 Okay, anyway, less than one talk. Yeah, right. I mean, the last talk, the last speaker is talking. I guess that's the way to say it. Okay. Okay. Yeah. So good afternoon, everybody. And I like you to welcome you to this plenary session. This afternoon session will be given by Professor Amanda Rothman. She's a professor at the University of Cape Town in South Africa. Professor Rothman is presently the NRS slash DHE guest South African research chair in physical cosmology and professor at the Department of Mathematics and Applied Maths. At the University of Cape Town. She's also the director of the high energy physics cosmology and also physics theory group and serves as the editor associate editor for mathematics, physics and astronomy for the South African Journal of Science. She completed her PhD under the supervision of Professor Brian Green at Columbia University. She's most well known for proposing the chameleon field theory, which involves a particle that could be responsible for costing the observed accelerated expansion of the universe. And she's very active in many areas related to promoting physics, in particular, she's active in promoting science. And for us, probably the most important thing for us in EFA is that she serves on a scientific advisory board. So she'll be giving us this talk today, talking about astronomy and fundamental physics in the radio sky. So, Professor Rothman, thank you very much. Thanks so much for the invitation to give this talk. It's a real honor to have this opportunity to talk to you all even if it means through the computer and in all of your own homes, rather than in the beautiful city of Kigali where I think I would certainly rather be right now. So, my plan for the talk is really to sort of walk you through some of what I think are really interesting problems at the moment for us as high energy theorists, cosmologists and people interested in astrophysics, and take you along the sort of intellectual journey that leads to why I think radio astronomy is an exceptionally compelling tool available for us to answer some really hard questions that we still have in fundamental physics. So I'll start with what problems I find interesting and talk you through cosmology and where the field is at the moment, and finally to the radio astronomy to the rescue, which is really the crux of the talk. And I will try to be as general as possible, but please if there are questions, I'm happy to answer them. I can't see the chat, but I'm trusting that the moderators will let me know if and when you want me to answer questions. So before I launch, I just wanted to thank all of you, just usually done at the end but I'm going to do it in the beginning. It's late, maybe some of you will not off but it's a real privilege I think to be able to talk about science, and to have our head in the stars, especially at a time when the rest of the world is really having to be very grounded in reality. So I just wanted to acknowledge the time that we're in, and what a privilege it is to be a part of a physics community at a time like this. So, what are the problems of interest to me they break up into really three sets of questions, and the, and I figured out the way to think about them is in terms of time. So the very early universe questions are possibly the very hardest. And so they're the ones that you sort of think about when you have, when you have tenure and you have the chance. So this is how did the universe make the transition from that very early quantum state to the classical state that we observe now. How do we even begin to solve quantum gravity. What are the, what is the way that the universe really went from became into an inflating universe and how did that stage exit. What is the nature of a beginning. Is the universe some kind of cycle these sort of very big questions that in some sense lean towards philosophy, if you're not careful. Then this sort of late universe questions in the formal practical and I think a lot of my research has been in that direction, which is what is the nature of dark energy and dark matter and I'll explain as much as I think we know to you all as we go. The role of beyond the standard model physics for cosmology. And then finally the questions that are completely timeless that I think we we sort of work on as we jump between the sort of bigger easier questions and the bigger now impossible questions. And that is, do we really have the right theory of gravity is Einstein's general theory correct. Why do we feel like we live in three plus one space time dimensions. Correct. Is this just our perception. Why does it appear as though we live in a special place in the universe, even though it's clear that it's that you know the earth is not in any special moment in space or time. It seems as though it is. And what is, you know, for me, a really interesting question completely not somewhere I expect physics to answer. Again, it falls into the philosophy side is the ideas of determinism and free will and consciousness and I can keep going. And then finally some very concrete questions which I think is a good place to start, which are the the plentitude of little puzzles that are in astrophysics. And what else can we learn about our universe by studying these seemingly narrow focused problems. So, I start with the with