I've read all posts in the Basic Quantum Mechanics section, plus many of the links from it and a handful of others (working through the rest, I'm still only three days into this). Quantum mechanics is something I've had vague explanations of from education and discussions with educated people, but it seemed extremely complicated and confusing due to almost precisely the issues touched on in the normal way it's taught. Thank you for putting down the steps needed to walk me through rewriting my basic assumptions of reality to more accurately reflect how reality likely works, it's been very fun and interesting. I'm starting to feel like a native of the quantum universe, and.. it kinda makes sense. Definitely a whole lot more sense than my previous mangled understanding of probabilities and wave/particle duality. Having a base level reality which works very differently from high level phenomenon which feel more intuitive does not seem like a great surprise.

Anyway, one idea I've had which seems interesting to me, but I am not yet in knowledgeable to evaluate properly and would like thoughts on:

**Would you, under the many worlds interpretation, be able to experimentally test whether a universe is infinite in time but not space?**

I know that infinite time+finite space not a favored model for cosmology currently, but it's still interesting to me if quantum physics testably disproves a whole class of possible universes. And if by this (or similar) reasoning an infinite time/finite space universe is found to be incompatible with many worlds, finding evidence extremely strong evidence of an infinite time/finite space universe (highly unlikely as I understand it) would perhaps bring many worlds into question.

Possible line of reasoning:

- In a universe with finite space, there is a finite configuration space (finite amount of physical space, so finite possible universal states).
- Any particular blob of amplitude/branch/world will eventually evolve into a state of/near maximum entropy.
- Maximum entropy is not entirely stable even if no work can be extracted from it, so it is not a static point in configuration space.
- A non-static point in finite configuration space left to move for infinite time will eventually visit all possible arrangements of amplitude (configurations), infinite times. This includes Configuration A, which can be any possible point in configuration space.
- In both (particle left, sensor measures LEFT, human sees "LEFT") and (particle right, sensor measures RIGHT, human sees "RIGHT") blobs of amplitude, the universe evolves differently for a vast amount of time after the heat death of the universe, but given infinite time will at some point reach Configuration A with probability 1.
- Since both blobs of amplitude will, despite diverging for an unimaginable length of time, arrive at the same configuration as each other with probability 1, they are fully coherent allowing them to interact, and this is testable (and already falsified).

Points one, three, and four seems to me like the most likely weak link, but I'd be interested to know why this is not the case if it is indeed not the case. Perhaps at maximum-entropy each branch gets stuck in a unique infinite loop rather than visiting the rest of configuration space?

If the chain of reasoning holds and leads to the conclusions.. perhaps a stronger version of this argument could perhaps be constructed for a universe infinite in both time and space (depending on whether indefinitely expanding thermodynamic systems will reach all possible configurations given infinite time), though I'm already feeling somewhat out of my depth dealing with the weaker argument.

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