Einstein general theory of relativity is the best model for gravity so far, and has been confirmed in experiments and observations. According to the theory, regardless of one’s point of view (as measured by speed and direction), physical law and the speed of light are unchanged. This implies that measurements made in time and space are not absolute, but relative to your particular point of view or reference frame. General relativity led to concepts and theories such as black hole, parallel universes, worm holes, and space-time. Special relativity is Einstein’s rejection of the notion that space and time are absolute, based on the observation that the speed of light is independent of the motion of an observer. No matter how fast someone runs toward you with a flashlight, the speed of the light that flashlight emits will always remain the same. From this foundation, Einstein constructed a revolutionary model of gravity and a universe full of unexpected surprises like black hole, gravity waves, time dilation, and the equivalence of mass and energy: E=Mc^2. Astronomers and astrophysicists regularly use the theoretical tools of special relativity to interpret and analyze light.