Particles

A particle is a localized, identifiable unit of matter or energy with properties such as mass, electric charge, and spin. In quantum physics, particles are excitations of fields and can exhibit both particle-like and wave-like behavior. The concept covers both fundamental, indivisible entities (elementary particles) and composite systems made of smaller constituents. In everyday language, objects treated as particles are often macroscopic approximations of this idea.

Elementary particles are divided into fermions and bosons. Fermions include quarks and leptons; quarks come in six flavors (up, down, charm, strange, top, bottom) and combine to form hadrons, while leptons include electrons, muons, taus, and neutrinos. Bosons include gauge bosons—photon, gluon, W and Z bosons—and the Higgs boson. Fermions obey the Pauli exclusion principle; bosons do not.

Composite particles include hadrons such as baryons (for example, protons and neutrons) and mesons (such as pions and kaons), which are bound states of quarks held together by the strong force. At larger scales, atoms and molecules are bound systems of nuclei and electrons. The interactions among particles are mediated by fundamental forces and described by quantum field theories.

The Standard Model of particle physics describes electromagnetic, weak, and strong interactions in terms of particles and fields. Gravity is not yet incorporated in the same framework. Experimental study relies on high-energy collisions and particle detectors to measure properties such as masses, charges, lifetimes, and interaction probabilities. Many questions remain, including the nature of dark matter and physics beyond the Standard Model.