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  2. Shape of the universe - Wikipedia

    en.wikipedia.org/wiki/Shape_of_the_universe

    Negative curvature – a drawn triangle's angles add up to less than 180°; such 3-dimensional space is locally modeled by a region of a hyperbolic space H 3. Curved geometries are in the domain of non-Euclidean geometry. An example of a positively curved space would be the surface of a sphere such as the Earth.

  3. Anti-de Sitter space - Wikipedia

    en.wikipedia.org/wiki/Anti-de_Sitter_space

    Three-dimensional anti-de Sitter space is like a stack of hyperbolic disks, each one representing the state of the universe at a given time. [a]In mathematics and physics, n-dimensional anti-de Sitter space (AdS n) is a maximally symmetric Lorentzian manifold with constant negative scalar curvature.

  4. Ultimate fate of the universe - Wikipedia

    en.wikipedia.org/wiki/Ultimate_fate_of_the_universe

    The ultimate fate of the universe is a topic in physical cosmology, ... the geometry of space is open, i.e., negatively curved like the surface of a saddle. The ...

  5. Comoving and proper distances - Wikipedia

    en.wikipedia.org/wiki/Comoving_and_proper_distances

    On this usage, comoving and proper distances are numerically equal at the current age of the universe, but will differ in the past and in the future; if the comoving distance to a galaxy is denoted , the proper distance () at an arbitrary time is simply given by = where () is the scale factor (e.g. Davis & Lineweaver 2004). [2]

  6. Flatness problem - Wikipedia

    en.wikipedia.org/wiki/Flatness_problem

    Each curve represents a possible universe: note that Ω diverges rapidly from 1. The blue curve is a universe similar to our own, which at the present time (right of the graph) has a small | Ω − 1 | and therefore must have begun with Ω very close to 1 indeed. The red curve is a hypothetical different universe in which the initial value of ...

  7. Friedmann equations - Wikipedia

    en.wikipedia.org/wiki/Friedmann_equations

    In other words, the energy (relative to the origin) of a co-moving particle in free-fall is conserved. General relativity merely adds a connection between the spatial curvature of the universe and the energy of such a particle: positive total energy implies negative curvature and negative total energy implies positive curvature.

  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. 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.