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

A Universe having observed properties that appear identical in every direction.

→ isotropic; → universe.

A cosmological hypothesis, based on Einstein's relativity, in which the expanding Universe began from an exploding "primeval atom." In the Lemaître Universe the rate of expansion steadily decreases.

Named after Monsignor Georges Edouard Lemaître (1894-1966), a Belgian Roman Catholic priest, honorary prelate, professor of physics and astronomer; → universe.

A not well-defined concept describing a region of radius within ~ 20 → Mpc centered on the → Local Group of galaxies, corresponding to → redshift z ≤ 0.01. See also the → Local Volume.

→ local; → Universe.

A Universe in which the matter energy density (Ω_m ≈ 1) provides most of the total energy density. According to the → Big Bang model, in the early history of the → Universe a → radiation-dominated phase preceded the matter-dominated phase. This phase is characterized by R/R₀ ∝ t^2/3, where R is the → cosmic scale factor and t is time.

→ matter; → dominate; → Universe.

A model of the → Universe which is devoid of matter and where the → space-time is → open (Ω_M = 0, Ω_R = 0, Ω_Λ = 0, k = -1). The Universe will expand at a constant rate for ever. See also → empty Universe, → de Sitter Universe.

Put forward by Edward Arthur Milne (1896-1950), a British astrophysicist, who introduced the → cosmological principle; → cosmological; → model.

The extent of the Universe that we can see with the aid of the largest telescopes. Its ultimate boundary is determined by the → cosmic horizon size.

→ observable; → universe.

A → Freidmann-Lemaitre  → cosmological model in which → space is → infinite and of → negative  → curvature or → Euclidean, and which expands forever.

→ open; → universe.

A cosmological model in which the Universe is closed and undergoes a series of oscillations, each beginning with a big bang and ending with a big crunch.

Oscillating, verbal adj. of → oscillate; → universe.

Same as → oscillating Universe.

Pulsating, verbal adj. of → pulsate; → universe.

An early epoch in the history of the → Universe when the radiation → density parameter was Ω_r≈ 1, while other density parameters had negligible contributions. A radiation-dominated Universe is characterized by R/R₀ ∝ t^1/2, where R is the → cosmic scale factor and t is time. According to the → Big Bang model, the radiation-dominated phase was followed by the → matter-dominated phase.

→ radiation; → dominate; → Universe.

A closed Universe of finite volume with a constant radius of curvature.

→ static; → Universe.

The future evolution of the → Universe which is a subject of study in → cosmology. The ultimate fate of the Universe can be explored using → general relativity. And since there is more than one possible solution to the equations of general relativity, there is more than one possible ultimate fate of the Universe. Moreover, the fate will depend on three factors: the Universe's overall shape or → geometry, its → dark energy content, and the → equation of state parameter. See also: → oscillating Universe, → Big Rip, → Big Crunch, → Big Freeze, → heat death.

→ ultimate; → Universe.

1) The totality of all matter and energy that exists in the vastness of cosmos whether known to human beings or not. Related concepts: → world, → cosmos, → multiverse.
2a) Math.: A → set made of → subsets that contains all the elements relevant to a particular discussion or problem.
2b) Statistics: The entire population under study.
See also: → all, → general, → omni-, → public, → total.

M.E., from O.Fr. univers, from L. universum "the universe," noun use of neuter of adj. universus "all together," literally "turned into one," from unus, → one, + versus, p.p. of vertere "to turn," akin to Pers. gar-, gardidan "to turn, to change" (Mid.Pers. vartitan; Av. varət- "to turn, revolve;" cf. Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend").

1) Giti "world, material world, time," variants jahân, keyhân, geyhân "world;" Mid.Pers. gêhân "world," gêtig "the material world; wordly;" Av. gaēθā- "being, world, matter, mankind," gaya- "life, manner of living", root gay- "to live" (present tense jiva-), O.Pers. gaiθā- "live-stock," cognate with Skt. jīv- "to live," jīva- "alive, living;" Gk. bios "life," L. vivus "living, alive," vita "life;" PIE base *g^wei- "to live" (cf. O.E. cwic "alive;" O.C.S. zivo "to live;" Lith. gyvas "living, alive;" O.Ir. bethu "life," bith "age;" Welsh byd "world"). The Pers. words zistan "to live," zendé "alive," zendegi "life," and jân "vital spirit, soul; mind" belong to this family.
2) Hargân, from har "every, all, each," → holo-, + -gân suffix forming plural entities, from Mid.Pers. -gânag, -gâna, on the model of hamegân, → public.