How many microstates are defined to exist at absolute zero for a perfect crystal?

1 Answer

#-273°C# corresponds to #"0 K"# on the absolute scale.

The third law of thermodynamics states that in that case, the absolute entropy becomes zero for a perfect crystal:

#S = 0# at #T = "0 K"#.

Statistically, from Boltzmann's theorem, #S = k_B ln W#

#S = 0 implies ln W = 0#

where #W# is the number of microstates occupied.

Thus, #W = 1# which means that this is the most ordered state with number of microstates = 1.

However, quantum fluctuations make it difficult that such a state becomes localised because the fluctuations occurring are non-negligible compared to the energy available.

This has an important implication - absolute zero is difficult to maintain.