home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!zaphod.mps.ohio-state.edu!cs.utexas.edu!sdd.hp.com!usc!rpi!bu.edu!nntp-read!merritt
- From: merritt@macro.bu.edu (Sean Merritt)
- Newsgroups: sci.physics
- Subject: Re: Yet Another Preposterous Post
- Message-ID: <MERRITT.93Jan7104818@macro.bu.edu>
- Date: 7 Jan 93 15:48:18 GMT
- References: <HAGERMAN.93Jan6174824@rx7.ece.cmu.edu>
- Sender: news@bu.edu
- Distribution: sci
- Organization: Boston University Physics Department
- Lines: 74
- In-reply-to: hagerman@ece.cmu.edu's message of 6 Jan 93 22:48:24 GMT
-
- In article <HAGERMAN.93Jan6174824@rx7.ece.cmu.edu> hagerman@ece.cmu.edu (John Hagerman) writes:
-
-
-
- paul@mtnmath.uucp says:
-
- > Consider a singlet state photon pair that was emitted from a distant
- > galaxy. The photon paired with this has been traveling in the
- > opposite direction for billions of years. QM predicts that these two
- > are still connected. If you detect one photon in this pair by
- > looking at the night sky with polarizing sun glasses you will
- > instantly impose a constraint on the polarization of the other
- > photon billions of light years away according to existing theory. To
- > me such a prediction requires extraordinary justification.
-
- # "Requires" is pretty strong, and invites a reactionary response. But
- # that's why sci.physics is so much fun, right?
- #
- # Here's the chain of thought that I think leads to posts about collapse
- # being real. "QM is a good theory, but it has a flaw (it includes the
- # concept of instantaneous collapse, which is cause for concern). But
- # rather than consider it a flaw, what happens if we make it a postulate
- # and explore the implications? That's what Einstein did with the speed
- # of light, right?" The first step is easy, and leads to posts. The
- # second step is hard; perhaps beyond most readers of sci.physics, but
- # surely not beyond the experts. So what do the experts say? If I have
- # understood the discussion, instantaneous collapse does *not* imply the
- # ability for ftl communication of information, so there is no violation
- # of relativity. (Is this related to discussion about the difficulty in
- # defining/measuring delays?) What other implications are of interest?
-
- I've been staying out of this one but there is an approach offered
- by Aharonov while controversial, does offer some hope of a resolution
- to the problems of wave function collapse.
-
- let
-
- Psi1 = exp [ - i Int(t1 ->t)d(tau) H(t) ] |A=a> = |P1>
-
- that is operator with non degen. eigenvalues produced a measurement
- O|A> = a|A> at t=t1.
-
- at later time t=t2
-
- a eigenvalue was produced from a wavefuntion <B=b| having the form
-
- Psi2* = <B=b| exp [ -i Int(t ->t2)(dtau) H(t)] = <P2|.
-
-
- Now Aharonov and his collegues define a NEW concept which the call
- a "weak" measurement using these two wave functions.
-
- Given that |P1> was pre-selected(prepared) and that <P2|
- was postselected an expectation value
-
- _ <P2|A|P1>
- Aw = ---------
- <P2|P1>
-
- is defined as weak measurement and does not collapse the wavefunction.
-
- It starts to get weird after that and I think people should
- read the Papers for themselves:
-
- See Y. Aharonov,L. Vaidman Phys Rev A 41,11(1990)
-
-
- -sjm
-
-
- --
- Sean J. Merritt | "Every revolt is a cry of innocence
- Dept of Physics Boston University| and an appeal to the essence of being."
- merritt@macro.bu.edu | Albert Camus, The Rebel
-