A fermion is a fundamental particle characterized by Fermi-Dirac statistics and follows the [[Pauli Exclusion Principle]]. These particles are one of the two basic constituents of matter, the other being bosons. The key difference between fermions and bosons lies in their spin: fermions have half-integer spin (like 1/2, 3/2, etc.), while bosons have integer spin (like 0, 1, 2, etc.). ### Key Properties of Fermions: 1. **Half-integer Spin**: This property categorizes particles into fermions and is significant due to its implications in quantum mechanics. Spin affects the magnetic moment and statistics of the particle, influencing how it behaves under various physical processes. 2. **Pauli Exclusion Principle**: This principle is fundamental to fermions and states that no two identical fermions can occupy the same quantum state simultaneously within the same quantum system. This principle explains many physical phenomena, from the structure of the periodic table to the stability of matter. 3. **Antisymmetry of Wave Functions**: The wave functions of fermionic systems are antisymmetric with respect to the exchange of any two particles. This mathematical property results from their half-integer spin and underpins their statistical behavior. ### Types of Fermions: - **Elementary Fermions**: These are fermions that are not made up of other particles. They include the quarks and leptons. Quarks make up protons and neutrons, while leptons include electrons and neutrinos. - **Composite Fermions**: These are particles that are made up of an odd number of elementary fermions. Examples include protons and neutrons (each made up of three quarks). ### Role in Physics and the Universe: - **Atomic Structure**: The electrons that orbit the nucleus in an atom are fermions, and their arrangement in shells and subshells—determined by the Pauli Exclusion Principle—dictates the chemical properties of elements. - **Matter Stability**: The Pauli Exclusion Principle provides a quantum mechanical force that adds stability to matter, preventing atoms from collapsing under the pull of gravity or electromagnetic interaction. - **Superconductivity and Other Quantum Phenomena**: In some conditions, fermions can pair up (as in Cooper pairs in superconductivity) and behave collectively as bosons, leading to phenomena like superconductivity where electrical current flows without resistance. - **Statistical Mechanics**: Fermi-Dirac statistics describe the distribution of fermions over energy states in thermal equilibrium and are crucial for understanding the thermal and electrical properties of solids. Fermions are integral not only to the foundation of quantum physics but also to the very structure and operation of the universe, from the smallest scales of particles to the large-scale structure of matter in stars and galaxies. # References ```dataview Table title as Title, authors as Authors where contains(subject, "fermion") sort modified desc, authors, title ```