by Marcus Chown
SOLAR SYSTEM The Sun and its family of planets, moons, comets, and other assorted rubble.
SPACE-TIME In the general theory of relativity, space and time are seen to be essentially the same thing. They are therefore treated as a single entity—space-time. It is the warpage of space-time that turns out to be gravity.
SPECTRAL LINE Atoms and molecules absorb and give out light at characteristic wavelengths. If they swallow more light than they emit, the result is a dark line in the spectrum of a celestial object. Con-versely, if they emit more than they swallow, the result is a bright line.
SPECTRUM The separation of light into its constituent “rainbow” colours.
SPIN Quantity with no everyday analog. Loosely speaking, subatomic particles with spin behave as if they are tiny spinning tops (only they are not spinning at all!).
STAR A giant ball of gas that replenishes the heat it loses to space by means of nuclear energy generated in its core.
STRING THEORY See Superstring Theory.
STRONG NUCLEAR FORCE The powerful short-range force that holds protons and neutrons together in an atomic nucleus.
SUBATOMIC PARTICLE A particle smaller than an atom, such as an electron or a neutron.
SUN The nearest star.
SUPERCONDUCTOR A material that, when cooled to ultralow temperatures, conducts an electrical current forever—that is, with no resistance. This ability is connected with a change in the conducting particles from fermions to bosons. Specifically, electrons (fermions) pair up to form Cooper pairs (bosons).
SUPERFLUID A fluid that, below a critical temperature, develops bizarre properties such as the ability to flow uphill and squeeze through impossibly small holes. The best example is liquid helium, which becomes a superfluid below a temperature of 2.17 degrees above absolute zero. Superfluid liquid helium owes its weirdness to quantum theory and the fact that helium atoms are bosons.
SUPERNOVA A cataclysmic explosion of a massive star. A supernova may, for a short time, outshine an entire galaxy of 100 billion ordinary stars. It is thought to leave behind a highly compressed neutron star or even a black hole.
SUPERSTRING THEORY Theory which postulates that the fundamental ingredients of the Universe are tiny strings of matter. The strings vibrate in a space-time of 10 dimensions. The great payoff of this idea is that it may be able to unite, or “unify,” quantum theory and the general theory of relativity.
TACHYON Hypothetical particle that lives its life permanently travelling faster than light.
TELEPORTATION The clever use of entanglement to pin down the exact state of a microscopic particle, in apparent violation of what is permitted by the Heisenberg uncertainty principle. This enables the information necessary to reconstruct the state of the particle to be sent to a remote site.
TEMPERATURE The degree of hotness of a body. Related to the energy of motion of the particles that compose it.
THERMODYNAMICS, SECOND LAW OF The decree that entropy, or microscopic disorder of a body, cannot ever decrease. This is equivalent to saying that heat can never flow from a cold to a hot body.
TIME DILATION The slowing down of time for an observer moving close to the speed of light or experiencing strong gravity.
TIME LOOP See Closed Time-Like Curve.
TIME MACHINE See Closed Time-Like Curve.
TIME TRAVEL Travel into the past or future—in the case of the future, at a rate of more than 1 year per year.
TIME TRAVEL PARADOX Nonsensical situation that time travel appears to permit. The most famous is the grandfather paradox in which someone goes back in time and shoots their grandfather before he conceives their mother. How then could they have been born to go back in time and commit the act?
TOTAL ECLIPSE OF THE SUN The coverage of the Sun by the disc of the Moon when the Moon moves between the Sun and Earth.
TWIN PARADOX The paradox that arises when someone travels at close to light speed to, say, Alpha Centauri and back while their twin stays at home. According to special relativity, the space-travelling twin ages less. However, from another point of view, it is Earth that receded from the space-travelling twin at close to the speed of light and therefore the stay-at-home-twin who ages less. The paradox is resolved by realising that the two situations are not equivalent. The space-travelling twin must undergo a deceleration and an acceleration at the turnaround at Alpha Centauri, and accelerations require general relativity not special relativity.
