- Anti-gravity: It is the idea of creating a place or object that is free from the force of gravity. It does not refer to countering the gravitational force by an opposing force of a different nature; instead, anti-gravity requires that the fundamental causes of the force of gravity be made either not present or not applicable to the place or object through some kind of technological intervention. In Newton's law of universal gravitation, gravity was an external force transmitted by unknown means. It has replaced by the more general and complete description encoded in general relativity (GR). In GR gravity is not a force in the traditional sense of the word, but the result of the geometry of space itself. These geometrical solutions always cause attractive "forces". Under GR, anti-gravity is highly unlikely, except under contrived circumstances that are regarded as unlikely or impossible.
- Broken symmetry: It is a concept when an object breaks either rotational symmetry or translational symmetry. That is, when one can only rotate an object in certain angles or when one is able to tell if the object has been shifted sideways (unless one shifts by a whole number of lattice units).
- Butterfly effect: It is a phrase which encapsulates the more technical notion of sensitive dependence on initial conditions in chaos theory. Small variations of the initial condition of a nonlinear dynamical system may produce large variations in the long term behaviour of the system. The phrase refers to the idea that a butterfly's wings might create tiny changes in the atmosphere that ultimately cause a tornado to appear (or prevent a tornado from appearing). The flapping wing represents a small change in the initial condition of the system, which causes a chain of events leading to large-scale phenomena. Had the butterfly not flapped its wings, the trajectory of the system might have been vastly different.
- Calabi-Yau manifolds: They are a special class of manifolds used in some branches of mathematics (such as algebraic geometry) as well as in theoretical physics. For instance, in superstring theory the extra dimensions of spacetime are sometimes conjectured to take the form of a 6-dimensional Calabi-Yau manifold. The designation "Calabi-Yau space" for a member of this class was coined by physicists. Physical insights about Calabi-Yau manifolds, especially mirror symmetry, led to tremendous progress in pure mathematics.
- Calabi-Yau spaces: Calabi-Yau manifolds are sometimes named "Calabi-Yau spaces". In superstring theory the extra dimensions of spacetime are sometimes conjectured to take the form of a 6-dimensional Calabi-Yau manifold, which led to the idea of mirror symmetry.
- Chronology protection conjecture: It is Stephen Hawking's conjecture that the laws of physics are such as to prevent time travel on all but sub-microscopic scales. Mathematically, the permissibility of time travel is represented by the existence of closed timelike curves. The ideas of the chronology protection conjecture are completely serious. Many attempts to generate scenarios for closed timelike curves have been suggested, and the theory of general relativity does allow them in certain circumstances. Attempts to incorporate quantum effects into general relativity using semiclassical gravity seem to make plausible that vacuum fluctuations would drive the energy density on the boundary of the time machine to infinity, destroying the time machine at the instant it was created or at least preventing anyone outside it from entering it.
- Compactification: It means changing a theory with respect to one of its space-time dimensions. Instead of having a theory with this dimension being infinite, one changes the theory so that this dimension has a finite length, and may also be periodic. Compactification plays an important part in thermal field theory where one compactifies time, in string theory where one compactifies the extra dimensions of the theory, and in two- or one-dimensional solid state physics, where one considers a system which is limited in one of the three usual spatial dimensions. At the limit where the size of the compact dimension goes to zero, no fields depend on this extra dimension, and the theory is dimensionally reduced.
- Compton Scattering or the Compton Effect: It is the decrease in energy (increase in wavelength) of an X-ray or gamma ray photon, when it interacts with matter. Inverse Compton scattering also exists, where the photon gains energy (decreasing in wavelength) upon interaction with matter. The amount the wavelength increases by is called the Compton shift. Although nuclear Compton scattering exists, Compton scattering usually refers to the interaction involving only the electrons of an atom. The effect is important because it demonstrates that light cannot be explained purely as a wave phenomenon.
- CP-SYMMETRY: It is the product of two symmetries: C for charge conjugation, which transforms a particle into its antiparticle, and P for parity, which creates the mirror image of a physical system. The strong interaction and electromagnetic interaction seem to be invariant under the combined CP transformation operation, but this symmetry is slightly violated during certain types of weak decay. CP-symmetry was proposed to restore order after the discovery of parity violation.
- C-symmetry means the symmetry of physical laws under a charge-conjugation transformation. Electromagnetism, gravity and the strong interaction all obey C-symmetry, but weak interactions violate it.
- CPT symmetry: It is a fundamental symmetry of physical laws under transformations that involve the inversions of charge, parity and time simultaneously.
