Big Bang

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The Big Bang is the theory that the universe began by growing out from a single point about 13.7 billion years ago. Everything is now flying away, similar to the parts of a bomb. The theory is called the "Big Bang" because "bang" is the sound that a bomb makes. The point was very small, dense, and hot. All space, time, and matter was created when the point got bigger. Scientists that study cosmology, which is how the universe began and how it has developed, agree that this theory matches all the observations that we have made, but other theories do not.

Scientists base this theory on many observations. The most important is the redshift of very far away stars. When a star moves away from us, its light becomes more red and less blue, because of the Doppler effect. From this we can see that the stars are moving away from us. If we look at how fast they are moving, we see that they all started at one place about 13.7 billion years ago. Because most things become colder when they become bigger, the universe was also very hot when it started.

Other observations that support the Big Bang theory are the amounts of chemical elements, for example, hydrogen, helium, and lithium, and also the "cosmic microwave background radiation". The background radiation is radio waves that are everywhere in the universe. It is now very weak and cold, but a long time ago it was very strong and very hot.

Einsteine's time dialation theory also can be applied on it. As all body mass in univers come closer (when we think about what should be happened in past depending upon doppler effect) the gravity will be more and more stronger, accordingly more dialation of time with distance and velocity. When they will form a single body the dialation will become so high that the time tense to zero. So we can say that it was the begining of time, thus there is on meaning of words "before big bang". ..Dharmendra.