Time Dilation

Time Dilation

Special relativity, fully worked out by Einstein in his middle twenties, is supported by every experiment preformed too check it. Perhaps tomorrow someone will invent a theory consistent with everything else we know that circumvents paradoxes on such matters as simultaneity, avoids privileged reference frames and still permits travel faster than light. But I doubt it very much. Einstein’s prohibition against traveling faster than light may clash with our common sense. But in this question, why should we trust common sense? Why should our experience at 10 kilometers an hour constrain the laws of nature at 300, 000 kilometers per second? Relativity does set limits on what humans can ultimately do. But the universe is not required to be in perfect harmony with human ambition. Special relativity removes from our grasp one way of reaching the stars, the ship that can go faster than light. Tantalizingly, it suggests another and quite unexpected method.

Following George Gamow, let us imagine a place where the speed of light is not its true value of 300,000 kilometers per second, but something very modest: 40 km per hour, say – and strictly enforced (there are no penalties for breaking laws of Nature, because there are no crimes: Nature is self-regulating and merely arranges things that you are approaching the speed of light on a motor scooter… Relativity is rich in sentences beginning “Imagine…” Einstein called such an exercise a Gedankenexperiment, a thought experiment).

Close to the speed of light, from your point of view, the world looks very old. Image by © Megan Jorgensen (Elena)

As your speed increases, you begin to see around the corners of passing objects. While you are rigidly facing forward, things that are behind you appear within your forward field of vision. Close to the speed of light, from your point of view, the world looks very old – ultimately everything is squeezed into a tiny circular window, which stays just ahead of you. From a standpoint of a stationary, light reflected off you is reddened as you depart and blued as you return. If you travel toward the observer at almost the speed of light, you will become enveloped in an eerie chromatic radiance: your usually invisible infrared emission will be shifted to the shorter visible wavelengths. You become compressed in the direction of motion, your mass increases, and time, as you experience it, slows down, a breathtaking consequence of traveling close to the speed of light called time dilation. But from the standpoint of an observer moving with you – perhaps the scooter has a second seat – none of these effects occur.

These peculiar and at first perplexing predictions of special relativity are true in the deepest senss that anything in science is true. They depend on your relative motion. But they are real, not optical illusions. The can be demonstrated by simple mathematics, mainly first-year algebra and therefore understandable to any educated person. They are also consistent with many experiments. Very accurate clocks carried in airplanes slow down a little compared to stationary clocks.