Subject: Testing speed of light
Date: Wed Apr 20 19:14:12 1994


Pretty well all the experiments I've heard of that attempt to determine
the speed of light use some sort of reflective technique. That is,
they turn on a beam of light which is reflected off a target, and the
total time taken from turn on to when the beam is detected returning
is measured.

I was thinking that there is a problem with this. Consider the light
beam as an aircraft for a minute. If the aircraft is travelling in
a certain direction with a tailwind of 45 k/h, it will reach its
target sooner. But on its return journey it will have the wind against
it, and will take longer to return to its base. I realise that
analogies break down at some point, but my point is that if you
average the time taken to the target and the time returning, you will
get a consistant result each time. However this does not reflect if
light travels faster in one direction than another.

What I would suggest (if it hasn't already been done) is to use two
atomic clocks. The time on the first clock would be recorded when the
light beam is first switched on. The time on the second clock would be
recorded when the light beam is detected at the target.
If you repeat this experiment for the opposite direction and then
compare the difference in times for the two directions this should
show any difference in the speed of light in the two directions,
relative to the viewer's motion.

If something along this (or any other experiment of a type not
mentioned) line has already been conducted, I'd like to hear about it.

-Andrew  (agk@bbs.ausom.oz.au)