Special Relativity: Time is relative to the observer. The faster you go, the more your mass increases, and time slows down. In order to reach the speed of light, your mass must be infinite, which is impossible.

General Relativity: Time and space are actually one combined fabric. Gravity is just a by-product of the fact that the larger a mass is, the more it presses down on the space-time fabric.

G.R. also bends objects as they travel near large masses, such as light bending around a planet and changing course

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