海角社区

Meet Distinguished Research Master Joseph Giaime

Giaime is a professor in the 海角社区 Department of Physics & Astronomy and the head of LIGO, the Laser Interferometer Gravitational-wave Observatory (LIGO) in Livingston, Louisiana.

  

 

Joseph 鈥淛oe鈥� Giaime was part of the team that made the first detection of gravitational waves back in 2015, after roughly 20 years of fairly repetitive work, truly astronomical investments, and bordering-on-romantic scientific hope that it one day would be possible and overall worth the wait. Among the team members who were named for LIGO鈥檚 2017 Nobel Prize in Physics, besides Barry Barish and Kip Thorne, was Rainer Weiss, Giaime鈥檚 thesis advisor. After Giaime completed his PhD at MIT in 1995, where his research focused on laser interferometer design and vibration isolation systems for interferometric gravitational wave detectors, he joined the faculty at 海角社区 in 1999. Through a collaboration with Caltech, he leads the Livingston observatory, which runs what鈥檚 called Advanced LIGO since 2015 with two four-kilometer perpendicular arms stretching out into the flat, green landscape. In this interview, Giaime provides an overview of the last one hundred years of gravitational wave science, his recollections from the day when LIGO鈥檚 first detection was made, and some hopes for the future of research in a somewhat infinite field.
 
Patience is a big part of science in general, but seems particularly needed in your area?
 
Yes, when I give a history of where this science came from, I usually start a hundred years ago. It鈥檚 important to remind us that, sometimes, good things take a long time.
 
Tell me more about that.
 
So, 1915. Albert Einstein changed the way gravity is viewed by scientists and everybody else. Before Einstein, we had a simpler theory from Newton where two objects attract each other through some kind of mysterious action at a distance, where each object kind of knows the other one is there and feels a pull in that direction. Einstein introduced a new actor to physics, which is space-time. Einstein鈥檚 picture is that space-time curves in response to the presence of mass and energy, and that curvature in turn tells the matter and energy how to move, how lengths are determined, and a bunch of other things.
 
The math at the time was pretty challenging鈥攕till is, in fact鈥攗nlike Newton鈥檚. But because there was this new actor, space-time, Einstein, a year later, in 1916, published another paper saying, by the way, you can also have these little ripples in space-time that are self-sustaining like waves and other media. If matter and energy do just the right thing, they can excite these waves that travel out in space.
 
Then in 1918, he published another paper, saying, 鈥淥ops, there was a sign error in the first paper; otherwise the whole thing wouldn鈥檛 have worked.鈥�
 
I always cut myself a lot of slack because he screwed that up and it took him two years to fix it.
 
It鈥檚 a long time between 1915 and 2015, when you finally were able to prove him right.
 
It took quite a long time for anyone to work up the courage to try to measure these things. The difficulty with these ripples, which we call gravitational waves, is that the fundamental constants of nature add up鈥攐r multiply up, rather鈥攊n a really inconvenient way. It takes an enormous amount of motion, energy, and mass to make gravitational waves that are even conceivably measurable. Almost from the start, they figured out, the only thing that could really stand a chance is something as a big as a star. Unfortunately, we don鈥檛 have any kicking around here on Earth that we can manipulate. The numbers make it almost impossible to generate gravitational waves, unless you鈥檙e a sufficiently advanced civilization that you can sling around the solar systems. So, we couldn鈥檛 transmit them. That made the whole thing a lot harder.
 
We had to figure out if there were any emitted at all out in space and then figure out how they might be visible in experiments here on Earth, where we have to do our experiments. The first person who got the courage up to do that was Joe Weber at the University of Maryland. In the late 1960s and early 鈥�70s, he was taking these bars of aluminum and instrumenting them to see small vibrations that might get excited in the bars, kind of like reading a chime, from astrophysical events passing through. But whatever he was seeing wasn鈥檛 gravitational waves. He was a brilliant man and had a distinguished career, but they weren鈥檛 gravitational waves, so that messed up the field鈥攕ociologically鈥攆or a while. Everyone had to be very, very careful not to announce anything as a detection unless they were really, really sure.
 
Still, Weber started something.
 
