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From: graner@ut-ngp.UUCP (Nicolas Graner)
Newsgroups: net.physics
Subject: "speed of light" puzzle
Message-ID: <1720@ut-ngp.UUCP>
Date: Thu, 9-May-85 20:15:20 EDT
Article-I.D.: ut-ngp.1720
Posted: Thu May  9 20:15:20 1985
Date-Received: Sun, 12-May-85 00:02:38 EDT
Organization: U.Texas Computation Center, Austin, Texas
Lines: 21

I find it sad that people interested in physics (at least enough to
read net.physics) don't have *some* basic ideas about relativity,
as shown by the recent discussion about speed of light. Sigh.

Anyway, here is the puzzle:

I have a laser on a turntable in such a way that the beam falls on
the moon during each revolution. If my laser rotates at omega
rad/s and the moon is at distance D, the spot moves on the moon
at speed V = omega*D. Since I can make omega as big as I want,
V can be made very big, and certainly much more than C. (e.g.
with D ~ 300,000km and omega = 10rad/s, a very gentle speed,
V = 3,000,000km/s = 10*C)

How can anything move at 10*C without violating relativity ?

(I know the beam between earth and moon will be curved, but this is irrelevant)

Nic.                      {ihnp4,seismo,...}!ut-ngp!graner

*If Murphy's law can go wrong, it won't*