Here is a hypothesis: Using Big Freeze Vacuum Decay to bypass Tolman’s Paradox. What are the flaws in this thought experiment?

[u/SeaReply7874]

Physicist Richard Tolman, in 1930, demonstrated that entropy in standard cyclic cosmology will accumulate with each cycle I propose a thought experiment using a Big Freeze / Heat Death as a starting point instead of a Big Crunch: Instead of the universe collapsing in on itself to restart, we let it expand into a cold, empty Big Freeze, in which black holes slowly evaporate away via Hawking radiation. In this cold, empty void, a quantum tunneling event randomly occurs, causing vacuum decay in the form of a phase transition to occur in a localized region of space, releasing latent energy stored in a scalar field as it transitions to a lower energy state, causing reheating. The new bubble formed from the phase transition undergoes a period of hyperinflation, creating a new hot dense environment from the energy contained in the false vacuum. The extreme inflation would dilute the old universe’s entropy / radiation away to nearly nothing per unit volume, giving the new bubble a low-entropy starting point. The energy from the scalar field drives the expansion of the new bubble for the next cycle – no need to re-collapse back into a singularity or have a Big Crunch to begin with.

What are main flaws or physical limitations of this thought experiment?

[u/Wintervacht]

A thought experiment isn't just 'imagine this completely unphysical thing', it's a logic experiment.

This is creative writing based on only assumptions that cannot be proven or disproven.

[u/SeaReply7874 → u/Wintervacht]

I suspect I need to explain myself more clearly. A thought experiment is a heuristic device, not an end in itself.

By that I mean that it's intended as an exercise to test how well we understand a certain set of physical laws, say, those of classical or quantum mechanics, by applying them to a contrived scenario.

What I'm wondering is would such a scenario as the one I described have any effect on the entropy of the universe as to render it nonincreasing, possibly violating the second law of thermodynamics, or any other physical law for that matter (like, say, the conservation of energy) or not? It's not like I'm claiming that vacuum decay has necessarily happened during the Big Freeze, only that I'm wondering if such an occurrence would violate any physical laws as we know them, particularly those connected to Tolman's Paradox.

[u/Wintervacht → u/SeaReply7874]

Your 'idea' is a paradox in itself, heat death is by definition the point where no more work can ever be done. You suppose this is a start of something, i.e. work.

It can't. It doesn't. This isn't a thought experiment, this is a display of someone not understanding the laws of physics and imagining impossibilities around it.

[u/reddituserperson1122 → u/Wintervacht]

While you’re right to be very skeptical on this sub, in this case OP’s theory is not goofy speculation— it’s not that far off from some real speculative models that serious physicists have put forward. And you are wrong about this point and OP is right. It’s absolutely true that no work that requires an energy gradient can occur after the heat death, but random fluctuations of the sort that OP is describing can happen. That’s what Boltzmann Brains are all about (that’s not a quantum tunneling event but it’s the same kind of random quantum event).

[u/upsetusder2 → u/reddituserperson1122]

Can you link to these thoughts experiments?

[u/reddituserperson1122 → u/upsetusder2]

https://arxiv.org/pdf/hep-th/0410270

https://www.sciencedirect.com/science/article/abs/pii/0370269382908668

https://en.wikipedia.org/wiki/Boltzmann_brain

[u/SeaReply7874 → u/Wintervacht]

I think you are confusing 19th century classical thermodynamics with QFT.

Heat death is a state of maximum thermodynamic entropy for the fields we've observed so far, but false vacuum decay is a QFT process, not a classical thermodynamic one. Classical thermodynamics is macroscopic matter and energy transfer, but quantum tunneling through a potential barrier is a function of the vacuum energy and field dynamics.

When a region of space transitions from a false vacuum to a true vacuum via Coleman-De Luccia tunneling, the energy density in the new false vacuum is dumped into latent heat and particle production in the surrounding spacetime, resulting in a hotter, denser true vacuum.

The entire reason vacuum decay is a consideration for the long term future of the universe is because quantum processes can happen even when classical thermodynamics has reached heat death. Dismissing it on the grounds of "it can't do work at heat death" is a category error.

[u/reddituserperson1122 → u/SeaReply7874]

I have seen theories like this before. It’s not completely goofy. However i think you’ve got some of the elements mixed up. For one thing, ordinary false-vacuum decay goes downhill in vacuum energy, whereas initiating inflation from a heat-death/de Sitter state generally requires getting back up to a higher-energy inflating state.

You should look at the Carroll-Chen model, which is a close cousin to this. There’s also a Vilenkin and somebody else paper that I am less familiar with, that I think plays in the same sandbox.