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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 ...
The Hubble length or Hubble distance is a unit of distance in cosmology, defined as cH −1 — the speed of light multiplied by the Hubble time. It is equivalent to 4,420 million parsecs or 14.4 billion light years. (The numerical value of the Hubble length in light years is, by definition, equal to that of the Hubble time in years.)
Hubble radius, Hubble sphere (not to be confused with a Hubble bubble), Hubble volume, or Hubble horizon is a conceptual horizon defining the boundary between particles that are moving slower and faster than the speed of light relative to an observer at one given time. Note that this does not mean the particle is unobservable; the light from ...
The redshift given by the formula + = () Any function with a zero subscript denote the function evaluated at the present time t 0 {\displaystyle t_{0}} (or equivalently z = 0 {\displaystyle z=0} ). The last term can be taken to be 1 {\displaystyle 1} including the curvature state equation. [ 7 ]
a is the scale factor, G, Λ, and c are universal constants (G is the Newtonian constant of gravitation, Λ is the cosmological constant with dimension length −2, and c is the speed of light in vacuum). ρ and p are the volumetric mass density (and not the volumetric energy density) and the pressure, respectively.
A free (=) scalar field has =, and one with vanishing kinetic energy is equivalent to a cosmological constant: =. Any equation of state in between, but not crossing the w = − 1 {\displaystyle w=-1} barrier known as the Phantom Divide Line (PDL), [ 2 ] is achievable, which makes scalar fields useful models for many phenomena in cosmology.
The light-travel distance to the edge of the observable universe is the age of the universe times the speed of light, 13.8 billion light years. This is the distance that a photon emitted shortly after the Big Bang, such as one from the cosmic microwave background , has traveled to reach observers on Earth.
Space-based telescopes (such as Hubble, or a number of non-optical telescopes) always work at their diffraction limit, if their design is free of optical aberration. The beam from a laser with near-ideal beam propagation properties may be described as being diffraction-limited. A diffraction-limited laser beam, passed through diffraction ...