Note: Part of this glossary has been copied or modified from that of Reference B, Physics: Decade by Decade, with the permission of Alfred B. Bortz.
Explanatory words that are defined elsewhere in this glossary are shown in bold print.
absolute frame of reference: see frame of reference.
absolute temperature: measured from absolute zero, usually in degrees Kelvin.
absolute zero: the theoretical minimum of temperature that can ever be achieved.
acceleration: how rapidly the speed and/or direction of an object's motion is changed.
actinides: the fourteen elements of successively higher atomic number following actinium, atomic number 89.
alchemy: an early pseudoscience that professed to be able to convert one element into another (i.e., lead into gold), before the knowledge of nuclear fusion and fission, which do under special conditions produce transformations from one element to another.
algorithm: a self-contained set of logical mathematical operations. By carrying out these operations, a computer can make judgments or perform calculations based on input information.
alkali metals: the Group IA metallic elements, atoms of which are increasingly reactive (from those of lithium through those of francium) in giving up an electron in chemical combination with other elements.
alkaline earth metals: the Group IIA metallic elements, atoms of which are increasingly reactive (from those of beryllium through those of radium) in giving up two electrons in chemical combination with other elements.
alloy: two or more metals melted together as a solution and solidified into one or more solid solution phases.
alpha rays (or alpha particles): the least penetrating form of radioactivity. Alpha particles are helium nuclei, and the process that produces them is often called alpha decay.
amorphous: a kind of solid in which the atoms lack the orderly arrangement of a crystal.
ampere: a unit of current. The flow of electrical charge corresponding in magnitude to the passage of approximately six billion billion electrons per second.
angular momentum: a measure of the mass, radial extent, and rotating speed of an object. Rotating objects have angular momentum and an inertia of rotation in the same sense that traveling objects have momentum and an inertia of linear motion.
anion: see ion.
annihilation: an event in which two particles interact and destroy one another, such as the combination of an electron and a hole in a semiconductor or the combination of a particle and its antiparticle.
antimatter: a type of matter with identical properties to its normal-matter counterpart except for carrying an opposite electric charge and parity.
antiparticle: see antimatter.
ASCII (American Standard Code for Information Interchange): the representation of all letters, numbers, and other keyboard elements in a seven-bit register.
atom: the smallest particle of a substance that can be identified as a chemical element.
atomic number: the number of protons in the nucleus of an atom of an element, or the equal number of surrounding electrons. Its atomic number is used to specify an element's position in the periodic table.
atomic weight / atomic mass: a number that specifies the mass of a nucleus, equal to the total number of protons and neutrons it contains.
band gap: in solids, a “forbidden” zone, a gap in the band of states available to the electron.
baryon: a subatomic particle at least as heavy as a proton, that is composed of three quarks and responds to the strong nuclear force.
beta rays (or beta particles): a form of radioactivity that is more penetrating than alpha rays but less penetrating than gamma rays. Beta particles are electrons, and the process that produces them in nuclei is often called beta decay.
bit: every yes or no answer to a question represents a single “bit” of information. In computers, a bit is represented as a 1 or a 0, perhaps being represented physically by a transistor having a high or a low current flow.
blackbody radiation: the electromagnetic energy emitted by an object as a consequence of its temperature.
black hole: a collapsed star so dense that nothing can escape from it, including light.
Bohr theory: an early quantum theory of atomic structure assuming discrete energies for classical-looking electron orbits of the atom.
boson (gauge boson): generally, a subatomic particle with integral spin; particularly, a gauge boson that is exchanged to create a fundamental force, such as photons for the electromagnetic force, gluons for the strong nuclear force, and W and Z particles for the weak nuclear force.
bound state: see energy level.
BTU (British thermal unit): a unit of energy equivalent to approximately 0.0003 kilowatt-hours (kWh).
byte: a register of eight bits.
cathode ray: a stream of negative electricity emitted from a hot electrode in a vacuum tube, discovered in 1897 to be comprised of electrons.
cation: see ion.
