Best Direct Test of E=mc²

Albert Einstein's formulation of how matter and energy are equivalent is an important enunciation of the principle of conserved energy. As far as we know, it is at work at the moment an atom bomb explodes, when the fissioning of uranium is exploited for making commercial electricity, or when an electron and positron annihilate inside a PET scanner. A new experiment -- conducted by scientists from MIT, Université Laval in Quebec City, Canada, Florida State University, Oxford University, the National Institute of Standards and Technology, and the Institut Laue-Langevin in Grenoble, France -- keeps careful account of both matter mass and electromagnetic energy for a process in which ions of sulphur and silicon absorb neutrons, transforming them into new isotopes as they emit gamma rays. In this transaction Einstein's equation is shown experimentally to be true at a level of 0.00004 percent, a factor of 55 better than the previous best test.

Rainville et al., Nature, 22/29 December 2005