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  2. Shape of the universe - Wikipedia

    en.wikipedia.org/wiki/Shape_of_the_universe

    The curvature of the universe places constraints on the topology. If the spatial geometry is spherical, i.e., possess positive curvature, the topology is compact. For a flat (zero curvature) or a hyperbolic (negative curvature) spatial geometry, the topology can be either compact or infinite. [8]

  3. Lambda-CDM model - Wikipedia

    en.wikipedia.org/wiki/Lambda-CDM_model

    The model assumes that general relativity is the correct theory of gravity on ... The ΛCDM model assumes that the shape of the universe is of zero curvature (is flat ...

  4. Curved space - Wikipedia

    en.wikipedia.org/wiki/Curved_space

    Curved spaces play an essential role in general relativity, where gravity is often visualized as curved spacetime. [2] The Friedmann–Lemaître–Robertson–Walker metric is a curved metric which forms the current foundation for the description of the expansion of the universe and the shape of the universe.

  5. Friedmann equations - Wikipedia

    en.wikipedia.org/wiki/Friedmann_equations

    If k = −1, then (loosely speaking) one can say that i · a is the radius of curvature of the universe. a is the scale factor which is taken to be 1 at the present time. k is the current spatial curvature (when a = 1). If the shape of the universe is hyperspherical and R t is the radius of curvature (R 0 at the present), then a = ⁠ R t / R 0

  6. 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 ...

  7. Inhomogeneous cosmology - Wikipedia

    en.wikipedia.org/wiki/Inhomogeneous_cosmology

    Possible shapes of the universe. In terms of the curvature of space-time and the shape of the universe, it can theoretically be closed (positive curvature, or space-time folding in itself as though on a four-dimensional sphere's surface), open (negative curvature, with space-time folding outward), or flat (zero curvature, like the surface of a ...

  8. Milne model - Wikipedia

    en.wikipedia.org/wiki/Milne_model

    The Milne universe is a special case of a more general Friedmann–Lemaître–Robertson–Walker model (FLRW). The Milne solution can be obtained from the more generic FLRW model by demanding that the energy density, pressure and cosmological constant all equal zero and the spatial curvature is negative.

  9. Anti-de Sitter space - Wikipedia

    en.wikipedia.org/wiki/Anti-de_Sitter_space

    General relativity is a theory of the nature of time, space and gravity in which gravity is a curvature of space and time that results from the presence of matter or energy. Energy and mass are equivalent (as expressed in the equation E = mc 2). Space and time values can be related respectively to time and space units by multiplying or dividing ...