An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The branch of mathematics that studies sets. Set theory is closely associated with the branch of mathematics known as logic. It was initiated by the German mathematician Georg Cantor (1845-1918).

→ set; → theory.

A → cosmological model according to which the → Universe has no beginning and no end and maintains the same mean density, in spite of its observed expansion, by the continual creation of matter throughout all space. The theory was first put forward by Sir James Jeans in about 1920 and again in revised form in 1948 by Hermann Bondi and Thomas Gold. It was further developed by Sir Fred Hoyle to deal with problems that had arisen in connection with the alternative → Big Bang model. Observations since the 1950s have produced much evidence contradictory to the steady state theory and supportive of the Big Bang model. More specifically, the steady state theory attributed the → cosmic microwave background to → thermal radiation from → dust clouds, but this cannot account for a single → blackbody spectrum. Moreover, the steady state theory lacked a plausible mechanism for the creation of matter in space. See also → perfect cosmological principle.

→ steady; → state; → theory.

The latest theory of fundamental physics in which the basic entity is a one-dimensional → brane rather than the "zero-dimensional" point of conventional elementary particle physics. The one-dimensional string-like objects exist in the normal four dimensions of → space-time plus additional dimensions, the total dimensions being ten, eleven, or twenty-six depending on the version of the theory. Particles are strings that vibrate in different ways to account for their various properties.

→ string; → theory.

An interdisciplinary field of science which deals with the nature of complex systems in nature, society, and science, and studies complex parts of reality as systems.

→ system; → theory.

A theory put forward to provide a basis for a relativistic generalization of the → MOdified Newtonian Dynamics (MOND) paradigm. TeVeS is based on three dynamical fields: a tensor field, a vector field, and a scalar field. In contrast to general relativity, it has two metrics, an Einstein metric and a physical metric. TeVeS has attracted considerable attention, since it can explain many galactic and cosmological observations without the need for → dark matter. Proposed by J. D. Bekenstein, 2004, "Relativistic gravitation theory for the modified Newtonian dynamics paradigm", Phys. Rev. D, 70, 083509, arXiv:astro-ph/0403694.

→ tensor; → vector; → scalar; → theory.

A coherent set of verified facts, propositions, or principles analyzed in their relation to one another and used to explain and predict phenomena, e.g. the → theory of relativity. The criterion of the scientific status of a theory is its → falsifiability, → refutability, or → testability. See also → hypothesis, → model.

From L.L. theoria, from Gk. theoria "contemplation, speculation, a looking at, things looked at," from theorein "to consider, view, look at," from theoros "spectator," from thea "a view" + horan "to see."

Negaré, from negar present stem of negaridan, negaristan "to look, observe;" Mid.Pers. nigeridan, niger-, nikiritan, nikir- "to look, to watch, to notice, to consider;" ultimately from Proto-Iranian *ni-kar-, from *ni- "down, in, into," → ni- (PIE), + *kar- "to observe, to consider;" cf. Av. kar- "to remember; to impress on memory;" Skt. kal- "to observe, consider," kalayati "considers, observes;" Mid.Pers. kartan "to establish; to declare; to found," (h)angârtan "to consider, to bear in mind, to regard as," us-kâritan "to consider, deliberate, discuss," sikâl, sigâl "thought;" Mod.Pers. engâridan, engâštan "to suppose," segâl "thought," segâlidan "to think, to resolve to injure, to deceive."

Any theory that attempts to describe all the forces of nature including gravity in a single mathematical formalism; e.g. → grand unified theory. → string theory.

→ theory; every; M.E. every, everich; O.E. æfre ælc "ever each;" → thing.

Negaré, → theory; hamé, → all; ciz, → thing.

Any of the two theories put forward by Albert Einstein: → special relativity (1905) and → general relativity (1916).

→ theory; → relativity;

The theory that describes light as waves that spread out from the source that generates the light. It contradicts the → corpuscular theory of light proposed by Newton (1704). The idea of the wave nature of light was first put forward by Robert Hooke (1660). The wave theory was originally stated by Huygens (1690), who showed reflection and refraction could be explained by this theory. It was supported by → Young's experiment (1802) and established by the work of Fresnel (1814-1815). The wave theory received its most important support from Maxwell's → electromagnetic theory. See also → Huygens-Fresnel principle.

→ wave; → theory; → light.

A refinement of → Fourier analysis which enables to simplify the description of a complicated function in terms of a small number of coefficients. The formal history of wavelet theory began in the early 1980s when Jean Morlet, a French geophysicist, introduced the concept of wavelet and studied wavelet transform as a new tool for scientific signal analysis. In 1984, his collaboration with Alex Grossmann yielded a detailed mathematical study of the continuous wavelet transforms and their various applications. Although similar results had already been obtained 20-50 years earlier by several other researchers, the rediscovery of the old concepts provided a new method for decomposing functions.

→ wavelet; → theory.