Physics

The 2026 Nobel Prize in Physics went to Francis Halzen for his work on the IceCube Neutrino Observatory and the discovery of high-energy astrophysical neutrinos.

Absolute zero is the zero point of thermodynamic temperature, equal to 0 kelvin or −273.15 °C, at which thermal excitation reaches its limiting minimum.

Action is a scalar functional of a system’s history whose stationary values determine classical dynamics and whose phase governs quantum path integrals.

An adiabatic process is a thermodynamic change during which no heat is transferred between a system and its surroundings.

Albedo is a measure of the fraction of incident radiation reflected by a surface or astronomical body.

Albert Einstein was a German-born theoretical physicist who developed relativity and made foundational contributions to quantum theory and statistical physics.

Alpha decay is radioactive transformation in which an unstable nucleus emits a helium-4 nucleus, reducing its atomic number by two and mass number by four.

Alternating current is electric current that periodically reverses direction, forming the basis of most electrical power distribution systems.

The ampere is the SI base unit of electric current, defined by fixing the elementary charge at exactly 1.602176634 × 10⁻¹⁹ coulombs.

An experimental technique that measures photoelectron energies and emission angles to investigate the momentum-dependent electronic structure of materials.

The ångström is a non-SI unit of length equal to 10⁻¹⁰ metre, used chiefly for atomic dimensions, molecular structures, and wavelengths.

Angular momentum measures rotational motion and is conserved when the net external torque vanishes; in quantum mechanics, it includes orbital and intrinsic spin contributions.

Anharmonicity is departure from harmonic oscillation, producing nonlinear restoring forces, amplitude-dependent frequencies, unequal quantum energy spacings, and interactions between vibrational modes.

The anomalous magnetic moment measures a particle’s deviation from the Dirac magnetic-moment prediction and provides a precision test of quantum interactions.

Asymptotic freedom is the weakening of an interaction at increasing energy scales, a defining property of quantum chromodynamics.

ATLAS is a general-purpose particle-physics experiment at CERN’s Large Hadron Collider, designed to investigate fundamental particles and interactions.

The atomic nucleus is the compact, positively charged center of an atom, containing protons and usually neutrons and accounting for nearly all its mass.

A band gap is an energy interval without allowed electronic states, central to the electrical and optical properties of semiconductors and insulators.

A baryon is a composite particle with baryon number one, usually containing three valence quarks; protons and neutrons are the best-known examples.

BCS theory explains conventional superconductivity through electron pairing and the formation of a coherent quantum state.

A Bell state is one of four maximally entangled two-qubit states that form an orthonormal basis and serve as fundamental resources in quantum information.

Beta decay is a weak-interaction process that converts neutrons into protons or protons into neutrons, accompanied by leptons.

Blackbody radiation is the universal thermal electromagnetic radiation spectrum of an ideal absorber, determined solely by its absolute temperature.

The Boltzmann constant connects temperature with microscopic energy and statistical entropy, and its exact value defines the kelvin.

The Boltzmann distribution assigns equilibrium probabilities to physical states according to their energies and the temperature of a thermal reservoir.

The Born rule connects quantum states to measurement outcomes by assigning probabilities through squared amplitudes or equivalent operator formulas.

A quantum state of bosonic matter in which a macroscopic fraction of particles occupies a single quantum state, producing collective behavior and coherence.

Bose–Einstein statistics describes the quantum counting and equilibrium occupation of states by identical bosons, allowing multiple particles to occupy the same state.

A boson is a quantum particle with symmetric exchange statistics, allowing identical particles to occupy the same quantum state.

A geometric relation connecting wavelength, crystal-plane spacing, and the angles at which constructive diffraction occurs.

Brownian motion is the irregular thermal movement of particles suspended in a fluid and the continuous random process used to model such movement.

Calibration establishes relationships between reference values and instrument indications, including their uncertainties, so that indications can be converted into measurement results.

A calorie is a unit of energy originally defined by heating water, and on food labels it usually means the kilocalorie (kcal), while the SI unit of energy is the joule.

The canonical ensemble describes equilibrium systems with fixed particle number and volume that exchange energy with a reservoir at a prescribed temperature.

Capacitance quantifies the charge stored per unit electric potential difference, governing electrical energy storage and the behavior of capacitors.

The Carnot cycle is an ideal reversible thermodynamic cycle that establishes the maximum efficiency of a heat engine operating between two thermal reservoirs.

The center of mass is the mass-weighted mean position of a system, used to describe its overall motion and balance.

CERN is an intergovernmental research organization near Geneva that operates particle accelerators and supports international investigations into the fundamental constituents and interactions of matter.

Chemical potential measures how a system’s thermodynamic energy changes with composition and determines equilibrium in particle exchange, phase coexistence, and chemical reactions.

Chinese theoretical physicist who shared the 1957 Nobel Prize in Physics and co-developed Yang–Mills gauge theory.

Chien-Shiung Wu was a Chinese American experimental physicist whose work demonstrated parity violation in the weak interaction.

Classical mechanics describes motion, equilibrium, and mechanical interactions using Newtonian laws and analytical formulations, within limits set by quantum and relativistic effects.

CMS is a general-purpose experiment at CERN’s Large Hadron Collider that studies fundamental particles and interactions.

Color charge is the quantum property of quarks and gluons that determines their participation in the strong interaction.

Color confinement is the absence of isolated quarks and gluons as observable particles, a defining long-distance property of quantum chromodynamics.

Compton scattering is the interaction of a photon with an electron that changes the photon’s direction and energy through electron recoil.

Condensation is the change of a substance from gas to liquid, releasing latent heat and occurring in atmospheric processes and industrial equipment.

Condensed matter physics studies how interacting constituents produce the collective properties of solids, liquids, and related systems.

A conservative force does work that depends only on the initial and final positions, allowing its effects to be described by potential energy.

A Cooper pair is a correlated pair of fermions whose collective quantum behavior underlies conventional superconductivity and several forms of superfluidity.

Correlation length is the characteristic spatial scale over which fluctuations in a system remain correlated.

The coulomb is the SI unit of electric charge, equal to the charge transferred by a current of one ampere in one second.

Coulomb’s law describes the electrostatic force between point charges as proportional to their charge product and inversely proportional to their squared separation.

A critical exponent describes the power-law behavior of a physical quantity near a continuous phase transition.

A critical point marks the disappearance of a phase distinction in physics, or a zero or undefined derivative in calculus.

Crystallography studies the atomic arrangement, symmetry, and properties of crystals using mathematical analysis and experimental techniques.

Deep inelastic scattering probes the quark and gluon structure of hadrons through high-energy lepton collisions with large momentum transfer.

Degeneracy pressure is the resistance to compression produced by the quantum-state occupancy restrictions of fermions, persisting even at zero temperature.

Density is mass per unit volume, describing how much matter occupies a given space and how that quantity varies with material and physical conditions.

A density matrix represents a quantum state, encompassing pure states, statistical mixtures, and the reduced states of entangled systems.