A theory by a man called Albert Einsteins (with a crazy hairstylist)
which clearly defines :
0. E = MC^2, thats E for energy, M for mass and C for speed of light!
1. No matter can excede the speed of light
2. Speed of light is constant for all, irrespective of their motion.
3. You can not go back in time and have sex with elvis or anyone for that matter!
Some parts of the theory are still unproven practically, but only proven theorotically