Abraham–Minkowski controversy

The Abraham–Minkowski controversy is a physics debate concerning electromagnetic momentum within dielectric media. There are different ways to apportion the "kinetic" and "electromagnetic" portions of a medium-photon system's momentum, because the relativistic symmetries of Maxwell's equations do not preserve stress-energy. Hence, two incompatible equations seem natural to describe momentum transfer between matter and electromagnetic fields. These two equations were first suggested by Hermann Minkowski (1908) and Max Abraham (1909), from which the controversy's name derives. Both are supported by experimental data. The seeming paradox was resolved when Blount demonstrated that one equation described momentum while the other measured pseudomomentum.

This controversy inspired various theories admitting the existence of reactionless drives.

For electromagnetic fields in vacuum, the force density is given by the equation

${\displaystyle {\boldsymbol {f}}={\boldsymbol {\nabla }}\cdot {\boldsymbol {\tilde {T}}}-\epsilon _{0}\mu _{0}{\frac {\partial {\boldsymbol {S}}}{\partial t}}}$

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