Physicist at MIT Kavli Institute
LIGO and Gravitational Waves
We're in the process of getting our second generation of interferometer detectors up and running and it is a difficult process. It's not like buying an iPhone 6 and turning it on and it works.
Interview by Heidi Legg
Stars colliding and exploding, scientists who are curious enough to figure out what happens and how it might affect us, and the evolution of the universe. This, in an audacious attempt, encapsulates my conversation with Peter Fritschel, a key researcher on the collaborative, multi-decade initiative between MIT and Cal Tech to find and measure gravitational waves outside of earth. Is gravity the new frontier?
What’s on your desk?
We are looking for gravitation waves outside of the earth using laser interferometers. Our search is for ripples in space-time created by cataclysmic events in the cosmos. What we are doing is really more groundbreaking research. We are creating an astronomical tool that uses lasers to search for violent cosmic events trillions of miles from Earth.
Our group includes about 25 people at MIT, a collection of scientists, professors, graduate students, and technicians. We're part of a larger project called LIGO, which stands for Laser Interferometer Gravitational Wave Observatory. The goal of this project is to build and run detectors (we also call them observatories) to detect and measure gravitational waves.
The idea is that these gravitational waves would be coming from various things happening in the universe, both in our galaxy, the Milky Way, and nearby galaxies. There are an infinite number of galaxies as far as we know, but hopefully we will be measuring things from ours and relatively nearby galaxies.
Why are you doing what you are doing and why should the public care?
A couple of ideas from movies come to mind: You must have seen The Devil Wears Prada?
There's a great scene shortly after the Anne Hathaway character gets the job with the Meryl Streep character in fashion. Several co-workers are gathered around Streep while the latter talks about various details of some fashion shoot line-up. At some point the Hathaway character expressed her apathy about the minutiae being discussed. At this, Streep shot her a look of derision and went off on a monologue enlightening her about how the high-fashion world influenced her life in ways in which she had no idea.
I want to make an analogy here with basic science research. There are specific analogies that can be made, like how general relativity is crucial to the GPS in your smart phone that you use to get around. But there is also a general analogy. In many areas of our complex society, there is a lot going on 'behind the scenes' of which the general population isn't aware.
Another film that comes to mind is It's a Wonderful Life. What if, as a society, we just didn't do this type of curiosity-driven research? What would our world look like? I don't have much in the way of specifics, but it seems to me that we'd just be neglecting an important part of our humanity.
With LIGO, are there other countries involved?
LIGO Laboratory is officially an MIT and Cal Tech collaboration and we get money from the National Science Foundation, but the science that we do is part of a larger collaboration that involves lots of other universities both in the United States and in countries around the world.
There are a couple of other projects building these instruments with the same goal. The most prominent one right now is in Italy. It's a joint French-Italian project called VIRGO, and they're doing something very similar to us.
Do you feel competitive?
Yes and no. We collaborate. In this type of science, it helps to share data. We don't hold things out. Mostly it's a collaborative association.
What is an interferometer?
An interferometer is a scientific instrument that's been around since probably the early 1900s and nowadays we use lasers to do the measuring. It's a device to make very good measurements of distance using the wavelength of light as a ruler and, since the wavelength of light is very short, it can be a very fine ruler. When I talk about light, it's part of the whole electromagnetic spectrum. We talk in terms of nanometers.
A nanometer is a billionth of a meter and so the wavelength of light is similar between 400 nanometers and 800 nanometers. We actually use light that's a little bit longer than that, about a 1,000 nanometers, which is also known as a micron, which is a millionth of a meter.
The basic idea is you take a source of light, we use a laser, and you split the light into a couple different parts and direct them with mirrors to travel the paths that you're trying to measure in space and then bring those two beams back together. Once you combine them, that's what we call 'interference' and that's where the 'interfer' part of it comes from.
We follow these two paths of light traveling in space and if one of the paths changes, gets shorter or longer, the light in that path will take either a little bit longer or a little bit less time to travel before it interferes with the other beam. When they interfere they add up or subtract from each other; they'll either add up to make a bigger signal or subtract from each other to make a smaller signal.
What does that tell you?
We're looking to see if a gravitational wave passes through. If a gravitational wave passed through our interferometer, it would make one of the paths of the interferometer a little bit shorter than the other.
Is your only thesis to try to prove that gravitational waves exist outside of earth?
Here on earth, we're producing gravitational waves all the time just by moving around but they're very, very, very weak and they have no effect on our daily existence. The gravitational waves we're looking for would come from astrophysical bodies like black holes and stars because the gravitation would have to be strong enough for us to have any hope of detecting them. They have to come from something that is huge and has a lot of mass like a star or black hole. It also has to be moving really fast, moving even close to a good fraction of the speed of light. It’s pretty incredible to think of a really massive thing moving that fast but that's the kind of event needed to produce gravitational waves of sufficient strength for us to measure. It is also what makes it interesting, because now we have a tool to observe these really incredible objects out in the universe that are doing these incredible things.
