Photon-Photon Scattering

Light can bounce off light by exchanging virtual charged particles! This gives nonlinear corrections to Maxwell’s equations, even in the vacuum—but they’re only noticeable when the electric field is about 1018 volts/meter or more. This is an enormous electric field, able to accelerate a proton from rest to Large Hadron Collider energies in just 5 micrometers!

In 2017, light-on-light scattering was seen at the LHC when they shot lead ions past each other:

Direct evidence for light-by-light ...