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  2. Shape of the universe - Wikipedia

    en.wikipedia.org/wiki/Shape_of_the_universe

    The density parameter is the average density of the universe divided by the critical energy density, that is, the mass energy needed for a universe to be flat. Put another way, If Ω = 1, the universe is flat. If Ω > 1, there is positive curvature. If Ω < 1, there is negative curvature.

  3. Universe - Wikipedia

    en.wikipedia.org/wiki/Universe

    The observable universe is isotropic on scales significantly larger than superclusters, meaning that the statistical properties of the universe are the same in all directions as observed from Earth. The universe is bathed in highly isotropic microwave radiation that corresponds to a thermal equilibrium blackbody spectrum of roughly 2.72548 ...

  4. 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 notion of an expanding universe was first scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations.

  5. Flatness problem - Wikipedia

    en.wikipedia.org/wiki/Flatness_problem

    The local geometry of the universe is determined by whether the relative density Ω is less than, equal to or greater than 1. From top to bottom: a spherical universe with greater than critical density (Ω>1, k>0); a hyperbolic, underdense universe (Ω<1, k<0); and a flat universe with exactly the critical density (Ω=1, k=0). The spacetime of ...

  6. Expansion of the universe - Wikipedia

    en.wikipedia.org/wiki/Expansion_of_the_universe

    "Geometrically flat" space has three dimensions and is consistent with Euclidean space. However, spacetime has four dimensions; it is not flat according to Einstein's general theory of relativity. Einstein's theory postulates that "matter and energy curve spacetime, and there is enough matter and energy to provide for curvature." [29]

  7. Pythagorean astronomical system - Wikipedia

    en.wikipedia.org/wiki/Pythagorean_astronomical...

    A flat Earth facing away from the Central Fire would be consistent with the pre-gravity concept that if all things must fall toward the center of the universe, this force would allow the earth to revolve around the center without spilling everything on the surface into space. [5]

  8. History of the center of the Universe - Wikipedia

    en.wikipedia.org/wiki/History_of_the_center_of...

    The Flat Earth model is a belief that the Earth's shape is a plane or disk covered by a firmament containing heavenly bodies. Most pre-scientific cultures have had conceptions of a Flat Earth, including Greece until the classical period , the Bronze Age and Iron Age civilizations of the Near East until the Hellenistic period , India until the ...

  9. Flatness (cosmology) - Wikipedia

    en.wikipedia.org/wiki/Flatness_(cosmology)

    The geometry of spacetime has been measured by the Wilkinson Microwave Anisotropy Probe (WMAP) to be nearly flat. According to the WMAP 5-year results and analysis, “WMAP determined that the universe is flat, from which it follows that the mean energy density in the universe is equal to the critical density (within a 1% margin of error).