Could there be an edge to the Universe?

[KingOrdo]

The answer, I am told, is 'No'. But I do not understand why. Assume:

(1) The Universe is spatially flat. It will one day stop expanding.

(2) There is no weird dark energy.

These are, I think, plausible assumptions.

Then: What evidence is there to weigh against the conclusion that there is an edge to the Universe (and therefore a unique center)?

It is certainly compatible with the observed expansion, no? To use a rubber sheet example: Imagine the Universe is a standard 2D sheet of computer paper, but made of rubber. Stick coins to it to represent galaxies. Then stretch it apart to represent the expansion--fast at first, but slowing asymptotically to zero. Then we have (1) all galaxies receding from each other, (2) a unique center, but not one that would be easily (or perhaps even possibly) evident to the galaxies' inhabitants.

Thanks in advance.

 

[Contrapositive]

The answer, I am told, is 'No'. But I do not understand why.

Says who? Links would be nice.

(1) The Universe is spatially flat. It will one day stop expanding.

Why does the universe need to stop expanding to have an edge?

(2) There is no weird dark energy.

Again, I'm don't see what this has to do with the universe having an edge.

Then: What evidence is there to weigh against the conclusion that there is an edge to the Universe (and therefore a unique center)?

Well, no one has ever seen an the edge of the universe for starters. I can't think of any evidence to contradict the notion that the universe has an edge, but why would you want to think it has an edge? Because objects humans experience in daily life have edges?

It is certainly compatible with the observed expansion, no? To use a rubber sheet example: Imagine the Universe is a standard 2D sheet of computer paper, but made of rubber. Stick coins to it to represent galaxies. Then stretch it apart to represent the expansion--fast at first, but slowing asymptotically to zero. Then we have (1) all galaxies receding from each other, (2) a unique center, but not one that would be easily (or perhaps even possibly) evident to the galaxies' inhabitants.

I suppose it is compatible, if you think of it that simply. But I don't see how it is useful to think of the universe as having an edge. I mean, what would happen if I crossed this edge? Would I stop existing? Can you even reach it? If you can't reach it, then what does it matter, no one could ever study it.

 

[Sionnagh]

The answer, I am told, is 'No'. But I do not understand why.

Something to do with space-time being approximately flat if visualised as a two-dimensional model but space being curved. Euclidean geometry applies on a cosmological scale - parallel lines never meet etc.

(1) The Universe is spatially flat. It will one day stop expanding.

Recent data seems to suggest the rate of expansion is increasing, and has been for about the last 6 billion years. http://science.hq.nasa.gov/universe/science/expanding.html

(2) There is no weird dark energy.

Why?

Galaxies have been observed to rotate at a more or less constant rate. The laws of conservation (angular momentum etc) should apply and so stars farther from the centre should rotate slower than stars closer to the centre but it appears they don't. Rather, galaxies would appear to rotate as if they were solid discs, but there is not enough matter to permit that. The current accepted hypothesis is that dark matter which we can't see provides the mass to explain this phenomenon.

Then, since gravity is always attractive and due to the mass of the universe, it should still be expected that the expansion of the universe ought to be slowing. But it isn't.

Then: What evidence is there to weigh against the conclusion that there is an edge to the Universe (and therefore a unique center)?

If we regard the universe as having an edge, then it follows that there is an outside. What is outside? Nobody knows.

The limitation is that we are used to operating in 3 dimensions where everything has boundaries. When we look to extremely distant galaxies etc, at distances in the order of 10 billion light-years, we're seeing photons from stars which began traveling towards us 10 billion years ago, so what we're seeing is the universe as it was 10 billion years ago - looking into the past.

What if we're looking at it all wrong? If the result depends on the observer then perhaps how we're looking at it defines everything. The only constant in science is that understanding changes with discovery.

;)
Mick

 

[Chronos]

We are already at the temporal edge of the universe, so what is your point?

 

[adilghanty]

universe

As far as i am concerned there is no physical end to the universe, but you must remember that the universe is mostly "nothing" and only partly "matter." If we were to choose a point as the centre, then find the furthest out piece of matter, be it a star or galaxy or simply piece of rock, this would be the edge, or end of the universe, as beyond this point there would be nothing, just empty space. This would be the end of the universe. The universe is expanding, so this furthest out piece of matter would keep moving away from us, as would the end of the universe. However, we are unable to find the furthest piece of matter as our technology is limited, so we therefore are unable to find the edge of the universe

 

[Tomtom]

Now, I'm not at all an advanced physicist, but I have always considered the idea of "an expanding universe", as the physical matter in the universe moving outwards (from a centre), not that the "edge of the universe" is being constantly pushed. My impression is that there is an unlimited amount of "nothingness" out there, and that you could fly in a spaceship beyond the "edge of the universe". You would not find anything though.

If that is true, then it doesn't matter that the "universe" (physical sense) will stop expanding. The rest of the "nothingness" is still "there", and hasn't moved at all. Only the bits of matter are moving away from each other. Who said that the universe is only as far as the planets go?

