Einstein’s 1934 two-blackboard derivation of energy-mass equivalence

We use a famous and a rare picture of Einstein to reconstruct the context of a lecture he gave on the derivation of the equivalence of energy and mass in Pittsburgh in 1934. This lecture is interesting from a historical and sociological point of view because, at the time, Einstein was at the height of his fame, the equivalence of energy and mass was being discussed in newspapers, and his presence in Pittsburgh created much attention among the general public. Einstein exhibited his well-known intuitive style of using only the most important physical information in the zero-momentum frame derivation. His method was simple and direct and is relevant to those who teach the zero-momentum frame idea. From the perspective of the nonspecialists in the Pittsburgh audience, it was presented at an expert level without allowing for many explanatory concessions we would take for granted today. A definitive picture of Einstein, in front of his famous energy equation, was missed by photographers who posed him with the wrong blackboard in the background.