Celsius: see temperature scale.
chain reaction: a sequence of nuclear fissions in which neutrons emitted in one fission event cause one or more additional nuclei to fission, resulting in a rapid and intense release of energy.
charge: a fundamental property of the electron, designated by the symbol e. See also ampere and electron volt.
chemical properties: those properties of the elements primarily relating to the electronic structure of its atoms, or to the electronic structure of molecules composed of atoms.
chemistry: the science of substances and the composition of matter.
classical: reference to the physics that described the universe, and particularly the atom, before the advent of quantum theory and quantum mechanics. Classical physics is still valid for large objects, where even a grain of sand is large.
clock: a signal generator internal to the computer that sets the frequency with which a processor can perform sets of operations.
cloud: see probability cloud.
cloud chamber: a device in which condensation of a vapor reveals a trail of ions such as those produced along the path of a charged subatomic particle; cloud chambers were used in early studies of cosmic rays and subatomic particles.
coherence: when two or more photons are all in phase and of the same frequency and wavelength.
color: (a) the appearance of an object that has absorbed and therefore not reflected photons of particular wavelengths in the visible range, or the appearance of light consisting of photons of particular wavelengths. (b) the property of a quark that interacts with the strong nuclear force, equivalent to positive or negative charge for the electromagnetic force.
compound: a chemical substance made up of a combination of elements in definite proportions.
conduction band: a set of closely spaced electron energy levels in a solid in which the electrons belong to no particular atoms and thus move freely through the material.
continuous spectrum: see spectrum.
Copenhagen interpretation: an understanding of physics that assumes that the spin and spatial-state solutions of Schrödinger's equation for any physical situation can be used to provide the probability for the location of particles or the occurrence of events, and that the realization of any one of these locations or events occurs only upon observation.
correspondence: a region of physics in which two otherwise- conflicting theories may give the same practical results, one as an approximation to the other.
cosmic rays: energetic particles that come to Earth from distant parts of the universe or result from the interaction of such particles with the upper reaches of Earth's atmosphere.
cosmological constant: a quantity that arose in Einstein's mathematical description of general relativity; its value and algebraic sign determined the rate of change of the expansion or contraction of the universe.
cosmology: the scientific study of the universe as an entity.
covalent bond: a type of chemical bond in which the participating atoms share electrons.
critical current: the maximum current that a superconductor can carry without significant resistance.
critical temperature: the temperature below which a material becomes superconducting.
crystal: a solid substance that is characterized by a regularly repeating three-dimensional arrangement of its atoms.
cyclotron: a device that accelerates subatomic particles to very high energies as they follow a spiraling path in a very large magnetic field.
d: named after the “diffuse” spectral line, used as a label for the angular momentum quantum number l = 2.
dark energy: a form of energy suggested as responsible for the accelerated expansion of our universe over the last six billion years.
dark matter: matter that cannot be seen directly but is inferred from its influence on light and other matter in the cosmos.
decoherence time: the time in which an entangled state can be maintained.
defect: an irregularity in the regular stacking of atoms or molecules in a crystal.
diode: an electronic device that permits an electric current to pass through in only one direction.
discrete: having one of only a subset of specific allowed values within a continuous range of values. See, for example, spin and spatial-state angular momentum.
domain: a relatively large region within a ferromagnetic material, in which the spin and/or spatial-state magnetic moments of atoms spontaneously align with each other.
drift chamber: a device that uses the electrostatic attraction of ions and electrons to determine the track of particles created in particle accelerators.
ductility: the ability to draw a substance into wire—usually related to metals.
electrical potential: an electrical field of force and potential energy that drives the movement of an electron. Measured in volts. See also potential energy.
electrical resistance: a property of matter that impedes the flow of electricity through it.
electrolysis: decomposition produced by passing an electric current through a molten or dissolved compound, as for example the decomposition of water, H2O, into hydrogen and oxygen gases.