 

[pero]

What do you mean by the Universe.? For me it means everything together. This implies that there can be no space outside the edge. If there is an edge, what is its nature. If something arrives at the edge, what will happen to it? I can think of two possibilities, it ceases to exist, or it bounces of the edge back into the universe.

However, all this becomes complicated to reconsile with the present understanding of gravition as curvature of space-time. The only flat space-time is one without any masses.

 

[Tomtom]

Pero, wouldn't your first paragraph imply that "the edge" is ceasing to exist all the time, so the universe is moving inwards?
In any case, the fact that you consider "everything together" as the universe, does not imply that the universe has an edge. Rephrase please.

 

[nalA]

I have always considered the idea of "an expanding universe", as the physical matter in the universe moving outwards (from a centre), not that the "edge of the universe" is being constantly pushed. My impression is that there is an unlimited amount of "nothingness" out there, and that you could fly in a spaceship beyond the "edge of the universe". You would not find anything though.

If we were to choose a point as the centre, then find the furthest out piece of matter, be it a star or galaxy or simply piece of rock, this would be the edge, or end of the universe, as beyond this point there would be nothing, just empty space. This would be the end of the universe.

Isn't the size of the universe commonly regarded to be defined by the volume of space (nothingness) it has, not by where the matter is in it?

The concept of an 'edge' of space sounds like a paradoxical idea to me - if you have an 'edge' then there has to be something (more space) on the another side of it, so you can't have an 'edge' of space ...

I would have thought that if you assume the universe is spatially flat then to avoid the paradox of an 'edge' you would also have to assume that the volume of the universe is infinite (and there would also be no centre). There would be nothing to stop it being a stretchable universe of course.

If you assume the universe has a finite amount of space in it, the only way I can see of avoiding the paradoxical idea of an edge is to say that this finite volume of 3 dimensional space is curved around on it's self through some higher dimension to form some enclosed higher dimensional shape like a hyper-doughnut or hyper-sphere (and again there would be no centre on the 3 dimensional 'hyper-surface' (volume) of a hyper-sphere or hyper-doughnut).

So in my view it causes a paradox to assume the universe is spatially flat and has a finite volume of space in it (because it would need a paradoxical 'edge') ...

 

[adilghanty]

Tomtom my physics knowledge isn't brilliant either; I'm a 16 y.o. taking my GCSEs. I agree with you in that the universe is everything, and that there should not be an egde, as you can keep going way beyond any theoretical edge or boundary. But there is little need to go beyond the furthest point as it would simply be nothing. However, it is true to say that you would still exist and wouldn't explode or bounce back if you crossed this theoretical edge. The universe is expanding, yes, but there may possibly only be a theoretical boundary and not an actual or physical boundary, so it would not be affected by the expansion as it does not exist.

 

[russ_watters]

Now, I'm not at all an advanced physicist, but I have always considered the idea of "an expanding universe", as the physical matter in the universe moving outwards (from a centre), not that the "edge of the universe" is being constantly pushed. My impression is that there is an unlimited amount of "nothingness" out there, and that you could fly in a spaceship beyond the "edge of the universe". You would not find anything though.

If that is true, then it doesn't matter that the "universe" (physical sense) will stop expanding. The rest of the "nothingness" is still "there", and hasn't moved at all. Only the bits of matter are moving away from each other. Who said that the universe is only as far as the planets go?

That isn't how the theory currently works. There is no 'nothingness' outside of the universe - it isn't expanding into anything. And there is no center, just like there is no central point on the surface of an expanding balloon.

What you are describing is similar to what the OP is describing.

 

[pyrojelli]

I believe it is possible to have an endless universe and for it yet to have an edge. Think of the universe as a massive sphere, but its walls aren't true walls, but jump points. One point on the spherical wall can be connected directly to its twin jumpoint that is exactly opposite it on the other side of the universe, and so on for every other point on the wall. So if a spaceship (or comet, or light) would indeed reach the edge, they would never know because they would see more space in front of them which is really just the entrance to the other end of the universe. With that in mind, then light from stars, as we predict it to be billions of light years old, may very well be pretty young and very nearby, it may just be an illusion caused by going in and out of the jump points, traveling in a straight line, and yet going over the same space over and over, and eventually the light met with us. It could have "aged" because of some phenomenom of crossing from one edge of the time-space plane to the other. With a mirrored jump-point universe of this kind, we can have infinite linear mobility, just with repetition of areas traveled (a pseudo-multi-verse) and we can also have an expanding universe. This idea of a pseudo-multiverse may be able to explain why certain quantum theories, such as M theory, call for more than one universe (it may be just one universe that mirrors itself onto itself!) The universe may be expanding due to the theory that the jump-points are constantly trying to fall into each other (fall into the other side) and are thereby stretching the very fabric of the universe.

See, we can have both theories without contradiction! I have not ran over this theory of mine yet anywhere else, I would like to call it the jump-point mirrored universe theory. According to this theory, the universe could be smaller and younger than we could ever imagine. It is just that our perception is a little off...its the mirrors, LOL.

