Tachyons and all that

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Article #7365

#7365

From: David Eppstein
Date: Mon, 13 Oct 1986 17:58

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Ok, so FTL communications violate causality.  Can anyone give me a coherent
explanation of why this is such a big problem?  Seems to me it might even
have advantages; for instance with time loops you might be able to build a
working alternating Turing machine.

But anyway, let's assume for the moment that tachyons exist.  At "rest"
they are supposed to move with "infinite" velocity; that implies to me that
they are line-like rather than point-like (or equivalently point-like
particles in a dual space to the three dimensions we all know and love).
Can anyone come up with descriptions of time and motion for such an object
that make sense (e.g. geodesics dualize and we have some equivalent of the
speed of light)?

If we had Newtonian physics it would be easy.  Time is trivial and geodesic
motions could just be rotations about fixed points possibly including a
fictional point at infinity.  But we don't (sigh)...

p.s. does anyone know why I can't post to both net.physics and sci.physics?
-- 
David Eppstein, eppstein@cs.columbia.edu, seismo!columbia!cs!eppstein

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From: eppstein@garfield.columbia.edu (David Eppstein)
Newsgroups: sci.physics
Subject: Tachyons and all that
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Date: Mon, 13-Oct-86 13:58:27 EDT
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Posted: Mon Oct 13 13:58:27 1986
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