Subtle cosmic ripples kicked up by amazingly distant black holes have captured the public imagination. They also have grabbed the appreciation of a committee that evaluates Nobel Prize candidates. Today it announced the physics award would go to three Americans who laid the groundwork for the first direct detection of gravitational waves.
Rainer Weiss works at the Massachusetts Institute of Technology in Cambridge. Kip Thorne and Barry Barish work at the California Institute of Technology in Pasadena. Together, they will share the 9 million Swedish kronor (about $1.1 million) prize. Half will go to Weiss. Thorne and Barish will split the rest.
Researchers often wait decades before the Nobel committee recognizes their achievements. Not these three pioneers of LIGO. (That’s short for the Laser Interferometer Gravitational-Wave Observatory.) Not quite 20 months ago — on February 11, 2016 — LIGO announced the long-sought first detection of gravity waves. These particular ripples in spacetime had been generated by a pair of merging black holes.
The observation was the result of intense efforts by legions of scientists. It came a century after Albert Einstein had predicted such waves should exist. The frenzy of excitement that the waves generated captured front-page headlines around the world. Their confirmation was so monumental that the guiding team of physicists were honored almost immediately with a Nobel.
Indeed, says Clifford Will, “These detections were so compelling and Earth-shattering… Why wait?” Will is a physicist at the University of Florida in Gainesville and was not directly involved with the discovery. He said of the trio’s Nobel Prize today: “It’s fabulous. Absolutely fabulous.”
LIGO is an example of expensive, risky — but potentially revolutionary — science. “Gravitational waves contain information about their explosive origins and the nature of gravity that cannot be obtained from other astronomical signals,” France Córdova said in a statement. Córdova is the director of the National Science Foundation, a government agency that has invested some $1.1 billion into developing LIGO’s sensitive instruments. And now science is seeing a great payoff, she adds. LIGO’s observations “have created the new field of gravitational wave astronomy.”
Watching the arms of LIGO
LIGO was developed, in part, to test a prediction of Einstein’s general theory of relativity. Einstein had argued that rapidly accelerating massive objects would stretch and squeeze spacetime. This action should set in motion ripples that would move outward from the source. Despite looking for these waves for the better part of a century, none appeared — until last year.
“If Einstein was still alive, it would be absolutely wonderful to go to him and tell him about the discovery. He would be very pleased, I’m sure of it,” Weiss said at a news conference at MIT a few hours after he got word of the win. “But then to tell him what the discovery was, that it was a black hole, he would have been absolutely flabbergasted.”
An enthusiastic group of team members clad in LIGO-themed T-shirts gave the news conference celebrating the award a party-like atmosphere. There, Weiss stressed that the discovery was a group effort. “I’m a symbol of that. It’s not all on my shoulders, this thing,” he said. He then cited the large collaboration of scientists whose work led up to LIGO’s detection.
Scientists now hope to begin surveying the universe in a new way, by feeling for oh-so-subtle ripples in spacetime. Doing so “will allow us to see the parts of the universe that were not revealed to us before,” says Carlos Lousto. A LIGO team member, he works at the Rochester Institute of Technology in New York.
LIGO officially began collecting data in 2002. It ran on and off until 2010. Throughout, it turned up no hints of gravitational waves. So scientists designed a host of upgrades to make it more sensitive. The souped-up system is now known as Advanced LIGO. It began searching for spacetime ripples in 2015. Almost at once, scientists detected super-tiny ripples. They pointed to a black-hole collision. Those ripples, spotted on September 14, 2015, had journeyed to Earth from 1.3 billion light-years away. There, two colossal black holes had spiraled inward toward one another. Eventually they merged into one.
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Quivers from those converging black holes were converted into an audio signal. They made a tell-tale "chirp." It sounded a bit like a bird's cry. The particulars of that signature reveal details of the collision. “The beauty of the symphony is in what you can extract from the tiny wiggles, or the wiggles on tops of wiggles, in that signal,” Thorne said today at a news conference at Caltech.
