Explain Einstein's theory of relativity in layman's terms I want to know about this interesting theory, but I am not a physics professor or scientist. I am just a high-school student. Please explain the theory of relativity keeping this in mind. Don't involve too much mathematics.
 A: This is a really long theory, so in a few words:
Special Relativity:


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*laws of physics are invariant under all inertial reference frames (non accelerating)

*speed of light in vacuum is the same for all observers regardless of the motion of the light source
A very good example is the twin paradox, which if you understand, you will understand SR. Basically it will explain you why a twin who is traveling on a spaceship will age slower then the twin on Earth because the moving spaceship (close to speed of light) will cause that twin's clock to tick slower (then the on on Earth).
General Relativity:
Is the current description of gravity. It generalizes SR and Newton's gravity, providing a unified description of gravity as a property of spacetime.
The twin paradox can be explained even better in GR, because of the gravitational field or acceleration/deceleration (that the spaceship goes through at the returning point) will cause the traveling twin's clock tick slower.
A very good example is the Shappiro delay. It will basically tell you how stress-energy will bend spacetime and how that will make us (from Earth) see light travel slower then c next to the Sun.
