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A "closed universe" is necessarily a closed manifold. An "open universe" can be either a closed or open manifold. For example, in the Friedmann–Lemaître–Robertson–Walker (FLRW) model, the universe is considered to be without boundaries, in which case "compact universe" could describe a universe that is a closed manifold.
This term originally was used as a means to determine the spatial geometry of the universe, where ρ c is the critical density for which the spatial geometry is flat (or Euclidean). Assuming a zero vacuum energy density, if Ω is larger than unity, the space sections of the universe are closed; the universe will eventually stop expanding, then ...
Einstein's static universe is closed (i.e. has hyperspherical topology and positive spatial curvature), and contains uniform dust and a positive cosmological constant with value precisely = /, where is Newtonian gravitational constant, is the energy density of the matter in the universe and is the speed of light.
The universe could then consist of an infinite sequence of finite universes, with each finite universe ending with a Big Crunch that is also the Big Bang of the next universe. A problem with the cyclic universe is that it does not reconcile with the second law of thermodynamics , as entropy would build up from oscillation to oscillation and ...
The universe will become extremely dark after the last stars burn out. Even so, there can still be occasional light in the universe. One of the ways the universe can be illuminated is if two carbon–oxygen white dwarfs with a combined mass of more than the Chandrasekhar limit of about 1.4 solar masses happen
The universe's expansion rate, a figure called the Hubble constant, is measured in kilometers per second per megaparsec, a distance equal to 3.26 million light-years. A light-year is the distance ...
For the accelerating universe with nonzero Ω Λ that we inhabit, the age of the universe is coincidentally very close to the Hubble age. The value of the Hubble parameter changes over time, either increasing or decreasing depending on the value of the so-called deceleration parameter q , which is defined by
The de Sitter universe has infinite age, while the closed universe has the least age. The value of the age correction factor, F , {\displaystyle ~F~,} is shown as a function of two cosmological parameters : the current fractional matter density Ω m {\displaystyle ~\Omega _{\text{m}}~} and cosmological constant density Ω Λ . {\displaystyle ...