Late to the party, but I thought I'd clarify on what temperature really means. Many people are familiar with temperature as characterized by "average thermal v

Late to the party, but I thought I'd clarify on what temperature really means. Many people are familiar with temperature as characterized by "average thermal velocity" of, say, air molecules. However, in statistical mechanics (the physics of many particle systems), temperature is defined in terms entropy and energy. Specifically, temperature is the rate-of-change of energy with respect to entropy. (In math: T = dU/dS.) This arises as a natural definition if you think of temperature as "the thing that is equal between two systems in thermal equilibrium". Think about it this way: A cup of water and an ocean have VASTLY different energies. Similarly, the ocean has an enormous entropy compared to the cup. However, if they're at the same temperature, the unit change of entropy per energy added is the same. Coming back to the article, the temperature being reported by ALICE is derived from the entropy and energy of the collisions. Specifically, they're looking at quark-gluon plasma from the heavy-ion collision at LHC. Under normal conditions, quarks and gluons are confined to hadrons like protons and neutrons. Quark-gluon plasma occurs only at extreme energies, and in these collisions it is a essentially a chaos of quarks and gluons. The chaos (entropy) is not a thermal property but rather largely comes from the nature of the strong force. So, changing the energy of a quark-gluon plasma doesn't have a huge effect on its entropy. Conversely, you could say it takes a lot of energy to change the entropy, and so by the definition of temperature, you get a very large value!