|Posted by Devinder Kumar Dhiman on November 17, 2015 at 12:40 AM|
It all started with an idea that velocity of stars can be measured by using Doppler effect on the light coming from the stars. If a train is going away from us, the frequency of sound generated from its whistle is lesser than the frequency of sound generated by a stationary train. This is Doppler effect and when it was applied to light coming stars, it was reasoned that if the frequency of light coming from star is found less than the frequency of light from sun then the star should be going away from us and if it is found more then star should be coming towards earth.
Atn astronomer William Huggins collected data of various stars and he found that frequency of light coming from most of the stars was lesser than the frequency of light of sun, implying they are going away from the earth. He also measured distance of these stars using the brightness of stars. A graph was plotted between distance of stars and their velocity calculated from the red-shift in the frequency of their light. This graph slowed that further a star is, more its red-shift is. Since red-shift was related to velocity of star due to Doppler effect, it was observed that further a star is faster it is going away from Earth. Few years after this, Hubble extended the same principle for galaxies by making measurements for galaxies.
By that time L'emaitre had come up with an idea of 'Primordial atom' using Einstein's General theory of relativity. Combination of Hubble's finding that all galaxies are going away from earth and L'emaitre's idea of 'Primordial atom' led to an idea that there existed a huge 'Primordial atom' in the beginning of Universe, which exploded due to some unknown event and that its parts became stars and galaxies, which are still flying away from the 'Primordial atom'. This explanation was given the name 'Big Bang' by Fred Hoyle.
Thereafter, there have been many arguments against this theory and new findings have refuted those arguments.
First argument was that if Big Bang happened, then there must be its signature radiation still traveling in the universe. This radiation was called Cosmological Microwave Background Radiation, and was found in 1963 by two radio engineers. Then the question of size of ripples and homogeneity in CMBR went against the Big Bang theory. Inflation model was suggested by Alan Guth which solved some problems for Big Bang. Age of the Big Bang has been another cause of concern because Big-bang was calculated to have happened 13.8 billion years ago but super-clusters of galaxies and walls have been observed that could have developed in 80 to 100 billion years only. Overall, Big bang is not yet fully established theory of creation of universe, there are still many loopholes that require to be plugged in.