electromagnetic waves / electromagnetic radiation: quantum packets of alternating electric and magnetic fields that propagate through space at the speed of light and within a frequency and wavelength range from radio waves through microwaves, light, x-rays, and gamma rays; they are called photons primarily in the visible range of frequencies.
electromagnetism: an aspect of nature that includes both electricity and magnetism, the basis for electromagnetic waves, including light.
electron: a small subatomic particle of charge –e, found to determine an atom's chemical and electrical behavior and to be useful as the basis for electronic technology.
electron volt (eV): the energy change caused by the movement of an electron (of charge e) through a change in electrical potential of one volt. Also, the unit of measure used to describe an energy, energy difference, or energy level, as related to the atom or objects on an atomic or subatomic scale.
element: a chemical substance made up of only one kind of atom.
energy: (generally) the ability to cause motion (do work) or heat something, defined also as power (the rate of delivery or change in energy) times time. For electrical systems, energy is commonly measured in watt-hours or kilowatt-hours (kWh). Physicists define different forms of energy as follows: Objects that move around freely have a positive, kinetic energy of motion depending on how heavy they are and how fast they are moving. In contrast, a static object under some force of attraction is said to have a negative potential energy. The potential energy is made more negative if the object is placed closer to the source of attraction. The static object could be a hypothetical unmoving planet attracted by the gravity of the sun or a hypothetical unmoving electron attracted by the pull of its negative charge toward the positive charges of the protons in an atomic nucleus. If an object is in some sense moving (i.e., has kinetic energy) in the presence of an attraction, then it can break free of the attraction if its positive kinetic energy is larger than its negative potential energy so that the sum of the two energies is greater than zero. If this sum is less than zero, negative (that is, if the negative potential energy of attraction overcomes the positive kinetic energy of motion), then the object will be in a bound state, perhaps still moving around in some sense but unable to break completely free of the attraction. The more negative this total energy, the more tightly the object is bound.
energy level: the net energy of an electron in an atom.
entanglement: see quantum entanglement.
exclusion: see Pauli exclusion principle.
excited state: a state of an atom occupied by an electron while a lower energy state or states are unoccupied.
f: named after the “fundamental” spectral line, used as a label for the angular momentum quantum number l = 3.
Fahrenheit: see temperature scale.
ferromagnetism: a property of certain types of matter, such as iron, in which the spin and/or spatial-state magnetic moments of its atoms spontaneously align with each other in relatively large regions (domains) within the material.
fission: a process in which a nucleus of the atom of a heavier element splits into two smaller nuclei and several neutrons, usually with the release of a relatively large amount of atomic energy.
flavor: a term used to distinguish the different types of quarks; a quark's flavor can be up, down, strange, charm, top, or bottom.
frame of reference: a point of origin and set of directions in space (such as north–south, east–west, up–down) against which the relative position and motion of an object can be specified. The luminiferous ether was presumed to be an absolute, unmoving frame of reference until Einstein's special theory of relativity demonstrated that no such frame exists.
frequency: the rate at which an event repeats itself, such as the frequency with which the peaks of a wave passes a particular observation point (with respect to electromagnetic radiation, see Planck's constant).
fullerenes: a family of geometric structures having a monolayer surface of atoms (or molecules); one of these structures is the buckyball, another is the nanotube.
fundamental particles: make up all matter as we know it; as three generations of leptons and quarks plus gauge bosons, the latter carrying the action of the forces of nature.
fusion: a process in which the nuclei of the atoms of lighter elements are joined (usually under extremely high temperatures and pressures) to form the nucleus of a heavier atom, usually with the release of other particles and a relatively large amount of thermonuclear energy.
gamma rays (or gamma radiation): the most penetrating form of radioactivity. Gamma rays are high-energy photons.
gate: a set of transistors (bits) that can operate together to perform some logical function.
generic table of states: one table representing the many different actual tables of states, one each for the atoms of every element.
glass: an amorphous solid or a liquid of such high viscosity that it appears to be a solid.
gluon: the gauge boson exchanged between quarks, thereby acting as the carrier of the strong nuclear force.
grain: a crystalline region of particular orientation within a polycrystalline substance consisting of grains of many different orientations. See also recrystallization.
