with infinity so I don't know where that comparison comes from.

We've already estimated the size of the universe, although it's only based on our current knowledge we are "measuring the boundary" if you will.

[Tanelorn]

What is black space? And what is blacks space? Do you mean empty space?

I believe that the observable universe is just a tiny (like 10-30 or far smaller) part of the whole universe. I think Penrose proposes this. I also ask if the observed homogeneity of our observable universe only appears that way because we are looking at just a tiny grain of sand part of the whole. I also sometimes wonder if given the above scenario whether the universe could still be undergoing continous inflation at some point now a very great distance away, pushing the expansion of space everywhere else, including here. This would also be the same point that our observable universe inflated from 13.7B years ago. I recall that the Inflation and/or dark energy expansion of space can apparently separate any two points in space at a rate many, many times faster than the speed of light. However I am probably talking complete nonsense because I have little understanding of GR or advanced mathematics, I probably get my ideas from the water cycle here on earth!

So I guess I have to vote other!

[DevilsAvocado]

...that would put Earth at the centre of this sphere (at the "edges" of which something changes).

How can the Earth be at the centre of the universe? (or at the centre of the sphere at whose "edges" something changes?

Where is the center on the surface of a sphere?

I9Cjxd4Mjog

17jymDn0W6U


See these threads for further info:

expansion of space and looking back in time (http://www.physicsforums.com/showthread.php?t=365912)

The Known Universe Scientifically Rendered For All to See (by AMNH) (http://www.physicsforums.com/showthread.php?t=368057)

[Isaacsname]

Wow, I wish I understood more of this, it's fascinating even based on conjecture.

I found this site recently that shows the assumed scales of things in our universe as well as the size of what is unobservable ( Planck scale to 900m light years ) They say the observable is 190m light years, and the unobservable is 900m light years.:eek:

http://primaxstudio.com/stuff/scale_of_universe/

How does one come to the conclusion of the size of the unobservable areas ? Or is it a necessary to satisfy some cosmological model ?

Thanks,

Isaac

[JaredJames]

I found this site recently that shows the assumed scales of things in our universe as well as the size of what is unobservable ( Planck scale to 900m light years ) They say the observable is 190m light years, and the unobservable is 900m light years.:eek:


How big?

Try 93 billion light years in size, with the observable universe being ~48 billion light years if my memory is correct.

[Isaacsname]

What is black space? And what is blacks space? Do you mean empty space?

I believe that the observable universe is just a tiny (like 10-30 or far smaller) part of the whole universe. I think Penrose proposes this. I also ask if the observed homogeneity of our observable universe only appears that way because we are looking at just a tiny grain of sand part of the whole. I also sometimes wonder if given the above scenario whether the universe could still be undergoing continous inflation at some point now a very great distance away, pushing the expansion of space everywhere else, including here. This would also be the same point that our observable universe inflated from 13.7B years ago. I recall that the Inflation and/or dark energy expansion of space can apparently separate any two points in space at a rate many, many times faster than the speed of light. However I am probably talking complete nonsense because I have little understanding of GR or advanced mathematics, I probably get my ideas from the water cycle here on earth!

So I guess I have to vote other!

No, I think you are correct, at least according to what I understand so far myself.:tongue2:

Have you checked out Leonard Susskind's Stanford lectures on FLRW standard cosmology ? They're on Youtube, 8 of them , iirc, and he explains how the relative velocity of two galaxies in an expanding space traveling apart from each other can excede c by some factor, lecture 7 or 8 I think.

Good stuff, sometimes Susskind gets a little derailed with a train of thought, but still worth watching imho.

Isaac

[DevilsAvocado]

How does one come to the conclusion of the size of the unobservable areas ? Or is it a necessary to satisfy some cosmological model ?

Here is good info on the Observable universe:
http://en.wikipedia.org/wiki/Observable_universe

The diameter of the observable universe is estimated to be about 28 billion parsecs (93 billion light-years),[3] putting the edge of the observable universe at about 46–47 billion light-years away.


If you are puzzled by the fact the universe can be 93 billion light years 'wide', while it is 'only' 13.75 billion years old!? :eek:

The answer is: There is no speed limit for the expansion of the universe, but any object moving inside the universe is always limited to the speed of light.


