The Big Bang
In cosmology, the Big Bang is the scientific theory that describes the early development and shape of the universe.
The Big Bang Theory is the most accepted theory for the origin and evolution of our universe. The big bang theory states that at some time in the distant past there was nothing. It suggests that around 10 to 14 billion years ago, the part of the universe we can see today was only a few millimetres across. According to this theory, at the beginning of time, all of the matter and energy in the universe was concentrated in a very dense state, from which it "exploded" and this is known as the Big Bang.
The Big Bang marks the instant at which the universe began. From a dense, hot ball of gas, radiation and subatomic particles. This exploded and began expanding rapidly outward. As it expanded it cooled and electrons, protons and neutrons formed. As the universe grew in size, the temperature dropped, which eventually formed huge numbers of Hydrogen, Helium and Lithium nuclei. After many millions of years the expanding universe, at first a very hot gas, thinned and cooled enough to condense into individual galaxies and then stars. Stars and galaxies began to form about one billion years following the Big Bang. It has since expanded from this hot dense state into the vast and much cooler cosmos we currently inhabit.
Evidence for the Big Bang Theory
American astronomer Edwin Hubble provided some of the greatest supporting evidence for the theory with his 1929 discovery that the light of distant galaxies was generally shifted toward the red end of the spectrum, this is called the Red Shift. This happens when stars are moving rapidly away from Earth. This evidence means that it is obvious that the universe is expanding.
The second evidence is that this theory predicts that 25 percent of the total mass of the universe should be the helium that formed during the first few minutes, an amount that agrees with observations.
Thirdly, a cosmic background noise was the discovery in 1965, is received from every part of the sky. This background radiation has the same intensity and distribution of frequencies in all directions and is not linked with any individual celestial object. It has a black body temperature of -270 deg C and is interpreted as the electromagnetic remnant of the primordial fireball, stretched to long wavelengths by the expansion of the universe.
Other evidence that supports the big bang theory is the Isotropy of observable universe. Proponents of big bang also mention isotropy of the observable universe to one part in one hundred thousand as evidence that big bang is valid. They further state that what minute anisotropy does exist is consistent with big bang hypotheses which include the dark matter hypotheses.
Also Quasars are predicted to only be possible in the early stages of an active cosmos by the Big Bang theory, and observation evidence supports this, as quasar populations become denser the further away when you look at them.
Another piece of evidence for the Big Bang model is that it resolves Olbers' paradox of why the sky is black at night.
But the most convincing evidence is the presence of the cosmic background radiation, a theoretical prediction about photons left over from the big bang. The big-bang theory predicted this remnant radiation, which now glows at a temperature just 3 degrees above absolute zero. Cosmic Background Explorer (COBE) satellite, launched in 1989, showed that 99.97% of the radiant energy of the universe was released within the first year of the Big Bang event.
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