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The Universe Within 14 Billion Light Years – NASA Atlas of the Universe – Note, this map only gives a rough cosmographical estimate of the expected distribution of superclusters within the observable universe; very little actual mapping has been done beyond a distance of one billion light-years.
It represents the boundary between the observable and the unobservable regions of the universe, so its distance at the present epoch defines the size of the observable universe. Due to the expansion of the universe, it is not simply the age of the universe times the speed of light, as in the Hubble horizon, but rather the speed of light ...
An expanding universe typically has a finite age. Light, and other particles, can have propagated only a finite distance. The comoving distance that such particles can have covered over the age of the universe is known as the particle horizon, and the region of the universe that lies within our particle horizon is known as the observable universe.
The observable universe contains as many as an estimated 2 trillion galaxies [95] [96] [97] and, overall, as many as an estimated 10 24 stars [98] [99] – more stars (and earth-like planets) than all the grains of beach sand on planet Earth; [100] [101] [102] but less than the total number of atoms estimated in the universe as 10 82; [103] and ...
Hence, it is unclear whether the observable universe matches the entire universe or is significantly smaller, though it is generally accepted that the universe is larger than the observable universe. The universe may be compact in some dimensions and not in others, similar to how a cuboid [citation needed] is longer in one dimension than the ...
The age of the universe can be determined by measuring the Hubble constant today and extrapolating back in time with the observed value of density parameters ( ). Before the discovery of dark energy, it was believed that the universe was matter-dominated (Einstein–de Sitter universe, green curve).
The microwave background is a relic from when the universe was about 380,000 years old, but the neutrino background is a relic from when the universe was about two seconds old. If this neutrino radiation could be observed, it would be a window into very early stages of the universe.
As such, the observed size of the universe always increases. [ 1 ] [ 3 ] Since proper distance at a given time is just comoving distance times the scale factor [ 4 ] (with comoving distance normally defined to be equal to proper distance at the present time, so a ( t 0 ) = 1 {\displaystyle a(t_{0})=1} at present), the proper distance to the ...