We're measuring waves that come from somewhere else in our galaxy and then they travel out everywhere in the universe and we measure the part that comes to us.
How are your second generation laser interferometers different? And where are they?
We constructed the two observatories in the late '90s, and in the early 2000s we put in the first detectors and operated them for several years, looking for signals. We didn't find any and we weren't necessarily expecting to, given this was our first generation of instruments.
We are very sensitive to any other kind of vibration that will change the distance, so we have to locate these instruments outside of the middle of town. We have two in the US: one is in the southeast corner of Washington State called the Hanford Reservation owned by the Department of Energy. It’s actually where they developed plutonium material for the atomic bomb for World War II. It's a nice big flat area because these are fairly large detectors. The other one is in Louisiana between Baton Rouge and New Orleans.
We have now designed much more sensitive instruments and are in the process of building the components for what we call the second generation.
When will the second generation be ready?
It's on the cusp of being ready right now. We are in a process that we call 'commissioning' to bring the detectors to their proper sensitivity.
If you find these waves, what will they teach us?
There are particular objects that we expect to be able to detect. A typical example is a pair of neutron stars. Many of the stars in a given galaxy actually are mated with another star in what we call a binary system. While our sun is not in a binary system, but many of them are. Then there is this subset of stars, supernovas, that at the end of their life, after they’ve finished burning all the fuel that makes them bright like our sun, collapse into what's called a neutron star. That neutron star can also be a pulsar, emitting these pulses of electromagnetic waves, but essentially at that point it’s very, very dense. What you’re left with is something that has the mass of a sun but contained in something that's only maybe ten miles across. Then if these stars are in a binary system, two neutron stars or maybe a neutron star with a black hole, they are in an orbit together. We know they exist because we can see them from the electromagnetic radiation that they give off. Eventually they come closer and closer together and coalesce into one. In the last few minutes of that process they're giving out huge amounts of gravitational waves and we would be measuring those.
What will that mean for us?
It’s about discovering what's out there. There's certainly an element of curiosity. Some of it is motivated by these objects that we know exist and we would like to find out more about the physical processes that are behind them. We would like to pinpoint what is happening in these two masses as they coalesce. If they perform according to the Theory of Relativity, we'd be exploring that theory in a region where we really don't have any other way to explore very, very, very, very high gravitational fields. That’s a region of gravity that we can't test any other way because it's so powerful.
Can it be applied?
I wouldn't say that there are any direct applications. This is more curiosity-driven research that can often have unexpected offshoots that are hard to predict.
What is a supernova?
A supernova is when a star is at the end of a life where it burns out and can collapse. When it’s in the last throes, it can give off a lot of energy.
There's actually a relatively new idea that's come out around supernovas related to finding planets in other solar systems, planets similar to earth. It’s been a burgeoning field over the last sort of five or six years. There's a good argument that this is simply because there are so many other stars out there.
Part of this new research is around an astrophysical phenomenon called gamma ray bursts. (The Economist)These gamma rays are part of the full electromagnetic spectrum of which light is a small little slice. When you talk about telescopes, people think about a telescope that detects light but we also have radio telescopes, those dishes out in the desert. This is another kind of electromagnetic radiation.
Pretty much everything we know about the universe comes from making electromagnetic observations of the universe, and gamma rays are a part of that spectrum but they have a very, very short wavelength. We talk about a wavelength of light being in the hundreds of nanometers in length. Gamma rays are even shorter and they come in short bursts. You can see them with a telescope, these short bursts of gamma rays coming from various parts of the sky, and what we believe is that many of those are actually coming from a pair of neutron stars that are coalescing. So going back to gravitational waves, these neutron stars that are coalescing are giving off both gravitational waves and gamma ray bursts.
The idea is that there are these gamma ray bursts going off around the universe in our galaxy and other galaxies. We don't really know how often they're happening, but we do know with certainty that if you were too close to a gamma ray burst, it would just wipe out life. A current idea put forward is that this phenomena has dampened the sustaining of life of the universe. It’s an additional idea that beyond even an asteroid having the power to destroy life, there is the same power in a gamma ray.
Which one is a falling star we'd see in the sky?
A falling star is an asteroid.
Can the naked eye see a gamma ray?
What exciting discovery have you made recently?
Looking back over the last year, we're in the process of getting our second generation of detectors up and running and it is a difficult process. It's not like buying an iPhone 6 and turning it on and it works. It’s going to take a few years to get everything to work right, but we've been really encouraged over this last year by how well it's gone. Our rate of progress has been much better.
Do you account for gravitational pulses from the sun and moon's procession in your testing?
