How old is really our Universe. This a century old question which have captivated the mind of our ancestors for many centuries. Early human civilizations reckoned that all the living and non living things were created by gods. Their knowledge about the world was very limited and based predominantly on religious beliefs. Many ancient civilizations thought that the earth was flat and did not move. The most well developed theory in those times was the so called Ptolemy theory. It placed earth at the centre of all the universe. The earth was thought to be motionless and all the other celestial bodies went around it in a strictly predefined orbits. This theory was developed by the Greek scientist Ptolemy, who lived in Alexandria in 2 century AD. The curious thing about this theory was that it was widely accepted till the 16 and 17 century AD, when the new heliocentric theories of Galileo Galilee and Nicolas Copernicus overthrew it.

Nicolas Copernicus lived in Poland in 16 century. He developed his own system about the universe called heliocentric. It placed the sun at the centre of the universe and all the other planets were merely rotating around it. Although the theory was ahead of its time, it had many imperfections. For example it still could not explain the nature of the force which drove the planets around their orbits. It was thought that this force came from god and he was the one who set all the bodies in the system in motion. That is why the heliocentric theory was further developed by the two famous astronomers of that time Johannes Kepler and Galileo Galilee. Galileo Galilee , a famous Italian astronomer, first discovered four of the satellites orbiting around the planet of Jupiter. By this way he was able to prove that another celestial bodies rotated around another planet. That was the first blow taken by the Ptolemy’s system which was fiercely supported by the Catholic church. The other came from the astronomer Johannes Kepler. He was able to calculate exactly the orbits of the planets, which were slightly elliptical and not ideal circles as previously thought. Nevertheless Kepler was unable to define the nature of the force which moved all the planets around the sun. That force, today known as gravity was discovered by the English scientist Isaac Newton in 17 century. That put an end to the geocentric system and lay the foundations of the later theory of Bing Bang which was developed by Albert Einstein at the start of the 20 Th century.