1 00:00:00,630 --> 00:00:03,990 Hello and welcome to In Our Spare Time. 2 00:00:03,990 --> 00:00:12,000 For the next seven weeks, I will be joined by 21 students from across Oxford University discussing their academic and intellectual passions. 3 00:00:12,000 --> 00:00:18,540 Each week we will have a different theme, ranging from Marxism to mediaeval song Cicero to some time. 4 00:00:18,540 --> 00:00:27,300 Perhaps you will be able to guess the long running radio floorshow on which this concept is based answers on a postcard piece. 5 00:00:27,300 --> 00:00:31,230 For over three millennia, astronomers have been looking to the heavens. 6 00:00:31,230 --> 00:00:33,810 Yet less than 100 years ago, 7 00:00:33,810 --> 00:00:40,950 observations were made suggesting the existence of a previously unknown substance permeating the universe in vast abundance, 8 00:00:40,950 --> 00:00:47,460 yet invisible to even the most powerful telescope. This substance has been aptly christened dark matter. 9 00:00:47,460 --> 00:00:54,300 And though in nature it seems to be ubiquitous, all attempts to explicitly detect it have hitherto been unsuccessful. 10 00:00:54,300 --> 00:00:58,440 So what is dark matter? Why do we think it exists? 11 00:00:58,440 --> 00:01:04,920 And what has it got to do with a four ton tank of liquid argon two kilometres underneath Ontari? 12 00:01:04,920 --> 00:01:11,160 My name is Alice Walker, and with me to discuss current research into dark matter are Peter Hadfield, 13 00:01:11,160 --> 00:01:18,450 a 38 year old student at Lincoln College from day, a 38 year old student at Modelling College and Tulsa. 14 00:01:18,450 --> 00:01:22,560 Bromwich, a second year student, also modelling college. 15 00:01:22,560 --> 00:01:29,850 Thank you for joining me, Peter. Perhaps we could start by discussing the historical background of dark matter. 16 00:01:29,850 --> 00:01:36,660 What were the first experiments that people did to suggest that there was other stuff out there than what we could see? 17 00:01:36,660 --> 00:01:43,680 So the very first indication there might be some kind of substance out there in the universe that wasn't giving off light dates back to the 30s, 18 00:01:43,680 --> 00:01:51,010 it was only as early as the sort of 1920s that people actually grew to understand that there was things outside of our galaxy. 19 00:01:51,010 --> 00:01:58,330 The most famous evidence for the existence of dark matter came in the 60s and 70s, where people studied how these galaxies rotating. 20 00:01:58,330 --> 00:02:02,640 I'm sure everyone listening kind of knows the kind of iconic image of spiral galaxies. 21 00:02:02,640 --> 00:02:09,270 If you kind of look at the dynamics of how these stars are rotating, they appear to be rotating much faster than how much matter is. 22 00:02:09,270 --> 00:02:13,050 You can understand how much matters in stars and it's actually much faster. 23 00:02:13,050 --> 00:02:16,590 So people propose the existence of a new type of matter that we didn't know about. 24 00:02:16,590 --> 00:02:24,120 So if I understand it correctly, you'd expect from the matter we see that the stars around the middle would rotate quite fast, 25 00:02:24,120 --> 00:02:31,020 but then it would things would tear off as you got outside the galaxy and you said that's not what is observed. 26 00:02:31,020 --> 00:02:38,880 If you do a lot of how fast start rotating relative to how far away from the centre you would expect for this to drop off very fast. 27 00:02:38,880 --> 00:02:44,050 Whereas we see that one's even far on the outside of the galaxy are going extremely fast. 28 00:02:44,050 --> 00:02:50,430 This is directly contrary to the notion of what you would expect if there was only if all the mass in the galaxy was inside the stars. 29 00:02:50,430 --> 00:02:57,960 So you would be looking for. So what you're basically doing is you're it's it's like you're the centrifugal force 30 00:02:57,960 --> 00:03:02,310 equal to the gravitational attraction of all the matter that you've got in the middle. 31 00:03:02,310 --> 00:03:09,570 And what you're expecting is one over the square root of the distance from the from the centre of you, your galactic structure. 32 00:03:09,570 --> 00:03:15,300 And you'd expect that to fall off according to that relationship and that it would be very, very clear. 33 00:03:15,300 --> 00:03:21,150 I mean, is that sort of Newton's law of gravitation? Yeah. Yeah. So it's this is just a very technical term. 34 00:03:21,150 --> 00:03:26,820 Yeah. Yeah, very. But what's so dramatic about when you actually plot this, 35 00:03:26,820 --> 00:03:35,490 so you measure the velocity of different objects within the galaxy at various different places using their Doppler shift and other techniques. 36 00:03:35,490 --> 00:03:38,940 And what you find is that it radically diverges from that pattern. 37 00:03:38,940 --> 00:03:44,970 So you see a very, very flat distribution suggesting that even though when you look at the galaxy, 38 00:03:44,970 --> 00:03:50,610 you see that most of the stuff that's giving off light that we observe is concentrated in the middle. 39 00:03:50,610 --> 00:03:59,520 All of the stuff around the edges behaves as if as if there's like a continuous distribution of mass, almost like a halo around what you're seeing. 40 00:03:59,520 --> 00:04:02,850 And that's what's referred to often as a dark matter halo. 41 00:04:02,850 --> 00:04:07,640 So this kind of invisible mass that's causing things further out to be travelling much faster than they should be. 42 00:04:07,640 --> 00:04:12,570 You've got objects behaving as if there's mass there that you can't see. 43 00:04:12,570 --> 00:04:20,400 So that's where the name dark matter comes from, is because we it does not give off light in the way that other luminous matter does. 44 00:04:20,400 --> 00:04:25,420 So you'd expect you look up into the sky where you see light that's coming from stars. 45 00:04:25,420 --> 00:04:31,530 And so you assume that that is where the matter is concentrated. But this dark matter doesn't give off light in that way. 46 00:04:31,530 --> 00:04:35,370 So we can't detect it in traditional methods using telescopes and such. 47 00:04:35,370 --> 00:04:39,460 Yes, because this concept. Yes. Right. 48 00:04:39,460 --> 00:04:47,730 OK. So so where we are, we have these rotating galaxy clusters, which we can't explain with the mass we can see. 49 00:04:47,730 --> 00:04:54,210 But reading your notes, there are other ways since those early experiments that Peter's been telling us about, 50 00:04:54,210 --> 00:05:00,270 we want if you want to come in on on the other things, it's about gravitational lensing. 51 00:05:00,270 --> 00:05:08,130 A more recent observation that people have been able to come out to kind of confirm these ideas as the idea of gravitational lensing, 52 00:05:08,130 --> 00:05:15,780 Einstein's theory of general relativity is the kind of upgrade to Newtonian gravity that explains how things behave. 