Do you find the "Big Crunch" comforting?

[asdfasdf32]

As atheists, do you find the idea of a 'big crunch' (and a forever oscillating universe) more comforting than the idea of a cold dying universe?

I personally do and don't know why.

[thylacine]

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As atheists, do you find the idea of a 'big crunch' (and a forever oscillating universe) more comforting than the idea of a cold dying universe?

I personally do and don't know why.

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You should read `The Life of the Cosmos' by Lee Smolin.

[luckyme]

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As atheists, do you find the idea of a 'big crunch' (and a forever oscillating universe) more comforting than the idea of a cold dying universe?

I personally do and don't know why.

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I do somewhat and I think it's because it seems more interesting that way, rather like the way coming to the end of a journey can be a bit of a letdown.
"comforting" seems a tad too far though.

luckyme

[Metric]

Oscillating universe models still have thermodynamic problems, though nobody likes to talk about them. Rather than having a beautiful, pristine "new universe" all ready to teem with life after each big bang, you should actually expect nothing but a bunch of black holes and scattered radiation. Simply having a big crunch does not mean you automatically get to cheat and have entropy decrease. It's easy to see that our destiny is heat death in an open universe, but I don't see any reason to expect anything different in a bouncing model, either.

[m_the0ry]

It's comforting most in the sense that the singularity of the big crunch would effectively mark the end of time. We have established with the Big Bang theory that there is a beginning of time. It seems aesthetically proper - perhaps only because as humans we tend to be dissonant with infinities - for there to consequently be an end to time.

I am curious to see how the recent progress in dark matter observation has an affect on the fate of the cosmos. Heat death seems to be the most likely based on experimental evidence and I have to admit this is a pretty bleak interpretation.

[Metric]

Yeah, the bouncing models stick around purely because people want to get creative with their models, or have some desire to believe something like that. The most straightfoward interpretation of observation suggests an open universe, forever expanding -- dark energy making this more likely.

[bluesbassman]

Don't forget the possibility of a Big Rip (http://en.wikipedia.org/wiki/Big_Rip).

[Metric]

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Don't forget the possibility of a Big Rip (http://en.wikipedia.org/wiki/Big_Rip).

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Yeah, you can get pretty much anything if you postulate additional fields with weird equations of state. Unfortunately, if additional data comes in that continues to be consistent with a simple cosmological constant, a lot of these weird models can simply be tweaked to remain consistent with the new data -- an unfortunate state of affairs somewhat like string theory. They seem to be infinitely good at explaining why you can't find any evidence of their existence.

[FortunaMaximus]

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Oscillating universe models still have thermodynamic problems, though nobody likes to talk about them. Rather than having a beautiful, pristine "new universe" all ready to teem with life after each big bang, you should actually expect nothing but a bunch of black holes and scattered radiation. Simply having a big crunch does not mean you automatically get to cheat and have entropy decrease.

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Hmm. So entropy would continue its increase with each oscillation, and even in Big Crunch scenarios, each iteration would be less robust?

Bleh. "Oh, good, I thought you said we had 5 million iterations left."

[Metric]

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Oscillating universe models still have thermodynamic problems, though nobody likes to talk about them. Rather than having a beautiful, pristine "new universe" all ready to teem with life after each big bang, you should actually expect nothing but a bunch of black holes and scattered radiation. Simply having a big crunch does not mean you automatically get to cheat and have entropy decrease.

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Hmm. So entropy would continue its increase with each oscillation, and even in Big Crunch scenarios, each iteration would be less robust?

Bleh. "Oh, good, I thought you said we had 5 million iterations left."

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The reason this issue doesn't get discussed much is that most cosmological models are greatly simplified to ignore thermodynamic issues -- invoke enough symmetries and you are really looking at equations with just a few degrees of freedom. For example, it is well-known that standard Friedmann cosmologies resemble the equations of motion of a single particle running around in a certain potential.

So "bouncing cosmologies" are more or less a tweaked version of this. A simplified solution with some nice bouncing properties. But they don't really address the thermodynamic state of the universe (which is crucial to the emergence of life), and the 2nd law of thermodynamics, which is certainly not automatically overturned by the bouncing character of the solution.

