 All right, well, I want to thank you all for coming out to see me here today. This will be a little bit of a change of pace, I think, from the talks you've been listening to, but I hope an interesting one. So I'm going to talk to you today about gravitational waves and the astronomy that we can do with it. So start us off. I'm sure many of you know what's in this picture. On the left here, this is a picture of the Hubble Space Telescope. And the right is an image that it is produced of a spiral of galaxies at some distance. Now, I'm sure many of you have known, you know, we've been able to use telescopes in some sense for hundreds of years since the time of Galileo. And we've learned a huge amount about our universe since then. And one of the things that we always find is that any time we open a new avenue onto the universe, a new way to observe it, we keep finding more things. And so what we're hoping to do is to find a completely new way to study the universe. And we've done that, and we're just in the early days of this. And so how does this work? Well, first of all, what are gravitational waves? I don't expect everyone to be familiar with this. But of course, you know, just over 100 years ago now, Albert Einstein first proposed general relativity. And one of his early predictions was the concept of gravitational waves. So how does this work? What happens is that you have masses that can orbit around each other, or rotate around each other, and they will produce radiation in a very analogous way that charges will, and you produce electromagnetic radiation. So it's a very similar concept. But what many people aren't familiar with is, you know, how does that actually affect matter? How does that actually affect things? How do you measure it? So first of all, I want to give you guys an idea, and we'll do a little thought experiment together. Let's imagine that you have a ring of particles, and these are floating in space. They're not acting under any other force, except for gravity. Now, we're going to imagine here that this ring is on this board. And we're going to have a gravitational wave, a very strong one, pass through this board. And I'm going to show you what that would look like. Well, it looks like that. So the ring, which would start off stationary, would oscillate. And in particular, it will oscillate back and forth. Of course, the key thing to look at is what is the strength of this gravitational wave. This is a very strong one. And I just want to point out that one of the ways we look at how strong these things are is by how much the position changes relative to the stationary one and relative to the overall length. Normally, we state this in a change of length over, say, the width of this object. So we'd normally characterize this by a delta L over L, which in this case is huge, about a half. And now we should think about this as, you know, how large are gravitational waves normally? And we have a quote here from a famous physicist. It is obvious that the amplitude of gravitational radiation has in all imaginable cases a practically vanishing value. And there's sort of a corollary to Chekhov's gun here, which is that, of course, if I'm going to quote someone, it's going to have to be Einstein. He was actually not a believer that we would ever be able to detect these things. It was obvious to him, maybe not to everyone here and not to the future generations, that you wouldn't be able to. But it's not without some reason. So let's go through that. So as I said, gravitational waves are produced by moving masses. And so you can produce them. I'm producing them right now with my hands. But how strong is that? So here we have a device on the left. This is actually a gravitational wave generator. It does produce gravitational waves. There's two masses, those masses span around. They're connected to a motor in the center and it rotates very quickly. So the question is, how strong are those gravitational waves? And as I said, the key measure that we'll be looking at is the change in length over length that you can actually measure. In this case, you can estimate what this is and we've done so. It's 10 to the minus 50. That's a small number. Okay, that's pretty hopeless. Okay, let's scale this up. Maybe that was just too small. Maybe we can do a better thing. So next we have, this is actually a centrifuge at NASA. You can put much larger masses at this. They can go fairly high velocity as well. Well, how large of a gravitational wave does that produce? 10 to the minus 46. That's pretty small too. Okay, so this isn't looking very hopeful for us to be able to produce gravitational waves. So I think it's pretty reasonable what Einstein said. Now, one of the things that is, though, is that the universe is a better imagination than most of us. And one of the things that's true is that you get larger gravitational waves, the faster objects are moving and the higher their velocities. So we can think about this. Where can we make this the most extreme? And here's where you do it. This is a simulation of two black holes and they are orbiting around each other. They emit gravitational waves that causes them to lose energy and then they merge. Okay, this is actually not in real time. These black holes have actually been moving a significant fraction of the speed of light by the time they merge, so it's slowed down quite a lot. So they are moving as nearly as quickly as we can get them to go. Because they're black holes, we can put in, say, 20 or 30 times this mass of the sun into a very small area. So they're as massive as we can make them. This is probably the best case scenario we have to be able to produce gravitational waves in our universe. So how strong are those? That's 10 to the minus 21. Okay, that's still pretty small, but that's a good 20, 30 orders of magnitude better than anything else. So this is our best bet. So we're going to try to go after this. So how do we measure that? Well, because what's happening is that lengths are actually changing and in particular it shrinks in one direction at the same time that it grows and lengthens the other. So what you can do is build this kind of experiment. You have a laser that splits into two beams. It hits a mirror at the end, which are essentially, you can consider them as in free fall, as in sort of open space. The beams come back, they interfere with each other, and