The linear optical response of the quantum vacuum

Abstract

We show that the interpretation of $\mathbf{D}={\epsilon }_0\mathbf{E}$ as vacuum polarization is consistent with quantum electrodynamics. A free electromagnetic field polarizes the vacuum but the magnetization and polarization currents cancel giving zero source current. The speed of light is a universal constant while the fine structure constant that couples the EM field to matter runs. In that sense, the quantum vacuum can be understood as a modern Lorentz invariant ether.

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