> I think space is a little like an insanely low-friction version of water, i.e. a quantum foam [1] (or similar fluctuations caused by the structure of space-time). It may not be perceivable but it would mean that space could exert a drag in the same way water does. You could imagine it pulling out energy from a photon and red-shifting it, until eventually it just absorbed it. If that was true, it would also add a distance-based offset for all observations of the Universe and affects things like the Hubble constant
As I understand it, expansion of the universe is expansion of the fabric of spacetime. It's not about objects just travelling away from each other. Thus the quantum foam friction analogy (even if true) wouldn't really apply.
> We have simulated closed-loop systems of many kinds, I think we can make educated guesses about how they may behave.
Don't mistake the incompleteness of our models for the truth. They are approximations for testing out ideas about the universe but that doesn't mean the approximations themselves exist.
> As long as all state transitions undergo a reversible function, it should eventually return to its original state?
But we know that non-reversible functions exist, both in terms of entropy and time irreversibility, & these functions happen all the time in our universe.
> Then where did that energy go?
Waste heat that can't be recovered to reverse entropy because it's already diffused throughout the universe & thus there's no local maximum to exploit. That's what the heat death of the universe refers to.
As I understand it, expansion of the universe is expansion of the fabric of spacetime. It's not about objects just travelling away from each other. Thus the quantum foam friction analogy (even if true) wouldn't really apply.
> We have simulated closed-loop systems of many kinds, I think we can make educated guesses about how they may behave.
Don't mistake the incompleteness of our models for the truth. They are approximations for testing out ideas about the universe but that doesn't mean the approximations themselves exist.
> As long as all state transitions undergo a reversible function, it should eventually return to its original state?
But we know that non-reversible functions exist, both in terms of entropy and time irreversibility, & these functions happen all the time in our universe.
> Then where did that energy go?
Waste heat that can't be recovered to reverse entropy because it's already diffused throughout the universe & thus there's no local maximum to exploit. That's what the heat death of the universe refers to.