Theoretical Physics Glossary

A particle with the same mass as its corresponding matter particle but opposite charge and quantum numbers.

A particle with integer spin that mediates forces between fermions. Examples include photons, gluons, W/Z bosons, and the Higgs boson.

A principle stating that a particular measurable property of an isolated physical system does not change over time.

The unknown energy driving the accelerating expansion of the universe, constituting approximately 68% of total energy content.

Non-luminous matter inferred from gravitational effects, comprising approximately 27% of the universe's mass-energy content.

The relativistic wave equation for spin-$\frac{1}{2}$ particles such as electrons. Predicted the existence of antimatter.

A quantum state in which a particular observable has a definite value. Measurement of that observable will yield the corresponding eigenvalue with certainty.

The boundary of a black hole beyond which events cannot affect an outside observer. The point of no return for matter and light.

A particle with half-integer spin that obeys the Pauli exclusion principle. Includes quarks and leptons, the building blocks of matter.

A force-carrying particle arising from gauge symmetry. The photon, gluons, and W/Z bosons are gauge bosons.

The shortest or extremal path between two points in curved spacetime. Free-falling objects follow geodesics.

The hypothetical quantum of the gravitational field, predicted to be a massless spin-2 boson. Not yet detected.

A function summarizing the dynamics of a system, equal to kinetic energy minus potential energy. Central to modern theoretical physics and the principle of least action.

A class of elementary fermions that do not experience the strong nuclear force. Includes electrons, muons, taus, and their associated neutrinos.

Mathematical equations relating the space and time coordinates of two observers moving at constant velocity relative to each other in special relativity.

The massless quantum of the electromagnetic field. Mediates the electromagnetic force and travels at the speed of light.

A fundamental constant ($h$) relating the energy of a photon to its frequency via $E = h\nu$. Its reduced form ($\hbar = h / 2\pi$) appears throughout quantum mechanics.

An elementary fermion that experiences all four fundamental forces. Quarks combine to form hadrons such as protons and neutrons.

A set of techniques for dealing with infinities in quantum field theory by redefining physical parameters at different energy scales.

A point where physical quantities such as density or curvature become infinite, indicating the breakdown of the current theoretical framework.

An intrinsic form of angular momentum carried by quantum particles. It has no classical analog and determines whether a particle is a fermion or boson.

The quantum principle that a system can exist in multiple states simultaneously until measured, at which point it collapses to a single state.

The energy of empty space arising from quantum fluctuations. Related to the cosmological constant and the cosmological constant problem.

A transient fluctuation in a quantum field that mediates forces between real particles. Cannot be directly observed but their effects are measurable.

A mathematical function ($\psi$) whose square modulus $|\psi|^2$ gives the probability density of finding a particle in a given state or position.