 

[pyrojelli]

With that in mind, then light from stars, as we predict it to be billions of light years old, may very well be pretty young and very nearby, it may just be an illusion caused by going in and out of the jump points, traveling in a straight line, and yet going over the same space over and over, and eventually the light met with us. It could have "aged" because of some phenomenom of crossing from one edge of the time-space plane to the other. With a mirrored jump-point universe of this kind, we can have infinite linear mobility, just with repetition of areas traveled (a pseudo-multi-verse) and we can also have an expanding universe. QUOTE]


A seemingly distant star could be a very near star whose light is coming through a jumpoint(s)!

 

[KingOrdo]

Thanks for the input, but these responses aren't quite addressing what I'm getting at.

(1) I'm talking about a standard FRW model in which Omega=1. To answer Contrapositive's question, it's vital that the Universe be flat because if, say, the geometry were S^3, then there's obviously no edge. It's also vital that there's no dark energy because if dark energy exists, then even in E^3 the Universe will keep expanding.

(2) To answer Sionnagh: My (1) and (2) are assumptions. I know some people claim that the Universe is open. And they might be right. But my (1) and (2) are plausible--note: not true--assumptions to make.

And it is perfectly reasonably to talk about finite geometries. Think of an ant on a (idealized 2D piece) of computer paper, floating in air. The ant may one day reach the boundary of his world. He can no longer go in one direction.

There seems to be a lot of quasi-religious sentiment against an edge, but where is the evidence?

Thanks again.

 

[marcus]

I like the first part of your post. And agree with part of it.

Thanks for the input, but these responses aren't quite addressing what I'm getting at.

(1) I'm talking about a standard FRW model in which Omega=1. To answer Contrapositive's question, it's vital that the Universe be flat because if, say, the geometry were S^3, then there's obviously no edge. It's also vital that there's no dark energy because if dark energy exists, then even in E^3 the Universe will keep expanding.

(2) To answer Sionnagh: My (1) and (2) are assumptions. I know some people claim that the Universe is open. And they might be right. But my (1) and (2) are plausible--note: not true--assumptions to make.

And it is perfect reasonably to talk about finite geometries. Think of an ant on a (idealized 2D piece) of computer paper, floating in air. The ant may one day reach the boundary of his world. He can no longer go in one direction.

I like that you point out that if the universe is spatially S^3, then there is no edge (and of course it could be expanding as the data seems to indicate.)

I think you may be mistaken about one or two details. I first studied my cosmology before there was any talk of "dark energy" and one assumed the cosm. const. Lambda was zero, just like you want to assume. What we learned was that the spatial flat case kept on expanding forever.

But you say because if dark energy exists, then even in E^3 the Universe will keep expanding. It sounds like by E^3 you mean the flat (i.e. euclidean) case, which is fine, but you think it NEEDS dark energy in order to expand forever. Conventional wisdom is that it doesn't need. With your assumptions (1) and (2), flat and zero DE, it is already going to expand forever. But that is only a mistake in detail. I don't think it matters to your main message. Maybe it does so if it is important please explain how.

There seems to be a lot of quasi-religious sentiment against an edge, but where is the evidence?

Here I disagree strongly. You've got a basically reasonable approach but I think you have the shoe on the wrong foot. The key thing is Occam's razor. We don't need an edge to make model fit data, so an edge would be an unnecessary detail. Occam says don't complicate your model with unnecessary detail. So the burden of proof is on the people who want an edge in the picture. THEY have to supply evidence.

To use myself as an example, I don't assume an edge. There is no evidence for one. The moment that data appears which favors some kind of boundary to space (I can't imagine what such data would be like but supposing) I will be instantly willing to entertain the notion. My preferences are in no way fanatical or "quasi-religious".

So based on my own experience, I reject the idea that there is some kind of ideological or quasirelgious sentiment against spatial topology with boundary. AFAIK that simply is not true. I think what we do see is understandable skepticism of people saying "show me. show me evidence of boundary in the observational data". And in the absence of such evidence, they will not wish to add that unnecessary complication to the picture.

 

[Garth]

There seems to be a lot of quasi-religious sentiment against an edge, but where is the evidence?

Only that we observe an sky that more of less looks the same in all directions. If we were near enough an edge to observe it then we would observe a gross anisotropy, the galaxies would go on forever in one direction and they would come to an abrupt end in the other.

If the edge is further away than our particle horizon then we would not observe it, although the sky in that direction might show evidence of something 'different ' beyond the horizon, a change in temperature of the CMB for example.

The "quasi-religious sentiment" is actually a fundamental principle used in theoretical cosmology, that of the homogeneity and isotropy of the universe on the largest scales. It might be sheer pragmatism, as a way of solving the Einstein GR field equation in the cosmological case, but it seems to work as far (in the spatial sense) as we know.

BTW - a very warm welcome to all the 'PF newbies': Contrapositive, Sionnagh, kinshuk, adilghanty, Tomtom and nalA who have responded in this thread.