Since that first detection, LIGO scientists have observed three additional black-hole collisions. Additional gravitational ripples may already be in the bag: There are rumors that LIGO scientists have detected a smashup of neutron stars. Weiss hinted that another announcement is planned for October 16.
LIGO consists of two enormous L-shaped detectors. One stretches across the wooded landscape of Livingston, La. The other sprawls across a desert in Hanford, Wash. Each has two 4-kilometer- (2.5-mile-) long arms. A laser’s light bounces back and forth between mirrors at the elbow of LIGO’s L-shape and the ends of the arms that project out from it.
Gravity waves passing through a detector will stretch one arm very slightly. At the same time, they will shorten the other. LIGO compares the arms’ lengths using the laser light. It can detect differences in length that are smaller than the size of a proton.
“LIGO is probably one of the best and most amazing instruments ever built by mankind,” Barish said at the Caltech news conference. But building it was a risky endeavor. No one had previously attempted anything like it. And no one could say for sure whether the effort would succeed. “What’s fundamental is you have to be willing to take risks to do great things,” Barish said.
In August 2017, both LIGO detectors teamed up with a similarly designed Virgo detector near Pisa, Italy. The latest sighting of a spacetime ripple was made seven weeks ago. It showed up in all three detectors. This allowed scientists to pinpoint more precisely than ever the site of a pair of colliding black holes.
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Getting to LIGO
In the 1960s, Weiss came up with the idea for a laser gravitational-wave detector. It was while he was teaching a class on general relativity. (Other researchers had independently proposed the technique as well.) The work began with some scribbles on scraps of paper. It eventually moved on to early prototypes.
Thorne became inspired by a conversation with Weiss. He assembled a team to work on the technique at Caltech in the ’70s. (Thorne, by the way, was a 1958 semifinalist in the Science Talent Search. It’s a program of Society for Science & the Public, which publishes Science News for Students.)
Ronald Drever, another LIGO founder, died in March. In the ’70s, he had been working on gravitational-wave detectors at the University of Glasgow in Scotland. Eventually, Drever joined Thorne at Caltech in 1979. Weiss and Drever each worked individually on prototypes. Then Weiss officially teamed up with Thorne and Drever in 1984 to create the initial LIGO device. Drever did live to hear of the first detection, Will says. Still, the Florida researcher adds, “It’s sad that he didn’t live to see it all.”
Barish joined the project later. In 1994, he became director of LIGO. He stayed on in that role for more than 10 years. Over that time, he elevated LIGO from scientists’ daydreams into reality. Barish oversaw the building of the LIGO detectors as well as their first searches for gravity waves. “He entered the experiment in a crucial moment,” notes Alessandra Buonanno. She is a LIGO team member and works at the Max Planck Institute for Gravitational Physics in Potsdam, Germany. This was a time “when it was necessary to bring the experiment to a different level, make it a big collaboration,” she says.
Speculation that LIGO would nab a Nobel began as soon as the first discovery was announced last year. “We were certainly expecting this,” says LIGO team member Manuela Campanelli. She works at the Rochester Institute of Technology.
But expecting it didn’t make the win any less sweet. “I feel in a dream,” says Buonanno.
LIGO and Virgo are currently in a shutdown period. Scientists are tinkering with the detectors to further improve their sensitivity. The hunt for ripples in spacetime will resume next year. Besides black-hole mergers and neutron-star smashups, scientists might one day also spot waves from an exploding star, known as a supernova. Future generations of these detectors might even sense trembles generated in the Big Bang. That would provide a glimpse of the universe’s beginnings.
Scientists might even turn up phenomena that have not yet been predicted. “I await expectantly some huge surprises in the coming years,” Thorne says.
astronomy The area of science that deals with celestial objects, space and the physical universe. People who work in this field are called astronomers.
