I don’t understand how atoms that are in the “negative tempretures” have 0 entropy while being insanely hot. I also dont get how negative temperatures are hotter than infinity if (planck’s temperature forbids this; dont really know if it does). Please explain!
In: Physics
basically temperature is the direction in which entropy rises (with energy). For macroscopic systems, the number of possible states (the entropy) usually rises (very strong) with energy. Hence temperature is positive. if you have two macroscopic systems they will exchange energy such that their combined entropy will be maximized. That means some tiny bit of energy lost here will reduce the entropy precisely as much as it will rise the entropy there. Hence they will equalize in temperature.
For quantum systems, the number of states can reduce with energy. (take semiconductors near their bandgap). In this scenario the temperature is negative: as you increase the energy less states become available. Since two systems will still try to find maximum entropy, the negative temperature part will drain it’s energy and pump it into the positive temperature part until both (then positive) temperatures are equal.
The temperatures still equalize, but the energy flow is reversed (from the negative to the positive temperature parts, instead from the higher to the lower temperature parts). So in a way, regarding energy flow, negative temperature parts are hyper-hot, as they dump their energy into anything with positive temperature.
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