More than 200 years ago, the English scientist Thomas Young carried out a famous test known as the “double-slit experiment”. He shone a beam of light at a screen with two slits in it, and observed the light that passed through the apertures formed a pattern of dark and bright bands.
At the time, the experiment was understood to demonstrate that light was a wave. The “interference pattern” is caused by light waves passing through both slits and interfering with each other on the other side, producing bright bands where the peaks of the two waves line up and dark bands where a peak meets a trough and the two cancel out.
