The linear optical response of the quantum vacuum

Abstract

We show that the interpretation of D = ε 0 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.Quantum electrodynamics (QED) is the most successful theory in human history, but it is normally relegated to short range or high energy phenomena such as the Lamb shift, collisions of high energy particle beams and ultra-intense laser fields. Except for photon emission and absorption and the Casimir effect, its relevance to low-energy laboratory physics and every day life is unclear [1,2].Recently it has been proposed that D =ε 0 E is the vacuum polarization due to virtual pairs of all types of charged elementary particle in Nature [3,4,5]. This is a paradigm shift in our physical picture of the vacuum, but we will show here that this interpretation of ε 0 is consistent with QED.In a dielectric material the electric displacement is D = ε 0 E + P, where P = ε 0 χ e E is the polarization due to the electric field E and χ e is the electric susceptibility. If the material