Grand Unification Theory (GUT): a goal of theoretical physicists who are seeking a theory to unify all the fundamental forces.
graphene: the basic structural configuration for many forms of carbon, including some fullerenes, including nanotubes, and the more familiar graphite, charcoal, and soot.
gravity / gravitational field: a basic force of nature that creates an attraction between any two bodies that have mass. The attraction of gravity on a mass produces a force that we measure as weight.
ground state: the situation in an atom when its electrons all occupy the lowest energy states available to them.
groups: sets of elements with similar chemical properties, one group per column of our modern periodic table.
halogens: elements in Group VIIA of the periodic table, whose atoms are very aggressive in seeking to gain one electron in reaction with other elements.
heat: see temperature.
hole: a region in a semiconductor in which an electron is missing and behaves as if it is a mobile positive charge.
hybridization: the combination of the states of the electron in an atom to form a new set of states with energies more favorable to a particular bonding situation.
hypothesis: the yet-to-be-tested suggestion of a theory or law.
inflation: a theory that explains the unexpected uniformity of the cosmic background radiation by a very brief period just after the big bang when the cosmos and space-time itself expanded at a rate much faster than the speed of light.
inert: in reference to the noble gases, the tendency of an atom of an element not to react or combine with other atoms to form molecules.
inertia: proportional to mass, the tendency for an object in motion to stay in motion or an object at rest to stay at rest.
interference: a phenomenon that occurs when waves overlap; for two light waves of the same wavelength, this results in a series of bright and dark bands.
ion: an electrically charged atom (or combination of atoms). An atom with positive charge through the loss of one or more electrons is called a cation. An atom with negative charge through the acquisition of one or more electrons is called an anion.
ionic bond: a type of chemical bond in which the participating atoms exchange electrons, thereby becoming oppositely charged ions held together by electrical attraction.
ionization: the creation of electrically charged atoms (or combinations of atoms) called ions.
ionization energy: the positive energy that must be supplied to lift an electron free of its bound, negative energy-level state in an atom or ion. Usually in relation to the outermost, least negative energy-level electrons.
isotope: one of several nuclei with the same atomic number but different atomic masses.
Josephson junction: consists of two superconductors coupled by a weak link, which can be either a thin insulator, a short section of a normal metal, or a weakened superconductor. It has important application in quantum-mechanical circuits, such as SQUIDs and qubits.
Kelvin: see temperature scale.
key: a string of bits used, for example, in the one-time pad to encode and decode a message.
key distribution: the method used to distribute the key to one or more receivers of a coded message.
kinetic energy: see energy.
ℓ: the angular momentum quantum number.
Lamb shift: a slight splitting in the spectrum of hydrogen, first observed by Willis Lamb and critical to understanding quantum electrodynamics.
lanthanides: the fourteen elements of successively higher atomic number following lanthanum, atomic number 57.
large object: something of a size observable in an optical microscope, or larger.
laser: light amplification through the stimulated emission of radiation, in which photons released in the transition of an electron from one higher energy state to a specific lower energy state in an atom stimulate similar transitions in other atoms to create a pulse or beam of coherent light.
law: see theory.
lepton: a light subatomic particle that does not respond to the strong nuclear force; leptons include electrons, muons, taus, and their neutrinos and antiparticles.
light: electromagnetic radiation in the visible range of frequency and wavelength.
line spectrum: see spectral line.
luminiferous ether: a hypothetical substance once presumed to permeate all space as the carrier of electromagnetic waves.
m: the magnetic quantum number.
macroscopic: the quality of being directly observable with the human eye.
magnetic moment: for the purposes of this book, something to be visualized as having the properties of a tiny bar magnet.
main groups: the eight groups of the periodic table whose elements have outer electrons in the s and p blocks of states.
malleability: a property, usually of metals and alloys, that allows them to be pressed or hammered into different shapes.
many worlds: the idea that all possible outcomes of an event are represented in separate worlds, each of which includes the observers of the outcome.
mass: a measure of the amount of matter. Mass has inertia, and in a gravitational field is acted upon by a force that we call weight.
matter: any collection of particles.