The sun and moon have a big gravitational effect on earth in the form of tides, the ocean rising and falling every twelve hours. And there’s an effect of the tide on land. The land actually stretches at that same twelve hours. It doesn't have as dramatic an effect as it does on the sea level but we're measuring distances, really finely, over several miles. The interferometer has a baseline and our instruments are configured in an L and each leg of the L is four kilometers or about two and a half miles, and over that distance the tide actually stretches the earth by several hundred microns. It's very small but that's actually a big effect for us. We're looking for gravitational waves that are oscillating much more quickly than that, tens of times per second.
Have you ever found a gravitational wave?
Not directly. Not with our instrument.
There have been two indirect discoveries. For a long time there has been this very solid but indirect evidence of gravitational waves that comes back to my explanation of the pair of neutron stars orbiting each other. In 1993, the Nobel Prize in Physics was given for the discovery of the Hulse-Taylor Pulsar (PSR 1913+16).
And last spring, Harvard claimed that they had detected the effect from gravitational waves from very, very early in the universe, right at the beginning of the Big Bang. They do not have instruments that measure gravitational waves directly, which is what we hope to do. They measure using something called the cosmic microwave background.
Measuring cosmic microwave was discovered in the late 60s at the Bell Labs, which is electromagnetic radiation. These are much longer waves, about a cm long. The idea is that there is a period in the evolution of the universe, less than 400,000 years after the Big Bang, where you had a mix of matter, electromagnetic radiation, plasma, and a universe that expands and cools. At some point, when the temperature drops enough, the matter can start to form atoms and when it does it reacts differently with the radiation that is there, no longer interacting with the matter that was in the universe, at least in the way it was before. That matter stayed in the universe and kept bouncing around.
It was a fortuitous discovery in the 60s. The Bell Lab scientists were testing their new microwave receiver, pointed it up to the sky, and measured this white noise background. It was a higher level than was expected, and they realized that they were actually measuring microwaves coming from the universe, and that it was a relic of the evolution of the universe from 400,000 years after the Big Bang. The idea is that when this microwave radiation was created, there were also gravitational waves existing in the universe that were themselves formed much, much earlier in the universe, within the first seconds of the Big Bang.
As the technology got better and better, people had hopes to make measurements good enough to see this alteration that would have been produced by the gravitational waves. And that’s what this project claimed to have done at Harvard. Now there's more controversy over whether they actually measured what they claimed.
Well there aren’t many of us out there that can challenge them! How should we as a society stay in conversation with astrophysicists? Do they care if we understand what is going on?
Not every astrophysicist, but hopefully enough of a fraction of astrophysicists like Neil DeGrasse Tyson and Bryan Green who have really have taken it on to be the public voices of astrophysics. It’s very helpful.
How do you not get frustrated with the slow pace of science?
It can take a long time. I think it's also a product of where we are right now in science. We've become more and more capable of doing new things as technology advances, but projects take a long time. Take the discovery of the Higgs boson. It takes a large team of people and it takes a long time to do. It's not quick.
How do you deal with the frustration?
It can be very challenging. I try to focus my attention on learning something new because whenever you're doing that, it can renew your interest and I'm an experimentalist and it's much more closely related to engineering than theoretical physics. In many ways we are on the cutting edge of engineering and engineering that nobody's done before.
How did you choose this for a career?
I studied physics in college and afterwards found a job working with lasers. I was at Raytheon and I found that to be really fun, although I didn't really see myself doing that for very long because is was this domain of incremental process progress of science. I decided to go back to graduate school and that's whenI got involved in this stuff.
Make a pitch to kids on why they should do this sort of long format research.
In some sense, maybe it's easier for younger kids because they are more curiosity-driven and they're not thinking of the next Media Lab invention. They're just wondering about the world. So that's probably where it's easier to make the pitch.
If wondering about the world is what gets you excited, then there's a lot still to be discovered.
Is there a public opinion you'd like to change?
In comparison with other first world cultures like Europe or South America, I think scientists in this country are not as respected. I think there's more public interest in science in many other first world cultures than there is in the United States. I'm not quite sure why it is that way.
Do you know how we can change it? Why should Americans be excited about this work?
We are the leader right now in this particular field, but I think that the more general question is ‘why should the country put resources into basic science research that isn't directed to the next invention?’ I think a good argument is that it's something that gets young people excited about doing science or technology in the first place.
It raises possibility. Take Elon Musk, who created these incredible companies: Tesla and Space X. He studied physics and he says that physics is the greatest thing, the best thing to study to then go out into technological endeavors.
Do you have a secret source?
Over many years I had established a relationship with one of the wine buyers at Formaggio Kitchen and I would get most of my wines from her recommendations. When I found out she was leaving earlier this year, I was quite disappointed. But the silver lining is that she has moved to Italy to work with some of the vineyards she was familiar with and now runs a wine club for her friends and acquaintances she has left behind. So now I get wines in small batches directly from Italy!
Where do you get your news?
NPR, NYT, The Economist, The Financial Times and Zite
Is there an event you are looking most forward to?
We (LIGO) will start taking data with our new detectors in 2015, and the sensitivity should be good enough that we could make our first detection of gravitational waves.