Gravitational Waves (extra footage)

now the black hole's fit into all of this because they seem to be the thing that everyone talks about it when they when it comes up well they're not the only possible way you can produce gravitational waves and as I said all you need to create a gravitational wave is something accelerating and so it could be for example a star collapsing is an acceleration there it's a little actually more complicated because it turns out if it really collapses entirely spherically symmetrical you don't produce gravitational wave but as soon as you have any kind of distortion to it then you end up producing gravitational wave so a supernova a star collapsing and then it blowing up could well be a sort of gravitational wave but the nice thing about black holes is you've got two very massive objects and they're in orbit if they've got a pair of them in orbit around each other so a binary black hole system of course when something's moving around on a circular orbit is he's actually accelerating because non accelerating things just carry on in a straight line so something moving in a circle is undergoing centripetal acceleration it's actually accelerating so that object accelerating around another black hole the two orbiting around each other will end up producing gravitational waves because you've got a mass which is being accelerated as the two objects get closer and closer together they travel faster and faster so they end up accelerating at a more and more rapid rate so the amount of gravitational radiation goes up and up and up and so actually the reason why we're interested in the merger is because that's when you get this absolute burst of gravitational waves in that last kind of gasp as the thing merges into a single object and so the classic signature of these merging black holes is kind of a chirp signal that the the frequency of it kind of goes up in audio terms it would be something that went kind of like so kind of rising tone whistle and the reason why it's rising in tone is as the two objects are getting closer and closer together they're whizzing around each other at higher and higher rates and so that produces this kind of classic chirp signature that the people who've been hunting for gravitational waves have been looking for and yet we didn't feel anything we didn't go oh what was that that just went through me but that's because it was a billion light years away so by the time it's got here it's actually spread out through space so much that actually the the signal that we get is absolutely tiny the signal close to the you know if you've been standing too close to that merging black hole pair while all those bad things would have happened but you would have probably got ripped to shreds by the gravitational waves as they kind of tore you apart as they were past cool this is pretty cool say one of the things you can infer from the signature we get from this is all these properties about what the black hole merger actually was from that you can actually figure out what its kind of intrinsic luminosity was how big those gravitational waves were to start with and then of course we've measured how big the gravitational waves are once they reached us putting those two things together tells you how far away this thing happened and the answer is huge distance away a billion light years away so big distance away it feels like it should be a famous object now it feels like we owe it to ourselves to go and find find it now and say thank you you were the one is there a chance we'll ever nail it down it's very tough because because of the directional information we got out of the current generation gravitational wave directions just say it's somewhere over there there's an awful lot of somewhere over there so actually really nailing it down to where it is is tough to do interestingly there was a slightly marginal detection of a gamma-ray burst burst of gamma rays at the same time which probably has rather better directional information associated with it so potentially we might be able to track down even before we get really good positional information from the gravitational wave detectors if we start seeing several of these things and they're coincident with other you know optical phenomena like gamma-ray bursts and those kinds of things that we can actually really pinpoint then we might actually start being able to really get figure out exactly where these events happen but probably it it is at least in the short-term going to be dependent on the gravitational wave bursts being coincident with something else that we can detect with more kind of conventional telescopes the reason why these two black holes spiral in together in the first place rather than just because you know if you think about things in orbit around one of them like the earth around the Sun they'll just stay there forever right the reason why these two black holes spiraling together is because even when they were some distance apart the worst they were still accelerating around one another so that they were producing at a rather more modest level at that point gravitational waves and so they were still radiating energy away from the system and so as they lost energy these two things spiraled in towards each other because they were just losing some of their potential energy converting it into these gravitational waves and so the reason why these black holes were spiraling in together in the first place was gravitational waves and in fact so there has already been a Nobel Prize for the action gravitational waves which is there's this famous thing called the binary pulsar which is actually two neutron stars in orbit around one another and by studying that studying the motions of these two neutron stars around each other they have actually been seen to be slowly spiraling in towards each other and so that they're losing energy to something but then the energy doesn't seem to be coming out in any visible form but it's actually losing energy at exactly the rate that would have been predicted by general relativity if