Re: subjective reality

From: <kurtleegod.domain.name.hidden>
Date: Thu, 25 Aug 2005 14:40:25 -0400

Hi Serafino,

 I am not sure I can give you a decent answer to your
 query since I am not an Everrettista myself and so a lot
 of their subtleties escape me. But I think they would
 probably remind you that they believe that superpositions
 only give way to more superpositions so that, after each
 measurement event there will be more branches added
 to each of the original two and you will find yourself on
 the one that is factored out by the successive series of
 eigenvalues you detect. What he will not tell you is
 why you find yourself on that particular one since they
 were all equiprobable to start with. If you insist they
 will say that quantum mechanics does not tell you that
 either, and than you will say: "but regular QM does not
 introduce many branches!" and your head will start
 spinning, etc...


 Godfrey Kurtz
 (New Brunswick, NJ)

 -----Original Message-----
 From: scerir <scerir.domain.name.hidden>
 To: everything-list.domain.name.hidden
 Sent: Wed, 24 Aug 2005 23:38:05 +0200
 Subject: Re: subjective reality

 Godfrey:
 'MWI + Projection postulates should reproduce
 regular Copenhagenian QM since MWI is basically
 QM - Projection Postulates!'



 Imagine a superposition like this

 |'spin_z' +1> |'detector' +1> +
 |'spin_z' -1> |'detector' -1>

 It describes a superposition of spin up/down
 states, and the entagled (or relative) states of a
 detector.

 Now imagine a second - whatever, human? - device,
 to measure a specific observable of the above
 superposition.

 Let this observable be such that the ray generated by
 the above superposition state is an eigenspace of this
 observable, corresponding to a definite eigenvalue,
 the eigenvalue 'yes'. Since neither component of
 the above superposition state lies in the eigenspace
 of this observable, this observable fails to commute
 with the 'spin_z' observable, and fails to commute
 with the 'detector' observable.

 We can write (canonically) ...
 |'z-spin' +1> |'detector' +1> |yes> +
 |'z-spin' -1> |'detector' -1> |yes>

 In a MWI, a world should instantiate an eigenvalue
 for an observable if the superposition term associated
 with that world is an eigenstate of the observable
 corresponding to that eigenvalue.

 So, after the (second) measurement, what would
 an Everettista write?

 This one?

 |'z-spin' +1> |'detector' +1> |?> <=> world A
 |'z-spin' -1> |'detector' -1> |?> <=> world B

 (Since, in each world, the observable measured by
 the second - whatever, human? - device does not
 commute with the 'spin_z' observable, so it has no
 predeterminate value, that is to say that the outcome
 of the (second) measurement must occur by chance.)

 Or this one?

 |'z-spin' +1> |'detector' +1> |yes> <=> world A
 |'z-spin' -1> |'detector' -1> |yes> <=> world B

 (In this case the fact that the second device would later
 record the state |yes> seems to be fixed ... in advance
 of the measurement itself. And this is magic. White Rabbit?
 What else?)

 Godfrey:
 'I believe that YD is incompatible with
 the whole formalism of QM which I don't quite
 think is simply reducible to Unitary Evolution
 plus Collapse, by the way.'

 Maybe.

 s.

 [It is too late here, I cannot write more, and I cannot
 check the above :-)]








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Received on Thu Aug 25 2005 - 14:46:09 PDT