Researchers at Aalto University, Finland, have created a Bose-Einstein condensate of light coupled with metal electrons, so-called surface plasmon polaritons. Nearly 100 years ago, Albert Einstein and Satyendra Nath Bose predicted that quantum mechanics could force a large number of particles to behave in concert as if they were only a single particle. This form of matter was called a Bose-Einstein condensation, and it wasn’t until 1995 that researchers created the first such condensate of a gas of alkali atoms.