they were producing gravitational waves so we have already indirectly detected gravitational waves by that method and that already won a Nobel Prize so this isn't really in some sense the first detection of gravitational waves and it won't be the first Nobel Prize for gravitational waves but it is the first direct detection of gravitational waves it's been an interesting thing because so I've been doing astronomy for 30 odd years now and it's one of those things I've been going to the seminars colloquia about the detection of gravitational wave for most of their time and all the time all that time they've been saying we're really close to be really close it's gonna be five or ten years and then we'll have it we'll have it and so it's one of those things that's been this kind of big build-up for over a very long period of time and it is you know but both fundamental physics in the sense that it really confirms general relativity but also very exciting because it gives us a whole new way of doing astronomy and so there has been in the astronomical community a lot of expectation and how buildings a set up the experiment and they find they still didn't quite have the sensitivity to so to finally get that point where they really are detecting something very exciting indeed we see the moon because of electromagnetic waves don't we police is it slight light waves causes to see the moon but it's not waves that cause the moon to orbit the Earth that's not how gravity communicates no I mean so if you quantum mechanically gravity communicates by what are known as gravitons so the analog with the light that we've been you've just been discussing is the quantum mechanical equivalent of electromagnetism of the photons of light the small packets of light that that that communicate between two objects and then lead to the interaction between those objects and the the there's an equivalent thing at the level of quantum mechanical and Mechanics for which is the graviton now it's one of the big unsolved problems is how to actually properly describe the graviton in a consistent theory we don't yet know how to do that that's the area known as quantum gravity but we we can describe it classically through the gravitational field which we learn about at school so these gravitons we've we've not not seen we've not been able to detect the individual gravitons and and and certainly the gravity that we talk about in terms of why that's where we have tides we don't put down to the graviton although if you were to have a fully quantum theory and you it would be the explanation we would be able to understand the the propagation of the gravitons leading to the interactions with matter that for exact in this case water which leads to the tides but we don't have a description at that level we have a classical description of that it sounds like they're not very important like they're having effect in the universe really they're just kind of they're just a debris or a shadow or a little bit of leftover rubbish there they're not causing anything to happen in the universe yeah there that's that's an interesting thought to have that what you're seeing I don't like the idea of the debris but in fact they're incredibly important debris there because they're allowing us the key thing which is potentially opening up a new area of astronomy called gravitational wave astronomy is that we know these gravity these gravitational waves are distortions of the space-time okay that's a things moving in the space-time that's getting distorted as the gravitational waves propagate through that means they don't care what's in their way if light comes from a distant object and hits something in between you the detector and that and and where the light has come from it you can't go anywhere right the early universe we can't see the light from the early universe because the only universe was full of ions sort of electrons and hydrogen ions protons and the light would be bouncing off the me couldn't propagate very far gravity waves don't care about of this they'll just propagate all the way through because they're just distorting the space-time in which this matter is existing they just propagate through happily this means that this court debris is actually if we can detect this debris we're finding out about events that could have cured right at the beginning of the universe because the gravitational waves if we were able to detect them from that era will have propagated all the way through not being affected by anything else now in this case the debris again is it is it's a very small amount of energy that has ended up in our detectors but it has actually come from a really quiet cataclysmic event that will describe in a few minutes where a lot of energy was released in gravitational waves and this is in fact the only way we can really detect gravitational waves because having some huge event but produces masses of gravitational waves they gradually damp off as their energy drops off as the propagate just like the light light right so we know that the amplitude of light drops as it propagates that's why if your eye hold a candle and you you move away when it's nearby you can see it if you go up to the top of the hill you can't see this candle anymore because the light's still there but it's its amplitude its intensity is dropped in the same with gravitational waves they drop off so in order to be able to see them today detect them you need some quite cataclysmic event early on that well that generated them things that create gravitational waves matter beer your hand wafting through this room or giant black holes spiraling to their death what do they do with the space-time that causes the interaction how does it give it a shake what's the interaction plane to do so it's a direct interaction between the matter and the space-time that so there's the the matter actually is coupled to the space-time it's not it's not that the space-time is there and the matter is going through it and that it's coupled directly so that varies but it is part of it in the sense of it