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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 earliest and most direct observational evidence of the validity of the theory are the expansion of the universe according to Hubble's law (as indicated by the redshifts of galaxies), discovery and measurement of the cosmic microwave background and the relative abundances of light elements produced by Big Bang nucleosynthesis (BBN).
Hubble's results for Andromeda were not formally published in a peer-reviewed scientific journal until 1929. [29] Hubble's classification scheme. Hubble's findings fundamentally changed the scientific view of the universe. Supporters state that Hubble's discovery of nebulae outside of our galaxy helped pave the way for future astronomers. [30]
Experimental observations confirm expansion of universe according to Hubble's law. Since the universe is expanding, the equation for that expansion can be "run backwards" to its starting point. The Lambda-CDM concordance model describes the expansion of the universe from a very uniform, hot, dense primordial state to its present state over a ...
An important parameter in fate of the universe theory is the density parameter, omega (), defined as the average matter density of the universe divided by a critical value of that density. This selects one of three possible geometries depending on whether Ω {\displaystyle \Omega } is equal to, less than, or greater than 1 {\displaystyle 1} .
Hubble's idea allowed for two opposing hypotheses to be suggested. One was Lemaître's Big Bang, advocated and developed by George Gamow. The other model was Fred Hoyle's Steady State theory, in which new matter would be created as the galaxies moved away from each other. In this model, the universe is roughly the same at any point in time.
Evaluating the Hubble parameter at the present time yields Hubble's constant which is the proportionality constant of Hubble's law. Applied to a fluid with a given equation of state, the Friedmann equations yield the time evolution and geometry of the universe as a function of the fluid density.
The redshift hypothesised in the Big Bang model would by itself explain the darkness of the night sky even if the universe were infinitely old. In the Steady state theory the universe is infinitely old and uniform in time as well as space. There is no Big Bang in this model, but there are stars and quasars at arbitrarily great distances.