ULTRAVIOLET Type of invisible light that is given out by very hot bodies which is responsible for sunburn.
UNCERTAINTY PRINCIPLE See Heisenberg Uncertainty Principle.
UNIFICATION The idea that at extremely high energy the four fundamental forces of nature are one, united in a single theoretical framework.
UNIVERSE All there is. This is a flexible term once used for what we now call the solar system. Later, it was used for what we call the MilkyWay. Now it is used for the sum total of all the galaxies, of which there appear to be about 100 billion within the observable Universe.
UNIVERSE, EXPANSION OF The fleeing of the galaxies from each other in the aftermath of the Big Bang.
UNIVERSE, OBSERVABLE All we can see out to the Universe’s horizon.
URANIUM The heaviest naturally occurring element.
VIRTUAL PARTICLE Subatomic particle that has a fleeting existence, popping into being and popping out again according to the constraint imposed by the Heisenberg uncertainty principle.
VISCOSITY The internal friction of a liquid. Treacle has high viscosity and water has low viscosity.
WAVE FUNCTION A mathematical entity that contains all that is knowable about a quantum object such as an atom. The wave function changes in time and space according to the Schrödinger equation.
WAVELENGTH The distance for a wave to go through a complete oscillation cycle.
WAVE-PARTICLE DUALITY The ability of a subatomic particle to behave as a localised billiard ball-like particle or a spread-out wave.
WEAK NUCLEAR FORCE The second force experienced by protons and neutrons in an atomic nucleus, the other being the strong nuclear force. The weak nuclear force can convert a neutron into a proton and so is involved in beta decay.
WHITE DWARF A star that has run out of fuel and that gravity has compressed until it is about the size of Earth. A white dwarf is supported against further shrinkage by electron degeneracy pressure. A sugar cube of white dwarf material weighs about as much as a family car.
WORMHOLE A tunnel through space-time that connects widely spaced regions and so provides a shortcut.
X-RAYS A high-energy form of light.
FURTHER READING
ATOMS AND QUANTUM THEORY
Quantum: A Guide for the Perplexed, by Jim Al-Khalili (Weidenfeld & Nicolson, London, 2003).
Taming the Atom, by Hans Christian von Baeyer (Penguin, London, 1994).
Minds, Machines, and the Multiverse, by Julian Brown (Little Brown, New York, 2000).
The Magic Furnace, by Marcus Chown (Vintage, London, 2000).
The Fabric of Reality, by David Deutsch (Penguin, London, 1997).
Thirty Years That Shook Physics, by George Gamow (Dover, New York, 1985).
The Great Physicists from Galileo to Einstein, by George Gamow (Dover, New York, 1988).
The New Quantum Universe, by Tony Hey and Patrick Walters, 2nd edition (Cambridge University Press, Cambridge, England, 2004).
The Feynman Lectures on Physics, edited by Robert Leighton et al. (Addison-Wesley, New York, 1989).
RELATIVITY AND COSMOLOGY
Afterglow of Creation, by Marcus Chown (University Science Books, Sausalito, California, 1994).
The Universe Next Door, by Marcus Chown (Headline, London, 2002).
Cosmology, by Edward Harrison (Cambridge University Press, Cambridge, England, 1991).
The River of Time, by Igor Novikov (Cambridge University Press, Cambridge, England, 1998).
Einstein’s Legacy, by Julian Schwinger (Scientific American Library, New
York, 1986).
The Physical Universe, by Frank Shu (University Science Books, Sausalito, California, 1982).
