ALGORITHM—a step-by-step set of mathematical and logic-based instructions to undertake a calculation or solve a problem. Most computer programs use algorithms.
BLACK BODY—a theoretical object that absorbs all the light energy that falls on it, and emits light with colors that are purely dependent on its temperature.
COSMIC RAYS—high-energy particles that hit the Earth’s atmosphere from outer space. On impact, cosmic rays produce a whole range of extra particles, including positrons.
DETERMINISTIC—something that is theoretically entirely predictable if we have all the details about it (as opposed to being random).
DIFFRACTION—the bending of a wave (typically light) when it hits an obstacle or slit. The amount the wave bends depends on its frequency.
DIFFRACTION GRATING—a plate with a repeated pattern of thin bars or ridges that break a beam of light into its spectrum, either by passing through it or reflection, more effectively than a prism.
ELECTRODYNAMICS—the physics of moving electrical charges.
ELECTROMAGNETIC RADIATION—a phenomenon produced by the interaction of an electric and a magnetic wave. Includes radio, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
ELECTRON—a fundamental matter particle with a negative electric charge, responsible for electricity and found around the periphery of atoms.
FIELD—a phenomenon that has a value throughout space that may vary with time. Examples include electrical, magnetic, and gravitational fields.
FREQUENCY—the number of times a wave goes through its cycle of oscillation, returning to the same position, in one second.
HALF-LIFE—the time in which half of the atoms of a radioactive substance will have undergone spontaneous nuclear decay.
GLUONS—fundamental particles that carry the strong nuclear force, which ties quarks together and holds protons and neutrons in the atomic nucleus.
HIDDEN VARIABLES—the idea that quantum particles have values for properties such as position and momentum at all times, but these values are not accessible.
IMAGINARY NUMBER—any multiple of i, the square root of −1. When combined with an ordinary number, makes up a complex number, for example, 3 + 4i.
INTERFERENCE—a wave effect where two or more waves interact. In areas where the waves are oscillating in the same direction, interference strengthens the waves; elsewhere, it weakens them, producing an overall pattern.
ION—an electrically charged atom that has either gained or lost electrons.
LOCAL REALITY—“local” means that an occurrence at one point in space cannot influence another point in space without sending something to cause that influence. “Real” means that objects have properties at all times, even if those properties are not accessible.
MATRIX—a set of numbers set out in a rectangle of rows and columns. Matrixes (also known as matrices) undergo mathematical processes such as addition and multiplication, but when multiplying matrixes A and B, A × B is not the same as B × A.
MODEL—in science, an analogy used to predict how an aspect of nature will behave. Traditionally based on the behavior of familiar objects, but now tend to be based solely on mathematics.
MOMENTUM—the mass of an object multiplied by its velocity.
NEUTRON—a particle found in the nucleus of an atom with no electrical charge, composed of three quarks.
NOBLE GAS—elements in the final column of the periodic table that have a full outer shell of electrons and rarely react: includes helium, neon, argon, krypton, xenon, and radon. Also called an inert gas.
NUCLEAR FUSION—joining together protons and neutrons to form an atomic nucleus: the power source of stars.
ORBITAL—the mathematically derived description of the locations where an electron in an atom is most likely to be found.
PARADOX—an apparently contradictory statement that is against common sense or accepted wisdom. Unlike a fallacy, a paradox may be true.
PHOTOELECTRIC EFFECT—the release of electrons and hence the production of an electrical current when light hits a metal or semiconductor.
PHOTON—a fundamental particle that is a component of a beam of light and that is the carrier of the electromagnetic force.
POSITRON—a fundamental particle that is the antimatter equivalent of an electron: like an electron but with a positive charge. Also known as an antielectron.
PRISM—a block of transparent material that has a triangular cross section. When light hits a prism at the correct angle, it is broken into its constituent colors.
PROTON—a particle found in the nucleus of an atom with a positive electrical charge, composed of three quarks.
QUARKS—a group of six fundamental matter particles that combine in twos and threes to form other particles, notably neutrons, protons, and mesons.
RELATIVISTIC SPEEDS—speeds that are sufficiently close to the speed of light that Einstein’s special theory of relativity gives a better description of their movement than Newton’s laws.
SEMICONDUCTOR—a substance that is neither an electrical conductor nor an insulator, allowing the limited passage of electrical charge. Central to the development of solid-state electronics.
SHELL—structure around an atom that can be occupied by one or more electrons, with a fixed maximum of electrons in each shell.
SPACE-TIME—Einstein’s relativity shows a strong link between space and time where it is no longer practical to refer to the two separately, but rather as a combined phenomenon called space-time.
SPECTRUM—the range of colors (often represented by frequencies, wavelengths, or energies) that are present in a beam of light.
SUPERPOSITION—the ability of a quantum particle to be in a state where one or more of its properties does not have a specified value, but rather two or more possibilities with different probabilities.
VACUUM ENERGY—a special case of zero-point energy: the energy present in a total vacuum due to the quantum energy fluctuations predicted by the uncertainty principle.
VIRTUAL PHOTON—a photon that is never observed but that carries the electromagnetic force when two charged particles interact.
WAVE EQUATION—an equation describing mathematically the behavior of a wave over time.
WAVE FUNCTION—a mathematical description of the state of a quantum system, typically combining a number of different properties.
WAVELENGTH—the distance in which a wave goes through a single cycle, returning to the same point in its oscillation.