Maxwell's equations: a set of four formulas that describe the interrelationships between electricity and magnetism and predict the existence of electromagnetic waves that travel at the speed of light.
meson: a middle-weight subatomic particle that consists of a quark and an antiquark; the first usage of the term referred to pions.
metal: an element that tends to give up electrons in combination with other elements; this includes most of the elements toward the bottom and left of our periodic table, and which become increasingly metallic in that direction. Metals conduct electricity, and they tend to exhibit a lustrous appearance and to be malleable and ductile.
metalloid: also known as a semiconductor or semimetal, this is an element whose atoms have properties between those of the metals and those of the nonmetals.
microscopic: requiring the use of an optical microscope to be seen.
microwaves: see electromagnetic radiation.
molecule: a combination of atoms making up the smallest particle of a substance that can be identified as a particular compound.
momentum: the mass of an object times its velocity.
MRI (magnetic resonance imaging): uses the sensitivity to chemical surroundings of the spins of the nuclei of certain elements to view the tissues of the body.
muon: a subatomic particle that is the second-generation equivalent of the electron in the Standard Model.
n: the primary quantum number.
nanotube: or, more specifically, the carbon nanotube has been made as narrow as one nanometer in diameter, the span of about seven carbon atoms; these tubes can be made millions of times longer than their diameters.
neutron: a subatomic particle with slightly more mass than a proton but without electric charge; nuclei are made up of protons and neutrons bound together by a strong nuclear force.
neutron star: a super-dense star in which all its matter has been compressed into neutrons (see also pulsar).
noble gases: those elements whose atoms tend to be inert. They are listed in the Group VIIIA column of the modern periodic table.
nonmetal: an element that tends to acquire electrons in combination with other elements; most of the elements toward the top and extreme right of the periodic table are increasingly nonmetallic in that direction.
n-type semiconductor: a semiconductor with an excess of electrons over holes.
nucleon: a proton or neutron; the atomic mass of a nucleus is the total number of nucleons it contains.
nucleus: (plural: nuclei) the tiny, positively charged central part of an atom that contains most of its mass; the nucleus is composed of protons and neutrons.
one-time pad: a method of encryption that allows a single key (string of bits) to be used for coding and decoding a message.
orbital: what we in this book call a “spatial state” because the term orbital, retained from the early days of developing quantum theory, misleadingly connotes a specifically located particle and orbit. See spatial state.
p: named after the “principal” spectral line, used as a label for the angular momentum quantum number l = 1.
parity: an inherent left- or right-handedness of a subatomic particle.
Pauli exclusion principle: also called exclusion—originally that no two electrons can occupy the same state. More generally, that no two indistinguishable fermions can do so.
periodic table of the elements: an arrangement of the chemical elements in rows and columns that reveals similarities in their physical and chemical properties.
phase: (a) liquid, solid, or gas, or a solid with a particular crystalline stacking of atoms; or (b) the relative alignment of waves of the same wavelength and frequency, as to whether their peaks line up or are shifted somewhat “out of phase.”
photoelectric effect: a phenomenon in which shining a light can cause electrons to be emitted from a metal surface.
photon: a quantum or packet of light or electromagnetic energy.