INDEX
A
Acceleration
curvature of space and, 1
gravity and, 1
Adams, Douglas, 1, 2
Aging
general theory of relativity, 1
gravity effects, 1
special theory of relativity, 1, 2
Allen, Woody, 1
Alpha particle
decay, 1, 2
definition, 1
escape from nucleus, 1, 2
scattering studies, 1, 2
tunnelling, 1
Alpher, Ralph, 1
Anaxagoras, 1
Antimatter, 1n, 2
Aspect, Alain, 1
Aston, Francis, 1, 2
Atkinson, Robert, 1
Atmosphere, 1
Atomic theory
atomic decay, 1, 2
chemical properties, 1, 2
duration of atoms, 1, 2
nature of light, 1, 2
origins and development, 1
quantum theory and, 1
size of atoms, 1, 2
structure and properties of atoms, 1, 2, 3
structure and properties of matter, 1, 2
types of atoms, 1
uncertainty principle, 1
Atomic weight, 1, 2
Attraction, atomic, 1
B
Becquerel, Henri, 1
Beginning of Universe. See Big Bang
Bernoulli, Daniel, 1
Big Bang
cosmic background radiation as evidence of, 1, 2, 3
distribution of matter after, 1, 2
entanglement and, 1
expansion of universe after, 1
explanatory power, 1
general theory of relativity and, 1, 2
inflation theory, 1
singularity at moment of, 1
visibility of stars and, 1
Big Crunch, 1
Binary calculations, 1n
Binnig, Gerd, 1
Biosphere, 1
Black body, 1
Black holes
definition and properties, 1, 2, 3
Einstein’s theory, 1
energy conversion in, 1
event horizon, 1
gravity in, 1
in quasars, 1
singularity in, 1
space-time distortions in, 1, 2
Bohr, Niels, 1
Bose-Einstein condensation, 1
Bosons
behaviour in presence of other bosons, 1
definition, 1
fermions behaving as, 1
Boyle, Robert, 1
Bragg, William, 1
Breathing, shared atoms in, 1
Brown, Julian, 1
Brown, Robert, 1
Brownian motion, 1, 2
Bruno, Giordano, 1
C
Carbon, 1
Centrifugal force, 1
Chance, in quantum theory, 1
Chandrasekhar, Subrahmanyan, 1
Chandrasekhar limit, 1
Charge, atomic, 1, 2n
Chemistry, atomic basis of, 1, 2
Chiao, Raymond, 1
Chronology protection conjecture, 1
Cloud chamber, 1
Comets, 1, 2, 3
Compton effect, 1
Computers, quantum. See Quantum computers
Contraction of universe, 1
Cooper pairs, 1
Copenhagen Interpretation, 1
Cosmic Background Explorer Satellite, 1
Cosmic background radiation, 1
Big Bang theory and, 1, 2, 3, 4
discovery, 1
distribution of, 1, 2, 3
temperature, 1, 2
Cosmology, 1
Critical mass, 1, 2
D
Dark matter, 1, 2
Decay
atomic, 1
of organic matter, 1
Decoherence, 1, 2
Degeneracy pressure, 1, 2
Democritus, 1, 2
Deutsch, David, 1
Double slit experiment
design, 1
indistinguishability and, 1
interference pattern, 1, 2, 3
particle physics of, 1, 2, 3
significance of, 1, 2, 3
uncertainty principle and, 1
Duration of atoms, 1, 2
E
Eclipse, solar, 1
Eddington, Arthur, 1, 2, 3
Einstein, Albert, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21
Electric force, 1, 2
Electricity
atomic theory, 1, 2
electric current, 1
electrical charge, 1
photoelectric effect, 1
Electromagnetism
light and, 1, 2
special theory of relativity, 1
theory of, 1, 2, 3
Electrons, 1
atomic structure, 1, 2, 3
in Cooper pairs, 1
discovery, 1
ejection event, 1
indistinguishability, 1
nucleus and, 1, 2, 3
orbitals, 1, 2, 3, 4, 5
