Plain English

Glossary

Every term we use, defined without gatekeeping. The real word, explained simply.

Alpha particle: A small, fast, positively charged particle thrown out by some radioactive atoms. It is actually the nucleus of a helium atom: two protons and two neutrons.
Ampere (also: amp): The Ampere is the standard international (SI) unit for measuring electric current, representing the flow of one coulomb of electric charge per second.
Anderson Localization: The phenomenon where waves, such as the quantum wave of an electron, become trapped and unable to spread through a medium containing disorder.
Aneural: Lacking a nervous system, meaning no brain or nerve cells. Organisms that are aneural must coordinate their actions through other means, such as direct cell-to-cell communication or physical forces.
Anomalous Mobility Edge (also: mobility edge): An energy threshold that separates quantum states with different mobility properties, such as localized states from critical states.
Astronomical Unit (also: AU): An astronomical unit (AU) is a unit of distance used in astronomy, approximately equal to the average distance from the Earth to the Sun.
Atom: The smallest unit of an element that retains the chemical identity of that element.
Atomic nucleus (also: nucleus): The tiny, dense core at the centre of an atom. It holds nearly all the atom's mass and its positive charge, with the rest of the atom mostly empty space.
Bending Wave: A wave-like motion that travels along the length of a flexible object, like the tail of a sperm, causing it to bend and generating propulsion.
Blackbody Radiation: Blackbody radiation is the electromagnetic radiation emitted by an idealized object that absorbs all incident radiation and reflects none.
Caloric Theory: An early scientific theory, popular in the 18th and early 19th centuries, which proposed that heat was an invisible, weightless fluid that flowed from hotter to colder bodies. While later disproven, it was used by Sadi Carnot in his foundational work on heat engines.
Chandrasekhar Limit: The maximum mass that a stable white dwarf star can have, which is approximately 1.4 times the mass of the Sun.
Charge Density Wave (also: CDW): A state of matter in some materials where the density of electrons forms a static, repeating wave-like pattern.
Chirality (also: handedness): A property of an object or phenomenon that makes it distinguishable from its mirror image. In physics, it can refer to the spin or intrinsic angular momentum of a particle or excitation.
Chromosphere: The layer of the Sun's atmosphere located just above the visible surface (the photosphere) and below the corona.
Cilia: Tiny, hair-like structures on the surface of cells. They often beat in a rhythmic, coordinated fashion to create fluid movement, either moving the cell itself or moving substances over the cell's surface.
Circuit Quantum Acoustodynamics (also: cQAD): A field of physics that studies the interaction between superconducting quantum circuits (like qubits) and mechanical motion (acoustic waves).
Circularly Polarized Resonant Inelastic Light Scattering (also: CP-RILS): An advanced experimental technique that involves shining circularly polarized light on a material and analyzing the energy and polarization of the scattered light.
Composite Fermion (also: CF): A type of quasiparticle used to describe the fractional quantum Hall effect. It is a bound state of an electron and an even number of magnetic flux quanta (vortices).
Conservation of energy: The principle that energy is never created or destroyed, only converted from one form to another. The total amount in a closed system stays the same.
Continuous Variable: A property of a system that can take on any value within a given range, as opposed to having only discrete, separate values.
Corona: The outermost layer of the Sun's atmosphere, composed of extremely hot, thin gas, or plasma. It is visible to the naked eye only during a total solar eclipse.
Coupling: The strength of the interaction or connection between different parts of a physical system.
Critical State: A special quantum state that exists at the precise transition point between being localized and extended, exhibiting properties of both.
Cross Section: A measure of the probability that a specific interaction will occur between particles in a collision. A larger cross section means the interaction is more likely.
Delocalized Dynamics: The behavior of a quantum system over time where a particle's wave function spreads out instead of remaining in one place.
Diffraction Grating: A surface with a regular, repeating pattern of lines or elements that splits and scatters waves, such as light or sound, into different directions based on their wavelength.
Domain Wall: A type of boundary that separates regions (domains) within a material where a physical property is different. For example, it can separate regions of different magnetic alignment or, in this case, different patterns of ciliary motion.
Eclipse: An eclipse occurs when one celestial body passes into the shadow of another, or when one body passes in front of another from an observer's perspective, blocking its light.
