General relativity is the theory by Albert Einstein that many characteristics we observe about the universe depend on our frame of reference. The theory includes the observation that the speed of light in a vacuum is one of the few measureable constants that does not change depending on an observer's frame of reference.
Implications of the theory
- Objects that approach the speed of light experience some odd conditions, such as a relative slow-down in how they perceive the passage of time.
- It is impossible for anything to travel faster than light.
- Theory of Relativity at AllAboutScience.org