The special theory of relativity is said to be the most
revolutionary theory ever put. It was formulated by Albert Einstein in 1905 as
a paper named On The Electrodynamics Of
Moving Bodies. In the same year, Einstein had put forward 5 papers
(including special relativity) which are said to be so important that each of
them deserves one Nobel Prize. That year is said to be the Miracle Year of
Einstein. The special theory of relativity was the fourth paper in that year.
The results of this theory were very strange but as it turned out, they were
very accurate.
The special theory of relativity is based on two principles.
1. All laws of
physics are same is any inertial frame of reference.
2. The speed
of light is same for all observers and it is c (which is 3 x 108
m/s)
The first principle is called the Principle of Relativity. It
was put forward much before Einstein by Galileo. Galileo thought that if a
closed room was moving in the empty space in a straight line with a constant
velocity then the people inside the room can do no experiment or no test that
will verify that they are moving. And if now an observer outside the room is
standing still relative to the room then for the people inside the room the
person is moving. And in reality both are equally correct.
The second principle says that light has a constant speed and
that its speed will not vary whatever be the constant velocity of the frame.
Let us take a simple assumption and make this clear. Two
frames of reference are moving in at a relative motion. One observer is
standing at rest to the other. Now a car is moving at some speed relative to
the first observer. The second observer will certainly see a different speed
for the car. So the speed of the car is different for the two inertial frame of
reference. The second postulate says that it is not in case of light. If a beam
of light in fired then both the observers will see the same speed of light.
Taking this assumption, all the results have been derived.
Using a simple thought experiment, we can see a very
important result. Suppose a ship is moving with certain speed and a member is
inside it and a beam of light is fired perpendicular to the direction of its
motion. A person is outside the ship and observes the beam of light. The person
and ship member, both observes the time for the beam of light to reach the
roof. The ship member records a time t.
For the person, he sees a diagonal path of the beam as the ship is moving
forward. Therefore its length is now more than the previous original length.
But as we told the speed of light will not change, it is constant. So the light
beam will take a longer time to travel that longer distance. Thus the person
will observe a longer time. So we see that time is different for different frame
of reference.
From this special theory of relativity it was found that time
is not an absolute quantity. It is in fact a relative quantity and is another
dimension of the universe. Special relativity also explains that length of
objects change with motion and also their mass. All these results have
experimental evidence. In simple worlds, special relativity has changed the
concept of space and time for us.
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