Quantum gas goes below absolute zero

[tama]

9. Thermodynamic beta

"Thermodynamic beta is essentially the connection between the information theoretic/statistical interpretation of a physical system through its entropy and the thermodynamics associated with its energy. It can be interpreted as the entropic response to an increase in energy. If a system is challenged with a small amount of energy, then ? describes the amount by which the system will "perk up," i.e. randomize. Though completely equivalent in conceptual content to temperature, ? is generally considered a more fundamental quantity than temperature owing to the phenomenon of negative temperature, in which ? is continuous as it crosses zero where T has a singularity.[1]"

And in fact negative beta is "hotter" than any positive beta, as "If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system."

More: http://en.wikipedia.org/wiki/Negative_temperature