The current success of the big bang model relies on several key areas of observational evidence and predictions. These are discussed briefly below.
Evidence for the Big Bang Model
There are several key areas of observational support for the big bang model. These are:
Observed recession of galaxies: The consensus among astronomers is that Hubble's relationship between the distance to galaxies and their recession velocity is due to the expansion of space. More distant galaxies or clusters of galaxies exhibit higher redshift of their spectral lines than closer galaxies. This is then interpreted as more distant galaxies receding from us faster than closer ones. Note it is important to realise that it is the space between galaxies that is expanding. Galaxies themselves do not appear to expand as the local effects of gravity dominate over any space expansion.
Cosmic Microwave Background Radiation: In 1965 two scientists working for Bell Telephone Laboratories, Arno Penzias and Robert Wilson were adapting a horn-shaped antenna near New York for use in radio astronomy. They encountered noise in the system and despite repeated and thorough attempts were unable to remove it or find its cause. They eventually realised that this "noise" was in fact remnant radiation from the big bang. Such radiation had been predicted by Gamow in the late 1940s. As the Universe expanded it cooled so that today the background radiation corresponds to a temperature of 2.725 K and has a black body spectrum.
Over the last 15 years observations of this cosmic microwave background radiation (CMBR) from space-based missions such as COBE and WMAP and balloon-based missions such as BOOMERanG that operated in the Antarctic have provided a wealth of details. We can now view the slight fluctuations or anisotropies in the CMBR with unprecedented detail and compare observations with theory more thoroughly. The image below shows how the resolution of the CMBR has improved since its discovery in the 1960s. These slight fluctuations in the CMBR intensity are thought to provide information about slight variations in density in the early Universe.
Ratios of primordial elements. Astronomers are able to measure the relative amounts of the light nuclei hydrogen, deuterium (an isotope of hydrogen with one proton and one neutron), helium-3, helium-4 and lithium-7 in distant, unmixed clouds of primordial gas. The relative abundances of these nuclei correspond with the calculated predicted ratios from the Big Bang model.
Observed evolution of extragalactic objects over cosmic time. Evidence for this initially came from radio surveys which showed that the more distant (hence older) parts of the Universe appeared to contain stronger radio sources than the local region. Quasars, for instance, are not found in our local region but are far more common at redshifts of 2 or 3.
Recent observations by the Hubble Space Telescope and other telescopes have provided our deepest ever views of the Universe and clearly show evidence of galactic evolution and earlier stages in their formation.
...