EDIT:
Check out this thread for info expansion of the universe: expansion of space and looking back in time (http://www.physicsforums.com/showthread.php?t=365912)

[Isaacsname]

How big?

Try 93 billion light years in size, with the observable universe being ~48 billion light years if my memory is correct.

Yoikes, reminds me to always check the source. Had I just looked on the wiki page for " Observable universe " I would have found that the ~ 180/190m lightyear estimation originated from a model that stated an age of 15.8b years for the age of the universe. ( ...under " misconceptions " )

I guess the idea was flawed..:tongue2: and shown to be incorrect.

http://en.wikipedia.org/wiki/Observable_universe

from

http://www.astro.ucla.edu/~wright/old_new_cosmo.html#05Aug06

" The claim that the Universe would be 15% larger is partially incorrect. Even though relatively nearby galaxies would be 15% further away the actual size of the Universe would go from infinite (flat) to finite (closed) but very big, which is a smaller Universe. The distance to distant quasars at redshift z=6 would increase by only 4%, and the distance to the last scattering surface changes less than 0.5% because this is what is fixed by the CMB. "

Thank you, I just learned some things.

[pibb]

could antimatter lay beyond the universe?

[JaredJames]

could antimatter lay beyond the universe?

Judging by your two posts you have something for antimatter.

The answer to this one is basically no, but we could also say who knows.

I'd be swinging against that option though.

[awhalen]

Listen to yourself! Do events we can never know about exist or not? How the hell can you or I or anyone ever know? It's just a fantasy!

If a tree falls in a forest and nobody is there to hear it, see it, feel it, or observe it does it still fall and affect its surroundings?

Yes it does even though nobody knows about it. and if you go back to the spot at which it fell you could figure out what happened.

So asking the questions about this universe may lead us to understand whats outside our space time even though we will never observe it it still occurs

As Einstein said "everything is relative"

[Darken-Sol]

sorry i just jumped to the end. how about a process like quarks. is it possible all light sent out pops back to feul the big bang? i came to this conclusion with wild speculation and the use of a magic 8 ball.

[DaveC426913]

As Einstein said "everything is relative"
And Ted Stevens said "the internet is a series of tubes".

Spurious out-of-context quotes don't help much.

sorry i just jumped to the end. how about a process like quarks. is it possible all light sent out pops back to feul the big bang? i came to this conclusion with wild speculation and the use of a magic 8 ball.
:biggrin: Magic 8 ball.

[awhalen]

universe is not flat it has three and some say it has four dimentions philosophically we can call it infinite. No one can measure its boundary if we say that the universe is finite its like counting sand in the shore ^_^ in the end even if the universe is finite or infinite we cannot measure its boundary .................

the universe is said to have four basic dimensions that make up our three dimensional space.
There are another seven that deal on a subatomic level.

This being said how can we philosophically call the universe infinite based on the information you provided?

[DaveC426913]

the universe is said to have four basic dimensions that make up our three dimensional space.
There are another seven that deal on a subatomic level.

This being said how can we philosophically call the universe infinite based on the information you provided?

I wouldn't spend too much time examining periot's argument. It's an 'argument by befuddlement'*, as in: after enough enough smoke and mirrors, one can simply finish with 'so no one can say otherwise'.

* © DaveC426913 20110412

[StateOfTheEqn]

I voted 'other' because the observable universe is just our past light-cone. Our past light-cone is like a slice of the onion and we make inferences about the entire onion from that one slice.

[SirFishSlayer]

Our guess the space and time in our universe is finite. However it is just hard to believe there was no time before the big bang and no content beyond our observable universe. It doesn't make sense how things can by finite. I mean what happened before the big bang and why are there boundaries at the ends of our universe?

By studying the universe and the physical world one can truly see things aren't orderly per se. They far beyond the realms of organized imagination and can only be understood with observation and empiricism. Limits on the universe would truly make things beyond confusing.

BTW, what do scientists think happened before the big bang. Since the universe is expanding according to most of the evidence today, the cyclical big crunch is unlikely. What do scientists think are the likely choices?

There is the "shell" of our universe which is our expansion into the emptyness of the "Greater Universe". Lets call that the "Greater Universe" the ExtraVerse. Within the ExtraVerse there may be other universes that are expanding into it...maybe even expanding towards ours.