the known knowns. And I'm not quite quoting rumsfeld here though many think I am this is an old NASA quote, which is to figure things out into their classes so the known knowns. I believe that we need four ingredients to build a solid theory of our universe. The first is a theory of gravity, our best bet for that theory of gravity is Einstein's general theory of relativity. The second thing we need is a theory of matter and it's non gravitational interaction. So this is where the matter is interacting with itself but is not the coupling to gravity. So there is a standard model. I've got a picture of my son from Trees there last year you can see he's in the ICTP T shirt, which is a firm family favorite. And there you have your standard model action and your gravity your Einstein Hilbert action in front. So your gravity and your standard model are all sitting there on that T shirt. The other two ingredients are not given to us by either of those theories. So the first is a choice of symmetries that the innate symmetries within your universe, the geometry of your universe. So there we use observation to tell us to feedback into the theory but it's an input the theory doesn't spit out the correct geometry for us. So the input that we get from our data is that we don't live in a special place in the universe, neither in space or time, the universe is homogeneous and isotropic so it's the same in all directions, and the same everywhere. And so that's a sort of statement about geometry. And the last option is a choice of topology and again the theory doesn't give this to us Einstein's Geo does not tell us the topology of the universe. Multiple topologies can also give us the same geometry. So you can have a flat infinite universe or a flat toroidal universe completely different topology, same flat geometry. And I've just got some images there, just to give you a sense of what I mean but topology but those are inputs. So this is sort of the ingredients that we need to build our universe. So those simple ingredients alone. We arrive at the sort of startling and dramatic conclusion that the universe began in a hot, dense state everything was very close together very high temperature. And that has expanded into what we now see as the CMB. So we're looking back to the sort of almost earliest parts of the universe. We're seeing this sort of constant three Kelvin background temperature glow. I've got this, the improvement from Kobe to W map here plank is even more impressive but I haven't included in the slide. But you can see that there these first of all in the first slide use the first image you see the green is that sort of background temperature at, at the level of sort of three, three significant figures, and that's almost three Kelvin. On the next slide you can the next image you can see is the is the dipole and isotropy. So that is because the whole solar system is moving and it's moving towards the photons that are coming towards us that part is red it's hot. And the part that's moving away as blue is cold. The, the cosmology matches what you learned in primary school art that cold colors are cold and hot colors are hot. The red band across the middle is the galactic plane and these, these all get removed sort of manually by the phenomenal people who work in this area. And so the fluctuations are on the scale of 10 to the minus five that's the sort of size of an isotropy those fluctuations. What we're seeing there really is the surface of last scattering sets the point at which matter and light separate from each other. Very much like when you look out at a cloud. The last point your eye can see is where the light has left the sort of water surface of the cloud the light the light can't go through. And this is very much the same. So the CMB feels like it's the very very early universe, but actually it's quite late relative to the very early universe that we're finding much harder to probe, because light has already separated from matter at that point. So to give you a sort of visual. I've got a video here from W map and we zoom in first on a cold spot. So this is going back to the very early universe that's a cold spot meaning it's under dense. And at some point, the slight perturbations in the background density, cause matter to cluster, and eventually as matter clusters not surprisingly stars, eventually happen those cluster, so that you get galaxies, which continue to cluster you get fragments, and eventually you get clusters, and then super clusters, etc. And so you see that the sort of the formation of structure was really seeded by those tiny anisotropies in the very early universe. And there's W map looking back at the CMB and that little blue spot that we talked about. I'm including another one of these videos because I think, you know, one question that I've found always very interesting is whether or not we understand the curvature of the universe correctly. We sort of a lot of the time in cosmology we assume that it's flat because it's roughly flat, but the ways that we infer that are quite complicated. One of them is illustrated absolutely beautifully here, which is that if we look at trying to project the characteristics spot size from the CMB onto the telescope, you can see that if the universe is flat, all your photons moving straight lines and you get