Garth

 

[joshman]

I would say that empty space has no limitations, and if the universe is being defined
as "all matter" then yes the edge of the universe would be the furthest piece of that matter from a given center.

However if space travel was advanced enough to reach that furthest piece of matter, then the spacecraft venturing past that piece would always be "at" the edge of the universe only by definition. I cannot imagine any type of barrier that could exist as an edge, only as what we define as the edge of the universe. But the idea that many people i believe are confused on is if empty space has a limitation or edge, in which I would believe does not.

On a somewhat related topic, I believe that there would be a good possiblility that the entire universe as we know it, being that it is now likely expanding and will one day stop, could be one of several "universes" out there in the same fashion of multiple galaxies. I don't believe in a billion more years of human civilization that we will ever find the last and final piece of matter that is out there, but we will continue to find more, and when we think we have found it all, we will find some more.

I really like the final scene in men in black where our entire galaxy or universe is just a marble in someone elses game of marbles.

 

[KingOrdo]

I think you may be mistaken about one or two details. I first studied my cosmology before there was any talk of "dark energy" and one assumed the cosm. const. Lambda was zero, just like you want to assume. What we learned was that the spatial flat case kept on expanding forever.

But you say because if dark energy exists, then even in E^3 the Universe will keep expanding. It sounds like by E^3 you mean the flat (i.e. euclidean) case, which is fine, but you think it NEEDS dark energy in order to expand forever. Conventional wisdom is that it doesn't need. With your assumptions (1) and (2), flat and zero DE, it is already going to expand forever. But that is only a mistake in detail. I don't think it matters to your main message. Maybe it does so if it is important please explain how.

Okey, I may be confused at this point. Assume Lambda=0. My understanding is: if Omega>1, then the Universe is S^3, and there is sufficient matter to overcome the expansion, and the Universe will eventually collapse. If Omega<1, then the Universe is H^3, and will expand forever.

Now, what I'm interested in: If Omega=1, then there's just enough matter to halt the expansion of the Universe, but not enough such that it will collapse. The expansion will slow and slow, asymptotically to zero. Is this right?

And in that case, even if there's not a hard-and-fast 'wall-like' edge (like in the case of ants marching on a 2D piece of paper), wouldn't there necessarily be a pseudo-edge where matter ends?

Also, if the Universe is infinite and expanding everywhere, how could any finite amount of matter halt the expansion? If Omega=1, doesn't that mean that the amount of matter in the Universe is finite (and therefore, the Universe is, too)?

Only that we observe an sky that more of less looks the same in all directions. If we were near enough an edge to observe it then we would observe a gross anisotropy, the galaxies would go on forever in one direction and they would come to an abrupt end in the other.

Right. Of course isotropy we take as a presumption (perhaps a very reasonable one); but it's not as if there is empirical evidence in favor of it. But under the model I've been discussing, it wouldn't be surprising that we find ourselves on a planet where the Universe appears boundless: If there were an edge, only a very tiny minority of planets/star systems/galaxies would abut it.

 

[marcus]

If Omega=1, then there's just enough matter to halt the expansion of the Universe, but not enough such that it will collapse. The expansion will slow and slow, asymptotically to zero. Is this right?
.

That is basically RIGHT, but the previous words aren't. Expansion does not HALT. Expansion continues forever without bound, just slower and slower. So arbitrarily large expansion is attained if you wait long enough.
In this case (Lambda = 0, and Omega = 1) if you pick some expansion target, no matter how large, like a thousand
YOU WILL EVENTUALLY REACH THAT TARGET. That is an interval between two galaxies that is today a Gpc will eventually reach 1000 Gpc. Or pick another target, like a million. distances will eventually reach a million-fold.

So saying "expansion will halt" gives the wrong idea. It doesn't halt, but it does get slower and slower, in this case.

And in that case, even if there's not a hard-and-fast 'wall-like' edge (like in the case of ants marching on a 2D piece of paper), wouldn't there necessarily be a pseudo-edge where matter ends?

As I just said, in the case you are talking about, based on your assumptions, there is no such limit on expansion. But you are confusing expansion FACTORS with an imagined length or diameter. In the typical flat (Omega = 1) case the universe STARTS OUT INFINITE DIAMETER. It always was and always will be of infinite spatial extent.

You have to be able to picture an infinite flat piece of paper and visualize it expanding 1000-fold. The overall size doesn't get any bigger because it was already infinite to start with. What gets bigger by a factor of 1000 is the distance between two points you pick.

Anyway, in the case you are looking at there is no wall and there is no pseudo edge or any limit on expansion.

Also, if the Universe is infinite and expanding everywhere, how could any finite amount of matter halt the expansion? If Omega=1, doesn't that mean that the amount of matter in the Universe is finite (and therefore, the Universe is, too)?

Good thinking. It COULDNT. But in your flat case the amount of matter is not finite. Infinite volume of space and roughly evenly distributed matter, roughly constant density throughout, means infinite amount of matter.

If you like finite volume and finite amount of matter, try thinking about the S^3 case.

