From: gts (gts_2000@yahoo.com)
Date: Wed Nov 27 2002 - 15:08:37 MST
--- scerir <scerir@libero.it> wrote:
> gts:
> > [...] under the Many Worlds interpretation of
> > QM, the observer of an experiment with n possible
> > outcomes splits into n different alternates at the
> > moment that the measurement changes the state of
> > the observer(s), such that each alternate observer
> > is created in a different state [...]
...
> Note, also, that the RSI speaks of 'compositions'
> of 'subsystems', which is different from and more
> general than 'measurements' by observers.
Yes, and I understand the observer as a subsystem.
> So: just measurements (irreversible) or also quantum
> interactions (not irreversible) can cause the
> splitting of the worlds? [Imo quantum interaction
> could also cause a sort of de-splitting, or fusion
> of worlds, because of the unavoidable interference].
This question is treated in the faq I referenced
previously at www.hedweb.com/everett/everett.htm#fuse
*****
Q17
Why don't worlds fuse, as well as split?
Do splitting worlds imply irreversible physics?
This is really a question about why thermodynamics
works and what is the origin of the "arrow of time",
rather than about many-worlds.
First, worlds almost never fuse, in the forward time
direction, but often divide, because of the way we
have defined them. (See "What is decoherence?", "Why
do worlds split?" and "When do worlds split?") The
Planck-Boltzmann formula for the number of worlds (See
"How many worlds are there?") implies that where
worlds to fuse together then entropy would decrease,
violating the second law of thermodynamics.
Second, this does not imply that irreversible
thermodynamics is incompatible with reversible (or
nearly so) microphysics. The laws of physics are
reversible (or CPT invariant, more precisely) and
fully compatible with the irreversibility of
thermodynamics, which is solely due to the boundary
conditions (the state of universe at some chosen
moment) imposed by the Big Bang or whatever we chose
to regard as the initial conditions. (See "Why can't
the boundary conditions be updated to reflect my
observations in this one world?")
*****
Concerning the question whether observers split
actually, or only in terms of memory states, I like
this quote of Everett, posted near the bottom:
******
Q35 Was Everett a "splitter"?
Some people believe that Everett eschewed all talk all
splitting or branching observers in his original
relative state formulation [2]. This is contradicted
by the following quote from [2]:
[...] Thus with each succeeding observation (or
interaction), the observer state "branches" into a
number of different states. Each branch represents a
different outcome of the measurement and the
corresponding eigenstate for the object- system state.
All branches exist simultaneously in the superposition
after any given sequence of observations.[#] The
"trajectory" of the memory configuration of an
observer performing a sequence of measurements is thus
not a linear sequence of memory configurations, but a
branching tree, with all possible outcomes existing
simultaneously in a final superposition with various
coefficients in the mathematical model. [...]
****
-gts
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