The Third Law of Thermodynamics: Absolute Zero

Today I will discuss the third law of thermodynamics, which concerns absolute zero.

What Is the Third Law?

Simply put, it explains that a system's entropy approaches a constant as its temperature approaches absolute zero.
What is entropy? It measures irregularity or disorder, numerically expressing how many different states a system can have.

Absolute Zero

Absolute zero is -273.15°C, or 0 K (kelvin), a temperature theoretically unattainable. At this point, atomic motion stops and the system can lose no further thermal energy, reaching its minimum-energy ground state.

Residual Entropy and Microstates

A ground-state system may possess residual entropy. This is generally near zero except in amorphous solids. Interestingly, noncrystalline solids such as glass can theoretically have nonzero residual entropy because they lack a unique ground state.

Microstates indicate the probability of a system occupying a particular state. At absolute zero, only one microstate is possible, meaning all atoms and possible arrangements are identical. Entropy is therefore calculated as Boltzmann's constant k_B times the natural logarithm of the number of possible microstates Ω.

Calculating Entropy

S = (k_B)*(ln(Ω))

If Ω is one, meaning only one microstate, ln(1) = 0 and entropy S becomes zero. This indicates a completely ordered system with no room to increase disorder.

The third law is thus a very important physics concept, greatly contributing to understanding the universe's fundamental workings.
That was today's discussion of the third law. Keep up the good work, everyone!