X-Message-Number: 5275
Date: Mon, 27 Nov 1995 10:08:16 -0500
Subject: signal speed

A minor correction to John Clark's #5270:

He discusses signal speeds with electrons conducting electric current vs.
heavy ions. But the signal speed is not the same as the speed of the
particles involved, if there are particles. (You don't have to have charged
particles moving to get electric current; you only need changing magnetic
fields, as in Maxwell's equations.) Ordinary  electic currents involve moving
electrons, but the electrons move much more slowly than the signal, which
moves with the speed of light. For an analogy, imagine a long train, and ask
yourself how long it takes, after the engine begins to move, before the
caboose begins to move. The speed of the cars has very little to do with it;
it is the tightness of the coupling that counts.  

Neurological signals (those that have been studied) are indeed much slower
than signals in a telephone wire, but not because heavy ions necessarily
imply a slow signal--rather, apparently, because the neurological signals
seem to have other components besides the purely electrical. 

Robert Ettinger

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