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Superposition In quantum
physics, the principle that, until
it is measured, a particle such as
an electron exists in all its possible
states at the same time.Thermodynamics The branch of
physics that deals with heat and
its relation to energy and work.Transpiration The process
by which plants emit water vapor
from the surface of their leaves.Uncertainty principle A property
of quantum mechanics that means
that the more accurately certain
qualities, such as momentum, are
measured, the less is known of
other qualities such as position,
and vice versa.Uniformitarianism The
assumption that the same laws
of physics operate at all times in
all places across the universe.Valency The number of chemical
bonds that an atom can make with
other atoms.Velocity A measure of an object’s
speed and direction.Vitalism The doctrine that living
matter is fundamentally different
from nonliving matter. Vitalism
posits that life depends on a special
“vital energy.” It is now rejected by
mainstream science.Wave An oscillation that travels
through space, transferring energy
from one place to another.Weak nuclear force One of
the four fundamental forces,
which acts inside an atomic
nucleus and is responsible for
beta decay.Positron The antiparticle
counterpart of an electron, with
the same mass but a positive
electric charge.
Pressure A continual force
pushing against an object. The
pressure of gases is caused by
the movement of their molecules.
Proton A particle in the nucleus
of an atom that has positive charge.
A proton contains two up-quarks
and one down-quark.
Quantum electrodynamics
(QED) A theory that explains the
interaction of subatomic particles
in terms of an exchange of photons.
Quantum mechanics The branch
of physics that deals with the
interactions of subatomic particles
in terms of discrete packets, or
quanta, of energy.
Quark A subatomic particle
that protons and neutrons are
made from.
Radiation Either an
electromagnetic wave or a
stream of particles emitted
by a radioactive source.
Radioactive decay The
process in which unstable
atomic nuclei emit particles or
electromagnetic radiation.
Redshift The stretching of
light emitted by galaxies moving
away from Earth, due to the
Doppler effect. This causes
visible light to move toward
the red end of the spectrum.
Refraction The bending of
electromagnetic waves as they
move from one medium to another.
Respiration The process by which
organisms take in oxygen and use
it to break down food into energy
and carbon dioxide.Salt A compound formed from the
reaction of an acid with a base.Sigma bond A covalent bond
formed when the orbitals of
electrons meet head-on between
atoms. It is a relatively strong bond.Singularity A point in space-time
with zero length.Space-time The three dimensions
of space combined with one
dimension of time to form a
single continuum.Special relativity The result of
considering that both the speed
of light and the laws of physics are
the same for all observers. Special
relativity removes the possibility of
an absolute time or absolute space.Species A group of similar
organisms that can breed with one
another to produce fertile offspring.Spin A quality of subatomic
particles that is analogous to
angular momentum.Standard model The theoretical
framework of particle physics in
which there are 12 basic fermions
—six quarks and six leptons.String theory A theoretical
framework of physics in which
pointlike particles are replaced
by one-dimensional strings.Strong nuclear force One of the
four fundamental forces, which
binds quarks together to form
neutrons and protons.GLOSSARY