The Third Law of Thermodynamics states that as a substance cools to a temperature near absolute zero (-273.15°C or 0 Kelvin), its entropy, which is a measure of disorder or uncertainty in the system, approaches a constant and finite value.
This law postulates that reaching absolute zero would require an infinite number of steps, being unattainable in practice. Furthermore, it suggests that all systems would reach a state of maximum order and theoretical minimum disorder at that extreme temperature, which has fundamental implications in fields such as quantum physics and the study of new materials with extraordinary properties at ultra-low temperatures.
Here are some examples that illustrate this principle:
Example 1: Ice crystals
When water cools to temperatures close to absolute zero, ice crystals form. As the temperature decreases, the water molecules lose energy and organize themselves into a highly ordered structure.
At absolute zero, the ice crystals would reach their maximum ordering.
Example 2: Superconductivity
Superconductivity is a phenomenon in physics that occurs in certain materials when cooled below a specific critical temperature. At this critical temperature, superconducting materials exhibit a unique property: electrical resistance disappears completely, allowing electricity to flow without loss of energy.
The Third Law of Thermodynamics explains the relationship between superconductivity and entropy reduction at ultra-low temperatures.
Under normal conditions, when we apply an electric current through a conductor, such as a copper wire, the electrons that carry the electricity face obstacles and collide with the ions of the material, which generates resistance to the flow of electrons. This resistance is responsible for the loss of energy in the form of heat and limits the efficiency of electrical devices.
However, in a superconducting material, at very low temperatures close to absolute zero, something amazing happens: electrons form "Cooper pairs". These pairs are made up of two electrons coming together and moving together through the crystal without experiencing resistance.
Example 3: Liquid helium
Helium, a gas at room temperature, becomes a liquid at extremely low temperatures, close to absolute zero.
As helium cools and becomes a liquid, its atoms reduce in energy and move with less agitation, resulting in a significant decrease in entropy.
Example 4: Bose-Einstein Condensates
At temperatures close to absolute zero, some atoms stick together in a special aggregation state called the Bose-Einstein condensate.
In this quantum state, the atoms lose their individuality and behave as a single quantum entity. This phenomenon is possible thanks to the Third Law of Thermodynamics, which states that entropy decreases as extremely low temperatures are reached.
This phenomenon was predicted by Albert Einstein and the Indian physicist Satyendra Nath Bose in the 1920s. The idea is based on Bose-Einstein quantum statistics, which describe the behavior of identical and indistinguishable particles, such as photons of light or the atoms that make up certain elements.
Under normal conditions, at higher temperatures, the particles follow a statistical Fermi-Dirac (for fermions) or Maxwell-Boltzmann (for bosons) distribution.
However, when the particles are cooled to extremely low temperatures, their collective quantum behavior begins to dominate, and they tend to "collapse" into the lowest possible energy state. At this point, a large number of particles occupy a single quantum state, forming what is known as the Bose-Einstein condensate.
In this quantum state, the particles lose their individuality and behave like a collective "superparticle", with macroscopic quantum properties. All substance becomes a single quantum entity
Example 5: Solid Helium
At temperatures close to absolute zero, liquid helium can also solidify. In its solid state, helium exhibits unusual behavior such as superfluidity, where it can flow without resistance through extremely narrow capillaries, defying the classical laws of physics.
Example 6: Dry ice
Dry ice is carbon dioxide (CO2) in a solid state at temperatures much lower than the freezing point of water. Unlike water, which freezes at 0°C, CO2 solidifies directly as dry ice at -78.5°C (-109.3°F) at normal atmospheric pressure.
When dry ice is at temperatures close to absolute zero, it behaves similarly to other solids at those extremely low temperatures. The CO2 molecules that make up dry ice have their kinetic energy drastically reduced, resulting in a highly ordered structure and a significant decrease in entropy. In this state, dry ice would reach its maximum possible thermal ordering at room temperature.
Dry ice is widely used in applications as a refrigerant, in the food industry, in transporting heat-sensitive materials, and as a special effect in the theater and entertainment industry.
