Notes on Relativity and Cosmology - Physics Department, UCSB

Chapter 3
Einstein and Inertial
Frames
Read Einstein, ch. 8-14, Appendix 1
In the last chapter we learned that something is very wrong. The stellar aberration
results indicate that the earth is moving through the ether. But, Michelson
and Morely found results indicating that the ether is dragged along perfectly
by the earth. All of the experiments seem to have been done properly, so how
can we understand what is going on? Which interpretation is correct?
3.1 The Postulates of Relativity
In 1905, Albert Einstein tried a different approach. He asked “What if there is
no ether?” What if the speed of light in a vacuum really is the same in every
inertial reference frame? He soon realized, as we have done, that this means
that we must abandon T and S, our Newtonian assumptions about space and
time.
Hopefully, you are sufficiently confused by the Michelson and Morely and stellar
aberration results that you will agree to play along with Einstein for awhile. This
is what we want to do in the next few sections. We will explore the consequences
of Einstein’s idea. Surprisingly, one can use this idea to build a consistent
picture of what is going on that explains both the Michelson-Morely and stellar
aberration. It turns out that this idea makes a number of other weird and
ridiculous-sounding predictions as well. Perhaps even more surprisingly, these
predictions have actually been confirmed by countless experiments over the last
100 years.
We are about to embark on a very strange path, one that runs counter to the
intuition that we accumulate in our daily lives. As a result, we will have to tread
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