Is the Universe Truly Infinite and Ever-Expanding?

AI Thread Summary
The discussion centers on the nature of the universe, debating whether it is finite or infinite. Participants argue that the universe is expanding at an accelerating rate, suggesting it has a finite size but is unbounded, allowing for infinite travel in one direction. The concept of a "bifurcation point" is introduced to explain the transition from pre-existence to our current universe, while others propose models like a three-dimensional torus to illustrate a finite yet unbounded universe. The conversation acknowledges the philosophical implications of what lies outside the universe, emphasizing that definitive answers remain elusive. Ultimately, the debate reflects ongoing uncertainty in cosmology regarding the universe's structure and boundaries.
  • #51
ok I think I understand know. Thanks. mmm ...I understand that you guys are all crackpots! hehehe xDD (joke) :wink:

But seriously, ok so you are modelling the universe from the time of the Big Bang (more of which, if not all of which, was causally connected before inflation than is the case now); and this model universe atleast contains our observable universe. Fair enuff, still I reckon you are asking questions that you will never be able to answer... =)
 
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  • #52
Danger said:
Oops! :redface:
I was reading the linked tutorials at the bottom of the page. Unfortunately, I still can't quite grasp the concept. It was always my understanding that the entire universe erupted from the BB. This makes it look as if BB happened inside a pre-existing universe. What the hey am I missing here? :confused:

Actually, I'm now thinking that link was somewhat deceptive. What he's trying to say, I think, is that these models describe a universe that is always infinite, from the present day all the way back to the big bang. At the "moment" of the big bang, the universe would still have an infinite spatial volume, but it would also be at an infinite density. As EL said, it just becomes a matter of definition at that point. However, there would be no question about the volume of our observable universe at t=0. Since it occupies a finite volume at the present time, it must occupy zero volume when compressed to infinite density. Saying that the entire universe's volume suddenly drops to zero at t=0 would create a discontinuity, so it makes more sense to keep calling it infinite.

I wouldn't worry yourself so much with these questions, however. Although we have no good physical reason to say that the universe isn't infinite, we do have good physical reason to think that the Big Bang isn't actually a singularity. Unfortunately, we'll need a theory of quantum gravity to describe how the universe behaves before the Planck time, so a more detailed answer will have to wait for new physics.
 
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  • #53
Dmstifik8ion said:
Infinity does not exist in nature (out there in reality land). It is a creation of the human mind, (an abstract in mathematics, like zero), to help us to comprehend the relationship between nothing and everything else. Things, (that are inclusive in the set of existents) seem infinite when we are no longer able to attach any concepts or ideas to what something is (its nature). Learning about, understanding and defining the universe will lead us to an appreciation of its finite quality.

I think a lot of physicists would agree with you, but I'm afraid it's not something you could ever prove. For now, we'll be responsible scientists and just say what the data are or are not consistent with.
 
  • #54
Thanks, Mr. Tiger. I couldn't quite follow what EL was proposing (my fault, not his), but you have once again managed to explain things in a manner that is clear to someone without the requisite background in the subject. Your impending guruship is well deserved.
 
  • #55
Danger said:
I couldn't quite follow what EL was proposing (my fault, not his)
Sorry for making a mess out of it.

but you have once again managed to explain things in a manner that is clear to someone without the requisite background in the subject. Your impending guruship is well deserved.
I think we all can agree on that! (https://www.physicsforums.com/showthread.php?t=102199 )
 
  • #56
If the universe were infinite, wouldn't that violate laws of thermodynamics?

If two particles are infinitely apart from each other, the potential energy between them would be infinite.

If two particles infinitely away attract to each other at a constant acceleration, wouldn't they eventually accelerate to the limit of C, where either that limit has to be invalid? or if they are infinitely away, the force equations must end up at 0 force interaction between them to begin with? Wouldn't that then cause conflicts about locality??

I'm very unskilled in physics, and don't have the knowledge to answer my questions or show the flaw in my reasoning :(
 
  • #57
Danger said:
It puzzles everyone. We just have to get over it. :biggrin:

The problem is that there isn't really any 'outside'.

I came here to log in purely to commend your answer. The notion of "outside" is conceptual. When space ends, there's no "outside."

And if time ends, there's (presumably) no ability for motion towards the outside. (Can anyone reflect on this second point?)
 
  • #58
think universe as a balloon as its expanding as you can see it will expand for every.
 
  • #59
I think universe is out of the boundry of finite and infinite.
It is neither finite nor infinite
In other words it is both finite and infinite

It is also the possibility that there can be more than 1 Universe.
In Sanatan Vedic Dharma, it is written that there are 14 Universes and the rules and laws of Physics are quite different from each other.

