Is the universe infinite?

[Spacedog]

I would like to take advantage of those of you who know a lot about physics and ask a few questions, if you would be kind enough to lend me your time...

Just the light topic of the ultimate nature of the universe... haha

1. Is everything in the universe in equilibrium with something else?

2. If this is true could this be evidence that the universe is infinite (equilibrium = infinity)?


I found this interesting:

The Retroactive Universe by Avi Rabinowitz (1993);

"According to one of the most basic laws of physics, known as "the second law of thermodynamics", the amount of disorder - or "entropy" - in the universe is constantly increasing. However, this does not mean that order or organization or complexity cannot increase anywhere in the universe - it can, but only at the expense of a yet greater net increase in disorder in the universe as a whole. Thus the net entropy of the universe as a whole always increases, even for processes which cause a local increase of order and complexity."

3. Is this guy's science correct?

4. Could the universe be explained as an accumulation of unlikely increases in order, which happen because they've had infinite time to do so? I.e. monkeys on typewriters

Personally I've always found infinity to be the only comfortable model for the universe, it satisfies "If God created the universe then what created God?" and "Why are the laws of physics the way they are?"

Thanks
Spacedog

[Alex K]

Hi!

First of all, it is not known whether the universe is spatially finite or infinite. Temporally, the matter is unclear as the mechanisms behind the early big bang such as inflation are not tested well enough.

The quoted statements about entropy sounds like standard statistical mechanics. However, I would like to point out that the second law is a law only on average and for a large number of degrees of freedom involved. Its violation is merely extremely improbable, and as the number of involved degrees of freedom such as particles tends to infinity, the probability tends to zero. It could be violated statistically, for example if you have a box full of gas, and by accident all molecules randomly flying about gather in one half of it. This can in principle happen and corresponds to a strong decrease in entropy. The probability is 1/2 for one particle, 1/4 for two, 1/1024 for ten, and you can guess what it is for one mole of gas with 10^23 molecules. Still, it is merely extremely unlikely, not absolutely forbidden that entropy suddenly decreases like this.

Another matter is the embedding of all that in an expanding or contracting spacetime - then, things are not so obvious any more.

So I'd answer your fourth question in the affirmative, but I don't think a balance needs to be strictly kept.

I don't quite understand how you conclude that the universe is infinite.

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Btw, why don't you write an intro post!

[Spacedog]

Thanks for the reply!

First of all, it is not known whether the universe is spatially finite or infinite.

I didn't think it was known, I was just hoping for an educated guess

The probability is 1/2 for one particle, 1/4 for two, 1/1024 for ten, and you can guess what it is for one mole of gas with 10^23 molecules. Still, it is merely extremely unlikely, not absolutely forbidden that entropy suddenly decreases like this.

As you say we do not know if the universe really is infinite, but if we speculate that it was, no matter how unlikely an increase in order becomes, surely it will still happen?

Another matter is the embedding of all that in an expanding or contracting spacetime - then, things are not so obvious any more.

Could you elaborate or will it be over my head?

So I'd answer your fourth question in the affirmative, but I don't think a balance needs to be strictly kept.

Rabinowitz goes on to write after the original quote; "Guided by gravitational attraction, planets are formed from chaotic combinations of gases, so that the resulting planet has a much more complex structure than the material it was formed from. Nevertheless, when all the subtle aspects of the process of planetary formation and its effect on the surrounding space are taken into account, it can be shown that it gives rise to a net increase in entropy. (Furthermore, although the action of the gravitational force leads to greater order, so that it would seem that order is increasing in the universe, and was at a minimum at the big bang, when taking into account the expansion of space-time which is an unavoidable consequence of the same law of nature which 'produces' gravity, one can see that entropy always increases.)"

I'm guessing you disagree with him here? As he seems to believe there is a perfect balance while you don't think it's not necessarily always adhered to?

How does dark matter come into this by the way? I understand that theoretically it should be perfectly balanced with matter, although we have not got the experimental evidence to prove it?

I don't quite understand how you conclude that the universe is infinite.

I don't conclude it is infinite, I wouldn't be so brash when I have such little knowledge, but if I speculate that it is, everything makes a lot more sense. By that I mean the mind boggling complexity that is required for reality to exist as we know it. Layers upon layers of systems - individual parts ordering themselves together, parts made up of other parts. Thinking about it has led many not stupid people to believe in God - because it all seems so damn unlikely! But given infinite time, everything that can happen will happen.

