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In the case of accelerated expansion, ¨ is positive; therefore, ˙ was smaller in the past than today. Thus, an accelerating universe took a longer time to expand from 2/3 to 1 times its present size, compared to a non-accelerating universe with constant ˙ and the same present-day value of the Hubble constant. This results in a larger light ...
The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. [1] It is an intrinsic expansion, so it does not mean that the universe expands "into" anything or that space exists "outside" it. To any observer in the universe, it appears that all but the nearest galaxies ...
Physical cosmology. Current observations suggest that the expansion of the universe will continue forever. The prevailing theory is that the universe will cool as it expands, eventually becoming too cold to sustain life. For this reason, this future scenario once popularly called "Heat Death" is now known as the "Big Chill" or "Big Freeze". [1 ...
Big Crunch. The Big Crunch is a hypothetical scenario for the ultimate fate of the universe, in which the expansion of the universe eventually reverses and the universe recollapses, ultimately causing the cosmic scale factor to reach zero, an event potentially followed by a reformation of the universe starting with another Big Bang.
The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. [1] The notion of an expanding universe was first scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations.
The thinning of matter over time reduces the ability of gravity to decelerate the expansion of the universe; in contrast, dark energy (believed to be a constant scalar field throughout the visible universe) is a constant factor tending to accelerate the expansion of the universe. The universe's expansion passed an inflection point about five or ...
Cosmic age problem. The cosmic age problem was a historical problem in astronomy concerning the age of the universe. The problem was that at various times in the 20th century, the universe was estimated to be younger than the oldest observed stars. Estimates of the universe's age came from measurements of the current expansion rate of the ...
Space and time, according to the prevailing cosmological theory of the Big Bang, emerged together 13.787 ± 0.020 billion years ago, [11] and the universe has been expanding ever since. Today the universe has expanded into an age and size that is physically only in parts observable as the observable universe, which is approximately 93 billion ...