His approach grew up and got sophisticated. Taking bars, instrumenting them even better, cooling them down to absolute zero, and suspending them very carefully to avoid contamination by vibrations. When you cool them down to absolute zero, it lowers the fundamental noise that afflicts them. Bill Hamilton鈥檚 group here at 海角社区 was really on top of that. He came here from Stanford in 1970 and made two bars, one here and one at Stanford, and those two ran for decades. They were the steadiest and most reliable ones in the world. That was really the start of gravitational wave research at 海角社区, 50 years ago.
 
Another bunch, led by my old thesis advisor Rainer Weiss, based at MIT and Caltech, was developing another approach, which was to use lasers to measure gravitational waves. The whole thing culminated in a proposal to the National Science Foundation in 1989 to build two long-baseline detectors, using lasers to measure changes in the shape of space-time. Kind of a miracle happened; the proposal was approved, and generally quickly. They broke ground in Livingston, Louisiana in 1995 and in Harford, Washington toward the end of the previous year.
 
Now, you might ask, how were these two sites chosen? Because there was this group at 海角社区 that was a pioneer already, and the two sites had to be far apart.
 
How did you get involved?
 
Part of the deal with NSF was that 海角社区 would hire two assistant professors to devote to this project and although it was never spelled out exactly who those two were, I like to think of it as me and Gabriela Gonzalez. We鈥檝e both devoted our whole careers to it. I got here in 1999, and she, a couple of years later. All of the research we have done and all of the work our students have done has really been devoted to this one mission, to make LIGO work and start up the field of gravitational astronomy.
 
How is your role different from Gabriela Gonzalez鈥檚?
 
I鈥檓 closely tied with the facility and the site, while Gabriela has a broader research portfolio and was the spokesperson for several years for the whole collaboration, including the most pivotal years when our first discovery was made. She had to herd about a thousand cats that were very excitable and somehow keep a very steady scientific vision. Meanwhile, I had to work with about 40-50 to run a facility and handle everything from hiring to making sure the right people were taking care of the sewerage. The only thing we get from the outside is electricity; everything else has to be provided.
 
Sounds like you鈥檙e the mayor of a small town?
 
We have to have our own everything, so most of what I do is administration. And since I went to physics school, I didn鈥檛 necessarily know how to do any of this stuff. But luckily, we had a lot of time to work it all out before the science came.
 
Tell me about the 1995-2015 stretch; that鈥檚 another 20 years.
 
So, we broke ground in 1995 and got the thing to work about 10 years later, in 2005, right after Katrina. Then it ran for a couple of years in tandem with our sister site in Washington, and 鈥� we saw nothing.
 
Nothing?
 
Yes, nothing. We made improvements to try to extend the range. If you look out further, you can see a lot more potential sources. Like, if you blow up a balloon twice as big, there鈥檚 eight times more volume in that balloon. If nature sprinkles sources evenly through space, a difference in range makes a big difference in potential. So, we ran with those improvements until October 2010 and also, saw nothing.
 
By that time, the National Science Foundation had re-upped. They approved another $200M to replace all of the technical bits of the detector鈥攏ot the outside; you wouldn鈥檛 know standing outside鈥攂ut there had been two decades of technology improvement. So, we shut down in October 2010 and started tearing out the old stuff and putting in new stuff, and that took about five years. By fall 2015, we did our first run with the new detector, the so-called Advanced LIGO detector, and almost right away, we saw the first gravitational wave.
 
Wow.
 
It was worth the wait. Now we have many dozens of events, depending on how you count. If you count potential events we haven鈥檛 published thoroughly on yet, we have over 60. Most experiments in a lot of science, if you improve your experiment鈥檚 sensitivity by two you get twice the precision, twice the 鈥渟cience.鈥� But the amazing thing about LIGO is that twice the sensitivity multiplies the number of events by eight. The initial detector that saw nothing could see neutron stars in-spiraling out to 15 megaparsec [one parsec is about 19 trillion miles or just over three light-years]. Right now, we鈥檙e running about 100 megaparsec range.
 
Then, we cube that ratio in terms of events we might see. Of course, you can multiply zero by anything and still have zero. That was always the worry. Is there really anything out there?
There had been no actual evidence鈥攏one at all.
 
Yet, LIGO persisted.
 
