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From: flink@umcp-cs.UUCP (Paul V Torek)
Newsgroups: net.physics
Subject: Blimey, Rimey!
Message-ID: <2629@umcp-cs.UUCP>
Date: Mon, 23-Dec-85 14:03:05 EST
Article-I.D.: umcp-cs.2629
Posted: Mon Dec 23 14:03:05 1985
Date-Received: Tue, 24-Dec-85 22:11:36 EST
References: <117@ucbmiro.ARPA>
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Organization: U of Maryland, Computer Science Dept., College Park, MD
Lines: 57
Summary: Ultra-belated reply on QM, Many-Worlds

Many moons ago, Ken Rimey posted an explanation/endorsement of the Many
Worlds interpretation of QM.  I tried to mail to him, but no luck.  I
noticed he's still around today, so here's my reply:

>You may have noticed that, in describing a theory in which the
>universe is deterministic and measurement is not a fundamental
>idea, I sure refer to measurement and probability a lot.  The
>point is that these ideas are involved only in the interpretation
>of the mathematical object that represents the state of the universe.
>They don't clutter up the theory of how to calculate that object.
>In particular, in the Many-Worlds view, wave functions don't "collapse".

Then what do measurements measure, in the Many-Worlds view?  Are "position"
and "momentum" fictions?

>Many-Worlds is indistinguishable experimentally from the more popular
>variant of quantum mechanics that talks about wave functions
>collapsing.  Then why is Many-Worlds interesting?  Indeed, Many-Worlds
>is less a theory than an argument that some of the conventional
>postulates of quantum mechanics are not fundamental. 

What do you mean, "some of the ... not fundamental".  And why is it
important to argue that point?

>  Many working
>physicists will, if you ask them, express doubt as to whether quantum
>mechanics is really applicable to cats and such. 

And one interpretation of QM has it that it doesn't, because macroscopic
objects like cats and such involve entropy (i.e. when the cat dies, entropy
is increased, thus an irreversible process has taken place).  Why should
I prefer the Many Worlds view to this view?  (Or, if you don't think we
have to choose a single view:  why should I even *bother* with the Many
Worlds view.)

>On the other hand, it is often suggested that quantum mechanics is
>incomplete.  The problem is that the rules for how a system changes
>state when it is measured seem to be central features of quantum
>mechanics, and yet these rules make explicit reference to measurement,
>as if the observer played a distinguished role in the universe.  This
>difficulty motivates much crackpot physics.  

Yeah, the "Copenhagen Interpretation", but there's a similar view
(which I just described) that does not give comfort to the crackpots.

On the "incompleteness" charge -- I assume you refer to the EPR thought-
experiment -- how does the Many Worlds view answer the misgivings of
EP&R?  How about the Bell theorem (does that pose any problem for the
Many Worlds view)?

>					Ken Rimey
>					rimey@dali.berkeley.edu

--Paul V Torek, umcp-cs!flink

P.S.  Sorry for the tone of some questions, but I'd really like to get to
the bottom of the business of interpreting QM.