# A link between particle physics and Maxwell's equations

## Newsletter 6

Surprisingly there seem to be unexplored links between classical optics and quantum physics. Maxwell introduced his system of four equations in 1864 and it is astounding that the later revolutions leading to special relativity and quantum physics did not change these equations. They were Lorentz invariant from the start and they also describe the mode functions used in quantum electrodynamics. Yet, with one exception, the parameters in Maxwell's equations determining the spatio-temporal dynamics of light have not been related to the typical relativistic quantum properties of space-time through which they propagate. These parameters are the speed of light, the impedance of the vacuum and implicitly also the zero-energy-value of the fine structure constant. Now—it seems—the link has been found. Particles and anti-particles appear and disappear in the vacuum of the Universe. With these virtual pairs modelled as electric dipoles causing a polarization of the vacuum, the impedance of empty space depends only on the sum of the square of the electric charges of particles (but not their masses). If this model is correct, the value of the velocity of light combined with the value of vacuum impedance gives an indication of the total number of charged elementary particles existing in nature. The energy dependence of the fine structure constant, determined through experiments, supports this hypothesis.

**Contact: **gerd.leuchs(at)mpl.mpg(dot)de**Group:** *Leuchs Division***Reference:** G. Leuchs et al., Eur. Phys. J. D **67**, 57 (2013).