Albert Einstein is considered one of the greatest minds of all time due to his creation of a very large branch in present-day physics called Relativity. Relativity is a theory that consists of two other theories. The first is called Special Relativity which we’ve already gone over, and while it sounds pretty special this theory was only applicable to bodies in a constant state of motion. Which is why in 1907 Albert Einstein published his theory of General Relativity, the second of the two theories of relativity.

General Relativity, takes the theory of Special Relativity and applies it to objects that experience a change in their velocity also known as acceleration, which is something that Special Relativity does not mention. General Relativity was at first designed to combine the theory of Gravitational Mass and the theory of Inertial Mass which were basically two theories designed by Newton expressing the same concept.

Gravitational Mass is described by the equation of F = m1m2/r^2, and this theory explains how much something weighs within the gravitational field. Inertial Mass is described by the equation F = ma, and represents the amount of force needed to push an object and cause it to move. Gravitational Mass and Inertial Mass had been found to be the same thing over time. Since it made no sense to have two separate theories explaining the same phenomenon, Einstein decided to publish the theory of General Relativity.

An example Einstein used was that if a person in outer space was free falling towards earth, he or she would not feel the effects of gravity upon them as they accelerated, and if a person in an enclosed elevator that was accelerating upwards through outer space with no gravitational force, he or she would still feel gravity due to the rate they were accelerating at.

In simplest terms, imagine that you’re sitting on an airplane and it begins to take off. You feel pressure pulling you down into your seat as the airplane begins to take off. Even though the force of gravity has remained the same as to when you were on earth you feel its effect due to your acceleration through air caused by the plane, which is why it’s always important to sit in your seat as an airplane takes off in order to keep yourself from falling if you were standing up. Through this Einstein found the Principle of Equivalence which states that the effect of gravity and the effects of acceleration are equivalent to each other which is what we know today as the General Theory of Relativity.