Planck's constant: a fundamental ratio in nature that relates the energy of a quantum to the frequency of its corresponding electromagnetic wave.
polarization: either a photon having either plus or minus one unit of angular momentum or a molecule having poles of net plus or minus charge concentration.
positron: the antimatter counterpart of an electron.
potential energy: see energy.
power: the rate of delivery or change of energy from one form to another. For electrical systems it is usually measured in watts. It is the electric potential (that drives the flow of electrons, usually measured in volts) times the flow of the electrons (comprising the electrical current, usually measured in amperes). When the current and voltage are in phase, one volt-ampere = one watt. For motors, generators, and large electrical delivery systems, power is often measured in megavolt amperes (MVA), and that part of the energy actually consumed (the in-phase voltage and current component) is measured in megawatts.
precipitate: the appearance of one phase within another phase, as in the precipitation of water droplets out of the air or of one solid phase of an alloy out of another primary solid phase.
prime number: an integer that can be divided evenly only by the number 1 and itself.
privatdozent: a lecturer in Germany or Switzerland who was paid directly by his students and given a place to teach but without a professorial position at the university.
probability cloud: a visual representation for any particular spatial-state solution to Schrödinger's equation in which the probability of finding an electron at any point in space surrounding the nucleus of an atom is portrayed in the figures and tables of this book as whiteness (in proportion to the probability) against a black background.
processor: that part of a computer that manipulates information, usually according to a set of instructions.
proton: a subatomic particle having one unit of positive electric charge and one unit of atomic mass; the nucleus of normal hydrogen is a single proton.
pulsar: a type of star that produces light that pulsates at very regular intervals, now known to be a rapidly rotating neutron star.
p-type semiconductor: a semiconductor with an excess of holes over electrons.
quantum (plural: quanta): a packet of energy devised by Planck to explain the shape of blackbody radiation; later generalized to be a packet of any physical entity, such as electric charge or a particle's angular momentum, that varied in steps rather than continuously.
quantum dots: nanoscale local peaks (on the surface of a solid) in the attraction of electrons to the positive charges of the nuclei of atoms.
quantum electrodynamics (QED): a subfield of physics that restructures Maxwell's theory so that it is consistent with the quantum nature of matter and energy.
quantum entanglement: a phenomenon in which determination of the quantum state of one particle immediately affects the quantum state of another particle some distance away because a relationship between those states had been established previously; Einstein referred to the phenomenon, when first predicted, as “spooky action at a distance.”
quantum mechanics: the formal mathematical formulation of the broader quantum theory.
quantum number: a value that describes a physical property that can take on integer multiples of a fundamental value, such as Planck's constant (or half-integer values, in the case of spin).
quantum states: see spatial state and spin.
quantum theory: either the early quasi-classical ideas used to portray the atom, otherwise generally known as the Bohr theory, or the overall description of a subfield of physics based on the quantum description of matter and energy as having a dual wave-particle nature, more formally and mathematically characterized as quantum mechanics.
quark: a type of subatomic particle that is considered the fundamental building block of baryons and mesons, that is, particles that interact via the strong nuclear force.
qubit: a quantum bit; unlike classical bits, the qubit can simultaneously represent a 1 and a 0 or combinations of both.
radioactivity: the spontaneous fission (splitting apart) of an atomic nucleus.
radio waves: see electromagnetic radiation.
recrystallization: the growth of new, relatively defect-free, crystalline grains from the defect-ridden grains within a work-hardened metal or alloy.
reduction: the argument that the properties of the elements and the periodic table can be completely derived directly from the underlying physics. (We do not claim that here.)
register: a succession of bits.
relative frame of reference: see frame of reference.
renormalization: a mathematical technique applied to quantum electrodynamics that enables the equation to handle infinities that were problems in previous approaches.
resistance: the resistance to the flow of electrical current in a wire or circuit. In Standard International (SI) units it is measured (in ohms) as the electrical potential (in volts) applied to a wire or circuit divided by the electrical current that then flows through it as a result as measured (in amperes).
resistivity: the intrinsic resistance to the flow of electrical current in a metal, insulator, or semiconductor. It is usually presented in ohm-cm units, which when multiplied by the length of the material and divided by the area of its cross section provides a measure of the resistance of an actual piece of material.
resonance: a phenomenon with a natural frequency that occurs in response to stimulation, such as the vibration of a the string or air column of a musical instrument.
s: named after the “sharp” spectral line, used as a label for the angular momentum quantum number l = 0.
salt: an ionic combination of elements to make a molecule that tends to dissolve in water into constituent ions (e.g., common table salt, NaCl).
scattering: a phenomenon in which a stream of particles or energy is diverted by interaction with a target. The resulting pattern reveals details of the target, as the scattering of alpha particles revealed the nuclear structure of atoms.
