In 2000, Betsy Weaver got hooked on a vision of things unseen.
As a student at Washington State University, Weaver’s physics program was visited by a group of scientists who lectured on the search into deep, deep, deep outer space. They spoke of phenomena mapped out by Albert Einstein, but so far undetected by humankind. Among these concepts, one stood out: Gravity waves.
Einstein’s math says they exist. Today’s astrophysicists agree. Gravity waves are transmitted from black holes and colliding neutron stars, neither of which has ever “seen” for real. Their existence could open the door to a new way of studying space, beyond optical and radio astronomy, because they can punch through astronomical obstacles that block light, noise and electro-magnetic waves.
Years later, Weaver still reflects on the visit as “fascinating.” So much so, that the encounter changed how she’s spent her life since. Upon graduating as a physicist, Weaver has spent the last 15 years in the dry, brown sagebrush of the Hanford nuclear reservation, designing and building equipment to explore the universe in ways most people don’t know exists.
Weaver, 38, is a detection engineer for the Laser interferometer Gravitational Wave observatory (LIGO), part of a worldwide effort to design the largest “microphone” mankind has ever built. And in coming months, her research will turn a corner, entering a new phase that’s been a century in the making.
The Laser Interferometer Gravitational Wave Observatory in Hanford.
The LIGO “microphone” refers to a network of lasers, super mirrors, vacuums and the most sensitive electronic sensors in existence. It’s a huge piece of machinery in the desert, with two horizontal “legs” each about two and a half miles long. Its purpose at Hanford is to catch gravity waves like a microphone catches sound waves, in partnership with its sister observatory in Livingston, Louisiana. Multiple LIGOs must work in tandem, as a potential gravity wave detected by only one would essentially be unconfirmed.
Starting in 2000, the two observatories searched the universe together, hunting for waves many light years away. This ended in 2010, when they both shut down for a massive five-year upgrade.
The scientists pushed the LIGOs’ equipment as far as it could go in the decade of operation, with faint hopes of actually finding a real gravity wave. Their initial goal was to make sure the equipment could be built and the concepts would work.
But 20th century technology could not give the physicists the 660-million-light-year range that 21st-century technology could. By 2010, equipment had advanced enough to catch up to the scientists’ wishes, and they began replacing almost everything within the LIGOs.
Five years, $250 million in federal money, and $30 million in foreign investment later, the upgrades are nearly complete. The Hansen LIGO will begin an initial three month test of its equipment in August, before launching its first coordinated hunt with Louisiana’s LIGO in 2016.
An aerial view of the Hanford LIGO.
Once the pair of LIGOS are searching together again, they can still take years to detect a gravity wave. Nonetheless, there is a palpable sense of excitement among staff to get started on this new phase of their research.
“To do something hard like this, you have to have a sense of postponed pleasure. It is what you signed up for,” said Fred Raab, a physicist from Cal Tech who has been with the project since it was only an idea in the 1980s. Cal Tech and the Massachusetts Institute of Technology are partners in the operation of the Hanford and Louisiana LIGOs.
“I think we’re out of woods in going home empty-handed in 10 years,” Weaver said of the revamped LIGO. A finish line is in sight.
The search for gravity waves is, in a sense, a hunt for black holes.
This holds different areas of fascination for Raab and Weaver. Raab is deep into the astrophysical hunt, searching for these cosmic voids, neutron stars and the secrets of the universe. In conversation, he’s the type who can casually work in references to anti-matter, and a theory that gravity can be siphoned off into an extra dimension. Weaver is a technology aficionado. To her, the thrill is inventing, fixing things, and tweaking LIGO’s new measurement equipment to perform feats never before accomplished by science.
Together, they are involved in a search that dates back 99 years.
In 1916, Einstein mathematically wove space and time together, and theorized that massive objects can warp and curve "space-time." The theory makes gravity a property of space-time. All this leads to the idea that space-time can vibrate, something like a rock landing in a pond with a splash, sending out ripples.
In outer space, those "rocks" could be stellar explosions. Or dying stars collapsing. Or black holes and neutron stars circling each other. Or black holes being created.
A visitor to Hanford's LIGO stares at the stars.
Enter a device called an interferometer. In the 1980s, Cal Tech and the Massachusetts Institute of Technology huddled and decided to build the world's biggest and most sensitive interferometer network. With $372 million in
National Science Foundation funds, the two-LIGO network was created.
The LIGO's interferometer shoots an infrared laser beam about the diameter of a flashlight at an angled piece of polished glass, which splits it in two directions. The split laser beams are then further reflected to travel over two miles down two huge vacuum tubes, hitting mirrors at the end to bounce back.
If everything is perfect, every bit of light returns to the laser. But if a gravity wave jiggles a mirror slightly, some light goes in another direction to be caught and studied.
Hanford and Livingston were picked as sites in the early 1990s because they were isolated, meaning they were free from interference from most outside vibrations. Even these remote locations still have vibrations that can mess with the detection equipment, however, such as the commuter traffic entering and leaving Hanford. These interferences must to be nailed down and calibrated out.
Hunting for black holes is a formidable task, as you can’t actually see them. They are an enormous absence in the universe, a spot in space whose gravitational pull is so intense that even light and electro-magnetic waves cannot escape. The best way to hunt for them, therefore, is to look for gravity waves rippling from it.
One theoretical cause of a black hole is two colliding neutron stars, a once-in-a-million-years event in a galaxy, Raab says. The key, then, is to search in as many galaxies as possible. Until 2010, the two LIGOs could detect gravity waves originating from maybe 50 million light years away. Starting in August, Hanford’s LIGO will boast a detection range on maybe 660 million light years — enough to grab gravity waves from beyond the Milky Way, and in the neighboring Virgo Cluster of 1,300 to 2,000 galaxies galaxies.
When a gravity waves gets “caught” to be detected, it will move the two LIGOs’ measuring instruments by 1 billionth of the diameter of an atom. It would take 10 trillion such moves to equal the width of a human hair.
In its search for these infinitesimally small movements, humanity is entering uncharted territory. Right now, there are four gravity-wave-detection interferometers in the world, with a fifth under construction and a sixth on the drawing board.
Besides the two American LIGOs, a similar observatory dubbed Virgo with four-kilometer laser legs is set up near Pisa, Italy. It is going through its own upgrades similar to the American sites. A small German LIGO with 600-meter-long laser legs — less sensitive to gravity waves — has been operating while the others have been offline.
An underground Japanese LIGO with three-kilometer laser legs is scheduled to become operational in 2020. Meanwhile, India is considering building its own LIGO, with 2022 being the earliest potential operational date.
There’s a reason mankind is bringing more “ears” to the hunt. Raab noted than nuclear science existed for decades solely on scientific curiosity, with no real world functions until 1939, when atomic bombs and nuclear power reactors moved them toward reality. The same with X-rays, a scientific curiosity before they advanced the field of medicine.
Similarly, gravity waves could open the door to “seeing” a new, unexplored dimension of the universe. The scientific implications are intangible, but could be immense.
“It’s the frontier of knowledge,” Raab said, “and we never know where knowledge will take us.”