Warped Passages (72 page)

projection
A definite prescription for creating a lower-dimensional representation of an higher-dimensional object.

proton
An ingredient of the atomic nucleus in which two up quarks and a down quark are tightly bound to each other.

QCD (quantum chromodynamics)
The quantum field theory of the strong force.

QED (quantum electrodynamics)
The quantum field theory of electromagnetism.

quantum
A discrete unbreakable unit of a measurable quantity; the smallest unit of that quantity.

quantum contribution
A contribution to a physical process due to virtual particles.

quantum field theory
The theory used to study particle physics with which one can calculate the rates for processes in which particles can interact, be created, or be destroyed. According to quantum field theory, fluctuations of fields manifest themselves as particles.

quantum gravity
A theory of gravity that incorporates both quantum mechanics and general relativity.

quantum mechanics
The theory that is based on the assumption that all matter consists of discrete elementary particles that have associated wavefunctions.

quark
An elementary fermionic particle that experiences the strong force.

quasicrystal
A solid material whose crystalline structure is derived from higher dimensions.

redshift
The lowering of frequency of a wave when the object emitting the wave is either moving away (Doppler redshift) or is slowed down by a strong gravitational field (gravitational redshift).

relativity
One of Einstein’s two theories of spacetime:
special relativity
, which unifies space and time, and
general relativity
, which explains gravity as the curvature of spacetime.

renormalization group
A calculation technique for relating quantities that apply in different energy or distance regimes.

rotational invariance
The independence of the results of experiments on orientation (or direction).

selectron
The superpartner of the electron.

sequestering
The physical separation of different elementary particle types in extra dimensions.

singularity
A region where a mathematical description of an object breaks down because some quantity becomes infinite.

slepton
The superpartner of a lepton.

spacetime
The concept that unifies space and time into a single framework; the mathematical formulation of the region where physical processes can occur.

special relativity
The theory of gravity that describes motion in inertial frames of reference.

spectral lines
Discrete frequencies at which non-ionized atoms emit or absorb light.

spectrum
A function that gives the spread of energy emitted across all frequencies.

spin
See
intrinsic spin
.

spontaneously broken symmetry
Symmetry that is preserved by physical laws but broken by the actual physical state of a system.

squark
The superpartner of a quark.

Standard Model (of particle physics)
The effective theory that describes all known particles and nongravitational forces and the interactions among them.

strange quark
A short-lived, heavier version of the down quark.

string
A one-(spatial)dimensional extended object whose oscillations constitute elementary particles.

string coupling
A quantity that determines the strength of the interaction between strings.

string theory
The theory that posits that the ingredients of the universe are fundamental strings and which should consistently incorporate quantum mechanics and general relativity.

strong force
One of the four known forces; the strong force is responsible for binding quarks in a proton or neutron, for example.

structure
Constituents of matter.

substructure
More elementary ingredients of constituents of matter.

supergravity
A supersymmetric theory that includes gravity.

superpartner (of a particle)
The particle that supersymmetry pairs with another particle; if the original particle is a boson, the superpartner is a fermion, and vice versa.

superspace
An abstract space that incorporates the familiar four dimensions as well as theoretical fermionic dimensions.

superstring theory
The supersymmetric version of string theory without
tachyons
that includes fermions in addition to gravity and gauge bosons.

supersymmetry
A symmetry that interchanges partnered bosons and fermions.

symmetry
A property of an object or a physical law such that certain physical operations are undetectable.

symmetry transformation
A manipulation of a physical system that does not change its properties or behavior; the action that transforms different configurations that are related by symmetry into each other.

T-duality
An equivalence between physical phenomena in a universe with a small rolled-up dimension and another universe with a large one (the size of the radius of a curled-up dimension is exchanged with its inverse).

tachyon
A particle that signals an instability and superficially appears to have negative squared mass.

tau
A short-lived particle with identical charge to the electron and muon but heavier than either.

tension
Resistance to being stretched that determines how readily a string will oscillate and produce heavy particles.

TeV (teraelectronvolt)
A unit of energy equal to one trillion eV.

Tevatron
The high-energy collider currently in operation at Fermilab that collides beams of TeV-energy protons with TeV-energy antiprotons.

theory
A definite set of elements and principles with rules and equations for predicting how those elements interact.

thought experiment
An imagined physics experiment through which you can evaluate the consequences of a given set of physical assumptions.

top quark
A short-lived, heavier version of the up quark; the heaviest known quark.

translational invariance
The independence of physical laws of location in space.

transverse polarization
Wave oscillation perpendicular to the direction of motion.

ultraviolet catastrophe
An infinite energy emitted at high frequencies that is predicted by the classical theory of a blackbody.

uncertainty principle
The basic principle underlying quantum mechanics that restricts the accuracy with which pairs of quantities (such as position and speed) can be simultaneously measured.

up quark
One of the elementary quarks that compose the proton and the neutron.

vacuum
The state of the universe with the lowest possible energy and no particles.

vacuum energy
The energy carried by the vacuum, the state in which particles are absent; also known as the
cosmological constant
.

velocity
The quantity that specifies both speed and direction of motion.

virtual particle
An ephemeral particle allowed only by quantum mechanics; virtual particles carry the same charge as the corresponding true physical particles but have the wrong energy.

warp factor
The overall scaling of a metric that varies with respect to one coordinate.

warped spacetime geometry
Spacetime that would be flat (more generally, each slice would have the same shape) except for an overall scaling that varies with the position in a particular direction.

wavefunction
A quantum-mechanical function that determines the relative likelihood of the corresponding object being at any point in space.

weak force
One of the four known forces; the weak force is responsible for beta decay of neutrons into protons, for example.

weak gauge boson
An elementary particle (with three varieties, W
⁺
, W
^-
, and Z) that communicates the weak force.

weak scale energy
The energy at which the symmetry associated with
the weak force is spontaneously broken. The weak scale energy determines the masses of elementary particles.

weak scale length
The length, 10
^-16
cm, or one ten thousand trillionth of a centimeter, that corresponds (via quantum mechanics and special relativity) to the weak scale energy. It is the range of the weak force—the maximum distance between particles that can influence each other through this force.

weak scale mass
The mass that is related to the weak scale energy (of 250 GeV) through the speed of light. In conventional mass units, the weak scale mass is 10
^-21
grams.

Math Notes

1
. This isn’t really a math note, but the Saturday Night Baby is three-dimensional. [Figure M1]

Figure M1.
Saturday Night Baby.

2
. A metric on space can take the form
ds
²
+
a
_x
dx
²
+
a
_y
dy
²
+
a
_z
dz
²
, where
x
,
y
,
z
are the three coordinates of space, and
a
_x
,
a
_y
, and
a
_z
can be numbers or they can be functions of
x
,
y
, and
z
. The metric determines lengths, distances, and angles between lines. For example, the length of a vector pointing from the origin to the point with coordinates (
x
,
y
,
z
) is √(
a
_x
x
²
+
a
_y
y
²
+
a
_z
z
²
). If
a
_x
=
a
_y
=
a
_z
= 1, we have flat space, and distances and lengths would be measured in the familiar manner. For example, the length of a vector pointing from the origin to (
x
,
y
,
z
) would be √(
x
²
+
y
²
+
z
²
). More complicated metrics can have cross terms, such as
dxdy
. In that case, the
metric must be described by a tensor with two indices that tells the coefficients
a
_ij
of each term in the metric of the form
dx
_i
dx
_j
. Later, when we discuss relativity, the metric will also have a term
dt
²
and could also have terms of the form
dtdx
_i
.