Travel At The Speed Of Light?

By MICHAEL D. LEMONICK

It would be terribly convenient to circumnavigate the earth in a fraction of a second, to make a round trip to the sun in just over a quarter of an hour, to go to Neptune and back in a workday. Modern life is too busy to waste time getting from here to there, and flitting around at the speed of light--about 186,000 miles per second--would take a lot of the drudgery out of travel.

Forget it, though. You'll never go that fast. Albert Einstein said so. His special theory of relativity had at its heart an astonishing claim: the speed of light in a vacuum is always the same, for all observers. Shine a flashlight out into space and the light goes at 186,000 m.p.s. Jump into a spaceship and chase the beam at 185,000 m.p.s. and it recedes from you not at 1,000 m.p.s. but at 186,000 m.p.s. If you head in the opposite direction at 185,000 m.p.s., the light beam still moves away at...you guessed it.

This strange idea leads to even stranger consequences, including the fact that as an object goes faster, its mass increases (the reasons are dizzyingly complex, but it's been verified in particle accelerators). The faster you go, the harder it is to get yourself going faster still. As you near the speed of light, your weight heads for infinity, which makes it infinitely hard to go faster. So while we might reach 99% of light-speed, or even 99.99999%, the last little bit will forever lie just beyond our grasp.

--By Michael D. Lemonick