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- From: mcirvin@husc8.harvard.edu (Mcirvin)
- Newsgroups: sci.physics
- Subject: Re: Aristotle and the Modern Physicist
- Message-ID: <mcirvin.712271293@husc8>
- Date: 27 Jul 92 21:08:13 GMT
- Article-I.D.: husc8.mcirvin.712271293
- References: <mcirvin.711906105@husc8> <1992Jul24.024619.28944@nuscc.nus.sg> <24JUL199220140602@zeus.tamu.edu> <151aebINNkmb@agate.berkeley.edu>
- Lines: 44
- Nntp-Posting-Host: husc8.harvard.edu
-
- aephraim@physics.Berkeley.EDU (Aephraim M. Steinberg) writes:
-
- >Anyway, I'm not convinced that the center of mass of a system can be
- >different in two parts of a coherent superposition.
-
- Trivially, it can. Just look at the different position
- eigenstates of the expanding wavefront of an electron. As
- for magnifying the effect by using a Schrodinger's cat type
- apparatus to shove weights around, I think your objection
- about the center of mass is sound.
-
- >I'd be slightly
- >more inclined to believe that you could superpose two distributions with
- >different QUADRUPOLE moments or something like that, affecting more subtle
- >things than the simple force on a nearby object.
-
- The aftermath of a cat-box experiment probably shouldn't be
- called a *coherent* superposition in the modern sense of the
- term, but you could indeed rig one so that the quadrupole
- moment would depend on the outcome. Just replace the hammer
- above the poison jar with a mechanism that pushes apart two
- large weights when the decay occurs. This *would* affect the
- fall of a nearby object, if it's close enough. Imagine that
- it's near the end of the box where one of the weights ends up
- in the event of a decay.
-
- >The reason I really respond is just because it's amusing that you come
- >up with this particular example. I wonder if you're aware that it's exactly
- >what Aharonov uses in one of his latest proposals? In conjunction with his
- >theory of "weak measurements," he uses such a system, in which the rate of
- >a clock depends on the state of the mass shell and can thus be placed in
- >a superposition state, to create a time machine.
-
- It is quite an ingenious proposal. Now that you mention it,
- let me correct a blatant error in the recent Scientific
- American article about measurement theory: the "time machine"
- is not the usual variety in which one can travel into the
- past and violate causality. Rather, it's a device for
- reversing the time evolution of a system, returning it to
- a younger state. It's not so much a time machine as a
- kind of rewind button.
-
- --
- Matt McIrvin mcirvin@husc.harvard.edu
-