Emerald Robinson: Hi, I am Emerald Robinson and in this What is? video we are going to discuss one of science's most famous theories; Albert Einstein's theory of relativity.
The theory of relativity has two parts; special relativity and general relativity. Special relativity states that the laws of physics apply no matter how fast you are moving. For example, the same rules of gravity applied to a brick tossed out of a moving airplane as to one dropped off a building.
Einstein applied this principle to light, stating that the speed of light represented by c is constant. Light always travels at the same speed for all observers no matter how fast you are moving, or how fast the source of the light is moving. The light that comes from a car's headlights always moves at the same speed whether the car is parked or moving at 65 miles an hour.
The theory of special relativity changed the ways scientists thought about time. Until Einstein's theory it was thought that everyone experienced time the same way. Special relativity determined that the rate at which time passes to you depends on your speed, the faster you are moving the slower that time passes.
Special relativity is also the place where one of world's most famous mathematical formulas comes from e=mc2. In this equation e stands for energy, m represents mass and c is the speed of light. In other words energy and mass are equivalent; one can't exist without the other.
Based on the theory of special relativity, Einstein became convinced that space and time are not separate. General relativity is a theory that gravity is caused by bending time and space. It's been used to explain how light bends around objects in space, like the light we see during a solar eclipse.