Who discovered that E = mc2? It’s not as easy a question as you might think. Scientists ranging from James Clerk Maxwell and Max von Laue to a string of now-obscure early 20th-century physicists have been proposed as the true discovers of the mass-energy equivalence now popularly credited to Einstein’s theory of special relativity. These claims have spawned headlines accusing Einstein of plagiarism, but many are spurious or barely supported. Yet two physicists have now shown that Einstein’s famous formula does have a complicated and somewhat ambiguous genesis – which has little to do with relativity.
One of the more plausible precursors to E = mc2 is attributed to Fritz Hasenöhrl, a physics professor at the University of Vienna. In a 1904 paper Hasenöhrl clearly wrote down the equation E = 3/8mc2. Where did he get it from, and why is the constant of proportionality wrong? Stephen Boughn of Haverford College in Pennsylvania and Tony Rothman of Princeton University examine this question in a paper submitted to the arXiv preprint server.
Hasenöhrl’s name has a certain notoriety now, as he is commonly invoked by anti-Einstein cranks. His reputation as the man who really discovered E = mc2 owes much to the efforts of the antisemitic and pro-Nazi physics Nobel laureate Philipp Lenard, who sought to separate Einstein’s name from the theory of relativity so that it was not seen as a product of “Jewish science”.
‘Leading Austrian physicist of his day’
Yet all this does Hasenöhrl a disservice. He was Ludwig Boltzmann’s student and successor at Vienna, and was lauded by Erwin Schrödinger among others. “Hasenöhrl was probably the leading Austrian physicist of his day”, Rothman told physicsworld. com. He might have achieved much more if he had not been killed in the First World War.
The relationship of energy and mass was already being widely
discussed by the time Hasenöhrl considered the matter. Henri Poincaré had stated that electromagnetic radiation had a momentum and thus effectively a mass, according to E = mc2. German physicist Max Abraham argued that a moving electron interacts with its own field, E0, to acquire an apparent mass given by E0 = 3/4 mc2. All this was based on classical electrodynamics, assuming an ether theory. “Hasenöhrl, Poincaré, Abraham and others suggested that there must be an inertial mass associated with electromagnetic energy, even though they may have disagreed on the constant of proportionality”, says Boughn.
Robert Crease, a philosopher and historian of science at Stony Brook University in New York, agrees. “Historians often say that, had there been no Einstein, the community would have converged on special relativity shortly”, he says. “Events were pushing them kicking and screaming in that direction.” Boughn and Rothman’s work, he says, shows that Hasenöhrl was among those headed this way.
Hasenöhrl approached the problem by asking whether a black body emitting radiation changes in mass when it is moving relative to the observer. He calculated that the motion adds a mass of 3/8c2 times the radiant energy. The following year he corrected this to 3/4c2.
A different style of scientific paper
However, no-one has properly studied Hasenöhrl’s derivation to understand his reasoning or why the prefactor is wrong, claim Bough and Rothman. That’s not easy, they admit. “The papers are by today’s standards presented in a cumbersome manner and are not free of error.