LIGO gravitational wave discoverers win 2017 Nobel Prize in physics
Two projects born a century ago in the mind of Albert Einstein, and the scientific leaders behind them, won the 2017 Nobel Prize in physics for detecting gravitational waves. Rainer Weiss won one half of the $1.1 million prize, while Barry C. Barish and Kip S. Thorne split the second half.
The initial detection by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in 2015 proved ripples course through and disrupt the fabric of spacetime, which can reveal “unseen worlds,” the Nobel Prize committee said.
Who are the winners: Rainer Weiss, whose 85th birthday was last Friday, is a German-born American physicist and professor emeritus at the Massachusetts Institute of Technology. In 1967, he was the first to develop the key device needed to detect gravitational waves: a laser interferometer capable of canceling out all background noise aside from that created by light particles. More on that later….
— The Nobel Prize (@NobelPrize) October 3, 2017
Theoretical astrophysicist Kip Thorne, 77, engineered a similar interferometer prototype at the California Institute of Technology in the 1970s, and his group’s designs and discoveries laid the foundation for the LIGO. Planning for the MIT/Caltech observatory began in 1980s, backed by funding from the National Science Foundation.
The NSF appointed experimental physicist Barry C. Barish, 81, as LIGO director in 1994. Over the next decade, Barish “transformed LIGO from a limited MIT/Caltech endeavour to a major international, gravitational-wave project,” Nobel Prize committee wrote. He led the construction of the two LIGO facilities — in Hanford, Washington and Livingston, Louisiana — and oversaw the installation of the project’s interferometers.
What they did: Ok, let’s talk about these interferometers. Wiess’ device was inspired by an invention in the late 1800s by physicist (and fellow Nobel Prize winner) Albert Michelson.
A Michelson interferometer is two vacuum-sealed tubes positioned in an L-shape, with a laser set positioned where the two arms meet. A beam splitter — a type of mirror — also sits directly in this corner. As its name suggests, it splits light from the laser, sending two identical beams down each arm of the interferometer. Two regular mirrors are positioned at the ends of the arms, and they reflect the light beams back toward the beam splitter.
Here’s the trick. When those two light waves return, they should be identical when they hit the final detector, unless the device’s arms been moved or interfered with. Get it? INTERFERometer.
Weiss devised an interferometer that blocked out or accounted for all types of earthly interference: seismic noise, gravitational field gradients, heat gradients, laser instabilities, on and on. The only thing left would be vibrations in the light itself that, if Einstein’s general theory of relativity could be trusted, had to be caused by cataclysmic physical shifts in spacetime (or gravitational waves). The gravitational waves literally moved one of the two interferometer arms.
The disruption behind such a shift would need to be enormous, given it is creating waves that move at the speed of light and distort the physical makeup of the universe. Hence why the initial gravitational waves spotted by LIGO came from two massive black holes — both 30 times bigger than our sun — crashing into each other near the speed of light.
Big waves require big detectors, and Weiss worked out that an interferometer would need to be miles long to catch such an event. LIGO’s interferometers have 2.5 mile-long vacuum tubes — about 144,000 times bigger than Michelson’s original instrument.
The project relied on two facilities in the U.S. separated by 3,000 miles and a third in Italy (VIRGO) because it is unlikely that interferometers located far apart would feel the same local vibrations and the same time. But they could feel the same gravitational waves at the same time, given those vibrations are much bigger; and thus, instantly confirm a reading. Since their initial discovery two years ago, three more gravitational waves have been documented.
Why it matters: On an interstellar scale, LIGO found that black holes create tsunamis in space that course across galaxies until they reach the three human-made detectors on Earth. But even you, dear reader, are creating changes in spacetime.
“If you wave your hand and move your body, it will actually change a little bit of the shape of the space around it.” That’s how Robbert Dijkgraaf, director of the Institute for Advanced Study where Einstein worked, once described gravitational waves to me.
— The Nobel Prize (@NobelPrize) October 3, 2017
The concept is somewhat awe-inspiring.On a small scale, every movement we’ve ever made has wiggled the physical Jell-o of spacetime that defines everything around us, propelling waves that stretch and squeeze space itself. Maybe one day, this knowledge will lead to hyperdrive transportation, uncover how black holes form or reveal the origins of the universe, but for now, it’s just kind of cool.