53 00:05:15,780 --> 00:05:23,280 I'm going to get really strong. And that actually describes that when there's a gravitational force, light is curved around, 54 00:05:23,280 --> 00:05:27,570 that this was the first reason that evidence that showed that gravity was right. 55 00:05:27,570 --> 00:05:30,990 People observed libraries being bent around the sun during the eclipse. 56 00:05:30,990 --> 00:05:37,290 We can do the same with dark matter if you look at the galaxy and see how strong the light has been around it. 57 00:05:37,290 --> 00:05:42,060 That implies that there's much more mass there than you can see in the actual stars, which again, 58 00:05:42,060 --> 00:05:45,960 agrees with the amount of mass that we would infer exists there from the rotation of the galaxies. 59 00:05:45,960 --> 00:05:53,550 So you have one object that's to be closer to another side of the galaxy that's behaving as the lens is kind of close to us. 60 00:05:53,550 --> 00:05:57,660 And then you've maybe got another galaxy or something else far away in the distance. 61 00:05:57,660 --> 00:06:03,570 And illusion, perhaps like a lens can focus light around it in the strength of that light is dependent on the 62 00:06:03,570 --> 00:06:07,470 distribution of mass for that distribution of mass doesn't agree with where the stars are, 63 00:06:07,470 --> 00:06:10,740 but it does agree with the distribution of mass that one would infer from the 64 00:06:10,740 --> 00:06:15,150 rotation that we were discussing earlier now where the interest of fairness, 65 00:06:15,150 --> 00:06:18,540 we ought to say, is although the main theory, 66 00:06:18,540 --> 00:06:25,140 it's not the only theory that's been posited to explain these gravitational anomalies for want of a better term, 67 00:06:25,140 --> 00:06:28,830 a modified Newtonian dynamics is what you said. 68 00:06:28,830 --> 00:06:35,430 A friend wants to tell us a bit about that and why it's not the main theory before it tries to tell us. 69 00:06:35,430 --> 00:06:41,640 And the idea is modifying Newtonian dynamics is that rather than introducing a new particle, 70 00:06:41,640 --> 00:06:51,970 we could change Newton's law of gravitation or change the laws of dynamics to accommodate these new observations. 71 00:06:51,970 --> 00:06:56,400 And it actually works quite well for observations and galaxies. 72 00:06:56,400 --> 00:06:59,890 But there are problems with modifying Newtonian dynamics. 73 00:06:59,890 --> 00:07:07,860 For example, it was recently observed we had this great observation of something called the bullet cluster, 74 00:07:07,860 --> 00:07:15,660 and this is two galaxy clusters that are colliding. So this is a really spectacular event and we're really lucky to have been able to observe it. 75 00:07:15,660 --> 00:07:22,640 How many light years across? We're talking about for these clusters of millions and millions of things. 76 00:07:22,640 --> 00:07:24,840 I think it's about three billion light years away. 77 00:07:24,840 --> 00:07:34,690 And then in the order of millions of light across, yes, I knew that big objects, they're the largest gravitationally bound structures in the universe. 78 00:07:34,690 --> 00:07:37,230 They're huge. And these two are colliding. 79 00:07:37,230 --> 00:07:43,740 And we can use these gravitational lensing techniques to work out where all of the mass in the collision is. 80 00:07:43,740 --> 00:07:50,280 So we can sort of map out the mass and we can also see whether or not there is with telescopes. 81 00:07:50,280 --> 00:07:56,940 And what you see is that the visible matter is getting this like horrible jumble in the middle where they collided. 82 00:07:56,940 --> 00:08:02,370 If you imagine two cars colliding, you've got like a car crash and it would all be horrible place. 83 00:08:02,370 --> 00:08:10,800 And that's what we see with the visible matter. But when we Mapai the dark matter is dark matter is most of the mass of the clusters, 84 00:08:10,800 --> 00:08:14,580 we find that it's basically just passed straight through each other night. 85 00:08:14,580 --> 00:08:21,300 If you if you had two waves of water, just go straight through each other. 86 00:08:21,300 --> 00:08:26,520 So you have this horrible crash in the middle and dark matter on either side. 87 00:08:26,520 --> 00:08:34,500 And this is exactly what we'd expect from dark matter, because dark matter doesn't really interact with normal matter or wave itself very much. 88 00:08:34,500 --> 00:08:43,420 So it doesn't really do collision if it just passes through. And it's very hard to see how you get that pattern with modified Newtonian dynamics. 89 00:08:43,420 --> 00:08:47,580 It's currently can't be explained by no, I haven't seen anything. 90 00:08:47,580 --> 00:08:52,260 Have you seen an attempt to do it? I, I haven't not with the example of the cluster. 91 00:08:52,260 --> 00:08:59,010 I mean, the bullet cluster is used as one of the sort of smoking gun of the existence 92 00:08:59,010 --> 00:09:04,340 of dark matter as like a particle as opposed to a modified gravity theory. 93 00:09:04,340 --> 00:09:13,470 Yeah. So we have these particles, but there are also lots of particles in the universe that they could be. 94 00:09:13,470 --> 00:09:23,400 So do one of you. Maybe people want to take us through some of the candidates that people came up with, for what dark matter could be. 95 00:09:23,400 --> 00:09:31,410 You know, how some of the dust. So as a kind of the seventies when people who kind of originally measuring the rotation curves, 96 00:09:31,410 --> 00:09:35,100 my understanding was that there wasn't enough understanding of the astrophysics, 97 00:09:35,100 --> 00:09:40,020 of how stars and galaxies behaved, that it could have still been like another form of matter. 98 00:09:40,020 --> 00:09:44,100 Look, we know that actually only a very small amount of normal matter is in stars. 99 00:09:44,100 --> 00:09:45,570 Most of it is kind of gas around the galaxy. 100 00:09:45,570 --> 00:09:54,030 So are kind of people's understanding of gas wasn't sophisticated enough at the time to definitively say that we needed a new type of particle? 101 00:09:54,030 --> 00:09:59,720 And subsequently, since people have kind of understood more where the gases we've understood like how many? 102 00:09:59,720 --> 00:10:03,100 Brown's wolves, which are like a kind of like I didn't start, 103 00:10:03,100 --> 00:10:07,570 maybe they could have been loads of them that we didn't know about, but now we think we can rule that out. 104 00:10:07,570 --> 00:10:11,950 And slowly, kind of like all these kind of conventional solutions, it's kind of been ruled that people are like, 105 00:10:11,950 --> 00:10:18,520 well, neutrinos or a type of particle that doesn't really interact with anything. Maybe there's just a lot more to tarantulas than we thought. 