Northwest Arkansas Democrat-Gazette
Gravity waves detected in victory for Einstein theory
Scientists on Thursday announced the detection of gravitational waves, validating decades of effort and opening a window into outer-space phenomena such as black holes that make up some of the most turbulent elements of the universe.
“We’re hearing or seeing things that we couldn’t detect any other way,” said University of Arkansas physicist Daniel Kennefick, not a part of the discovery team but author of a 2007 book on the history of gravitational waves in science.
An international team of astrophysicists used a newly upgraded and excruciatingly sensitive $1.1 billion set of twin instruments known as the Laser Interferometer Gravitational-wave Observatory, or LIGO, to detect a gravitational wave from the crash of two black holes 1.3 billion light-years from Earth.
To make sense of the raw data, the scientists translated the wave into sound. On Thursday, they played what they called a “chirp” — the signal they heard on Sept. 14.
“It is an entirely new phenomenon of nature,
predicted by theory 100 years ago,” said Kennefick, an associate professor at UA and author of Traveling at the Speed of Thought: Einstein and the Quest for Gravitational Waves.
The waves came alive mathematically in 1915 as a result of Albert Einstein’s Theory of General Relativity, a groundbreaking work of theoretical physics that redefined gravity and opened new conceptions of the universe.
Yet Einstein vacillated as to whether gravitational waves truly existed. In basic terms, they are the ripples emanating through spacetime. The gravity of large objects warps space and time, or space-time as physicists call it, the way a bowling ball changes the shape of a trampoline as it rolls around on it.
The crash detected by LIGO involved two incredibly massive bodies and a tremendous outpouring of energy, something equivalent to an object three times more massive than the sun being converted into gravitational waves.
“It was very stormy, and we’re feeling the distant ripples,” Kennefick said.
The path to the discovery was not smooth sailing. Einstein stated it was unlikely that gravitational waves could be detected, according to Kennefick, a co-author of An Einstein Encyclopedia and a scientific editor for the Einstein Papers Project at the California Institute of Technology. Others, too, had doubts. “If you look at the history, what’s striking is even the people who were most convinced that gravitational waves existed kept emphasizing how impossible it would be that they would ever be detected,” said Kennefick.
In the 1960s, a scientist using a radio telescope first detected a neutron star, a very dense star thought to be the remnant of what was once a much more massive star. Further theoretical work advanced the idea of black holes, regions of space with a gravitational field so strong that not even light can escape.
Around this time, most scientists began to agree about the existence of gravitational waves. But that still left the problem of actually detecting them.
In 1979, the National Science Foundation decided to give money to Caltech and the MIT to come up with a way to detect the waves.
Twenty years later, scientists started building two LIGO detectors in Hanford, Wash., and Livingston, La., and they were turned on in 2001.
Each LIGO has two giant perpendicular arms more than 2 miles long. A laser beam is split and travels both arms, bouncing off mirrors to return to the arms’ intersection. Gravitational waves stretch the arms to create an incredibly tiny mismatch — smaller than a subatomic particle — in the beams’ locations. That mismatch is what LIGO detects.
As a doctoral student at Caltech in the 1990s, Kennefick joined a theoretical physics group led by Kip Thorne, earning “something of a front-row seat” to a key stage in the search for gravitational waves.
“Mere weeks after I joined the group, he arrived to our group meeting and presented us with a sheaf of papers,” recalled Kennefick. The documents laid out the milestones that would have to be reached along the way before scientists could say they had truly detected gravitational waves, Kennefick said.
“The signal would be barely bigger than the noise. If that’s the case, you really have to be sure what you’re looking for,” Kennefick said, describing Thorne as presenting “a sketch of all those things to do” in order to make LIGO work.
“In hindsight, I can realize the importance of this day,” Kennefick said.
But at the time, the task seemed very daunting, he added, praising the vision of Thorne.
“He was a great motivator. He saw a need for such a thing at a time when most people felt this is probably beyond the bounds of what was possible,” Kennefick said.
After years with no luck, scientists built a more advanced system, which was turned on last September.
“They really did have to persevere. That’s a remarkable testimony to the doggedness of the people involved, not only Kip but all of the others who made it a reality,” Kennefick said.
The new LIGO in some frequencies is three times more sensitive than the old one and is able to detect ripples at lower frequencies that the old one couldn’t. More upgrades are planned.
Bret Lehmer, an assistant professor of physics at UA, studies star systems involving a neutron star or a black hole.
“It’s giving us information about extreme types of objects,” Lehmer said of the detection of gravitational waves.
The discovery is like when scientists realized they could use not just visible light to see the stars, but also telescopes that detect infrared radiation, Lehmer said.
“In infrared, you see new aspects of things you knew existed before, so that gives you new pieces of information. This is exactly the same concept, I would say,” Lehmer said, calling it “very likely” that more observations of gravity waves will follow.
Kennefick said another gravitational wave detector is set to go on line in Italy, with another possibly to be built in India.