Why do cosmologists consider the cosmos infinite?

[shunyadragon]

I looked through several threads on questions concerning whehter the universe(s?) was infinite or finite. Most of the answers seemed to be focused on our universe. Even though the many models of multiverses are contraversial and still lack significant objective support in the evidence, some sort of multi-verse existence that is infinite and eternal seems to be the dominant view of our physical existence.

The best conclusion I am able to reach is Quantum Mechanics and Quantum Time do not reflect a finite existence like relative time/space relationship functions in our universe, and that the present math describing our cosmos does not work with a finite temporal existence. The sum of the arguments seems to indicate that there is at present no way to conclude either way, but the best fit is for an infinite eternal physical existence.

Conceptually I often describe the infinite eternal nature of the cosmos as the Infinite Matrix (IM) within which the matter, energy, singularities, universes exist. Does anyone else use a suitable term to describe this concept I call the IM?

 

[Dmitry67]

the question if OUR universe is finite or not is absolutely different from the existence of the multiverse/other unvierses.

The first one belongs general relativity/consmology
The second one belongs to phylosophy/Beyond the Standard Model

 

[shunyadragon]

the question if OUR universe is finite or not is absolutely different from the existence of the multiverse/other unvierses.

The first one belongs general relativity/cosmology
The second one belongs to phylisophy/Beyond the Standard Model

Actually in a way it is not absolutely different, but the models for our universe would only apply to the possible universe(s) and their histories. Standard Model? I do not believe that anyone model would qualify as a truly standard model. All models are at present unsatisfactory to even explain the history of our own universe.

Philosophy is not the answer. Cosmologists do not base there conclusions on philosophy. I am looking for the basis in math models and concepts, and Quantum Mechanics theory that would be used by Physicists and cosmologists to consider the cosmos as infinite and eternal.

 

[Dmitry67]

"Beyond the Standard Model" is a section on this forum to discuss superstrings and related stuff (branes, parralel universes on branes etc)

regarding the cosmos - we don't know if it is finite or infinite
But definitely it is not eternal (there was a finite time after BB)

 

[shunyadragon]

"Beyond the Standard Model" is a section on this forum to discuss superstrings and related stuff (branes, parralel universes on branes etc)

regarding the cosmos - we don't know if it is finite or infinite
But definitely it is not eternal (there was a finite time after BB)

Again we are not talking about our universe, but the cosmos it resides in. No, not all consider there to be a finite time after the big bang.

 

[Chronos]

The observable universe [the one we can see with telescopes, etc.] is temporally finite in the minds of most scientists. Is it a subset of an infinite universe? That is unknown, and possibly unknowable. That is a question many scientists view as irrelevant until a valid test method is proposed. A cyclical universe would be testable. That would satisfy requirements for an eternal, but, observationally finite universe. The curvature of the universe [as measured by WMAP, et al], is almost exactly 1.000, which rains on the cyclical universe parade.

 

[Dmitry67]

Again we are not talking about our universe, but the cosmos it resides in. No, not all consider there to be a finite time after the big bang.

Then you should first provide a context.
Like, consider that our Universe is just a bubble or a brane in the many-worlds bulk. (this is an example).
As there are different and non-testable multi-worlds theories, it is nothing to discuss until you specify what exactly you want to discuss.

 

[shunyadragon]

Then you should first provide a context.
Like, consider that our Universe is just a bubble or a brane in the many-worlds bulk. (this is an example).
As there are different and non-testable multi-worlds theories, it is nothing to discuss until you specify what exactly you want to discuss.

I thought in these views our universe is not a bubble or a brane but a part of or on a bubble or a brane. The context of the multi-verse or many worlds involves a number of different theories. Each cosmologist or research group focuses on one or several models, but they still consider the greater cosmos to be either boundless or infinite and eternal beyond our own universe. Our universe may have had a beginning, and suffer a heat or cold death, but the view remains that it is boundless.

My question would relate to anyone cosmologist or research group, bubble or brane, or none of the above. Any reference for any model would be sufficient.

It may be that I need to start a thread in the section that deals with 'Beyond the Standard Model' section since I am asking the question concerning 'beyond our universe.'

What is the basis for considering the greater cosmos as either boundless or infinite, and eternal beyond our universe?

 

[Chronos]

Any 'beyond our universe' hypothesis demands an observationally testable consequence to be relevant. Current measurements of omega do not rule out an infinite universe, nor do they insist it must be infinite. That is an example of as an observationly testable consequence.