106 00:10:18,520 --> 00:10:24,580 But again, like that's been ruled out for various reasons. And slowly, we've kind of like ruled out everything, conventional leaving. 107 00:10:24,580 --> 00:10:28,270 But it has to be some new type of particle that we think we don't know about. 108 00:10:28,270 --> 00:10:35,310 But hopefully we'll find these things, those machoism wimps, as is so much as. 109 00:10:35,310 --> 00:10:42,880 Well, it's a it's an acronym cimetidine much I think is a massive compact object, et cetera. 110 00:10:42,880 --> 00:10:43,360 Yes. 111 00:10:43,360 --> 00:10:55,120 So those would actually, I think, be made out of normal matter to be something like how many black hole or if in fact the only thing that have stars. 112 00:10:55,120 --> 00:11:03,410 Yeah, yeah. Yeah. So I think you can still have models where these work, but it's a bit of a stretch these days. 113 00:11:03,410 --> 00:11:07,120 So we say rules out maybe. Could you develop this a bit. 114 00:11:07,120 --> 00:11:09,220 So how do we move these things out? 115 00:11:09,220 --> 00:11:18,010 So what's really interesting about dark matter is that it's kind of it's the way a lot of particle physicists are now working on it, 116 00:11:18,010 --> 00:11:23,470 the evidence and limitations that we place on it. A lot of those come from astrophysical constraints. 117 00:11:23,470 --> 00:11:33,220 So in terms of the dark matter density required in the universe for these very complex models that we have of how the universe evolved. 118 00:11:33,220 --> 00:11:44,770 So it's called the lander called Dark Matter Model. It places very strict constraints on the mass and the the velocity of these particles. 119 00:11:44,770 --> 00:11:51,880 So when we say like machos ruled out, that tends to be from astrophysical measurements. 120 00:11:51,880 --> 00:12:01,030 We don't see enough of them to account for the density required to fulfil the conditions of this kind of evolution of the galaxy 121 00:12:01,030 --> 00:12:09,040 that very much agrees with what we observe in the universe today and how we would explain the evolution of the universe. 122 00:12:09,040 --> 00:12:16,300 So it's interesting that you sort of you're looking for something very specific on a very small scale in particle physics realm. 123 00:12:16,300 --> 00:12:25,330 But the constraints that you place and how you rule out potential particles or windows of other things is based on astrophysical theories. 124 00:12:25,330 --> 00:12:29,350 And that's kind of a lot of historical fruitful interaction between particle physics and astronomy. 125 00:12:29,350 --> 00:12:36,280 Like the chemical element, helium was first discovered on the sun through emission of specific frequencies of light. 126 00:12:36,280 --> 00:12:43,180 That helium gave off before we discovered constraining how many neutrino species the world was kind of constrained 127 00:12:43,180 --> 00:12:47,770 through cosmological observations before particle physics could kind of understand how that was working. 128 00:12:47,770 --> 00:13:00,430 So hopefully the same will happen. Yeah. So we've ruled out brown dwarfs out neutrinos or neutrinos moved out in the same cosmological 129 00:13:00,430 --> 00:13:06,040 approaches or I think they're not they don't exist in sufficient quantities and also they're too hot. 130 00:13:06,040 --> 00:13:12,910 The issue is that one of the other reasons, yet another reason that we need dark matter is for structure formation. 131 00:13:12,910 --> 00:13:18,880 So you look in the sky, you see all kinds of structures that stars and galaxies and galaxy clusters. 132 00:13:18,880 --> 00:13:26,800 And if you trace the evolution of the universe from the Big Bang to today, just looking at normal matter, 133 00:13:26,800 --> 00:13:32,890 there just wasn't time for that amount of structure to form because all the normal matter within what we call a thermal soup. 134 00:13:32,890 --> 00:13:38,230 So it was all just really hot and interacting with each other so it wouldn't have gravitationally clusters. 135 00:13:38,230 --> 00:13:44,680 So you need dark matter to decouple from that family soup early because it doesn't really interact 136 00:13:44,680 --> 00:13:53,800 much and then cluster it forms kind of blobs which are gravitational gravitational well, 137 00:13:53,800 --> 00:13:58,090 which the normal matter can then falling to and form galaxies and stuff. 138 00:13:58,090 --> 00:14:03,190 Neutrinos can't do that because they're too light, so they just move really fast for ages. 139 00:14:03,190 --> 00:14:11,680 So you're saying dark matter is responsible for the universe being in the sort of galaxies with have formed without dark matter? 140 00:14:11,680 --> 00:14:19,270 Yeah, we've heard of neutrinos, ruled out ground rules and we're down to constrain possibility. 141 00:14:19,270 --> 00:14:23,410 So there are these wimps that we began to talk about. 142 00:14:23,410 --> 00:14:30,460 And also some of the friends will come in on actual accidents from. 143 00:14:30,460 --> 00:14:36,250 Yeah, so an accident or an interesting kind of dark matter. 144 00:14:36,250 --> 00:14:47,590 So an accident is kind of like a particle that is motivated by various problems in particle physics, and it's also motivated by string theory, 145 00:14:47,590 --> 00:14:55,210 sorry, string theory, which you might know is kind of our only working theory of particle physics at very, very high energies. 146 00:14:55,210 --> 00:15:00,200 Totally unconfirmed, of course, and at motile is. 147 00:15:00,200 --> 00:15:04,400 As little vibrations, the strings, which is not as silly as it sounds, 148 00:15:04,400 --> 00:15:12,200 I know string theory predicts loads and loads of accidents, axioms now accidents are very, very light particle. 149 00:15:12,200 --> 00:15:19,700 And you might remember I just said that light particles can't be dark matter. So Acción Dark Matter works a bit differently. 150 00:15:19,700 --> 00:15:24,890 So we kind of have to take a step back and ask what is the particle? 151 00:15:24,890 --> 00:15:32,780 And today, particle physicist believe that particles are ripples on quantum Fayose, 152 00:15:32,780 --> 00:15:37,910 which are like fundamental failures that span the whole of space and time, like ripples on water. 153 00:15:37,910 --> 00:15:45,140 And that's a particle and a normal particle. It's like a little bit like if you have like you mess up a bathtub when you see, 154 00:15:45,140 --> 00:15:52,370 like a little bit on the surface with Axium dark matter, we're doing something different to the field. 155 00:15:52,370 --> 00:16:00,140 We're making it oscillate all as one. Like, if you drop something really heavy in a bathtub and it will flush from one side to the other. 