Why does a body with $0\ K$ temperate does the internal energy NOT become $0\ J$? My lecturer said it had to do with some quantum mechanics, but I never really got any answers from him. I really want to understand this to better understand thermal physics.


If the internal energy becomes zero, that means the particles constituting the body come to complete rest. This implies that the particles constituting the body have a definite position and momentum. According to Heisenberg's uncertainty principle

$\Delta x \Delta p \geq \frac{\hbar}{4\pi}$

So if a particle is at rest i.e has a definite position and zero momentum, this inequality isn't satisfied and hence it is not possible to have zero internal energy at absolute zero.

  • $\begingroup$ Yes, "zero-point energy" if one wants to search for more details. $\endgroup$ – Pieter Oct 22 '18 at 8:31

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