You ask "If Omega=1, doesn't that mean that the amount of matter in the Universe is finite ?" No it doesn't mean that. However Omega > 1 means finite spatial volume and amount of matter. It's a more intuitive case to study for that very reason IMO.
First understand the Omega >1 case of spatial S^3 and then you can visualize the flat case, if you like, as a kind of limit taking larger and larger spheres.

 

[Bumbleflea]

I known't we'r there be an edge or not, yet this conversation keenly outlines the concept of infinity.

 

[FX89]

A seemingly distant star could be a very near star whose light is coming through a jumpoint(s)!

Now that would be a big disappointment for space exploration, wouldn't it?


But if that is the case, i see an interesting scenario:

Presumptions:
1) the universe (at least the matter in it) is expanding at an increasing rate
2) the universe is a folded plane in which we go one way and we come out the other way

Conclusion: Light from cosmic bodies is mentained in the same finite space and as it travels in and out of the jump points it fills up this finite space. As a result, after the universe comes apart, instead of darkness, we'll have absolute light and the acomplishment of creation :P

 

[chinoquezada]

Hello. I'm CQ, I'm a physics geek, and I'm new here.

To add to this debate, i have the following:

We could argue that the edge of the universe is given by the Geometry of spacetime (a la General Relativity).

We could also add that since matter shapes SPACETIME, it could be that matter is a manifestation of a change in geometry of SPACETIME.

Now the thing is that matter only "curves" E^3 space in a way that could only be graphically fathomable in E^4. We feel the effects of curvature in E^3 but we can only represent them as Tensors of Geometry (like not knowing how a linear function looks but only knowing its slope)

How would an EDGE in spacetime affect, well... spacetime?

We know curvature propagates an "apparent" force of gravity at the speed light in SPACETIME, but what would an Edge do?
After asking this question, we could think the following:

If the only effect that we have detected (however limited our detecting equipment is) in the geometry of spacetime has been "curvature" in the form of the "apparent" force of gravity, it could follow that there is no edge, since no other disturbances in spacetime have appeared.

If an edge exists, we would be constantly bombarded with its "edge waves" (similar to gravitational waves"), and this effect should come from every direction in the sky.Now the problem here is that gravitational waves are such small disturbances that they are almost impossible to detect apart from theoretical discussions, and the same could happen with "edge waves".

So there may well be an edge, or not, and we would be unable to detect it.Please feel free to criticize everything and anything written here.
I'm sure my theoretical knowledge of physics is at its infancy yet, and that I may have committed a few mistakes here.

CQ

 

[Tomtom]

I like the way you are thinking, chinoquezada. Could I partly summarize that: If the universe has a "edge", which upon collision, sends an object to the other side of the universe; Why haven't we been measuring some huge "edge wave"?

Any way: Isn't this a bit on the side of wishful thinking? What evidence, if any at all, suggests that this is possible? I've felt (especially after that Men In Black comment), that many here are wishing for a "cool explanation".

But then again, if most here are students (myself being an 18 year old IB Physics HL), it really doesn't matter. As long as the ideas keep coming, we will get somewhere in the end.

 

[Flatland]

Your question makes absolutely no sense whatsoever. Please rephrase and ask again.

 

[KingOrdo]

Your question makes absolutely no sense whatsoever. Please rephrase and ask again.

Whom are you addressing? It is, I trust, not me.

 

[Dozent100]

The answer, I am told, is 'No'. But I do not understand why. Assume:

(1) The Universe is spatially flat. It will one day stop expanding.

(2) There is no weird dark energy.

These are, I think, plausible assumptions.

Then: What evidence is there to weigh against the conclusion that there is an edge to the Universe (and therefore a unique center)?

It is certainly compatible with the observed expansion, no? To use a rubber sheet example: Imagine the Universe is a standard 2D sheet of computer paper, but made of rubber. Stick coins to it to represent galaxies. Then stretch it apart to represent the expansion--fast at first, but slowing asymptotically to zero. Then we have (1) all galaxies receding from each other, (2) a unique center, but not one that would be easily (or perhaps even possibly) evident to the galaxies' inhabitants.

Thanks in advance.

I believe that several of your assumptions are wrong.
1) The universe is not believed to be flat, It expands in all Directions.
2) There is not only weird Dark Matter, probably 98% of the universe is Dark Matter.
3) Relativity is a huge factor in Calculations dealing with the Universe.
4) There is a tremendous amount that we just do not know about the Universe and what makes it tick.
5) The question of an Edge of the Universe, is basically of no import. The current thinking is that there may be an infinity of Universes. Or there may just be One. If many, they will likely overlap in ways that are impossible to detect. If only one, then again what constitutes an edge becomes very hard to define. So both give rise to the same answer. No, there is no edge, because we can't find one.

 

[gutti]

I don't know a lot about physics but the way I see it is that the centre of the universe is the point where it started expanding from and that if positioned at points across the universe and measuring the direction of expansion then theoretically we could find the centre of the universe and I think that space as a vacuum is infinite but the matter in it is expanding and increasing so the edge would be the edge of matter but space would go on forever but I think there is no point in trying to go past the edge because after that it is just a vacuum and there is nothing to see and noothing new to learn.