156 00:16:00,140 --> 00:16:03,470 So it's the feel of moving in a different way. 157 00:16:03,470 --> 00:16:11,750 And when you work, work it all out, that behaves like it was a heavier particle like particle, dark matter. 158 00:16:11,750 --> 00:16:18,020 OK, your power of metaphor is wonderful, seeing the bottom in my mind's eye. 159 00:16:18,020 --> 00:16:22,070 OK, so we have actions. On the one hand, we have wimps. 160 00:16:22,070 --> 00:16:29,120 What do we stand for. So wimp stands for weakly interacting massive particle basically. 161 00:16:29,120 --> 00:16:38,510 So what's really tantalising about sort of having a particle dark matter is that we have lots of theories that predict particles that could, 162 00:16:38,510 --> 00:16:43,190 if they existed, fulfil the criteria necessary. 163 00:16:43,190 --> 00:16:49,760 So as well as axioms, we have heard of supersymmetry and the supersymmetric particles. 164 00:16:49,760 --> 00:16:56,510 So which is Bahadoor? So it's basically an extension to the standard model where you have a whole 165 00:16:56,510 --> 00:17:01,410 nother set of of particles to the existing ones that we know about the heavier. 166 00:17:01,410 --> 00:17:08,190 And these are predicted by supersymmetric theory to explain various problems that we have with the standard model. 167 00:17:08,190 --> 00:17:14,120 So a standard model is it's our basic kind of like the periodic table for particle physics. 168 00:17:14,120 --> 00:17:19,700 It's the particles we know of and how they relate to each other as embodied in a series of equations that 169 00:17:19,700 --> 00:17:25,790 we can use to predict how they will interact and explain how they work on a fundamental sort of level. 170 00:17:25,790 --> 00:17:30,170 So these are the particles that go together to form a nucleus of atoms. 171 00:17:30,170 --> 00:17:34,820 Yes. As well as other particles, such as we've mentioned previously, 172 00:17:34,820 --> 00:17:43,490 neutrinos and electrons going around the outside of the atoms, as well as more kind of exotic things. 173 00:17:43,490 --> 00:17:50,720 But things that have been measured and found and that we understand quite well from experiments such as the Large Hadron Collider, 174 00:17:50,720 --> 00:17:51,830 where we study them. 175 00:17:51,830 --> 00:17:59,750 So the hope is that this new dark matter particle, whatever it ends up being, we could add to the standard model or be slightly separate. 176 00:17:59,750 --> 00:18:06,200 Yeah, no. So the these I mean, there are lots of suggestions the standard model is incomplete as it stands at the moment. 177 00:18:06,200 --> 00:18:12,890 So which is why there's so much active research into looking for explaining contradictions that we see. 178 00:18:12,890 --> 00:18:18,530 One of the things that's dominated particle physics studies for quite a number of years now is the supersymmetric theory, 179 00:18:18,530 --> 00:18:22,970 this idea that there's this whole other family of heavier particles and we are now at the 180 00:18:22,970 --> 00:18:28,070 stage where we have colliders that can reach the energies to detect these particles. 181 00:18:28,070 --> 00:18:36,680 And the hope is that we'll start seeing some of them soon. Now that we're at those energies at the LHC, they none of them have been detected yet. 182 00:18:36,680 --> 00:18:43,130 But if they are, some of the lightest amongst them are very good dark matter candidates. 183 00:18:43,130 --> 00:18:52,070 And they all come under the class of these wimps weakly interacting massive particles that cigarettes very nicely into dark matter detection. 184 00:18:52,070 --> 00:18:57,590 We have the substance that makes up 80 percent or more of all matter. 185 00:18:57,590 --> 00:19:00,350 But how can we try to detect it, 186 00:19:00,350 --> 00:19:08,870 given that we can't see it and it doesn't interact with itself or with with other matter to talk mainly about the astrophysical experiments? 187 00:19:08,870 --> 00:19:15,440 Peter. Yeah. So there's lots of ways you can indirectly constrain properties of dark matter, 188 00:19:15,440 --> 00:19:19,610 for example, wasn't discussed other galaxies to form in these dark matter halo. 189 00:19:19,610 --> 00:19:23,870 So by learning how these galaxies, what we can kind of tell how the dark matter of behaving, 190 00:19:23,870 --> 00:19:28,310 which kind of like it can lead us closer and closer to understanding how it behaves, 191 00:19:28,310 --> 00:19:32,990 although we've been talking about that might have been something that weakly interacts if it interacts just a tiny, 192 00:19:32,990 --> 00:19:38,160 tiny bit, if it's dense enough, if there's enough dark matter, you can still see it interacting with itself. 193 00:19:38,160 --> 00:19:42,770 So some people believe that if you look to a part of the universe where there's the densest bit of dark matter, 194 00:19:42,770 --> 00:19:50,780 you might be able to see photons being given off by particles finally being dense enough that they're colliding with each other. 195 00:19:50,780 --> 00:19:59,650 So there's maybe some hints that this has been detected through photons being given from these really dark, dense regions of dark matter. 196 00:19:59,650 --> 00:20:06,790 That we think could only be produced by these particles collide and give them a function that's still kind of in a kind of speculative. 197 00:20:06,790 --> 00:20:15,040 What is this part, the line spectra that take the pulse of exactly what we're talking about? 198 00:20:15,040 --> 00:20:23,190 Yeah. So this is as you said, when we look at galaxy clusters, we see an excess of photons. 199 00:20:23,190 --> 00:20:27,970 So particles of light over what we would expect, one really small energy. 200 00:20:27,970 --> 00:20:35,200 So all the extra photons have very similar energies. And that's quite exciting programme that had different energies. 201 00:20:35,200 --> 00:20:39,790 You're thing maybe we've just modelled how the cluster works a bit wrong, 202 00:20:39,790 --> 00:20:45,010 but when they all have the same energy as very few ways you can produce that one, 203 00:20:45,010 --> 00:20:51,400 which is what we call an atomic line, which is when the electrons in atoms change from one energy level to another, 204 00:20:51,400 --> 00:20:57,820 they produce a photon and that produces a light. So all the programmes have the same energy. 205 00:20:57,820 --> 00:21:02,230 When we say light, we're talking about spikes on a graph. Yeah, it's not quite a line. 206 00:21:02,230 --> 00:21:06,610 It's like a very narrow bump, a very narrow. But it might as well be. 207 00:21:06,610 --> 00:21:11,830 Yeah, it might as well be a light is the point. All the photons are basically the same energy. 