Twin's Paradox

Ever feel like time moves really quickly or really slowly? Like how the hours fly by when you're hanging out with your best friend or how seconds drag on endlessly when you're stuck inside on a rainy day. But you can't really slow time down or speed it up, right? It always flows at the same rate.

Einstein didn't think so. His idea was that the closer we came to traveling at the speed of light, the more time would slow down for us relative to someone not moving. He called the slowing of time due to motion, time dilation.

No way, you say? Well, imagine this. You're standing on Earth holding a clock. Your best friend is in a rocket zooming past you at 250,000 km per second (lucky friend!). Your friend is also holding a clock. If you could see your friend's clock, you'd notice that it seems to be moving a lot more slowly than yours. Your friend, on the other hand, thinks the clock in the rocket is moving just fine, and it's your clock that seems to be moving more slowly. Still sounds confusing? Well, remember it took Einstein years to figure this out, and he was considered a genius.

Einstein came up with an example to show the effects of time dilation which he called the "twin paradox." It's a lot like the Time Traveler game. Let's try it out with a pair of pretend twins, Eyne and Stine, both of whom are 10 years old in their pretend universe.

Eyne decides she has had enough of Earth and needs a vacation. She's heard great things about rock resorts in the Alpha-3 star system, which is 25 light years away (a light year is the distance light travels in a year). Stine, who has a math test next week, must stay at home to study. So Eyne sets out on her own. Wanting to get there as quickly as possible, she decides to travel at 99.99 percent of the speed of light. The trip to the star and back takes just over 50 years. What happens when Eyne returns? Stine is now 60 years old, but Eyne is only ten and a half! How can this be? Eyne was away for fifty years but only aged by half a year!

Hey, has Eyne just discovered the fountain of youth?

Einstein's idea about time slowing down sounds fine and all in theory, but how can you be sure he's right? One way would be to hop in a rocket and travel near the speed of light. Yet, so far, everything we know about physics says we can't do that. There are other ways, however, to put his ideas to the test.

How do we know Einstein had it right? This experiment might "shed some light" on his idea!

Atomic clocks are very accurate clocks that can measure tiny amounts of time —billionths of a second. In 1971, scientists used these clocks to test out Einstein's ideas. One atomic clock was set on the ground and another was sent around the world on a jet traveling at 966 km per hour (600 mph). At the start both clocks showed the same time.

What happened when the clock flown around the world returned to the spot where the other clock was? As Einstein predicted, the clocks no longer showed the same time —the clock on the jet was behind by a few billionths of a second! Why such a small difference, you ask? Good question! Well, 966 km per hour is fast but no where near the speed of light. To see any significant differences in time, you'd have to be traveling a whole lot faster.


Source: Nova Online∞
See also: Twin's Paradox∞, AlbertEinstein

CategoryScience