““If there weren't any charges, there would be neither absorption nor emission nor any scattering. Light would not impact on the matter it passes through nor be impacted by it, and we would have to rely on the action of gravity to notice the existence of light. (If there were no electric charges, we could not exist ourselves, of course.) Light would simply pass through matter (if there were matter, that is). It would not be scattered even by other light; it turns out that light-light scattering happens only because the vacuum fluctuations produce short-lived pairs of charged particles and antiparticles, which can absorb and emit light.””
