Elegant Universe - Book Glossary Flashcards
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
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 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.
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 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.
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 field
Force field of the electromagnetic force, consisting of electric and magnetic lines of force at each point in space.
Electromagnetic force
One of the four fundamental forces, a union of the electric and magnetic forces.
Electromagnetic gauge symmetry
Gauge symmetry underlying quantum electrodynamics.
Electromagnetic radiation
The energy carried by an electromagnetic wave.
Electromagnetic wave
A wavelike disturbance in an electromagnetic field; all such waves travel at the speed of light. Visible light, X rays, microwaves, and infrared radiation are examples.
Electron
Negatively charged particle, typically found orbiting the nucleus of an atom.
Electroweak theory
Relativistic quantum field theory describing the weak force and the electromagnetic force in one unified framework.
Eleven-dimensional supergravity
Promising higher-dimensional supergravity theory developed in the 1970s, subsequently ignored, and more recently shown to be an important part of string theory.
Entropy
A measure of the disorder of a physical system; the number of rearrangements of the ingredients of a system that leave its overall appearance intact.
Event horizon
The one-way surface of a black hole; once penetrated, the laws of gravity ensure that there is no turning back, no escaping the powerful gravitational grip of the black hole.
Extended dimension
A space (and spacetime) dimension that is large and directly apparent; a dimension with which we are ordinarily familiar, as opposed to a curled-up dimension.
Extremal black holes
Black holes endowed with the maximal amount of force charge possible for a given total mass.
Families
Organization of matter particles into three groups, with each group being known as a family. The particles in each successive family differ from those in the previous by being heavier, but carry the same electric and nuclear force charges.
Fermion
A particle, or patter of string vibration, with half a whole odd number amount of spin; typically a matter particle.
Field, Force Field
From a macroscopic perspective, the means by which a force communicates its influence; described by a collection of numbers at each point in space that reflect the strength and direction of the force at that point.
Flat
Subject to the rules of geometry codified by Euclid: a shape, like the surface of a perfectly smooth tabletop, and its higher-dimension generalizations.
Flop 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.
Force charge
A property of a particle that determines how it responds to a particular force. For instance, the electric charge of a particle determines how it responds to the electromagnetic force.
Frequency
The number of complete wave cycles a wave completes in each second.
Gauge symmetry
Symmetry principle underlying the quantum-mechanical description of the three nongravitational forces; the symmetry involves the invariance of a physical system under various shifts in the values of force charges, shifts that can change from place to place and from moment to moment.
General relativity
Einstein’s formulation of gravity, which shows that space and time communicate the gravitational force through their curvature.
Gluon
Smallest bundle of the strong force field; messenger particle of the strong force.
Grand unification
Class of theories that merge all three nongravitational forces into a single theoretical framework.
Gravitational force
The weakest of the four fundamental forces of nature. Described by Newton’s universal theory of gravity, and subsequently by Einstein’s general relativity.
Graviton
Smallest bundle of the gravitational force field; messenger particle for the gravitational force.
Heterotic-E string theory (Heterotic E8 X E8 string theory)
(should be E subscript 8 x E subscript 8)
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.
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 stand 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 numbers 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 tow 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
Chargeless species of particle, subject only to the weak force.
Neutron
Chargeless particle, typically found in the nucleus of an atom, consisting of three quarks (two down-quarks, on up-quark).
Newton’s laws of motion
Laws describing the motion of bodies based on the conception of an absolute and immutable space and time; these laws held sway until Einstein’s discovery of general relativity.
Newton’s universal theory of gravity
Theory of gravity declaring that the force of attraction between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. Subsequently supplanted by Einstein’s general relativity.
Nonperturbative
Feature of a theory whose validity is not dependent on approximate, perturbative calculations; an exact feature of a theory.
Nucleus
The core of an atom, consisting of protons and neutrons.
Observer
Idealized person or piece of equipment, often hypothetical, that measures relevant properties of a physical system.
One-loop process
Contribution to a calculation in perturbation theory in which one virtual pair of strings (or particles in a point-particle theory) is involved.
Open string
A type of string with two free ends.
Particle accelerator
Machine for boosting particles to nearly light speed and slamming them together in order to probe the structure of matter.
Perturbation theory
Framework for simplifying a difficult problem by finding an approximate solution that is subsequently refined as more details, initially ignored, are systematically included.
Phase
When used in reference to matter, describes its possible states: solid phase, liquid phase, gas phase. More generally, refers to the possible descriptions of a physical system as features on which it depends (temperature, string coupling constant values, form of spacetime, etc.) are varied.
Phase transition
Evolution of a physical system from one phase to another.
Photoelectric effect
Phenomenon in which electrons are ejected from a metallic surface when light is shone upon it.
Photon
Smallest packet of the electromagnetic force field; messenger particle of the electromagnetic force; smallest bundle of light.
Planck energy
About 1,000 kilowatt hours. The energy necessary to probe to distances as small as the Planck length. The typical energy of a vibrating string in string theory.
Planck length
About 10^-33 centimeters. The scale below which quantum fluctuations in the fabric of spacetime would become enormous. The size of a typical string in string theory.