that expected size, if the universe is closed as positive curvature, then the spot size is much larger. And if the universe is open, negative curvature the spot size is much smaller. So you can, you can see that that's not surprising when you see this sort of image. And so it's really sort of exciting that we can understand critical pieces about our universe, just by being able to look back at that CMB. I've sort of spent my career bridging life as a cosmologist and life as a particle physicist and the ways that we view the world are really very different. So the inputs of particle physics we've tried very hard to sort of make a periodic table of elements because we know how powerful it was to organize and order the chemical elements in the periodic table. A particle physicist sort of view the world in terms of the heavy stuff which is the quarks and the light stuff which is the leptons, the mass carrying stuff which is the fermions, and the force carrying stuff on the right hand side here which are the bosons. And so that's sort of the worldview of a particle physicist. But it turns out that basically all of that stuff only makes up a tiny, tiny fraction of the worldview of a cosmologist. On the left hand side here you can see that all of the elements are made up of these, of, you know, bound combinations of protons, neutrons and electrons. If you're an element, all that matters is your number of protons. All of those are sitting in the heavy elements there which is 0.03% really very little. The free hydrogen and helium really makes up the majority of the matter stuff at 4%. The light stuff essentially stars and the gases is only half a percent and neutrinos are a tiny fraction, not surprisingly. The light stuff together is roughly 5%. The number sort of varies with each observation but not that much. The rest is actually dark. And by dark I mean does not interact electromagnetically. It is not sitting in that particle physics table. So everything we study as particle physicists makes up sort of less than 5% of the universe, the energy budget of the universe, and everything we experience in our everyday lives is also less than 5% of the universe. So that's kind of a real surprise. And so the bulk of what we seem to be made of is this dark matter and dark energy and that's I think the stuff that cosmology people are working on to some extent at every level. So just to talk through those, these are the known unknowns. You know, we know they exist but we don't know very much about them. First of all, our understanding of dark matter is only inferred by indirect measures. Every single direct detection test of dark matter has brought up nothing. We have not directly observed it in any way. So we can only inferred existence from gravity and the way that it changes our gravitational observations. And so how do we know about it. They're actually on every scale on every astrophysical scale we see the effects but the two most striking are the velocity rotation curves. So we can actually weigh how much stuff is inside a galaxy by looking at the speed of the stars as they are moving around on the outside. And so this is sort of high school math really going on here, which is just that the higher the greater the mass inside, dependent on the radius of course, because otherwise the object would not be bound, right? So to keep these objects bound in a galaxy requires that the velocity to mass ratio, oh sorry, is fixed. So the prediction there is sitting in the blue curve. But what we observe are those data lines, the sort of yellow data lines that the turquoise curve fits best. And that just tells you that we're missing this whole chunk of matter as you go further and further on. It just doesn't make sense. Something is missing. And if you put in dark matter that sort of closes that gap and you get that theory curve that would work. There are other observations. So GR tells us that light must bend around massive objects. And so we expect the sort of lensing where light has gone around multiple massive objects and we may see it coming at us at a different position or multiple images of it. And that allows us to actually weigh the matter that it's gone around. This is sort of a crude image but I think it's very effective to explain. And you can see there's some exceptional lensing images. I've just included a bunch of varied ones over here just to show you how dramatic it is. You can see those curves are sort of really strongly lensed objects that have gone around very massive objects. So we can learn about matter in between the source and us by using gravitational lensing. And so dark matter has these really indirect ways of observing it, but all of our candidates are yet to bring about a direct measure. So we have a whole bunch of really compelling and exciting candidates and different ways to rule them out. You know, this is what's very exciting, but none of them have been observed directly. And so there's a lot of impacts yet to be made here and there's potential, you know, for South Africa and Africa to have impact through the telescopes that are being built in the sort of radio astronomy direction, the Meerkat and SKA, which will be spread across Africa. Dark energy is very much the same in that regard. We see only its indirect effects. So we see dark energy is not a sort