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From: mcgeer%ucbkim%Berkeley@sri-unix.ARPA
Newsgroups: net.physics
Subject: Re:  Light
Message-ID: <388@sri-arpa.ARPA>
Date: Fri, 12-Jul-85 17:39:41 EDT
Article-I.D.: sri-arpa.388
Posted: Fri Jul 12 17:39:41 1985
Date-Received: Wed, 17-Jul-85 06:17:49 EDT
Lines: 32

From:  Rick McGeer 

	From: ihnp4!inuxc!inuxd!claus@BERKELEY (David Claus)
	Subject: Re:  Light
	Article-I.D.: <778@inuxd.UUCP>
	In-Reply-To: Article(s) <345@sri-arpa.ARPA>
	
	The speed of light is not always constant.  Einstein assumed that
	the speed of light was constant through any round trip.  The
	speed of light through one leg of that trip can be greater than
	the speed through another leg.
	
	Take for example a light pulse being sent from the earth to the moon
	and back.  Light will travel faster on the way back than on the way
	there because of gravity effects.  Does general relativity take this
	into account somehow?  It is proven that gravity bends light waves
	(through sun eclipse experiments) so why shouldn't gravity also increase
	the speed of the light wave?  Has there been an experiment that has
	measured the speed of light during a one way trip through some
	gravitational potential?  Most measurements I've heard of involve
	the reflection back and forth of a light wave here on earth.
	
	Can anyone explain this to me.
	
	Dave Claus
	AT&T/Indy

Gravity won't accelerate a light wave. *Nothing* accelerates a light wave in a
vacuum.  Instead, the wavelength is affected, in much the same way that the
wavelength of light varies as the observer's velocity wrt to the source varies.

					Rick.