The Universe is a vast space filled with billions of trillions of galaxies including of all physical matter and such as planets, stars, dust etc..the Universe is commonly termed as the
cosmos. The Greeks were the first to propose that the universe possessed infinite space and existed eternally. Scientific revolutions in the ages that followed led to the discoveries of the elements of the universe. Scientists started to realize that the earth and its planets revolved around the sun and thus called this system as the
solar system. Greek
'sol' meaning
'the sun'.
The Solar System
Then with the improvements in the field of astronomy, scientists discovered that the solar system was situated along
with other billions of stars in the galaxy called as the Milky way galaxy.
The milky Way galaxy was seen and studied by the Greeks in the B.C periods. The sky looked like as if milk was poured in it and thus called it milky way galaxy.
The Big Bang:
No one in the world knew how the universe began. A number of scientists tried but none but
Georges Lemaitre succeeded. He proposed that the universe began 13 billion years ago. All the matter was contained in a space of 100 million light years. That place was very hot because of the collision between matter. But with a huge explosion causing all matter to scatter in different directions the universe had formed to what we know today. Edwin Hubble provided a proof for this by blowing a balloon with many spots on it. After he blew air into it, the spots scattered giving a very good proof that the universe began with a huge explosion.
This theory is called the
Big Bang Theory.
Some things to remember:
1) The universe began 13 billion years ago.
2) The Sun was formed 7 billion years ago.
3) The Earth and other planets formed 4.5 to 5.5 billion years ago.
However most of the night sky that we look at in the night is dark. The vast space is filled with space which is dark in colour not understood by man. This space of darkness is called the
Dark Matter.
From the Big Bang theory, the scientists expect that universe to grow more and more and further apart. One key piece of evidence for the big bang is the observed amount of helium in the universe. In 1948, Russian-born, physicist George Gamow and his collaborators, American physicists Ralph A. Alpher and Robert Herman, worked out in detail the nuclear reactions that would have occurred during the big bang. Their calculations indicated that 25% of the mass of the normal matter now present in stars and galaxies is helium. Astronomical observations have since confirmed this calculation.
Two more theories:
1) Steady State theory: This theory offers yet another explanation of basic observations. According to this theory, the universe has always existed in its present state. As the galaxies move apart, new matter appears between them.
2)Cosmic Inflation theory: According to this theory, the universe expanded by an enormous amount in the early moments of the big bang.The inflationary expansion would have tended to smooth out temperature variations occurring over widely separated parts of the universe. Small variations in density would have led to the formation of galaxies.
But the big bang therory is the most widely accepted of all the theories.
