In 1920 a famous debate took place between Harlow Shapley and Heber D. This idea of an expanding spacetime would eventually lead to the Big Bang and to the Steady State theories.īefore the advent of modern cosmology, there was considerable talk as to what was the size and shape of the universe. When this metric was applied to the Einstein equations, the so-called Friedmann equations emerged which characterized the expansion of the universe based on a parameter known today as the scale factor which can be considered a scale invariant form of the proportionality constant of Hubble's Law. However, a few scientists continued to pursue the dynamical universe and discovered that it could be characterized by a metric that came to be known after its discoverers, namely Friedmann, Lemaître, Robertson, and Walker. Applying the most general principles to the question of the nature of the universe yielded a dynamic solution that conflicted with the then prevailing notion of a static Universe. In the decade before Hubble made his observations, a number of physicists and mathematicians had established a consistent theory of the relationship between space and time by using Einstein's field equation of general relativity. As of the 2006 data, that figure has been refined to 70 +2.4 −3.2 (km/s)/Mpc. The most recent calculation of the constant, using the satellite WMAP began in 2003, yielding a value of 71 ± 4 (km/s)/ Mpc. It is considered the first observational basis for the expanding space paradigm and today serves as one of the most often cited pieces of evidence in support of the Big Bang. The law was first formulated by Edwin Hubble and Milton Humason in 1929 after nearly a decade of observations. Hubble's law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. Related subjects: Space (Astronomy) Physical cosmology
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