Muhamad Tahir's Key Ideas from Relativity: The Special and General Theory
by Albert Einstein

• Second, light travels at an unvarying speed of 186,000 miles a second. 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.

Starting from these two postulates, Einstein showed that space and time are intertwined in ways that scientists had never previously realized. Through a series of thought experiments, Einstein demonstrated that the consequences of special relativity are often counterintuitive — even startling.

Essentially, it’s a theory of gravity. The basic idea is that instead of being an invisible force that attracts objects to one another, gravity is a curving or warping of space. The more massive an object, the more it warps the space around it.

For 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. As a result, Earth and the other planets move in curved paths (orbits) around it.

Over the last century, many experiments have confirmed the validity of both special and general relativity. 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.

In 1971, scientists tested both parts of Einstein’s theory by placing precisely synchronized atomic clocks in airliners and flying them around the world. 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.

The disparity resulted from the speed of the planes (a special relativity effect) and their greater distance from the center of Earth’s gravitational field (a general relativity effect).