208 00:21:11,830 --> 00:21:16,240 Yeah. But we know all the time because we can measure them on. 209 00:21:16,240 --> 00:21:23,200 So we can subtract those off. And once you've done that, you're left with this line at three and a half electron balance. 210 00:21:23,200 --> 00:21:29,320 And this could be dark matter particles, decaying entity photons. 211 00:21:29,320 --> 00:21:34,960 And then the energy of the photons would just be set by the mass of the dark matter particle. 212 00:21:34,960 --> 00:21:37,780 So that would then reduce this very narrow line. 213 00:21:37,780 --> 00:21:45,430 But this is so speculative because astrophysics is just so complicated that maybe there's just something else that we hadn't really thought of yet. 214 00:21:45,430 --> 00:21:50,210 I think some people have suggested that maybe there's some potassium. 215 00:21:50,210 --> 00:21:57,970 So, yeah. So to subtract off the atomic lines is quite a hard procedure. 216 00:21:57,970 --> 00:22:05,260 And one thing you've got to do is work out all the abundant sets of all the different elements in the cluster. 217 00:22:05,260 --> 00:22:10,180 And that is the suggestion that we did it wrong for potassium and the paper. 218 00:22:10,180 --> 00:22:20,290 Yeah, the paper was called Dark Matter Going Bananas. It was a cunning pun because bananas have lots of fruit. 219 00:22:20,290 --> 00:22:25,040 So do you really have to take into account, like, all like hundreds. 220 00:22:25,040 --> 00:22:33,310 So do you think there not a hundred because the very heavy elements are found in clusters. 221 00:22:33,310 --> 00:22:39,820 You can only really make them artificially on earth, but you do have to take into account a lot of them. 222 00:22:39,820 --> 00:22:45,270 It's a really big job. There's really only been made possible by computers. 223 00:22:45,270 --> 00:22:51,370 OK, so that's the astrophysical observations you made to tie up something that you spoke 224 00:22:51,370 --> 00:22:56,740 earlier that Einstein thought we could try to find dark matter in particle accelerators? 225 00:22:56,740 --> 00:23:02,980 Yes, definitely. And there's lots of active research working on exactly that at the moment at the LHC. 226 00:23:02,980 --> 00:23:11,290 So what you're doing there is in a similar way to the astrophysics where you're looking for an excess of photons, where you're not expecting it. 227 00:23:11,290 --> 00:23:16,180 There they as I said, as we've mentioned, that don't match particles, you can't detect them. 228 00:23:16,180 --> 00:23:22,630 So when we do these massive collisions in like linear colliders like the LHC, 229 00:23:22,630 --> 00:23:29,000 how you would identify the dark matter particles have been produced is that you see kind of a lack of energy. 230 00:23:29,000 --> 00:23:34,660 So, for example, if you imagine two things colliding and one of them, you see bounce back the other way, 231 00:23:34,660 --> 00:23:40,030 but there's nothing in the other direction you that that violates conservation of momentum. 232 00:23:40,030 --> 00:23:44,020 So you've got some missing momentum, some missing energy from that collision. 233 00:23:44,020 --> 00:23:48,760 And that's how you infer that's something else that you're not detecting is being produced. 234 00:23:48,760 --> 00:23:53,080 So you look for these very specific events where, for example, monologist, 235 00:23:53,080 --> 00:23:58,120 where you get like a huge jet of hadrons in one direction and nothing in the other direction. 236 00:23:58,120 --> 00:24:06,090 So forgive my ignorance. What's a natural? So hydrogen is what you generate loads of in the LHC? 237 00:24:06,090 --> 00:24:11,740 Yes. Yes. So Hadron is is something that's made of quarks. 238 00:24:11,740 --> 00:24:20,380 So it's the stuff the ordinary matter is composed of. So because we're smashing together hadrons in the LHC, generally, when you smash them together, 239 00:24:20,380 --> 00:24:25,640 you're going to produce a whole bunch of hadrons alongside anything else that you're interested in. 240 00:24:25,640 --> 00:24:31,330 So you just call it a hydrogen jet because it's a mass of hadrons that gets chucked in one direction. 241 00:24:31,330 --> 00:24:38,170 And they're very useful because you get this very strong signal in one direction and then nothing in the other direction. 242 00:24:38,170 --> 00:24:43,420 So one of the difficulties is that, of course, neutrinos, as we've mentioned before, 243 00:24:43,420 --> 00:24:49,120 are also not detected and they're inferred in the same way from the sort of missing momentum. 244 00:24:49,120 --> 00:24:54,940 But what they're doing in collider is looking for potential decays where you 245 00:24:54,940 --> 00:24:59,510 do see this sort of this mono jet or some sort of similar interaction with. 246 00:24:59,510 --> 00:25:06,310 Momentum more often than can be explained by neutrinos and therefore you infer that 247 00:25:06,310 --> 00:25:10,760 there's some kind of other non detectable particle being created in that machine, 248 00:25:10,760 --> 00:25:15,610 but I wouldn't necessarily be what we observe in the bullet cluster. 249 00:25:15,610 --> 00:25:23,260 Exactly, exactly. Which is why, although these experiments are very interesting in terms of looking for possible regions, 250 00:25:23,260 --> 00:25:28,780 for dark matter, in terms of isolating even more precisely what mass to expect and things like that, 251 00:25:28,780 --> 00:25:36,850 the only way that we can actually say that we have detected dark matter is through actually detecting the dark 252 00:25:36,850 --> 00:25:43,660 matter that's all around us and that involves a very different type of detector and different type of experiment. 253 00:25:43,660 --> 00:25:47,950 You are involved in the design of some next generation of accelerators. 254 00:25:47,950 --> 00:25:54,190 It's a football programme. Terminix is one of the things that you're looking towards. 255 00:25:54,190 --> 00:25:58,030 Detectors are designed in a very different way to the LHC. 256 00:25:58,030 --> 00:26:05,320 So I actually work on I mean, we talked about the fact that the LHC is Hadron Collider, so I actually work on future Lepton colliders. 257 00:26:05,320 --> 00:26:10,720 So leptons are more fundamental. So that's things like electrons. 258 00:26:10,720 --> 00:26:17,470 And what we're doing in these future machines, hopefully, is it means that the collision is much, much cleaner. 259 00:26:17,470 --> 00:26:25,480 So we have a much, much more detailed picture of the energy that we're putting in and the energy that we're getting out. 260 00:26:25,480 --> 00:26:27,910 So the problem with hadrons is they're made of quarks. 261 00:26:27,910 --> 00:26:33,130 So it's a bit like smashing two balls together, but inside each ball is lots of other little balls. 262 00:26:33,130 --> 00:26:38,080 So you're never sure from which little ball collision has actually generated your event. 