If we talk about time as being the point of creation of our universe then we must also assume that it will end at the last light of the last star....or at maybe when the dust and black holes break down as they expand outwards into the ExtraVerse. But is that correct?

Should we think of time existing only as our universe expands into the ExtraVerse? That is silly. If we could some how transport ourselves outside of our universe (lets say 5 minutes in distance), and watch for it in that 5 minutes as it expands towards us...would we even see it coming towards us? Probably not since it is the very light and energy that is our known universe that makes up the edge of it. But getting back to us sitting there, waiting for it to come to us...if we transported ourselves with a watch, that watch would be ticking. So we wouldn't just come into existance as the edge of the universe passes us and we become a part of it again.

I like to think of time as something that existed forever before and will exist forever afterwards...our universe just exists in a minute portion of it.

[DaveC426913]

Should we think of time existing only as our universe expands into the ExtraVerse? That is silly. If we could some how transport ourselves outside of our universe (lets say 5 minutes in distance), and watch for it in that 5 minutes as it expands towards us...would we even see it coming towards us?
Funny thing about invoking magical abilities such as instant teleportation in thought experiments - they tend to run afoul of established inderstanding - such as SR.


I like to think of time as something that existed forever...
Ah but so did Newton. Einstein showed him up.

[SirFishSlayer]

[QUOTE=DaveC426913;3304988]Funny thing about invoking magical abilities such as instant teleportation in thought experiments - they tend to run afoul of established inderstanding - such as SR. QUOTE]

No "magical abilities"...just putting the variable out there.

Seems to be that our universe isn't creating more of itself as it expands. It is not creating anything, it is just expanding into a "space" that is void of anything until you put something in it.

So, what IF there is another universe whose edge was approaching ours? If they are living in their own universe's space and time and we are living in ours, then does the 2 space-times collide? What happens? Whose space-time would rule? Would they just merge if their universe's laws are the same as ours?

[Jake4]

you're making some large assumptions..

who's to say 'space' exists beyond our universe.

[SirFishSlayer]

Who is to say it doesn't.

Is there a truly empty place waiting for a universe to encroach upon it, or is the universe creating it as it goes along?

Again, what if there is the Multi-Verse thing happening and has been happening...Our universe in the grander scheme of the ExrtaVerse. Then there is something else out there and and so it is not empty. What do we call that "place" in between universes?

We would assume that it is truly empty...but we used to think that of deep space until we realized that there is stuff out there and our universe if filled with it, even if we can't see it.

BTW, love the discussion. Thanks guys.

[DaveC426913]

It is not creating anything, it is just expanding into a "space" that is void of anything until you put something in it.

No, that is not the current understanding. The universe is not expanding into any void.

[Jake4]

I love the discussion as well :)

I would say that it doesn't need to be one or the other.

The universe could be expanding, without creating and without there being a void in which it is expanding.

as Dave said above.. the current understanding doesn't claim the existence of a void. Truthfully I don't know how one would really describe this void anyways.

Outside of the universe, the void would have to be space-less, and time-less.

The issue with most of cosmology (at least in my limited experience) is that the real mathematical representations cannot be efficiently translated into simplified conceptualizations.

I feel like that's the issue with most physics these days, and with the increase in pop-sci books.. the truth is being twisted and contorted into a conceptual mold that it just can't fit in, which is the only con.

The pro, is that more everyday people are becoming interested in science. That is such an amazing thing... even if it's storybook science, the bottom line is everyday people are starting to be curious :) and I like that.

[DaveC426913]

The issue with most of cosmology (at least in my limited experience) is that the real mathematical representations cannot be efficiently translated into simplified conceptualizations.

I feel like that's the issue with most physics these days, and with the increase in pop-sci books.. the truth is being twisted and contorted into a conceptual mold that it just can't fit in, which is the only con.

Well said. Formulae can accurately describe structures that cannot be adequately represented by human-understandable analogies, which are, by-definition, faulty.

Most of us strive to understand the unknown by comparing to known concepts, and therein lies the flaw. There is no comparison for the universe.


That being said, it is all right to create analogies to help understand how a model works, but it's lossy process. You can't do the reverse; you can't use the analogy to extrapolate back to the model. (A massive object may form a gravity "funnel" - but we do not then go looking for a cosmic drain plug!)

[SirFishSlayer]

I agree with that...space-less and time-less. Both are associated with our universe...neither existing into what we are expanding into.

