The Elegant Universe - Brian Greene [222]
Absolute zero. The lowest possible temperature, about -273 degrees Celsius, or 0 on the Kelvin scale.
Acceleration. A change in an object's speed or direction. See also velocity.
Accelerator. See particle accelerator.
Amplitude. The maximum height of a wave peak or the maximum depth of a wave trough.
Anthropic principle. Doctrine that one explanation for why the universe has the properties we observe is that, were the properties different, it is likely that life would not form and therefore we would not be here to observe the changes.
Antimatter. Matter that has the same gravitational properties as ordinary matter, but that has an opposite electric charge as well as opposite nuclear force charges.
Antiparticle. A particle of antimatter.
ATB. Acronym for "after the bang"; usually used in reference to time elapsed since the big bang.
Atom. Fundamental building block of matter, consisting of a nucleus (comprising protons and neutrons) and an orbiting swarm of electrons.
Big bang. Currently accepted theory that the expanding universe began some 15 billion years ago from a state of enormous energy, density, and compression.
Big crunch. One hypothesized future for the universe in which the current expansion stops, reverses, and results in all space and all matter collapsing together; a reversal of the big bang.
Black hole. An object whose immense gravitational field entraps anything, even light, that gets too close (closer than the black hole's event horizon).
Black-hole entropy The entropy embodied within a black hole.
Boson. A particle, or pattern of string vibration, with a whole number amount of spin; typically a messenger particle.
Bosonic string theory. First known string theory; contains vibrational patterns that are all bosons.
BPS states. Configurations in a supersymmetric theory whose properties can be determined exactly by arguments rooted in symmetry.
Brane. Any of the extended objects that arise in string theory. A one-brane is a string, a two-brane is a membrane, a three-brane has three extended dimensions, etc. More generally, a p-brane has p spatial dimensions.
Calabi-Yau space, Calabi-Yau shape. A space (shape) into which the extra spatial dimensions required by string theory can be curled up, consistent with the equations of the theory.
Charge. See force charge.
Chiral, Chirality. Feature of fundamental particle physics that distinguishes left-from right-handed, showing that the universe is not fully left-right symmetric.
Closed string. A type of string that is in the shape of a loop.
Conifold transition. Evolution of the Calabi-Yau portion of space in which its fabric rips and repairs itself, yet with mild and acceptable physical consequences in the context of string theory. The tears involved are more severe than those in a flop transition.
Cosmic microwave background radiation. Microwave radiation suffusing the universe, produced during the big bang and subsequently thinned and cooled as the universe expanded.
Cosmological constant. A modification of general relativity's original equations, allowing for a static universe; interpretable as a constant energy density of the vacuum.
Coupling constant. See string coupling constant.
Curled-up dimension. A spatial dimension that does not have an observably large spatial extent; a spatial dimension that is crumpled, wrapped, or curled up into a tiny size, thereby evading direct detection.
Curvature. The deviation of an object or of space or of spacetime from a flat form and therefore from the rules of geometry codified by Euclid.
Dimension. An independent axis or direction in space or spacetime. The familiar space around us has three dimensions (left-right, back-forth, up-down) and the familiar spacetime has four (the previous three axes plus the past-future axis). Superstring theory requires the universe to have additional spatial dimensions.
Dual, Duality, Duality symmetries. Situation in which two or more theories appear to be completely different, yet actually give rise to identical physical consequences.
Electromagnetic