Our first discovery was that black holes can be observed from Earth using this technique. The second discovery was that black hole mergers exist in the Universe in sufficient quantities that we saw one. And then other things piled in from that discovery, such as limits on the degree to which gravity theory might differ from Einstein鈥檚鈥攖he answer is, very little鈥攁nd a whole bunch of other more technical results.
 
Before we talk about that specific day when you made the first discovery, tell me how you got started in this field of research to begin with?
 
I was undergraduate at MIT and didn鈥檛 really know what to do next, to be honest. I took a job as a technical instructor at the physics department, and half the time I was a technician in Dr. Weiss鈥� lab. I loved working there, wanted to keep going, so applied to grad school.
 
How did Weiss inspire you?
 
Weiss would always tell people that amazing things would happen in about five years. He did that for 30 years. It wasn鈥檛 necessarily a surprise that it would take so long, and since most of us liked playing in the lab, it wasn鈥檛 much of a hardship.
 
Did you have any misgivings about your choice?
 
Gravitational wave research was seen as a bit of a dodgy thing by some in the physics and astronomy community. One, the early un-reproduced claims. And the more concrete reason is that the math makes the signal very, very small. The size of the signal we measure at LIGO, is one one-thousandth the diameter of a proton, measured across four kilometers. And the more physics you know, the crazier it sounds to measure something that small. It takes time to make people consider that it鈥檚 possible. It took a leap of faith. It was high-risk, and if nature had sprinkled fewer of these out in space, we could still not have seen any of them by now.
 
But doubts, no. The only time in my career I ever considered leaving was late in my postdoc when I got a job offer from NIST to work on quantum metrology.
 
Now, please tell me about that fateful day in September 2015 when you first detected gravitational waves.
 
It was early in the morning. I was probably asleep when it happened. But the way we make these discoveries鈥攚e calculate in advance the family of wave forms these mergers can create. Then, those are all put into the computer, and as the data flow in, our systems compare the signal that comes in from the detector with all member of the family, from black holes and neutron stars鈥攁 variety of masses鈥攐ver and over again. By the time I woke up, our systems had spotted something that was very unlikely to be from chance. But the detector had just started its run and we had a lot of questions.
 
In previous runs, we鈥檇 had these things called hidden injections. We were worried that the collaboration was getting so good at vetoing the data that looked like it was corrupted in some way that it could be vetoing data that had the signals in it. So, we decided to have a small group secretly injecting data at the two observatories and not tell anyone until the analysis was done to make sure we would actually be able to detect something. I was one of the ones who did it; I was the designated secret keeper for Livingston.
 
So that morning, one concern was, did someone on our team do it, even accidentally? Maybe in some kind of double-secret arrangement we weren鈥檛 supposed to know about?
 
So, faked results introduced by gravitational wave double agents?
 
Yet, but that was pretty easy to work out; they hadn鈥檛 done that. The data were real. But there was a mountain of tests that had to be done and because we鈥檇 just started our run, we were honor-bound to run in the same state for several weeks to gather statistics. Maybe these new detectors we鈥檇 just built, maybe they did this all the time, and we just didn鈥檛 know about it yet? There was this rush of happiness and excitement and then we all had to put our noses back near the grindstones to just run for several weeks until the statistics could be gathered. It took a lot of discipline to not keep screwing around with things, trying to make them better, as that would change the statistics.
 
Why did it take five months for the news about the discovery to come out?
 
We didn鈥檛 tell anyone! We kept it secret. We did it old-school; we wanted a paper to be written and accepted in a journal before we told anybody. And that took a while. The event was in September and the press release didn鈥檛 go out until February in the next year. Our paper is one of the highest cited papers in the world and it had to be right; it had to be good and it had to be readable. We knew the next couple of generations of grad students would be forced to read this thing and probably would have to write about it in their astrophysics classes, and we didn鈥檛 want to look foolish.
 
There were actually a lot of worries. Maybe an outside trickster had logged into our computers and faked the results; maybe lightning had struck halfway between the two sites? Luckily, there are ways to check all of these things, with space weather, lightning detectors, etc., which we had to do, although it took time. Also, there were one or two leaks, but the leaks were of low quality and they were more wrong than right.
 
The real worry was that some collaborator had printed out our paper on a departmental printer somewhere and another person had picked it up by accident and sent it to a science journalist; that would have been bad鈥攂ecause early versions of the paper were wrong! That鈥檚 why there were early versions. But that didn鈥檛 happen, which was kind of neat.
 
