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But if you are going to say that - why describe it as a “split”, as opposed to two separate universes which happen to identical in contents up to some point, no

But if you are going to say that - why describe it as a “split”, as opposed to two separate universes which happen to identical in contents up to some point, non-identical thereafter? Also, what you say about dollars is true because they have certain properties - effectively they have two different criteria of identity, one economic, the other physical. What is the criterion of identity for universes/branches?

thfuran 4y ago
>But if you are going to say that - why describe it as a “split”, as opposed to two separate universes which happen to identical in contents up to some point, non-identical thereafter? But they are (presumed under this model to be) splitting. You posited a case where two later happen to be identical, but that doesn't mean they merge. You'd just have two of them. >Also, what you say about dollars is true because they have certain properties - effectively they have two different criteria of identity, one economic, the other physical. What is the criterion of identity for universes/branches? I'd guess that there is none, like electrons. But though those are even more indistinguishable than dollars, you can still have two of them.
- skissane 4y ago
  > But they are (presumed under this model to be) splitting. Okay, but what's the actual model here? Let's talk about two different versions of many-worlds: Version 1: Universes splitting Version 2: No "splitting" per se ever actually occurs, universes are identical up to time t, different thereafter Is there any difference between 1 and 2 from a physics perspective–any difference in the maths, or in conceivable results of observation or experiment? Or are they just different ways of wording it? A metaphysical/philosophical difference, but not an empirical/mathematical one? Also, if the theory is symmetric with respect to time, you'd expect merger as well as splitting, since the former is just the time reversal of the latter – isn't QM supposed to have T-symmetry? Does MWI have T-symmetry?

thfuran 4y ago

>But if you are going to say that - why describe it as a “split”, as opposed to two separate universes which happen to identical in contents up to some point, non-identical thereafter? But they are (presumed under this model to be) splitting. You posited a case where two later happen to be identical, but that doesn't mean they merge. You'd just have two of them. >Also, what you say about dollars is true because they have certain properties - effectively they have two different criteria of identity, one economic, the other physical. What is the criterion of identity for universes/branches? I'd guess that there is none, like electrons. But though those are even more indistinguishable than dollars, you can still have two of them.

skissane 4y ago
> But they are (presumed under this model to be) splitting. Okay, but what's the actual model here? Let's talk about two different versions of many-worlds: Version 1: Universes splitting Version 2: No "splitting" per se ever actually occurs, universes are identical up to time t, different thereafter Is there any difference between 1 and 2 from a physics perspective–any difference in the maths, or in conceivable results of observation or experiment? Or are they just different ways of wording it? A metaphysical/philosophical difference, but not an empirical/mathematical one? Also, if the theory is symmetric with respect to time, you'd expect merger as well as splitting, since the former is just the time reversal of the latter – isn't QM supposed to have T-symmetry? Does MWI have T-symmetry?