 

[torquil]

What is the basis for considering the greater cosmos as either boundless or infinite, and eternal beyond our universe?

If I understand this question correctly, there is no real scientific basis for an aswer to this question (yet).

There are probably many models of the universe that have been put forth, which assume that the complete universe is something bigger than the 4D spacetime we observe, even with more dimensions. But we don't know which of these theories are correct (or if any of them are).

It would be incorrect to claim that any of those models give a scientific answer to this question. It would simply be speculation. First we need to try to falsify those models by checking them against observed phenomena. If one theory turns out to pass all our tests, then one could start worrying about what it predicts regarding these more exotic questions.

I could proclaim that our universe is resting on top of a sleeping tortoise, but it wouldn't be a scientific truth, since my theory has not gained any credibility through scientific scrutiny. It would simply by a hypothesis, which in itself is worth nothing.

Torquil

 

[Chronos]

I agree, there is no scientific basis to assume our universe rests on 'turtles', or other imaginary edifices. What we see is what we get. We reside in a temporally finite universe until otherwise proven. Simple logic insists a temporally finite universe cannot be spatially infinite.

 

[torquil]

Simple logic insists a temporally finite universe cannot be spatially infinite.

How do we know by logic alone that a physical process that suddenly creates an infinite space does not exist? Either at the moment of a Big Bang or going from a finite to an infinite universe instantaneously at some later time? I don't see a purely logical reason for this to be impossible.

Torquil

PS: Nice signature!

 

[Chronos]

The finite speed of light limits the observable volume of a temporally finite universe.The fact that it appears much different in the distant past suggests it is spatially finite.

 

[torquil]

The finite speed of light limits the observable volume of a temporally finite universe.The fact that it appears much different in the distant past suggests it is spatially finite.

I agree that the observable volume is limited, of course.

As far as I know, the following assumptions are not inconsistent with observation or the finite speed of light:

1) Spacetime is $$\mathbb{R}^+ \times \mathbb{R}^3$$
2) Speed of light is fixed

This model should be able to undergo a comsmological time evolution that is consistent with observation.

I'm not saying that I believe in one choice over the other (finite/infinite), because I really onle concern myself with the observed universe. I was just puzzled by the claim that one could proove it using logic.

Of course, it always good to be corrected, but I'm not convinced yet :-)

Torquil

 

[Chronos]

Observational evidence to date favors a universe that is temporally and spatially finite. Logic is merely an extension of this evidence. Alternative theories require observational evidence to overcome these logical barriers.

 

[torquil]

Observational evidence to date favors a universe that is temporally and spatially finite. Logic is merely an extension of this evidence. Alternative theories require observational evidence to overcome these logical barriers.

Ok, I think I understand your point. I interpret your position as based on a philosophy of science where one should not assume the existence of something that has not been observed/measured. With this I actually completely agree.

My position was not to argue the existence of an infinite universe, but I got sort of hung up in the question about what is logic and what is not, but that is not particularly important.

Of course, not everybody places the same trust in all scientific observtions, so even the positions of different cosmologists will vary. But I usually let the general scientific consensus decide what I believe, when it comes to cosmological matters :-)

Torquil

 

[shunyadragon]

Observational evidence to date favors a universe that is temporally and spatially finite. Logic is merely an extension of this evidence. Alternative theories require observational evidence to overcome these logical barriers.

Actually no, the observational evidence is inclusive as to whether the nature of our physical existence containing the universe, or if you chose, our universe is temporally and spatially finite, or eternal and infinite.

 

[shunyadragon]

Observational evidence to date favors a universe that is temporally and spatially finite. Logic is merely an extension of this evidence. Alternative theories require observational evidence to overcome these logical barriers.

The following a an interesting article that goes into a math model that describes an infinite and eternal universe.

