It is a big blast that created entire universe

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According to most astronomers, the universe started with a gigantic explosion-the Big Bang- of a cosmic egg about billions of years ago. Atoms and later molecules were formed as a result of this explosion. They ultimately formed a giant cloud of gases and tiny dust particles called the nebula. The nebula had a spinning motion and its own gravity. Fragments of the nebula were attracted to one another and collided at tremendous speed. This gave out enormous amount of heat which resulted in growth of glowing bodies like stars.
This is the BIG BANG THEORY. 
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