A year later, scientists keep listening to gravitational waves, the soundtrack of the cosmos
L IVINGSTON, La. — The speed limit on the LIGO access road is 10 mph, which is preposterously slow, particularly after you’ve spent the last hour hurtling across the bayou country on elevated freeways. You have to creep toward the guard booth. The scientists and engineers don’t actually care how fast you drive; it’s the braking that’s the problem. Deceleration exerts a force on the road that can throw off exquisitely sensitive instruments nearby.
This is basic physics, and it’s a headache for LIGO — the Laser Interferometer Gravitational-wave Observatory.
True story: A few years back, Amber Stuver, a physicist, was sitting in the LIGO control room on a quiet day, with no seismic activity, no wind. The lasers were functioning perfectly. Suddenly, everything went haywire.
“What just happened?” Stuver asked her co-workers. “FedEx guy,” someone answered. The FedEx guy! Comes every day at 4:30 to the loading dock, impatient driver, hit the brakes too hard — and rendered deaf an instrument designed to hear gravitational waves from exploding stars and black-hole collisions billions of light-years away.
The point is that LIGO is a delicate business.
One year ago, LIGO scientists gathered in Washington to announce their historic discovery of gravitational waves — ripples through the fabric of space and time, something theorized by Albert Einstein exactly a century earlier but dismayingly elusive. The waves in that initial discovery came from the unimaginably violent merger of two black holes in a distant precinct of the universe.
Now scientists at LIGO think they’re on the verge of a string of cosmic breakthroughs, but they also havea new set of concerns, and they don’t involve the FedEx guy. The question is: What’s going to happen to science in the Age of Trump?
LIGO involves, according to its own count, 1,006 scientists from 83 different institutions in 15 nations. A number of students who work on LIGO-related research were affected by the Trump administration’s travel ban and foresee stringent immigration policies under this administration, according to LIGO’s chief spokeswoman, Gabriela Gonzalez, a physicist at nearby Louisiana State University.
This is a new scientific field, and it will benefit dramatically from observatories being built in Italy, Japan and India. The European Space Agency is also preparing a space-based gravitational-wave detector, called LISA.
Gonzalez emphasized the need for a global network of detectors. This is not a feel-good concept but a simple function of geometry. Detectors spaced far apart can triangulate the origin of a gravitational wave. This is a global project because scientists want a truly planet-sized network to sharpen their detection skills.
Because LIGO has only two detectors, both in North America, scientists have only an approximate notion of where any particular wave comes from. They can point to a general region of the sky, oblong in shape, and say it came from over thataway.
“The bigger the triangle, the better the precision,” Gonzalez said. “We need the network.”
Funding is another concern, though LIGO would seem better positioned than many other scientific endeavors, particularly climate-change and socialscience research, which are likely targets for cuts by the Trump administration and the Republican majority in Congress. Basic science research, however, has traditionally enjoyed bipartisan support.
LIGO is funded by the National Science Foundation, an independent agency of the federal government with an annual budget of about $7.5 billion. In the past two decades, NSF has spent about $1.1 billion on LIGO, which is operated by Caltech and MIT and includes a second site, the LIGO Hanford Observatory in eastern Washington.
The chairman of the House Science Committee, Lamar Smith (R-Tex.), has supported the project, according to committee spokeswoman Kristina Baum. She wrote in an email, “The Chairman’s priorities include ensuring more NSF funding is directed towards the hard sciences and groundbreaking research like gravitational waves, and less funding to frivolous or marginal projects.”
LIGO certainly meets the definition of hard science.
There’s only one stoplight in Livingston, a small town about an hour north of New Orleans. If you look closely, you’ll see a tiny sign, with an arrow, saying “LIGO.” It’s easy to miss next to the three billboards advertising a personal-injury attorney, a $5,000 reward for tips to Crime Stoppers, and “Top Dollar Paid” for gold and guns at a pawn shop.
But if you head west a couple hundred yards, and then turn north at the Fireworks Warehouse, and drive a few miles on a winding country road, you’ll eventually reach the place where the theory of gravitational waves became a reality.
LIGO is, in some ways, an incredibly
improbable enterprise because of its physical scale and esoteric scientific ambition. There is no obvious application for the knowledge gained. The cost of the project could easily have led to a kind of gravitational collapse ending in oblivion. And although it had a firm theoretical foundation — who would bet against Einstein? — it required levels of engineering never before attories tempted.
