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From: emh@bonnie.UUCP (Edward M. Hummel)
Newsgroups: net.physics
Subject: Re: Left, Right, and Mirrors
Message-ID: <495@bonnie.UUCP>
Date: Fri, 7-Jun-85 19:29:14 EDT
Article-I.D.: bonnie.495
Posted: Fri Jun  7 19:29:14 1985
Date-Received: Sat, 8-Jun-85 03:52:10 EDT
References: <235@sask.UUCP>
Organization: AT&T Bell Laboratories, Whippany NJ
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>An interesting, related bit of trivia is the fact that "left" and
>"right" are concepts which can only be communicated among two
>parties if both parties can "see" each other.  In other words, if
>we ever contact an alien civilization which is so far away that we
>can communicate with them only by radio, and there is no astronomical
>object which both we and they can view, then we would have no way to
>tell them what we mean by "left" as opposed to "right"--or, for that
>matter, how to tell the north pole of a magnet from the south pole.

	Parity violation in the weak interactions has been known to
exist since the mid-1950s.  (Yang, Lee, Wu, et al.)  Just tell your alien
to measure the spin of any neutrino he has handy.  All neutrinos in the
universe seem to be "left-handed" (helicity=-1; spin counter-clockwise
as they travel away from you; etc.).  All anti-neutrinos seem to be
"right-handed".  This certainly gives you a way to define "clockwise" as
opposed to "counterclockwise", or "left" as opposed to "right".
	Well, you ask, how can I be sure he is looking at a neutrino
and not an antineutrino?  CP violation has been around since 1964.
(Cronin, Fitch, Christenson, et al.)  Just tell your alien to study the
decay of neutral K mesons.  By comparing results you can unambiguously
define the particle K0, as opposed to its antiparticle, K0-bar.
This gives you a way to define "matter" vs. "antimatter", and thus
neutrinos vs. antineutrinos.
	I haven't read Gardner's book so I can't comment on what he
intended.

					Ed Hummel