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  2. Outer space - Wikipedia

    en.wikipedia.org/wiki/Outer_space

    A wide field view of outer space as seen from Earth's surface at night. The interplanetary dust cloud is visible as the horizontal band of zodiacal light, including the false dawn [29] (edges) and gegenschein (center), which is visually crossed by the Milky Way. Outer space is the closest known approximation to a perfect vacuum.

  3. Shape of the universe - Wikipedia

    en.wikipedia.org/wiki/Shape_of_the_universe

    The curvature of any locally isotropic space (and hence of a locally isotropic universe) falls into one of the three following cases: Zero curvature (flat) – a drawn triangle's angles add up to 180° and the Pythagorean theorem holds; such 3-dimensional space is locally modeled by Euclidean space E 3.

  4. Expansion of the universe - Wikipedia

    en.wikipedia.org/wiki/Expansion_of_the_universe

    It is an intrinsic expansion, so it does not mean that the universe expands "into" anything or that space exists "outside" it. To any observer in the universe, it appears that all but the nearest galaxies (which are bound to each other by gravity) move away at speeds that are proportional to their distance from the observer , on average.

  5. Space (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Space_(mathematics)

    In ancient Greek mathematics, "space" was a geometric abstraction of the three-dimensional reality observed in everyday life. About 300 BC, Euclid gave axioms for the properties of space. Euclid built all of mathematics on these geometric foundations, going so far as to define numbers by comparing the lengths of line segments to the length of a ...

  6. Big Bang - Wikipedia

    en.wikipedia.org/wiki/Big_Bang

    The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. [1] The concept of an expanding universe was scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations.

  7. Space - Wikipedia

    en.wikipedia.org/wiki/Space

    Debates concerning the nature, essence and the mode of existence of space date back to antiquity; namely, to treatises like the Timaeus of Plato, or Socrates in his reflections on what the Greeks called khôra (i.e. "space"), or in the Physics of Aristotle (Book IV, Delta) in the definition of topos (i.e. place), or in the later "geometrical conception of place" as "space qua extension" in the ...

  8. Empty space - Wikipedia

    en.wikipedia.org/wiki/Empty_space

    Outer space, especially the relatively empty regions of the universe outside the atmospheres of celestial bodies; Vacuum, a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure; Free space, a perfect vacuum as expressed in the classical physics model

  9. Void (astronomy) - Wikipedia

    en.wikipedia.org/wiki/Void_(astronomy)

    The most striking aspect is that it requires a different definition of what it means to be a void. Instead of the general notion that a void is a region of space with a low cosmic mean density; a hole in the distribution of galaxies, it defines voids to be regions in which matter is escaping; which corresponds to the dark energy equation of ...