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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 ...
The comoving distance from Earth to the edge of the observable universe is about 14.26 gigaparsecs (46.5 billion light-years or 4.40 × 10 26 m) in any direction. The observable universe is thus a sphere with a diameter of about 28.5 gigaparsecs [27] (93 billion light-years or 8.8 × 10 26 m). [28]
The Hubble eXtreme Deep Field (XDF) was completed in September 2012 and shows the farthest galaxies ever photographed at that time. Except for the few stars in the foreground (which are bright and easily recognizable because only they have diffraction spikes), every speck of light in the photo is an individual galaxy, some of them as old as 13.2 billion years; the observable universe is ...
Beyond the observable universe lie the unobservable regions from which no light has yet reached the Earth. No information is available, as light is the fastest travelling medium of information. However, uniformitarianism argues that the Universe is likely to contain more galaxies in the same foam-like superstructure. [54]
The distinction between "observable" and "unobservable" is similar to Immanuel Kant's distinction between noumena and phenomena.Noumena are the things-in-themselves, i.e., raw things in their necessarily unknowable state, [3] before they pass through the formalizing apparatus of the senses and the mind in order to become perceived objects, which he refers to as "phenomena".
Rather, the conformal time is the amount of time it would take a photon to travel from where we are located to the furthest observable distance, provided the universe ceased expanding. As such, η 0 {\displaystyle \eta _{0}} is not a physically meaningful time (this much time has not yet actually passed); though, as we will see, the particle ...
The time on the symbolic clock was set at 90 seconds to midnight, the same as in 2023. Prior to that it had stood at 100 seconds to midnight, closer to destruction than at any point since it was ...
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 ...