Constants of nature are expected to remain, well, constant, but physicists now find that the masses of protons or electrons might have varied over time. Researchers at the Free University of Amsterdam and their colleagues investigated the wavelengths absorbed by hydrogen gas irradiated with extreme ultraviolet laser beams in their laboratory. They compared it with readings taken at the European Southern Observatory in Chile from the glow of hydrogen clouds that had absorbed radiation from distant quasars, light that originated 12 billion years ago. The positions of certain wavelengths in both cases depend on the proton-to-electron mass ratio. Currently protons are roughly 1,836 times the mass of electrons. In the April 21 Physical Review Letters, the scientists reported that the proton-toelectron mass ratio has apparently decreased by one fifty-thousandth in the interval since the universe's youth.

These findings complement recent contentious observations that the fine-structure constant, which describes the overall strength of the electromagnetic force, has increased slightly.