X-Message-Number: 20903
Date: Fri, 17 Jan 2003 20:27:42 -0700
From: Mike Perry <>
Subject: Many Histories versus Many Worlds

Robert Ettinger, ##20890:

>David Deutsch thinks the "multiverse" is deterministic, although a
>particular "universe" is not from the point of view of its inhabitants; but
>he also thinks that, in any universe, the past is fixed. If he is wrong, and
>there are "many histories" instead of many worlds, that's a different kettle
>of fish.

This can be interpreted in more than one way, and I'm not sure what is 
intended. Deutsch (in *The Fabric of Reality*) does note that, in a sense, 
time doesn't flow--the apparent flow of time is an artifact of how we 
observers see things. Each scenario at a particular time in a particular 
universe comprises a "snapshot" (think of one frame of a movie) that is 
unaffected by what comes before or after--or that's the way I read it. (And 
you will have to deal with certain problems posed by relativity, to decide 
just what to include in your "snapshot"--that is to say, which events at 
different points in space are considered simultaneous. It appears there are 
many possible overlaps or points in common with different snapshots.) In 
any case, that "the past is fixed" in a given universe is not the same as 
saying that history has a unique timeline. Under the many-worlds 
formulation worlds can split but can also fuse. (A "world" also is not 
necessarily a whole universe but can be a localized region.) The fusion, if 
it occurs, will obliterate any differences in histories between the 
components that fuse, thus, I think, rendering their distinguishing pasts 
unrecoverable. The loss of information inherent in this fusion in effect 
makes the past ambiguous. It seems, then, that, along with many worlds, 
each world will, as a rule, have many histories.

Mike Perry

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