For example,
In our universe, if north-north pole goes away from each other but they can come together from each other in other universe.
 
  • #60
CMB, as well as other studies, indicate omega is so close to exactly 1.0, it is too close to call - meaning the universe is virtually dead flat. A dead flat universe, under current space-time models, is spatially infinite. Now just what 'spatially infinite' means is a horse of different color. It is, however, safe to say it means the observable universe does not curve back on itself - i.e., you will never see the back of your head no matter how powerful your telescope.
 
  • #61
Danger said:
Now you're just teasing... :-p

What I was getting at is that if it formed a finite time ago, and is expanding at finite speed, it can't be infinite. There's a maximum size that it could have reached by now. 'Infinite' implies that it had no beginning, not just no end.
Perhaps I'm using the wrong definition of 'infinite' here, but that's what it means to me.

The Universe could have been of infinite size when it was formed. A singularity need not be a point.

In fact, this has recently been declared to be the "standard model."
 
  • #62
EL said:
Sure, that's also possible. No one knows wheter the universe is infinite or not. (And it certainly does not care about "opinions" :-p )

I agree with this, as in the ball would be space that you could get to given enough time. The only issue I have with that is if there is a ball in a room, which represents the finite universe in space, there's still a whole room around the ball, what would be around the finite universe? If that makes sense? I'm not very good at explaining :P
 
  • #63
Axuality said:
There is only one 'infinity'.

The set of integers, or negative numbers for example, is not infinite. That is a misuse of the word 'infinite'.

There can be only one infinity and that is the sum of all things in existence.

So with that in mind, what do we REALLY mean by an infinite universe?

The reason that these things seem paradoxical is because we're not seeing what we're looking at.

Reality is mental. Matter is simply one of a large number of possible thoughts.

Mind and its thoughts is all that exists.


This sounds like philosophical nonsense run amuck, and should be posted in the philosophy section, not here where we base our statements on evidence.
 
  • #64
phinds said:
This sounds like philosophical nonsense run amuck, and should be posted in the philosophy section, not here where we base our statements on evidence.
That was from 2009, I deleted it. People keep posting to this old thread.
 
  • #65
Evo said:
That was from 2009, I deleted it. People keep posting to this old thread.

OOPS ... sorry :redface:
 
  • #66
CallumBoson said:
I agree with this, as in the ball would be space that you could get to given enough time. The only issue I have with that is if there is a ball in a room, which represents the finite universe in space, there's still a whole room around the ball, what would be around the finite universe? If that makes sense? I'm not very good at explaining :P

It makes sense to me. And the answer would be, no one knows what, if anything, is outside our Universe.
 
  • #67
If they all collided and merged it wouldn't be a mega star. It would be a black hole.
 
  • #68
Something infinitely large can't expand because it is already everywhere. That would be like saying that you can add another floor to a building of infinite number of floors. Infinity cannot be increased. If what is called infinite can be increased by an addition, then it was not infinite to begin with.
 
  • #69
Radrook said:
Something infinitely large can't expand because it is already everywhere. That would be like saying that you can add another floor to a building of infinite number of floors. Infinity cannot be increased.

No, you have that exactly backwards. Look up Hilbert's Hotel.
 
  • #70
The paradox
Consider a hypothetical hotel with countably infinitely many rooms, all of which are occupied – that is to say every room contains a guest. One might be tempted to think that the hotel would not be able to accommodate any newly arriving guests, as would be the case with a finite number of rooms.
[edit] Finitely many new guests
Suppose a new guest arrives and wishes to be accommodated in the hotel. Because the hotel has infinitely many rooms, we can move the guest occupying room 1 to room 2, the guest occupying room 2 to room 3 and so on, and fit the newcomer into room 1. By repeating this procedure, it is possible to make room for any finite number of new guests.
[edit] Infinitely many new guests

It is also possible to accommodate a countably infinite number of new guests: just move the person occupying room 1 to room 2, the guest occupying room 2 to room 4, and in general room n to room 2n, and all the odd-numbered rooms will be free for the new guests.
http://en.wikipedia.org/wiki/Hilbert's_paradox_of_the_Grand_Hotel

Adding guests doesn’t affect the hotel’s infinity in any way.
But if we add a room, or height, then the hotel wasn’t infinite to begin with because we cannot add to what is literally infinite. Perhaps you are confusing sequential infinity with literal infinity. They are completely different from each other.


Sequential infinity is represented by a number line with two arrows indicating that the number sequences go on forever. In short, that we can always add one more to the sequence.

