The Elegant Universe - Brian Greene [227]
Special relativity. Einstein's laws of space and time in the absence of gravity (see also general relativity).
Sphere. The outer surface of a ball. The surface of a familiar three-dimensional ball has two dimensions (which can be labeled by two numbers such as "latitude" and "longitude," as on the surface of the earth). The concept of a sphere, though, applies more generally to balls and hence their surfaces, in any number of dimensions. A one-dimensional sphere is a fancy name for a circle; a zero-dimensional sphere is two points (as explained in the text). A three-dimensional sphere is harder to picture; it is the surface of a four-dimensional ball.
Spin. A quantum-mechanical version of the familiar notion of the same name; particles have an intrinsic amount of spin that is either a whole number or half a whole number (in multiples of Planck's constant), and which never changes.
Standard model of cosmology. Big bang theory together with an understanding of the three nongravitational forces as summarized by the standard model of particle physics.
Standard model of particle physics, Standard model, Standard theory. An enormously successful theory of the three nongravitational forces and their action on matter. Effectively the union of quantum chromodynamics and the electroweak theory.
String. Fundamental one-dimensional object that is the essential ingredient in string theory.
String coupling constant. A (positive) number that governs how likely it is for a given string to split apart into two strings or for two strings to join together into one—the basic processes in string theory. Each string theory has its own string coupling constant, the value of which should be determined by an equation; currently such equations are not understood well enough to yield any useful information. Coupling constants less than 1 imply that perturbative methods are valid.
String mode. A possible configuration (vibrational pattern, winding configuration) that a string can assume.
String theory. Unified theory of the universe postulating that fundamental ingredients of nature are not zero-dimensional point particles but tiny one-dimensional filaments called strings. String theory harmoniously unites quantum mechanics and general relativity, the previously known laws of the small and the large, that are otherwise incompatible. Often short for superstring theory.
Strong force, Strong nuclear force. Strongest of the four fundamental forces, responsible for keeping quarks locked inside protons and neutrons and for keeping protons and neutrons crammed inside of atomic nuclei.
Strong force symmetry. Gauge symmetry underlying the strong force, associated with invariance of a physical system under shifts in the color charges of quarks.
Strongly coupled. Theory whose string coupling constant is larger than 1.
Strong-weak duality. Situation in which a strongly coupled theory is dual—physically identical—to a different, weakly coupled theory.
Sum-over-paths. Formulation of quantum mechanics in which particles are envisioned to travel from one point to another along all possible paths between them.
Supergravity. Class of point-particle theories combining general relativity and supersymmetry.
Superpartners. Particles whose spins differ by 1/2 unit and that are paired by supersymmetry.
Superstring theory. String theory that incorporates supersymmetry.
Supersymmetric quantum field theory. Quantum field theory incorporating supersymmetry.
Supersymmetric standard model. Generalization of the standard model of particle physics to incorporate supersymmetry. Entails a doubling of the known elementary particle species.
Supersymmetry. A symmetry principle that relates the properties of particles with a whole number amount of spin (bosons) to those with half a whole (odd) number amount of spin (fermions).
Symmetry. A property of a physical system that does not change when the system is transformed in some manner. For instance, a sphere