 I'm going to talk about something which is really at the edge of what you probably are coming here for. But it's an interesting experiment that was done both at MIT and Caltech and then by a very large number of people. And it opened a new field. And I'll try to tell you a little about that. It does have to do with space, but not necessarily something you will experience very easily. So let me start by telling you a little about gravity. And where is this clock that does? It says 9.15, but it isn't counting down. All right? Somebody better get that right, otherwise I'll go on for hours, OK? The thing that you learned in high school and you learned certainly at MIT as an undergraduate is the idea of Newton and gravity. In fact, there is a force that makes gravity. It holds us to the ground. It pulls apples down. It makes space difficult to get out there. But once you're out there, you don't have much to deal with it. But it turns out to be the wrong theory. And the theory that actually got evolved in the early part of the 1900s was Einstein's theory of general relativity, which is a theory of gravity. I won't go into any more to say, except what that theory did, was it replaced the gravitational force by something that is the geometry of space and time. I won't go any further than that. It's a lovely theory. And many people still don't believe it, but it's getting to the point where you have to begin to take it very, very seriously. Because things that it predicted are beginning to show up. And that's the first thing I want to show you. Let's see if this plunger thing works. All right. There we go. Good. One of the things that was early on known already in the 1900s was that things could not move faster than the velocity of light. And in Newton's theory, that gravity moves. There is nothing really talked about moving gravity. But the implication is that gravity moves faster than the speed of light. In fact, it moves infinitely fast. You never talked about the fact that if you plucked the sun away from our solar system, that suddenly you would have assumed, if you took Newton's theory right, that the Earth would start going off on a tangent. It doesn't do that. It takes about nine minutes before it does that. And you don't know about the sun disappearing if it was disappearing until nine minutes after it's happened. So there is already a delay in the whole thing. And one of the things that's predicted by Einstein's theory was gravitational waves. Those are things which send gravitational new information around the universe with the speed of light. And here's a picture of a gravitational wave, which I'll show you in a second moving. But there are waves that come from, well, all right, now it's moving. But OK. Look at me for a while. It'll make you sick if you look at that too long. What it is, it's a transverse wave, just like electromagnetic waves. It's a wave that moves at the velocity of light toward you. And that's what's doing in that picture. It's coming at you. But at the same time, it does its dirty work, transverse to the direction it's moving. So this is what that wave does. If you sprinkle a whole bunch of masses out in space and you're at that red spot right there, this is what it would look like. All the dots, you'll notice two pieces of the pattern that are very important. One piece of the pattern is it looks like things are compressing in one dimension and they are expanding in the other. I hope you see that. The other thing that's going on is that the amount of distance between two dots, like that one and that one, is bigger, the amount of change of motion of those two. The difference between their positions gets bigger than the two that are next to you. And that is the same kind of motion you would get if you pulled on a rubber band, if you put marks on a rubber band. So there are two attributes of this that are important to understand. It stretches space in one dimension, contracts it in the other and that keeps inverting back and forth. And the other thing, it's a field of strain. Change in length divided by length is a constant in that picture. One case is positive and the other case is negative. So how do you then use an instrument to detect this? And that's the next thing I want to talk about. Whoops. Clicker. Okay, good. Don't move it yet. So what this is, a most primitive way of doing it. Imagine that gravitational wave coming down from above and here is a laser. That isn't looking, it looks like a laser but it's supposed to be a laser. And then here is a device that splits light. Light comes out of it, splits light. Half of it will be heading to that mirror. The other half of it will go heading to that mirror. In other words, there's a reflection and then there's a transmission through this that's called a beam splitter. And these are two mirrors that send the light back and here is a photo detector. Okay, let's get this thing moving and here's a light comes out of the laser. Wherever there's light power, it's red but this is the wave, the electric field in the light and