of matter as such in the sense that it's supposedly the energy of the vacuum. We see that the universe is expanding, it's expanding ever faster with time. So it's essentially accelerating and that implies some kind of negative pressure pushing things out from inside. But we know that gravity makes things cluster. It's, you know, massive objects have positive charge, so to speak, they're attracted to each other only there is no negative charge in terms of mass. And so this idea of something that causes everything to expand outwards and accelerate is very counterintuitive to gravity. And so the fact that we observe this is really a surprise. This is a lovely video. If you want to look at it later, I've left it on my slide so that people can watch it at any point. These are screenshots from it made by Sean Carroll. And essentially it illustrates the idea that I'm explaining here. So why do we even think dark energy exists? And again, here they hints on lots of different scales. And I think already in the 80s, it was already thought that something that the evidence was already there from the way that galaxies and clusters form. But the, the community still expected the universe to be decelerating. And so the deceleration parameter was positive. And eventually when we saw acceleration, it was like having a negative deceleration, which I think was a surprise. And so the major compelling evidence comes from type one a supernovae, and they're essentially really good standard candle so way for us to measure distances with fixed light sources. And so we see that the universe is accelerating. And the sort of very dramatic result that we appear to live in a universe that is mostly explained by dark energy, and probably flat. One, the, the 2011 Nobel Prize. So that's, you know, quite quite a dramatic result, especially given that Nobel Prizes tend to be awarded for directly detected observations, you know, gravitational waves, only one the Nobel Prize. Once they were directly detected that there was no Nobel Prize for the indirect detection. It was not for gravitational waves. So the observation is quite striking and we really do take dark energy, very, very seriously. It brings about a whole host of other problems, because the universe hasn't always been accelerating this dark energy has only started to dominate the total energy budget of the universe in the last sort of about Richard one to two. So that's relatively recently in cosmological timescales. And so it happens to be in the timescales in which the earth has existed and formed humans and there's this coincidence that we happen to be there happens to be enough matter to form Earth's and us to be able to observe this. If the cosmological constant was much larger, the universe would have accelerated before we would have existed. If it was much smaller, it would accelerate later but we wouldn't be here to notice it. So there's definitely this sort of nuanced question as to why it is that this has happened now. And I think there are only really two approaches the one is to leave your cosmology alone and come up with new standard model stuff, or beyond the standard model stuff and the other is to to figure out that something is not quite right with the way we move from gravity and to new physics alone. And those are different classes of approaches. And South Africa again has a lot of potential impact here, as does Africa more broadly, especially through the SKA because these large radio arrays will allow us to probe dark energy far better than we could do it with only sort of optical telescopes. So it gives us the chance to actually make really dramatic, dramatic observations of dark energy at the point of transition and I'll explain that slightly more a little further on. So essentially everything we know about the dark universe is inferred from observations or indirect detection none of them are directly detected. And each of those items dark energy or dark matter requires some kind of new physics. And that sort of lends itself to the telling of the story of a bundle of area which I'll tell quite quickly. If you've never heard of him he was the man who discovered a planet with a point of his pen. So he studied celestial dynamics which in those days involved a fortune of very careful calculations, and Uranus has always had the slightly odd wobble, aside from its odd tilt which you can see illustrated gorgeously in that in that image. And it had this wobble that was not explained by all the existing planets. And so a bundle of area figured out that the only way to explain the motion of Uranus was if there is a planet further than Uranus. And so he proposed the existence of Neptune and sent this telegram to the Berlin Observatory and they looked that night and discovered Neptune that day. That night. So we never really get to have such rapid scale discoveries certainly not in our time. And this was a great triumph really for celestial celestial dynamics so he had this, he had this sort of solution to this problem. Then he took he had also been studying the problem of Mercury, why the procession of the Perihelion of Mercury did not match the calculated expectations. And you know, I think like many of us when you have a hammer everything is a nail. And so he figured that the problem there was another missing planet. And so