Scientists at the United States National Institute of Standards and Technology and University of Colorado have created a new form of matter called a Fermionic gas. The new gas follows the laws of quantum mechanics, the branch of science that describes the world of the very small in which everything, matter, energy and even space and time comes in lumps or quanta. It means that the new gas will behave in ways that can only be observed in small systems and a million atoms of Potassium is certainly very small in nature's terms. Every particle in nature can be classified as either a Fermion or a Boson.
Fermions are the type of particles that make up the atom, ie electrons, protons and neutrons.
The best known example of a boson is a photon, a particle of light. Bosons and Fermions behave in very different ways exemplified by the Pauli exclusion principle first proposed by the Physicist Wolfgang Pauli in the 1920s. Stated in technical terms, it says that no two Fermions can occupy the same energy state. In simpler terms it gives protons, neutrons and electrons a sort of identity, a space of their own that cannot be invaded by any other particle. The Pauli exclusion principle is the reason why atoms exist at all.