Question

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

Answer 1

`-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.