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- Path: sparky!uunet!ogicse!das-news.harvard.edu!husc-news.harvard.edu!husc8!mcirvin
- From: mcirvin@husc8.harvard.edu (Mcirvin)
- Newsgroups: sci.physics
- Subject: Re: Uncertainty Principle [T.Bollinger => LONG]
- Message-ID: <mcirvin.715709157@husc8>
- Date: 5 Sep 92 16:05:57 GMT
- Article-I.D.: husc8.mcirvin.715709157
- References: <1992Sep4.170847.235@prim> <1992Sep5.071519.16554@asl.dl.nec.com>
- Lines: 37
- Nntp-Posting-Host: husc8.harvard.edu
-
- terry@aslws01.asl.dl.nec.com (Terry Bollinger) writes:
-
- >THE FOURIER TRANSFORM INTERPRETATION OF QUANTUM UNCERTAINTY
-
- [nice explanation thereof deleted]
-
- This is the right way to see the existence of an uncertainty principle
- *for position and momentum*. For other things, such as various
- components of spin, this kind of picture no longer works. Remember that
- the spatial wave function, with its single phase and amplitude, describes
- only the spatial degrees of freedom of a particle; to describe spin you
- have to put a spinor into the wave function as well, and then you can
- get uncertainty relations that have nothing to do with Fourier duality.
- The important thing is that the associated operators don't commute. What
- you've really shown is that the position and momentum operators don't
- commute, but there are other kinds of non-commutation as well.
-
- >SIZE ASYMMETRY OF MATTER IN SPACE/MOMENTUM UNIVERSES
-
- >The two relationships are seen in the size of our universe. If you truly
- >tried to build a universe that was "symmetrical" in its distribution of
- >paticle memberships between Space space and Momentum space, it would
- >instantly go ka-BLOOEY and expand drastically into the Space side of things.
- >Why? Because it's cheaper that way -- the long intial corkscrews in Momentum
- >space would act like very energetic springs trying to collapse back together,
- >and in the process of doing so they would cause an explosion in the no-cost-
- >to-expand corkscrews of regular Space.
-
- I'm not sure about this bit. Remember that although the universe is
- very large, most of the matter in it is fairly well-localized-- the
- wave functions of electrons are a few Angstroms big, and those of
- nuclear particles are smaller still. The key is that in a bound system,
- like an atom or a nucleus, there *is* a cost associated with spreading in
- position space-- it's the binding energy.
-
- --
- Matt McIrvin, Cambridge, Massachusetts, USA
-