Abraham-Minkowski controversy

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The Abraham-Minkowski controversy is a physics debate concerning electromagnetic momentum within dielectric media. The preponderance of evidence in the debate suggests that the Abraham equation is correct^[1], but some investigators disagree.

Two equations exist describing momentum transfer between matter and electromagnetic fields. Both seem to be supported by contradicting experimental data. The two existing equations were first suggested by Max Abraham and Hermann Minkowski, from which the controversy name derives. Both define the momentum of an electromagnetic field permeating matter. Abraham's equation suggests that in materials through which light travels more slowly, electromagnetic fields should have lower momentum, while Minkowski suggests it should have a greater momentum. Minkowski suggested that Abraham only accounted for the momentum of the electromagnetic fields, and his equation was an attempt to take into account the momentum of the material as well. More recent work suggests that this characterization is incorrect.

At least one report has suggested Minkowski's formulation, if correct, would provide the physical base for reactionless drive^[2]. However, an independent review from the Air Force Academy concluded that there would be no expected net propulsive forces, and a NASA report determined that "The signal levels are not sufficiently above the noise as to be conclusive proof of a propulsive effect."^[3]

The two equations for the momentum in a dielectric with refractive index n are: