Experiment reveals evidence for a previously unseen behaviour of light

Beams of light do not, generally speaking, bounce off each other like snooker balls. But at the high energies in the Large Hadron Collider at CERN they have just been observed doing exactly that

Light is useful, versatile and perplexing. We see with it - that is, we make sense of our surroundings (sometimes) using signals that our eyes send to our brains when light impinges upon them. We also use it to "see" far beyond the limits of our own sense organs. We peer deep into space, or - as at the shiny new light source just opened in Hamburg - into the complexities of atoms and molecules.

Often we think of light as a wave, and that is how it often behaves. But we know that light comes in little packets - quanta - called photons. The paper which swung the scientific consensus in favour of the existence of photons was published by Albert Einstein in 1905, and yet in 1951 he wrote to an old friend