atom The smallest bit of matter than can be identified as a certain chemical element.
boson A class of subatomic particles that includes the Higgs, the photon, and others that are the carriers of nature’s fundamental fields.
electrodynamics A field of physics that describes the interactions and movement of particles due to electromagnetism.
electromagnetic wave A form of energy resulting from the interrelationship of changing electric and magnetic fields that flows through space at the speed of light.
electromagnetism A fundamental force of nature, or property of matter and energy, that includes electricity, magnetism, and electromagnetic waves, such as light.
electron A very light subatomic particle (the first to be discovered) that carries negative charge and is responsible for many important properties of matter.
emission Sending out something that has been produced, such as the emission of a photon from an atom when an electron drops from a higher to a lower energy level.
energy level One of many values of energy that quantum mechanics permits for a physical phenomenon, such as for the allowed states of an electron in an atom.
interference A phenomenon that occurs when two waves meet, resulting in some regions of higher intensity and some of lower intensity, in particular the light and dark bands produced when two light waves meet.
laser A device that produces a sharp, powerful beam of light by the process known as light amplification through stimulated emission of radiation.
light-emitting diode (LED) A device made of advanced materials that produces light of a particular color much more efficiently than incandescent light.
molecule The smallest bit of matter that can be identified as a certain chemical compound.
nucleus The very tiny, positively charged, central part of an atom that carries most of its mass.
photoelectric effect A phenomenon in which light can, under some circumstances, knock electrons out of atoms. Einstein’s explanation of this effect led to scientific acceptance of the photon as a particle.
photon A particle of electromagnetic energy, such as light energy.
quantum (plural quanta) A subatomic particle with properties that have only certain allowed values related to Planck’s constant. A photon is a quantum of light with energy equal to Planck’s constant times its frequency.
quantum electrodynamics (QED) A formulation of electrodynamics that accounts for quantum mechanical phenomena, such as the dual wave-particle nature of matter and energy.
quantum mechanics A field of physics developed to describe the relationships between matter and energy that accounts for the dual wave-particle nature of both.
reflect The phenomenon that occurs when an electromagnetic wave strikes a substance and bounces off.
refraction The change of direction experienced by an electromagnetic wave as it passes from one material and into another.
spectrum (plural spectra) The mixture of colors contained within a beam of light, or the band produced when those colors are spread out by a prism or other device.
uncertainty principle Developed by Werner Heisenberg, a statement that nature provides fundamental limits on how well we can know two interrelated values, such as the position and speed of a particle.
wave function The quantum mechanical description that expresses the wavelike properties of a particle.