Swimming in a sea of superfluid light

o the best of our knowledge, it is not clear whether such questions ever crossed Newton's thoughts. In the following decades, the rising success of Huygens' wave theory of light completely deflected the interest of the physics community from these speculations. Even though the corpuscular theory of light had a sudden revival at the beginning of the twentieth century when Einstein put forward his theory of the photo-electric effect, the idea of observing collective hydrodynamic behaviour in a fluid of interacting photons had to wait another few decades until the very recent spectacular observations of superfluidity of light.