Date: Tue, 2 Nov 2004 20:37:55 -0500 From: Marc Ramirez <marc.ramirez@bluecirclesoft.com> To: Mike Jeays <Mike.Jeays@rogers.com> Cc: Mark Murray <mark@grondar.org> Subject: Re: Speed of light? [was Re: GPL vs BSD Licence] Message-ID: <200411022038.03412.marc.ramirez@bluecirclesoft.com> In-Reply-To: <1099441245.761.6.camel@chaucer.jeays.ca> References: <200411021821.iA2ILI3N092806@grovel.grondar.org> <200411021412.44009.marc.ramirez@bluecirclesoft.com> <1099441245.761.6.camel@chaucer.jeays.ca>
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--nextPart2433223.nXTdfhFHX6 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline On Tuesday 02 November 2004 07:20 pm, you wrote: > On Tue, 2004-11-02 at 14:12, Marc Ramirez wrote: > > More precisely, gravity is what we call the curvature of spacetime.=20 > > Light always heads in the straighest possible line, but in a curved > > spacetime... Also, if light is emitted in an area of lower potential and > > is absorbed in an area of higher potential (e.g., from Sun to Earth) it > > will be redshifted. Other way around, it will be blueshifted. If you are > > using the frequency of light as a clock (and you basically have no other > > choice), you will notice this effect as "time moving more slowly around > > massive bodies." > > > > Marc. > > Doesn't this equate to defining the speed of light as constant, and then > adjusting the metre and second appropriately? I thought the constancy > of the speed of light was a basic assumption taken by Einstein; the > slowing of time and reduction of lengths of moving objects, or those in > a gravitational field are a consequence. Yes, that's absolutely right. In fact, one way to unify space and time und= er=20 GR is to define distance in seconds. (I remeber Grace Hopper coming on the= =20 Late Night back with Dave Letterman and giving him a piece of wire that was= a=20 nanosecond long.)=20 The invariance of the speed of light under various states of movement,=20 rotation, acceleration, and gravitation is pretty well established=20 experimentally. Relativity takes this excellent experimental agreement, an= d=20 moves it up to the status of a postulate (a.k.a. definition). The challenge= =20 now, of course, is to think up new experiments. Right now, we know of no=20 conditions where the speed of light is anything but c. But without that,=20 yes, the speed of light is defined as constant in relativity. =20 The postulates of special relativity: 1. The laws of physics are independent of the observer's reference frame. "The laws by which the states of physical systems undergo change are not=20 affected, whether these changes of state be referred to the one or the othe= r=20 of two systems of co-ordinates in uniform translatory motion." 2. The speed of light, c, is the same in all reference frames. " Any ray of light moves in the 'stationary' system of co-ordinates with t= he=20 determined velocity c, whether the ray is emitted by a stationary or by a=20 moving body. Hence velocity equals [length of] light path divided by time=20 interval [of light path], where time interval [and length are] to be taken = in=20 the sense of the definition in =A71." General Relativity extends this to: 3. Uniform acceleration is equivalent to a gravitational field (the Princip= le=20 of Equivalence). (Can't find the Einstein quote, sorry :) These are the general constraints (you'll see your comment restated as=20 postulate #2). These are the constraints (along with extra assumptions I won't go into), a= nd=20 General Relativity is an explanation of the universe which fits within thes= e=20 constraints. Like I say, so far all of these have been confirmed to a grea= t=20 degree of accuracy, so any new theories will have to either accept these=20 postulates or explain why they seem to be so pervasive. Thanks for taking my mind off Lisp! :) Marc. =2D-=20 Marc Ramirez Blue Circle Software Corporation 513-688-1070 (main) 513-382-1270 (direct) http://www.bluecirclesoft.com http://www.mrami.com (personal) --nextPart2433223.nXTdfhFHX6 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.6 (FreeBSD) iD8DBQBBiDZ6g1EgpGw750IRAjCnAJ9fFLU5+UuPgdgXSbizwWZE9NM5PQCff68H 4tS8bLKfFKrMLubmIghDSJA= =BDG5 -----END PGP SIGNATURE----- --nextPart2433223.nXTdfhFHX6--
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