Big Bang The rapid expansion of dense matter that, according to current theory, marked the origin of the universe. It is supported by physics’ current understanding of the composition and structure of the universe.
black hole A region of space having a gravitational field so intense that no matter or radiation (including light) can escape.
cosmic An adjective that refers to the cosmos — the universe and everything within it.
field An area of study, as in: Her field of research was biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory.
gravity The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
laser A device that generates an intense beam of coherent light of a single color. Lasers are used in drilling and cutting, alignment and guidance, in data storage and in surgery.
light-year The distance light travels in one year, about 9.48 trillion kilometers (almost 6 trillion miles). To get some idea of this length, imagine a rope long enough to wrap around the Earth. It would be a little over 40,000 kilometers (24,900 miles) long. Lay it out straight. Now lay another 236 million more that are the same length, end-to-end, right after the first. The total distance they now span would equal one light-year.
LIGO (short for Laser Interferometer Gravitational wave Observatory ) A system of two detectors, separated at a great geographical distance, that are used to register the presence of passing gravitational waves.
neutron star The very dense corpse of what had once been a star with a mass four to eight times that of our sun. As the star died in a supernova explosion, its outer layers shot out into space. Its core then collapsed under its intense gravity, causing protons and electrons in its atoms to fuse into neutrons (hence the star’s name). Astronomers believe neutron stars form when large stars undergo a supernova but aren’t massive enough to form a black hole. A single teaspoonful of a neutron star, on Earth, would weigh a billion tons.
Nobel Prize A prestigious award named after Alfred Nobel. Best known as the inventor of dynamite, Nobel was a wealthy man when he died on December 10, 1896. In his will, Nobel left much of his fortune to create prizes to those who have done their best for humanity in the fields of physics, chemistry, physiology or medicine, literature and peace. Winners receive a medal and large cash award.
physics The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in such areas is known as a physicist.
proton A subatomic particle that is one of the basic building blocks of the atoms that make up matter. Protons belong to the family of particles known as hadrons.
prototype A first or early model of some device, system or product that still needs to be perfected.
relativity (in physics) A theory developed by physicist Albert Einstein showing that neither space nor time are constant, but instead affected by one’s velocity and the mass of things in your vicinity.
Science Talent Search An annual competition created and run by Society for Science & the Public. Begun in 1942, this event brings 40 research-oriented high school seniors to Washington, D.C. each year to showcase their research to the public and to compete for awards. Since spring 2016, this competition has been sponsored by Regeneron Pharmaceuticals.
spacetime A term made essential by Einstein’s theory of relativity, it describes a designation for some spot given in terms of its three-dimensional coordinates in space, along with a fourth coordinate corresponding to time.
star The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
subtle Some feature that may be important, but can be hard to see or describe. For instance, the first cellular changes that signal the start of a cancer may be visible but subtle — small and hard to distinguish from nearby healthy tissues.
supernova (plural: supernovae or supernovas) A massive star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass.
technology The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.
theory (in science) A description of some aspect of the natural world based on extensive observations, tests and reason. A theory can also be a way of organizing a broad body of knowledge that applies in a broad range of circumstances to explain what will happen. Unlike the common definition of theory, a theory in science is not just a hunch. Ideas or conclusions that are based on a theory — and not yet on firm data or observations — are referred to as theoretical. Scientists who use mathematics and/or existing data to project what might happen in new situations are known as theorists.
universe The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).
wave A disturbance or variation that travels through space and matter in a regular, oscillating fashion.
Journal: The LIGO Scientific Collaboration and the Virgo Collaboration. Observation of gravitational waves from a binary black hole merger. Physical Review Letters. Vol. 116, February 11, 2016, p. 061102. doi: 10.1103/PhysRevLett.116.061102.
Journal: The LIGO Scientific Collaboration and the Virgo Collaboration. GW151226: Observation of Gravitational Waves from a 22-Solar-mass Binary Black Hole Coalescence. Physical Review Letters. Vol 116, June 15, 2016, p. 241103. doi: 10.1103/PhysRevLett.116.241103.
Website: The Nobel Prize in Physics 2017. Nobelprize.org, October 3, 2017.