Around 1909 Abraham and Minkowski proposed different forms for the electromagnetic stress-energy tensor. Since that time a long-simmering (but fairly quiet) debate over which form to use has continued. The crux of the matter is the question of what the correct expression is for the momentum of a photon in a dielectric medium. While we all agree that in vacuum the momentum is hv/c, in a dielectric with index of refraction n it is under debate: hv/nc or hvn/c? While a number of thought experiments have been devised, and one answer is generally accepted, the gedanken results have not been absolutely convincing to all involved. It is devilishly difficult to design an experiment that is capable of actually addressing the question, let alone providing a clear answer. By taking advantage of recent advances in cold atom physics, however, we may finally be able to perform an experiment that can decide - at least under special circumstances.

Contact: Bei-Lok Hu.