Question

What is theory of relativity ? Can there be an example ?

Answer 1

According to the theory of relativity the laws of physics are same for all non-accelerating observers, and the speed of light within a vacuum is the same no matter the speed at which an observer travels.
Example- electromagnetism.

Answer 2

The concept of relativity goes back to the time of Galileo and is present everywhere in our every day lives.Galilean relativity says the law of motion hold in all inertial frames. An inertial frame is an imaginary set of axes attached to an object. If you take two objects, they each have their own inertial frame and if one moves relative to the other, then we say object A is moving relative to object B at whatever speed and direction.Lets say both object A and B are two glass boxes deep in space and they are moving away from each other at a constant velocity. How do we know which box is moving? We don’t… Imagine yourself sitting in box A - you are now in the same inertial frame as box A. You will see box B moving away from you at a certain speed, so you would say box B is moving away. The opposite is just as valid as if you were sitting in box B watching box A move away. Because both of these answers are valid, the laws of motion are consistent between what is viewed from box A and from box B.Lets add another box C. Let’s say we have observers in box A and B measuring the movement of box C. The observer in box A can calculate what the observer in B is seeing if A knows the relative velocity of B with respect to himself. This calculation is called a frame transformation - we account for the movement between B and A to figure out what we would see if we were sitting in box B.This is the most basic understanding of relativity. In terms of everyday use, when we look at our odometers, we make sure our relative velocity with respect to the speed camera in front of us is less than the allowed limit! When we play sport that involves balls flying through the air, we judge how fast we have to run to intercept it in time - you can probably think of many other examples.Relativity starts to get tricky when the relative velocity between box A and box B starts to increase. This is because of the unique property of light - it has the same velocity measured in all reference frames. What does this mean?If box A is stationary and box B is moving to the right (we are sitting in box C which happens to be in the same inertial frame as A), then if a ball is thrown in box B towards the right, then it makes sense to say the ball is moving away from box A faster than box B is. The velocity would be:velocity of ball away from A = the velocity of box B + the velocity of the ball in box BHowever if we shone a torch in box B and measured the speed of light, it would be the same no matter how box B is moving. Instead of velocities changing, lengths in space and time change to accommodate this. This is what special relativity deals with and there is a special factor called the Lorentz factor which is used to adjust lengths. The observed length distortions and changes in time are REAL, not an illusion or simply a mathematical construct. however special relativity at the speeds we encounter in our everyday lives has a negligible effect on us. The Lorentz factor simplifies to 1 and we recover the original equations from Galilean relativity.At an even higher level you have general relativity. I personally have not studied it, however I do know that without it, our GPS system would not work with the accuracy it has today. There is also the famous quote “Spacetime tells matter how to move; matter tells spacetime how to curve” which gives you an idea on what the theory deals with.