you can set it up such that the light would destructively interfere so that normally there would actually be no light being output to a sensor. And when one of the arms changes length, so one grows in length relative to the other, you no longer, you break that destructive interference and you get some light out. And so you can use that to measure very precisely the difference in length between two orthogonal directions. And this is the idea of how you do this. Of course, the other thing you can do is you can make your instruments large as possible. And that's what we've done. This is the LIGO instrument in Hanford, Washington. It's on an old weapons testing site. This is four kilometers long for each arm. Of course, if we could have had it bigger, that would have been good too. But that's what we can do. That's what we have done. And of course, we don't just have one of these. It has a brother in Livingston, Louisiana. And of course, there's the Vergo Observatory, which is three kilometers long, in Caschina. And in fact, we have a worldwide network of these now placed all over the planet. So you can see where the two instruments, the LIGO instruments in the United States are. Vergo over in Caschina. There's a shorter instrument, Geo 600 in Germany. In fact, a lot of the technology was developed. And then we have future sites that are under construction. So there's another experiment being developed in Japan. That would be a very interesting one. And we have another one being built in India. So why do you want to do that? Well, you want to build it all over the planet. Because the more that you can observe the same source, you can also pinpoint where it is in the sky. And that will become important later. Okay. So I've sort of set this up. We've built it. We have the strongest source that we can think of. Well, can we find it? And of course, the answer is that we did. So what our instrument measures is a change in length over length. And that's what's normally called in physics parlance as a strain. And what we essentially record looks like a time series. So it looks like an audio track or any sort of simple thing. In fact, it's at a very audio-like frequency. It's 16 kilohertz. It's not even very high quality audio. But we have a few different channels with multiple instruments. And you can see here in this top plot here, what we have is a function of time. You can see the change in length that we measure. And this top graph shows what we saw in both the LIGO instruments that we're observing at this time. That's the top row. You can see that's the actual data we collected. This middle row is what we would predict if we were to say ahead of time what we would think a binary black hole would actually do to our instrument. And you can see they match up very well. And the bottom plot is, in fact, what happens when you do a time frequency plot of this. So a very unique, it's a nice way to understand our data. And of course, this is a famous event now. I'm sure many of you might have heard it in the news, it happened. We detected a binary black hole merger back in 2015, September 4th. It is aptly named GW 5914. It rolls right off the tongue, I'm sure. But for us, it does. If you say it enough, it will. It's the merger of 36 into 29 solar mass black hole. So this is much more massive than the sun. And of course, it's very far away. It's 1.4 billion light years. But because these things are moving so fast and they're so massive, they can still produce a signal strong enough for us to see. And of course, I'd be remiss just to mention, of course, that some of the people who are critical to actually developing the instrument and developing the science were recently awarded with the Nobel Prize. Okay, well, black holes are great. But one thing about them is that they're dark. And if you have a merger of black holes, what happens is as they are getting closer and closer together, they sweep away any matter that might have been around. So when they merge, in fact, we're the only ones you can really hear them, in a sense. There's no other corroborating evidence that they actually happened, existed or merged. There's no other way to observe it. But that's not true of all sources. So I'm going to show you now a simulation of another kind of source, neutron stars merging. And you'll see that this is very different. So they will orbit around each other. They'll emit gravitation waves. And as they do tilt, they'll eventually merge. But when they merge, this time, neutron stars, of course, are extremely dense stars, made primarily of neutrons with a thin crust of other materials. And they're the densest stars that we know of outside of black holes. And in fact, they're very small. They have a sun in just a 10-kilometer diameter, in fact. So they're very dense stars. But what they do produce is they will actually throw off some of this matter and produce radiation when they actually collide. Which, of course, for most people who like to set out fireworks, that's the exciting part. So I think that's something we're also trying to look for. And in fact, many of you may already be aware, we've actually found this. So what I want to first show you, and I'm going to need everyone to be quiet when I do this, is I'm going to show you actually what we observed in terms of gravitational radiation. And as I said before, the signal that we measure is very much like an audio signal. So what we're actually going to do is we're going to pipe the audio from the instruments directly to you guys and the speakers. It's going to sound a lot like static for a while. But you should actually be able to hear a lot of this system about to merge just before it does. And you'll hear basically a kind of chirping sound to start at low frequency and then go high very quickly. So we're going to play this now. So again, this is actually the data that we have. There's a time frequency spectrum out of it. I have carefully removed the signal ahead of time, so you don't see it there. But now we're going to listen to it in real time. And at the very end, you should be able to hear something. Everyone take a moment to be quiet and we'll try to listen. You can start to see the track forming. But you can't quite hear anything yet. It's a too low a frequency. That was it. You guys hear it? Okay, so I've done this one for other audiences and it actually really depends on the audio