The two observative in Louisiana and Washington state had to be built in remote, seismically stable locations. The dominant feature of each facility is the pair of 2.5-mile-long beam lines,
set perpendicularly. These are tubes in which laser beams pass through an almost perfect vacuum.
“We had to correct for the curvature of the Earth,” Stuver said, standing on a bridge overlooking one of the beam line tubes as it receded into the pineywoods — timber land owned primarily by Weyerhauser. “From the corner there to the end of the arm, the Earth curves down away a little bit more than four feet.”
A reporter drove a rental car the length of the arm, with Stuver serving as narrator. The beam line is encased in heavy concrete. Stuver said that so few atoms and molecules remain in the vacuum tubes that if you could gather them all up, from the entire 2.5-mile length, and compress them to normal atmospheric pressure, they’d amount to one thimbleful of air.
Hunting stands are nearby in the woods, but they pointaway from the beam lines. The scientists met with local hunting clubs, and made a simple request: Don’t shoot the observatory.
The essential concept of LIGO is that a gravitational wave, when it passes through Livingston, will stretch one arm while contracting the other that runs at a 90-degree angle. Space itself will change dimensions. Two arms normally of identical length will suddenly be slightly mismatched. This effect, however, is smaller than the width of an atom.
That’s where the lasers come in. A laser beam is split into two beams, one for each arm. The beams travel the length of the arms and bounce off mirrors at the end. They circulate hundreds of times in the arms before finally reconverging at the corner where the arms meet.
If there’s no gravitational wave rolling through town, the wavelengths of the beams will continue to line up perfectly. But if, say, a couple of black holes have collided, and the ripple of the event passes through the Earth, the shift in the laser wavelengths can reveal the signature of that distant cataclysm.
The first big run of LIGO, from 2002 to 2010, had yielded bupkis. The observatory just wasn’t sensitive enough. But the experiment got some upgrades, and suddenly the universe became audible. At precisely 4:51 a.m. CDT on the morning of Sept. 14, 2015, the Livingston detector picked up a signal — a hum, building in intensity and ending in a chirp.
A fraction of a second later, the detector 1,865 miles away in Hanford, Wash., picked up the same signal — and in the process confirmed that gravitational waves move at the speed of light. The signal fit precisely with the theoretical models for what happens when black holes collide.
A month later, another apparent gravitational wave passed through though scientists can’t be absolutely sure it wasn’t caused by some terrestrial noise.
“I have an 87 percent confidence that this is a gravitational wave from an astrophysical source,” Stuver said. That sounds pretty good, but scientists don’t consider a 87 percent probability as very robust.
In December 2015, a third event happened, and that one passed the confidence test. Thus during a roughly four-month detection run, LIGO picked up two certain events and one possible event.
LIGO scientists were deliberate in announcing their discovery. First they had to make sure that someone had not programmed a fake signal in the detectors as a way of testing the instruments. Then they had to prepare a scientific paper with more than 1,000 co-authors. They finally booked a room at the National Press Club in Washington and flew in the pioneers of LIGO for the Feb. 11, 2016, news conference.
Here in Livingston, life changed. LIGO had been around for years, but many locals didn’t know anything about it. They may have heard about it from schoolkids who went to the facility on field trips (there is an impressive science center with exhibits on lasers, gravity and basic physics). But at the first open house after the announcement, 1,292 people showed up to see what the fuss was about.
“For the first time in my life, I saw people standing in line for a science tour as though it was a ride at an amusement park,” Stuver said.
Until LIGO came along, information about the universe came almost exclusively from wavelengths of light in the electromagnetic spectrum. That includes optical, X-ray, gamma-ray and infrared telescopes. But gravitational waves carry information, too.
“This is like Galileo turning the telescope to the sky for the very first time,” Stuver said.
At a congressional hearing last year before the House Science Committee, Rep. Smith asked a panel of LIGO leaders, “What are the practical consequences of — or, practical applications of gravitational waves?”
LIGO scientists answered by saying that the experiment has already led to technological advances in “vibration isolation” and “laser stabilization,” as well as precision timekeeping. This is also a training ground for scientists moving into other arenas.
But no one really sells LIGO on practical grounds. The main selling point: It’s knowledge for its own sake. LIGO probes the darkness, and reveals hidden and universal truths.