watch now what happens. If you make the distances of the beam splitter to these end mirrors identical, you'll see something interesting. No light goes to the photo detector. There's the waves cancel and that's what this picture indicates. Now, if you come down with a gravity wave and stretch space in one dimension and contract it in the other, that's what happens. You will see whenever you disturb that condition of equal times, you will get light to the photo detector. You see what's going on? I hope, please tell me you see what's happening, right? Okay, great. So that is the whole idea of LIGO. There's no more than that. That's the basis of the way it works. In other words, the gravitational wave comes along and it disturbs the condition of no light at the photo detector. That's the basis of it. And then comes along a guy who many of you know, Kip Thorne, who by the way, why do you might know him is because he's the guy who instigated Interstellar, the movie Interstellar. And how many people knew this? I'm just curious, some of you. I mean, he made up the script and he's very, very proud of in the guise of what the introduction of this thing here is actually, he fits right into this place because he wrote a book about him making that movie and he said he made no physics, he had to not compromise on any physics ideas in that movie. Now if you've seen the movie, I didn't understand the movie, to be honest with you. Okay. But it was too complicated for me. Especially in the end, I couldn't. But much of it, but much about Kip will tell you and if you read his book about it, you will see what he had in mind. What he meant is it's not mathematically impossible. In other words, nature didn't choose maybe to go that way. But much of the things in that happen and as we'll see in a minute. Now Kip was in this business of what do gravitational waves look like? Where might they come from for many, many, many years? He's at Caltech and very early on he predicted that if you wanna ever detect a gravitational wave or there had been attempts to try to do this ahead of this when they were failed attempts. But people hadn't done the arithmetic right and know enough about the universe, what's out there and know enough about general relativity, make this prediction. But he said, he told us all, look, if you wanna get in the business you have to look for strains, which is H, which are smaller than 10 to the minus 21. That's a terribly small number. I mean, I hope all of you know 10 powers of 10. Okay. This is not a high school, okay. But the thing is that when you build an instrument that had those mirrors at four kilometers from the beam splitter, the motion that you have to measure is very small. And this I wanna set the context. That strain amounts to about 10 to the minus 18 meters of motion at the end. That's 1,000th the size of a nucleus. That's just very, very difficult to do. And what it turns out to be, and this was a challenge that Kip's calculations threw at us as experimenters. Namely, first of all, if you're gonna try to measure 10 to the minus 18 meters with light, you have to somehow figure out how to use light which is 10 to the minus six meters and get it down to 10 to the minus 18 meters. So you have a factor of 10 to the 12 you gotta deal with just in the measurement of the position of the end of the mirrors with light. So that was another challenge number one. I'll show you how we go at it. Then the other challenge is just as serious, in fact, much harder. And that is even though you might have a wonderful way of measuring the position of the mirrors, you've gotta have a way of stopping the mirrors from shaking. And if they're tied to the ground, you have another factor of 10 to the 12. Why? Because all of us in this room are shaking by about 10 to the minus six meters right now just from the ocean hitting the shore all the time. Okay, add many other things, cars and everything else happening around us. It's probably worse than that. So you had two big factors to make it experiment work. 10 to the minus 12 in two different areas. And that's the next piece of the story. So let's see. But again, this is, you're gonna have to move the slide for me. Okay, this is, I won't go into this detail, but this is the instrument that actually made the measurement. It's schematic of it. I'll walk you through a little of it, not all of it. What you're familiar with is the laser and the beam splitter and the test mass and the test mass. Now all this other stuff is important to get that factor of 10 to the 12. One of the things you do is you put another mirror on each leg and let the bounce, let take the light. It's not a mirror. It's a partially reflecting mirror and it transmits some light. And by doing that, you let the light bounce back and forth, something like 100, maybe 300 times back and forth in this arm, 300 times back and forth in this arm. So you get a big factor of gain out of that already. But that's not all. Okay, you have another thing. When that condition that you, I told you about, when no light