Eigenstate: One of the specific, stable states that a quantum system is allowed to be in, each with a definite energy.
Einstein-Podolsky-Rosen Correlations (also: EPR correlations, EPR steering): A strong form of quantum correlation, first described in a thought experiment by Einstein, Podolsky, and Rosen, that is considered stronger than entanglement.
Electric Charge: A fundamental property of matter that causes it to experience a force when placed in an electromagnetic field. It can be positive or negative.
Electric current (also: current): A flow of electric charge, usually electrons moving through a wire. It is what powers and connects almost every electrical device.
Electric Field: A region of space around an electrically charged particle or object within which a force would be exerted on other electrically charged particles or objects.
Electrodynamics: The branch of physics that studies the interactions between electric currents and the magnetic fields they produce.
Electromagnetic induction (also: induction): The effect where a changing magnetic field creates an electric voltage in a nearby wire. Move a magnet near a coil, or change the magnetism through it, and current flows. This is how generators turn motion into electricity.
Electromagnetic Wave (also: EM wave, light wave): A wave made of oscillating electric and magnetic fields that travel through space at the speed of light, carrying energy.
Electron: A fundamental subatomic particle with a negative electric charge, found in all atoms.
Electron Degeneracy Pressure: A quantum mechanical pressure that arises when electrons are packed so densely that they resist further compression, preventing two electrons from occupying the same quantum state.
Electroweak Production: A process in particle physics where new particles are created through the electroweak force. The electroweak force is the unified description of the electromagnetic and weak nuclear forces.
Element: A pure substance consisting only of atoms that all have the same number of protons in their atomic nuclei.
Elementary Charge: The magnitude of the electric charge of a single proton or electron. It is the smallest possible amount of free electric charge.
Energy: The capacity to do work or cause change. It comes in many forms, including motion, heat, light, and chemical energy, and can be converted between them.
Entanglement: A quantum mechanical phenomenon in which the quantum states of two or more objects are linked together, regardless of the distance separating them.
Epithelium: A type of tissue that forms a thin, continuous layer covering the external surfaces of a body and lining its internal cavities. Skin is a form of epithelium.
Exoplanet: A planet that orbits a star outside of our solar system.
Extended State: A quantum state where a particle's wave function is spread out across the entire system or material.
Extreme Ultraviolet (also: EUV): A high-energy portion of the electromagnetic spectrum, between ultraviolet light and X-rays. Astronomers use EUV light to observe very hot plasma, such as that found in the Sun's corona.
Field (also: physical field): A region of space where a physical quantity (like force) has a specific value at every point.
Filling Factor (also: ν): In the quantum Hall effect, the filling factor is a dimensionless ratio that describes the density of electrons relative to the number of available quantum states created by the strong magnetic field.
Flagellum (also: flagella): A long, whip-like tail on a cell, such as a sperm, that is used for movement.
Flare Ribbons: Bright, elongated structures in the Sun's chromosphere that mark the "footprints" where high-energy particles from a solar flare impact the lower atmosphere.
Fourier Series (also: Fourier decomposition): A mathematical way to represent almost any repeating pattern or signal as a sum of simple sine waves, each with its own amplitude and frequency. This process is also known as Fourier decomposition.
FQH Graviton (also: chiral spin-2 neutral excitation): A specific type of collective excitation in a fractional quantum Hall system. It is a quantized fluctuation of the system's internal geometry, not a particle that mediates the force of gravity.
Fractional Quantum Hall Effect (also: FQH effect): A collective quantum state of matter that occurs when electrons are confined to two dimensions at very low temperatures and in a strong magnetic field. In this state, the electrons act together as a quantum fluid, giving rise to emergent particles that appear to carry a fraction of an electron's charge.
Frequency: How often a repeating event or wave pattern occurs in a given amount of time. Higher frequency means more repetitions per second.
Gravitation (also: Gravity): Gravitation is the fundamental force of attraction that exists between any two objects that have mass. The more massive the objects, the stronger their gravitational pull.
Heat: Energy that flows from a hotter object to a cooler one because of the temperature difference between them. Heat is energy in transit, not a substance stored inside things.
