Negative temperature
In physics, absolute zero (0 K) is the coldest temperature. At that point, subatomic particles stop moving (entropy is at its minimum). Certain things can reach temperatures below absolute zero, known as negative temperatures. This is very difficult to do, and only very small objects can reach negative temperatures.
It might seem absurd, but things at negative temperatures are actually hotter than things at positive temperatures (above absolute zero). If something with a negative temperature comes in contact with a positive-temperature object, heat will go from the negative object to the positive. This is because temperature is a trade-off between energy and entropy. If you add energy to a positive-temperature object, it will increase in entropy. If you add energy to a negative-temperature object, it will decrease in entropy.
Many objects cannot achieve negative temperatures, because adding energy to them will increase their entropy. Only very small things discussed in quantum mechanics can reach this state.
Negative Temperature Media
SI temperature/coldness conversion scale: Temperatures on the Kelvin scale are shown in blue (Celsius scale in green, Fahrenheit scale in red), coldness values in gigabyte per nanojoule are shown in black. Infinite temperature (coldness zero) is shown at the top of the diagram; positive values of coldness/temperature are on the right-hand side, negative values on the left-hand side.
When the temperature is negative, higher energy states are more likely to be occupied than low energy ones.
