From: utzoo!decvax!harpo!ihnp4!ihldt!bnp
Newsgroups: net.space
Title: Einstein's Universe?!
Article-I.D.: ihldt.1313
Posted: Mon Feb  7 12:59:40 1983
Received: Wed Feb  9 01:30:29 1983
Reply-To: bnp@ihldt.UUCP (Bruce Peters)

	This query may be a repeat of an old question, but it has been
bothering me for some time so...
	I have never had a good qualitative understanding of Einstien's'
theories of relativity (both special and general), and a friend recommended
a book entitled "Einstein's Universe" by Nigel Calder, as a good
introduction to the subject.  I got a copy from a local library and
began reading, but quickly ran into trouble when the author began
describing the differences in the Doppler shift mechanisms which apply
to light vs. sound.  I was hoping that someone on the net could provide
a better explanation, or recommend a good book.
	I can see how in air, the magnitude of a Doppler shift will
depend on whether the observer or the source of the sound is moving,
but I cannot understand how the two cases can be treated identically
for light.  I have heard the arguments about the lack of an "either"
through which the light moves, but that doesn't seem to explain the
mechanism causing the Doppler shift when the observer is moving
relative to the source of the light.
	Please respond by mail, and if other similiar queries
appear, I will summarize.
				Thanks,
					Bruce Peters
					BTL - Naperville