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Chapter 19
In The Beginning
term:
anthropic principle
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definition:
The idea that since we exist, the Universe must
have certain properties or it would not have
evolved so that life formed and humans
evolved.
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term:
cosmic microwave radiation
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definition:
Isotropic millimeter and submillimeter radiation
following a black-body curve for about 3 K;
interpreted as a remnant of the big bang.
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term:
electromagnetism
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definition:
The combined force of electricity and
magnetism, which follows the formulae unified
by Maxwell.
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term:
electroweak force
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definition:
The unified electromagnetic and weak forces,
according to a recent theory.
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term:
flatness problem
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definition:
One of the problems solved by the inflationary
theory, that the Universe is exceedingly close to
being flat for no obvious reason.
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term:
grand unified theories (GUTs)
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definition:
Theories unifying the electroweak force and the
strong force.
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term:
gravity
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definition:
The tendency for all masses to attract each
other; described in a formula by Newton and
more recently described by Einstein as a result
of a warping of space and time by the presence
of a mass.
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term:
horizon problem
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definition:
One of the problems of cosmology solved by
the inflationary theory: why the Universe has
the same average temperature in all directions,
even though widely separated regions could
never have been in thermal equilibrium with
each other since they are beyond each other's
horizons.
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term:
inflation
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definition:
The theory that the Universe expanded
extremely fast, by perhaps 10 to the 100th
power, in the first fraction of a second after the
big bang. The concept of inflation solves
several problems in cosmology, such as the
horizon problem.
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term:
multiverse
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definition:
The set of parallel universes that may exist, with
our observable universe as only one part.
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term:
perfect cosmological principle
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definition:
The assumption that on a large scale the
Universe is homogenous and isotropic in space
and unchanging in time.
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term:
phase transition
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definition:
Change from one state of matter to another, as
from solid to liquid or liquid to gas; phase
transitions in the early Universe marked the
separation of the fundamental forces.
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term:
Planck time
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definition:
The time very close to the Big Bang, 1043 seconds, before which a quantum
theory of gravity would be necessary to
explain the Universe and which is
therefore currently inaccessible to our
computations.
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term:
primordial nucleosynthesis
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definition:
The formation of the nuclei of isotopes of
hydrogen (such as deuterium), helium, and
lithium in the first 10 minutes of the Universe.
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term:
quark
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definition:
One of the subatomic particles of which modern
theoreticians believe such elementary particles
as protons and neutrons are composed. The
various kinds of quarks have positive or
negative charges of 1/3e or 2/3e, where e is the
unit of electric charge.
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term:
steady-state theory
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definition:
The cosmological theory based on the perfect
cosmological principle, in which the average
properties of the Universe are unchanging over
time.
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term:
strong nuclear force
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definition:
The strong force.
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term:
supercooled
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definition:
The condition in which a substance is cooled
below the point at which it would normally make
a phase change; for the Universe, the point in
the early Universe at which it may have cooled
below a certain temperature without breaking its
symmetry; the strong and electroweak forces
remained unified.
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term:
superstring (string) theories
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definition:
A possible unification of quantum theory and
general relativity in which fundamental particles
are really different vibrating forms of a tiny, onedimensional "string" instead of being localized
at single points.
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term:
symmetric
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definition:
A correspondence of shape so that rotating or
reflecting an object gives you back an identical
form; symmetry of forces in the early Universe
corresponds to forces acting identically that now
act differently as the four fundamental forces:
gravity, electromagnetism, weak nuclear force,
and strong nuclear force.
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term:
weak nuclear force
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definition:
One of the four fundamental forces of nature,
weaker than the strong force and the
electromagnetic force. It is important only in the
decay of certain elementary particles, such as
neutrons.
[ End of chapter 19]
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