 So, today I'm going to talk to you about the Nobel Prize in Physics for last year, which was one for the detection, the final detection of gravitational waves by these gentlemen, Vice Barish and Thorn. Vice worked at, or works at MIT and the second two at Caltech in California. All Americans because the detectors that finally detected the waves was actually built in the U.S. I need to explain to you three things today, or try to. Firstly, what the hell is a gravitational wave and why it's different from gravity? Secondly, why they were hard to detect and what the detector did that finally found these things. And finally, why it's so important for the future of astronomy that this was actually finally found. This timer in front of me gives me 15 minutes, so I have 16 minutes, I've only just turned it over. So, I need to give you in your head a model of gravity in the universe. I want you to imagine if you can a rubber sheet. Sort of thing you might have on a bed, rubberized for certain reasons. Some of you might have one of these at home. I want you to imagine one of these stretched into a big square like this and then you place a heavy ball on top of it. It's going to form a dent into this rubber sheet. And this is a model of how Einstein's general theory of relativity looks at gravitational attraction. It looks at it as a dent in space and another ball might slide down this sheet down to the middle or you can imagine it rolling around the outside of this sheet in an orbit. It's a very, very, very simple model of how gravity works. However, if I grab hold of this ball on my rubber sheet and start to oscillate it up and down, you can imagine some little ripples appearing in this fabric. And it's these ripples that are the gravitational waves. These are not, this is not the gravity that holds the earth in orbit around the sun. This is not the force that keeps me standing on the ground. This is something totally different. And this is predicted by Einstein's theories. Now, one of the problems with detecting gravitational waves is they are incredibly weak. It takes enormous forces in the universe to create a gravitational wave that we even have the remotest chance of detecting here on the planet earth. Imagine if you will two black holes orbiting around each other. Now, a black hole is formed when a star much bigger than our sun, maybe five, ten times larger than our sun, reaches the end of its life, explodes in a supernova, and the remains of the star start to collapse under its own gravitational force. And it collapses and collapses, and the gravity is so strong that it's able to pull the whole mass, the whole ten masses of our sun into a point infinitesimally small. This is an incredibly dense thing known as a singularity, but it contains the mass of maybe 10, 20, 30 stars. Now, imagine two of these caught in an orbit around each other. As they start to spiral around, they lose energy. They actually lose energy through giving off these gravitational waves. And eventually, they get faster and faster spiraled together and crashed together. And it takes an event that big for us to have the remotest chance of detecting it here on planet earth. The other event that can cause this is two neutron stars collapsing. Now, a neutron star can be viewed as a failed black hole, which is a little bit mean to neutron stars, but it's how it's often said. Something maybe two or three times as the mass of our sun reach at the end of its life, it starts to collapse. Its gravity isn't quite strong enough for it to overcome the final force of physics that's holding the star together. Something the size of our sun would collapse as something that was around 10 kilometers in diameter. It would be so dense, or they are so dense, that one teaspoon of matter from that neutron star would weigh the same amount as Mount Everest. And again, it takes two of these to clash together for us to have the remotest chance of detecting it here on earth. Now, the question is, when a gravitational wave leaves here, and I can show you here in nice dribbles, what does it actually do when it hits the planet earth? Well, what it does is it affects space and time on earth in a very small fashion. So imagine the earth. Let's pretend it's a sphere for a second. It's almost a sphere. It will be squished like this, and then like this, and then like this, and then like this, as the oscillations happen. Now, the only problem is that I'm slightly exaggerating it. Actually, I'm massively exaggerating it. The entire width of the planet earth changes by the width of one atom, if one of these events happened. Now, we then need to find a way on earth to detect something that fine. The entire planet earth shifted by the width of one atom. How do we do it? This has taken scientists and physicists and engineers 50 years to build a machine that can do this. This is a very simple model of what it does. It wants to measure the distance from here to here and the distance from here to here. It does that basically by splitting a laser beam and timing the amount of time