[samsonite2100]

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it is well-known that standard Friedmann cosmologies resemble the equations of motion of a single particle running around in a certain potential.

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I find your use of the term "well-known" to be interesting.

[thylacine]

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The reason this issue doesn't get discussed much is that most cosmological models are greatly simplified to ignore thermodynamic issues -- invoke enough symmetries and you are really looking at equations with just a few degrees of freedom. For example, it is well-known that standard Friedmann cosmologies resemble the equations of motion of a single particle running around in a certain potential.

So "bouncing cosmologies" are more or less a tweaked version of this. A simplified solution with some nice bouncing properties. But they don't really address the thermodynamic state of the universe (which is crucial to the emergence of life), and the 2nd law of thermodynamics, which is certainly not automatically overturned by the bouncing character of the solution.

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What about big bangs that come from black holes? Is there any compelling reason why the big bang formed could not have low entropy? The old universe is still around to take the high entropy.

[Metric]

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What about big bangs that come from black holes? Is there any compelling reason why the big bang formed could not have low entropy? The old universe is still around to take the high entropy.

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I don't really know -- the main issue is that the situation is hugely simplified by invoking symmetries, which tend to mask a lot of the precise thermodynamic questions you could ask relating to the spacetime itself.

One thing that makes me suspicious of Smolin's idea of universes created via black hole formation is this scenario: I have a star, it collapses to form a black hole and a new universe. In this new universe, then, I have a new star form which is more or less the same as the one that collapsed to generate the universe to begin with. This seems very similar to the thermodynamic description of a perpetual motion machine -- a system that goes through a cycle, returning to its ititial state, and in doing so generates a bunch of other useful energy/lower entropy (i.e. a bunch of other stars and galaxies). I am not sure if this is exactly precise (I haven't tried to formalize this argument), but it's close enough to give me that "funny feeling" that some fundamental principles are getting abused. I suppose it could be that some fundamental principles simply need to be thrown out the window in a context like this -- still, I've not really seen a compelling argument that this should be the case. I mean, we're still dealing with mechanical systems here, however exotic...

[thylacine]

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What about big bangs that come from black holes? Is there any compelling reason why the big bang formed could not have low entropy? The old universe is still around to take the high entropy.

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I don't really know -- the main issue is that the situation is hugely simplified by invoking symmetries, which tend to mask a lot of the precise thermodynamic questions you could ask relating to the spacetime itself.

One thing that makes me suspicious of Smolin's idea of universes created via black hole formation is this scenario: I have a star, it collapses to form a black hole and a new universe. In this new universe, then, I have a new star form which is more or less the same as the one that collapsed to generate the universe to begin with. This seems very similar to the thermodynamic description of a perpetual motion machine -- a system that goes through a cycle, returning to its ititial state, and in doing so generates a bunch of other useful energy/lower entropy (i.e. a bunch of other stars and galaxies). I am not sure if this is exactly precise (I haven't tried to formalize this argument), but it's close enough to give me that "funny feeling" that some fundamental principles are getting abused. I suppose it could be that some fundamental principles simply need to be thrown out the window in a context like this -- still, I've not really seen a compelling argument that this should be the case. I mean, we're still dealing with mechanical systems here, however exotic...

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FWIW the scenario I described does not assume any kind of symmetry. Note that the local universe can have a heat death, while the overall population of such universes does not, in this scenario. Cosmological Natural Selection actually needs something like this to be true, though I don't know if that has been made clear.

So what do you think about eternal inflation then? My guess is that it can't happen.

[m_the0ry]

Regardless of how universes are created - the creation of a universe after this one dies being no exception - I believe they must undergo a darwinian process. No matter what conclusion physics reaches about fundamental interactions and elementary particles, we will always be left with an arbitrary number of constants and an arbitrary number of mathetmatical constructs to describe our existence. Only a very finely tuned universe remains stable the way ours does. Only with certain continuous symmetries, certain values for constants, certain metrics for space and time. Dimensionality is a great example of this; there is no reason why there cannot exist a stable universe with four spatial dimensions. There are very compelling arguments for why _our_ universe is stable at 3, but we can't make a generalization about all universes.