- Decoupling describes the general phenomenon in which the interactions between some physical objects (such as elementary particles) disappear. In gauge theories, there are unobserved polarizations of elementary particles, such as the longitudinal photon. The experiments as well as theoretical consistency dictate that these polarizations cannot be produced by collisions of other particles. Consequently, their interactions with other (physical) particles must be equal to zero, and quantum electrodynamics confirms this expectation: decoupling is a consequence of gauge symmetry.
- Dilaton: Originally it referred to a theoretical scalar field; as photon
refers in one sense to the electromagnetic field. For the dilaton, also
known as the radion or graviscalar, it is the scalar field which appears
in Kaluza-Klein theory -as the component g55 of the metric tensor where
"5" is the additional circular direction- and obeys an inhomogeneous
wave equation, generalizing the Klein-Gordon equation, with extremely strong
electromagnetic field as source:
- Dimensionless or fundamental physical constants: They are universal physical constants that are independent of systems of units and hence are dimensionless quantities. However, the term may also refer to any dimensional universal physical constant, such as the speed of light, vacuum permittivity, and the gravitational constant.
- Dirac's constant: A closely related quantity is the reduced Planck constant (also known as Dirac's constant and denoted .
- Fine-structure constant or Sommerfeld fine-structure constant, usually
denoted : It is the fundamental physical constant characterizing the strength
of the electromagnetic interaction. It is a dimensionless quantity, and
thus its numerical value is independent of the system of units used.
The best value currently is:
. (numbers within parentheses are uncertainties), where is the elementary
charge, is the Dirac constant, is the speed of light in a vacuum, and is
the vacuum permittivity.
. The defining expression and the value recommended by 2006 CODATA as reported
by NIST reference on constants, units, and uncertainty is:
.
The name of the fine-structure constant refers to its earliest use in the
theory for the fine structure of atomic energy spectra. However, its modern
use is far from being as specialized as its name suggests.
- Gauge -symmetry- theories: In physics they are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. Sometimes, the term 'gauge symmetry' is used in a more general sense to include any local symmetry. Yang-Mills theories are a particular example of gauge theories with non-abelian symmetry groups specified by the Yang-Mills action.
- Gauge theories: They are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. This idea applies not only to field theories, but to finite-dimensional systems as well (i.e., systems described by ordinary differential equations).
- General covariance or diffeomorphism covariance or general invariance: It is the invariance of the form of physical laws under arbitrary differentiable coordinate transformations. The essential idea is that coordinates do not exist a priori in nature, but are only artifices used in describing nature, and hence should play no role in the formulation of fundamental physical laws. A physical law expressed in a generally covariant fashion takes the same mathematical form in all coordinate systems, and is usually expressed in terms of tensor fields. The classical (non-quantum) theory of electrodynamics is one theory that has such a formulation.
- Great Attractor: This is a gravity anomaly in intergalactic space within the range of the Centaurus Supercluster that reveals the existence of a localised concentration of mass equivalent to tens of thousands of Milky Ways, observable by its effect on the motion of galaxies and their associated clusters over a region hundreds of millions of light years across. These galaxies are all redshifted, in accordance with the Hubble Flow, indicating that they are receding relative to us and to each other, but the variations in their redshift are sufficient to reveal the existence of the anomaly. The Great Attractor lies at a distance of somewhere between 150 million and 250 million light years from the Milky Way, in the direction of the Hydra and Centaurus constellations.
- Hartle-Hawking state: It is the wave function of the Universe -a notion meant to figure out how the Universe started- that is calculated from Feynman's path integral. More precisely, it is a hypothetical vector in the Hilbert space of a theory of quantum gravity that describes this wave functional. It is a functional of the metric tensor defined at a (D-1)-dimensional compact surface, the Universe, where D is the spacetime dimension. Such a wave function of the Universe can be shown to satisfy the Wheeler-deWitt equation.
- Hidden Variable Theories: A minority of physicists argued that the statistical nature of quantum mechanics indicated that quantum mechanics is "incomplete". It was thought that if hidden variables exist, new physical phenomena beyond quantum mechanics are needed to explain the universe as we know it.
- Kaluza-Klein theory (or KK theory: It is a model that seeks to unify the two fundamental forces of gravitation and electromagnetism. The theory was first published in 1921 and was discovered by the mathematician Theodor Kaluza who extended general relativity to a five-dimensional space-time. The resulting equations can be separated out into further sets of equations, one of which is equivalent to Einstein field equations, another set equivalent to Maxwell's equations for the electromagnetic field and the final part an extra scalar field now termed the "radion".