the laser beam takes to reach the end of the tunnel and come back. Now, sounds simple. However, to make it more accurate, we need quite a long tunnel. So the tunnels look like this. There are two of these at right angles to each other. They're both four kilometers long. They're so long that the curvature of the earth has to be taken into account when building the tunnel. And it's one meter higher at one end than the other. To increase the effective length of it, the beam of light is bounced up and down this tunnel 250 times. And still, the tiny, tiny motion that needs to be detected in the mirror means that that mirror has to be the most stable thing on the planet Earth. So the one thing you don't want, and I don't know where this picture comes from, are trucks next to it that are going to rumble up and down. I'm assuming this picture was taken before they switched this thing on. It is, in reality, it's an exclusion zone. They're basically two mechanisms that are used to try to get rid of the problems of vibrations. So let's have a look at the mirror. This is a nice picture of the mirror that's here at one end of the tunnel. It's a 40 kilogram big chunk of a mirror. It's suspended on four pendulums. And at the top of it, there are electric motors trying to counteract any tectonic motions of the earth. At the very bottom end, it's suspended by four tiny, tiny, tiny filaments of glass. And still, it moves too much. The entire tunnel is evacuated, but I like to think of the model of a small ant sitting on top of the tunnel and farting. And that's enough to trigger this detector. This thing is so, so sensitive. So how else do we get over this problem? We assume that ants don't fart at the same time. So there's two detectors, one here and one here in America. There's also a third detector being built, which is now operational here in Italy. We know that a gravitational wave from Einstein's theories will travel at the speed of light. So that's about 10 milliseconds maximum between the two detectors in the US. So if we see a signal at one and we don't see it at the other, it's a farting ant. If we see it at both of them within 10 milliseconds, we have a suspicion that it might be a gravitational wave. We also know from the physics of the stars starting to spiral into each other that we're going to expect a signal that goes faster and faster, goes up and up in frequency and goes up and up in amplitude. They're looking for, they call it a chirp noise. It's going to get higher and higher and higher in frequency. The second reason to have these three detectors that are operational at the moment, because the GO1 is not in the same link, and the other ones that are being built, is very simple. Because we can time when the gravitational waves are detected at each detector, we can start to triangulate in space where they come from. These detectors have not been built just to prove that Einstein was right, because that's fairly boring, because we're kind of a steam Einstein was right, he was quite clever. The reason these detectors exist is to start to look for these new events happening in the world and gives us two opportunities. One, we can learn from the event itself. We can learn actually what it's like when two black holes collide from a gravitational wave point of view. But when two neutron stars collide, we can start pointing up other telescopes at that point in space. And for the first time, see the echoes of neutron stars colliding, and that's what actually happened. When the first two detectors at Hanford and Livingston were switched on, they were going through a test phase, and the local PR department had set a certain date when they were going to tell the press, it's live, it's all active, and have the big press release. Two days before that happened, this happened. And this is the chirp event I spoke about, and you can see these oscillations, and this was two black holes colliding. Now, slightly embarrassing, they actually was switched on, we lied to the press, and explain it had actually happened. It happened 10 milliseconds apart. It was exactly as expected. The interesting thing is this actually happened 1.3 billion years ago, and it's 1.3 billion light years away from us. So 1.3 billion years ago, two black holes collide, comes to us. We have just switched on the detector, and we see it. Fantastic. Yay! Happy scientists. Since then, they've seen a few more events happening in the universe. So we can see, basically, the further away they are from us, obviously a bit like light, the dimmer it gets, and the bigger the event has to be for us to be able to see. Detectors can currently see into a certain volume of space given their sensitivity. Both the detectors are actually switched off at the moment in America. They're being upgraded to give them three-fold sensitivity, which will give them 27 times the volume of space that they can start to monitor. At the moment, well, before they were switched off, they were seeing about one event a month. Now they're going to be able to see one event a day, and there's