Coming of Age in the Milky Way (64 page)

Quantum electrodynamics.
The quantum theory of the electromagnetic force, which it envisions as being carried by quanta called
photons
.

Quantum genesis.
Hypothesis that the origin of the universe may be understood in terms of a quantum chance.

Quantum leap.
The disappearance of a subatomic
particle
—e.g., an electron—at one location and its simultaneous reappearance at another. The counterintuitive weirdness of the concept results in part from the limitations of the particle metaphor in describing a phenomenon that is also in many respects a wave.

Quantum mechanics.
See
quantum physics
.

Quantum physics.
Physics based upon the quantum principle, that energy is emitted not as a continuum but in discrete units.

Quantum space.
Vacuum with the potential to produce
virtual particles
.

Quantum tunneling.
A
quantum leap
through a barrier.

Quarks.
Fundamental particles from which all
hadrons
are made. According to the theory of quantum chromodynamics,
protons, neutrons
, and their higher-energy cousins are composed of trios of quarks, while the
mesons
are each made of one quark and one antiquark. Held together by the
strong nuclear force
, quarks are not found in isolation in nature today; see
asymptotic freedom
.

Quasars.
Pointlike sources of light whose redshifts indicate that they lie at distances of billions of light-years. Thought to be the
nuclei
of young
galaxies
.

Radio.
Long-wavelength electromagnetic radiation.

Radioactivity.
Emission of
particles
by unstable elements as they decay.

Radio astronomy.
Study of the universe at the
radio
wavelengths of electromagnetic energy.

Radiocarbon dating.
Determination of the age of a substance containing radioactive carbon by means of its radioactive
half-life
. Radiometric dating. Determination of the age of objects—e.g., earth and moon
rocks—by means of the
half-life
of the unstable elements they contain.

Radiotelescopes.
Sensitive radio antennae employed to detect the radio energy emitted by nebulae, galaxies, pulsars, etc.

Recombination.
The capture of an electron by a proton. Numerous recombinations are thought to have occurred when the universe was a little less than one million years old, resulting in the formation of electron shells around helium and hydrogen nuclei to create complete
atoms
.

Red giants.
Large stars with an atmosphere that is relatively cool, and therefore looks redder in color than does that of a
main sequence
star.

Redshift.
Displacement of the spectral lines in light coming from the stars of distant galaxies, thought to be produced by the velocity of the galaxies outward in the expanding universe. See
Hubble law
.

Redshift-distance relation.
The correlation between redshift in the spectra of galaxies and their distances. See
Hubble law
.

Relativistic.
Approaching the velocity of light. Particles moving at these speeds demonstrate effects predicted by the special theory of relativity—increased mass, slowing of time, etc.—that must be taken into account by combining relativity with quantum theory if accurate predictions are to be made.

Relativity, general theory of.
Einstein’s theory
of gravitational force
.

Relativity, special theory of.
Einstein’s theory of the electrodynamics of moving systems.

Renaissance.
Generally, the period of cultural awakening in the West beginning at about 1350 and ending with the death of Giordano Bruno in 1600 or of Shakespeare in 1616.

Renormalization.
The removal of nonsensical infinities from quantum mechanics equations by a mathematical procedure in which other infinities are introduced in order to cancel them.

Retrograde.
Apparent motion of a planet in a direction opposite to its normal progress across the sky, produced by the orbital motion of the earth.

Right ascension.
Location in the sky along an east-west direction; the celestial equivalent of longitude. Compare
declination
.

Royal Society.
English organization founded in the seventeenth century and dedicated to the advancement of science.

Satellite.
An object in orbit around another, more massive object.

Scholastics.
Adherents to the philosophy and cosmology of Aristotle. Their dominance in the universities, which had been founded largely to study Aristotle, constituted an obstacle to acceptance of the Copernican system advocated by Kepler and Galileo.

Science.
Systematic study of nature, based upon the presumption that the universe is based upon rationally intelligible principles and that its behavior can therefore be predicted by subjecting observational data to logical analysis.

SETI.
The Search for Extraterrestrial Intelligence, by using
radiotelescopes
to listen for signals transmitted by intelligent alien beings.

Sextant.
Instrument employed to measure the elevation of astronomical objects above the horizon. Based upon an arc equal to a sixth of a circle, sextants are more compact and easier to use than are the
quadrants
that preceded them.

