Our Sun is an average star in the Universe. 10,000 crore such stars make the Milky Way Galaxy which is just an average galaxy. There are again 10,000 crore such galaxies in the known Universe. The known Universe has a diameter of about 1200 to 1500 crore light years. We are prefixing it with known because we do not know what lies beyond this. Perhaps a vast empty area with properties unknown to us, and then maybe another Universe, and so on. Even if our science develops for another million years still we would not be able to fathom the secrets of this cosmic whole.
What is the origin of the known Universe? Most of the Cosmologists have accepted the Big Bang theory as the most plausible explanation for the formation of the Universe. This was propounded by the Belgian Physicist and a Roman Catholic Priest Georges Lemaitre in 1927. As per this theory the entire matter in the Universe is concentrated as one single mass a long time ago. At that point of time there was neither space nor time and we cannot even imagine what is outside this mass. Space and time are relative concepts and when the entire Universe is in a single mass, then they cannot be measured at all and cease to have any meaning.
As such large amount of matter together gives rise to high gravitational attraction; all the matter got attracted towards its center. As the mass shrunk on account of this huge gravitational forces an enormous amount of heat was generated. This went on increasing to a point when the entire mass exploded and started scattering in all the directions. At that time the temperature of this mass was about 4,00,000 crore degrees Celsius. Comparatively our Sun’s core has a temperature of about 5 crore degrees Celsius. Atoms started forming only 377,000 years after the Big Bang which is estimated to have occurred some 14 billion years ago. Scientists have estimated the time when that single mass exploded by simply projecting back the possibility of an explosion and counting back from now.
There is an indirect proof for the explosion of the primeval atom (what else can we call it?) and it is known as Microwave Background Radiation. American radio astronomers Penzias and Wilson found in 1964 that a microwave radiation not corresponding to any star or a galaxy or an object is found in all directions of the Universe with the same wavelength and frequency. This relates to a certain homogenous temperature throughout the Universe which can be extrapolated to the Big Bang.
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