What are the alternative theories for the end of the expanding universe?

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SUMMARY

The discussion centers on alternative theories regarding the fate of the universe, particularly in the context of accelerated expansion and the concept of Boltzmann brains. Participants agree that the "Big Crunch" scenario is no longer viable, and they explore the implications of an infinite universe where all matter may eventually evaporate. They conclude that while Boltzmann brains are mathematically possible, observational evidence suggests they are unlikely to exist, particularly within our observable universe. The conversation emphasizes the complexities of probability in an infinite universe and the philosophical implications of such theories.

PREREQUISITES
  • Understanding of cosmological models, specifically accelerated expansion.
  • Familiarity with the concept of Boltzmann brains in theoretical physics.
  • Knowledge of probability theory, particularly in relation to infinite sets.
  • Basic grasp of the implications of heat death in cosmology.
NEXT STEPS
  • Research the implications of accelerated expansion on the future of the universe.
  • Study the concept of Boltzmann brains and their relevance in cosmology.
  • Explore probability measures in infinite sets and their applications in theoretical physics.
  • Investigate the philosophical implications of heat death and the nature of existence in an infinite universe.
USEFUL FOR

Astronomers, physicists, philosophers, and anyone interested in the long-term fate of the universe and the implications of theoretical cosmology.

  • #31
Chronos said:
Assuming all matter eventually evaporates [via Hawking radiation by black holes], the universe would then be empty of matter [a Milne universe]

This doesn't seem right. The universe after all matter has evaporated via Hawking radiation is not empty of stress-energy; the stress-energy is just in the form of radiation instead of matter. In the Milne universe, there is zero stress-energy (since the Milne universe is just Minkowski spacetime in a different coordinate chart).

Chronos said:
which would [presumably] resemble the state of the universe prior to the big bang

I assume by this you mean the state of the universe prior to inflation starting? Or are you assuming some other model? If you mean the state prior to inflation starting, that's not the same as the Milne universe either (or the same as a universe filled with Hawking radiation); at least, not as I understand the current contenders for inflationary models.
 
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  • #32
Why shall the future be a universe without the chance of life, though we live in a universe, which supports the existence of life? This kind of view is really depressive.
 
  • #33
Gerhard Mueller said:
Why shall the future be a universe without the chance of life, though we live in a universe, which supports the existence of life? This kind of view is really depressive.
Science evaluates things based on what experiment reveals rather than on what one would like to be true.
 
  • #34
jbriggs444 said:
Science evaluates things based on what experiment reveals rather than on what one would like to be true.
The experiment you are talking about is "nature"! And "nature" supports life. There is no experimental hint that this will change.
 
  • #35
Gerhard Mueller said:
Why shall the future be a universe without the chance of life, though we live in a universe, which supports the existence of life? This kind of view is really depressive.
How shall the universe create and preserve life in the far future if there is nothing else than cold photon gas?
 
  • #36
I did not follow the full discussion but I would like to mention (one of my favorites) that Big Rip and Quantum fluctuations theories predict that the next big bang will be in 101056 years!
Yeah! ... we got time! ...
 
  • #37
Stavros Kiri said:
I did not follow the full discussion but I would like to mention (one of my favorites) that Big Rip and Quantum fluctuations theories predict that the next big bang will be in 101056 years!

Oh, what a tremendous waste of time. I would really appreciate a theory whith a much shorter renewal time of about a hundred billion (100_000_000_000) years.

May be we should check the possibility of a coordinated explosion of all black holes, if they are not kept blown-up by products of star activity.
 
  • #38
Gerhard Mueller said:
May be we should check the possibility of a coordinated explosion of all black holes, if they are not kept blown-up by products of star activity.

Since they all have different masses and will evaporate at different times, the probability is zero.
 

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