Human thought and perception about the picture of universe has a long history from the starting of human colonization to the today’s twenty first century. The time before 0001 BC, which I like to call ancient era, the perception of people toward earth was a flat surface supported on the back by giant tortoise. Actually there was tower of tortoise, mathematically calling, an infinite tower of tortoise, and on the top our earth lies. Today’s people may think this as a ridiculous idea but what can we do for the great thinking of our forefathers of that era?
Among those great people, we shouldn’t forget the name Aristotle, a Greek philosopher (340 BC), wrote a book “On the Heaven” and became first to give a satisfactory picture of Universe. He was the first philosopher to give the revolutionary idea about the earth that earth is round, rather than flat. To support his idea, he gave example of eclipses of moon on which shadow of earth falls by blocking light coming from sun. The fact was the shape of shadow seemed curved rather than flat, which would be only possible if the earth was spherical. Another idea was the position of the north (pole) star, which used to appeared north in the sky. Greek people noticed that the position of north star appeared lower in the sky while they travel to the south. Obviously Aristotle was right about the earth, but wasn’t right about the universe. At his time, people knew about Sun, Moon, Stars and beside that the five planets: Mercury, Venus, Mars, Jupiter and Saturn. He believed that the earth was stationary and at the center of the universe. Sun, moon, planets and stars revolves around the earth.
Aristotle’s model of universe (Source: http://csep10.phys.utk.edu/astr161/lect/retrograde/aristotle.html).
At that ancient era, that might be a satisfactory picture of universe and ruled for about 1800 years over human mind, then in the sixteenth century Nicholas Copernicus came with the idea that sun was stationary at the center and other planets moved in the circular orbit around the sun. His idea was supported by Johannes Kepler and Galileo Galilei though they didn’t sure about the orbit of planets. And a revolutionary year came, 1609, when Galileo observed Jupiter with his telescope and found several moons revolving around it. This showed that everything shouldn’t have to orbit earth directly, which leads to the failure of Aristotle’s theory about universe. Then Kepler suggested the orbit of planets to be elliptical rather than circular. And soon the idea that sun was at center and other planets revolves around it came, which was the same idea that we learned in our primary level science course. Similarly each planet had its own satellite or moon, like earth had its moon.
The father of classical physics, who can forget his name, Sir Isaac Newton published his “
Philosphiae Naturalis Principia Mathematica” in which he developed mathematical equations to analyze the motion of planets, moons, sun and even stars. It helped to predict the motion of bodies in space and time. Moreover his postulate of “law of universal gravitation” suggested the reasonable existence of space bodies in the universe. The human conception about universe was taking into shape. Great secrets of universe were being reveled with the advancement of science and technology. The idea that sun wasn’t actually at the center of universe, but it was only a part of it, it revolves round our home galaxy, the Milky Way galaxy. Furthermore people found that there were number of galaxies with interstellar cloud
of dust
,
hydrogen gas, helium gas and other ionized gases
forming Nebula. Originally,
Nebula was a general name for any extended
astronomical object and there were uncountable number of those Nebulae. So the concept of infinite universe came. It leads to the idea that our universe nearly looks like same from all side of the earth.
Milky Way galaxy (source: http://en.wikipedia.org/wiki/File:Milky_Way_IR_Spitzer.jpg).
A beautiful picture of Nebula (source: http://en.wikipedia.org/wiki/File:Nursery_of_New_Stars_-_GPN-2000-000972.jpg).
Everyone knows something about Big Bang, most of you may have watched “The Big Bang theory”, a famous serial of today’s, but it has nothing to relate with the Big Bang that I am talking about. You may know about death of star forming black hole and other mysterious objects. I introduced the black hole since it has something to do with Big Bang. I want to introduce Penrose (theoretical physicist of todays), who carefully observed the death of star. During its death it increases its gravity in such an extent that it attracts its own mass inside it. This process continues until mass contracts to a point and the density is mathematically infinite. Another physicist of same time, Stephen Hawking analyzed Penrose’s idea and he thought it reversely. What if there was a point with infinite density at the beginning of universe, then big bang and then our entire universe formed. Though this was only a hypothesis, until 1970, when the joint paper by Penrose and Hawking was published. In that paper the hypothesis of big bang singularity was proved using Einstein’s general theory of relativity. Hence if Einstein was correct about relativity, then big bang must be correct. The famous saying of the paper that “there was in fact no singularity at the beginning of the universe” leads us to the starting of time. There was no time before the beginning of the universe and if there was something before big bang (beginning of the universe), that doesn’t affect anything after big bang.
Today, everyone believes that our universe is because of big bang and earth is a luckily formed planet in the continuous expansion of universe. Our scientists, physicists and astrologists are exploring our universe. One day, another general theory of universe might come and that might give us more accurate and more reasonable picture of our universe and answer our existence.
(This article is inspiration from "A Brief history of time" by Stephen Hawking)
