| Themes > Science > Physics > Cryogenics > Temperature > Is a negative Kelvin temperature possible? > Temperature |
The most often given answer to this question is something like "no, because at zero K, molecules are not moving anymore and you cannot have less than zero motion." This answer, while not completely wrong, ignores that temperature is not defined as motion of molecules. It is, for certain systems, equal to the mean kinetic energy of molecules, but this is an equality, not a definition. Temperature is usually taken as simple,
because we all can feel it. But have you ever tought of explaining it to
an alien who does not feel it? It would be What is correct in the above-cited answer is that negative Kelvin temperature cannot be achieved by cooling; moreover, not even zero K can be achieved by cooling, as you probably know. Let's have a closer look at that equality between temperature and mean kinetic energy of molecules, and see what we can get out of this. |
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