This is a schematic of the organic microcavity used to observe
superfluid flow. Scientists have known for centuries that light is composed of waves. The fact that light can also behave as a liquid, rippling and spiraling around obstacles like the current of a river, is a much more recent finding that is still a subject of active research. The 'liquid' properties of light emerge under special circumstances, when the photons that form the light wave are able to interact with each other.