Physics

Gauss’s law relates the electric flux through a closed surface to the net electric charge enclosed by that surface.

The General Conference on Weights and Measures is the intergovernmental authority responsible for international measurement policy and the International System of Units.

General relativity describes gravity as spacetime curvature and relates that curvature to the distribution of matter and energy.

Gibbs free energy is a thermodynamic potential that determines equilibrium and the capacity for non-expansion work at constant temperature and pressure.

A phenomenological field theory describing superconductivity through a spatially varying complex order parameter, with broader applications to phase transitions and critical phenomena.

A gluon is a massless elementary particle that carries the strong interaction between quarks and also interacts with other gluons.

A statistical description of an equilibrium system that exchanges energy and particles with a reservoir at fixed temperature, volume, and chemical potential.

Gravitational lensing is the deflection of light by gravity, producing changes in apparent position, shape, brightness, or image number.

A gravitational wave is a propagating disturbance in spacetime curvature that carries energy and reveals the dynamics of astronomical sources.

Gravity is the fundamental interaction that attracts objects with mass or energy. General relativity describes it as the curvature of spacetime.

A hadron is a color-neutral composite particle governed by the strong interaction, including protons, neutrons, mesons, and exotic multiquark states.

Hadronization is the nonperturbative process through which quarks and gluons form color-neutral hadrons.

Half-life is the time required for a decaying quantity to decrease to half its initial value, especially in radioactive decay and chemical kinetics.

Hamiltonian mechanics describes classical dynamics through generalized coordinates, conjugate momenta, and a Hamiltonian function on phase space.

The Hamiltonian operator represents a quantum system’s energy and generates its time evolution, linking measurable energy spectra with dynamical behavior.

Heat is energy transferred between systems because of a temperature difference, rather than a property stored within a body.

Heat capacity measures the heat required to raise a system’s temperature under specified conditions, reflecting its size, composition, and microscopic energy-storage mechanisms.

Helmholtz free energy is a thermodynamic potential that determines equilibrium at fixed temperature and volume and bounds the work obtainable in an isothermal process.

The Higgs boson is the elementary particle associated with the Higgs field, whose interactions explain how many fundamental particles acquire mass.

The Higgs field is a quantum field whose nonzero vacuum value generates the masses of several elementary particles in the Standard Model.

The Higgs mechanism generates masses for gauge bosons through a scalar field’s nonzero vacuum value while preserving gauge invariance.

High-temperature superconductivity is superconductivity at unusually high transition temperatures, found notably in copper oxides, iron-based compounds, and compressed hydrides.

Ibn al-Haytham was an eleventh-century scholar whose experimental and mathematical investigations transformed the study of light and vision.

A cubic-kilometre neutrino detector built into the Antarctic ice at the South Pole, used to study high-energy neutrinos from cosmic sources.

A theoretical gas whose pressure, volume, and absolute temperature obey the ideal gas law, providing a reference model for dilute gases.

Inductance quantifies the relationship between electric current, magnetic flux linkage, and the voltage induced by changes in current.

An inertial reference frame is a frame in which freely moving bodies maintain constant velocity and physical laws take their standard unaccelerated form.

Interference is the reinforcement or cancellation produced when overlapping waves or quantum probability amplitudes combine.

Interferometry uses wave interference to measure displacement, optical properties, celestial structure, and physical effects with high sensitivity.

Internal energy is the energy associated with a system’s microscopic constituents and interactions, excluding its overall motion and external potential energy.

The International Bureau of Weights and Measures coordinates international measurement standards, maintains reference time scales, and supports worldwide measurement comparability.

The International System of Units is the internationally agreed measurement system, defined through seven constants and organized into base units, derived units, and decimal prefixes.

Ionization is the formation of electrically charged atoms or molecules through electron removal, electron attachment, or chemical reactions.

English mathematician and natural philosopher whose work on motion, gravitation, calculus, and light shaped modern science.

The Ising model describes interacting two-state variables and provides a fundamental framework for studying magnetism, phase transitions, and collective behavior.

British physicist who discovered the electron, developed an early atomic model, and helped establish mass spectrometry.

American theoretical physicist who led Los Alamos during the Manhattan Project and later advised on nuclear policy.

Scottish physicist and mathematician who developed electromagnetic field theory and pioneered statistical approaches to gases and quantitative studies of colour.

English experimental physicist whose measurements established the quantitative relationship between mechanical work and heat and helped found thermodynamics.

The Josephson effect is phase-dependent supercurrent flow between weakly coupled superconductors, linking electrical voltage to oscillation frequency and enabling quantum sensors, voltage standards, and superconducting qubits.

The joule (J) is the SI unit of energy, work, and heat, equal to one newton metre or one watt second.

Joule heating is the conversion of electrical energy into thermal energy when an electric current flows through a resistive material.

The kelvin is the SI base unit of thermodynamic temperature, defined by fixing the numerical value of the Boltzmann constant.

The kilogram is the SI base unit of mass, defined by fixing the numerical value of the Planck constant.

Kinetic energy is the energy associated with motion, described by different expressions in classical mechanics, relativity, and quantum mechanics.

A Lagrangian is a function that encodes a physical system’s dynamics through stationary action, or combines an optimization objective with constraints.

The Large Hadron Collider is CERN’s underground particle accelerator, used to investigate fundamental particles and interactions through high-energy proton and heavy-ion collisions.

Latent heat is energy absorbed or released during a phase transition, typically without a temperature change under equilibrium conditions.

Lattice QCD is a discretized formulation of quantum chromodynamics used to calculate strong-interaction phenomena nonperturbatively through numerical simulations.

A lepton is an elementary spin-½ particle that does not participate in the strong interaction; the known leptons comprise three charged particles and three neutrino flavors.

Light is electromagnetic radiation, particularly the visible portion, exhibiting wave-like propagation and quantized exchanges of energy with matter.

The Lorentz force describes how electric and magnetic fields exert force on an electrically charged particle, governing its acceleration and deflection.

A Lorentz transformation relates spacetime coordinates while preserving the spacetime interval, providing the mathematical foundation for relativistic changes of reference frame.

Macroscopic quantum coherence is the persistence of quantum phase relationships across many-particle systems or between distinct collective states.

Macroscopic quantum tunneling is the passage of a collective physical variable through an energy barrier that classical dynamics would prevent it from crossing.

A magnetic field describes magnetic forces on moving charges and magnetic moments, arising from electric currents, changing electric fields, and magnetized matter.

Magnetic flux is the surface integral of the normal component of a magnetic field, governing electromagnetic induction and many electrical and superconducting devices.

Magnetic flux quantization is the restriction of superconducting fluxoid—and, under suitable conditions, magnetic flux—to discrete multiples of h/2e.

The magnetic flux quantum, h/(2e), is the fundamental unit of fluxoid quantization in conventional superconductors.

Magnetic susceptibility quantifies a material’s magnetization response to a magnetic field, revealing its magnetic behavior and microscopic interactions.