plans underway to increase the sensitivity of these detectors another 10-fold, which should mean that we should get 1,000 a day if the universe is big enough for us to see that many. When the neutron star collision was seen, as I said earlier, they very quickly switched around the optical telescope to look at the decay of the two neutron stars. Again, remember the neutron stars? They're 10 kilometers wide. One teaspoon is the same mass as Mount Everest. They've collided. That's a hell of a lot of energy. And for those of you who remember high school physics, it takes a lot of energy to make heavy particles, and it ended up in the press the fact that it had made as much gold, I think, to the same weight as a planet Earth or something ridiculous like that. So it's this kind of cataclysmic event that creates all the gold in the universe. So if anyone has any gold jewelry on, that is where the gold in your jewelry will have come from, will have come from an event like that. Why is this important? As I said earlier, it's because we're starting to look at the universe in a new way. Until now, we've looked at the universe through one of these things. This is the electromagnetic spectrum. This tells us that the series going from gamma rays through to radio waves, and these are the ways that we look at the universe today, but it's always the same way. It's always looking at what are known as photons coming in to see us. So radio telescopes have been around for a while. Microwave telescopes, this is how we look to the background radiation to look back to the Big Bang. If you remember that, we can see that. This is the most common one, obviously visible, ultraviolet x-rays, which are very useful for people with broken toes, and then all the way up to gamma rays where we actually can see particles generated in the atmosphere. But this was the only way that we could look at the universe until now. Now we have an entirely new way to see the universe. So imagine if you will that until now, we've been looking at an orchestra playing, and now we can hear it. We have a totally new channel to be able to do this. This is going to be the forefront of astronomy for the next few hundred years. The next couple of steps are going to happen in this. Building these things on Earth, as I said earlier, is complicated. Why not put them in space? Ants don't live in space. Also we can make these things further apart. We need to get very stable mirrors in space, so there's some concepts of building them in a square, four satellites in a square around the sun, and bouncing lasers between them. Gives us incredible, incredible accuracy. The first satellites have been test flown, just a single mirror just to see if it can stay, keep a mirror stable inside a vacuum floating in space. That experiment was successful. Probably 20, 30 years time will start to have gravitational wave detectors up in space, and everything we read about, as we discover more and more about the universe we based on that. So, thank you very much for listening. I hope that was understandable. If you have any questions, please let me know. Thank you very much indeed. Questions? So what are scientists actually hoping for to learn or to see because like three billion year old events is kind of new or new, right? It is old news. But old news is interesting news because we can find out about, because it's three billion years away, it's three billion years ago, so we can start to look back further and further and further into the history of the universe. Now, one of the problems that we have with looking through the universe this way, and we can't look back this far yet, is that after the Big Bang, 300,000 years after the Big Bang was when, it's called the ionization event, which is when the electrons and protons came together, and basically at that point, the universe became transparent to light. And until that point, the universe is opaque to light. So although we can look back with light microscopes a long way away and therefore a long way back in time, we can't look past this solid barrier. The gravitational waves will be able to look past that solid barrier and see new things. And the other thing that scientists will always look for is the unexpected. What if we built that detector and gravitational waves didn't exist, or they didn't look like we expected them to? Actually, it was quite boring. It looked exactly like we thought it would look. What if we find something for you? Do we find this thing elsewhere? Neutron stars, I think that would be the interesting thing. And also, it'll give us more of a use to how many binary neutron stars are binary events there are out there. Yeah? Yeah, please. This was clearly mind-boggling, but... So when you said that there are these tunnels all over the world and these are the detection, so I thought of the other particle, which also has all of these tunnels for its detection and its Higgs boson. Yeah. Do they have something in common? That's it, because it's also with the black holes and... In terms of technology, no, because the