From The Michael Slate Show
Interview with Physicist Joshua Smith on Discovery of Gravity Waves: "A completely new way to look at the universe"
February 29, 2016 | Revolution Newspaper | revcom.us
Joshua Smith was interviewed February 19, 2016, on The Michael Slate Show on KPFK Pacifica radio. This is a transcript of that interview.
Michael Slate: On Thursday, February 11, a worldwide team of scientists announced the first direct observation of gravitational waves, and this is a major scientific achievement. It directly confirms predictions of Einstein’s general theory of relativity made 100 years ago and opens up a whole new branch of astronomical investigation—a new window to understanding the entire universe. So there was this discovery and I was really pleased about that. I really wanted to understand more of it myself, so we hooked up with Joshua Smith, who directs the Gravitational Wave, Physics and Astronomy Center and is an Associate Professor of Physics at California State University, Fullerton, and we hooked up with Josh to talk with us about the significance of all of this. Josh, welcome to the show.
Joshua Smith: Michael, thank you very much for having me on.
Michael Slate: Good! Why all the excitement? What exactly happened and why all the excitement about gravitational waves? What actually are they and why are people excited about discovering them?
Joshua Smith: I think the excitement starts 100 years ago. Einstein predicted gravitational waves 100 years ago but he thought they’d be too small for us to ever measure them. If you fast forward, we’ve improved technology enough in the last 100 years that we now have a chance and we’ve actually done it. And then I think the reason they’re so exciting is because they give us a completely new way to look at the universe. As you said, they open a new window. We look at the universe every day with light in all its different forms: radio, X-rays, gamma rays, visible light with all different types of telescopes. Well, gravity tells us not about how electrons or charges move, which light does. It tells us about how masses move, so we can look at things like black holes that don’t give off light and we can look at them through ripples and gravity. And gravitational waves are ripples in gravity that travel at the speed of light.
Michael Slate: So, the significance of this? What difference does knowing all of this make?
Joshua Smith: Well, there are a couple of things. First of all, Einstein’s theory of gravity is the most accurate theory that we have for understanding how gravity works, how the orbits work in the solar system. We couldn’t even understand Mercury’s orbit accurately until Einstein improved upon the existing theory that Newton had. Newton said two masses have a force between them that depends on their masses and is inversely proportional to the square of their separation. And Einstein said it’s more like a curved rubber sheet, where a mass will curve that sheet and the amount of curvature you get is proportional to how strong the gravity is and that keeps the planets in their orbits. So, by understanding Einstein’s theories better we can understand gravity better, which is one of the major forces in the universe. The other thing it gives us is a new way to do astronomy. So that’s something everyone can partake in and right now we’re using LIGO, the Laser Interferometer Gravitational-Wave Observatory, to see black holes from across the universe.
Michael Slate: I want to get into that in a minute. But how does this all fit together? I’m trying to get my head around why these waves are so significant. It’s important for people to understand how the universe works, but to fit in this thing that was sort of a momentary chirp—to people who were reading the paper it was a momentary chirp—and it’s like, “Well, why are all you guys out there jumping up and down and screaming and having parties?”
Joshua Smith: I think it’s because we don’t think of it as a momentary chirp. We think of it as maybe that first radio transmission that was ever sent, or the first form of a new type of communication or a new sense for humanity. So this first chirp was signaling that our detectors worked well and can sense this type of signal from a billion light-years away. But this won’t be the last thing that we find. This actually is the first of many things that we’ll see using this new type of technology. So, I think the reason why we’re jumping up and down isn’t only because we’ve shown Einstein’s theory to be accurate in this one area, but also because we feel like it’s a start of a new way to do this science.
Michael Slate: There are so many questions, and that’s exactly what you want, when you actually have something of this magnitude and you’re actually getting people who really want to understand what’s happening this way. You talk about Einstein’s theory about gravity. How do gravitational waves fit into that theory?
Joshua Smith: In Einstein’s theory where he said that kind of mass makes a curvature in space and time, that’s Einstein’s general theory of relativity. He also has a special theory of relativity that said nothing can travel faster than the speed of light. What that means is, if you move a mass... like let’s say that we made the sun disappear, or better, maybe we had two stars rotating around each other, if you are far away from that system, information about the mass that had moved couldn’t get to you faster than the speed of light. And so Einstein’s theory made it necessary to have some sort of wave, which in this case is very similar to a ripple on a pond. Imagine if you drop a stone into a pond, the stone changes the surface of the water and the waves ripple out from that. This is very similar, except that dropping the stone, instead of that you have something like a star exploding. The waves would ripple out from that at the speed of light and provide information about the change in the curvature of space time. So, it’s necessary both for his special theory of relativity and his general theory of relativity to have waves.