Planck mass
About ten billion billion times the mass of a proton; about one-hundredth of a thousandth of a gram; about the mass of a small grain of dust. The typical mass equivalent of a vibrating string in string theory.
Planck’s constant
Denoted by the symbol (h with a slash), Planck’s constant is a fundamental parameter in quantum mechanics. It determines the size of the discrete units of energy, mass, spin, etc. into which the microscopic world is partitioned. Its value is 1.05 x 10^-27 grams-cm/sec.
Planck tension
About 10^+39 tons. The tension on a typical string in string theory.
Planck time
About 10^-43 seconds. Time at which the size of the universe was roughly the Planck length; more precisely, time it takes light to travel the Planck length.
Primordial nucleosynthesis
Production of atomic nuclei occurring during the first three minutes after the big bang.
Principle of equivalence
Core principle of general relativity declaring the indistinguishability of accelerated motion and immersion in a gravitational field (over small enough regions of observation). Generalizes the principle of relativity by showing that all observers, regardless of their state of motion, can claim to be at rest, so long as they acknowledge the presence of a suitable gravitational field.
Principle of relativity
Core principle of special relativity declaring that all constant-velocity observers are subject to an identical set of physical laws and that, therefore, every constant-velocity observer is justified in claiming that he or she is at rest. This principle is generalized by the principle of equivalence.
Product
The result of multiplying two numbers.
Proton
Positively charged particle, typically found in the nucleus of an atom, consisting of three quarks (two up-quarks and one down-quark).
Quanta
The smallest physical units into which something can be partitioned, according to the laws of quantum mechanics. For instance, photons are the quanta of the electromagnetic field.
Quantum chromodynamics (QCD)
Relativistic quantum field theory of the strong force and quarks, incorporating special relativity.
Quantum determinism
Property of quantum mechanics that knowledge of the quantum state of a system at one moment completely determines its quantum state at future and past moments. Knowledge of the quantum state, however, determines only the probability that one or another future will actually ensue.
Quantum electrodynamics (QED)
Relativistic quantum field theory of the electromagnetic force and electrons, incorporating special relativity.
Quantum fluctuation
Turbulent behavior of a system on microscopic scales due to the uncertainty principle.
Quantum geometry
Modification of Riemannian geometry required to describe accurately the physics of space on ultramicroscopic scales, where quantum effects become important.
Quantum gravity
A theory that successfully mergers quantum mechanics and general relativity, possibly involving modifications of one or both. String theory is an example of a theory of quantum gravity.
Quantum mechanics
Framework of laws governing the universe whose unfamiliar features such as uncertainty, quantum fluctuations, and wave-particle duality become most apparent on the microscope scales of atoms and subnuclear particles.
Quantum tunneling
Feature of quantum mechanics showing that objects can pass through barriers that should be impenetrable according to Newton’s classical laws of physics.
Quark
A particle that is acted upon by the strong force. Quarks exist in six varieties (up, down, charm, strange, top, bottom) and three “colors” (red, green, blue).
Radiation
The energy carried by waves or particles.
Reciprocal
The inverse of a number; for example, the reciprocal of 3 is 1/3, the reciprocal of 1/2 is 2.
Relativistic quantum field theory
Quantum-mechanical theory of fields, such as the electromagnetic field, that incorporates special relativity.
Resonance
One of the natural states of oscillation of a physical system.
Riemannian geometry
Mathematical framework for describing curved shapes of any dimension. Plays a central role in Einstein’s description of spacetime in general relativity.
Schrödinger equation
Equation governing the evolution of probability waves in quantum mechanics.
Schwarzschild solution
Solution to the equations of general relativity for a spherical distribution of matter; one implication of this solution is the possible existence of black holes.
Second law of thermodynamics
Law stating that total entropy always increases.
Second superstring revolution
Period in the development of string theory beginning around 1995 in which some nonperturbative aspects of the theory began to be understood.
Singularity
Location where the fabric of space or spacetime suffers a devastating rupture.
Smooth, Smooth space
A spatial region in which the fabric of space is flat or gently curved, with no pinches, ruptures, or creases of any kind.
Spacetime
A union of space and time originally emerging from special relativity. Can be viewed as the “fabric” out of which the universe is fashioned; it constitutes the dynamical arena within which events of the universe take place.
Spacetime foam
Frothy, writhing, tumultuous character of the spacetime fabric on ultramicroscopic scales, according to a conventional point-particle perspective. An essential reason for the incompatibility of quantum mechanics and general relativity prior to string theory.
Special relativity
Einstein’s laws of space and time in the absence of gravity.
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. 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 patter, 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 relatively, 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.
Symmetry
A property of a physical system that does not change when the system is transformed in some manner. For instance, a sphere is rotationally symmetrical since its appearance does not change if it is rotated.
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.
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 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.
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 string 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 sever 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 direction of an object’s motion.
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 that 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.
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 is wound around a circular spatial dimension.
World-sheet
Two-dimensional surface swept out by a string as it moves.
Wormhole
A tube-like region of space connecting one region of the universe to another.