goes to the photo detector, the light that comes out of the laser has got to go someplace. Well, what it does, it's very interesting in that picture that I earlier thing didn't show it. The light hits, no light goes this way, but all the light comes back to the laser and that's quite destructive. So that's why there's another mirror right here. And that mirror is again, a partially reflecting mirror. And what it does is it takes the light that comes out of the laser, which now is partially reflected. You don't see that, but it wouldn't. Because it's got a mirror on it, this light will come back, but it takes the light that comes back out of the interferometer. That's what this device is called. And that now comes through this thing and makes those two cancel each other. Just like the light to the detector. So what you've done by doing that is you take, let's say maybe 50 watts of light come out of the laser. Well, no, that's more like 10 right now. Well, 50 now, wait, what's 10 in the early days? That means there's something like several kilowatts of light in this little cavity and there's something like megawatts of light in here. And that's ultimately that business of being able to convert that laser into a megawatt laser with these little tricks is what made it possible. So that's how we got that first factor of 10 to the 12. And the next slide shows the other factor, how you get that. And some of you might be actually interested in this. If you have delicate apparatuses, you might want to use some of the techniques we've developed here, especially if you're doing microscopy and looking at very small things on a table and the table is shaking because the building is shaking. Okay, so there are two ideas. Here's that mirror, but you notice the mirror, this is one of the ideas. You don't just hang the mirror, you're hanging the mirror, but for many, many pendulums. It's just a pendulum. It turns out a pendulum is a wonderful way to isolate the ground motion. So there are four pendulums in series. Here's the ground. That's not the ground, but that's where it's supposed to be. Here's a pendulum hanging from it. And then there's another pendulum hanging from that. And then another pendulum with another object there and finally that very precious mirror. So you have four pendulums in series. That helps a lot. But then you do something which I will only describe to you. It's this complicated looking thing here. You can see this pendulum hanging from it. There it is. And what this gadget is, is up here is something which actually you could use in your own laboratory. And let me just describe it to you. I won't walk you through it. What it does, how many of you know these headphones that cancel noise? Just raise your hands if you, oh, all of you, okay, you guys are in business, okay. And so what happens is this is the same idea but applied to vibrations. What you do is you have a seismometer. That's a device like that. You can't tell you much. You put it on a platform and then you have pushers in a feedback system that nulls the seismometer. In other words, what you do is you make that platform with a seismometer which is the measure of inertial motion and you make it go to zero by pushing it so you cancel the ground motion. And you do that twice. And that's very effective. And that, by the way, you could, is a very useful thing for semiconductor manufacturing and anybody who wants to make something very tiny not move much in a noisy place. Okay, so let's go on. Okay, so now we have, let me tell you now, and now let me tell you a little about the science. This was the technology. And so there are two LIGO detectors. There's one in the United States. There's one in Hanford, Washington. And another one in Louisiana. There are the two. There's a detector in Italy which is very much like the ones in the United States. That's near PISA. There's a German detector which is not quite as big. It's a research detector. And for the future, since we are gonna talk about the future, there is one being built in Japan, another one being built inside of a mountain. And then there's one being built in India. Those are important and I'll try to motivate that as we go along. Okay, so there are that many detectors. And I wanna show you just what LIGO, the LIGO hit it again so that this becomes a movie. It's a, I give you a little travel log of what it looks like. Just hit the button again. Okay, good, you got it. Watch, this is a site in Louisiana. This is the site in Hanford, Washington. You can see these tubes. This is, these are not bad. This is enclosures, concrete enclosures. This is by the way, Louisiana. Concrete enclosures that are around this vacuum tube which is just like outer space. Very much like the space. This is people's working on a standard laser table. You probably have them right in your own labs here. And this is the control room for the living snow, the LIGO, Louisiana site. And people are learning how to run the instrument. Okay, let's go on. Now, stop right there. This is the first thing we discovered. And