Inflation without a beginning: a null boundary proposal (Dated: February 7, 2008)

by Anthony Aguirre
School of Natural Sciences, Institute for Advanced Study Princeton, New Jersey 08540, USA

and Steven Gratton
Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544, USA†http://arxiv.org/PS_cache/gr-qc/pdf/0301/0301042v2.pdf

The following is the introduction to the article[cite=[PLAIN]http://arxiv.org/PS_cache/gr-qc/pdf/0301/0301042v2.pdf][/PLAIN]
We develop our recent suggestion that inflation may be made past eternal, so that there is no initial cosmological singularity or “beginning of time”. Inflation with multiple vacua generically approaches a steady-state statistical distribution of regions at these vacua, and our model follows directly from making this distribution hold at all times. We find that this corresponds (at the semi-classical level) to particularly simple cosmological boundary conditions on an infinite null surface near which the spacetime looks de Sitter. The model admits an interesting arrow of time that is well-defined and consistent for all physical observers that can communicate, even while the statistical description of the entire universe admits a symmetry that includes time-reversal. Our model suggests, but does not require, the identification of antipodal points on the manifold. The resulting “elliptic” de Sitter spacetime has interesting classical and quantum properties. The proposal may be generalized to other inflationary potentials, or to boundary conditions that give semi-eternal but non-singular cosmologies.
© source where applicable

[/cite]

 

[Chaballa]

Universe is not infinite cos Earth is the centre of the universe, n it can't be the centre if the universe is infinite. hehe

Seriously i don't know the answer but if the universe is infinite we can find an exact copy of Sun/Earth/You/Me, etc. All you need to do is work out how many subatomic particles it's possible to cram into the observable universe. Calculate the number of possible configurations of those particles and multiply that by the diameter of that observable universe. = ~two to the power ten to the power 118 metres.

 

[Dmitry67]

Chaballa, this is correct - in Quantum Mechanics, contrary to Newton theory, there is no continuum of possible configurations, but number of different configurations of finite number of particles is countable. Even more, as temperature is finite, then this number is finite too.

Hence, in infinite universe, if God fills it with some stuff - no matter what stuff - at some distance he runs out of distinct configurations and has no choice but to create an exact copy.

 

[Passionflower]

Chaballa, this is correct - in Quantum Mechanics, contrary to Newton theory, there is no continuum of possible configurations, but number of different configurations of finite number of particles is countable. Even more, as temperature is finite, then this number is finite too.

Hence, in infinite universe, if God fills it with some stuff - no matter what stuff - at some distance he runs out of distinct configurations and has no choice but to create an exact copy.

Hmmm...

Let's start easy, in flat spacetime, are you are concluding for instance that the volume of an expanding sphere in space representing the front of light emanating from all directions is always finite?

 

[Dmitry67]

yes, it is always finite.

 

[Passionflower]

yes, it is always finite.

The volume is infinite.
One can pack an infinite number of galaxies in such an expanding sphere. Remember that objects closer to c get increasingly Lorentz contracted, so the more you go towards the edge of the sphere the more Lorentz contracted the space is.

While no longer practical for cosmological models I find the Milne model very educational in understanding this.

 

[Dmitry67]

No, Lorentz contraction does not play the role you expect in the expanding Universe, so we can see in our visible Universe only finite number of galaxies.

This happens because talking about the expanding Universe you can't use just SR - it had been shown many times on this forum - even space can be considered almost flat, spacetime is not flat in the expanding universe, and 'pure' SR is not applicable. You have to use GR.

 

[Passionflower]

No, Lorentz contraction does not play the role you expect in the expanding Universe, so we can see in our visible Universe only finite number of galaxies.

I did not say or imply anything like that.

This happens because talking about the expanding Universe you can't use just SR - it had been shown many times on this forum - even space can be considered almost flat, spacetime is not flat in the expanding universe, and 'pure' SR is not applicable. You have to use GR.

You are either misreading what I wrote or dodging it completely.
I simply was trying to demonstrate to you a situation where already in flat space we can have infinities. It seems I was not very successful in doing that.

 

[Dmitry67]

I see.
But these infinities do not create paradoxes. There are no experiments which outcome depend on the calculations based on these infinities. So these 'singularities/infinities' are absolutely harmless (contrary to real singularities and partly to the 'weak' singularities ('blue sheet', for example))

 

[shunyadragon]

yes, it is always finite.

Not in contemporary physics and cosmology

 

[Dmitry67]

Not in contemporary physics and cosmology

Lightsphere of the light, emitted at some moment t, is finite even in cosmology.

 

[shunyadragon]

Lightsphere of the light, emitted at some moment t, is finite even in cosmology.

Your previous statement was generalization that was false, specific example of something that may be finite, does not help your case.

 

[Dmitry67]

Lightsphere (after finite time) is always finite when curvature is finite.

The only example when it might become infinite is the final stages of the Big Rip scenario, but there curvature is infinite. Also, Goedel's solution, but it is an oodity as time is cyclical there.

What is your contre-example?