Cherenkov radiation

An often overlooked point is that the universe’s ultimate speed limit is the speed of light in a vacuum. When light passes through transparent materials, it can slow down significantly, and sometimes particles moving through the same medium can break this artificially lowered light-speed barrier. The result is a burst of bluish-coloured Cherenkov radiation – the light equivalent of a ‘sonic boom’ – which can be used to detect high-speed particles such as elusive neutrinos.