263 00:26:38,080 --> 00:26:43,480 So that's kind of an uncertainty on the energy that you're putting in, whereas with leptons, they're fundamental. 264 00:26:43,480 --> 00:26:46,990 So when you smash them together, you know very accurately how much energy you're putting in, 265 00:26:46,990 --> 00:26:53,440 which means you can much more accurately reconstruct your missing momentum from whatever happens afterwards. 266 00:26:53,440 --> 00:26:59,330 So the hope is that in these future machines, it'll be similar sorts of experiments to what's been done. 267 00:26:59,330 --> 00:27:04,510 GHC looking for these Monegasques with missing momentum that would be done with much higher resolution. 268 00:27:04,510 --> 00:27:12,040 So yeah, and also very light hearted high statistics, which is what's required for all of these experiments, 269 00:27:12,040 --> 00:27:16,740 because it's hard, because we're looking for like it's not even a needle in a haystack. 270 00:27:16,740 --> 00:27:20,500 Yeah. The Milky Way don't exactly. The Milky Way. 271 00:27:20,500 --> 00:27:26,890 So we start to talk about direct detection on Earth, which is quite a lot of research is going to. 272 00:27:26,890 --> 00:27:30,880 But I think before we do that, I'd really like to hear what some of you are doing at the moment. 273 00:27:30,880 --> 00:27:38,110 So we've heard a bit about Two-Thirds Collider design. Peter, what are you thinking about at the moment? 274 00:27:38,110 --> 00:27:46,840 So I'm thinking about the kind of interaction between how galaxies evolve and how the dark matter distribution evolves, as we discussed earlier. 275 00:27:46,840 --> 00:27:49,840 We think that dark matter halos, these blobs of dark matter, 276 00:27:49,840 --> 00:27:56,020 we believe exists are crucial for the formation of consciousness and said we are now being able to understand, like the structure of the universe. 277 00:27:56,020 --> 00:27:59,500 We kind of think of the universe that on large scales it's a kind of continuous thing. 278 00:27:59,500 --> 00:28:04,750 But if you kind of see Minta segments, this is kind of rich structure and you get the galaxies and clusters of galaxies, 279 00:28:04,750 --> 00:28:08,410 clusters of clusters of galaxies and so on. 280 00:28:08,410 --> 00:28:15,280 So I kind of use kind of what we believe is the kind of theoretical kind of structure of dark matter distribution. 281 00:28:15,280 --> 00:28:20,770 The universe. People are often surprised by this kind of like, well, isn't dark matter this kind of mysterious thing? 282 00:28:20,770 --> 00:28:24,340 Kind of in my work, the dark matter is the thing that we understand very well, 283 00:28:24,340 --> 00:28:30,640 because it doesn't matter in theory if if it is to be believed, it behaves in a very simple way. 284 00:28:30,640 --> 00:28:36,190 It doesn't interact with anything. So the structure of dark matter, we think is behaving this very simple way. 285 00:28:36,190 --> 00:28:39,010 What's much more complicated is how all the rest of the universe, 286 00:28:39,010 --> 00:28:43,810 the stars and galaxies and everything, kind of formed kind of on top of that structure. 287 00:28:43,810 --> 00:28:47,680 So all these kind of large groups around the world, 288 00:28:47,680 --> 00:28:53,320 data from telescopes in Chile and Hawaii to kind of probe what galaxies are doing kind of from right now. 289 00:28:53,320 --> 00:28:56,810 And as I'm sure some listeners know further away, is further back in time. 290 00:28:56,810 --> 00:29:01,270 So you can kind of plot galaxies from now back to 10 billion years ago and kind of look at how 291 00:29:01,270 --> 00:29:05,830 they're statistically arranged and kind of what structures in that can then relate that kind 292 00:29:05,830 --> 00:29:10,900 of observed structure of galaxies to the kind of theoretical distribution of dark matter and 293 00:29:10,900 --> 00:29:15,280 that kind of information about how these galaxies are forming in relation to that matter. 294 00:29:15,280 --> 00:29:21,490 So, for example, like the kind of core problem and this is if you can't imagine a halo of dark matter 295 00:29:21,490 --> 00:29:26,650 or the kind of DASSIN that is kind of believed to have fallen into the centre, kind of formed the galaxy. 296 00:29:26,650 --> 00:29:33,790 But if you kind of let go progressively more massive kind of dark matter holds, the galaxies do get bigger, but like not much. 297 00:29:33,790 --> 00:29:39,070 If you kind of go to a dark matter 10 times as big, the galaxy might only get two times as big. 298 00:29:39,070 --> 00:29:44,950 And kind of understanding why you get this diminishing returns, why kind of really hard to build these more massive galaxies, 299 00:29:44,950 --> 00:29:54,250 even though you've got all the gas in these halos, is a kind of ongoing problem of research from what's going on in the actual world at the moment. 300 00:29:54,250 --> 00:29:57,700 So I'm working on two sort of. 301 00:29:57,700 --> 00:30:08,150 Kind of. One is the dark matter is that we've already spoken about, but actions can also behave as what's called dark radiation. 302 00:30:08,150 --> 00:30:12,110 So this is just very fast particles that we can't see. 303 00:30:12,110 --> 00:30:16,310 So neutrinos, if you mentioned earlier, would be dark radiation. 304 00:30:16,310 --> 00:30:26,480 But we know what they are. So we just call them neutrinos. And I'm looking at detecting actions using the fact that in a magnetic field, 305 00:30:26,480 --> 00:30:32,510 actions have a very small chance to convert to a photon, which is converting to photons. 306 00:30:32,510 --> 00:30:42,470 What axioms want to do so? Well, I wouldn't say I want to be a bit anthropomorphic, but that's just. 307 00:30:42,470 --> 00:30:46,670 Yeah, that if you just work out like the equations of motion. 308 00:30:46,670 --> 00:30:51,170 So in the same way that if you set over a pendulum swing backwards and forwards, 309 00:30:51,170 --> 00:30:57,820 actions go backwards and forwards between axioms and photons, except they spend typically it starts off as an accident. 310 00:30:57,820 --> 00:31:05,750 It won't spend all that much time as a photon. It's slightly more complicated than that because it's a quantum thing. 311 00:31:05,750 --> 00:31:13,130 But it's so we have the small chance to convert into a photon. 312 00:31:13,130 --> 00:31:19,850 And it's like a very small chance, like a case in point in ten thousand to one in a billion, depending on the field spin, 313 00:31:19,850 --> 00:31:24,350 which is why they can still be dark matter, although, of course, you'd be able to see them. 314 00:31:24,350 --> 00:31:29,240 And happily that are magnetic fields and galaxy clusters. 315 00:31:29,240 --> 00:31:33,710 So galaxy clusters have these magnetic fields which stretch over billions of light years. 316 00:31:33,710 --> 00:31:38,030 So these are really ideal conditions to observe axioms. 