he said there must be a planet between Mercury and the sun, and he named that planet Vulcan. And of course there is no Vulcan, sadly, at least not between Mercury and the sun. And it turned out that to solve that problem, even though it looked very similar to the Uranus problem to solve that problem required another 50 years, and Einstein to come along and say actually our entire theory is wrong. We need a new theory of gravity. And it's only with general relativity that we can explain why Newtonian and the regular celestial mechanics derived from Newtonian gravity does not work for Mercury. So I sort of tell the story because I think they're really two different ways we revolutionize physics. The one is we discover new objects. And the other is we say the theory that we are working with is wrong and we need to revolutionize the theory. And it's sort of good to be on your toes and be willing to adjust between those sort of approaches rather than trying to hammer everything with the same, the same approach. So in terms of our cosmological parameters, I've listed them there. They've changed a little bit over the years, and you can see how beautiful it goes from Kobe to Plank. And really if I were to talk about the history of cosmology and go a little further back, I would tell you that really it used to be very much a philosophy. It was a way that we tried to figure out how humans fitted in with the world and trying to figure out the interconnections from the very largest scales to us. But the foundation of cosmology was philosophy and a belief system. And that foundation has radically changed since general relativity and Einstein and the foundations have become mathematics and astronomy. And over time cosmology has become exceptionally precise. The problem is whether or not it's accurate. So the precision you can see there from Kobe to Plank is fantastic. But there's a whole lot of discordance that's also coming along. So these little tensions that are telling us maybe something's wrong. We don't know what dark energy and dark matter are. We don't actually have a good candidate for inflation, which is our best way of explaining the bizarrely flat universe that we seem to live in. There are all kinds of missing baryons. We don't even fully understand how galaxies are formed. I think most striking and it's really come up a lot in the last few years is the H naught tension. So just to explain what that is, what is H naught? What is the Hubble constant? If we map the motion of galaxies away from us, the recessional velocity is their movement away from us, against distance, the distance away from us, you can see that it forms a straight line. And the slope of that line is essentially H naught or H. It's the Hubble constant and H naught is the Hubble constant today, naught in cosmology means today. So there are different ways that we can measure H naught. And when I was a grad student, it was considered that H naught was somewhere between 50 and 100, probably around 70, but no one was worried about the fact that the measurements were so far apart. For the simple reason that they had large errors in them, so it was okay that they had these big errors. Now, of course, as the errors are getting smaller, the measurements are not converging. And that's, I think that's kind of a big problem. So you can see here I've got the motion of H naught over time, and even more dramatically putting together each of the observations. So this was compiled by Colin Hill, putting together each of the observations of H naught, the top half are indirect and the bottom half are more direct observations. You can see that those error bars do not all include each other. And this isn't just a case of two experiments not agreeing. There's a there's a solid tension happening here something is not quite right. So it's really an opportunity to say, well, it looks like we've gone from philosophy to precision to crisis, but it's an opportunity to have a different way of looking at things. And so what are the possible solutions. I think the obvious one and everyone is doing this anyway. This is not at all my direction is to just keep re looking at that data. And if it's the data was taken and how it was analyzed, and saying we'll have, like, is there some massive systematic that's gone into most of these experiments that we've got wrong. And I think that will happen that has to happen that's part of honest good science. But there's also the possibility that there's really radical new physics going on here. I mentioned Julian Lorena and Rebecca who listen because they're members of my group, and they're working on the idea that possibly some kind of evolving dark energy or other new physics could be at work. That is a possibility, a different direction that I've taken two different directions. The one is, what if our theory is wrong, not that we need new physics but our theory of gravity is wrong. But when we test our theory of gravity, we tested with cosmology. And so we've sort of got this closed loop of what we're doing. If we can use gravitational waves to test our theory of gravity, we can then feed back what we understand about gravity into cosmology. And so separate gravity and cosmology in that way and use gravitational waves instead of the testing ground. And this my very excellent student Evan