Relativity Still Holds Up: 5 Recent Tests That Prove Einstein Right
Nearly a hundred years after it was first published, Einstein's theory of relativity has held up to rigorous scientific testing. And the tests keep coming. Here are five recent tests of theory. Yes, it still holds up.
Time Dilation
The latest test of Einstein's theory of relativity, published in September 2010 in Science, looks specifically at time dilation, a piece of the theory that predicts that two identical clocks resting at different heights or moving at different speeds will tick at different rates. Time dilation is most commonly thought of in terms of the twin paradox: If one twin goes asteroid-hopping on a rocket moving at extremely high speeds, he'll have aged less than his earthbound sibling when he gets home. Now, however, physicist Chin-Wen Chou and his colleagues at the National Institute of Standards and Technology have shown that time dilation can be observed even without a far-flung, fast-moving trip.
How It Was Tested
Using super-sensitive optical clocks, they measured changes in the clocks' tick rates at speeds of less than 25 miles per hour and at differences in altitude of about a foot. The optical clocks, each powered by a single aluminum ion, are nearly 40 times as accurate as the international-standard cesium-powered atomic clocks, giving researchers the ability to look at minute differences in tick rates. Sitting still at the same height, the clocks had the same tick rate. To move one clock, the researchers simply started one of the ions oscillating at a speed of their choosing. "It can be as slow as you sitting on a swing, swinging back and forth, or as fast as a bullet train," Chou says. When he set the ion moving at 10 meters per second (a little under 25 miles per hour), Chou found that that clock ticked at a measurably slower rate than the stationary clock. The same thing happened when the clocks were at slightly different heights. When Chou and his team used hydraulic jacks to lift one clock just over a foot, the lower clock's tick rate was ever-so-slightly lower than that of the higher clock. Because optical clocks allowed them to measure carefully enough, the researchers could see that Einstein's predictions played out even in everyday circumstances like the height of a footstool and the speed of a car on a residential street.
