What Is Beyond The Observable Universe?

[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 Hawking 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 into 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 traveled 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 into 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 traveled 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 what's 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.