Large Hadron Collider that look for the Higgs boson is a big circular thing. Some of the technology is similar in that they have massive evacuated tubes underground and that sort of thing. In terms of what they're looking for, there is some sort of overlap because there is some thought that with the Large Hadron Collider, we could create very, very small black holes. But no, apart from that, I don't think there's much. Well, I think what it might start to join together is the physics of the very small and the physics of the very big, so that there could be some overlap there. That's one of the questions. Okay. So you said that you can now actually visualize this space in the future, like you can set up mirrors and all of this and you could actually see this event happening. How frequent is this event? I think how often would you expect new phenostars to occur? Neutron stars to collide. I don't know the answer to that. What I do know is that the detection rate is expected to go up with the detectors to like once a day or something like that. But I think I'd have to go and look up how many would be in the entire universe. I don't think that's really well known. And can it be managed for something useful, like going to the form of energy? No. I mean, these things by their nature are, one, they're a long way away and two, they're a long time ago. So all I can tell you is that a really, really energetic event happened a long way away, 1.3 billion years ago. So it's the kind of not, it's only useful for us to improve our scientific models rather than get energy. Oh, sort of. Sorry. Please. Do you think that theoretically it would one day be possible to find the end of the universe this way? The beginning. Hopefully. I don't know how it started, but where it is. Do you mean the edge of the universe? The bigger it gets. The more volume of space that it can see. Okay, don't forget this, but we have a model in our mind of spaces this three-dimensional Euclidean, sorry, just flat thing. Whereas actually, the theory is that the model is that if you keep going in one direction long enough in the universe, you come back this way again. So it's more like simplistic model of being on the planet Earth. You couldn't find the edge of the planet Earth. I can keep walking, but I'm going to come back to where I came from. So I'm not going to find this sort of barrier at the end of the universe. So I'm just going to find that the space continues in the way that I don't expect. Please, please. We have also, we suppose that we have also a black hole in our solar system. In our galaxy. Yeah. And of course, bigger stars and whatever. If you have such a bigger gravitational effect, that you can measure the gravitational waves, but you cannot measure the gravitational waves from effects in our galaxy. How is it possible that the gravitational itself from our galaxy affects on us, affects us, but this particular big event doesn't affect us? So I would expect if it's big enough, if it's big enough. Okay, so you're talking about the black hole at the center of our universe, the center of our galaxy. Yeah, but we haven't, but we don't measure effects around this black hole. No, we don't, not gravitational wave effects. It's more near to us, right? Yeah, exactly. But still, yeah. The gravity from our environment, the galaxy, it has an effect on us. Yeah. I would expect that if you have an event so big that you can measure the gravitational waves, the gravitation itself of this effect or of this object should affect on us more than our environment in the galaxy. I see what you're saying, but no, because you have the inverse square law of gravity. So every time we, inverse square loss, every time we double the distance, you halve, you quarter the effect of the gravity and you imagine this event was 1.3 billion light years ago. Also, what would be the effect on us from a gravitational point of view? We didn't lose mass in the universe. Remember two masses that were this far apart became this far apart, yeah? They became one 30 sun's worth of black hole, yeah? So in terms of the gravitational effect of us, it didn't change. Ah, really? Yeah. I would expect that. The wave in the water also has the same effect. The wave, you're right, the wave carries energy, but it's enough energy to make the spiral together, but it's not losing a substantial amount of mass of the two black holes, yeah? So the two black holes stay the same. In terms of the waves, they are the same development inverse square, right? Yeah. So as well as the gravitational field of everything. Yeah, but the gravitational field, which doesn't carry energy, won't have changed much because these two collapsed together because they still exist as a mass. What we can detect is the waves caused by that change, which carries tiny, tiny, tiny energy to us, yeah? Does that make sense? If not, we can talk after this. Okay. Yeah, sorry, we cannot answer all the questions. We have to stick with timetable, but you're welcome to ask Graeme Aftere. Great, thank you guys, appreciate it. Thank you.