The Elegant Universe - Brian Greene [228]
Symmetry breaking. A reduction in the amount of symmetry a system appears to have, usually associated with a phase transition.
Tachyon. Particle whose mass (squared) is negative; its presence in a theory generally yields inconsistencies.
Thermodynamics. Laws developed in the nineteenth century to describe aspects of heat, work, energy, entropy, and their mutual evolution in a physical system.
Three-brane. See brane.
Three-dimensional sphere. See sphere.
Time dilation. Feature emerging from special relativity, in which the flow of time slows down for an observer in motion.
T.O.E. (Theory of Everything). A quantum-mechanical theory that encompasses all forces and all matter.
Topologically distinct. Two shapes that cannot be deformed into one another without tearing their structure in some manner.
Topology. Classification of shapes into groups that can be deformed into one another without ripping or tearing their structure in any way.
Topology-changing transition. Evolution of spatial fabric that involves rips or tears, thereby changing the topology of space.
Torus. The two-dimensional surface of a doughnut.
Two-brane. See brane.
Two-dimensional sphere. See sphere.
Type I string theory. One of the five superstring theories; involves both open and closed strings.
Type IIA string theory. One of the five superstring theories; involves closed strings with left-right symmetric vibrational patterns.
Type IIB string theory. One of the five superstring theories; involves closed strings with left-right asymmetric vibrational patterns.
Ultramicroscopic. Length scales shorter than the Planck length (and also time scales shorter than the Planck time).
Uncertainty principle. Principle of quantum mechanics, discovered by Heisenberg, that there are features of the universe, like the position and velocity of a particle, that cannot be known with complete precision. Such uncertain aspects of the microscopic world become ever more severe as the distance and time scales on which they are considered become ever smaller. Particles and fields undulate and jump between all possible values consistent with the quantum uncertainty. This implies that the microscopic realm is a roiling frenzy, awash in a violent sea of quantum fluctuations.
Unified theory, Unified field theory. Any theory that describes all four forces and all of matter within a single, all-encompassing framework.
Uniform vibration. The overall motion of a string in which it moves without changes in shape.
Velocity. The speed and the direction of an object's motion.
Vibrational mode. See vibrational pattern.
Vibrational pattern. The precise number of peaks and troughs as well as their amplitude as a string oscillates.
Vibration number. Whole number describing the energy in the uniform vibrational motion of a string; the energy in its overall motion as opposed to that associated with changes in its shape.
Virtual particles. Particles that erupt from the vacuum momentarily; they exist on borrowed energy, consistent with the uncertainty principle, and rapidly annihilate, thereby repaying the energy loan.
Wave function. Probability waves upon which quantum mechanics is founded.
Wavelength. The distance between successive peaks or troughs of a wave.
Wave-particle duality. Basic feature of quantum mechanics that objects manifest both wavelike and particle-like properties.
W bosons. See weak gauge boson.
Weak force, Weak nuclear force. One of the four fundamental forces, best known for mediating radioactive decay.
Weak gauge boson. Smallest bundle of the weak force field; messenger particle of the weak force; called W or Z boson.
Weak gauge symmetry. Gauge symmetry underlying the weak force.
Weakly coupled. Theory whose string coupling constant is less than 1.
Winding energy. The energy embodied by a string wound around a circular dimension of space.
Winding mode. A string configuration that wraps around a circular spatial dimension.
Winding number. The number of times a string