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Hubble's law can be easily depicted in a "Hubble diagram" in which the velocity (assumed approximately proportional to the redshift) of an object is plotted with respect to its distance from the observer. [30] A straight line of positive slope on this diagram is the visual depiction of Hubble's law.
The comoving distance from an observer to a distant object (e.g. galaxy) can be computed by the following formula (derived using the Friedmann–Lemaître–Robertson–Walker metric): = ′ (′) where a(t′) is the scale factor, t e is the time of emission of the photons detected by the observer, t is the present time, and c is the speed of ...
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 ...
with contributions from both the Hubble flow and peculiar velocity terms, where is the Hubble constant and is the distance to the object. Redshift-space distortions can cause the spatial distributions of cosmological objects to appear elongated or flattened out, depending on the cause of the peculiar velocities. [ 4 ]
The timeline in this schematic diagram extends from the Big Bang/inflation era 13.8 billion years ago to the present cosmological time. Observations show that the expansion of the universe is accelerating , such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time.
This correlation was first observed by Edwin Hubble and has come to be known as Hubble's law. Vesto Slipher was the first to discover galactic redshifts, in about 1912, while Hubble correlated Slipher's measurements with distances he measured by other means to formulate his Law. [64] Hubble's law follows in part from the Copernican principle. [64]
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 ...
Hubble's law implies that the universe is uniformly expanding everywhere. This cosmic expansion was predicted from general relativity by Friedmann in 1922 [ 62 ] and Lemaître in 1927, [ 65 ] well before Hubble made his 1929 analysis and observations, and it remains the cornerstone of the Big Bang model as developed by Friedmann, Lemaître ...