![]() ![]() A check of the timepieces after the planes landed showed that the clocks aboard the airliners were running a tiny bit slower than (less than one millionth of a second) than the clocks on the ground. In 1971, scientists tested both parts of Einstein’s theory by placing precisely synchronized atomic clocks in airliners and flying them around the world. In the first major test of general relativity, astronomers in 1919 measured the deflection of light from distant stars as the starlight passed by our sun, proving that gravity does, in fact, distort or curve space. Over the last century, many experiments have confirmed the validity of both special and general relativity. Its “field equations” describe the relationship between mass and the curvature of space and dilation of time, and are typically taught in graduate-level university physics courses. The equations involve nothing more complicated than high-school math. Special relativity is ultimately a set of equations that relate the way things look in one frame of reference to how they look in another - the stretching of time and space, and the increase in mass. What does relativity look like 'under the hood?' ![]() Subsequent experiments proved that this indeed happens. If your friend climbs to the top of a mountain, you’ll see his clock ticking faster compared to yours another friend, at the bottom of a valley, will have a slower-ticking clock, because of the difference in the strength of gravity at each place. But just as gravity can stretch or warp space, it can also dilate time. We tend to think of time as ticking away at a steady rate. This warping also affects measurements of time. As a result, Earth and the other planets move in curved paths (orbits) around it. Mach The 7 biggest unanswered questions in physicsįor example, the sun is massive enough to warp space across our solar system - a bit like the way a heavy ball resting on a rubber sheet warps the sheet. If you’re zooming along in a rocket and pass a friend in an identical but slower-moving rocket, for example, you’ll see that your friend’s watch is ticking along more slowly than yours (physicists call this "time dilation"). A page of the original manuscripts of the theory of relativity developed by Albert Einstein on display at the Israeli National Academy of Science and Humanities in Jerusalem on March 7, 2010. ![]() Through a series of thought experiments, Einstein demonstrated that the consequences of special relativity are often counterintuitive - even startling. ![]() Starting from these two postulates, Einstein showed that space and time are intertwined in ways that scientists had never previously realized. No matter how fast an observer is moving or how fast a light-emitting object is moving, a measurement of the speed of light always yields the same result. Second, light travels at an unvarying speed of 186,000 miles a second.Einstein recognized that if the motion is perfectly uniform, it's literally impossible to tell - and identified this as a central principle of physics. It’s a bit like when you look out a train window and see an adjacent train appear to move - but is it moving, or are you? It can be hard to tell. As long as an object is moving in a straight line at a constant speed (that is, with no acceleration), the laws of physics are the same for everyone. First, the natural world allows no “privileged” frames of reference. ![]()
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