Schrödinger's equation: one of several approaches to the mathematical formulation of quantum mechanics. The energy of a system is expressed in terms of wavefunctions which by the Copenhagen interpretation can be used to determine the probability of events or the location of particles.
screening: in the many-electron atom, the tendency of electrons with their negative charges to reduce the apparent charge of the nucleus seen by other electrons.
semiconductor: (adj.: semiconducting) a material with electrical properties between that of an insulator and a metal; the electrical conductivity of a semiconductor can be controlled by making small changes to its composition. Also called a metalloid or a semimetal.
semimetal: see metalloid or semiconductor.
shell: a set of states corresponding to particular quantum numbers. The chemical properties of elements show periodic behavior depending on the degree to which the states in particular shells are occupied.
small object: something so small as not to be observable in an optical microscope.
solid-state physics: a subfield of physics dealing with the properties of solid matter, later included in the broader category of condensed matter physics.
solution: a mixture of substances on an atomic or molecular scale so as to form a homogeneous single phase.
sound: the ear's sensing of waves of vibrations of molecules in the air or in liquid or solid substances, with the pitch increasing with the frequency of the vibrations and the corresponding decrease in wavelength.
space-time: a four-dimensional combination of space and time that resulted from Einstein's theory of relativity.
spatial state: one of the possible quantum states for the electron around the nucleus in an atom, as distinct from the intrinsic spin state of the electron that is present whether or not the electron is in an atom. Each quantum spatial state has a discrete energy, magnitude of angular momentum, and magnetic moment. In the Copenhagen interpretation of Schrödinger's wave-mechanics, the spatial state is a spread-out and diffuse wavefunction with these discrete properties that can be used to calculate or estimate the probability (in this book, clouds) for the spatial location of an electron around the nucleus of an atom.
spectral line: a measured distinct specific wavelength or frequency of electromagnetic radiation (specifically, a distinct color within the visible light spectrum), often produced by the emission of photons in the transition of electrons from one energy level to another in an atom.
spectral-line splitting: a phenomenon in which a single spectral line splits into several with the application of an external influence such as an electric or magnetic field.
spectrograph: an optical device that separates the photons of light (or other electromagnetic waves) according to their wavelengths where the photons produce markings on a screen.
spectrometer: an optical device that separates the photons of light (or other electromagnetic waves) according to their wavelengths and measures the intensity of the light (number of photons) at each wavelength and corresponding frequency.
spectrum: the various colors contained in light, or more generally the various wavelength in any energy carrying waves, often displayed as a continuous graph of intensity versus wavelength or as a series of lines specifying intensity (number of photons) at specific wavelengths.
speed of light, c: the speed with which all electromagnetic radiation propagates through empty space, approximately three hundred million meters per second.
spin: a fundamental property of an electron, represented by a plus or minus quantum number that corresponds to its intrinsic angular momentum and magnetism.
SQUID (superconducting quantum interference device): is built of superconducting lops containing Josephson junctions. It can be used for quantum computing, communication, and extremely sensitive measurements of magnetic fields.
