THE GRAVITY
OF LIGO

A BILLION DOLLAR FACILITY
AND THE PRICELESS BLIP THAT
WHISPERED THE ORIGINS
OF THE UNIVERSE.

STORY BY: RICK PAULAS

THE GRAVITY
OF LIGO

A BILLION DOLLAR FACILITY
AND THE PRICELESS BLIP THAT
WHISPERED THE ORIGINS
OF THE UNIVERSE.
STORY BY: RICK PAULUS

It

was

just

a

tiny

blip

on

a

graph…

an

event

that

took

place

a

long,

long

time

ago

when two black holes collided. The final split-second before convergence produced a signal with high enough frequency and amplitude that it rose above the space noise, travelled 1.3 billion years at the speed of light, and eventually reached the sensitive detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO). But more than what LIGO detected was what the signal suggested.

          “It was a regular day,” says Alan Weinstein, a professor of physics at Caltech and LIGO group leader. “We had no expectations.” That is, no expectations yet. That blip in the middle of the night on September 14, 2015, as LIGO was undergoing initial runs just to make sure everything was working properly after decades of overcoming hurdles – technological, political, personality-wise, you name it –, investing millions of man hours, and spending nearly a billion dollars, was evidence that Einstein’s theory of general relativity was true.

          Now the top physicists, engineers, and gravitational wave experts are using LIGO in Louisiana, and its twin facility in Washington, to discover even more about the origins of the universe. But on that fated September night, with only a skeleton crew on duty, the LIGO team got a very important mass email:

They’d finally found what they were looking for.

 

IN 1967, RAINER WEISS
HAD A PROBLEM.

          The students of the MIT physics professor had read about work being done by Joseph Weber at the University of Maryland that was upending the field. See, during Einstein’s life, there wasn’t technology around to test his general relativity theorem – very basically, the concept that enormous objects distort space and time, resulting in gravitational pulls. Times had changed. Weber believed he’d found a way to test the theorem. But, when Weiss’ students asked him questions, he couldn’t wrap his head around it.

          “I couldn’t for the life of me understand what he was doing,” said Weiss, in an interview for the Caltech Oral History Project in 2000. So, he devised his own testing method instead. “Let’s take freely floating masses in space and measure the time it takes light to travel between them,” he told the MIT News in 2016. “The presence of a gravitational wave would change that time.”

          While the concept lodged in his brain, it wasn’t until 1975 – when a chance shared hotel room with Caltech professor Kip Thorne, on his way to becoming one of the world’s leading astrophysics experts – that LIGO took shape. Weiss mentioned his idea, and the two spent all night detailing how it’d work. They’d need enormous vacuum tubes, two 5- to 10-kilometer L-shaped structures, and state-of-the-art laser and mirror technology. By night’s end, Thorne wanted in, but they needed help. Weiss suggested Ron Drever, a Scottish experiment physicist he’d never met. “I didn’t know Drever from a hole in the ground,” said Weiss. “But of all the people who had written stuff on this thing, he had come up with what I thought were some very clever ideas.”

          The brain trust had formed; now came the headaches. One problem was, as far as experimental science goes, LIGO wasn’t sexy. “It’s small science with a big price tag,” said Caltech physics professor Thomas Tombrello. “It wasn’t like high-energy physics, where you have an enormous lobby of professors in every university.” In 1987, Rochus (“Robbie”) Vogt was brought on as the project’s director. He unified the labs at MIT and Caltech and set about the unenviable task of obtaining funding. But despite an influx of money, the project got stuck. Caltech’s president was dragging his feet. Drever, upset at the progress, became difficult. Vogt wrangled financing, but didn’t know how to spend, so the money sat there.

It
was
just
a
blip
on
a
graph,
an
event
that
took
place
a
long,
long
time
ago
when two black holes collided. The final split-second before convergence produced a signal with high enough frequency and amplitude that it rose above the space noise, travelled 1.3 billion years at the speed of light, and eventually reached the sensitive detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO). But more than what LIGO detected was what the signal suggested.

