Fermi gas

In a classical ideal gas, particles can occupy the same energy state freely and the distribution follows Maxwell-Boltzmann statistics. In a Fermi gas, the Pauli exclusion principle forbids identical fermions from sharing the same quantum state, so particles fill up successive energy levels even at absolute zero, creating pressure independent of temperature.

The Fermi energy is the energy of the highest occupied quantum state in a Fermi gas at absolute zero temperature. It determines key properties of metals—such as electrical and thermal conductivity—and explains why electrons in a metal contribute to heat capacity much less than classical physics would predict.

Because fermions cannot occupy the same quantum state, compressing a Fermi gas forces particles into higher energy states rather than allowing them to collapse into the ground state. This generates an outward degeneracy pressure that persists even at absolute zero and is what prevents white dwarfs and neutron stars from collapsing under their own gravity.

Yes, researchers have created ultracold degenerate Fermi gases using fermionic atoms such as potassium-40 and lithium-6, cooled to temperatures near absolute zero using laser cooling and evaporative cooling techniques. These experiments, achieved in the late 1990s and 2000s, allow direct study of quantum statistical phenomena in controlled settings.