Teaching the gravitational redshift: lessons from the history and philosophy of physics

Abstract

The equivalence principle and the notion of an ideal clock running independently of acceleration suggest that clocks are unaffected by gravity. The apparent contradiction with the gravitational redshift points to a subtlety in general relativity theory. Indeed, early attempts for a clear derivation of the gravitational redshift were fraught with errors and ambiguities, and much confusion endured for the next two decades. This suggests that the subject should be treated carefully in introductory textbooks on relativity theory. I analyze the weaknesses of the presentation in five otherwise excellent modern introductory general relativity books (by Rindler, Schutz, Hobson et al., Weinberg, and Carroll). I also present some analysis from an history and philosophy of physics article, which proves to be a great resource to learn about, anticipate, and clarify problems in teaching the redshift.