          “It was a regular day,” says Alan Weinstein, a professor of physics at Caltech and LIGO group leader. “We had no expectations.” That is, no expectations yet. That blip in the middle of the night on September 14, 2015, as LIGO was undergoing initial runs just to make sure everything was working properly after decades of overcoming hurdles – technological, political, personality-wise, you name it –, investing millions of man hours, and spending nearly a billion dollars, was evidence that Einstein’s theory of general relativity was true.

          Now the top physicists, engineers, and gravitational wave experts are using LIGO in Louisiana, and its twin facility in Washington, to discover even more about the origins of the universe. But on that fated September night, with only a skeleton crew on duty, the LIGO team got a very important mass email:

They’d finally found what they were looking for.

 

IN 1967, RAINER WEISS
HAD A PROBLEM.

          The students of the MIT physics professor had read about work being done by Joseph Weber at the University of Maryland that was upending the field. See, during Einstein’s life, there wasn’t technology around to test his general relativity theorem – very basically, the concept that enormous objects distort space and time, resulting in gravitational pulls. Times had changed. Weber believed he’d found a way to test the theorem. But, when Weiss’ students asked him questions, he couldn’t wrap his head around it.

          “I couldn’t for the life of me understand what he was doing,” said Weiss, in an interview for the Caltech Oral History Project in 2000. So, he devised his own testing method instead. “Let’s take freely floating masses in space and measure the time it takes light to travel between them,” he told the MIT News in 2016. “The presence of a gravitational wave would change that time.”

          While the concept lodged in his brain, it wasn’t until 1975 – when a chance shared hotel room with Caltech professor Kip Thorne, on his way to becoming one of the world’s leading astrophysics experts – that LIGO took shape. Weiss mentioned his idea, and the two spent all night detailing how it’d work. They’d need enormous vacuum tubes, two 5- to 10-kilometer L-shaped structures, and state-of-the-art laser and mirror technology. By night’s end, Thorne wanted in, but they needed help. Weiss suggested Ron Drever, a Scottish experiment physicist he’d never met. “I didn’t know Drever from a hole in the ground,” said Weiss. “But of all the people who had written stuff on this thing, he had come up with what I thought were some very clever ideas.”

          The brain trust had formed; now came the headaches. One problem was, as far as experimental science goes, LIGO wasn’t sexy. “It’s small science with a big price tag,” said Caltech physics professor Thomas Tombrello. “It wasn’t like high-energy physics, where you have an enormous lobby of professors in every university.” In 1987, Rochus (“Robbie”) Vogt was brought on as the project’s director. He unified the labs at MIT and Caltech and set about the unenviable task of obtaining funding. But despite an influx of money, the project got stuck. Caltech’s president was dragging his feet. Drever, upset at the progress, became difficult. Vogt wrangled financing, but didn’t know how to spend, so the money sat there.

          In 1994, leadership was turned over to Barry Barish, freshly licking his wounds after Congress voted not to fund his Super Collider project in Texas. But when Barish looked at the project, he saw problems. Two technical reviews came back with harsh criticism about the methodology, but more than that, the stasis angered him. “This project can’t stand still,” said Barish, in 1998. “The whole idea is to build something that can evolve.” Barish forced the group to find ways to keep noise from the detection equipment, swap out analog circuitry for digital, and update their lasers that, in the five frozen years, had been surpassed by household CD players. Those tweaks cost money.

          As Tombrello tells it, funding came after clandestine action. A member of the NSF mentioned interest, but wanted to see specs. Tombrello couldn’t talk because it was Caltech’s project, but, he told the rep, “I’m going to go out for coffee for about 15 minutes and leave this manilla folder with the plans here behind.” Months later, LIGO secured $395 million in funding, then the largest sum granted by the NSF.

          With all that pesky business out of the way – and with lab sites finally being chosen in the towns of Hanford, Washington and Livingston, Louisiana – it was time for some actual science.

