"In the formula E = Mc2, M is measured in gram, E in erg and c in cm/sec" — elusive Einstein letter explaining his landmark mass-energy equation
TLS signed “A. Einstein,” one page, 8.5 x 11, blindstamped personal letterhead, April 21, 1946. Letter to high school student Jack Monsted, in full: “Your informations do not seem to be quite reliable to me. But there is no time to correct them. In the formula E = Mc2, M is measured in gram, E in erg and c in cm/sec.” The formula's equal sign, and the succeeding comma, are both written in pencil. In fine condition.
Accompanied by the original mailing envelope and a letter of provenance from the original recipient: “The letter from Albert Einstein, dated April 21, 1946, was written in response to a letter I wrote him about two weeks earlier. I was a senior in high school and was taking physics and the atom bomb, which had been dropped on Japan that previous August, was a subject in the class. I was unable to find out what the units of measurement the symbols in the equation E=MC^2 meant so I wrote this letter and asked him. The first sentence in his letter refers to a question I asked regarding the theory of relativity where I talked about a yardstick shrinking as it approaches the speed of light. I guess my information was not reliable.”
Einstein's theory of relativity—the foundation of modern physics—encompassed his pioneering concepts of special relativity and general relativity, respectively proposed and published in 1905 and 1915. With it came his famed equation, "E = mc2"—the mass-energy relationship—undoubtedly the most well-known equation ever set forth. In his later years, Einstein explained on-camera: ‘It followed from the special theory of relativity that mass and energy are but different manifestations of the same thing... Furthermore, the equation E is equal to m c-squared, in which energy is put equal to mass multiplied by the velocity of light squared, showed that a very small amount of mass may be converted into a very large amount of energy, and vice versa.' Letters from Einstein featuring his iconic "E = mc2" formula — undoubtedly the most well-known equation ever set forth — are tremendously rare and seldom offered for public purchase, distinctions that signal this offering as something of an event.