Fermions

Overview

Fermions are a class of particles that obey the Pauli Exclusion Principle, a fundamental principle in quantum mechanics. Named after the physicist Enrico Fermi, they are characterized by their half-integer spin and include particles such as quarks, leptons, and baryons. Fermions are one of the two basic constituents of matter, the other being bosons.

A collection of various fermions, including quarks, leptons, and baryons.

Characteristics

Fermions are distinguished by their intrinsic angular momentum, or spin, which is always a half-integer value. This property leads to a unique behavior known as Fermi-Dirac statistics, which describes the distribution of particles over energy states in systems composed of many identical particles that obey the Pauli Exclusion Principle. This principle states that no two fermions can occupy the same quantum state simultaneously.

Classification

Fermions can be classified into two categories: elementary fermions and composite fermions.

Elementary Fermions

Elementary fermions are the most basic building blocks of matter and cannot be broken down into simpler particles. They include quarks and leptons. There are six types of each, known as flavors. Quarks combine to form composite particles known as hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Leptons include the electron, muon, tau, and their associated neutrinos.

Composite Fermions

Composite fermions are made up of several elementary particles. They include baryons (which are made of three quarks) and mesons (which are made of a quark and an antiquark). Protons and neutrons are the most well-known baryons. Composite fermions also obey the Pauli Exclusion Principle.

Role in the Universe

Fermions play a crucial role in the structure and behavior of the universe. The properties of fermions, particularly their obedience to the Pauli Exclusion Principle, determine the structure of atoms, the properties of solids, and the behavior of electrons in electrical conductors. Fermions also play a key role in the nuclear reactions that power stars and in the physics of neutron stars.