THE LIGO
WORKS LIKE SO:

Electricity generates a 4-watt, 808nm beam of near-infrared laser light, that’s 800 times more powerful than everyday laser pointers. The beam is directed into the Non-Planar Ring Oscillator, a “fingernail-size” garnet crystal, that circulates the laser until it reaches a wavelength of 1064nm. That’s wavelength enough, but it needs 100 times more power, so – after an orchestrated route through 5cm long amplifier rods, another four-rod device called the High-Power Oscillator, and additional laser light funneled through fiber-optic cables – it’s boosted to nearly 200-watt.

          In 1994, leadership was turned over to Barry Barish, freshly licking his wounds after Congress voted not to fund his Super Collider project in Texas. But when Barish looked at the project, he saw problems. Two technical reviews came back with harsh criticism about the methodology, but more than that, the stasis angered him. “This project can’t stand still,” said Barish, in 1998. “The whole idea is to build something that can evolve.” Barish forced the group to find ways to keep noise from the detection equipment, swap out analog circuitry for digital, and update their lasers that, in the five frozen years, had been surpassed by household CD players. Those tweaks cost money.

          As Tombrello tells it, funding came after clandestine action. A member of the NSF mentioned interest, but wanted to see specs. Tombrello couldn’t talk because it was Caltech’s project, but, he told the rep, “I’m going to go out for coffee for about 15 minutes and leave this manilla folder with the plans here behind.” Months later, LIGO secured $395 million in funding, then the largest sum granted by the NSF.

          With all that pesky business out of the way – and with lab sites finally being chosen in the towns of Hanford, Washington and Livingston, Louisiana – it was time for some actual science.

THE LIGO
WORKS LIKE SO:

Electricity generates a 4-watt, 808nm beam of near-infrared laser light, that’s 800 times more powerful than everyday laser pointers. The beam is directed into the Non-Planar Ring Oscillator, a “fingernail-size” garnet crystal, that circulates the laser until it reaches a wavelength of 1064nm. That’s wavelength enough, but it needs 100 times more power, so – after an orchestrated route through 5cm long amplifier rods, another four-rod device called the High-Power Oscillator, and additional laser light funneled through fiber-optic cables – it’s boosted to nearly 200-watt.

LIGO-splash3-mobile

          That laser is sent into the LIGO’s massive vacuum tubes of spiral-welded 3mm thick stainless steel. Inside is 10,000 cubic meters with an air pressure of one-trillionth of an atmosphere, necessary to prevent sound waves from vibrating LIGO’s sensitive mirrors and destroying the laser’s quality. (The vacuums also keep out temperature variations, which would alter the mirrors’ shape.) Once built, it took 40 days of continuous pumpdown to get the vacuum pressure to the necessary level.

          Inside the vacuum, the laser is sent through a beamsplitter, so it becomes two. The two beams travel down the four-kilometer long tubes through a series of mirrors that have been coated and polished to nanometer smoothness, so they absorb only one out of every 3.3 million photons. (COlasers also heat the mirrors to counteract shape changes that occur from said absorption.) In all, the lasers make 280 reflections before impacting the final detectors, made of fused silica and cast from ultra-pure material with low hydroxide content, which minimizes infrared absorption.

         The final detector is where the big findings come. On the return trip, the two lasers recombine into one before hitting the sensor, which detects the beam as one lone entity again. However, if a gravitational wave were to run through one of the tubes – thusly stretching space in one tube, while contracting space in the other – the detector would pick up a distorted wave, proving the existence of gravitational waves. The purpose of the dual labs working in concert with one another is to provide added confirmation the signal interference came from outer space, and also to triangulate where exactly the signal came from.

LIGO-splash4-mobile

         During construction, the cost rose as modifications needed to be made. The sensing photodetectors, originally on tables of air, needed to be rebuilt in acoustically shielded “meat lockers.” The Louisiana site, on a timber logging plantation which gave assurance they’d cease operations, had to deal with new logging in the early 2000s, so the project added further seismic isolation. Oh yeah, the vacuum tubes needed further protection from the elements, and that protection needed even further protection from fires, car crashes, insects, rodents, and, in Louisiana, stray bullets. (“There are really only a very few bullet holes in our buildings,” says Weinstein. “This is not a big problem!”) After all that, in 2002 – 35 years after Weiss’ original concept, 87 years after Einstein’s work – the LIGO team flipped the switch in the hopes that they’d finally detect gravitational waves.

