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From: ogil@sphinx.uchicago.edu (Lord Julius)
Newsgroups: sci.philosophy.tech
Subject: Re: Aspect Experiment and Meaning of QM
Message-ID: <1828@sphinx.uchicago.edu>
Date: Tue, 26-May-87 01:55:14 EDT
Article-I.D.: sphinx.1828
Posted: Tue May 26 01:55:14 1987
Date-Received: Wed, 27-May-87 00:45:17 EDT
References: <1275@cci632.UUCP> <766@klipper.cs.vu.nl> <650@pbhyc.UUCP>
Reply-To: ogil@sphinx.UUCP (Lord Julius)
Organization: University of Chicago, Dept. of Physics
Lines: 62
Keywords: aspect light faster

[I removed sci.physics from the newsgroups line because this topic
has already been beaten to death there about two months ago].

In article <650@pbhyc.UUCP> djo@pbhyc.UUCP (Dan'l Oakes) writes:
>
>To believe that its spin was determined by your observation of the primary
>half-wit is sheerest anthropocentrism:  the belief that the universe must
>conform to the state of Man's knowledge.  The best reply to that belief was,
>and remains, Sir Arthur Eddington's famous remark that "the universe is
>not only queerer than we imagine -- it is queerer than we can imagine."  Or
>words to that effect; I'm quoting from imperfect memory.

I won't comment on the Aspect experiment because I haven't studied it, but Mr.
Oakes' statement quoted above is basically wrong.  The universe _does_ conform
to the state of man's knowledge (a very frightening thought on one level).
The best example that comes to mind is an interference experiment.  This example
was given in _QED_, by Richard Feynman.

If one takes a light source and filters it so only one photon emerges at a
time, aims it at a photon detector, and places a solid barrier with two very
small holes in it between the source and the detector, like this:
				|
				|
			     (hole)
	source>			|		<detector
			      (hole)
				|
				|

the probability that the detector will detect a photon varies depending on its
position (i.e. at one point it might detect the photon 4% of the time,
at another point never).  If the probability of detection is plotted vs. the
position of the detector one gets an interference pattern.

Now put two detectors in the holes, so you know which hole the photon went
through on its way to the detector.  Now the probability that the original
detector detects the photon is _independent of its position_!  Yes, just
placing those two detectors in the holes changed the results, demonstrating
that the universe does conform to the state of man's knowledge, at least
in one sense.

To make things even worse, if the two detectors in the holes are unreliable --
they don't always detect a photon -- the interference pattern is a combination
of the original, no detectors pattern and the unvarying, perfectly reliable 
detectors pattern.  This one never fails to amaze and confuse me.  It just
goes to demonstrate that our normal intuition is quite often (perhaps mostly)
wrong when it comes to the realm of subatomic physics. 

If you want a good, non-technical explanation of one field in subatomic
physics, I recommend _QED_.  Feynman doesn't water down his explanations of
quantum electrodynamics, he just leaves out the math that lets you predict
things.  He is delighted by the fact that nature is more bizarre than we
can imagine, and he makes much of the point that modern physics doesn't
explain _why_ the universe works the way it does, it just tells us _how_
it works.  A wonderful book.


-- 
__________________________________  Display me Aeolus above 
Brian W. Ogilvie               	 |    Reviewing the insurgent gales
...{uwvax,hao}!oddjob!sphinx!ogil|  Which tangle Ariadne's hair
    ogil%sphinx@uchicago.BITNET	 |    And swell with haste the perjured sails.