 

[Dozent100]

But with The Relativistic factors involved, It could be that Heisenburg comes into play. You can see it, but you can't locate it. Or if you can locate it, you can't see it. If your observers view point is the Universal plane, then the galaxies and solar systems can take on quantum attributes.

I kind of feel you guys are trying to count the number of angels dancing on the head of a pin! Not to dash water on the conversation, but I think you are chasing your tails here.
Sorry

 

[tkat]

dark energy, gravity and the rings of Saturn

I am thinking about the nature of gravity and I wonder about the concept of 'zero point energy'. Some inventors claim it is the source of free energy that runs their devices, both
magnetic and vortex turbines. I wait to be convinced but I try to have an open mind about all this. I have read some theories that relate this ZPE to the behavior of mass; that is Newtons laws, etc. It is also claimed that gravity originates from ZPE. I admit that I have read little information on this; but, what if? Could this dark matter be related to ZPE? Ialso saw some comments about the plane of rotation of galaxies, solar system, et al. This is where I get to Saturn.

I have wondered why the rings of Saturn remain so defined over centuries of observation. Now that we know that the 4 large planets all have rings, I see a clue
about the nature of gravity. Saturn has the largest rings and also has a sizeable core.
Jupiter is largely gas and appears to have no core. It has small rings. Uranus and Neptune
have cores but rotate much slower. All the ring planes are in the same plane as the respective planet's rotation. The Saturn rings clearly are composed of many different size particlessmall to big; all of which experience random collissions. So I ask myself why those rings haven't diffused into a 'fog' of dust and particles surrounding Saturn. Why do the rings maintain their integrety? The only theory I can raise is that the high rotation speed and large solid core create a reduction in the pull of gravity in the common plane of rotation of planet and rings. I theorize that a particle randomly ejected from the ring by a hit experiences a greater gravitational pull and 'arcs' back toward the planet curling back into the ring. That could be a conservation od angular momentum. My guess is that
the spin of the planet creates a distortion of the grav field by reducing it in the vicinity of the spin plane. The comment about galaxies having a flat plane and a 'flat' universe
also make sense to me using this far out theory. If anybody has anything to offer about ZPE, I would love to hear it. Tom

 

[ganstaman]

I don't know a lot about physics but the way I see it is that the centre of the universe is the point where it started expanding from and that if positioned at points across the universe and measuring the direction of expansion then theoretically we could find the centre of the universe and I think that space as a vacuum is infinite but the matter in it is expanding and increasing so the edge would be the edge of matter but space would go on forever but I think there is no point in trying to go past the edge because after that it is just a vacuum and there is nothing to see and noothing new to learn.

Not that this has anything really to do with your point or you, but that is a very long sentence. I imagined you speaking it in just one breath, so as you got closer to the end you started speaking faster and your voice got higher pitched. It was entertaining.

Now, to your actual point, there is no center of the universe. Everything is not moving away from a single point. Everything is moving away from everything else. Simplest over-used analogy: tape some pennies to a balloon and blow the balloon up. Now think of things just from the surface of the balloon (we're picturing a 2-D universe): the pennies are all moving away from each other, the surface of the balloon ("universe") is expanding, and yet no point on the balloon surface is the center or center of expansion.

 

[pyrojelli]

You forget that the matter out there (planets, black holes, gas clouds) absorb a great amount of light, and as light goes through more and more jump points, the probability of that photon being absorbed increases. So no, the universe would not fill up with light. Not only is light going through jump points but there are objects on the other side waiting to absorb it. And what exactly do you mean by "when the universe comes apart" ?

 

[pyrojelli]

Ah, gangstaman, but can you tell what is happening: is the universe expanding or are we shrinking? To answer that we would have to either find a particle that never shrinks or an area of the universe that is never expanding--happy hunting! And why does the universe have to be expanding, why can't it be that the dark matter in universe is slowly "aging" and that it is visually skewing galactic distancing in every direction. And back to my jump point mirrored universe theory. If indeed there were jump points but the universe were NOT expanding, the distances can still be expanding! Take for an analogy our planet earth: The continents at one time were one super-continent, they seperated, and if given enough time, they may rejoin on the "other side". An easier way to view the universe without jumpoints is to view it as a sphere of space-time. If you travel long enough in one direction, you will end up the same place where you started, just like "around the world in 80 days". This Globular universe is the inverse of my jump point theory. In a Globular Universe, space-time would be wrapped around a hollow sphere. Come to think of it, it is just another way of saying what I have been saying with the jump point theory: I am looking at a ball right now and imagining that I took a marker to it and drew a line about its circumference (in effect making a circle). If I start at the line and travel perpendicular to it, I will end up at that same point on the line as I rotate the ball. That is a single point on a Globular universe, but if I would slice the ball along the line, leaving a little marker on both ends of this new "plane", then the point is a twin jump point on a mirrored universe. The Globular universe is functioning on top of a sphere with single points its surface. The mirrored universe is functioning inside of a sphere with cojoined twin points universally opposite each other dotting its outer-edge. Sphere is used loosely obviously, since it need not be perfectly smooth.

