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Though my imagination hates me for it, I must defend the fact that time travel is theoretically infeasible. Traveling through time would soundly defeat the principal of causality. Causality is not just an axiom of physics; it is the very basis of physics. If I push, then you fall. If the sun burns, then we receive light and heat. If the particle decays, then Schrdinger's cat dies. Even in the world of quantum mechanics, we require that the causation event occurs before the reacting event by at least t=d/c (t is time, d is distance in three dimensions, and c is the speed of light). That is to say, the geodesic between two events in a cause/effect relationship is greater than or equal to zero.

An example will show how time travel contradicts causality: Imagine a laser in a closed system focused on a phototransistor. The phototransistor, in turn, powers the laser. There are no other light sources and the phototransistor absorbs all of the laser light. Negate loss to heat and other energy loss. Causality shows that if the laser is off' then it has been and will remain off forever, and, similarly, if it is on' at any given time it will always be so. Now, allow briefly for a single photon to travel backwards in time, from the on' laser at time t=0 to strike the photo transistor at some time t<0>s Razor would still point us away from such absurd possibilities, but the data that we have the capability to take would no longer fully define the event.

Time travel can not be theoretically feasible. If a theory were to allow for time travel, it would invalidate itself, and paradoxes prevent theory from being accepted.

Learn more about this author, Craig Lawrie.
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