A team of researchers from the University of Bonn, Heidelberg University and the National Autonomous University of Mexico has studied the critical behavior of light particles (photons) close to a phase transition. This critical scaling behavior, which sees thermodynamic quantities grow extremely large or diverge shortly prior to Bose-Einstein condensation, had never before been seen in photon gases until the researchers successfully secured precisely this proof.

In the research published in the journal Science Advances, the team measured the spatial correlations of a nearly non-interacting 2D photon gas trapped in a mirror box at the moment of condensation, determining the critical exponent—a quantity describing the rapid increase in the correlation length as the temperature changes near the phase transition.