this made all the noise about two years ago. And what is it? Let me quickly walk you through this. The top two pictures are a time. This is time going this way. So 0.2 seconds to 0.4. It's about 0.2 seconds. And this is the waveform we saw at Hanford, Washington. This is the waveform we saw at Livingston. Superposed on it is the Hanford waveform. But delayed, and then you'll see. So let's look at this waveform a little bit. This is noise, just junk. That's junk also. There's nothing there, but this is sort of coherent. And something is going on. And then you take those two signals because now you have gravitational waves coming from outer space. They have to do the same thing at the two sites. That was the philosophy of the experiment. And in fact, what you find when you do the analysis of this, it hit Louisiana before it hit Washington. So it tells you that it came from the south, somewhere in the south. That's not very good information for astronomers, but it was very important to us. We now know, and what is it? Well, we'll figure that out in a minute. But they superpose each other. If you move the signals by about seven milliseconds, they sit on top of each other. Here's a theoretical waveform that comes from the Einstein theory with a model I will give you in a minute. It turns out it's two black holes. I might use that water if you want to give it to me. No, you don't have to. You can throw it at me. OK, thank you very much. Hey, thank you. So what is in this picture is that is the theoretical waveforms that come from Einstein with a model you'll see in a minute. This is the real waveforms. And this is the residual between the theoretical one and the actual data. It looks pretty white. There's not much there. So you've got a pretty good match between the theory of what this is and the signal itself. And this, we're going to see again in other guises, so I better describe it. This is a spectrum. In other words, it's frequency. And this is the frequency. This is time. And this is the colors tell you where the frequency, for example, starting at about 30 hertz, up to about middle C, 256. There's this sweeping thing that goes whoop, just like that. And it's about the same in both sites, not exactly, because the noise is different than two sites. And you'll see pictures that I get again. And so what is it? So let me try this clicker. Yeah, wonderful. It worked. So this is what we think this is. What we thought it was, it was two black holes. And nobody knew that people knew about black holes. But we were hoping there would be black holes living together. It turns out nature is full of black holes living together. We didn't know that. And there are two of them. They're going around each other. The waveform is not to a filter. They're saying that's why it looks a little different. This is the actual waveform of these versus, again, time. This is the strain. And here is what's happening. This is getting closer. And you notice the frequency is changing as they get closer. And all of a sudden, these two black holes get really close. And this signal you absolutely can't do by analysis with. Analytically, you have to use computer solutions of the Einstein equations to be able to do this. And finally, you wind up with a black hole, single black hole that's bigger than the one that you had to be in with. But you don't get all the mass that you had in these two masses. Some of that mass gets radiated away as gravitational waves, as we'll see in a minute. So here's some sort of gee whiz numbers that go with this. For example, I think I'll only use one of them. You look at this green line. And this is this green line is the relative velocity of these two guys. And this is the velocity of light. 0.3, the velocity of light, sort of out there. And by the time they hit each other, they're going, these are massive things, 30 solar masses. And they're smashing into each other at about 0.6, the velocity of light. It's an unbelievable collision. I mean, and we'll talk a little more about that. So that's what we saw. And so now here's, we saw more of them. And otherwise, we really wouldn't have believed this. And here are the dates I don't want to go into. You can, well, you can figure it out for yourself. These are years, and these are months, and days, and month. So here's that one we just saw. This is now the strain again. And this is time. And we saw four of these guys. This was the first one we saw. Then we saw one we're not quite so sure of. And this one, completely different. And you'll see why they're different over here. They have different masses. This was one mass was 36 solar masses and 29. And three masses disappeared off into gravitational waves. Here in this one, it's much lighter. 