Martinez is working on. And it requires really exceptional attention to detail in in the code. And hopefully we will get somewhere on that. The other option is to try and find new probes of distances of cosmology that are not coupled to the existing ones. And that's where sort of the rest of my talk will be I think I've got. Yeah, I'm about halfway through. We will talk now about first radio bursts and why I think they can be really compelling ways for us to probe. Big questions that we have about cosmology gravity and fundamental physics. So there's some examples. Sorry, Amanda, there's a before you move on there's a question from the audience. What do you mean by new physics, as opposed to, for instance, new theory of gravity. Oh, so I separate. Yeah, separate the two new physics means that there's some kind of particle at work or, you know, if dark energy was not just a. Sorry. Just unmuted microphone. If, if, if, if there's a new particle at work. So if dark energy was some kind of evolving field that would be new physics, whereas a new theory of gravity is just gr is not correct. So you know when people modify gravity sometimes they put it on the left hand side and they say this is new gravity or they put on the right hand side and they say this is new physics. Yeah, I think this answers the questions. Thank you. You, but that's not always an honest thing to do, because I'm not dividing by zero so I think of the two is truly different. So, okay. Great. So, just, I don't know how much the audience knows about radio astronomy so I apologize if I'm showing you some very very basic things, but I'll admit that when I started to think about these things I knew absolutely nothing. Nothing I learned was new to me so I apologize if I subject you all to this new stuff again but, but the fact that the universe is emitting radio waves was only discovered by Jansky in the 30s. And of course he was like many of these great discoveries. He was working on something else he was trying to get rid of noise signals to improve telephones for Bell Labs. And then he set up this antenna and noticed that there was radiation that there was a noise coming in all directions and figured out it had to be cosmological as opposed to earthbound. They're extremely weak. So, you know, except for the solar ones because they're very close to us but if you add them all up that they're not enough to melt a snowflake which I find quite striking. They have a very large range that they occupy so they're the low frequency, long wavelength waves and they're in this very big band so in the terror hurts band, but all the way down to sort of a few megahertz. And the fact that there are such large wavelengths is fantastic for us because they go straight through dust. And so that means we can have radio telescopes on earth. We don't have to send them into space, like we do with so many of the other telescopes only the optical radio can be on earth. And so that's extremely useful for us and there's been a whole host of discoveries in the radio of course. And the question is really, what is next. So, my current kind of obsession are these, these objects called fast radio bursts or these bursts called fast radio bursts. So they are transients, meaning they, they're a sort of brief, bright burst of light and then they're over they're discovered for sort of very long scales, they're human life scales but actually millisecond scales. They're relatively recently discovered so 2007 was the first burst that was discovered and from being a few of them up until about last year there were, you know, maybe dozens now they're hundreds. And very soon we will have observed thousands or tens of thousands. The progenitor mechanism is not completely known, meaning the physics that drives them what causes these very very brief, very bright bursts in the radio is not totally known because there are at least 50 different mechanisms that people could explain such bursts. So it's possible that they're multiple different classes and each class of bursts has a different mechanism driving driving them. And some of them have been observed to repeat but not necessarily all of them. So that's again, quite a cool puzzle. So there's a whole possibility a whole world of science and discovery available. I've just put some of my papers here. And I think of most interest is really this catalogue that we've made which is all the theories, and I'm trying to rule them out. And my students have had a huge imprint here Emma Platt's champion this catalogue, Tony was my postdoc, Jake and Salona Gordon and Canty were both students. And you can see sort of the imprint of my students through all of this work they've played a very important role here so I just want to acknowledge that. Just before we sort of launch into the cosmology I wanted to try and map out for you the things that we think we know about fast radio burst so they're millisecond duration. We've observed them in a big range of frequencies so down to 300 megahertz, not below I think just because those bands have not been observing and up to eight gigahertz. Very few of them have been localized to hosts but some of them have which is really really important. We can get very far by localizing them. Only a fraction of the parameter space of them has been observed and that's because they're