Michael Slate: Why are they so hard to find? People have been searching for them for quite some time, right? Since Einstein predicted them, people have been trying to find them and they’ve been extremely difficult to find, right?
Joshua Smith: That’s right. So, in Einstein’s original papers, he predicted they would be hard to find. He had an equation and he said, “If you take this equation for the amplitude of gravitational waves and you put in any practical number you think about, the amplitude of gravitational waves would be practically vanishing.” But Einstein didn’t have in mind systems like two black holes going around each other. Those systems weren’t known to him at the time. And also, Einstein didn’t know the leaps that technology would take in the meantime. So, in the ‘60s, people started looking for ways to detect gravitational waves and since then the sensitivity has improved by orders and orders of magnitude and a lot of that is pushing technology—like lasers and mirrors and vacuum systems and seismic isolation, and also technology from the world, from companies, industry developing and being put back into science, so us using developments that were made in industry. And those things come together—the fact that you have these amazing astronomical objects and you have this great new technology to make the most sensitive instruments ever. And they need to sense incredibly tiny waves because the objects that are producing these big waves are far away. By the time the waves reach us they’re very, very small, because they spread out as a sphere from a source.
Michael Slate: Josh, you were working on this whole process, right?
Joshua Smith: That’s right. So, I have a team of students and professors here at Cal-State Fullerton, but I’m also part of the LIGO scientific collaboration that has about 1,000 people working on this and they’re all around the world. So, a number of universities and funding by the National Science Foundation. Yes, I’ve been working on this for 15 years. Some of my colleagues have spent their lifetimes working on this. And so, that February 11 announcement was a major day in many of our lives.
Michael Slate: Big party, huh? [Laughs]
Joshua Smith: [Laughs] That’s right.
Michael Slate: Tell me something; I read something that kind of struck me because it was said in such plain language and it was just so straightforward. We were just talking about how hard they are to find. But there was also something like a million different things that could happen to screw up the search for that, like just make a blip or cause something that just disguised it, or be out there and not be what you’re looking for—that there were a million different ways that this thing could have been missed. That was kind of intriguing to me because you guys fought through on this and you developed the technology to actually fight through on this, but there still was like a noise coming from someplace that could have completely turned things off. This was something you really had to use the scientific method very deeply and very profoundly in order to actually continue working on it and also to be able to sum up when you have actually made the discovery, right?
Joshua Smith: That’s a great point. This event happened in September and we didn’t announce it until February. And one of the primary things we were doing between September and February was vetting the event. And you’re right; locally, there are a lot of disturbances that can couple into the detectors. The detectors can be affected by earthquakes, by even much smaller things, by local, we call it anthropogenic, noise: people walking around, by cars driving. But we have a couple of things working in our favor. This was designed, designed this way so we could make a confident detection. We have two detectors: one is in Livingston, Louisiana, and one is in Hanford, Washington, separated by about as far as we could get them, given the land that we needed to purchase. And that means that it’s much easier to find coincident signals that aren’t local disturbances. It’s harder to have things that will couple into such widely separated detectors. And then the second thing that we can do is when we have a signal we can compare that signal to what we expect for wave forms from the sources calculated with general relativity, with Einstein’s theories. So here at Fullerton we have students and professors that use super computers to model what happens when two back holes collide. And they use those wave forms along with the LIGO scientific collaboration to match the data that we see. And this particular signal was an excellent match, whereas most of the blips and blops that you talked about, local noise and things like that, are very poor matches. And that gives us a lot of confidence but we still spent many months making sure that this was real and checking everything that we could.
Michael Slate: One of the things that I was wondering about too, this Laser Interferometer Gravitational-Wave Observatory and how it found these waves, you’re speaking to that to a certain degree now, but really, it just amazed me because this is something that was brand new, right? When you look at the various videos of what this thing looks like and how people actually figured out how to do this, it’s not like when somebody says, “We’re working with telescopes” or “we’re doing this” or “we’re doing that” or “we have an observatory” and people are looking at, almost like something out of cartoons where you’re standing there looking in a telescope and you’re looking out into space. But you guys actually designed something that was very particular in terms of finding this kind of thing and it was something that was brand new, right?