317 00:31:38,030 --> 00:31:45,950 So I'm looking at what kind of signal would expect from Axium to vary from conversions and galaxies and galaxy clusters. 318 00:31:45,950 --> 00:31:54,000 And then also mapping this to dark matter is for the three and a half billion signal, which we talked about earlier. 319 00:31:54,000 --> 00:31:59,720 Yes. And so if you make a prediction of where you should see this. 320 00:31:59,720 --> 00:32:04,340 Yeah. The signal for reactions to the functions of some of these experiments and see 321 00:32:04,340 --> 00:32:10,640 this without being used to make any kind of smoking gun corrections system. 322 00:32:10,640 --> 00:32:21,560 So we need improvements in astrophysics. Excitingly, that is an excessive X-ray photons and galaxy clusters to a straight line. 323 00:32:21,560 --> 00:32:30,800 And it's also known or in excess and low energy X-rays and galaxy clusters that could be explained by accident. 324 00:32:30,800 --> 00:32:38,480 But it's still debated because astrophysics is so complicated, it can be quite hard to work out whether you have an excess or not. 325 00:32:38,480 --> 00:32:46,400 And normally when you're putting particle physics against astrophysics, astrophysics, which occasionally. 326 00:32:46,400 --> 00:32:53,120 So it's just about looking at the anomalies that are there and thinking about how we could explain them 327 00:32:53,120 --> 00:33:01,010 in other ways and also making predictions so we can rule out high levels like temperature conversion, 328 00:33:01,010 --> 00:33:06,980 for example, by just the fact that we don't see loads of photons kind of ruling out a parameter space. 329 00:33:06,980 --> 00:33:09,890 It's almost as important as trying to discover things, 330 00:33:09,890 --> 00:33:19,100 because if we can just sort of rule out one of the particles that don't exist, then we'll have less particles that might be right. 331 00:33:19,100 --> 00:33:25,820 We have about 10 minutes left and we're moving to one of the most active areas of current research, 332 00:33:25,820 --> 00:33:34,070 which is trying to detect wimps, which is the other candidates at the moment for the atoms. 333 00:33:34,070 --> 00:33:42,110 What it might be say that there are loads of the experiments around the world, but no one will talk about now is called deep three 600. 334 00:33:42,110 --> 00:33:45,960 Yes, that's right. Yes. Which is under two kilometres. 335 00:33:45,960 --> 00:33:49,140 But that is kind of a little bit about that. Yeah. 336 00:33:49,140 --> 00:33:58,550 So before I shifted into designing accelerators, I did my master's project working on research and development for the deep three six hundred. 337 00:33:58,550 --> 00:34:02,540 So this basically this is the direct detection technique. 338 00:34:02,540 --> 00:34:08,240 So what you're trying to detect is dark matter particles in the universe that are flowing through 339 00:34:08,240 --> 00:34:14,390 the earth and through us all the time from our own galactic dark matter halo and how you do this. 340 00:34:14,390 --> 00:34:23,660 It's basically like a sort of a target experiment. So you go to somewhere, first of all, where there's not a lot else going on. 341 00:34:23,660 --> 00:34:31,890 And a good place for this is underground, which is why these experiments tend to be they tend to be very, very low elevations. 342 00:34:31,890 --> 00:34:38,540 So in particular, this one is at the Sudbury Neutrino Observatory in in Canada. 343 00:34:38,540 --> 00:34:41,060 And it is an active nickel mine. 344 00:34:41,060 --> 00:34:49,220 And it's two kilometres underground where they've created this laboratory for doing these type of neutrinos and dark matter experiments. 345 00:34:49,220 --> 00:34:57,140 Because if you're trying to detect something that's sort of flying through the atmosphere, the problem we've got is that it's very messy. 346 00:34:57,140 --> 00:35:05,070 So there's like a lot of other stuff going on. So cosmic rays hitting light as they hit our atmosphere, generate these massive showers of particles. 347 00:35:05,070 --> 00:35:09,720 So the problem is that most of the time, even if you did have a dark matter particle going through your detector, 348 00:35:09,720 --> 00:35:13,080 you wouldn't see it because there's too much else going on. What if we just go back a step? 349 00:35:13,080 --> 00:35:18,570 So we've been saying for sure that dark matter doesn't interact with matter. 350 00:35:18,570 --> 00:35:23,790 But you'll tell me that it does. Just a very small of it's very, very, very rarely. 351 00:35:23,790 --> 00:35:29,130 So you also don't know everything, don't you? 352 00:35:29,130 --> 00:35:37,800 The theory is that if it's a particle and if you throw enough of them antimatter and you watch for long enough, 353 00:35:37,800 --> 00:35:43,860 at some point you will get a head on collision between dark matter and ordinary matter. 354 00:35:43,860 --> 00:35:48,120 And this is actually how neutrinos have been detected in lots of Nobel prises 355 00:35:48,120 --> 00:35:53,040 recently for experiments that have made very detailed measurements of neutrinos, 356 00:35:53,040 --> 00:35:58,260 made fantastic discoveries using exactly this method of generating basically a massive 357 00:35:58,260 --> 00:36:05,010 target mass and then watching it under very clean conditions for these very rare times 358 00:36:05,010 --> 00:36:10,050 when these otherwise undetectable particles literally collide head on with something in 359 00:36:10,050 --> 00:36:18,150 your detector and generate either sort of photons of light or some kind of other sort of. 360 00:36:18,150 --> 00:36:23,280 It's usually a scintillating target so that when it receives the kick from this direct collision, 361 00:36:23,280 --> 00:36:31,560 it produces photons of light, which can then be detected. The huge challenge of this is that, as you said, this this happens. 362 00:36:31,560 --> 00:36:36,150 I mean, it's predicted to happen incredibly rarely, if at all. 363 00:36:36,150 --> 00:36:42,600 So you need massive, massive experiments and they need to be in very, very clean environments. 364 00:36:42,600 --> 00:36:45,420 So by going deep underground, well, 365 00:36:45,420 --> 00:36:53,610 that means is you've got two kilometres of rock to basically stop all the other mass that you've got going on from cosmic rays, 366 00:36:53,610 --> 00:36:57,750 whereas the dark matter doesn't care. It just go straight through most of the time. 367 00:36:57,750 --> 00:37:02,880 But I mean, the sad thing is, in a director of the kind of tunt scale, 368 00:37:02,880 --> 00:37:09,560 you're still expecting only a few events of these to happen per year, of course. 369 00:37:09,560 --> 00:37:13,050 So you have to watch very carefully. You have to make sure that, you know, 370 00:37:13,050 --> 00:37:19,770 everything else that could potentially be getting in there and creating signals that could look like dark matter. 