Relatively Simple: Explaining the Theory of General Relativity
Published in 1916, Einstein’s Theory of General Relativity is one of the towering accomplishments of 20th-century physics, completely changing our picture of the universe. While formulating his theory of special relativity, Einstein found that space and time are one and the same thing—they’re woven together into a single fabric called space-time. Everything that happens in the universe affects space-time, and space-time affects everything in the universe. Matter is embedded within this fabric, and so it warps, bends and distorts the space-time. Imagine setting a basketball on a trampoline—its mass will make a dent in the springy sheet. If you then rolled a marble around the basketball, the dent would cause the marble to spiral inwards towards the larger ball, much the same way as the gravity of the sun pulls at the Earth—like the basketball, the sun curves and warps the space around it. Newton postulates that smaller masses travel towards larger ones because of a force of attraction between them, but Einstein theorises that actually, massive objects cause a distortion in space-time, which is felt as gravitational influence. It’s a cool thought—that matter makes space-time stretch and warp, forming mountains and valleys that create ‘paths’ for objects to move through. The planets travelling around the sun are simply following the curvature of space-time. As theoretical physicist John Archibald Wheeler said, “Matter tells space-time how to curve, and curved space tells matter how to move.” Although we can’t actually see or measure space-time, it’s been confirmed by observing phenomena like gravitation lensing, which is the way light bends around massive objects such as black holes because of the warped space-time around them. Newton wasn’t wrong—matter is the source of gravity, and his equations still hold up most of the time—Einstein just delved further into how and why gravity exists.
(Image Credit: Wonders of the Universe)