On Mon, 23 May 2005, Brent Meeker wrote:

-----Original Message-----
From: Patrick Leahy [mailto:[EMAIL PROTECTED]

NB: I'm in some terminological difficulty because I personally *define*
different branches of the wave function by the property of being fully
decoherent. Hence reference to "micro-branches" or "micro-histories" for
cases where you *can* get interference.

Paddy Leahy

But in QM different branches are never "fully decoherent".  The off axis terms
of the density matrix go asymptotically to zero - but they're never exactly
zero.  At least that's standard QM.  However, I wonder if there isn't some
cutoff of probabilities such that below some value they are necessarily,
exactly zero.  This might be related to the Bekenstein bound and the
holographic principle which at least limits the *accessible* information in
some systems.

I'm talking about standard QM. You are right that my definition of macroscopic branches is therefore slightly fuzzy. But then the definition of any macroscopic object is slightly fuzzy. I don't see any need for a cutoff probability... the probabilities get so low that they are zero FAPP (for all practical purposes) pretty fast, where, to repeat, you can take FAPP zero as meaning an expectation of less than once per age of the universe.

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