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From: davidson@sdcsvax.UUCP (Greg Davidson)
Newsgroups: net.physics
Subject: Re: QM and Multiple Worlds
Message-ID: <1094@sdcsvax.UUCP>
Date: Tue, 10-Sep-85 03:10:12 EDT
Article-I.D.: sdcsvax.1094
Posted: Tue Sep 10 03:10:12 1985
Date-Received: Thu, 19-Sep-85 00:52:14 EDT
References: <486@talcott.UUCP> <1049@sdcsvax.UUCP> <565@baylor.UUCP>
Reply-To: davidson@sdcsvax.UUCP (Greg Davidson)
Distribution: net
Organization: EECS Dept. U.C. San Diego
Lines: 141
Keywords: Quantum Mechanics, Multiple Worlds, Reality
Summary: Problems raised by Multiple Worlds cannot be lightly dismissed.

In an earlier article, I presented problems with the multiple worlds
theory (MWT) as an interpretation of quantum mechanical reality.  Some
of the problems are old, first presented by Bohr, Heisenberg, and other
early QM theorists.  Some were unconventional ideas suggested by me,
with inspiration from a variety of sources.  I asked for participation
in exploring this often baffling topic.  These problems are as much
philosophical as physical, as they are constrained by the latter, but must
be addressed using the tools of the former.  It seems like a good game
we can all play, if we're careful to stick to the rules and tread
cautiously - this territory is very slippery.

Unfortunately, the two postings to reply so far have attempted to
dismiss the matter rather than address it.  I'll use the most
recent as an example.  If you read it through, I think you'll see
that it was not a responsible posting, although it partially addresses
some of my points.  The author's text is indented with tabs.  My
original text indented with >'s.

	From: peter@baylor.UUCP (Peter da Silva)
	Subject: Re: QM and Multiple Worlds
	Date: 28 Aug 85 11:34:34 GMT
	Organization: The Power Elite, Houston, TX

> issue.)  A MWT unconstrained by any laws of physics is preferable,
> because simpler, to one incorporating laws of physics, hence MWTs
> directly do violence to the notion of physics.  Now let me answer some

	How on earth do you figure that an unconstrained MWT is simpler
	or preferable. The fact that an unconstrained MWT produces a
	different observed universe than the one we see here is enough
	to reject that hypothesis.

As follows.  The conventional MWT, as I understand it, says that each
quantum mechanical event splits the universe into a superposition of
states, one for each possible outcome.  As observers, being restricted
to one universe/state, we can observe only one outcome.  We infer the
existence of superpositions by their effect on the probability of
occurrance of events; yet, those superpositions ``collapse'' or ``branch
away from us'' (depending on which interpretation you're using) as
soon as they interact with our process of observation .  Yet all
outcomes possible by physical law actually occur in some universe/state.

Because we cannot see beyond our own universe/state, we actually have
no idea of the true probability of events.  We could just happen to be
on a very low probability worldline in the state space of branching
universes.  The universe we wind up in always has a probability value
of 1, since we can only observe it after the fact.  We cannot predict,
since all predicted outcomes always occur.  (If you're familiar with
the Anthropic Principle in Cosmology, the argument here has a similar
[unpleasant] flavor.)

We need only extend this line of reasoning a little bit to see that
the presence of physical laws constraining the generation of states
is also unobservable.  Given branching universes, if all possible
outcomes of events were to occur, with no physical laws to constrain
them, there would be observers along worldlines inferring all kinds
of physical laws.  Imagine us as such observers, with a deceptive
history implying certain physical laws, now being presented with
evidence of multiple worlds.  What magnificent irony!

> Doug Gwyn wrote:
> > [1]  Not all the alternate worlds are equiprobable!  [2]  There is no
> > observable difference between the alternate-worlds QM and the
> > Copenhagen QM.
> [1] Maybe, but irrelevant to my point.  Also, Occam's razor would suggest
> abandoning any theory of structure in the generation of successor worlds.

	I see. What's happened is that you don't understand Occam's
	Razor, so you're applying it too broadly. Occams razor simply
	says that out of (n) hypotheses you should select the simplest
	and most testable hypothesis so that you know when you're wrong
	as soon as possible. It doesn't say the simples explanation is
	right, as you (and the creationists) seem to think. Since your
	view of how the EWG multiple worlds model works predicts a
	complete breakdown of causality we know it's wrong (or have you
	observed this breakdown of causality?). The next thing to do is
	look at the actual EWG theory. That I'll leave to someone
	better versed in it than I.

The principle you mention sounds like a nice principle for guiding
experimentation, but bears no relationship to Ockham's razor.  I just
checked the Encyclopedia of Philosophy (page 8-307) and found
that though I'd spelled his name wrong, I understood his principle
quite well.  They quote him as saying: ``What can be done with fewer
[assumptions] is done in vain with more.''  They go on to say:  `The
principal use made by Ockham of the principle of parsimony was in the
elimination of pseudo-explanatory entities....'  Well, in a MWT system,
physical laws become pseudo-explanatory entities.  No observation can
support their existence.

I object to your insulting style of argument.  You attack my argument
by belittling my understanding and comparing me with creationists!
Yet you neither check my argument carefully nor offer an alternative.
The problem of how to interpret quantum mechanical reality is a real
problem.  Great physicists tried hard to reject QM because of it.  Now
that we have been forced to accept QM, we must grapple with it.

> For some very interesting reading on these issues, I recommend some
> fictional stories designed to present relevant thought experiments.
> The earliest I know of are Jorge Luis Borges' stories ``The Garden
> of Forking Paths'' which explores the nature of MWTs, and ``The Library
> of Babel'', which explains how all possible writings (read `universes')
> can be generated by a finite library of books (read `world states').
> Both of these can be found in his collection ``Labyrinths'', New
> Directions Pub. Corp., 1964.

	Last I heard Borges wasn't a physicist.

He was not.  I recommend his stories for their clear presentation of
the philosophical consequences of certain physical models; models
which physicists have suggested, but which have neither been accepted
nor rejected.  You will not find the answers to these problems in
existing writings by physicists, you will only find the questions there.

> A more recent, and more devastating exploration of MWTs is Larry
> Niven's story ``All the Myriad Ways'', in his collection by the same
> name [Ballantine Books, 1971], and probably in other collections as
> well.

	Niven never postulated impossible worlds, as you do. His MWT is
	vanilla EWG. His objection is that EWG makes volition
	meaningless. He's probably right, but so does determinism.

His story is particularly devastating because it sticks closely to the
vanilla MWT, yet obtains bizarre results.  I'm glad you agree that such
models pose serious problems for volition.  I would not agree that
determinism does.  For clear arguments supporting the compatibility
of determinism and volition, I recommend Daniel Dennett's new book
``Elbow Room; the kind of free will worth having.''  Its published
by MIT Press.  Dennett is a professional philosopher who pays close
attention to the work of physicists and often collaborates with the
physicist and computer scientist Douglas Hofstadter.

So how about it folks?  Am I the only one disturbed by the philosophical
implications of QM?  Do you think that physics books have the answers?
If you see a hole in my arguments (or Einstein's, for that matter, but
check carefully if you think you see a hole in his!), please show me.  If
I've misunderstood the claims of QM, let me know that too.  If you have
another interpretation which avoids some of these problems, lets have it!

_Greg Davidson			Virtual Infinity Systems, San Diego