Literal infinity doesn’t allow that. The fellow who wrote the article is confusing the two as well. In fact, he contradicts himself semantically by saying that a hotel’s infinite number of rooms are countable. Countability requires finiteness.
 
  • #71
Radrook said:
Adding guests doesn’t affect the hotel’s infinity in any way.
But if we add a room, or height, then the hotel wasn’t infinite to begin with because we cannot add to what is literally infinite. Perhaps you are confusing sequential infinity with literal infinity. They are completely different from each other.


Sequential infinity is represented by a number line with two arrows indicating that the number sequences go on forever. In short, that we can always add one more to the sequence.

Literal infinity doesn’t allow that. The fellow who wrote the article is confusing the two as well. In fact, he contradicts himself semantically by saying that a hotel’s infinite number of rooms are countable. Countability requires finiteness.

I don't know enough math to argue with you, but that doesn't seem right and consider that that a huge number of physicists seem to have no trouble with the idea that our universe may be infinite and I'm sure they are all aware that it is expanding. How do you explain that? What am I missing?
 
  • #72
Radrook said:
Something infinitely large can't expand because it is already everywhere. That would be like saying that you can add another floor to a building of infinite number of floors. Infinity cannot be increased. If what is called infinite can be increased by an addition, then it was not infinite to begin with.

Yes and no.

You are right in a way, but not right in another way.

This stems from the problem of comparing two infinities. There are a number of ways to do it, which are not the same.

One way is Cantor's hierarchy of infinities. In this view the definition is that "you can make a bijection (one-to-one and onto mapping) from one set to another if and only if they are the same size." Then he defines any set that has a bijection with the integers is a countable infinity, and proves that the real numbers are not countable: they are a larger order of infinity than the integers.

The other way is measure theory. You have an infinite number of situations but somehow the probability sums to one. Each situation has the probability zero, so there seems to be a paradox. There are ways to get around this completely sensibly: usually you use calculus. But the upshot is that you CAN quite reasonably divide an infinity by an infinity if you are careful about it.

You seem to have heard of Cantor's ideas. But in physics the measure theory idea dominates. With good reason: it gives actual numbers.

Now in real life it is quite possible that we have an instance of an infinity divided by an infinity. The universe could be infinitely large and contain an infinite amount of mass. Nevertheless since we assume that that mass is evenly distributed, we can both define the ratio using measure theory, and actually measure that ratio in real life.

So while in the Cantor sense the Universe isn't getting any bigger, in the measure theory sense it is. We assume that the amount of mass is staying the same, then if that ratio is decreasing then the amount of space is getting larger.
 
  • #73
Would it be to much of a stretch to say that it would be impossible to ever determine the size and shape of our universe because we are naturally a part of the universe with a limited view.

If somehow we could detach ourselves from the universe (i.e an aerial view of the landscape reveals much more than being on the ground) then we would be able to determine the dimensions of the universe. Whilst we observe it as a whole
 
  • #74
shifty88 said:
If somehow we could detach ourselves from the universe (i.e an aerial view of the landscape reveals much more than being on the ground) then we would be able to determine the dimensions of the universe. Whilst we observe it as a whole

There IS no "outside" from which we can get such a vantage point, so your question is pretty much equivalent to asking if pigs had wings, could they fly?
 
  • #75
shifty88 said:
Would it be to much of a stretch to say that it would be impossible to ever determine the size and shape of our universe because we are naturally a part of the universe with a limited view.

If somehow we could detach ourselves from the universe (i.e an aerial view of the landscape reveals much more than being on the ground) then we would be able to determine the dimensions of the universe. Whilst we observe it as a whole

What phinds says is correct. If the Universe had an "outside" then it would not be the Universe. The Universe can be defined as: "the totality of everything that exists" therefore if something exists, by definition it is part of the Universe.

For their to be an "outside" would also require a "center" and an "edge" which would invalidate the cosmological principle of isotropy.

We can, however, measure curvature from within the metric to determine if space is euclidean or not - unfornutaley the degree of error is rather small and it is entirely possible that out little patch of the Universe we can see (The Observable Universe) is too small a piece of the whole (Whether finite or not) to determine curvature with any acceptable margin of error.

Global curvature is the key to the "shape" of the Universe in my opinion.

Hope this helps.

Cosmo
 
  • #76
phinds said:
There IS no "outside" from which we can get such a vantage point.
Obviously. Therefore we can never know for sure what shape or size the universe it.
We can only use our best educated guess from what observations we can make.
 
