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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]
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 observable universe is a phrase used to distinguish the extent of the universe observable to an Earth-based astronomer from the actual and unobservable current extent of the universe. Because light travels at a finite velocity (300,000 Km/s) we observe distant objects not as they are now but as they were when the light left them.
Cosmic time [5] [6]: 142 is a measure of time by a physical clock with zero peculiar velocity in the absence of matter over-/under-densities (to prevent time dilation due to relativistic effects or confusions caused by expansion of the universe). Unlike other measures of time such as temperature, redshift, particle horizon, or Hubble horizon ...
The Doomsday Clock is seen at 89 seconds to midnight, the closest the clock has ever been to midnight in its 78-year history. / Credit: SAUL LOEB/AFP via Getty Images
The observable universe is one causal patch of a much larger unobservable universe; other parts of the Universe cannot communicate with Earth yet. These parts of the Universe are outside our current cosmological horizon, which is believed to be 46 billion light years in all directions from Earth. [14]
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 ...