Standard Model of particle physics: a description of the fundamental particles that make up all matter as we know it as three generations of leptons and quarks plus gauge bosons; the latter are exchanged to create a fundamental force, such as photons for the electromagnetic force.
standing wave: a wave or wavelike mathematical function or variation in a physical property, in which a spatially fixed pattern of peaks and valleys oscillates in time from positive to negative values and back continuously.
state: see excited state, spatial state, and spin state.
strangeness: a quantum mechanical property that was found to be conserved during transformations of subatomic particles under the influence of the strong nuclear force, later recognized as the total number of strange quarks.
string theory: a mathematical approach devised to unify the fundamental forces and explain fundamental particles as allowed vibrations on a ten-dimensional string.
strong force: the force that binds the neutrons and protons together in the nucleus of atoms, overcoming the mutual repulsion of the positively charged photons.
strong nuclear force: a fundamental force of nature that acts between quarks and is responsible for binding protons and neutrons together in nuclei.
subatomic: on the scale of the constituents of the atom: electrons, the constituents of the atomic nucleus and various other particles.
submicroscopic: smaller than what can be seen with an optical microscope.
superconductivity: a quantum mechanical property of certain substances that causes them to lose all resistance to electric current below a certain critical temperature.
superfluidity: a quantum mechanical property observed in liquid helium in which it loses all viscosity, or resistance to flow below a certain critical temperature.
superstring theory: an improvement on string theory that adds an eleventh dimension.
temperature: a measure of the energy of particles, for example, the degree to which the atoms in a solid substance are agitated by heating, with those feeling hot to the touch jostling with greater energy than the atoms in the fingers that sense them.
temperature scale: in this book, either of three temperature scales: The Fahrenheit scale, which observes the melting point of water (at a standard atmospheric pressure) as 32 degrees and the boiling point of water as 212 degrees; the Celsius scale, which observes the melting point of water (at a standard atmospheric pressure) as zero degrees and the boiling point of water as 100 degrees; and the Kelvin scale, which has the same units of temperature as the Celsius scale but starts from the absolute zero of temperature and observes the melting point of water as 273 degrees and the boiling point of water as 373 degrees.
theory: a well-tested and predictive set of ideas, otherwise often called a law, as distinct from a hypothesis, which is an as-yet-untested suggested theory or set of ideas.
tokomak: a device to convert the energy of controlled fusion into electrical power, specifically one that traps a hot fusion plasma within a magnetic field that circles on itself in a toroidal (donut-shaped) geometry.
torus: (adj.: toroidal) a donut-like shape.
transistor: an electronic device made of semiconducting material that can function as an amplifier or a controllable switch.
transition: the change in occupancy of states of the electron in an atom, usually caused by the absorption or resulting from the emission of a photon.
transition elements / transition metals: the elements listed in the center blocks of our periodic table, those specifically tending to have the outermost electrons of their atoms primarily in either d or f states.
transmutation: the transformation of one nucleus into another by a radioactive emission.
transuranic elements: chemical elements with atomic numbers greater than uranium's 92.
uncertainty principle: a consequence of the quantum nature of matter and energy discovered by Werner Heisenberg, stating the existence of natural limits on the certainty and precision of measurement of the paired quantities energy and time or position and momentum.
unit: a standard quantity for projecting by theory or measuring, such as the pound or the kilogram for projecting or measuring weight, or the Celsius degree or the Fahrenheit degree for projecting or measuring temperature.
valence: a property of an atom expressed as a positive or negative number that describes the way that the atom accepts or contributes electrons in a chemical reaction.
valence band: a set of closely spaced electron energy levels in a solid in which the electrons are shared among a few atoms and are involved in chemical bonding within the material.
volt: a unit of electrical potential.
wavefunction: a mathematical representation used in the Schrödinger equation that describes the position of an object as a diffuse and spread out or wavelike variation in space rather than as a fixed point.
wavelength: the distance between successive peaks of a wave or wavelike entity.
weak nuclear force: a fundamental force of nature that acts within the nucleus and governs the process of beta decay.
weight: see gravity.
x-ray: a photon released during the transition of an electron into one of the inner, most negative energy states of one of the heavier elements. (See also electromagnetic radiation.)
x-ray diffraction: a phenomenon in which the interaction of x-rays with a solid produce a pattern of interference that reveals information about the solid's crystal structure.