setup. If you do this at home, you're going to need some good speakers to get the low frequency in there. These ones are quite good. Amazing that is what our real data sounds like. It's not the simulation. That is what we observed. And more than that, as I said, when neutron stars collide, they throw off matter. One of the things that happens is they can form a jet. They can produce a huge amount of radiation and they can cause an event that we call a gamma ray burst. And in fact, one was observed with this. This shows on the bottom the signal that we saw by the gravitational wave detectors. And above it is actually the signal observed by the Fermi telescope. So this is a satellite that is looking for gamma ray bursts. They found many of them. And they found one just 1.7 seconds after we saw the merger. Now you might ask, well, why is there this time delay? And the reason for that is, of course, it takes some time for the matter to actually form a jet and actually produce an emission. So it's not an instantaneous process. The other issue is that immediately after the explosion, there's a lot of material around. And if you have a lot of material, your surface can become opaque. It actually can prevent light from escaping. So sometimes you have to wait for it to cool down a bit. But in fact, we saw this with a gamma ray burst. And of course, we also saw everywhere across the spectrum. This is actually an image taken by the Swope and Magellan telescopes. This is an optical image. So this is actually what you might imagine you can see with an eye. The bright spot in the center is actually a galaxy. And just to the edge of the galaxy, you can see this bright spot. And you can see this is where we recorded on the 17th of August. And just a few days later, you can start to see it dimming. So this is the key sign that something happened right there. And of course, we didn't just see it in the optical. We also saw it in ultraviolet, infrared, and radio. In fact, weeks and months afterwards. It's probably one of the most study events in astronomy. In fact, it led to one of the papers with the most number of authors on it, as a result, with nearly a third of these transformational community not a single paper. So you can imagine how much work that was. So we see it everywhere. Well, what can we learn about that? One of the things that we can learn that I want to get across here is what happens when you throw off this much nuclear matter. So you started off with neutron stars. You slammed them into each other. And this very neutron-rich matter came off of it. So one of the things that can happen is called R-processed nucleosynthesis. You don't need to know the term. I'm not going to quiz you. But what can happen is the following. So here on the x-axis here, we have the number of neutrons, the vertical we have the number of protons. So what can happen is that you throw off all this neutron-rich matter, and it will decay. And one of the ways that it decays is that a neutron can turn into an electron, a proton, and an anti-nutrino. It's called beta decay. And what that allows you to do is you can create very high numbers of protons inside a nucleus. And in fact, this is one of the ways that we can produce the heavier elements in the universe. The heavier elements we see on Earth, like gold and all these other things that people find interesting. So to give you an example, to maybe refresh people's memory, I'm sure some people who already know this, initially after the Big Bang, the only things that were produced were hydrogen and some helium. The remainder is produced by nuclear reactions within stars and then released when they die. And some of these are not even produced in that. So some of them have to be produced in supernova and in the merging of stars like we just showed you. In fact, all these ones in orange here, that is approximately how much we think was produced of the solar system's total amount of it was actually produced in this kind of collision. So a huge fraction of what we have here on Earth and what we make advantage of was in fact blown out from one of these collisions and is one of the products of it. Okay, but we haven't just seen one event. We've seen one binary neutron star. So what I'm showing here is actually the signal that you'd observe. So this is the waveform that you get from different types of signals. So this first one at the top, that is that binary black hole that I showed you at the beginning. It's a very short signal. About 0.2 seconds is what we observed of it. And we've seen now a plethora of other binary black hole mergers. Here's an example of some of them. And of course at the bottom is the binary neutron star signal. You might notice there's a big difference between those. That difference allows us to measure properties of the system. We can measure what their masses are. We can measure what they're doing. And that allows us to learn about the universe. But this is just the first step. As I said, we're in early days. So what's coming next? We have space-based observatories with Lisa. Of course we're also looking at other frequencies. Really what we've done with ground-based detectors is very much just like looking at one part of the electromagnetic spectrum. You may know that we have telescopes looking at UV, we're looking at gamma rays, looking at optical light. Right now we really only have a part of the gravitation wave spectrum. And we don't know what we'll learn when we look at the other parts. So one of the things that's going to be coming online in the next, hopefully in the next 15, 20 years is we're going to be putting gravitation wave detectors in space. And I just want to maybe leave you guys with one thing. So I want to assure you guys that there is some association with open source in the scientific community. Probably more important for science, even more than open source is actually open data. So in fact the data that LIGO produces is regularly released. It's available, it's available from gwopenscience.org. I invite you guys to check that out if you're ever interested. As the introduction said, of course, I'm involved in actually putting together a lot of these analyses that try to find these kinds of events. And of course I write an open source toolkit to try to do so. And in with that I'd like to say thank you for having me and look forward to what's coming in the future.