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  2. Hubble's law - Wikipedia

    en.wikipedia.org/wiki/Hubble's_law

    The discovery of Hubble's law is attributed to work published by Edwin Hubble in 1929, [2] [3] [4] but the notion of the universe expanding at a calculable rate was first derived from general relativity equations in 1922 by Alexander Friedmann.

  3. Equation of state (cosmology) - Wikipedia

    en.wikipedia.org/wiki/Equation_of_state_(cosmology)

    In this case, the above expression for the scale factor is not valid and , where the constant H is the Hubble parameter. More generally, the expansion of the universe is accelerating for any equation of state w < − 1 / 3 {\displaystyle w<-1/3} .

  4. Friedmann equations - Wikipedia

    en.wikipedia.org/wiki/Friedmann_equations

    The Hubble parameter can change over time if other parts of the equation are time dependent (in particular the mass density, the vacuum energy, or the spatial curvature). Evaluating the Hubble parameter at the present time yields Hubble's constant which is the proportionality constant of Hubble's law .

  5. Cosmological constant - Wikipedia

    en.wikipedia.org/wiki/Cosmological_constant

    Using the Planck units, and the value evaluated in 2025 for the Hubble constant H 0 = 76.5 ± 2.2 (km/s)/Mpc = (2.48 ± 0.07) × 10 −18 s −1, [18] Λ has the value of = = = where is the Planck length. A positive vacuum energy density resulting from a cosmological constant implies a negative pressure, and vice versa.

  6. Cosmological principle - Wikipedia

    en.wikipedia.org/wiki/Cosmological_principle

    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 ...

  7. Cosmic distance ladder - Wikipedia

    en.wikipedia.org/wiki/Cosmic_distance_ladder

    The observational result of Hubble's law, the proportional relationship between distance and the speed with which a galaxy is moving away from us, usually referred to as redshift, is a product of the cosmic distance ladder. Edwin Hubble observed that fainter galaxies are more redshifted. Finding the value of the Hubble constant was the result ...

  8. Scale factor (cosmology) - Wikipedia

    en.wikipedia.org/wiki/Scale_factor_(cosmology)

    The current density of the observable universe is of the order of 9.44 · 10 −27 kg m −3 and the age of the universe is of the order of 13.8 billion years, or 4.358 · 10 17 s. The Hubble constant, , is ≈70.88 km s −1 Mpc −1 (The Hubble time is 13.79 billion years).

  9. Recessional velocity - Wikipedia

    en.wikipedia.org/wiki/Recessional_velocity

    where is the Hubble constant, is the proper distance, is the object's recessional velocity, and is the object's peculiar velocity. The recessional velocity of a galaxy can be calculated from the redshift observed in its emitted spectrum. One application of Hubble's law is to estimate distances to galaxies based on measurements of their ...