closed universe
Quick Summary
A closed universe is a cosmological model where galaxies, after initially moving apart, will eventually come back together. This concept is part of the Friedmann-Lemaître models, which describe an evolving universe originating from a Big Bang.1
In this model, the universe's fate—whether it expands forever or collapses—depends on its average density of matter and radiation. If this density exceeds a specific value, known as the closure density, gravity will eventually halt the expansion and cause a collapse, referred to as a "big squeeze". The closure density is calculated as 3H02/8πG, where H0 is Hubble's constant and G is the gravitational constant.2
Current observations suggest that the universe's average density, including dark matter and dark energy, is close to this closure density, making its ultimate fate a subject of ongoing study.23
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- cosmologyEinstein’s model
…and isotropic universe had a closed spatial geometry. As described above, the total volume of a three-dimensional space with uniform positive curvature would be finite but possess no edges or boundaries (to be consistent with the first assumption).
Read More…and isotropic universe had a closed spatial geometry. As described above, the total volume of a three-dimensional space with uniform positive curvature would be finite but possess no edges or boundaries (to be consistent with the first assumption).
Read More - cosmologyFriedmann-Lemaître models
…both positively curved spaces (“closed” universes) as well as negatively curved spaces (“open” universes). The difference between the approaches of Friedmann and Lemaître is that the former set the cosmological constant equal to zero, whereas the latter retained the possibility that it might have a nonzero value. To simplify…
Read More…both positively curved spaces (“closed” universes) as well as negatively curved spaces (“open” universes). The difference between the approaches of Friedmann and Lemaître is that the former set the cosmological constant equal to zero, whereas the latter retained the possibility that it might have a nonzero value. To simplify…
Read More - cosmologyFriedmann-Lemaître models
…geometry of space in Friedmann’s closed models is similar to that of Einstein’s original model; however, there is a curvature to time as well as one to space. Unlike Einstein’s model, where time runs eternally at each spatial point on an uninterrupted horizontal line that extends infinitely into the past…
Read More…geometry of space in Friedmann’s closed models is similar to that of Einstein’s original model; however, there is a curvature to time as well as one to space. Unlike Einstein’s model, where time runs eternally at each spatial point on an uninterrupted horizontal line that extends infinitely into the past…
Read More - cosmologyFriedmann-Lemaître models
For example, in a closed Friedmann model, there could be galaxies that started, when R was small, very close to the Milky Way system on the opposite side of the universe. Now, 1010 years later, they are still on the opposite side of the universe but at a distance…
Read MoreFor example, in a closed Friedmann model, there could be galaxies that started, when R was small, very close to the Milky Way system on the opposite side of the universe. Now, 1010 years later, they are still on the opposite side of the universe but at a distance…
Read More - cosmologyBound and unbound universes and the closure density
…large timescales in the Friedmann closed and open models and the Einstein–de Sitter model allow a different classification scheme than one based on the global structure of space-time. The alternative way of looking at things is in terms of gravitationally bound and unbound systems: closed models where galaxies initially separate…
Read More…large timescales in the Friedmann closed and open models and the Einstein–de Sitter model allow a different classification scheme than one based on the global structure of space-time. The alternative way of looking at things is in terms of gravitationally bound and unbound systems: closed models where galaxies initially separate…
Read More - cosmologyBound and unbound universes and the closure density
…the universe is bound (closed) and, though currently expanding, will end in a crush of unimaginable proportion. If it is less, the universe is unbound (open) and will expand forever. The result is intuitively plausible since the smaller the mass density, the smaller the role for gravitation, so the…
Read More…the universe is bound (closed) and, though currently expanding, will end in a crush of unimaginable proportion. If it is less, the universe is unbound (open) and will expand forever. The result is intuitively plausible since the smaller the mass density, the smaller the role for gravitation, so the…
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