Re: Quantum Computers [was Read any good books lately?]
Tue, 17 Aug 1999 12:54:06 -0700

John Clark, <>, writes:

> <> On  Tuesday, August 17, 1999 Wrote:
>     >This points up an ambiguity in the MWI, which is, when do other universes
>     >exist?  That is, when does the universe split?  You can give two answers.
>     >One is that it splits whenever there is an alternative which is explored
>     >in the quantum realm.  The other is that it splits whenever there is
>     >a measurement which causes what would conventionally be called wave
>     >function collapse.
> I've never heard of that second version of the MWI before, I always
> thought it's entire advantage was that it didn't have to explain what
> a measurement is.

As an example of the second interpretation, see the Many-Worlds FAQ,

: Q7 When do worlds split?
: ---------------------
: Worlds irrevocably "split" at the sites of measurement-like interactions
: associated with thermodynamically irreversible processes. (See "What
: is a measurement?") An irreversible process will always produce
: decoherence which splits worlds. (See "Why do worlds split?", "What is
: decoherence?" and "When does Schrodinger's cat split?" for a concrete
: example.)
: [...]
: The advantage of linking the definition of worlds and the splitting
: process with thermodynamics is the splitting process becomes
: irreversible and only permits forward-time-branching, following the
: increase with entropy. (See "Why don't worlds fuse, as well as split?")

John's version is the second one above, Mike Price's (author of the FAQ) is the first. Both versions are fairly widely used.