The theory which deals with the relativity of motion and rest is called the theory of relativity. Length is relative. We can compare the length of anything we relate with something big or small. Similarly, the position is also an example of a relative. Time is relative. We can explain time is relative by the time of different places all over the world. Velocity or motion is relative. In our daily life, almost everything is relative.

**Theory of Relativity**

By the above examples, we can say that theory of relativity is it is a kind of theory which deals with the relativity of motion and rest. We can measure and analysis the different properties of different objects and their different parameter. The special theory of relativity deals with constant speed.

A body is at rest then it should be in rest and if it is at any speed then it should be moving. Newton’s law of inertia is valid for this condition. The theory is published in the name of Newtonian Relativity. In 1916 general theory of relativity was published. The general theory of relativity deals with accelerated objects. In the case of the general theory of relativity, the scientist gives an explanation of low-speed objects and the objects which rotate.

**The Frame of Reference**

There are two general frames of reference- one is an inertial frame of reference and another one is the non-inertial frame of reference. The frame of reference is a coordinate system or 3D axes with respect to time. We can write the position of an object by indicating the [x,y,z] direction in 3D axes. Now inertial frame of reference is where Newton’s law of inertia is valid. And Newton’s law of inertia is not valid for a non-inertial frame of reference. In case of the inertial frame of reference, the body is un- accelerated and in case of non-inertial frame of reference the body is always accelerated and the objects are always rotating objects. Earth is an example of a non-inertial frame of reference. Any object which is in rest is an example of the inertial frame of reference.

**Galilean Transformation Equations**

Galilean transformation equations are those equations which relate the co-ordinate of a particle or object in two different inertial frames.

Let’s consider the S frame of reference. S is a stationary frame or the frame is in rest. S’ frame is a non-stationary frame or the frame is in motion and the frame is in motion in [x] direction. The velocity of S’ frame is [V] and the velocity [V] is constant. O and O’ are observers. The two frames are an inertial frame of reference. Now consider there is point P from where a rocket is launching.

Now we have to calculate the coordinates of point P from both the observer. So we can calculate the co-ordinates by using Galilean transformation equations. Now consider the distance between O and P is [x] and the distance between O’ and P is [x’]. Let consider O’ observer start moving from the same point of O observer. So the distance between two observers is [Vt]. They start at the same time.

So the Galilean transformation equation states,

From for figure of S’ frames,

[x’=x-Vt]

[y’=y]{No motion along [y&z]axis}

[z’=z]{No motion along [y&z]axis}

[t’=t]

**FAQs about Relativity**

Q.1 What is Occam’s Razor principle?

Answer: Occam’s Razor is a principle which states that “Entities should not be multiplied unnecessarily.” The principle has used to justify the uncertainty of quantum mechanics.

Q.2: How do you consider velocities in special relativity?

Answer: Let consider a particle A is moving with a velocity [V] relative to another particle B and B particle is moving with a velocity of [U] with relative to another particle C in the same direction. So we can relate the velocity of A and the velocity of C by using the special theory of relativity. By the special theory of relativity, we can write the velocity of A relative to C is

[W= \(\frac{U+V}{1+\frac{UV}{C^{2}}}\)]

Q.3: What is gravitational radiation?

Answer: Gravitational radiation is produced when massive weights accelerate. We can accelerate any bodies to produce such type of radiation but it is impossible. Gravitational radiation generates only when massive supernovae and black holes collide with each other. These things are very much far from us. Gravitational radiations have such polarization pattern which causes different objects to expand in one direction while the objects are contracting perpendicularly.