Light waves squeezed through ‘slits in time’

A celebrated experiment in 1801 showed that light passing through two thin slits interferes with itself, forming a characteristic striped pattern on the wall behind. Now, physicists have shown that a similar effect can arise with two slits in time rather than space: a single mirror that rapidly turns on and off causes interference in a laser pulse, making it change colour. The result adds a new twist to the classic double-slit experiment first performed by physicist Thomas Young.