Shadow matter.
Theoretical classes of particles, their existence intimated by
supersymmetry theory, that participate in few if any of the four known fundamental
forces
. Planets, stars, and galaxies made of shadow matter could conceivably exist in the same space and time we occupy without our sensing their presence.

Singularity.
A point of infinite curvature of space where the equations of general relativity break down. A
black hole
represents a singularity; so, perhaps, did the universe at the first moment of time.

Solar system.
The sun, its planets, and the asteroids and comets that, like the planets, orbit the sun.

Space.
Traditionally, the three-dimensional theater within which events transpire, explicable by means of euclidean geometry. In
relativity
, space is depicted in terms of noneuclidean geometries as well. In
quantum physics
, space may be constructed out of any of a variety of abstractions, such as a “charge space” employed in dealing with electrically charged particles or the “color space” in which
quarks
can for convenience be plotted.
See geometry
.

Spacetime.
Arena in which events are depicted in the theory of
relativity
. The orbit of a planet, for instance, can be described as a “world line” in a four-dimensional spacetime continuum.

Spectrograph.
A device, usually based on a finely etched grate that performs the function of a prism, for breaking up light into its constituent parts and making a photographic or electronic record of the resulting
spectrum
. When lacking a means for recording the spectrum, the device is called a spectroscope.

Spectroscopic binary.
A double star in which the individual stars cannot be resolved, but can be detected through their effects on the
spectrum
of the system—e.g., the relative motions of the stars may be detected from
Doppler shifts
in the spectral lines of starlight.

Spectroscopy.
Scientific investigation of an object by studying its
spectrum
.

Spectrum.
A record of the distribution of matter or energy (e.g., light) by wavelength. Spectra can be studied to learn the chemical composition and motion of stars and galaxies.

Spherical space
.
See geometry
.

Spin.
The intrinsic angular momentum of an elementary
particle
, as by the particle’s spinning on its axis. Spin is quantized in units of Planck’s constant of action,
h
, so that, e.g., “spin 1,” means spin = 1
h
. Particles with integral spin (0, 1) are called
bosons;
those with half spin
are fermions
.

Spiral nebulae.
See
nebulae
.

Spiritualism.
Belief that material interactions alone cannot account for all phenomena, and that some—e.g., thought—are due to the fundamentally insensible actions of intangibles.

Standard model.
The theories of the four
forces
, which, taken together, can predict the outcome of every known fundamental
interaction
.

Star.
A celestial object that generates energy by means of nuclear fusion at its core. To do this it must have more than about 0.08 the sun’s mass. If, for instance, the planet Jupiter were some fifty to one hundred times more massive than it is, fusion reactions would transpire in its core and it would be a star. See
planet
.

Star clusters.
Gravitationally bound aggregations of stars, smaller and less massive
than galaxies. “Globular” clusters are the largest category; they are old, and may harbor hundreds of thousands to millions of stars, and are found both within and well away from the
galactic disk
. “Open” clusters are smaller, have a wide range of ages, and reside within the disk. Statute mile. See
mile
.

Steady state.
Theory that the expanding universe was never in a state of appreciably higher density—i.e., that there was no “big bang”—and that matter is constantly being created out of empty space in order to maintain the
cosmic matter density
.

Stellar evolution.
The building of complex atomic nuclei from simpler nuclei in stars, with the result that succeeding generations of stars and planets contain a greater variety of chemical elements than did their predecessors. See
evolution
.

Stochastic cooling.
The gathering (i.e., focusing) of clouds of subatomic
particles
in an accelerator by monitoring their scattering vectors and altering the magnetic environment in an accelerator
storage ring
to keep them close together. First employed in storing particles of
antimatter
, which are expensive to manufacture and ought not to be wasted.

Storage ring.
A ring in which particles are kept in a circular motion, suspended in a magnetic field, until they can be injected into the larger ring of an
accelerator
.

String theory.
Theory that subatomic
particles
actually have extension along one axis, and that their properties are determined by the arrangement and vibration of the strings.

Strong nuclear force (or interaction).
Fundamental force of nature that binds
quarks
together, and holds
nucleons
(which are comprised of quarks) together as the nuclei of
atoms
. Portrayed in
quantum chromodynamics
as conveyed by quanta called
gluons
.

Subatomic.
Of a scale smaller than that of an atom. Subatomic particles. See
particles
.

Sum over histories.
Probabilistic interpretation of a system’s past, in which quantum
indeterminacy
is taken into account and the history is reconstructed in terms of each possible path and its relative likelihood.