 

[pyrojelli]

Just in the mood of extrapolation here: what if we combined both the theories of a Globular universe with a Jump-point universe? The surface of the Sphere would be our three dimensional plane, and the inside would be all the other dimensions called for in the new quantum theories out there. This theory would allow jump-points to appear everywhere just beneath the surface of our three dimensions. This might explain quantum tunneling, and particles cojoined over massive distances (could be the same particle with one foot in the door and one foot outside), and the like. Think about it, quantum jump points...

 

[arzie2000]

Based on my own opinion, (point of view, intuition): I think the universe has no edge, if you start at one point moving in a single direction, you will end up on the point you started. Same thing goes, when two or more objects travel on different directions (regardless of angle) and assuming the same velocity, they will end up meeting each other. I have no scientific explanations for this, but that's what i feel it is.

 

[Chronos]

OK, let's try a different approach. Supposition: We already live at the temporal edge of the universe. Refutation: Does it look 'older' in one direction compared to another? Cite any papers you have in mind supporting this perspective.

 

[FX89]

And what exactly do you mean by "when the universe comes apart" ?

I've heared in many places that according to the expansion theory all matter has a tendency to move away from other matter. They extrapolated that sooner or later, even atoms will disintegrate. This is known as the big rip.

Check out this article: http://en.wikipedia.org/wiki/Big_Rip

 

[docbill]

You guys are forgetting, the edge of the universe, does not need to be the edge of space, it could just be an edge to interesting space. Perhaps, there is only a finite region of space were matter can form... Maybe the initial "egg" of matter that formed the universe was of finite size. It could be that the mass distribution in the universe is not constant, but indeed there is an edge. Beyond that, there is no matter. Of course, because matter would continue to expand out at the speed of light, we could never physically reach that edge. However, eventually we would be able to see it.

Of course, I am not saying this is the case. But given our current level of understanding, we could neither prove or disprove this conjecture at this point in time.

 

[docbill]

Another thing to consider is in our current models, the universe is finite.

Consider, when we look out into space, we can only see a finite amount. Eventually, if we look far enough, we see the very beginning of the universe. This is known as the observable universe, which consists of a finite number of particles, with a finite number of possible states. Now, consider every point in the real universe is the center of a finite universe. Since every observable universe has a finite size, and there are only a finite number of possible states for a finite system, there are a finite number of unique observable universes.

A basic premise of physics is when two objects are indistinguishable, they are the same object. Ergo, there are only a finite number of observable universes. Since the universe is the sum of all observable universes, the universe is finite. If you could travel far enough you would end-up back where you started... But then since you are the center of your observable universe, you would also find you had never left where you started from.

Of course, this argument is assuming the number of possible states is finite...

 

[Valjean]

The edge of what?

It seems to me that...Isn't considering the edge of the universe, not just that occupied by matter but the entire home for everything occupied or not, about the same as considering the end of time, the edge of it, or even the beginning of it? As far as everything being the center of the universe...everything moves. If one thing is considered the center, at rest, then everything else is moving as one unit in relation to it. That would require the entire universe to move as a unit but since the entire universe takes up the entire space there is no way it can move. There's no room for it to move.

 

[SpaceTiger]

I have no scientific explanations for this, but that's what i feel it is.

Let's keep in mind that this is a science subforum and that idle speculation and philosophizing should be kept to a minimum. These discussions sometimes have a tendency to get philosophical, but cosmology is still a scientific discipline that is not conducted by feelings, opinions, or popular vote.

The discussion so far is mostly reasonable, but this reminder should be noted by everyone contributing.

 

[pyrojelli]

I second the motion

 

[CERDES]

Is it not possible to postulate that there is an endless "area" in which the known universe (ours) as well as many other separate universal constructs exist, endlessly, multiplicatively?
This would imply an infinity worth of separate spatial sectors (universes) each with the same or perhaps totally dissimilar sets of physical laws. Making up an Omniverse based on the aggregate of all said systems. Wondering.
CERDES

The answer, I am told, is 'No'. But I do not understand why. Assume:

(1) The Universe is spatially flat. It will one day stop expanding.

(2) There is no weird dark energy.

These are, I think, plausible assumptions.

Then: What evidence is there to weigh against the conclusion that there is an edge to the Universe (and therefore a unique center)?

It is certainly compatible with the observed expansion, no? To use a rubber sheet example: Imagine the Universe is a standard 2D sheet of computer paper, but made of rubber. Stick coins to it to represent galaxies. Then stretch it apart to represent the expansion--fast at first, but slowing asymptotically to zero. Then we have (1) all galaxies receding from each other, (2) a unique center, but not one that would be easily (or perhaps even possibly) evident to the galaxies' inhabitants.

Thanks in advance.