I think we should make the cosmologist translate the math into concepts. Tell them to just give us the Cliff's Notes version, in 150 words or less, each theory they used (or created) to come to their conclusion...otherwise the grant money goes away. I'd think it would be cool to see a head explode...or implode.

The thing that has always keeps itching me is: what if we are not alone. What if there are more universes out there expanding like ours is. What if that is the natural order of things. When our universe finally fizzles out, will there be just a bunch of black holes out there eating those smaller ones around them. Assuming that they will still be traveling. Maybe at some point, when they have consumed enough, they can start another universe. Or do they just fizzle out themselves through leakage? Then what?

[SirFishSlayer]

Well said. Formulae can accurately describe structures that cannot be adequately represented by human-understandable analogies, which are, by-definition, faulty.

Most of us strive to understand the unknown by comparing to known concepts, and therein lies the flaw. There is no comparison for the universe.

Agreed. We are just along for the ride.

My personal "Heaven" would be to have it all explained to me, after I was given the capacity to understand it, then let me watch the re-run...with the remote control with the buton to zoom in and out.

[Trenton]

I personally postulate that the observable universe is a very large black hole sitting in a universe that is infinite in extent and populated with all the objects we have in our universe as well as other ultra massive black holes.

This is not about Russian dolls or wormholes but it does fly in the face of more established notions such as that in which all time and space was crunched in a singularity that somehow exploded - the key implication being that there was no 'before' or 'outside'.

Ultimately, any theory rests on one or more points of faith. For example, that the fundamental constants and the laws of physics are the same everywhere and are invarient with time. We don't know if this is the case and we have very little in the way of proof but we would all think the burden of proof would rest with anyone who disputed it as we would all ask the question 'why would the laws of physics change?' - and not come up with any answers.

To me, a hardcore believer in the invarience of the phycial laws and constants, the idea of an 'act of creation' is totally abhorent. Indeed the big bang as a unique event directly contravenes the principle of the invarience of the phycial laws and constants.

For the moment forget general relativity and quantum mechanics and go back to what we were learning when still in dypers. 1 + 1 = 2 The question is this. Was there ever a 'when' or a 'where' in which 1 + 1 did not equal 2?

It would seem not. 1 + 1 = 2 is true regardless of wether or not there are any entities to add. It is completely independent of the existence of time and space, of matter and energy.

So are all the laws of math - and the laws of physics. It does not matter if there were no photons, the speed of light would still be c.

Extending the concept (the faith) further - to the laws of physics as they really are (rather than as we understand them), the existance of matter and light, space and time, must be a direct conseqence of the laws of physics. Therefore these entities must have always existed and extended to the complete (infinite) set of legal coordinates. Therefore there was a 'before' and an 'outside'

[Jake4]

I like to think of the possiblity of different mathematical operators.. other than our standard +,-,÷,* .. in other universes :)

[Trenton]

I like to think of the possiblity of different mathematical operators.. other than our standard +,-,÷,* .. in other universes :)

I wouldn't. It would contravene the principle of invariance of math and physical laws. Besides they are not other universes, meerly other multi-billion lightyear radius black holes. By definition [of the word], there can only be one universe.

There is in any case, no shortage of math operators as things stand. What there is a shortage of are decent accounts of the workings and implications of some of the more exotic ones (eg derivation of the equation for the Schwartzchild radius and its implications)

[Tanelorn]

What is beyond the observable universe? The unobservable universe.

What is the unobservable universe like? The unobservable universe is like the observable universe except that we cannot observe it because it is beyond the observable universe.


Am I missing something?

[SirFishSlayer]

What is beyond the observable universe? The unobservable universe.

What is the unobservable universe like? The unobservable universe is like the observable universe except that we cannot observe it because it is beyond the observable universe.


Am I missing something?

Stating it that way makes waaaay more sense. Now that you've explained the easy stuff, explain women to me...remember, under 150 words. Thanks mucho!

[Darken-Sol]

What is beyond the observable universe? The unobservable universe.

What is the unobservable universe like? The unobservable universe is like the observable universe except that we cannot observe it because it is beyond the observable universe.


Am I missing something?

prove it

[Trenton]

Women have a fundamentaly different neurology - and more eratic hormones. (10 words)

But what you are missing over and above what all men miss, is that you have forgotten to postulate what make the unobservable universe unobservable. In what sense is it beyond the observable? Is it too far away? behind event horizons?

