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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 <JGA MIT-MC AT>
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 <JGA@MIT-MC>
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.
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