2017 Nobel-winning research on gravitational waves, LIGO and gravity explained
The discovery of gravitational waves won the 2017 Nobel Prize in physics Tuesday. The three award winners, Rainer Weiss, Barry C. Barish and Kip S. Thorne, are members of the LIGO scientific collaboration, which stands for Laser Interferometer Gravitational-Wave Observatory. They detected gravitational waves for the first time just two years ago, the echoes of a massive collision of two supermassive black holes.
When that detection was announced, The Washington Post explained why gravity is such a mysterious force and why it was so difficult to detect gravitational waves, even though they were predicted by Einstein. The explanation is republished below:
Gravity is invisible, as you may have noticed, and a little bit spooky, because it seems to reach across space to cause actions at a distance without any obvious underlying mechanism. What goes up must come down, but why that is so has never been obvious.
Physicists tell us there are four fundamental forces in the universe: gravity, electromagnetism, the strong nuclear force and the weak nuclear force. Of these, gravity is the most anemic, and yet over cosmic expanses it has shaped the universe. In our solar system, it governs the planets and moons in their orbits. On Earth, it motivates the apple to fall from the tree. You can feel it in your bones.
Aristotle believed that an object fell to Earth because it sought its natural place. Heavier objects, Aristotle believed, fell faster; weight was an inherent property of the object.
In the late 16th and early 17th centuries, Galileo brought scientific experiments into the conversation, and he discovered that a heavy object and a light object actually fall at the same speed. One biographer claimed that he proved this by dropping two spheres from the Leaning Tower of Pisa, but the story may be apocryphal. (In 1971, Apollo 15 moonwalker David Scott did his own version of the experiment, dropping a geologist’s hammer and a feather and showing that they hit the lunar surface simultaneously.)
Galileo also discovered that objects always fall with constant acceleration and along a parabolic curve. “Galileo’s observation that all falling objects trace a parabola is one of the most wonderful discoveries in all of science,” physicist Lee Smolin writes in his book “Time Reborn.”
Then came Isaac Newton. In the second half of the 17th century, he developed a universal law of gravity. He calculated that the attraction between two bodies was equal to the product of their masses divided by the square of the distance between them. This is true on Earth as well as in space. It explains the tides. It explains the motions of the planets around the sun. This is a basic law of nature, true anywhere in the universe.
But even Newton admitted that he didn’t understand the fundamental nature of this force. Newton could describe gravity mathematically, but he didn’t know how it achieved its effects.
In the early 20th century, Albert Einstein finally came up with an explanation, and it’s rather astonishing. First he grasped that gravity and acceleration are the same thing. His General Theory of Relativity, formulated in 1915, describes gravity as a consequence of the way mass curves “space-time,” the fabric of the universe. It’s all geometry. Objects in motion will move through space and time on the path of least resistance. A planet will orbit a star not because it is connected to the star by some kind of invisible tether, but because the space is warped around the star.
“Gravity, according to Einstein, is the warping of space and time,” Brian Greene wrote in his book “The Elegant Universe.”
The physicist John Wheeler had a famous saying: “Mass grips space by telling it how to curve, space grips mass by telling it how to move.”
Einstein’s great theory has been tested and retested and has always come out on top. Most famously, the British astronomer Arthur Eddington observed a solar eclipse in May 1919 and concluded that starlight passing close to the sun was, indeed, bent in a manner consistent with Einstein’s theory. Eddington’s endorsement triggered global publicity for Einstein that made him a celebrity and the personification of scientific genius.