Heat Engine: A device that converts thermal energy (heat) into mechanical energy (work) by exploiting a temperature difference between a hot source and a cold sink.
Heavy-Fermion Compound (also: heavy-fermion material): A type of metallic material containing elements with electrons that behave as if they have a much larger effective mass than a free electron, sometimes hundreds of times greater.
Helioseismology (also: solar seismology): The study of the Sun's interior by watching the sound waves that ripple across its surface. Just as geologists read earthquakes to map the inside of the Earth, physicists read the Sun's surface vibrations to map what lies beneath it.
Heralding Efficiency: Heralding efficiency is the probability of successfully detecting a signal that announces ("heralds") that a desired quantum event, such as the creation of an entangled pair of particles, has occurred.
Hydrophilic: A property of a surface that attracts water. Water on a hydrophilic surface tends to spread out into a thin film.
Hydrophobic: A property of a surface that repels water. Water droplets on a hydrophobic surface tend to bead up into a sphere.
Imaginary Charge Density Wave: The theoretical mechanism that gives rise to loop current order. It is a quantum mechanical wave describing electron movement between atoms that results in circulating currents rather than static charge pile-ups.
Inelastic Neutron Scattering (also: INS): An experimental technique where a beam of neutrons is scattered off a material to probe its atomic and magnetic structure and dynamics.
Interference: The phenomenon where two or more waves overlap and combine to form a new wave of greater, lower, or the same amplitude.
Inverse-Square Law: The inverse-square law describes how the strength of a physical quantity, such as gravitational force, decreases proportionally to the square of the distance from its source.
Jet: A narrow cone of particles produced in high-energy particle collisions. Jets are the observable result of a fundamental particle like a quark or gluon being created.
Joule (also: J): The standard unit of energy, named after James Joule. One joule is about the energy needed to lift a small apple one metre.
Kagome Lattice: A specific geometric arrangement of atoms that resembles a woven pattern of corner-sharing triangles, similar to a traditional Japanese basket weave (kagome).
Kondo Destruction (also: Kondo breakdown): A quantum process where the collective screening of localized magnetic moments by a sea of conduction electrons breaks down.
Lepton: A class of fundamental particles that do not experience the strong nuclear force. The most familiar lepton is the electron; muons and neutrinos are also leptons.
Light Curve: A graph that shows the brightness of an object, like a star, over a period of time.
Light-time (also: signal delay): Light-time refers to the duration it takes for light to travel a specific distance through space.
Line Tension: The excess free energy that exists at the three-phase contact line where a solid, a liquid, and a gas meet. It is analogous to surface tension, but acts along a line rather than across a surface.
Localized State: A quantum state where a particle's wave function is confined to a small, limited region of a system.
Longitudinal: Pertaining to longitude, which measures the east-west position on a celestial body.
Loop Current Order: An exotic state of matter where electrons spontaneously organize into microscopic, circulating current loops within a material.
Lossy Channel: A lossy channel is any communication path, such as an optical fiber or open air, where part of the signal can be lost or degraded during transmission.
Magnetic field: The region around a magnet or an electric current where magnetic forces act. It is what turns a compass needle and what links electricity to magnetism.
Magnetic Reconnection: A physical process in which magnetic field lines break and rapidly reconnect, converting stored magnetic energy into heat and kinetic energy. This process powers solar flares and other energetic events.
Mechanical equivalent of heat: The fixed exchange rate between mechanical work and heat, showing the two are forms of the same thing, energy. James Joule measured it precisely.
Mechanical Oscillator: An object or system that exhibits periodic motion, moving back and forth around an equilibrium point, like a pendulum or a vibrating string.
Molecular Dynamics Simulations (also: MD simulations): Computer models that calculate the movement and interactions of individual atoms and molecules over time according to the laws of physics.
Multipartite Entanglement (also: many-body entanglement): A complex form of quantum entanglement linking the properties of three or more particles together in a way that cannot be described by pairwise connections alone.
Nematic Transition: A type of phase transition where a material's electronic properties lose rotational symmetry, meaning they behave differently along one direction compared to others, without changing the underlying crystal structure.
Neutrino: A type of lepton that has a very small mass and no electric charge. Neutrinos interact very weakly with other matter, making them extremely difficult to detect.