         “It was a clean nothing,” Weiss told MIT News. “The detectors had run at design and we saw no anomalies that could be interpreted as gravitational waves.” But this wasn’t all a bust. “We always thought of initial LIGO as a ‘pathfinder’ for Advanced LIGO,” says Weinstein. It was more important that the project achieved the detection sensitivity they were going for, and not the actual results. It was more proof-of-concept than anything else. So when they went back to the NSF for another round of funding in 2008, they were given a hearty thumbs up.

“WE ALWAYS THOUGHT OF INITIAL LIGO AS

A ‘PATHFINDER’ FOR ADVANCED LIGO.”

          Advanced LIGO (aLIGO) improved the old concept. It swapped 10 kg mirrors for 40 kg that were “polished to an average smoothness of one atom, coated to be 99.999% reflective for laser light.” The single-pendulum suspensions were replaced with high-performing quadruple-pendulum suspensions. Passive seismic isolation systems became active. The 30-watt main laser gave way to the 200-watt. More complex thermal compensation system, optical configurations, and digital controls were installed. Think about the difference between your current smartphone and the computer that was whirring on your desktop in the late 90s, and you can get a sense of the difference.

         Bringing us back to that “regular day” in mid-September, 2015. The team turned on aLIGO and found signal GW150914. It lasted all of 0.2 seconds and “chirped” like a bird. After weeks of analysis to confirm it was real – and to triangulate exactly where, and when, it came from – the group announced its findings to the world: They’d found the signal everyone had been trying to find all these years.

         “I feel an enormous sense of relief and some joy, but mostly relief,” Weiss said at the time. “There’s a monkey that’s been sitting on my shoulder for 40 years, and he’s been nattering in my ear and saying, ‘Ehhh, how do you know this is really going to work? You’ve gotten a whole bunch of people involved. Suppose it never works right?’ And suddenly, he’s jumped off.”

         With that primary goal checked off the list – sincerely: way to go, Einstein! – what’s next? A billion dollar price tag better have some benefits beyond a few press releases.

         It’s worth keeping in mind this project isn’t yet complete. The VIRGO station in Cascina, Italy will being sharing data with the two aLIGOs in 2016. A similar station in Japan is scheduled to be ready in 2018. A LIGO is being developed in India (site: TBD) with the hopes of achieving “good sensitivity” by 2020. There’s also the development of the third-generation gravitational wave detector, The Einstein telescope, which will include 10-kilometer vacuum tubes and placed deep underground to suppress seismic disturbances even further. All of these will be working together to provide unique information about nuclear matter at extreme densities and temperatures, theoretically detecting signals from binary neutron stars, collapsing massive stars, and who knows what else. They may even finally hunt down experimental physics’ great white whale: Gravitational waves from the universe’s earliest moments, a tiny fraction of a second after the Big Bang.

         “That’s just scratching the surface of a vast scientific enterprise,” says Weinstein. “[It’s only] now just beginning.”

“THERE’S A MONKEY THAT’S BEEN SITTING
ON MY SHOULDER FOR 40 YEARS,
NATTERING IN MY EAR, ‘EHHH, HOW DO YOU
KNOW THIS IS REALLY GOING TO WORK?

YOU’VE GOTTEN A WHOLE BUNCH OF PEOPLE
INVOLVED. SUPPOSE IT NEVER WORKS
RIGHT?’ AND SUDDENLY, HE’S JUMPED OFF.”

“THERE’S A MONKEY THAT’S BEEN SITTING
ON MY SHOULDER FOR 40 YEARS,
NATTERING IN MY EAR, ‘EHHH, HOW DO YOU
KNOW THIS IS REALLY GOING TO WORK?
YOU’VE GOTTEN A WHOLE BUNCH OF PEOPLE
INVOLVED. SUPPOSE IT NEVER WORKS
RIGHT?’ AND SUDDENLY, HE’S JUMPED OFF.”

[Wow-Modal-Windows id=1]

2 Comments
  1. R Pitman

    This is incredible….

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