Answer to Question #134621 in Mechanics | Relativity for alfraid

Question

Explain third law of thermodynamics.

Answer 1

Second law of thermodynamics postulates existence of entropy as a function of the state of the system, so the change in entropy of a system is determined by its initial and final states. It follows that entropy is defined only to particular constant that is unknown.

The third law of thermodynamics helps to fix this. It postulates that for all bodies when $T \to 0$ $S \to 0$. So, $S_0 = 0$. This gives an opportunity to define absolute value of entropy. What does $S_0=0$ mean physically? S is measure of chaos. When $S=0$ for a system of particles, this mean that there is no chaos, no difference in states of those particle, therefore all particles must be in one state. This state is called Bose-Einstein condensate. Any material at $T=0$ becomes Bose-Einstein condensate.