The infinitely old universe

[Stranger]

Call me old fashioned but what is it that keeps this perpetual motion machine going? Why is this system not subject to heat death.

I suggest that Roger Penrose (who's published papers with Stephen Hawking and who proposed the idea) has a better understanding of physics than anybody on this forum. However, it's basically about the re-scaling of the phase space of the universe. The metric of the universe at heat death is remarkably similar to that of the big bang, with the exception of the scale factor. If every particle eventually decays into massless particles (this is a conjecture), then there is no way for the universe to keep track of time or space.

Trouble is we need a real life infinity also it may be argued that this order of energy, if enough to start a universe is going to get less and less each universe. However the idea of entropy being probabilistic does raise the intriguing idea that the universe could suffer instantaneous heat death if what you say is true.
Therefore the whole system runs down to heat death. What is heat death anyway? The loss of the ability to do useful work.

I don't see any problem with a real life infinity and you suggested it in the title of this thread. You also seem to be confusing energy with entropy. The energy of the universe will always be the same*. There is no physical reason why entropy can't be reversed to any arbitrary degree, it's just very, very improbable, but given enough time, it will eventually happen, and given an infinite amount of time, it definitely will happen.

It is however true that the universe may suffer an instantaneous heat death, it's also true that, in this scenario, Boltzmann brains would be far more common than entire universes. Maybe that doesn't matter, though. How would you tell if your life was a series of Boltzmann brains, each thought separated by vast amounts of time?

* Actually energy conservation is problematic in general relativity anyway.

[Walt Zingmatilder]

I suggest that Roger Penrose (who's published papers with Stephen Hawking and who proposed the idea) has a better understanding of physics than anybody on this forum. However, it's basically about the re-scaling of the phase space of the universe. The metric of the universe at heat death is remarkably similar to that of the big bang, with the exception of the scale factor. If every particle eventually decays into massless particles (this is a conjecture), then there is no way for the universe to keep track of time or space.

I don't see any problem with a real life infinity and you suggested it in the title of this thread. You also seem to be confusing energy with entropy. The energy of the universe will always be the same*. There is no physical reason why entropy can't be reversed to any arbitrary degree, it's just very, very improbable, but given enough time, it will eventually happen, and given an infinite amount of time, it definitely will happen.

It is however true that the universe may suffer an instantaneous heat death, it's also true that, in this scenario, Boltzmann brains would be far more common than entire universes. Maybe that doesn't matter, though. How would you tell if your life was a series of Boltzmann brains, each thought separated by vast amounts of time?

* Actually energy conservation is problematic in general relativity anyway.

I can’t fault anything here. A thread considering what you say about Boltzmann brains might be entertaining.

I have one question. How much quantum tunnelling has to happen to restore maximal order for a new Big Bang? Is it the whole universe?

Does every photon of energy remaining have to tunnel at the same time?And to the same place or state as it were?

What is the smallest unit that energy will break down into?

Isn’t the spontaneous formation of parts of universes more likely than the formation of the pre Big Bang singularity?


I know that this does not affect the likely hood of these events happening. I’m just wondering if a new Big Bang has to contain all of the remains of the previous one.

[Sebastian Toe]

I have one question.

I counted six.
Is that the same as "I only had one drink"?

[Walt Zingmatilder]

I counted six.

Fffffffff..........no I mustn’t........... .gehhhhh........no I shouldn’t.........Oh shit I can’t keep it in.....
Sebastian my dear friend......Have you considered getting a life?

[Stranger]

I can’t fault anything here. A thread considering what you say about Boltzmann brains might be entertaining.

I have one question. How much quantum tunnelling has to happen to restore maximal order for a new Big Bang? Is it the whole universe?

Does every photon of energy remaining have to tunnel at the same time?And to the same place or state as it were?

What is the smallest unit that energy will break down into?

Isn’t the spontaneous formation of parts of universes more likely than the formation of the pre Big Bang singularity?


I know that this does not affect the likely hood of these events happening. I’m just wondering if a new Big Bang has to contain all of the remains of the previous one.

Sorry, I don't understand why you think this has anything to do with tunnelling.

The notion is based on relativity, rather than quantum mechanics. It's just that the mathematical description of a universe filled with entirely with massless particles (hence, all travelling at light speed) is remarkably similar to that of the earliest moments of this universe and with everything travelling at light speed, there is nothing that can keep track of time or distance.

Added: That was about conformal cyclic cosmology, the reversal of entropy is just statistical, it has nothing to do with tunnelling either.

[Walt Zingmatilder]

Sorry, I don't understand why you think this has anything to do with tunnelling.

The notion is based on relativity, rather than quantum mechanics. It's just that the mathematical description of a universe filled with entirely with massless particles (hence, all travelling at light speed) is remarkably similar to that of the earliest moments of this universe and with everything travelling at light speed, there is nothing that can keep track of time or distance.

Added: That was about conformal cyclic cosmology, the reversal of entropy is just statistical, it has nothing to do with tunnelling either.

Alright forget tunnelling for the time being.

How do you propose getting every thinly distributed piece of energy across infinite distances to form a maximally ordered pre Big Bang singularity? It doesn’t sound as if even light speed is going to do the job and if mass has gone, no Big Crunch either.

[Stranger]

Alright forget tunnelling for the time being.

How do you propose getting every thinly distributed piece of energy across infinite distances to form a maximally ordered pre Big Bang singularity? It doesn’t sound as if even light speed is going to do the job and if mass has gone, no Big Crunch either.

Firstly, I don't propose anything, I offered Penrose's conjecture as an example of how it might be possible for an infinitely old universe to exist (other conjectures are available). I don't fully (mathematically) understanding the idea, but I have to assume that somebody of Penrose's stature knows what he's talking about.

Given that, the way he describes it (see Cycles of Time), it's because everything is travelling at light speed, nothing experiences either space or time, so the concepts loose any physical meaning. The metric that describes the space-time of the universe has 10 independent values and 9 of them are identical in the final stages of a universe in which everything decays to massless particles (and all black holes have evaporated due to Hawking radiation), to those of the very first moments of our universe, and the one that's different is the one that describes the spatial scale (which has become meaningless).

The idea of "maximally ordered" is also rather misleading. The entropy of the universe is not a simple matter (largely due to gravity tending to clump things together) and Penrose also suggests that what made the BB have such low entropy was simply that the Weyl curvature tensor was zero - which would also be the case at in the final stages of a universe in which everything becomes massless.

[Walt Zingmatilder]

Firstly, I don't propose anything, I offered Penrose's conjecture as an example of how it might be possible for an infinitely old universe to exist (other conjectures are available). I don't fully (mathematically) understanding the idea, but I have to assume that somebody of Penrose's stature knows what he's talking about.

Given that, the way he describes it (see Cycles of Time), it's because everything is travelling at light speed, nothing experiences either space or time, so the concepts loose any physical meaning. The metric that describes the space-time of the universe has 10 independent values and 9 of them are identical in the final stages of a universe in which everything decays to massless particles (and all black holes have evaporated due to Hawking radiation), to those of the very first moments of our universe, and the one that's different is the one that describes the spatial scale (which has become meaningless).

The idea of "maximally ordered" is also rather misleading. The entropy of the universe is not a simple matter (largely due to gravity tending to clump things together) and Penrose also suggests that what made the BB have such low entropy was simply that the Weyl curvature tensor was zero - which would also be the case at in the final stages of a universe in which everything becomes massless.

Thanks for your post, very informative.