Nuclear Quadrupole Resonance (also: NQR): A highly sensitive spectroscopic technique that probes the local electric and magnetic environment around an atomic nucleus.
On-Site Potential: The amount of potential energy a particle has at a specific location or "site" in a system.
Orbit: An orbit is the curved path an object takes around another object due to gravitation. It is a continuous state of falling while also moving sideways fast enough to miss the central object.
p-mode (also: pressure mode, acoustic mode): One of the Sun's natural sound-wave patterns, where ordinary gas pressure is the force pushing the wave along (the "p" stands for pressure). These are the main waves helioseismologists measure.
Parton (in FQH): A theoretical quasiparticle in the fractional quantum Hall effect. The parton theory proposes that electrons in this state fractionalize into multiple constituent quasiparticles, which are broadly categorized as low-energy and high-energy partons.
Perpetual Motion Machine of the Second Kind: A hypothetical device that would continuously extract useful work from a single heat reservoir by cooling it down, without needing a colder sink to dump excess heat. Such a machine is impossible according to the Second Law of Thermodynamics.
Photon: A photon is the smallest possible particle of light, representing a single quantum of the electromagnetic field.
Photon Loss: Photon loss is the disappearance of photons as they travel through a medium like an optical fiber or the atmosphere. It is a primary challenge in building long-distance optical quantum communication systems.
Piezoelectric Effect (also: piezoelectricity): A property of certain materials that causes them to generate an electric charge in response to applied mechanical stress, and conversely, to change shape when an electric field is applied.
Planck's Constant: Planck's constant is a fundamental physical constant that relates the energy of a quantum of energy to its frequency.
Polar Vortex: A stable, whirlpool-like pattern of electric polarization that can form at the nanoscale in certain materials.
Quantization of Charge: The principle that electric charge does not exist in arbitrary amounts but only in discrete, integer multiples of the elementary charge.
Quantum (also: quanta): A quantum is the smallest possible discrete unit of any physical property, such as energy or matter.
Quantum Correlations: The statistically dependent relationships between two or more quantum systems, where the properties of the systems are linked in ways not possible in classical physics.
Quantum Critical Point (also: QCP): A point in a material's phase diagram, at absolute zero temperature, where a continuous phase transition occurs, driven by quantum fluctuations instead of thermal energy.
Quantum Entanglement: Quantum entanglement is a phenomenon where two or more quantum particles become linked in such a way that their properties are correlated, regardless of the distance separating them. Measuring a property of one particle instantly influences the corresponding property of the other(s).
Quantum Fisher Information (also: QFI): A quantity from quantum information theory that measures how much information a quantum state carries about a specific parameter. It is also a direct measure of the degree of quantum entanglement in a system.
Quantum Metrology: The study and application of making ultra-high-precision measurements by using principles of quantum mechanics, such as entanglement and superposition.
Quantum Simulator: A controllable quantum system used to model the behavior of other, more complex quantum systems that are too difficult to study directly or solve with classical computers.
Quantum State: A complete description of a quantum system, containing all information about its properties, such as energy, momentum, and position.
Quantum Teleportation: Quantum teleportation is a process that transfers the quantum state of a particle from one location to another without moving the particle itself. It relies on a pre-shared entangled state and a classical communication channel.
Quasiparticle: An emergent, particle-like entity that arises from the collective motion of many individual particles (like electrons) in a solid, liquid, or other medium. While not a fundamental particle, it behaves like one within the system.
Quasiperiodic Lattice: An ordered but non-repeating arrangement of atoms or potentials, providing a unique environment for studying quantum phenomena that differ from both perfect crystals and random disorder.
Quasiperiodic Model: A theoretical model of a system where the physical properties, like the energy at each site, are arranged in an ordered but non-repeating pattern.
Radioactivity (also: radioactive decay): The spontaneous emission of penetrating rays or particles from the nucleus of an unstable atom.
Reptation: A model in physics describing the movement of very long, flexible chain-like molecules (polymers) through a dense mesh of similar molecules.
Riblets: Fine-scale, downward-flowing structures observed in the solar atmosphere just above flare ribbons during a solar flare.