Somehow, you managed to keep your secret.
 
Even if we also collaborate with Virgo, which is a detector in Europe. They were part of the paper, too.
 
Would it have been possible to detect gravitational waves much earlier than 2015, if science had gone in a different direction in the 1970s, let鈥檚 say?
 
Hard to say, but not much earlier.
 
You can think of general relativity as being something called the Einstein equation. Solutions to the Einstein equation are things that are possible in his theory. And since it鈥檚 really hard to do calculations using the Einstein equation, the relativity community has this precious catalogue of exact solutions. There really weren鈥檛 that many even when I was in grad school; even people who were experts at this couldn鈥檛 calculate the in-spiral wave form of a pair of black holes. They were estimating, in intelligent ways, but couldn鈥檛 calculate exactly. It鈥檚 really only in the last 20 years or so that people have been able to numerically solve some of these problems using very powerful computers. People toiled at this with pen and paper for decades, and they couldn鈥檛 do it.
 
I consider myself an experimenter, and of course, it鈥檚 an experimenter鈥檚 dream to have data that the theorists don鈥檛 know how to analyze yet, but in this case, it was completely the other way around. Their ability to calculate the waveforms helped us discover them.
 
What do people get wrong or have a tough time understanding about your work?
 
Sometimes, people ask, 鈥淲hat good is this?鈥� 鈥淗ow is detecting gravitational waves going to help people?鈥� That鈥檚 always a tough question with astronomy. Everything we see is far away. But one thing LIGO has contributed is a community of graduates鈥攕cientists and engineers who consider it possible to do things that are nearly impossible or at least thought to be nearly impossible. That鈥檚 something.
 
Also, people like to look out of windows, just to see what鈥檚 there. Even in cold parts on the planet where it doesn鈥檛 make sense to have them, people want windows. I think that鈥檚 part of the popularity of astronomy. It鈥檚 good to know what鈥檚 going on out there, even if it might never affect us.
 
Do you have any idea what the future might hold?
 
So far, we鈥檝e only seen a small handful of neutron star binaries, and we want to see a lot more. The first neutron star binary we saw was in 2017, and it was the birth of multi-messenger astronomy that includes gravitational waves. That鈥檚 a fancy way of saying a whole bunch of astronomers with a whole bunch of instruments looking at the same thing at the same time to learn as much as possible about an object.
 
Unlike other sciences, in astronomy, you can鈥檛 repeat a discovery; it happens out there in space, the waves come by Earth, and they鈥檙e gone. So, in astronomy, when we see something or expect to see something, we work very hard to alert astronomers as fast as possible so they can point their instruments in the right direction. Black holes probably won鈥檛 allow that; there is no light to see, there will only be gravitational waves. But neutron stars allow some wonderful measurements to happen. They glow and they鈥檙e made of regular matter, not mystery black hole stuff. They鈥檙e massive enough to generate gravitational waves and they also do crazy things like scrape up against each other and expel illuminated clouds of nuclear matter. The only time we were able to do this, where a lot of astronomical observers looked at a neutron star merger all at once, we published a giant paper with 3,500 authors and had the argument of our lives. Naturally, we want to do more of that.
 
 
Giaime was elected a fellow of the American Physical Society in 2009 for his contributions to gravitational wave physics. He is also a member of the American Association for the Advancement of Science (AAAS), the American Astronomical Society (AAS), the International Society on General Relativity & Gravitation (ISGRG), and the International Astronomical Union (IAU).

Since 1972, the 海角社区 Council on Research has presented the award of Distinguished Research Master to two 海角社区 faculty on an annual basis in recognition of outstanding career accomplishments in research and scholarship. One recipient is chosen within the fields of the arts, humanities, social, and behavioral sciences, and another recipient within the fields of science, technology, engineering, and mathematics. The award consists of a University Medal, a certificate designating the recipient as a Distinguished Research Master, and a salary supplement.

 

Meet Distinguished Research Master Heather McKillop

Gravitational Waves Detected 100 Years After Einstein鈥檚 Prediction

 

 

Elsa Hahne
海角社区 Office of Research & Economic Development
225-578-4774
ehahne@lsu.edu