More than one brain behind E=mc2 (Vol. 44 No. 2)

The present article reveals the contribution of a little known Austrian physicist, Friedrich Hasenöhrl, to uncovering a precursor to Einstein famous equation in establishing the proportionality between the energy (E) of a quantity of matter with its mass (m) in a cavity filled with radiation.

The author argues how Hasenöhrl’s work, for which he now receives little credit, may have contributed to the famous equation E=mc². He believes the notion that mass and energy should be related did not originate solely with Hasenöhrl. Nor did it suddenly emerge in 1905, when Einstein published his paper, as popular mythology would have it.

Given the lack of recognition for Hasenöhrl’s contribution, his original work on blackbody radiation in a cavity with perfectly reflective walls is examined. This study seeks to identify the blackbody’s mass changes when the cavity is moving relative to the observer.

The reason why the Austrian physicist arrived at an energy/mass correlation with the wrong factor, namely at the equation: E = (3/8) mc², are then explored. Hasenöhrl’s error would stem from failing to account for the mass lost by blackbody while radiating.

Before Hasenöhrl focused on cavity radiation, other physicists including French mathematician Henri Poincaré and German physicist Max Abraham, showed the existence of an inertial mass associated with electromagnetic energy. In 1905, Einstein gave the correct relationship between inertial mass and electromagnetic energy, E=mc². Nevertheless, it was not until 1911 that German physicist Max von Laue generalised it to include all forms of energy.