Second Law of Thermodynamics: A fundamental principle of physics stating that the total entropy (disorder) of an isolated system can only increase over time, or remain constant in ideal, reversible processes. It implies that heat naturally flows from hotter to colder bodies and that it's impossible to convert all heat into useful work.
Seminal Vesicle: A small sac in males of many species where sperm is stored after production and before ejaculation.
Sine Wave: A smooth, symmetrical, repeating wave pattern, like the ripples on a pond or the path of a pendulum. It describes a regular, oscillating motion.
Solar Flare: An intense burst of radiation from the Sun's surface, caused by the sudden release of magnetic energy.
Solar Mass: A standard unit of mass in astronomy, equal to the mass of our Sun (approximately 2 x 10^30 kilograms).
Standard Deviation (also: sigma): A statistical measure of how much a result deviates from what is expected. In particle physics, a result with a significance of 3 standard deviations is considered "evidence," while 5 standard deviations is required for a "discovery" or "observation."
Standard Model of Particle Physics (also: Standard Model): The theory describing the fundamental forces and elementary particles that make up the universe. It successfully explains a vast range of experimental results but does not include gravity or dark matter.
Strain Wave (also: acoustic wave): A wave of mechanical deformation, such as stretching or compressing, that travels through a material. Sound is a common type of strain wave.
Strange Metal: A state of matter where electrical resistance changes linearly with temperature at low temperatures, unlike in ordinary metals where it changes with the square of the temperature.
SU(1,1) Interferometer: A type of interferometer that uses a specific quantum process, often involving squeezing, to achieve measurement sensitivity beyond standard limits.
Superconducting Qubit (also: qubit): A quantum bit, the basic unit of quantum information, built from a tiny electrical circuit made of superconducting materials.
Terahertz (also: THz): A unit of frequency equal to one trillion (10^12) cycles per second.
Terminator: The dividing line between the illuminated (day) side and the unilluminated (night) side of a planet or moon.
Tetrahedral Order: The specific, pyramid-like geometric arrangement that water molecules tend to form due to hydrogen bonding with their neighbors.
Thermal Dissociation: The process by which molecules break apart into smaller components, like atoms, due to high temperatures.
Thermodynamic Efficiency: The ratio of the useful work output by a heat engine to the total heat energy supplied to it, indicating how effectively heat is converted into work.
Tidally Locked: The state where a celestial body's rotation period is the same as its orbital period, causing it to always show the same face to the object it orbits.
Time-Reversal Symmetry: A fundamental principle in physics stating that the laws of physics should work the same forwards and backwards in time.
Topological Defect: An irregularity or imperfection in a regularly ordered medium, such as a crystal or an aligned group of liquid crystals. In this context, it is a disruption in the parallel alignment of sperm.
Topological Structure (also: topological defect): A feature in a material whose properties are protected by its overall shape or structure (its topology), making it robust against small disturbances.
Transit: An event where a planet passes directly between a star and an observer, causing a small, temporary dip in the star's brightness.
Transmission Spectroscopy: A method used to study the atmosphere of an exoplanet by analyzing the starlight that filters through it during a transit.
Transmission Spectrum: The result of transmission spectroscopy, which shows how much light a planet's atmosphere absorbs at different wavelengths or colors.
Trichoplax adhaerens: A species of extremely simple, multicellular marine animal that resembles a small, flat disc. It is one of the most basic known animal structures, lacking organs or a nervous system.
Two-Mode Squeezing Interaction: A quantum mechanical process that creates strong correlations between two different systems (or "modes").
Ultrahot Jupiter: A class of gas giant exoplanets with temperatures over 2,000 K (about 3,140°F or 1,727°C) that orbit extremely close to their host stars.
Wavelength: The distance between two consecutive peaks or troughs of a wave.
Wetting: The ability of a liquid to maintain contact with a solid surface, resulting from the balance between the liquid's internal cohesion and its adhesion to the surface.
White Dwarf: A very dense, compact stellar remnant, typically the size of Earth but with the mass of the Sun, formed after a star like our Sun has exhausted its nuclear fuel.
Work: In physics, work is energy transferred when a force pushes or pulls something through a distance. Lifting a weight or stirring water both do work.
Z Boson: A fundamental particle that carries the weak nuclear force, one of the four fundamental forces of nature. It is electrically neutral and very massive.