## General theory of relativity

Albert Einstein published the general theory of relativity in 1915 for challenging newton's theory of gravitation. Einstein was one of the greatest scientists of his century. A very strange thing about Einstein was, he never proposed any theory on any experimental basis, but he only gives all his theories and hypothesis on the basis of his imagination and mathematical equations.

Einstein was lashed with a great power of visualisation.

Theory of relativity is just one of the theory proposed by Einstein but this theory changed everything. This theory changes our view to see the universe.

As we know, speed is present in the every particle of the universe but we are able to measure this speed mathematically about 300 years ago. This task was done by "Sir Issac Newton" by proposing his laws of motion.

According to Newton, any body initially at rest comes in motion if any external force applies on it. Newton also said that time is abloslute , what that means?

Well, it means time passes with equal speed at any corner of the universe, this means that time for a astronaut travelling in a space ship is equal to the time passes for a person on earth. In another case, time for a person near a black hole behaves same as time of earth, but the fact on it is not true.

Einstein was a great thinker, his visualisation power was excellent. He visualises that if a 'A' person is sitting in a train and another person 'B' is watching him then, For B, A is moving in forward direction with some velocity, but for A he and all other passengers sitting in that train are in rest. This was a great paradox for the scientists of 20th century that, which frame of reference is correct to measure the speed of A.

The conclusion comes out was, Both the references was absolutely right but the problem was speed. Einstein suggested that speed is not absolute but it is relative.

Newton also said in his classical theory of relativity, "law of physics do not very with velocity of body", but if we apply physics on A and B then results will comes out against the Newton's classical theory of relativity.

In starting of 20th century, scientists have found that there is also a thing in the nature whose speed doesn't depend on frame of reference and that is light. The speed of light is 300000 m/sec which does not vary with frame of reference. It does not matter from where we will observe light it's value will comes out to be same.

This absolute speed of light stunned Albert Einstein and he starts thinking that what will happen if we travel with the speed of light and he goes with a simple formula which says speed depends upon the product of time and distance , because speed of light is constant hence Einstein conclude that space and time must vary itself.

According to Einstein, nature will not allow anything to break it's law and it forces them to follow all the laws. Speed of light is also a fundamental property of nature hence for keeping it as a constant, nature makes some changes in space and time.

For understanding this let's take our previous example, this time A is sitting in a train whose speed is same as speed of light. They both measure time when A starts moving and after some days A comes out from that train. He will find that his friend B is nearly 10-20 years older than before, he will found a different world or we can say, a future world. This concept of Einstein also gave birth to a fictional phenomenon "time travel".

This theory of Albert Einstein was now ready to shake the whole scientific society. Nowadays general theory of relativity is one of the most important weapon to fight and find the hidden fact of this unpredictable universe.

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