Einstein's Least Famous Equation?

In 1980, my first year in graduate school, the English physicist, Paul Dirac, Nobel Prize 1933 awardee, came to the University of Colorado to give a popular talk at The Gamow Memorial Lecture. As a big fan of Dirac, I dragged all my non-physicist friends to the “popular” lecture early to get good seats in the middle and second row from the front. The place was packed with the mayor, the chancellor, the provost, the deans, all the physics professors, a blonde woman from the Sufi community dressed in a turban and a white cloak sporting ceremonial dagger in  her waistband, and so forth. (This is Boulder, Colorado, after all.) Dirac gave what I thought was a very interesting talk on the history of quantum theory, but with no slides, no notes, no audiovisual aides, and no nothing. He just stood at the podium and talked for an hour. He was 78 years old at the time and he spoke in a very soft high-pitched, English-accented, mouse-like voice. So soft it was that you could barely hear him at all and the technicians kept cranking up the amplifiers until it screeched periodically from the feedback. The talk put all the non-physicists in the audience immediately to sleep. Then Dirac got to the part where he discovered the Dirac equation predicting the existence of antimatter.

He clearly gets a bit excited and impossibly goes up an octave, whereupon the feedback kicks in waking everybody up, and Dirac says, “I was led to the idea of the discovery of antimatter by considering Einstein’s most famous equation, E = ….” All my buddies from the English department began to nudge me and the crowd visibly perked up. They had not understood a goddamn thing but for sure even the English majors knew what “…Einstein’s most famous equation, E = ???” was going to be. Dirac continues triumphantly onward to the hushed auditorium, E = the square root of p-squared times c-squared plus m-squared times c to the fourth!?"

(Einstein’s least famous equation?) The audience visibly collapsed upon themselves in utter disappointment—they understood nothing—and I in the tomb-like quiet that followed in the hallowed Rocky Mountain granite of the vast Macky auditorium— burst out laughing uncontrollably. (And I was the only one.) Dirac, normally an endearing bird-like little man, scowled, halted the talk, stepped out from behind the podium, and stared down at me in silence, vulture-like, for a full minute. The rest of the audience looked back and forth between Dirac and me as they coughed and inspected their watches. Then, without a word, after my torturous minute was up, he returned behind the podium and finished his talk as if nothing had happened at all.

From: Schrödinger's Killer App: Race to Build the World's First Quantum Computer (Page 42). Taylor & Francis Press.