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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