I suspect that advances in telescopes will come to widen the observable, ultimately by orders of magnitude. After all I can remember being told that 'all the matter in the universe amounts to less than 1 percent of that needed to ultimately bring about a big crunch'

Today I note that there is an article on Wikipeadia stating the Schwartzchild radius of the (observable) universe is approx 10 billion lightyears. That shows we have counted up many times more matter than before - because we have better telescopes.

[Jake4]

Women have a fundamentaly different neurology - and more eratic hormones. (10 words)

But what you are missing over and above what all men miss, is that you have forgotten to postulate what make the unobservable universe unobservable. In what sense is it beyond the observable? Is it too far away? behind event horizons?

I suspect that advances in telescopes will come to widen the observable, ultimately by orders of magnitude. After all I can remember being told that 'all the matter in the universe amounts to less than 1 percent of that needed to ultimately bring about a big crunch'

Today I note that there is an article on Wikipeadia stating the Schwartzchild radius of the (observable) universe is approx 10 billion lightyears. That shows we have counted up many times more matter than before - because we have better telescopes.


Farther, yes, but more.. no...

the universe is expanding at speeds much higher than the speed of light, thus it is physically impossible for us to see any more of it.

That is what causes it to be 'unobservable'

And I'll state again, that I do like thinking of different operators :) Not in any serious way, but it's fun :P

[DaveC426913]

Women have a fundamentaly different neurology - and more eratic hormones. (10 words)

But what you are missing over and above what all men miss,

What???

[Chronos]

'Outside the universe' is logically inconsistent given the universe, by definition, includes all aspects of nature that have observable consequences - or in simpler terms, 'all that is possible to see'.

[ummm]

Okay! I read about the first three pages of this discussion and skipped ot the last page, having the last post on May18-11, 10:16. I guess classes are out for summer, but I noticed that the discussion seems to be repeating the SOS. Since I didn't read all of the pages I'll probably get flamed for not doing so if my questions have already been asked but here goes:

1) If, at the time of the big bang, the entire universe was in, say, maybe a little ball, maybe the size of a baseball, or golf ball, or smaller like a grape or my brain (okay nothing's that small), then what was outside that little ball? What did the parts or gas or whatever, that was in the little ball of universe, expand into? Whatever it expanded into, obviously had to be outside the little ball of universe.

2) Since I'm not a physics phD, I'm still laboring with the notion that nothing is faster than the speed of light. If that is true, how can the universe be expanding faster than that?

Thanks for any answers.

[DaveC426913]

1) If, at the time of the big bang, the entire universe was in, say, maybe a little ball, maybe the size of a baseball, or golf ball, or smaller like a grape or my brain (okay nothing's that small),

Much smaller than an atom.


then what was outside that little ball? What did the parts or gas or whatever, that was in the little ball of universe, expand into? Whatever it expanded into, obviously had to be outside the little ball of universe.

It did not expand into anything. The universe - everything - was simply very small. There was - and still is - no 'outside'.

2) Since I'm not a physics phD, I'm still laboring with the notion that nothing is faster than the speed of light. If that is true, how can the universe be expanding faster than that?

Space expanding is not a 'thing'. The expansion of space between things does not violate relativity.

[marcus]

...
2) Since I'm not a physics phD, I'm still laboring with the notion that nothing is faster than the speed of light. If that is true, how can the universe be expanding faster than that?

Thanks for any answers.

In usual motion, you get somewhere. In the uniform pattern of expanding distances nobody gets anywhere.

There isn't any destination that you are approaching (aside from some small local motions galaxies have in their surrounding space, which are much slower than light).

So expansion is not usual motion you ordinarily think of---the speed limit of special relativity does not apply to it.
================

relativity developed in two stages first special (1905) which gave us the speed limit for ordinary motion in our local surrounding space

and then general (1915) which allowed geometry to be dynamical and changing (especially over large time and distance scales, if less noticeably close by)

changing distances between stuff that is not, in an ordinary sense, moving is another name for spacetime curvature. (I didn't say space curvature. the curvature may not be purely spatial, it may only show up in spacetime) the approximately uniform pattern of expanding distances is just one type of spacetime curvature.

if you accept the 1915 general theory, then you have to allow for geometry to change dynamically----among other things this means distances can change at rates faster than c.
But those effects normally only show up at very large distances and long timescales.