Joshua Smith: Well, that’s right. It is very particular. Gravitational waves, the way we can measure them is that gravitational waves, when they pass through you they stretch space time. So, if a gravitational wave passes through the Earth, it stretches it in one direction and squishes it in the other. We can use that property to make the measurement. So, we built detectors that have very long arms, two and a half miles, four-kilometer-long arms. And what I mean by arms is at each end of those two-and-a-half-mile vacuum tubes—they’re like big tunnels—there are mirrors. And in between the mirrors, we shine a laser beam and it very accurately measures the distance between the mirrors. And we make it an “L” shape so like when I said the Earth gets squashed and squished in different directions, one part of the “L” gets squished and the other gets lengthened and a little bit of light, from the interference of light, will come out and we’ll measure it at a photo detector. So, we use laser light to very accurately measure the distances and we look for passing waves. And this is called an interferometer. And you’re absolutely right, it’s not like looking into a telescope. We don’t get an image of the system, it’s more like we record a wave form from the system, so it’s something a little bit more like a microphone. And by recording the wave form with multiple detectors we can get confidence that they were coincident at the two detectors within the travel time of gravitational waves and we can get information of where in the sky they came from, but we don’t form a picture. We more measure like a sound. It’s not a sound. It’s a wave form of gravity.
Michael Slate: Now, this LIGO, as I understand it, is only working at one-third its potential right now?
Joshua Smith: Yeah, that’s right. And this is another part of the reason why we’re all so excited about this. As I mentioned, we hope that this is the first of hopefully many signals. That’s part of the reason. When we make LIGO more sensitive, that one-third of its sensitivity is talking about the distance that LIGO can “see.” But looking out into the universe when you make the distance longer, you’re actually expanding the distance along a whole sphere. So you would cube that distance that you’re going to make it more sensitive and we would expect to see 27 times the number of sources if it just gets three times more sensitive in distance.
Michael Slate: Wow!
Joshua Smith: So, there are engineers and scientists at the LIGO site that are working right now to improve the detectors. We’ve taken the detectors offline. We’re going to perform analyses on the remaining data and publish those, but right now the detectors are being improved further and will come online in the summer with even better sensitivity and start another run.
Michael Slate: Alright. Let me ask you this, and this is kind of a strange question because it involves some philosophy too, in terms of epistemological approaches to things. You went into this, you guys all had to go into this—and again, it’s also related to the scientific method question—you went into this thinking, “OK, Einstein had talked about gravitational waves and we want to prove that these exist.” But you weren’t going in to prove something. Your approach to examining the universe wasn’t so that we can find this. It was actually, if they exist we’re aiming to find them. If they don’t, though, we’ll also have to deal with that because you couldn’t approach this as sort of, “Well, we know what we’re going to find and we’re just going to find what we know we’ll already find. You’re actually exploring what was going on in a part of the universe that really hadn’t been examined in the way that you examined it. And you had to be open to whatever it was that you would find, right?
Joshua Smith: I think that’s right. I will say that we took a safe bet. Einstein’s theory has been right in every way that we’ve tested it. In 1993, there was a Nobel Prize awarded to Hulse and Taylor, who discovered a system of neutron stars called pulsars that were orbiting around each other. And later work, which is continuing even today, saw that these two neutron stars, as their orbits went around, their orbits got smaller and smaller and they behaved as though they were emitting gravitational waves, and it precisely agreed with Einstein’s theory. So, we had very good information that gravitational waves do exist but nobody had ever set up a detector to catch them. So, I think we took a safer bet in that sense. But you’re absolutely right that within the error bars of our knowledge, we did not know that we would see black holes. We did not know we would see them so early. And we were all very excited and pleasantly surprised to see two black holes 30 times the mass of the sun, orbiting around each other a fraction of the speed of light at a billion light-years away. That was an unexpected source, or at least was on the optimistic end of what we expected. And we didn’t take a safe bet on that astrophysics, and I think we’ve made out very well and it looks like nature’s been very kind and we’re going to have a lot of interesting things to look at with our gravitational wave detectors.
Michael Slate: Yeah, I’ll say! [Laughs] I want to follow up with you often, OK? Again, if you hadn’t been able to detect these—we’re going to talk in a minute about what actually happened, what’s the result of having discovered this, but if you hadn’t been able to detect these gravitational waves or if they didn’t exist or if you somehow proved that they didn’t exist to a certain extent, that would have thrown a whole hell of a lot of physics and astronomy into question right now, right?
