The silence is unnerving. Not another car in sight as I drive through the desolate Hanford nuclear area. The road unfolds in an eerie lacework of tarred concrete until finally I see it gleaming in the distance—the Laser Interferometer Gravitational Wave Observatory (LIGO.)
LIGO is home to Earth’s most sensitive optical instrument, uniquely designed to intercept gravity waves. These elusive cosmic waves—or ripples in space-time—are so miniscule that Einstein thought them impossible to view and measure. And so far, he’s been right. Yet if detected, gravitational waves could transform our fundamental understanding of the universe.
They also, incidentally, play a starring role in the hit film Interstellar—a science fiction thriller replete with black holes, time travel, and ultimately, the quest to harness gravity.
A bit of that movie magic imbues LIGO, which was cofounded in 1983 by theoretical physicist Kip Thorne. Thorne wrote the initial story concept for Interstellar and was also an executive producer on the film. At LIGO, Thorne and other descendants of the Einstein legacy are pushing science to extreme limits. Here astrophysicists fine-tune the newly updated instrument for its maiden run, confident of spotting gravity waves 250 million light years into their galactic journey.
I pull into the LIGO parking lot and step out into bleaching sunlight. To the west, I catch a glimpse of the L-shaped interferometer whose concrete arms stretch two and a half miles into the distance. Fred Raab ushers me into the air-conditioned main office.
Raab is head of LIGO Hanford and an adjunct professor in astronomy and physics at Washington State University. He is also a member of the WSU Relativity Group led by physics professor Sukanta Bose.
Thorne personally recruited Raab in 1988 to help build LIGO, which is funded by the National Science Foundation and operated by the California Institute of Technology and Massachusetts Institute of Technology. Raab was handed the reins in 1994.
“I’ve spent the last 25 years focused on designing and inventing technologies to get the first gravity wave detection,” says Raab. “I knew it would take a long time.”
The concept of gravitational waves originated with Einstein’s general theory of relativity in 1915. Among other things, his hypothesis states that space and time are linked, creating a type of “fabric” comprising our universe.
Like bowling balls on a trampoline, the sun and other massive celestial bodies stretch this space-time fabric. As smaller objects pass by, they follow the curving fabric downward in what we know as gravity. Planets, moons, and asteroids become trapped in these gravitational channels and orbit like little balls in a roulette wheel.
A catastrophic event can also shake space-time fabric into generating “gravity waves.” The violent forces of a supernova or the formation of a black hole can flip the fabric like a sheet causing waves to flow out in ripples. These waves then travel the universe at lightspeed for eons before gradually losing intensity.
In 2000, Initial LIGO was launched to try to observe these ripples. Although it failed to detect a gravitational wave, Raab says they have since updated and improved the instrument’s sensitivity and call it Advanced LIGO. The inaugural run began with high hopes in September.
Thorne had intended that Initial LIGO detect the gravitational anomalies prompting Interstellar’s adventures. Director Christopher Nolan eventually cut the Hanford scene but still permitted gravity, with its ability to travel back and forth in time, to claim the spotlight.
Raab leads me to a bridge overlooking LIGO’s long, pipe-like arms. He points out the corner station, which houses the interferometer.
During the instrument’s operation, a laser beam is split, directing light down giant vacuum tubes in each arm. The light is reflected back to a detector by polished mirrors delicately suspended on wires. Since the two arms are identical in length, light naturally cancels out at the detector.
Should a gravity wave pass by, relativity says it will cause space to stretch and squeeze making one arm appear momentarily longer and the other shorter. Then the pattern reverses. In this case, laser light reaches the detector, signaling a possible hit.
A duplicate LIGO observatory is also listening in rural Louisiana. If both instruments detect the same signal, it confirms the discovery.
“These are the most radically sensitive machines in the world,” says Raab. “They are at our limit of knowledge and extremely complex. We are looking for a circle of space with a two and a half mile radius to go out of round about one-billionth the size of an atom.”
“We are controlling noise—or vibration—to a ridiculous precision,” he says. “Like a large orchestra, there are 350 high-performance servo-control systems all working together in perfect harmony.”
Although LIGO observatories are built in remote rural areas, vibrations from volcanoes, earthquakes, wind, traffic, logging, and even ocean waves thousands of miles away can skew the instrument’s readings.
Just walking near the instrument can be disturbing. Vehicles are therefore banned. Bright yellow delivery tricycles shuttle supplies into the corner station. Garbage is dutifully pedaled back out.
Gregory Mendell, LIGO senior scientist and WSU adjunct professor, says it’s likely the first detection will come from the “coalescence” of a double neutron star formed perhaps 250 million years ago. Coalescence occurs long after supernova when a pair of dying stars spiral, crash, and merge, releasing gigantic gravity waves—large enough to make the trip to LIGO.
Radio telescopes have detected similar moments of destruction, which are audible as a descending ring ending in a chirp. Mendell calls these star sounds cosmic bells, and says the discovery of gravitational waves will add song, melody, and rhythm to our comparatively muffled sense of the cosmos.
LIGO scientists say they can’t wait. Everything we know about the universe is based on observations made with electromagnetic waves—light, radio, x-rays, gamma rays. Gravitational waves are altogether different, promising breakthroughs in a wide range of areas including nuclear matter, quantum mechanics, and relativity.
If all goes well, history may place LIGO alongside the first telescope and microscope, says Raab—celebrated as the “primitive” instrument that laid bare mysteries of time, space, and gravity.
On the web
The hunt for Albert Einstein’s missing waves (article and video on Advanced Virgo, the European group searching for gravitational waves; BBC News, Nov. 25, 2015)