"So, Professor Einstein, how might we test this theory of yours?"

Nearly a century ago, Einstein developed the theory of Special Relativity, which is now a cornerstone of modern physics. The basic assumption of the theory is that every observer measures the speed of light to be the same number, independent of the motion of the observer or the direction the light is traveling.

Some efforts to unify the known forces and particles in nature, including some string theories, predict very small effects that are forbidden in Special Relativity. One such effect is that the polarization of light would change as the light travels through empty space. The polarization of light isn't directly detectable by the human eye, but its existence is familiar to many people through the behavior of polarized sunglasses, and it can be measured by special instruments.

In these theories, light traveling greater distances is predicted to undergo a bigger change in polarization, with the amount of the change depending on the frequency (color) of the light. Using measured polarization of infrared, visible, and ultraviolet light from very distant galaxies and looking for this change, the authors have placed the most stringent bound on violations of Einstein's Special Relativity to date.

Fundamental Physics investigator Alan Kostelecky of IndianaUniversity reports that his group has recently published "Cosmological Constraints on Lorentz Violation in Electrodynamics," by Alan Kostelecky and Matthew Mewes, in Physical Review Letters, vol 87, id 251304 (2001).

NOTE: Animations created to illustrate the effects discussed in this paper can be found at: (animation 2).
A discussion of the underlying ideas is at: