Negative temperature

Uncommon card · No. 173336

Certain thermodynamic systems can achieve negative thermodynamic temperature; that is, their temperature can be expressed as a negative quantity on the Kelvin or Rankine scales. This should be distinguished from temperatures expressed as negative numbers on non-thermodynamic Celsius or Fahrenheit scales, which are nevertheless higher than absolute zero. Temperature is related to how particles are distributed among the available energy states of a system. At ordinary positive temperatures, lower-energy states are more likely to be occupied than higher-energy states. At negative temperatures, this distribution is reversed, so higher-energy states become more populated than lower-energy ones. For this reason, a system with a truly negative temperature on the Kelvin scale is hotter than any system with a positive temperature. If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system. A standard example...

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