The Elegant Universe - Brian Greene [224]
Heterotic-O string theory (Heterotic O(32) string theory). One of the five superstring theories; involves closed strings whose right-moving vibrations resemble those of the Type II string and whose left-moving vibrations involve those of the bosonic string. Differs in important but subtle ways from the Heterotic-E string theory.
Higher-dimensional supergravity. Class of supergravity theories in more than four spacetime dimensions.
Horizon problem. Cosmological puzzle associated with the fact that regions of the universe that are separated by vast distances nevertheless have nearly identical properties such as temperature. Inflationary cosmology offers a solution.
Infinities. Typical nonsensical answer emerging from calculations that involve general relativity and quantum mechanics in a point-particle framework.
Inflation, Inflationary cosmology. Modification to the earliest moments of the standard big bang cosmology in which universe undergoes a brief burst of enormous expansion.
Initial conditions. Data describing the beginning state of a physical system.
Interference pattern. Wave pattern that emerges from the overlap and the intermingling of waves emitted from different locations.
Kaluza-Klein theory. Class of theories incorporating extra curled-up dimensions, together with quantum mechanics.
Kelvin. A temperature scale in which temperatures are quoted relative to absolute zero.
Klein-Gordon equation. A fundamental equation of relativistic quantum field theory.
Laplacian determinism. Clockwork conception of the universe in which complete knowledge of the state of the universe at one moment completely determines its state at all future and past moments.
Light clock. A hypothetical clock that measures elapsed time by counting the number of round-trip journeys completed by a single photon between two mirrors.
Lorentz contraction. Feature emerging from special relativity, in which a moving object appears shortened along its direction of motion.
Macroscopic. Refers to scales typically encountered in the everyday world and larger; roughly the opposite of microscopic.
Massless black hole. In string theory, a particular kind of black hole that may have large mass initially, but that becomes ever lighter as a piece of the Calabi-Yau portion of space shrinks. When the portion of space has shrunk down to a point, the initially massive black hole has no remaining mass—it is massless. In this state, it no longer manifests such usual black hole properties as an event horizon.
Maxwell's theory, Maxwell's electromagnetic theory. Theory uniting electricity and magnetism, based on the concept of the electromagnetic field, devised by Maxwell in the 1880s; shows that visible light is an example of an electromagnetic wave.
Messenger particle. Smallest bundle of a force field; microscopic conveyer of a force.
Mirror symmetry. In the context of string theory, a symmetry showing that two different Calabi-Yau shapes, known as a mirror pair, give rise to identical physics when chosen for the curled-up dimensions of string theory.
M-theory. Theory emerging from the second superstring revolution that unites the previous five superstring theories within a single overarching framework. M-theory appears to be a theory involving eleven spacetime dimensions, although many of its detailed properties have yet to be understood.
Multidimensional hole. A generalization of the hole found in a doughnut to higher-dimensional versions.
Multi-doughnut, Multi-handled doughnut. A generalization of a doughnut shape (a torus) that has more than one hole.
Multiverse. Hypothetical enlargement of the cosmos in which our universe is but one of an enormous number of separate and distinct universes.
Neutrino. Electrically neutral particle, subject only to the weak force.
Neutron. Electrically neutral particle, typically found in the nucleus of an