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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 spatial region from which we can receive light is called the observable universe. The proper distance (measured at a fixed time) between Earth and the edge of the observable universe is 46 billion light-years [49] [50] (14 billion parsecs), making the diameter of the observable universe about 93 billion light-years (28 billion parsecs). [49]
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".
In physics, an observable is a physical property or physical quantity that can be measured. In classical mechanics , an observable is a real -valued "function" on the set of all possible system states, e.g., position and momentum .
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 ...
In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is uniformly isotropic and homogeneous when viewed on a large enough scale, since the forces are expected to act equally throughout the universe on a large scale, and should, therefore, produce no observable inequalities in the large-scale structuring over the course ...
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 ...