Pauli exclusion principle, 1, 2
in photoelectric effect, 1
properties, 1, 2
spin, 1
in stars, 1
uncertainty principle, 1
velocity, 1
vibration, 1, 2
wave frequency, 1
See also Fermions
Elements, 1, 2
E=mc2, 1, 2
Emptiness
of matter, 1, 2, 3
quantum vacuum, 1
Energy
atomic weight and, 1
in black holes, 1
dark energy, 1
in electron orbit jump, 1
in empty space, 1
gravity effects, 1
hydrogen bomb, 1
mass and, 1, 2
mass converted into, 1
of motion, 1
to reach speed of light, 1
as source of gravity, 1, 2
of stars, 1
transformation of, 1, 2, 3
weight of, 1, 2
Entanglement, 1
Equivalence, Principle of, 1, 2
Event horizon, 1
Everett, Hugh, III, 1
Exclusion principle. See Pauli exclusion principle
Expanding universe
discovery of, 1
future of, 1
rate, 1
See also Inflation of Universe
F
Faraday, Michael, 1
Fermions
boson behaviour in, 1
definition, 1
probability waveflipping and, 1
Feynman, Richard, 1, 2, 3, 4, 5n, 6, 7
Fourth dimension, 1
Frame dragging, 1
Free fall, 1, 2, 3
Frequencies, wave, 1
Friction, 1, 2n
Friedman, Aleksandr, 1
G
Gaarder, Jostein, 1, 2, 3, 4
Galaxies
dark matter of, 1
distribution, 1
in expanding universe, 1
Galileo, 1, 2
Gamboge particles, 1
Gamow, George, 1, 2n, 3
Gas, pressure of, 1
Geiger, Hans, 1, 2, 3
General theory of relativity
bending of light in, 1
cosmological application, 1, 2
goals, 1, 2
gravity waves in, 1
nonlinearity of, 1
principles of, 1
quantum theory and, 1
real-world implications, 1, 2
time travel and, 1
Geodesics, 1
Gravitational red shift, 1n
Gravitons, 1
Gravity
acceleration and, 1
&nbs
p; bending of light by, 1
of black holes, 1, 2
creation of gravity by, 1, 2
of dark matter, 1
effects on time, 1
experience of, 1
frame dragging, 1
general theory of relativity, 1
as inertial force, 1
mass and, 1
Newtonian conceptualisation, 1
particle carriers of, 1
in production of energy, 1
quantum theory of, 1
repulsive force and, 1
sources of, 1
speed of, 1
as warped space, 1
waves, 1, 2
without mass, 1
Ground state, 1
Guth, Alan, 1
H
Hawking, Stephen, 1, 2
Heisenberg, Werner, 1
Helium
alpha particles, 1, 2
liquid, 1
nuclear fusion, 1
properties, 1
structure, 1, 2n, 3
Helium-3, 1
Herman, Robert, 1
Houtermans, Fritz, 1
Hoyle, Fred, 1n
Hubble, Edwin, 1
Hubble’s law, 1
Hydrogen, 1
atomic structure, 1n, 2
nuclear fusion, 1, 2
Hydrogen bomb, 1
I
Indistinguishability of microscopic objects
electron spin and, 1
interference and, 1, 2
Pauli exclusion principle and, 1
significance of, 1, 2
Inertia, 1
Inflation of Universe, 1
Interference
decoherence and, 1
evidence of, 1
indistinguishability and, 1
Many Worlds idea and, 1
obstacles to, 1
particle physics, 1, 2, 3
pattern smearing, 1
superposition and, 1
uncertainty principle, 1
Inverse-square law, 1
Ions, 1, 2n
K
Kepler, Johannes, 1
Kerr, Roy, 1
L
Lamb shift, 1n
Lasers, 1
Lavoisier, Antoine, 1
Leibniz, Gottfried, 1n
Lemaître, Georges-Henri, 1
Light
ability to penetrate matter, 1
atomic theory and, 1
bending of, by gravity, 1
boson behaviour and, 1
cosmic background radiation, 1
curvature of space and, 1
dual wave-particle nature, 1
effect of gravity of time and, 1