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Btw, why don't you write an intro post!

I don't think it would be very interesting! I just need a place to vent my constant existential questioning, sadly it's not something I feel able to discuss with anyone in my day to day life. Other people don't seem to care very much about such issues, far more interested in day to day normality, friends, boyfriends, girlfriends, what's for dinner?... Or perhaps a lot of people do have the same thoughts but don't feel comfortable discussing them, more than likely a bit of both.

Plus there's hopefully a lot of knowledge between the people using these forums that I can benefit from!

[IATIA]

It also depends on what is considered the universe. Just the matter within or all the matter and what it is expanding into. The matter is considered to be finite and measurable. (issues here)

The Big Bang was a singularity that expanded into nothing.

Any definition put to nothing makes it something, (Stir that around for a while).

This nothing becomes something as our universe expands into it and any attempt to go beyond that boundary puts something which is still tied to our universe into nothing which makes the nothing something. So in effect, the universe is unbounded, ergo infinite.

With that said, it also depends upon the structure of space-time and the matter contained within that creates a curvature which binds the universe within itself creating the 'illusion' of infinity were one to try and escape.

There are a myriad of other theories and few agree on any one.

I believe it to be unbounded and infinite.

[Heywood]

"According to one of the most basic laws of physics, known as "the second law of thermodynamics", the amount of disorder - or "entropy" - in the universe is constantly increasing. However, this does not mean that order or organization or complexity cannot increase anywhere in the universe - it can, but only at the expense of a yet greater net increase in disorder in the universe as a whole. Thus the net entropy of the universe as a whole always increases, even for processes which cause a local increase of order and complexity."

In a closed system entropy can achieve a maximum....so his statement that entropy always increases isn't necessarily true. In order for the net entropy of the universe as a whole to always increase you need the universe to be an open system. A model like Eternal Inflation allows for the net entropy of the universe as a whole to always increase.

[vorlon13]

The amount of increasing 'disorder' in the sun (and to a far lesser degree in the radioactive elements decaying in the body of the earth) massively and overwhelmingly exceeds the amount of 'order' life forms on earth have managed to scrape together.

Having noted that, however, does not preclude humans with an extremely advanced gamma ray 'laser' device of great power (as described by Carl Sagan back in the 60s) from blowing up the sun, should they wish to demonstrate the device. But realize, in order to do so, the power source for the gamma ray device would undergo a massive increase in disorder during the test.

You can't beat the second law of thermodynamics.

[Anomalocaris]

1. Is everything in the universe in equilibrium with something else?

No. Equilibrium means no overall change. That is evidently not the case since as much of the universe as we have ever observed is undergoing accelerating expansion.

2. If this is true could this be evidence that the universe is infinite (equilibrium = infinity)?

No, even an infinite universe can't be in equilibrium unless is it also uniform and homogenous down to well near quantum scale. Otherwise its stuff would just starts to gather into clumps.

3. Is this guy's science correct?

Without nit picking, yes.

4. Could the universe be explained as an accumulation of unlikely increases in order, which happen because they've had infinite time to do so? I.e. monkeys on typewriters.

Romeo and Juliet can even be explained by monkeys brawling in an ink warehouse. Anything can be explained by a sufficiently unlikely accumulation of individually unlikely events. But is that the best and least unlikely explanation available?

[Whateverist]

It may or may not be infinite but no one has found the edge of it yet.

[Anomalocaris]

It may or may not be infinite but no one has found the edge of it yet.

If it loops in on itself it can be finite and you would never find the edge.

[Surgenator]

1. Is everything in the universe in equilibrium with something else?

No. Our sun is beaming energy to Earth.

2. If this is true could this be evidence that the universe is infinite (equilibrium = infinity)?

No. Infinity has nothing to do with equilibirum.

3. Is this guy's science correct?

Yes.

4. Could the universe be explained as an accumulation of unlikely increases in order, which happen because they've had infinite time to do so? I.e. monkeys on typewriters

First off, the universe started out ordered and got more complex and disordered. Second, there are other physical laws that create pockets of order. I don't think there is anything "unlikely" about it.