Scientists who have spent decades peering into outer space announced Thursday they have detected gravitational waves, the ripples in spacetime that Albert Einstein long ago predicted.
“We have detected gravitational waves. We did it!” David Reitze, a physicist and executive director of the LIGO Scientific Collaboration, announced at the National Press Club in Washington, to applause.
Gravitational waves, often said to look like ripples in a pond, are able to answer questions about creation of astronomical phenomena and disturbances, such as the merging of black holes, collision of neutron stars, supernova explosions and more. Gravitational waves were discovered by physicist Albert Einstein’s general theory of relativity, 100 years ago.
All of Einstein’s theory had been proved except for the presence of gravitational waves, but that all changed Thursday.
“It’s mind-boggling,” Reitze said.
Einstein was right, said Rainer Weiss, co-founder of LIGO and a professor of physics emeritus at the Massachusetts Institute of Technology.
David Reitze, executive director of the LIGO Scientific Collaboration
“His equations have worked so well, in ways he never could have imagined,” Weiss said.
The discovery might be one of the major scientific discoveries in decades, just as important as Galileo and his telescope 400 years ago, Reitze said.
“As we open a new window into astronomy, we may see things we’ve never seen before,” Reitze said.
Reitze described how, last Sept. 14, tiny blips of a signal, a “chirp,” were detected seven milliseconds apart by the massive observatories in Louisiana and Washington state. That signal led scientists to the collision of two black holes more than a billion years ago.
The collision of two black holes caused ripples – akin to a pebble tossed into a pond – that traveled for 1.3 billion light-years until they reached Earth. It was the exact way Albert Einstein had predicted gravitational waves would be discovered.
“Up until now, we have been deaf to the universe,” Reitze said. “Today, we were able to hear for the first time.”
These black holes were each about 93 miles in diameter – roughly 50 miles wider than the width of Washington, D.C.
“Pack 30 times the mass of the sun into that, then accelerate it to about half the speed of light,” and that is just for one black hole, Reitze said.
That collision unnerved nearby stars and caused ripples that spread outward, traveling for 1.3 billion light-years, passing through stars and other objects, until they reached Earth and were detected that September day. It was the exact way Einstein had predicted that gravitational waves would be discovered.
“The gravitational waves detected agree perfectly with predictions from Einstein’s theory of relativity,” said Kip Thorne, a co-founder of LIGO and a consultant for the 2014 movie “Interstellar.”
The waves were so tiny, Reitze said, that only LIGO can measure them. “It’s like trying to measure something that is 1/10,000th the diameter of a proton.”
The researchers said they had all been in shock when they got the first reading in Louisiana, and they couldn’t be sure LIGO was reading gravitational waves, not just environmental noise, until they could examine a second reading at the other observatory.
“We know it’s real because seven milliseconds later, we saw the same (reading) in the Hanford detector,” said Gabriela González, a physicist at Lousiana State University and spokeswoman for the LIGO Scientific Collaboration. “The signals grow in frequency and amplitude and then settle down. That’s the prediction we know from solving Einstein’s theory.”
This detection also proves that binary black holes – a system of two black holes orbiting each other – can exist, Reitze said.
“This is the first time a binary black hole has been directly observed,” Reitze said.
Until now, Thorne said, scientists have seen spacetime only as if it were the surface of a calm ocean. Now, he said, they’re seeing a storm: the collision of the black holes, a 20-millisecond event that briefly generated 50 times the power of all stars in the universe put together.
LIGO can measure this astronomical storm using two 4-kilometer-long (about two and a half miles), L-shaped lasers, two mirrors and a detector. The light from the lasers bounces off a mirror to the detector. When a gravitational wave passes by, the path of the laser stretches slightly and hits the detector a little differently.
“All of this technology wasn’t available to Einstein,” Weiss said. “I bet he would’ve invented LIGO.”
And this detection is just the beginning, González said. “Now that we have detectors, now that we know it’s out there, we’ll be listening to the universe.”
At best, LIGO in its current state is at a third of its maximum sensitivity, Weiss said. “Over years, the noise level will be brought down, and LIGO will be three times better and see three times farther,” Weiss said.
Scientists all over the world are working on developing laser detectors like LIGO. Virgo, an interferometer like LIGO in Europe, is expected to be ready to join LIGO in measuring waves later this year, González said.
Researchers in Japan are working on Kagra, another interferometer, and the LIGO laboratory is working to establish another LIGO detector in India, which should be operational in 2022, according to a National Science Foundation news release.
I don’t think (LIGO) is going to bring us any closer to time travel.
Kip Thorne, co-founder of LIGO, the Laser Interferometer Gravitational-Wave Observatory
“It took a worldwide village to do this,” González said. The more interferometers there are across the world measuring gravitational waves, the easier it will be to find the black holes or other astronomical disturbances in the universe, González said. As of now, researchers have only a general idea where the black holes collided.
Despite the growing understanding of how warped spacetime behaves, Thorne said, scientists aren’t dabbling in the realm of science-fiction yet. “I don’t think (LIGO) is going to bring us any closer to time travel,” Thorne said with a chuckle. “LIGO is heading in a different direction.”
Scientists have been working on detecting gravitational waves for 40 years, largely with the support of national science grants. Reitze thanked “U.S. taxpayers and Congress, who supported this research.”
“We’re seeing our universe through new eyes in an entirely new way,” said France Córdova, National Science Foundation director. “Einstein would’ve been beaming.”
Jess Nocera: 202-383-6022, @jessmnocera
Andi Cwieka: 202-383-6033, @acwieks