According to the big bang theory all matter in the universe was concentrated as a single extremely dense and hot fire ball. An explosion occured about 20 billion years ago and the matter was broken into pieces, thrown off in all directions in the form of galaxies. Due to < > 105 Light years Sun Galactic centre < > 27,000 Light years Fig. 4.21 Milky Way galaxy 183 continuous movement more and more galaxies will go beyond the boundary and will be lost. Consequently, the number of galaxies per unit volume will go on decreasing and ultimately we will have an empty universe. This is the big bang theory, from my textbook, which I have typed.
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big bang theory was formulated in the early part of 20th century by Edwin Hubble.this theory says that the universe was born 10 to 15 billion years ago with a tiny speck of matter,that was smaller than a grain of sand, which had a temperature of trillions of degree centigrade.there was a tremendous explosion in the space and the matter was sent hurling in all possible the matter cooled down,atoms were formed and than slowly,over billions of years, all the stars and the galaxies came into exist.
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