Introduction to the Universe.
Universe may be defined as the collective name of all the known and unknown celestial objects e.g, the solar system, the stars, the galaxies, constellations and all the matter which lies in the space between these objects. According to an estimate, the universe is 10-20 thousand million years old and measures 1010 light years across. There are many theories about the origin of universe. Out of these the Big-Bang Theory says that the universe flashed into existence from a very small agglomeration (mass or collection of things) of matter of extremely high density and temperature. Subsequently, it expanded a dense-hot globule of gas. After 200 million years, the first star came into being. Similarly the Sun was formed about 4.5 billion years ago. This process continued for millions of years till all the celestial bodies came into existence.
Theories about the Origin of Universe:
There have, so far, been presented three famous theories about the origin of Universe.
- The Big-Bang Theory
- The Oscillating Universe Theory
- The Steady State Theory
(1). The Big-Bang Theory:
According to this theory, the Universe originated as a result of a big explosion that took place about 10-20 thousand million years ago. The matter scattered around and condensed into lumps called galaxies. The Universe has been expanding during all this period. With the passage of time, it has been thinning out. The galaxies are still rushing out. This theory was born of the observation that other galaxies are moving away from our own at great speed in all directions as if they had all been propelled by ancient explosive force. This theory was suggested by a Belgian Priest in 1020s. He theorized that Universe began from a single primordial atom. The idea was boosted further when Edwin Hubble observed that galaxies are speeding away from us in all directions.
(2). The Oscillating Universe Theory:
According to this theory the expansion of Universe will be followed by the contraction of the galaxies resulting another Big-Bang. The process of the Universe continues in endless cycle of expansion and contraction. Each phase has its own laws of nature.
(3). The Steady State Theory:
This theory states that the Universe never originated instantly and will continue for ever. With the expansion of universe, new matter comes into existence and fill the spaces. This theory was put forwarded in 1948 by two Austrian Astrologers, Herman Bondi and Thomas Gold.