Current expansion of distances is only 1/140 of one percent per million years. And only applies between objects not bound together by gravity or other forces. So widely separated galaxies. 1/140 of one percent change in a million years is tiny tiny tiny percentagewise.
but if the distance base is long enough it could amount to a rate faster than light.

[DevilsAvocado]

1) If, at the time of the big bang, the entire universe was in, say, maybe a little ball, maybe the size of a baseball, or golf ball, or smaller like a grape or my brain (okay nothing's that small), then what was outside that little ball? What did the parts or gas or whatever, that was in the little ball of universe, expand into? Whatever it expanded into, obviously had to be outside the little ball of universe.

THAT QUESTION IS VERBOTEN!! :grumpy:

No no sorry, silly joke, of course you have the right to ask, and I actually 'struggled' with exactly the same question for years, and got several times the same 'reaction' as in my first sentence. :smile:

First hint you will find in Chronos comment, just before your post. That’s the short version.

The longer version is that we just don’t know... :rolleyes: i.e. we don’t know if the universe is finite or infinite!

If the universe is infinite, your question becomes 'invalid', because it just goes on and on and on and on and… etc for all eternity. If you would like to make a 'picture'; imagine a computer that just adds a (random) number at the end of a (already) very large number:

38221153454624957170750674987874079497881357315286 73054535077643206589562337920052293117729930570495 48155758228845860778017611126014402141...

There’s (AFAIK) no law stating that the computer ever will run out of a 'new' number to add. :smile:

If the universe is finite, the simple answer is related to Chronos comment, the universe we live in and do science and physics in – is all there is to 'investigate'. I.e. our mathematics describes the natural laws inside our universe, and does not say anything about what’s 'outside'. Furthermore, science is about making testable predictions, which can be verified or refuted by physical experiments (you never get a Nobel without experiments, ask Stephen Hawking). It’s tuff to go 'outside the universe' to make any experiment... If you wish to penetrate the 'outside business', you end up with 'supernatural things'. This is not what physics and cosmology is about.

However, to complicate this just a little bit – this last claim of mine is not entirely true... :blushing:

There are very bright scientists, like Max Tegmark, who indeed speculate about multiverse, i.e. a lot of parallel universes (that are separated). Don’t ask me how Tegmark could ever verify this experimentally. Also in String theory there are 'mathematical investigations' dealing with the possibilities of "Branes" and larger extra dimensions. We are however forever "locked in" in our 3D world, our "Brane".

(Hope I didn’t make things worse... :uhh:)

2) Since I'm not a physics phD, I'm still laboring with the notion that nothing is faster than the speed of light. If that is true, how can the universe be expanding faster than that?

Thanks for any answers.

This question is even better! And this almost drove me crazy (:biggrin:) before I found the simple answer:
There is NO speed limit for the expansion of the universe; however every object moving inside the universe is always limited to the speed of light.

You can read more about it here: Michael S. Turner and Craig Wiegert – Great Discovery Great Question (http://www.fnal.gov/pub/ferminews/ferminews00-05-12/p5.html).


P.S. Welcom to PF ummm!

[bcrowell]

1) If, at the time of the big bang, the entire universe was in, say, maybe a little ball, maybe the size of a baseball, or golf ball, or smaller like a grape or my brain (okay nothing's that small),
We don't know whether the universe is finite or infinite. We have a FAQ entry on that topic: http://www.physicsforums.com/showthread.php?t=506986


then what was outside that little ball? What did the parts or gas or whatever, that was in the little ball of universe, expand into? Whatever it expanded into, obviously had to be outside the little ball of universe.
Even if it's finite, it doesn't have an edge; it wraps around.

http://www.astro.ucla.edu/~wright/cosmology_faq.html#XIN



2) Since I'm not a physics phD, I'm still laboring with the notion that nothing is faster than the speed of light. If that is true, how can the universe be expanding faster than that?
We have a FAQ entry on that:
http://www.physicsforums.com/showthread.php?t=508610

[bcrowell]

Since this thread dates back to 2006, I'm going to close it.

@ummm, if the replies you've received haven't answered your questions, please feel free to open another thread.