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Saturday, 8 February 2014

Relativity of SIMULTANEITY- A logical proof for special relativity


One of the special things about special relativity is that it has many interesting consequences. 
One of the direct consequences of special relativity is the relativity of simultaneity. It means that one cannot be sure that two events takes place simultaneously or at different times. This can be demonstrated by a famous thought experiment by Einstein. Einstein imagined a train buggy moving with constant velocity and inside it are three people. One person is standing exactly at the middle of the buggy and the other two are standing at the opposite ends of the buggy so that they are equidistant from the person standing at the middle. Now the person at the middle lights up his lighter which sends out two beams of light towards the two other men standing at the ends of the buggy. Now as the two are standing equidistant from the middle and as the speed of light does not depend upon the speed of the source (here the speed of the source i.e the person at the middle is same as the speed of the train), the person at the middle should observe that the light from his lighter should reach the other two persons at the exact same time.

Now let’s view the situation from perspective of a person outside the train. Suppose the train passes through a platform and a person standing on the platform happens to observe the experiment. So, what would he observe?

He would observe that both the people at the ends of the buggy would be moving along with the train but the 1st person would be moving towards the source of light (the man at the middle) while the 2nd person would be moving away from the source of light. So, it is obvious that the man on the platform would conclude that the 1st person receives the light earlier than the 2nd person. So, now who is correct, the person in the middle of the buggy or the person on the platform? This may sound strange, but according to special relativity, both are correct because in special relativity time is relative to the observer. 

Now you see how awkward it is that two events occurring simultaneously for one observer may not be simultaneous for another observer. So, this is relativity of simultaneity. It can be considered as a logical and simple proof for special relativity as it clearly demonstrates how time can be relative.

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