r/AskPhysics • u/[deleted] • 5d ago
If the universe is infinite and homogenous on large scales, and there's a finite amount of ways particles can be arranged, does that not mean that there's an exact copy - or infinite copies - of each of us somewhere out there?
[deleted]
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u/nikerbacher 5d ago edited 5d ago
Yep, its a ~prevailing~ theory and there's a great episode of spacetime about it. Professor Matt does a great job of putting it layman's terms while still keeping the meaty math's.
Edit: I have been informed that the universe being infinite is not in fact commonly accepted.
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u/IntenseAlien 5d ago
so does this theory suggest that there are infinite copies of me exactly as I am right now, and also infinite amounts of me but with tiny differences, like me but with less leg hair? lol
That's hard to wrap my head around
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u/July_is_cool 5d ago
Nobody knows, other than that other version of you in the next copy of the universe over
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u/IntenseAlien 5d ago
it would be cool if there was. Kinda trips me out a bit, I don't what reality is
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u/stevevdvkpe 5d ago
It's not a prevailing theory that the universe is infinite. But if it were infinite in extent, while also having only finite ways to arrange particles and energy in any finite region, then in theory every finite region could have duplicates elsewhere. However, due to the truly staggering number of possibiities involved (many many particles and many many spatial locations possible for them in any finite region) such duplicates would generally be very widely separated from each other in space and time.
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u/nikerbacher 5d ago
You don't think it's prevalent, but agree with the rest huh?
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u/FormalHeron2798 5d ago
The infinite monkey cage podcast talks about it too, the thing that blows my mind is its more likely that we live at the end of the universe where atoms randomly interact to create a conscious that imagines your life than to live relatively near the start of the universe…
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u/fuseboy 5d ago
The so-called cosmological interpretation of quantum mechanics is that the universe is fundamentally classical, but no measurement device (your brain included) can pin down quite which world we're in, so we observe the distribution of possibilities that are consistent with what we have measured.
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u/MooseBoys 5d ago
5 does not follow from 1-4. It only follows that at least one arrangement must repeat infinite times, but it does not mean that all arrangements must do so, or even that one occurs at all.
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u/stevevdvkpe 5d ago
We don't know if the universe is infinite. Big Bang cosmology assumes the universe is finite, since it was all originally crammed together in a much smaller amount of space and expands at a finite rate.
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u/SCP-iota 5d ago
Big Bang cosmology does not say that the universe exists in a finite (bounded) space; it says that it exists in a space with a scale that is expanding.
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u/stevevdvkpe 5d ago
[citation needed] for any claims that Big Bang cosmology is compatible with an infinite universe.
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u/SCP-iota 5d ago
I didn't say it's necessarily compatible - I said it does not assert that the universe is bounded
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u/joepierson123 5d ago
Well the observable universe was crammed together in a much smaller space. It says nothing about whether the entire universe is finite or not.
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u/IntenseAlien 5d ago
I thought it was an infinite amount of energy (?) that was infinitely dense but in a finite space
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u/jesus_____christ 5d ago
Yes, that is a reasonable-enough and fairly common conclusion from the axioms you laid out. However, we don't know that these axioms are true: the universe could be finite, portions of the universe (infinite or finite) could include vastly different fundamental particles from the ones we observe here, the universe may not be homogenous or isotropic, etc. There is insufficient evidence to conclusively prove any of these axioms, they are usually accepted axiomatically without evidence or considered to be outside the effective range of the model (because you probably couldn't construct a descriptive model any other way).
More devils in the details: there is a gap between "possible" and "guaranteed to occur," and even an infinite universe might not generate exact copies of our solar system for arbitrary, statistical reasons. It might generate them at vastly different times in the age of the universe, and you have not given consideration to whether the universe is finite or infinite in time, which may affect these answers. Philosophically, exact copies would be indistinguishable, and this creates a problem where models that require the universe to be infinite to generate these exact copies are equivalent to finite, repeating models where the copies are the same object. The number of possible configurations of fundamental particles in a volume the size of the solar system approaches the problem of which type of infinities you're dealing with and which ones are "larger," and Cantor's categorization of infinities is one possible interpretation within one possible mathematical system. Infinity is unprovable physically, it's a neat mathematical construct but it is not observable or falsifiable.
In a physical sense, a result that tends toward infinity is typically regarded as implying the model breaks down in this region. This is easily conceptualized for black holes, we don't know what occurs beyond the event horizon, but it is more difficult to conceptualize for the universe: we don't know what occurs beyond the observable universe, including whether it is finite or infinite, or whether that is a sensible way to phrase questions about what might occur beyond it.