Third Law of Thermodynamics
The law stating that as system temperature approaches absolute zero (0 K), entropy of a pure crystalline substance approaches a minimum constant value of zero.
Governing formula
lim (T → 0) S = 0
SI unit
J/K
In depth
At absolute zero, a perfect crystal has exactly one unique quantum ground state (Ω = 1), so S = kB ln(1) = 0. Implies absolute zero cannot be reached in a finite number of physical steps.
Examples in the real world
Cooling liquid Helium to near 0 K where atomic thermal jitter ceases and quantum superfluidity emerges.