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The universe is bathed in highly isotropic microwave radiation that corresponds to a thermal equilibrium blackbody spectrum of roughly 2.72548 kelvins. [7] The hypothesis that the large-scale universe is homogeneous and isotropic is known as the cosmological principle. [116]
The End of Greatness is an observational scale discovered at roughly 100 Mpc (roughly 300 million light-years) where the lumpiness seen in the large-scale structure of the universe is homogenized and isotropized in accordance with the cosmological principle. [56] At this scale, no pseudo-random fractalness is apparent. [66]
In the 2000s and 2010s, it was shown that, since the universe is inhomogeneous as shown in the cosmic web of large-scale structure, acceleration effects measured on local scales in the patterns of the movements of galaxies should, in principle, reveal the global topology of the universe.
When the size of the universe at Big Bang is described, it refers to the size of the observable universe, and not the entire universe. [ 143 ] Another common misconception is that the Big Bang must be understood as the expansion of space and not in terms of the contents of space exploding apart.
Mathematically, the expansion of the universe is quantified by the scale factor, , which is proportional to the average separation between objects, such as galaxies. The scale factor is a function of time and is conventionally set to be = at the present time.
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 ...
Visualization of the whole observable universe.The inner blue ring indicates the approximate size of the Hubble volume. In cosmology, a Hubble volume (named for the astronomer Edwin Hubble) or Hubble sphere, Hubble bubble, subluminal sphere, causal sphere and sphere of causality is a spherical region of the observable universe surrounding an observer beyond which objects recede from that ...
Neither time nor size are to scale. The size of the whole universe is unknown, and it might be infinite in extent. [20] According to the Big Bang theory, the very early universe was an extremely hot and dense state about 13.8 billion years ago [21] which rapidly expanded.