Gravitational redshift : The electromagnetic radiation of an object is stretched out slightly inside a gravitational field. Think of the sound waves that emanate from a siren on an emergency vehicle; as the vehicle moves toward an observer, sound waves are compressed, but as it moves away, they are stretched out, or redshifted . Known as the Doppler Effect, the same phenomena occurs with waves of light at all frequencies. In 1959, two physicists, Robert Pound and Glen Rebka, shot gamma-rays of radioactive iron up the side of a tower at Harvard University and found them to be minutely less than their natural frequency due to distortions caused by gravity.
relativity text appeared in the sixties, with a second edition in
1992. It emphasizes the invariants in special relativity, such as
the "proper time" reading on a clock carried directly between
two events and the invariant mass of a particle or of a system of
particles. It contains a wealth of applications to current experiments.
The careful definition of the limits of inertial frames sets the
groundwork for the later introduction to general
relativity . Associated software, described below, immerses the
student actively in the strange world of the very fast.
For self study and those without access to the second edition:
download the first chapter of the 1965 first edition , with exercises and solutions