From: epfaith@twinkies.berkeley.edu (Edward Paul Faith)
Newsgroups: rec.arts.sf.science
Subject: Re: Parallel Universes
Date: 15 Apr 1992 11:14:04 GMT
Organization: U.C. Berkeley Math. Department.
NNTP-Posting-Host: twinkies.berkeley.edu

In article <1992Apr15.040437.16828@latcs1.lat.oz.au>, burns@latcs1.lat.oz.au 
(Jonathan Burns) writes:

]There _is_ a theory of splitting universes, generally known as Everett's
]Many-Worlds Interpretation. It has been fairly deeply reasoned through.
]It stands up as a _consistent_ interpretation of quantum measurement.
]
]Its problem, inasfar as it has one, is that it adds no predictions
]which would allow us to distinguish it experimentally from, say, the
]Copenhagen Interpretation in which the measuring event somehow chooses
](at random) one outcome from the many which are superimposed in the
]wave-function left behind by the experimental setup. So yes; there is
]no experimental evidence.
 
The many-worlds interpretation has some advantages.  It gets rid of
the bugaboo of God playing dice with the universe.  It returns to the
universe an out-thereness, when other views come dangerously close to
saying that there is no clear objective world.  It lets things happen
independently of whether they are watched or not.  In short, it is
very appealing in some important ways.  Certainly it is not testable,
but neither are any competing interpretations.  Certainly it allows
there to be a superposition of worlds, but don't all interpretations
effectively allow this at least on the subatomic level?  In fact, its
beauty is that, while the other systems nervously chop off the extent
of superposition at the subatomic level (and are not really sure when
to chop it off, only that it must be chopped off before it becomes
macroscopic), the many-worlds interpretation allows this superposition
to continue until there is a clear empirical need for it to end, and
as it turns out there is no such need.  In particular, the "collapse of
the wave function", which would seem to signal the point at which
superimposed worlds become one again, is not useful here, because
the same experimental results are explained by the collapse occurring
at different times.

]The Cat is not on the QM scale, obviously. The Cat Paradox is a
]way of asking, "What can it be that we _mean_ by measuring
]apparatus (or observer), when the apparatus is itself a system
]we have to measure, to see what it reads?" 
]
]The usual exploration of the question is that two humungous skeins
]of worlds emerge from the quantum trigger that kills/doesn't kill
]the cat, and that it is unlikely to the power of (molecules per cat)
]that all the right molecules will stay unresolved for it to remain
]ambiguous to the very moment of the box opening whether we are in
]a live-cat world or a dead-cat world.
]
]To be a bit more specific, a cell for example will live or die
]depending on whether it gets enough oxygenated red corpuscles.
]For a particular r.c. to be in two places, each of its molecules
]would need to be in those two places, nearly exactly. Each
]independently, and all at once. Unlikely to the power of (molecules
]per r.c.). It seems that mundane outcomes like live-cat and dead-cat
]are just thermodynamically far more likely than superpositions of
]such outcomes.

I disagree with this feeling.  Consider the following:

Each molecule of a cat is in two places at
once (say), but each appearance of the molecule is "tagged", so that
there is an appearance tagged "A" and one tagged "B".  The way
superposition works on the macro scale, the A molecules will form
one cat, and the B molecules will form the other cat.  There is no
mixup, and the B molecules will hang together just the way a cat
is supposed to, and so will the A molecules.  The laws of physics
will prevent the A molecules and the B molecules from getting mixed
up.  There is no problem with thermodynamics, other than the
problem of how each cat alone will hang together.  By analogy,
two cats are not much harder to own than one cat.  When I buy my
second cat, it does not confuse itself with the first cat and
dissolve.