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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 ...
An important parameter in fate of the universe theory is the density parameter, omega (), defined as the average matter density of the universe divided by a critical value of that density. This selects one of three possible geometries depending on whether Ω {\displaystyle \Omega } is equal to, less than, or greater than 1 {\displaystyle 1} .
The first one to address the problem of an infinite number of stars and the resulting heat in the Cosmos was Cosmas Indicopleustes, a 6th-century Greek monk from Alexandria, who states in his Topographia Christiana: "The crystal-made sky sustains the heat of the Sun, the moon, and the infinite number of stars; otherwise, it would have been full of fire, and it could melt or set on fire."
One of the unanswered questions about the universe is whether it is infinite or finite in extent. For intuition, it can be understood that a finite universe has a finite volume that, for example, could be in theory filled with a finite amount of material, while an infinite universe is unbounded and no numerical volume could possibly fill it.
Another possibility based on M-theory and observations of the cosmic microwave background (CMB) states that the universe is but one of many in a multiverse, and has budded off from another universe (e.g., one that macroscopically looks like static empty space) as a result of quantum fluctuations such as quantum foam, as opposed to our universe ...
In cosmology, a static universe (also referred to as stationary, infinite, static infinite or static eternal) is a cosmological model in which the universe is both spatially and temporally infinite, and space is neither expanding nor contracting. Such a universe does not have so-called spatial curvature; that is to say that it is 'flat' or ...
On the other hand, some scientists, theories and popular works conceive of a multiverse in which the universes are so similar that humanity exists in many equally real separate universes but with varying histories. [95] There is a debate about whether the other worlds are real in the many-worlds interpretation (MWI) of quantum mechanics.
Some physicists, such as Lawrence Krauss, Stephen Hawking or Alexander Vilenkin, call or called this state "a universe from nothingness", although the zero-energy universe model requires both a matter field with positive energy and a gravitational field with negative energy to exist. [2]