- Lawson criterion: In nuclear fusion research it is an important general measure of a system that defines the conditions needed for a fusion reactor to reach ignition, that is, that the heating of the plasma by the products of the fusion reactions is sufficient to maintain the temperature of the plasma against all losses without external power input. As originally formulated the Lawson criterion gives a minimum required value for the product of the plasma (electron) density ne and the "energy confinement time" ?E. Later analyses suggested that a more useful figure of merit is the "triple product" of density, confinement time, and plasma temperature T. The triple product also has a minimum required value, and the name "Lawson criterion" often refers to this inequality.
- Mirror symmetry: It is a surprising relation that can exist between two Calabi-Yau manifolds. It happens, usually for two such six-dimensional manifolds, that the shapes may look very different geometrically, but nevertheless they are equivalent if they are employed as hidden dimensions of string theory. The classical formulation of mirror symmetry relates two Calabi-Yau threefold M and W whose Hodge numbers h1,1 and h1,2 are swapped; string theory compacted on these two manifolds can be proved to lead to identical physical phenomena.
- Planck constant (denoted h): It is a physical constant that used to describe the sizes of quanta. It plays a central part in the theory of quantum mechanics, and is named after Max Planck, one of the founders of quantum theory. A closely related quantity is the reduced Planck constant (also known as Dirac's constant and denoted . The Planck constant is also used in measuring energy emitted as photons, such as in the equation E = h?, where E is energy, h is Planck's constant, and ? is frequency. The Planck constant and the reduced Planck constant are used to describe quantization, a phenomenon occurring in subatomic particles such as electrons and photons in which certain physical properties occur in fixed amounts rather than assuming a continuous range of possible values.
- Planck energy: It is the unit of energy, denoted by EP, in the system
of natural units known as Planck units.
1.956 × 109 J 1.22 × 1019 GeV 0.5433 MWh
where c is the speed of light in a vacuum, is the reduced Planck's constant
and G is the gravitational constant.
Or equivalently,
where tP is the Planck time.
The Planck energy is equivalent with the Planck mass according to E = mc².
The Planck energy is not only the energy (in principle) necessary to probe
the Planck length, but it is probably also the maximum energy that can fit
into a region of that scale - which in this case will immediately collapse
to a (very hot) Black Hole.
Particle physicists and cosmologists often use the reduced Planck energy,
which is
0.390 × 109 J 2.43 × 1018 GeV
- Planck length, denoted by , is the unit of length approximately 1.6 × 10?35 metres, 6.3 × 10?34 inches, or about 10?20 times the diameter of a proton. It is in the system of units known as Planck units. The Planck length is deemed "natural" because it can be defined from three fundamental physical constants: the speed of light, Planck's constant, and the gravitational constant.
- Planck mass: It is the unit of mass, denoted by mP, in the system of
natural units known as Planck units.
? 1.2209 × 1019 GeV/c2 = 2.176 × 10-8 kg
Particle physicists and cosmologists often use the reduced Planck mass,
which is
? 4.340 µg = 2.43 × 1018 GeV/c2.
- Planck time (tP): it is the unit of time in the system of natural units
known as Planck units. It is the time it would take a photon travelling
at the speed of light in a vacuum to cross a distance equal to the Planck
length.
It is defined as
where:
is the reduced Planck constant
G is the gravitational constant
c is the speed of light in a vacuum
tP is in seconds.
The two digits between the parentheses denote the uncertainty in the last
two digits of the value.
- Scale invariance: It is a feature of objects or laws that do not change
if length scales (or energy scales) are multiplied by a common factor. The
technical term for this transformation is a dilatation (also known as dilation),
and the dilatations can also form part of a larger conformal symmetry.
. In mathematics, scale invariance usually refers to an invariance of individual
functions or curves.
. In classical field theory, scale invariance most commonly applies to the
invariance of a whole theory under dilatations.
. In quantum field theory, scale invariance has an interpretation in terms
of particle physics. In a scale-invariant theory, the strength of particle
interactions does not depend on the energy of the particles involved.
- Schrödinger equation: It is an equation that describes how the quantum state of a physical system varies. According to the Copenhagen interpretation of quantum mechanics, the state vector is used to calculate the probability that a physical system is in a given quantum state. Schrödinger's equation is primarily applied to microscopic systems, such as electrons and atoms, but is sometimes applied to macroscopic systems (such as the whole universe). The Schrödinger equation is commonly written as an operator equation describing how the state vector evolves over time. By specifying the total energy (Hamiltonian) of the quantum system, Schrödinger's equation can be solved, the solutions being quantum states.
