Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84 exptools; site ihlpg.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!ihnp4!ihlpg!tan From: tan@ihlpg.UUCP (Bill Tanenbaum - AT&T Bell Labs - Naperville IL) Newsgroups: net.physics Subject: Re: Light Message-ID: <857@ihlpg.UUCP> Date: Mon, 15-Jul-85 13:43:11 EDT Article-I.D.: ihlpg.857 Posted: Mon Jul 15 13:43:11 1985 Date-Received: Wed, 17-Jul-85 06:19:35 EDT References: <393@sri-arpa.ARPA> Organization: AT&T Bell Laboratories Lines: 21 > From: Doug Gwyn (VLD/VMB)> > Gravity doesn't "bend light waves" according to general relativity; > it warps the structure of spacetime. Light follows a null > geodesic (think of it as the "shortest path") in all cases, > so that it appears to take a bent path to an observer who does > not take the space-time curvature into account. > > It is really meaningless to question whether the "speed of light > is constant" without describing how units of space and time > measurement are to be determined, since speed will be measured in > such units. The concept of "null geodesic" is invariant with > respect to any choice of units. The statement "speed of light is constant" is meaningful and correct if the speed is always measured locally. The curvature of space-time can be ignored if the domain is small enough, i.e. space-time is locally flat. It does not matter what units we use. The magnitude of a physical quantity does not depend on the units of measurement. -- Bill Tanenbaum - AT&T Bell Labs - Naperville IL ihnp4!ihlpg!tan