Wise guy: tests confirm Einstein's formula correct

Scientists at Massachusetts Institute of Technology and the National Institute of Standards and Technology (NIST) will report in tomorrow's (Dec. 22) issue of the journal Nature that Albert Einstein's formula, E=mc², is correct.

The researchers conducted what they claimed was the most precise direct test ever of the universe-ordering formula about the nature of energy and the underpinning of Einstein's theory of special relativity. They used an instrument developed by NIST (Gaithersburg, Md.) called GAMS4 to again confirm that energy and matter are intimately related: energy (E) equals mass (m) times the square of the speed of light (c²).

GAMS4 (show, below), now located at the Institut Laue Langevin (Grenoble, France), measured the angle at which gamma rays are diffracted by two identical crystals. The crystals were made of atoms separated by a known distance.

Photo by Artechnique, Courtesy of ILL

By comparing NIST measurements of energy emitted by silicon and sulfur atoms and MIT measurements of the mass of the same atoms, the scientists found that E differs from mc² by at most 0.0000004, or four-tenths of 1 part in 1 million. The researchers said the result was "consistent with equality" and is 55 times more accurate than the previous best direct test of Einstein’s formula.

According to the basic laws of physics, every wavelength of electromagnetic radiation corresponds to a specific amount of energy. The NIST team determined the value for energy in the Einstein equation by precisely measuring the wavelength of gamma rays emitted by the silicon and sulfur atoms.

The tests relied on a well-know process: When the nucleus of an atom captures a neutron, energy is released as gamma ray radiation. With one extra neutron, the atom's mass is predicted to equal the mass of the original atom, plus the mass of a solitary neutron, minus a value called the neutron binding energy. The neutron binding energy is equal to the energy given off as gamma ray radiation, plus a small amount of energy released in the recoil motion of the nucleus.