Third law of thermodynamics
, sometimes referred to as the third law of thermodynamics
, states that the entropy
of a system at zero absolute temperature
is a well-defined constant. This is due to the fact that a system at zero temperature exists in its ground state
, so that its entropy is determined by the degeneracy
of the ground state. Many systems, such as crystal lattices, have a unique ground state, and therefore have zero entropy at at absolute zero (since ln(1) = 0).