it affects the space-time and then the effect that it has on that space-time then determines the trajectory the this matter will take and so it is intimately coupled and that's in Einstein's equation there you you you don't you don't disentangle the two that the right-hand side of Einstein's equation has the matter the left-hand side has the space-time and whatever the matter does it affects the space-time and as the space-time gets distorted it determines the trajectory that that matter takes but do they actually do anything like cause planets to form or stars to collapse or galaxies like do they have a do they have a role that's an it's an interesting question that I mean people have thought about gravitational waves in the very early universe and actually if you if you collide gravitational waves together then potentially you can generate enough energy density in a small enough region that you can generate black holes for example that people have thought about that but in terms of astronomy it's the we think more of the gravitational waves is that as the product of something happening and so their detection will tell us something about the events that are happening as opposed to gravitational waves themselves causing those events we don't tend to think of it that way around so there's two things involved well there's a lot of things involved what two things come to mind one is the optics of the experiment which actually was pioneered in Glasgow and is such that they can basically shield you from lots of different sources of fluctuations so that you they're confident that when they see this interference pattern it's because of the distortion in the length of the arm due to gravitational waves but the second thing is of course you have a separate detector you have another interferometer you've had one in Louisiana at Hanford is that not not Hanford Hamptons in Washington they had one in Louisiana and then they had one in Washington State and that so you now look for for any for that event to reappear and that event this the ring down and The Associated pattern that you get that in there interference patterns they saw seven milliseconds later in Washington so it happened so the wave came through hit Louisiana first and then the light travel time because they're going at the speed of light then passed through the Washington detector exactly the same profile seven milliseconds later which corresponds to the light travel time and that enabled them to sort of give an estimate of where in the sky this original thing had started from and by knowing what its amplitude that wave amplitude was and the pattern that the wave had they were able to combine it with their numerical simulations of black holes going around one of the to determine the sizes of the black holes and the properties of the actual event they have this amazing isolation system that is what I mean about the optics so that they so the laser beams are going along the arm and they're hitting a mirror right and they go back and forth many many many many times but it's very important as you say that you view you're confident that if a if a lorry goes past the the along the written nearby road that it it's of course it's going to just distort the the ground and so this this arm will change there's already to a detector Virgo as I think it's based in Italy see they were unlucky right they they were in their shutdown mode when this gravitational wave passed through it travels for a billion years it was there those detectors were up and running maybe a few months earlier but they just shut down as it passed through this link can you miss it and literally in this case and so they but server goes up and running but India they've just commissioned basically as a LIGO like a lag as a name of this interferometer a LIGO light detector and the one of the nice things about having three there's this heard of triangulation it will mean that if you get three coincidence events then you can draw the draw the rail line the paths back and determine much more accurately which bear the sky and this event came from and then there's a whole thing is going to now open up I think and that is that people will if you find a gravitational wave or you think you found a source of gravitational waves then quite often there'll be other stuff being produced as well by these you know massive events there'll be light produced there'll be neutrinos produced perhaps there'll be high-energy cosmic rays that are getting thrown out and so people will there'll be an alert sent and and all these other detectors will start telescopes will start going and looking at that region of the sky to see whether or not they see anything shouldn't they make bigger and better detectives and start seeing more and more and we have a whole bunch of them around the world and they're super they're on the job if I gave you the keys for a week and said the detectors are all yours forget all the other astronomers and cosmologists in the world where you want to point out and what you want to look for for the next week what would you do with it oh by Wow good question I think I mean for me I personally I love the idea of the early universe having impact on this so I would be trying to see whether or not there are any remnants of the early universe they the lots of things will produce gravitational waves anything that sort of is going to distort the space-time will produce gravitational waves so these cosmic strings that I mentioned I'd be trying to see whether or not I can see any evidence of particular features of these and other features that we might try and see there's bubble collisions in the early universe there's lots of weird and wonderful objects that could form called solitons and non topological solitons these can all produce gravitational waves and would and I'd be I'd be searching out there for them

Channel: nottinghamscience

Views: 95,689

Rating: 4.9535332 out of 5

Keywords: gravitational waves, gravity, relativity

Id: 2uYEayOBj1k

Length: 17min 8sec (1028 seconds)

Published: Fri Apr 22 2016