Light is complicated as it can act as both a wave and a particle. Choosing how we want to talk about light - wave or particle - is only a matter of convenience.

What is Interferometry?

Interferometry is a technique used by scientists and engineers. Tools called interferometers add together 2 or more waves of light. When they do this, the waves of light interact (or interfere) with each other. This can add the waves together, making them brighter. It can also cancel the waves out. Interference only takes place if the waves come from the same object or have the same frequency. We call these types of wave coherent.