14 solar masses, seven solar masses are the two. And they only one mass, solar mass, disappeared off into gravitational waves. So this is what we knew until last August. But let me say, there's a few more things to say before that. What we were not good at is telling an astronomer where it was in the sky that these things existed. In other words, that was a real problem. We have no way of taking these detectors and pointing them. It's not like a real telescope. So we only can tell where things are by differences in time. I don't understand that clock. I have to tell you, OK? That says I have 10 minutes left, which is good. I'm fine. I can do it. But so these are sort of, this is a picture of the sky. If you made it, here's one end of the sky all the way, the other east, west, north, south. And these giant bananas are the sort of uncertainty circles you get from the timing. And that's crummy. You can't go to an astronomer and say, find something that is half the sky. You can't do that. They won't know what to do with it. And so there was a very important event that just happened last year in August, the 14th of August, in fact. And the other detector, this was Virgo. This is the one Italy also saw the black hole. And this is the fifth black hole we saw. But here's the important thing I want to show you. Here are these waveforms. And this is, I've forgotten. This is Hanford. This is Livingston. That's Louisiana. That's Washington state. And this is Italy. It's not quite as good. The detector is not yet fully tuned up, but they were able to see it. And by doing that, you could take a sky picture, which this would be LIGO alone, those two detectors. And here you add Virgo to it. And you can now make the error circle much smaller. This is thousands of square degrees. And that is hundreds of square degrees. That's a little better. Remember, the moon is one quarter of a degree. So it won 16th of a square degree. So you're not doing it. You're telling astronomers it's still much bigger than the moon. But still, it's a great deal of progress. And that's the reason, as you'll see in a minute, why we want more detectors. And so let's go on. Here is sort of the zoo of ones we've seen. I think I'm not going to dwell on this very hard. This is just a nice picture showing you the black holes that people knew about. And these are the black holes now that we have discovered with this new technique. I'd like to go to the next slide. Here, this is the next spectacular thing that happened to us. It turned out August of 17 was the most dramatic year and the most dramatic month for gravitational wave detection. But that's what we saw. This is another event. And this event is a completely different thing. Here, the only way we can really show it to you is here is its time series. This is time. This is the strain. And look what does. It goes whoop, like that. Well, a really nice long, like a glissando on the piano. Really lasts, I mean, for 10 seconds. And what was done is it turned out there was a satellite, an x-ray and a gamma ray satellite called Fermi, up in the sky. And they saw something 1.7 seconds after the endpoint when these two whatever objects they were, they crashed into each other. Well, once we saw that, we knew we were not looking at black holes anymore. We were looking at something called two neutron stars. These are stars the size of the sun made entirely of nuclear matter. And they were discovered back by Jocelyn Bell and, well, Jocelyn Bell discovered them. She never got the Nobel Prize for it, which is most unfortunate. But she was a graduate student at the time and she was the one who discovered the pulsars. And that's what this is. And she found that. So what we now have found is two neutron stars doing the same thing, going around each other. And they smashed into each other. And the interesting thing that came of it, we knew that might happen, is that it was seen as an electromagnetic pulse, a gamma ray burst. A little bit after, and this is one instrument on the Fermi satellite, that's another one. And there's another satellite, which you also saw it, it's a little bit not as well seen. That was dramatic. And what this did is it gave, and Virgo, didn't see it, but for complicated reasons, even though it didn't see it, it gave us position information. I'll answer that if there are questions. It's too complicated to explain in the few minutes that I have left. And so what happens is that here is sort of the, this is the error circle in the sky that comes from the Fermi measurement. This is the, yeah, this one is the error circle that comes from the two LIGO detectors. And here, oh, I'm sorry, I lied to you. There are two versions of the, the smallest error circle came from another instrument. Smaller of the electromagnetic ones came from Fermi on this big circle here. But this is the LIGO uncertainty in position in the sky. And then when you add Virgo, not seeing it, it turns out, then that's it, you get this tiny little circle. And now it turns out, as soon as people had this information and we send it out right away as a telegram, people with real telescopes were able to look at it and they looked at a galaxy called NGC 4493. It's just another of zillions of galaxies. And what they had pictures of, what was going on around that galaxy is two months ahead of that. And you can see this pattern, there's the