From: burns@latcs1.lat.oz.au (Jonathan Burns)
Newsgroups: rec.arts.sf.science
Subject: Re: Parallel Universes
Date: 15 Apr 92 04:04:37 GMT
Organization: Comp Sci, La Trobe Uni, Australia


In article <29EB7073.1817@noiro.acs.uci.edu> cortese@hepxvt.ps.uci.edu
 (Janis Maria Cortese) writes:

>> alberti@mudhoney.micro.umn.edu (Albatross) writes:
> >
>>> Schroedinger's Cat is one example of different universes:  a cat is placed
>>> in a "black box" from which nothing can escape unless the box is opened.
>>> With the cat is a sample of radioactive iodine with a short half-life and
>>> a device which, upon detecting a radioactive emission from the iodine,
>>> releases a poison gas which kills the cat.  The box is closed and left
>>> closed for a time sufficient that the chance of such a radioactive emission
>>> is exactly 50/50.
>
>>> When the box is opened, two universes split off -- one in which the cat is
>>> dead, the other in which the cat is alive.  Quantum physicists like to point
>>> at the unopened box and crow that the box contains a cat which is exactly
>>> half-dead, but none of them are willing to get in the box in order to report
>>> precisely what being half-dead feels like.

[Janis says:]

> Physics says absolutely NOTHING about "universes splitting off"
> ANYWHERE.  It says only that, through the act of observation, we have
> influenced the universe in some way -- that you can't say that you
> "just" observe anything.  It says that the observer and the observed
> interact with one another through the act of observation.  "Splitting
> universes" are a science-fiction extension of this idea, the same way
> the Special Relativity was "extended" by some sci-fi crackpot to mean
> "Oh, we travel backward in time when we go faster than light!"
> (I'm using sci-fi in the most denigrating way possible here.)
> 
> Try to keep track of what physics says, and what "sci-fi" says physics
> says.  Splitting universes are a nice idea, but (unfortunately, because
> physicists are intrigued by the idea, too) there is NO THEORETICAL OR
> EXPERIMENTAL EVIDENCE FOR IT.

Excuse if I contradict.

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.

Also, on the quantum-measurement scale, universes can rejoin. The
double-slit experiment _can be interpreted as_ the generation of
two worlds. In each, a photon goes through one or other slit. At
the receiving screen, there are many outcomes for photon position,
and each of these is observed in some world, and each of these
worlds is a coalescence of the two worlds mentioned above.

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.

Besides, the box will radiate, and give the game away.

An expressed reaction to all this (I forget the source) is that the
Many-Worlds view is just too much "metaphysical baggage" to carry.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jonathan Burns        | Dawgunnit! TOTAL ECLIPSE! And just when I was
burns@latcs1.lat.oz.au| getting set for a quiet night of "Moon Hating".
Computer Science Dept | Oh well, might as well get back on the beat...         
La Trobe University   |    - Geo. Herriman
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