Joshua Smith: Yeah, I think that’s right. A lot of times I’ve heard my colleagues over the years say, “You know, it might be the most interesting result if we don’t detect anything.” I didn’t agree with them. [Laughs]
Michael Slate: Thank you! [Laughs]
Joshua Smith: I’m really happy that we started this new field of astronomy, but that’s right. I think one of the most exciting things in life, and especially in science, is when you find out something that you really don’t know or you find out something that isn’t quite right. It’s an opportunity to learn more about the universe. And if we had found that some of our theories weren’t quite right the hard way by not detecting something, that might have actually been a lead in another direction. I’m really happy that that’s not the case, but you’re right and I’m very happy that the National Science Foundation supported this project and that we’ve had so many colleagues around the world that have worked so hard to make it happen.
Michael Slate: Yeah, and there’s also a lesson that the people at large can learn in terms of pursuing the truth without fearing what that might be actually, because whatever you can find that’s true actually can help you in a certain sense, just by knowing it, even if it’s something that’s a terrible truth and you have to go back and, “Oh my God! Einstein was a crackpot!” [Laughs] But, you’d have to figure it out. You couldn’t just give up. Better that you found that out than you never found it out and you were pursuing something that was completely wrong, but instead you found something very different. And I thought in terms of epistemology that was pretty important in terms of the approach that people take. Because science is not a subjective thing. It’s not something where what’s true and what isn’t is based on who’s doing the observing. It’s objective and that’s very important. You put a lot on the line pursuing this, in a certain sense, and actually now you’ve got this whole other thing that’s opened up and let’s talk about that. What actually is opened up? People are talking about it. You mentioned it. In a certain way, there’s a whole new level of science that’s been unleashed right now. Let’s talk about that.
Joshua Smith: Yeah, so I think the big change that’s happened is that recently, there’s been a rebirth in astronomy. People are looking at astronomy through other channels. It started with light and then you looked at light in all the parts of the light spectrum; from gamma rays to radio waves. And you found different things whenever you looked in those different channels. And in past decades people have started looking at other particles like neutrinos and doing astronomy with other channels. Now, what we’ve done here is opened up a way to look at the universe with gravity and you can look at objects that don’t give off light, but you can learn about them based on the motion of their masses. Or, you can look at objects that do give off light but you can see a different side of them, because you can see what their mass is doing, not necessarily what their charges are doing like you learn from light. So, I think with this first signal we’ve seen the first glimpse of that and as the detectors get more and more sensitive we’ll probe farther out into space and hopefully see different types of sources and we’ll start to be able to do this new style of astronomy based on gravity. And there are things there that you can learn that you just can’t learn from light.
Michael Slate: There’s actually a point where you wouldn’t be able to investigate parts of the universe based on light because there’s no light there. It’s too muddy or whatever. This thing of being able to go back all the way perhaps to the Big Bang has a lot to do with these gravitational waves providing a way to view all of this. That was pretty mind-blowing there.
Joshua Smith: Yeah, that’s right. So, cosmologists think, and I’m not a cosmologist, but we have a lot of really smart people who are looking into this. Cosmologists think that in the evolution of the universe, there was a period where the universe was opaque, so light couldn’t pass through it. And so, that’s like a wall on how far back in time we can look with light. Gravitational waves, because they couple—gravitational waves are so weak and they’re so hard for us to measure here on Earth, because they couple so weakly to things. Coupling means you have a wave, how much of it you can grab or how much energy you can extract from it. They couple very, very weakly, which means that they pass right through objects. Our detectors on one side of the Earth or the other side of the Earth, there’s no shielding from the Earth. Gravitational waves can’t be jammed. They pass right through things. And that means they provide an opportunity for us to look back farther in time because of how they pass through things.
And so we have a group of people involved in the LIGO scientific collaboration that are looking at gravitational waves from what we call “stochastic” sources: from kind of rumbling sources from the time of the early universe, from the Big Bang. And there are also other projects that are going to have sensitivity in other frequency ranges and sort of fill in the gravitational wave spectrum. LISA [Laser Interferometer Space Antenna] in space and also pulsar timing and those projects will also be looking for what you mentioned, gravitational waves from the very earliest moments of the universe.
Michael Slate: Yeah, very cool. One more question, and this is more of a reaction from you on this: Szabolcs Marka, a member of the LIGO team, there’s a quote from him that says: “Until this moment we had our eyes in the sky and we couldn’t hear the music.” And I thought the poetry of that in relation to what we’ve been talking about is pretty intense and I wanted to get your thoughts on that.
Joshua Smith: It’s a beautiful way to put it and another way that I’ve heard, that actually a person that I was speaking with yesterday said, is that humanity has gained another sense through this discovery. I think that’s apt. Although we’ve seen only one event so far, it’s a new sense we have. We use our tools to sense it, but we can now sense the ripples in gravity from far- away objects like black holes, and I think that’s really amazing.
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