For a universe so finely tuned as ours to occur with any probability, There must be a great number of universes (or attempts at a stable universe).


Very speculative, just my two cents.



As far as black holes, as awesome as the idea of forming universes inside of black holes goes, there are some (mostly thermodynamic) paradoxes that still challenge their very existence (http://www.physorg.com/news101560368.html)

[thylacine]

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Regardless of how universes are created - the creation of a universe after this one dies being no exception - I believe they must undergo a darwinian process. No matter what conclusion physics reaches about fundamental interactions and elementary particles, we will always be left with an arbitrary number of constants and an arbitrary number of mathetmatical constructs to describe our existence. Only a very finely tuned universe remains stable the way ours does. Only with certain continuous symmetries, certain values for constants, certain metrics for space and time. Dimensionality is a great example of this; there is no reason why there cannot exist a stable universe with four spatial dimensions. There are very compelling arguments for why _our_ universe is stable at 3, but we can't make a generalization about all universes.

For a universe so finely tuned as ours to occur with any probability, There must be a great number of universes (or attempts at a stable universe).


Very speculative, just my two cents.



As far as black holes, as awesome as the idea of forming universes inside of black holes goes, there are some (mostly thermodynamic) paradoxes that still challenge their very existence (http://www.physorg.com/news101560368.html)

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I agree with evolutionary proposals such as Cosmological Natural Selection and I disagree with anthropic arguments. There is a big difference as explained by Smolin and Dawkins.

One big difference is that in the evolutionary proposals, the number of universes, although huge, is relatively extremely tiny compared to the number of universes in anthropic arguments.

By comparison to biology, although the number of species (or individuals, cells, genotypes etc) on Earth is large, the total number species (or individuals, cells, genotypes etc) that could hypothetically exist is enormously larger.

Anthropic arguments basically postulate some mechanism that actually produces every possible thing in a one-off non-iterative process, thereby `explaining' the existence of the particular thing you want to explain.

By contrast evolutionary arguments use the repeated iteration of replication, variation and selection to efficiently explore an extremely tiny subset of all possible things.

[Metric]

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FWIW the scenario I described does not assume any kind of symmetry. Note that the local universe can have a heat death, while the overall population of such universes does not, in this scenario.

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I'm not quite clear on exactly the scenario you have in mind (parent universes serving as a kind of "entropy sink" for next generation universes?). I'm simply noting that reducing the dimension of the phase space of the system via invoking symmetries is the standard way to handle cosmology, but in doing so you lose some ability to make stat-mech arguments.

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So what do you think about eternal inflation then? My guess is that it can't happen.

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It's an idea that is not without its charm, but inflation in general doesn't work as a way to make the thermodynamic state of the universe more acceptable -- I think we're both familiar with Penrose's argument on the matter, which I find pretty convincing.

[thylacine]

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FWIW the scenario I described does not assume any kind of symmetry. Note that the local universe can have a heat death, while the overall population of such universes does not, in this scenario.

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I'm not quite clear on exactly the scenario you have in mind (parent universes serving as a kind of "entropy sink" for next generation universes?). I'm simply noting that reducing the dimension of the phase space of the system via invoking symmetries is the standard way to handle cosmology, but in doing so you lose some ability to make stat-mech arguments.

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So what do you think about eternal inflation then? My guess is that it can't happen.

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It's an idea that is not without its charm, but inflation in general doesn't work as a way to make the thermodynamic state of the universe more acceptable -- I think we're both familiar with Penrose's argument on the matter, which I find pretty convincing.

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I agree that the use of symmetry arguments may mask entropy issues.

But now suppose that all the processes were truly understood (i.e. no simplifying assumption such as symmetry allowed), and that the 2nd law of thermodynamics were truly universal. Then it would seem to me that the big crunch to big bang scenario could not escape the thermodynamic problems you mention. By contrast it would seem to me that the black hole to big bang scenario could actually escape the thermodynamic problems you mention, by having high entropy stay in the old universe, or `parent universes serving as a kind of "entropy sink" for next generation universes' as you phrase it. I'm merely claiming that I don't see why it is not plausible. But let me know if there is any obvious blunder in my thinking.