  • #77
The observable universe is obviously finite, so it can expand to its heart's content without offending our logical sensibilities. It is also very close to being dead flat - according to WMAP and supernova studies. This suggests the universe is much larger than the part observationally accessible to us. In is, however, possible the universe could be both flat and finite.
 
  • #78
shifty88 said:
Would it be to much of a stretch to say that it would be impossible to ever determine the size and shape of our universe because we are naturally a part of the universe with a limited view.

If somehow we could detach ourselves from the universe (i.e an aerial view of the landscape reveals much more than being on the ground) then we would be able to determine the dimensions of the universe. Whilst we observe it as a whole

To me it seems impossible for a finite being to observe an infinity.

It would be possible though to deduce an infinity, by showing that a contradiction occurs if the infinity is not there.

Detaching ourselves from the Universe is by definition impossible. But it could be that our current conception of the Universe is wrongly limited, and there is another view within our Universe that would look at our current conception from outside. Indeed the geometry of spacetime is hyperbolic, and a hyperbolic geometry is one way to fit an infinity inside of a finite space. If there are more than four physical dimensions in our Universe it is possible that there is a perspective in which 4D spacetime is a bounded subset within some other space.
 
  • #79
Chronos said:
The observable universe is obviously finite, so it can expand to its heart's content without offending our logical sensibilities. It is also very close to being dead flat - according to WMAP and supernova studies. This suggests the universe is much larger than the part observationally accessible to us. In is, however, possible the universe could be both flat and finite.


What do you mean? Spatially infinite but inhomogeneous with a finite amount of matter? That could be.
 
  • #80
There are at least four possible topologies that are flat, finite and obey the cosmological principal.
 
  • #81
The universe is finite but like explain earlier with an ant on a beach ball to the eye it would seem infinite because the only dimensions we can see is the ones we are in. If you were born and lived on an island all your life you might think that the island is all there is. So if you cannot see an edge to the universe it doesn't make it infinite. To be able to prove non mathematically that our universe is finite we would have to go beyond our own universe but since we cannot detect past the 4th dimension we are stuck.
 
  • #82
vanvlizr said:
The universe is finite

This is pure speculation on your part and should be stated as an unsupportable opinion, not a fact.
 
  • #83
that is my unsupportable postion atleast with current technology, but it is a fathamable and possible theory. as of now there is no way to be sure, everything about this topic is speculation.
 
  • #84
phinds said:
This sounds like philosophical nonsense run amuck, and should be posted in the philosophy section, not here where we base our statements on evidence.


Can you specify exactly what is so nonsensical about what he just said.
 
  • #85
phinds said:
This is pure speculation on your part and should be stated as an unsupportable opinion, not a fact.


The question is why state opinion as if it were fact in the first place. If indeed the universe is finite then it is bounded. Which brings up the question as to what is outside those boundaries. If indeed there is nothing outside, then that answer itself becomes nonsensical because it is self contradictory. In short, it is identical to the "Who created God" paradox of infinite regression. The only way around it is to negate the existence of dimensionality and to declare its perception as a sensory illusion.
 
  • #86
Radrook said:
Can you specify exactly what is so nonsensical about what he just said.

Uh ... did you READ the post that was in response to?
 
  • #87
Its hard to actually understand how exactly did they measure the size of the universe? I am also quite concerned with the fact that there could still be an outer void of nothingness located somewhere out of the universe. What if dimensions aren't tightly packed like said in string theory

1: is a straight line that has 2 directions of spatial freedom and is infinite (is also infinitely thin)
2: is a combination of two 1 dimensional lines and has 4 directions of spatial freedom it is also infinitely thin (because it has no depth)
3:It is an increase in spatial freedom in which is depth is the increase (since it has depth then we would now assume it is not infinetly thin
4: Now there is the temporary dimension which is used for measurement of physical change and then there is the spatial dimension which is a tesseract.
now it may seem pointless to have told you this but its confusing how we would consider dimensions tightly compressed. So why does string theory assume its tightly compressed as moving forwards in dimensional states increases physical state ?
 
  • #88
The outside of the universe is literally nothing. We observe the end of the universe, though it is not the true end of the universe because the time-space continuum doesn't allow us to view the true edge. The universe is forever expanding and new galaxies far away have been created, possibly billions of years ago, but because of the distance, the light reflecting off of those galaxies may not have reached us yet, allowing us not to view them, or if the light has recently reached us, we would view it as a new galaxy, though it was truly just too far to allow the reflected light to reach us. It is only logical that the universe is constantly expanding because the entropy within the universe is forever increasing. There is a good point made in this article http://www.allaboutscience.org/theory-of-relativity.htm
Only if we could go the speed of light could we determine the current dimensions of the universe
 
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