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From: karsh@geowhiz.UUCP (Bruce Karsh)
Newsgroups: net.physics
Subject: Re: "speed of light" puzzle
Message-ID: <184@geowhiz.UUCP>
Date: Fri, 10-May-85 19:25:41 EDT
Article-I.D.: geowhiz.184
Posted: Fri May 10 19:25:41 1985
Date-Received: Mon, 10-Jun-85 20:20:02 EDT
References: <1720@ut-ngp.UUCP>
Organization: UW Madison, Geology Dept.
Lines: 21

> 
> 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 ?

  No particle is moving faster than C.

  This is the difference between group velocity and phase velocity.

-- 
Bruce Karsh                           |
U. Wisc. Dept. Geology and Geophysics |
1215 W Dayton, Madison, WI 53706      | This space for rent.
(608) 262-1697                        |
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