- Spontaneous symmetry breaking: in physics this takes place when a system that is symmetric with respect to some symmetry group goes into a vacuum state that is not symmetric. At this point the system no longer appears to behave in a symmetric manner. The symmetry group can be discrete, such as the space group of a crystal, or continuous (i.e. a Lie group), such as the rotational symmetry of space. An example is a ball sitting on top of a hill where it is in a symmetric state but not a stable one as the ball can easily roll down the hill. At some point, the ball will spontaneously roll down the hill in one direction or another. The symmetry has been broken because the direction the ball rolled down in has now been singled out from other directions.
- Supergravity (supergravity theory): It is a field theory that combines the principles of supersymmetry and general relativity. Together, these imply that, in supergravity, the supersymmetry is a local symmetry (in contrast to non-gravitational supersymmetric theories, such as the Minimal Supersymmetric Standard Model).
- Supersymmetry (SUSY): In particle physics it is a symmetry that relates elementary particles of one spin to another particle that differs by half a unit of spin and are known as superpartners. In a supersymmetric theory, for every type of boson there exists a corresponding type of fermion, and vice-versa. As of 2008 there is no direct evidence that supersymmetry is a symmetry of nature. Since superpartners of the particles of the Standard Model have not been observed, supersymmetry, if it exists, must be a broken symmetry allowing the 'sparticles' to be heavy. If supersymmetry exists close to the TeV energy scale, it allows the solution of two major puzzles in particle physics. One is the hierarchy problem -on theoretical grounds there are huge expected corrections to the particles' masses, which without fine-tuning will make them much larger than they are in nature. Another problem is the unification of the weak interactions, the strong interactions and electromagnetism. Supersymmetry is also a consequence of most versions of string theory, though it can exist in nature even if string theory is wrong.
- Symmetry refers to features of a physical system that exhibit the property of symmetry -that is, under certain transformations, aspects of these systems are "unchanged", according to a particular observation. The transformations may be continuous (such as rotation of a circle) or discrete (e.g., reflection of a bilaterally symmetric figure, or rotation of a regular polygon). Continuous and discrete transformations give rise to corresponding types of symmetries. Continuous symmetries can be described by Lie groups while discrete symmetries are described by finite groups (such as Symmetry group). Symmetries are frequently amenable to mathematical formulation and can be exploited to simplify many problems.
- Technicolor models: They are theories beyond the Standard Model which do not have a scalar Higgs field. Instead, they have a larger number of fermion fields than the Standard Model and involve a larger gauge group. This larger gauge group is spontaneously broken down to the Standard Model group as fermion condensates form. The idea of technicolor is to build a model in which the sort of dynamics we see in quantum chromodynamics (QCD) can be used to explain the masses of the W and Z bosons. In QCD, there are quarks that feel both the weak interaction and the strong interaction. The strong interaction binds them together in condensates which spontaneously break electroweak symmetry. In fact, QCD itself gives masses to the W and Z bosons, but these masses are tiny compared to the observed masses. Technicolor uses a QCD-like theory at a higher energy scale to give the observed masses to the W and Z bosons.
- Vacuum permittivity or electric constant -denoted by the symbol ?0: It
is a fundamental physical constant relating the mechanical quantities (time,
length, mass) to the units for electrical charge, for example, in Coulomb's
law. In SI units the speed of light in vacuum c0 is defined as the numerical
value c0 299 792 458 m s-1 and the magnetic constant ?0 is defined as 4?
x 10-7 H · m-1, leading to an electric constant defined in free space
by:
- Wave-particle duality: It is the concept that all matter exhibits both wave-like and particle-like properties. A central concept of quantum mechanics, duality addresses the inadequacy of classical concepts like "particle" and "wave" in fully describing the behaviour of objects. Various interpretations of quantum mechanics attempt to explain this ostensible paradox. Current scientific theory holds that all particles also have a wave nature. This phenomenon has been verified not only for elementary particles, but also for compound particles like atoms and even molecules. In fact, according to traditional formulations of non-relativistic quantum mechanics, wave-particle duality applies to all objects, even macroscopic ones; we can't detect wave properties of macroscopic objects due to their small wavelengths.
- Wheeler-DeWitt equation: It is a functional differential equation very
important in theoretical physics, especially in quantum gravity. It is a
functional differential equation on the space of three dimensional spatial
metrics. The Wheeler-deWitt equation has the form of an operator acting
on a wave functional, the functional reduce to a function in cosmology.
Contrary to the general case, the Wheeler-deWitt equation is well defined
in mini-superspaces like the configuration space of cosmological theories.
An example of such a wave function is the Hartle-Hawking state.
Simply speaking, the Wheeler-DeWitt equation says
where is the total Hamiltonian constraint in quantized general relativity.