 

[Valjean]

could there be an edge to the universe

Space Tiger...Keep in mind, also, that many advances in cosmology and other scientific areas, especially those considered breakthrough, were originally little more than gut feelings that let to an opinion that led to submitting for consideration and eventual acceptance. Even Einstein's views were initially disregarded until he proved right on a couple things, like light waves bending around a large mass, and then popular vote led his views to prominence and accceptance.

 

[SpaceTiger]

Space Tiger...Keep in mind, also, that many advances in cosmology and other scientific areas, especially those considered breakthrough, were originally little more than gut feelings that let to an opinion that led to submitting for consideration and eventual acceptance. Even Einstein's views were initially disregarded until he proved right on a couple things, like light waves bending around a large mass, and then popular vote led his views to prominence and accceptance.

This is not a place to be presenting personal theories. Even if it were, I still would not accept a "gut feeling" alone as justification for an argument. Einstein's ideas were a response to specific experiments that couldn't be explained in the classical framework and were presented quite rigorously. He didn't just go up to his colleagues and say, "I have a feeling that Mercury's orbit is responding to the curvature of spacetime". If an idea starts as a gut feeling, then you must hash it out logically before you can meaningfully converse with other people.

I am a scientist by trade, so I know how the process works. Discussion here is much more pedagogical, but the basic mode of discourse is the same. If what you have to say is supported by scientific research and/or general knowledge, then say it and present your support. If not, then you can either ask about it or keep it to yourself.

 

[Dr_Zinj]

There is an 'edge'

Given: This universe came into existence with the big bang.
Given: This universe expanded from a point source (actually this is a couple of givens; one, that the universe came from a point source, and two, that the universe expanded).
Given: That this universe only exists where matter and energy from the big bang exist.

Therefore: The point source could be considered the "center" of the universe.
Therefore: The edge of the universe can be considered to be the wave front of light, or matter, expanding from the big bang.

The mapping of galaxies and galactic clusters, along with their movements, is done in part, for the goal of establishing where the center of the universe is, and for finding where the 'edge' is.

Of course the universe may be expanding from all space within it as virtual particle pairs come into existence and then fail to annihilate each other.

 

[rogerperkins]

How can there be an edge if it is 4 deminisional (at least), the universe is expanding 4 deminsionally, if time is the 4th deminision then we must already be on the edge. i.e. Since the universe was smaller in the past and will be larger in the future, that means that currently we must be on the edge.

 

[Dr_Zinj]

Part of the problem is an imprecise definition of what an "edge" is. Edges are traditionally the termination of a two dimensional surface; a discontinuity between something and something (or nothing) else. The edges of a piece of paper are generally the top, bottom and sides of a paper as you view it from a point normal to the largest surface area; if you treat the paper as a two-dimensional object only. But the edge could also be the front or the back of the paper as viewed from the side, being an extreme case of viewing it three-dimensionally. This would be the same as saying the edge of the top of a box; the top being treated as a two-dimensional surface.

If we were to set it up as a calculus, as the number of sides of a fixed volume container approaches infinity, the length of the edges of each surface approach zero. So for a perfect sphere, the surface would have no edge. The edge only comes back into being as a concept if we take a 2-dimensional plane through the sphere, in which case the edge is the circle that represents the intersection of the plane with the sphere. Assuming the universe is a sphere of some sort (not necessarily true, but let's work with it); any plane through it would intersect the outer surface and the circle representing that intersection can then be referred to as an edge. If the intersection of any plane with the surface of a sphere generates an edge two-dimensionally, then we could be safe in saying that the surface of any sphere represents the edge of that sphere.

Somehow this almost sounds like a quantum theory definition. When the edges of all the sides disappear, the whole surface becomes the edge.

 

[SpaceTiger]

Given: This universe expanded from a point source

The universe did not expand from a point in three-dimensional space; rather, space itself expanded. As such, when we go back to t=0, the physical size of the universe (space included) approaches zero, but matter and energy fill space just as completely as at earlier times. The universe need not have an edge.

 

[Contrapositive]

I have a quick question: does an edgeless universe necessarily imply that the universe loops back on itself, for lack of a better word. For example, if the universe wasn't expanding and I moved forward, would I eventually circle back around to were I started? Like circumnavigating the Earth.

 

[KingOrdo]

There's been a lot of very interesting commentary on this thread, and I thank everyone for that. However, my fundamental question has not been addressed; let me put it another way that might be clearer:

Assuming Omega=1 and the Universe is spatially R^3--therefore one day reaching a maximum volume (or asymptotically approaching a maximum volume), what empirical evidence is there that the Universe is not bounded?

I certainly understand that this scenario (R^3) is compatible with an infinite universe--but it also seems compatible with a universe that has a boundary. Imagine, again, a sheet of rubber, with pennies stuck to it representing (e.g) galaxies: You stretch the paper out, fast at first, but slowing asymptotically to some maximum area. Little spaceships leaving the galaxies and going in one direction would, eventually, run into a 'brick wall' which they could not penetrate.

As far as I know, all our observations are totally compatible with this picture: But am I wrong about this? That's really what I want to know.

I understand that the assumption of isotropy means that there is no boundary. But isotropy is not empirical evidence--it is an assumption.