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From: leon@hhb.UUCP (Leon Gordon)
Newsgroups: net.physics
Subject: Re:  Light
Message-ID: <110@hhb.UUCP>
Date: Wed, 17-Jul-85 14:31:39 EDT
Article-I.D.: hhb.110
Posted: Wed Jul 17 14:31:39 1985
Date-Received: Sat, 20-Jul-85 16:22:54 EDT
References: <393@sri-arpa.ARPA>
Organization: HHB-Softron, Mahwah, NJ
Lines: 23


	just a comment on the deflection of light by gravity:

	1) light is deflected by a grav field in the same sense that 
	   particles in free fall are - one can take the point of view
	   that there is a grav. interaction, or one can take the point
	   of view that there is no force, but rather an altered geometry.
	   I agree that the latter view is more appropriate to a relativistic
	   analysis; I just want to point out that the effect on a beam of
	   light is conceptually similar to the effect on a stream of particles.

	2) The old classic by Eddington (Relativity, Thermodynamics, and
	   Cosmology) contains a simple relativistic calculation of the 
	   deflection of a pencil of light by a gravitational field.  
	   Interestingly enough, light is deflected twice as much as particles
   	   of the same energy content.  This is because of the radiation
	   pressure terms in the stress-energy tensor which are negligable
	   for (classical) particles.


							leon

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