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  2. 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.

  3. Shape of the universe - Wikipedia

    en.wikipedia.org/wiki/Shape_of_the_universe

    In a universe with zero curvature, the local geometry is flat. The most familiar such global structure is that of Euclidean space, which is infinite in extent. Flat universes that are finite in extent include the torus and Klein bottle. Moreover, in three dimensions, there are 10 finite closed flat 3-manifolds, of which 6 are orientable and 4 ...

  4. Lambda-CDM model - Wikipedia

    en.wikipedia.org/wiki/Lambda-CDM_model

    The ΛCDM model assumes that the shape of the universe is of zero curvature (is flat) and has an undetermined topology. In 2019, interpretation of Planck data suggested that the curvature of the universe might be positive (often called "closed"), which would contradict the ΛCDM model.

  5. 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 ...

  6. 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

  7. Spacetime diagram - Wikipedia

    en.wikipedia.org/wiki/Spacetime_diagram

    The original position on your time line (ct) is perpendicular to position A, the original position on your mutual timeline (x) where (t) is zero. This timeline where timelines come together are positioned then on the same timeline even when there are 2 different positions. The 2 positions are on the 45 degree Event line on the original position ...

  8. 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.

  9. Big Bang - Wikipedia

    en.wikipedia.org/wiki/Big_Bang

    The overall geometry of the universe is determined by whether the Omega cosmological parameter is less than, equal to or greater than 1. Shown from top to bottom are a closed universe with positive curvature, a hyperbolic universe with negative curvature and a flat universe with zero curvature.