Before i start my topic i will tell you
about frame reference What is frame of reference? you will find much detail
about this but here i will tell you a little. Let first define it "A frame
of reference is any coordinate system relative to which measurements are
taken". For example suppose some measurements for an experiment are taken
in laboratory then laboratory is the frame of reference. Another example is
suppose a body is palced in car then car is a frame of refence. Lets move
further. There are two types of frame of reference.

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1) Principle of relativity:

1) Inertial frame of reference

2) Non inertaial frame of reference

In above example if the body is at rest or
moves with consatnt velocity so that no acceleration is produced then it is
called inertial frame of reference.

And if the body moves with some variable
velocity so that acceleration is produced then it is called non inertial frame
of reference.

Now back to topic.

Special theory of relativity treats the
problems involving inertial frames of reference and do you know? there is
another theory called general theory of relativity that treat the problems
involving non inertial frames of refernce.

In 1905, a paper entitled " on the
electrodynamics of moving bodies" Einstein offered the following
postulates which are the basis of the special theory of relativity.

The two postulates are:

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1) Principle of relativity:

The laws of physics are same in all inertial frames of reference.

2) The constancy of the speed of light:

Speed of light in free space(vacum) is constant(has same value c) in all
inertial frames of reference.

Now we will discuss the above two
postulates.

The first postulate declares that the laws
of physics that hold for an observer in inertial frame of reference cannot be
violated for an observer in an other inertial frame of reference.

To accept the second postulate we consider
the three observers at rest in three different inertial frames of reference.

The flash of light emitted by observer A is measured by him to be travel
at speed c. If the frame of

observer B is moving away from A at a speed of c/4, then Galiliean kinematics predicts that B

measures the c-c/4=3c/4 for the speed of light emitted by A. If the observer C is moving towards A

with a speed of c/4, then the Galilean kinematics predicts that C measures the value c+c/4=5c/4 for

the speed of light emitted by A.

observer B is moving away from A at a speed of c/4, then Galiliean kinematics predicts that B

measures the c-c/4=3c/4 for the speed of light emitted by A. If the observer C is moving towards A

with a speed of c/4, then the Galilean kinematics predicts that C measures the value c+c/4=5c/4 for

the speed of light emitted by A.

**BUT**

Second postulate tells that all three observers measures the same speed
c for the speed of light.

However, some experiments are conducted which satisfies second
postulate. This is a big problem

and confusion which must be solved in future.

and confusion which must be solved in future.

Now we will discuss some consequences(results) of special theory of
realativity. There are many

consequences but here i willl discuss only three consquences which are important.

These are

**i) Time Dilation**

**ii) Length Contraction**

**iii) Mass Variation**

Here i will more focus on time dilation. Lets discuss these consequences
one by one.

1) Time Dilation:

1) Time Dilation:

From centuries it is considered that time is an absolute quantity. Time
is running, running and running.

But

Einstein said time is not an absolute quantity it depends on velocity,
it depends on motion of frame of

reference.

reference.

Now suppose an observer is stationary in an inertial frame of reference.
He observes the time interval

between the two events in this frame let it be t

with velocity v with respect to frame of events, then the time measured by observer would not be it

will be t

given as

between the two events in this frame let it be t

_{0 }. This is called proper time. If the observer is movingwith velocity v with respect to frame of events, then the time measured by observer would not be it

will be t

_{0}given as

As the quantity of right hand side is less than 1, so t is always greater than t

_{0}.
There are many verses in Holy Book Quran that tells that time is not an
absolute quantity. Time is not

same for all. It is different for diffferent persons.

same for all. It is different for diffferent persons.

In Quran,

"The angel and spirit ascend to Him in day whose length is fifty
thousand years"

(Chap.29, Surah Al-Maarij 70:4)

(Chap.29, Surah Al-Maarij 70:4)

AND

"They ask you to hasten the punishment God will not break His
promise. A day with your Lord is

equivalent to a thousand years in the way you count" (Al-Quran 22:47)

equivalent to a thousand years in the way you count" (Al-Quran 22:47)

Now focus on this picture.

Here people are working together and time is passing on Earth which is t

spaceship is t. Focus on above two clocks you can see that

_{0}and time passing onspaceship is t. Focus on above two clocks you can see that

More time pass on Earth

Less time pass in spaceship

So from above verses and example it is clear that time is not an
absolute quantity.

2) Length Contraction:

2) Length Contraction:

Suppose an observer in spaceship is at rest in space. The observer
measured the length of a rod

(say 1 meter), which is ℓ

space then the length measured by the observer will not be 1 meter it will be less than 1 meter, denoted

by ℓ and

given as

(say 1 meter), which is ℓ

_{0 }and called proper length. And if the observer moves with spaceship in aspace then the length measured by the observer will not be 1 meter it will be less than 1 meter, denoted

by ℓ and

given as

3) Mass Variation:

Suppose an observer in a spaceship is at rest in space. The mass of an
object meaured by the

observers m

time maesured by observer will not be 1 kg, it will be greater than 1 kg. denoted by m and

given as

observers m

_{0 }(say 1kg), called proper mass. Now, if the observer moves at high speed, then thetime maesured by observer will not be 1 kg, it will be greater than 1 kg. denoted by m and

given as

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