371 00:37:19,770 --> 00:37:24,720 And you have to go to such precautions to make sure that your equipment. 372 00:37:24,720 --> 00:37:29,190 Some people urged, yes, everything has to be completely radio pure because, I mean, 373 00:37:29,190 --> 00:37:36,390 if your detector has anything that's naturally radioactive decay that's going to generate particles within your detector, 374 00:37:36,390 --> 00:37:40,380 that could look like a dark matter signal and not be. So it is. 375 00:37:40,380 --> 00:37:44,820 It is it is worse than a needle in a haystack because you have to cut out so much. 376 00:37:44,820 --> 00:37:51,330 But as I said, what's what's hopeful about these experiments is that they have worked for neutrinos in the past in detecting in a very similar way. 377 00:37:51,330 --> 00:37:57,950 So it's a known technology that's now being sort of expanded and evolved for dark matter. 378 00:37:57,950 --> 00:38:03,770 So we're running out of time, but perhaps just before we leave that topic and move on to a few closing remarks, 379 00:38:03,770 --> 00:38:08,540 you could tell me where the allegation comes in. So basically, I've seen a wonderful picture. 380 00:38:08,540 --> 00:38:12,290 It's basically a big bowl of all. 381 00:38:12,290 --> 00:38:19,490 So the noble gases are fantastic for dark matter detection because they scintillate and they're transparent to their own citizens. 382 00:38:19,490 --> 00:38:21,420 So they give off photons when you hit them. Yeah. 383 00:38:21,420 --> 00:38:25,550 So when you give them a bit of extra energy, they they produce these photons, which you can then detect. 384 00:38:25,550 --> 00:38:28,760 So the deep three 600 experiment uses liquid argon. 385 00:38:28,760 --> 00:38:38,340 There are other experiments such as the Lux experiment, which currently holds the world record for dark matter detection, which is liquid xenon. 386 00:38:38,340 --> 00:38:44,570 I thought we hadn't detected it. No, no. So it's when I say world record for detection, 387 00:38:44,570 --> 00:38:51,850 what we mean is so basically we've got these constraints on what we're trying to measure for this dark matter based on these astrophysical things. 388 00:38:51,850 --> 00:38:58,580 It's got to be a certain mass. It's got to interact a certain at a certain rate, but that's still quite a large window. 389 00:38:58,580 --> 00:39:01,280 So what these experiments are doing is they're trying to get more and more 390 00:39:01,280 --> 00:39:05,690 sensitive to look at more and more of that kind of parameter space and then say, 391 00:39:05,690 --> 00:39:11,840 OK, we've looked at all of these masses at this, you know, cross section and we haven't seen anything. 392 00:39:11,840 --> 00:39:20,720 So at the moment, it's basically a null result. So the Lux experiment has ruled out the lowest cross section at a certain mass. 393 00:39:20,720 --> 00:39:25,490 It's not seen as a world record for dark matter. 394 00:39:25,490 --> 00:39:29,010 Non-taxable. Yeah, yeah. 395 00:39:29,010 --> 00:39:35,560 So a couple of years ago when the results came out, the headlines were very amusing of big news, dark matter, not the. 396 00:39:35,560 --> 00:39:42,060 But I mean, that's how it works. You keep proving these spaces until you gradually narrow it down and you hopefully discover something. 397 00:39:42,060 --> 00:39:46,340 Yeah, maybe it's a funny few. Collins The floor is open next five years. 398 00:39:46,340 --> 00:39:51,500 What are your predictions? What the new experiments being built, what you think might happen? 399 00:39:51,500 --> 00:39:57,170 Well, the exciting part that's coming up in astronomy from our perspective, are probably things like the Euclid satellite, 400 00:39:57,170 --> 00:40:01,280 which will probe galaxies going back to the beginning of the universe, like I was talking about earlier. 401 00:40:01,280 --> 00:40:06,470 But the survey I work on is looked at a patch of sky the size of the moon in the sky. 402 00:40:06,470 --> 00:40:11,300 So a small patch of sky will extend that to the whole sky. 403 00:40:11,300 --> 00:40:15,110 Just a huge amount of data that we have to kind of probe the dark matter distribution, 404 00:40:15,110 --> 00:40:20,240 much more accurate ways to understand how kind of structural it behaves over time. 405 00:40:20,240 --> 00:40:26,990 And somehow that interacts with galaxies. The sky will do the same in radio, and this will give us lots of information not only about the galaxies, 406 00:40:26,990 --> 00:40:33,170 but how the structures and to read things like Light Rasenberg or special events and 407 00:40:33,170 --> 00:40:37,150 looking at galaxies in different frequencies gives you different information about them, 408 00:40:37,150 --> 00:40:42,770 used to look at different parts of the universe and so on. And there's a lot of surveys that look at, for example, 409 00:40:42,770 --> 00:40:47,630 the Sloan Digital Sky survey or start a new project on detecting something called baryonic acoustic oscillations, 410 00:40:47,630 --> 00:40:56,660 which are basically detecting kind of sound waves of dark matter, which is an exciting project that's detected so far. 411 00:40:56,660 --> 00:40:59,390 But we'll be able to that's been detected in the universe today, 412 00:40:59,390 --> 00:41:06,260 but we'll be able to kind of put that back to kind of like the last six billion years, how these waves have kind of grown. 413 00:41:06,260 --> 00:41:09,210 So that's what we're looking at over the next five to 10 years. 414 00:41:09,210 --> 00:41:18,810 From two to say one exciting thing about the three and a half billion figure, I was told is that the satellite going up, 415 00:41:18,810 --> 00:41:23,610 that's got a much better energy resolution and it will be able to tell by looking at 416 00:41:23,610 --> 00:41:27,810 the line whether it's dark matter or astrophysics because they're different shapes. 417 00:41:27,810 --> 00:41:32,730 So anyway, I'm afraid that would be the talk of the century. So that's very exciting. 418 00:41:32,730 --> 00:41:40,290 And a final sentence from telephone. So if the LHC finds supersymmetric particles in the current run in the next couple of years, 419 00:41:40,290 --> 00:41:45,510 that would be incredibly exciting because they would be fantastic dark matter candidates. 420 00:41:45,510 --> 00:41:53,220 And in the meantime, there are something up to 50 direct dark matter detection experiments worldwide looking to directly detect it. 421 00:41:53,220 --> 00:41:58,050 So any one of those could find a signal at any time. So it's very exciting. 422 00:41:58,050 --> 00:42:02,200 So we should just keep our eyes peeled as you improve. 423 00:42:02,200 --> 00:42:06,785 You're a fascinating 45 minutes next week scissoring.