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The Elegant Universe: Glossary
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big bang
The accepted theory that the universe began evolving some 13.7
billion years ago from an infinitely dense and hot substance that
has been expanding since the first extremely small fraction of a
second after its origin.
black hole
A region of space formed when an object collapses to the point where
its gravitational field is so strong that it traps everything within
its vicinity, including light.
Calabi-Yau shape
A configuration that could possibly contain the curled-up extra
dimensions required by string theory. Tens of thousands of possible
configurations exist; none have yet been verified to represent the
additional dimensions predicted by string theory.
electromagnetism
One of four fundamental forces. Governs all forms of electromagnetic
radiation, including radio waves, light, X-rays, and gamma rays.
Also binds negatively charged electrons to positively charged
nuclei. The residual electromagnetic force binds atoms and
molecules. Acts over an infinite range.
elementary particle
Indivisible unit from which all matter is made and forces are
communicated. Currently known elementary matter particles are
grouped into categories of quarks and leptons and their anti-matter
counterparts. These particles interact through fundamental force
carrier particles, which include the gluon, photon, and W and Z
particles, and the theorized-but-undiscovered graviton.
extra dimensions
Additional spatial dimensions predicted by string theory beyond the
three familiar extended dimensions; cannot be detected with current
technologies. The initial version of string theory required six
extra spatial dimensions; the more current version, M-theory, calls
for seven extra spatial dimensions.
force carrier particle
Particle that mediates (transmits) one of the four fundamental
forces. The gluon is the force carrier particle for the strong
force; the photon is the force carrier particle for
electromagnetism; the W and Z are the force carrier particles for
the weak force; and the as-yet-unobserved graviton is the
theoretical force carrier particle for gravity.
fundamental force
Any of the four natural forces: gravity, electromagnetism, the
strong force, or the weak force. Transmitted by force carrier
particles.
general theory of relativity
A theory developed by Albert Einstein that maintains that the force
of gravity is the result of the warping of spacetime and that space
and time communicate the gravitational force through this curvature.
graviton
A hypothetical particle thought to be the force carrier particle of
the gravitational force.
gravity
The weakest of the four fundamental forces at the level of
elementary particles; gravitation is the observed effect of the
force of attraction between objects that contain either mass or
energy; thought to be mediated by the theorized force carrier
particle, the graviton. Acts over an infinite range.
hadrons
Particles built from quarks, such as protons and neutrons. Two types
of hadrons exist: baryons (made from three quarks) and mesons (made
from a quark and an antiquark). Governed by the strong force.
leptons
A family of elementary matter (or antimatter) particles that
includes the electrically charged electron, muon, and tau and their
antimatter counterparts. The family also includes the electrically
neutral electron-neutrino, muon-neutrino, and tau-neutrino and their
antimatter counterparts.
M-theory
A theory that unites five previous versions of string theory;
predicts 11 spacetime dimensions and introduces membranes as one of
the most fundamental elements in nature. M-theory is the latest
incarnation of string theory ideas.
particle accelerator
A machine that speeds up particles before aiming them at a fixed
target or colliding them together. Detectors capture the results of
these particle interactions.
quantum field theory
A relativistic quantum theory that uses fields to describe the
behavior of particles, especially during particle collisions. It
describes how particles can be created and annihilated, as well as
how they scatter in different directions and how they form bound
states.
quantum mechanics
The physics theory that allows for the mathematical description of
matter and energy consistent with their behavior as both
particle-like and wave-like. It allows the calculations of
probability of finding an object at a particular point in space and
time, given its starting position and the forces acting upon it. The
uncertainty principle of quantum mechanics (a manifestation of
wave-like properties) implies that it is not possible to
simultaneously know both the precise position and momentum of a
particle.
quarks
A family of elementary matter (or antimatter) particles that
includes the electrically charged up, charm, top, down, strange, and
bottom quarks and their antimatter counterparts. Quarks make up
protons and neutrons.
special theory of relativity
Einstein's theory that describes the motion of particles moving at
any speed, even close to the speed of light. The theory proposes
that the measured speed of light is a constant even if the source or
observer of the light is moving. In contrast, measured distance,
time, and mass all depend on the relative velocity of the source and
observer.
Standard Model
A quantum-mechanical model that explains the three nongravitational
forces—electromagnetism, the strong force, and the weak
force—and their interactions with matter. Most of the
particles predicted by the Standard Model have been indirectly
observed or detected experimentally (the theoretical Higgs boson has
not been confirmed). Gravity is not part of the Standard Model.
string
Tiny one-dimensional vibrating strands of energy
that—according to string theory—make up all elementary
particles. A string has length (about 10-33 centimeters)
but no width.
strong force
The strongest of the four fundamental forces; binds quarks together
and keeps protons and neutrons together in atomic nuclei. Mediated
by gluons; acts over a short range.
superstring theory
A theory of the universe based on vibrating strings as the most
fundamental units in nature; incorporates supersymmetry.
supersymmetry
The idea that all elementary matter particles have corresponding
superpartner force carrier particles and that all force carrier
particles have corresponding superpartner elementary matter
particles. The theorized superpartners, thought to be more massive
than their counterparts, have not yet been observed.
topology
The study of the properties of geometric figures or solids that
demonstrate continuous transformations that are not changed by
stretching or bending.
weak force
One of the four fundamental forces; governs decay of elementary
particles. Mediated by W and Z particles; operates over a short
range.
wormhole
A theoretical structure in spacetime that forms a tube-like
connection between two separate regions of the universe.
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