Theory of relativity

Theory of Relativity


1. Introduction


The theory of relativity was proposed by Albert Einstein in the early 20th century.
It revolutionized physics by changing our understanding of space, time, motion, and
gravity.


Two parts:


Special Theory of Relativity (1905)


General Theory of Relativity (1915)




2. Special Theory of Relativity (STR)


Postulates of STR


1. Principle of Relativity – The laws of physics are the same in all inertial frames of
reference (frames moving at constant velocity).



2. Constancy of Speed of Light – The speed of light in vacuum is the same for all
observers, regardless of the motion of the source or the observer.




Consequences of STR

, (a) Time Dilation


Moving clocks tick slower compared to stationary clocks.


Formula:


t' = t / √(1 - v²/c²)
t = proper time


v = velocity of moving frame


c = speed of light



Example: An astronaut traveling close to will age slower compared to people on Earth.




(b) Length Contraction


Objects moving close to the speed of light appear shorter in the direction of motion.


Formula:



L' = L √(1 - v²/c²)




(c) Relativity of Simultaneity


Two events that appear simultaneous in one frame may not be simultaneous in
another moving frame.