From: utzoo!decvax!duke!harpo!ihps3!houxi!houxj!houxn!houxg!lime!houti!trc
Newsgroups: net.physics
Title: train - light race
Article-I.D.: houti.140
Posted: Fri Aug 20 17:37:02 1982
Received: Sat Aug 21 06:29:08 1982

My physics book seems to say that light appears to travel at the same velocity,
regardless of the reference frame that it originates in, and regardless of the
frame it is taken in reference to.   I think it argues that this is because
there is no prefered inertial reference frame.

In the classic thought experiment with a train and light flashes, suppose 4
lights are used - two on *stationary* poles, two on board the train.
They will be set off at the instant that the train and stationary lights
are adjacent - since they are the same distance apart (in appearance to
both frames - so that any relativistic effects on length can be ignored),
this should be an acceptable means of getting simultaneity.

>From the stationary point of view, all light flashes should arrive
simultaneously at the center of the two stationary flashes.
>From the trains inertial frame, they should all meet at the center
of the two train lights.
Unfortunately, the centers will not be the same, by the time the light
arrives, since the centers will have moved apart. This effect should
be apparent to both the train and stationary observer, as the position
at which the flashes meet can be determined regardless of time dilation
or length shortening.

Where does the problem lie here?  Is one of my inital assumptions
false?

				Tom Craver
				houti!trc