Asri-unix.1063 net.space utcsrgv!utzoo!decvax!ucbvax!C70:sri-unix!A.exp@Berkeley Fri Mar 19 17:02:50 1982 >From JGA@MIT-MC Fri Mar 19 06:16:11 1982 Date: 19 March 1982 09:14-EST From: John G. Aspinall To: A.exp at UCB-C70 Date: 17 Mar 1982 17:10:41-PST From: A.exp at Berkeley Subject: Thought experiment in general relativity Is the path followed by a light ray which is known to intersect tangentially at one point an infinitely rigid straight rod always along the rod? What does "intersect tangentially at one point" mean? If it means "passes through the point", then the answer is that the light ray is the best definition of "straight" you've got. John Aspinall Intersect tangentially at one point means that the light ray passes through some point of the rod, and is tangent to that point. If the rod is first rendered straight by aligning it with a beam of light in a gravitational field in any given region of the universe, since it is rigid when it is transported to another region it will remain straight, so it follows the geodesic of the old region when it is moved to the new one. The beam of light in the new region will follow the geodesic in the new region, so will it follow the beam? The beam of light may be the best standard of strightness in one region but is this the same as the straight line defined by another beam of light in a different region? The purpose of the rigid rod in the experiment is to allow comparison. ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.