galaxy and there are these stars. And then here it is, there's a new thing that showed up right there. And that's this neutron star collision. And that then started a avalanche of electromagnetic, electromagnetic. I won't, you can't read this slide. The intent of this slide is just to show you that people in all different gamma rays, x-rays, UV, optical, infrared, radio, all of this is a timeline, all began to focus on this thing. And they learned an incredible bunch of stuff from this. And this is one of the things they learned. They learned what it was. They learned that it was a thing which is called now a hypernova. And what is it? It's like a supernova, but it's two stars, these two stars colliding. There they are. And they make a new thing, which is a black hole because you can't make neutron stars bigger than a certain mass. And putting these two neutron stars together and smushing all that nuclear matter together makes the thing that's too heavy. So a black hole forms. And that black hole emits a gamma ray burst, but we were not looking at the people in the satellite. We're not looking directly at the gamma ray burst. They were looking at an angle. We now know that. And here is the debris that came from this collision. And the debris from that collision made, and this is a very nice story. It made, we now know because of this one event and all the follow-up measurements that were made, we now know where all the heavy elements are made in the universe. Up to now, we know hydrogen started with a big bang. We had a little helium, a little bit three minutes after the big bang. And then we got a little bit of brilliant, all those light things in the periodic table. We got lithium, but you got stopped at boron. You can't make any heavier thing than boron. People realized that you could make those in stars. So supernova became the culprits that made all the things up to iron. But people couldn't figure out where gold came from. Or platinum, or uranium came from, and now we know. And it comes from neutron star collisions all over the universe. So that was a big discovery. And the other thing that was nice, I think I'm gonna go on, this is something which you can do cosmology with this. I wanna go on because I'm gonna run out of time. There are many, many other sources that we can look at, and we will once we get back into business and running. But I wanna give you a little feel for where we're heading so that you have an idea where the field is going. And here's the first thing. This is what I already anticipated for you. These are these sort of error circles on the sky that you get if you have Hanford, Livingston, and Virgo. Virgo is the Italian detector. And you can see these bananas all over the sky. And you can improve the detectors a little bit, and that's what this is, a little improvement, a little improvement just in those detectors. But you add India to that, and boy, look what happens. All these error circles turn to the things the whole of the size of the moon. And you can really begin to do what's called multi-messenger astronomy. And that's the reason we want to have more detectors on the ground than people have recognized that now. The other thing is, and this is a curve I'm not gonna describe, but you can get the spirit of it right off. What this is is noise, and this is frequency. And so you identify a point. For example, the place where we were operating with LIGO to make this detection is this line right there, that purple line. And that purple line is where we were about a year ago in terms of our sensitivity. The place where we ought to be, this is the design sensitivity, is a little better. Going down in this curve is better. This is, every one of these things is a factor of 10. So we have, first of all, got to get to design. That's our biggest challenge right now. But there are already many, many ideas of how to go another factor of three. And another factor of three. And then there are ideas in the world, both in Europe and in the United States, of making completely different gravitational wave detectors on the ground that could get you another factor of about 10. And with that, you could look at the whole universe. Here's sort of a picture. The whole universe in black holes, all the way to the beginning of the formation of stars. That's sort of a redshift, if you know what that is, all back to about a Z of 20. And that's not back to the Big Bang. That's something else. But it's back to the very first star production. And that would be fascinating. So there is a huge movement for making bigger, better detectors, now that the field has started. And here is my last slide. And I want to talk a little about what the real future looks like. So what this is, and I'll be a little more careful with this one, is that this is frequency of the gravitational waves. Over here is 10 to the 4 hertz. And this is LIGO's domain. And here is the strain. So LIGO and all the ground-based things are sort of good between 10 hertz to about 10 kilohertz. It's the audio band, in effect. And between