There are several different expressions for the electromagnetic force density inside a material. In addition to the canonical Lorentz force density, there exist at least four other expressions based on the Abraham, Minkowski, Einstein-Laub, and Chu formulations of electrodynamics. Experiments to distinguish the various expressions are sparse because differences are apparent only under exotic conditions such as inside deformable media or media moving at relativistic speeds. In this work, we carefully examine the seminal 1973 experiment by Ashkin and Dziedzic to look for clues to isolate a single true force density expression. The experiment consisted of high-powered laser pulses directed onto an air-water interface, which caused the interface to bulge upwards (opposing gravity) regardless of the illumination direction. The results have been interpreted using both the Minkowski and Abraham formulations of electrodynamics. What remains is to analyze the results using the other formulations.
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