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From: torek@umich.UUCP (Paul V. Torek )
Newsgroups: net.physics
Subject: Re: Blimey, Rimey (QM & Many-Worlds)
Message-ID: <408@umich.UUCP>
Date: Wed, 22-Jan-86 12:39:25 EST
Article-I.D.: umich.408
Posted: Wed Jan 22 12:39:25 1986
Date-Received: Thu, 23-Jan-86 21:46:51 EST
Distribution: net
Organization: University of Michigan, EECS Dept., Ann Arbor, MI
Lines: 54

Ken Rimey (>> > and >) writes:

>> >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".
>> 
>> >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 I mean is that it is unnecessary to postulate that wave functions
>collapse during measurements.  Measurements are ordinary physical
>interactions of matter with matter, and are adequately described by
>ordinary equations of motion.

OK, fine, except for one thing.  You speak of "a theory in which the universe
is deterministic."  Then how come, when one performs a measurement on a
"mathematical object that represents the state of the universe", the outcome
is only *probable*.  That is, given two electrons (fired in sequence through
the famous "two slits") represented by the same mathematical equation, and 
using a single measuring device, one nevertheless can get different 
measurements.

So, while this interpretation of QM may show that observers aren't so special,
I don't see how it can affirm a deterministic universe.

[Whoops!  I deleted a sentence of Rimey's here, thereby misleading my readers
by making them think I was responding to the one below.  I wasn't.
I have inserted bracketed clarifications into my own posting below to
remove the confusion]				
>> >Many working
>> >physicists will, if you ask them, express doubt as to whether quantum
>> >mechanics is really applicable to cats and such. [RIMEY]
>> 
>> And one interpretation of QM has it that it [QM] doesn't [crucially depend
>> on an "observer"], 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). [TOREK]

>That is not an interpretation of QM.  It is simply wrong.

It is?  What's your evidence?  (Or were you misinterpreting me?  What I meant
was that one could assume that wave packets collapse whenever entropy is
increased (or maybe it's, increased *by a sufficient amount*).  Thus, one
can admit wave packet collapse without deifying observers and encouraging
crackpots.)

--Paul V. Torek							torek@umich