strains of 10 to minus 20 to 10 to minus 25. It turns out there's a very important space project. And since you're celebrating space, this is about as old as LIGO, invented about the same time. And what it is is to do this whole thing in space. It's called LISA, laser interferometer space antenna. And that is three satellites in orbit around the sun, just like the Earth is, but with a length of the arms of 10 to the 6 kilometers. And that's where they get their sensitivity. And they hope to see the things like what's going on in the black hole in the middle of our own galaxy, or other black holes, big black holes colliding with each other. They're going to see plane stars interact with each other. Another experiment that's already going on, but at periods of frequencies of 10 to minus 12 hertz, but let's say, frequent periods of years, is to look at pulsars. Just use all the pulsars that you were given. And they're fast ones, and they pulse. And if you look in the northern sky, you look in the southern sky, and you'll notice as a gravitational wave comes through our galaxy, it changes the rate at which the pulsars pulse. And if you look north and south, that they'll go a little faster, let's say. And if you look east and west, all those will go a little slower. And that experiment is going on right now as a radio astronomy experiment. And to me, the one that I'm really looking forward to is this one. That experiment's been going on for a while. This is to look at the cosmic background radiation, which is the radiation that associated the Big Bang, and look at structure in the Big Bang to see if there were primeval gravitational waves. And that's most exciting, because we expect that there are some. What were the gravitational waves that associated the formation of the universe? That is a spectacular question. Thank you. Now, how does it work? You take questions? Who's the shamans here? Is there a shamans for this place? I mean, you know, the person who organizes. How does it work? You answer questions or you do that later? Let's take two questions from the audience. It's up to you. It's your schedule. Two questions? OK. We can't let you leave without a question. Pick the person. Let's see. Anybody interested? And I see the back in the hand. Yes, that's easy. You can do it yourself. No, that's real easy. You can get the masses from the Newtonian part of those orbits. What you do is just forget about Einstein, except for one thing. You need to know something called the quadrupole formula, which is the amount of energy that is taken away by gravitational waves due to the motion. That's a simple formula. And add that to your Newtonian description of the motion. And you will get then, with that together, you will be able to solve for both masses in those problems. And you will also solve for the energy that is at least emitted before it gets to the near the velocity of light. When it gets to the point where they're making the black hole, you've got to use general relativity. But that's the way you make your first guess. You do a Newtonian calculation. You calculate the masses from that. And knowing how much radiation is emitted from the quadrupole formula, which is a formula that is an approximation formula that comes out of general relativity. That's how it's done. See another hand? Go ahead and stand up. Well, wait a minute. Ask it again. What about gravitational waves being the same? Can be nullified. You mean, can they be canceled? Sure they can, but that's a very, very unlikely thing. Let me just, can I? Yes, please. Let me say, gravitational waves are extremely I didn't point out because it's a limited time. The amount of energy carried by the gravitational waves is unbelievable. If you took and put that pair of events, the first event we saw, and put it at the position of the sun, the strain that you would experience here on the earth would be 10 to the minus 6, which is zilch. Your body being stretched by a part of a million, you wouldn't even notice it. But 10 to the 25 watts per meter squared is going through you. That's a huge number. The sun puts out a kilowatt per meter squared of light and all electromagnetic. So it's a very, very hard to squeeze space. It's also extremely hard to bend, push, or scatter gravitational waves. So with gravitational waves, you can look all the way to the beginning of the universe. Nothing gets touched. I mean, I'm exaggerating a little bit, but you do not have to worry about scattering, which means that there are no sources around that you will have. If you have two comparable sources, they will cancel each other just like any wave will. But it's so unlikely that what we're seeing is we're seeing it. And that's one of the important parts of this field. You're looking right at what's happening in nature without any disturbance of scattering or interference or scattering of any kind. It's free. That's what makes this such an interesting field. And I'm waiting for a supernova to happen. We'll find out finally what goes on in the supernova. Anyway, thanks. Yeah.