h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Time travel occurs for all of us all the, um... time. As has been stated already, time varies inversely according to velocity. The faster you go, the slower time moves for you. So, if you run past someone, you're traveling slower in time relative to the other person. An airplane flight from, say, San Fransisco to New York, will have you arrive a few nanoseconds into the future... plus travel time, of course. This has been proven; scientists put an atomic clock in an airplane, took it for a joyride, and compared it to a ground-based one; the one in the airplane gained a couple nanoseconds on the other. So, according to this line of thought, the speed of light is the universal speed limit because if you were to exceed it you would get negative time. This also explains some subatomic phenomena, especially with electrons. The electrons of an atom move close to the speed of light, which is why their locations are shown as a "cloud" rather than set orbits... in addition, quantum tunneling could be explained because of relativistic effects. Quantum tunneling essentially is that, for example, if you were to put your hand up against a wall, your hand would go right through the wall as if it wasn't there... it's more complicated than that, but that's the general gist of it. Of course, if you were to try once a second constantly, the chances of actually doing it leaves you accomplishing it sometime in the next few billions of years...