not they haven't they have mostly not been observed in real time. Now in recent years we are observing them in real time but many of the early ones were found by looking through archival data. And so what really happened is that there wasn't a technological revolution that allowed us to suddenly see these bursts, you know it's unusual to discover something so new so recently. It's actually just that we looked at the data in a different way. And so because they have these very short times, you can imagine that if you look in bins, they would be integrated out and you would just get a flat light instead of a very sort of localized peak. And so it's really a different way of looking at the data that allowed us to discover these. So there's a lot more yet to be discovered and there's the expectation is that there are tens of thousands of these happening somewhere in the universe every day. Though it's possible that we cannot observe all of them because they're not bright enough if they're too far away. Some of them have been known to repeat. We can't figure out if the repetitions are necessarily a periodic. One of them appears to be but again it's not clear because we don't observe them full time we observe them for chunks of time. So we're doing kind of detective work here. They are mostly extra galactic meaning outside of our galaxy and bright enough to see so they are cosmological. They are at red shops that we consider to be cosmological meaning far enough away. They trace the source environments incredibly well and we can learn a lot from them because of that, but it's critical to somehow separate the effects of the host the intergalactic medium and then work out those uncertainties that that that leak in because of the possible host I'll explain that in a moment. And because there are so many theories it is possible that there's more than one mechanism right now magnetize are the most compelling source and the soft gamma ray repeats in our own galaxy. It's named thereby its location has recently this year published only sort of two weeks ago been observed to emit first radio bursts. So, and that's a magnet so now we know at least that magnetize are our sources and the very first counterpart was seen with that magnetize which was this extra counterpart. And so it's possible that there are other counterparts out there. So there's immense potential for multi messenger and multi wavelength astronomy with fast radio burst so the counterparts can be x-ray or gamma ray, but they could also be neutrinos or possibly even gravitational waves. So those are different messengers inherently. So there's a lot still to learn and possibly the most important tool we have at our disposal is this DM the dispersion measure. So as the electron is traveling to us sorry as the photon is traveling to us from the source to to the observer. It's traveling through the cold plasma of our universe, which is essentially lots of lots of electrons, and the interaction with the electron slows down the photon in a way that is dependent on the frequency. And so you get this delay in the arrival time that goes like one of the frequency squared called the dispersion measure. And so we can study everything based on this equation essentially we can study everything between us and the source by studying this integral of the number of electrons between us and and the source. And so because they are extra galactic, we can do cosmology with them so to speak. So how do we do that I've sort of included this is a very nice paper led by my current post Doc Tony Walters. And essentially, because the dispersion measure involves the number of electrons on the right hand side, all the cosmology sits within that right hand side so first of all we have to average the left hand side over the intergalactic medium. Because it's just too difficult to deal with the inhomogeneity so we're making some simplifying assumptions. And on the right hand side all of cosmology sits. So you can see there, the sort of the usual terms omega matter that's the energy density and matter. Omega dark energy is energy density and dark energy, and we've included curvature in our study because we wanted to see if we could get curvature constraints. That was sort of the original problem was can we better constrain curvature using radio astronomy. And so these little bits of astronomy are in input in various places but you can really see that the equation of states of dark energy is in there so if dark energy is evolving. If there's curvature all these sort of big cosmology questions can in principle be probed by a large catalog of fast radio bursts. So the only the intergalactic medium part of the dispersion measure matters for us right that's the cosmology part. The rest is to us junk we want to get rid of it. So the Milky Way contribution is well known from studying galactic pulsars they also have this dispersion measure and so we can just subtract off the contribution that the Milky Way would give to the DM. The host galaxy part is not known because we don't know where it's coming from within the host we don't know what type the host is it's much harder. And so the more fps we have easier it is to marginalize over the host contribution. And if we can get fps very far away like redshift three four five. Then the fractional contribution of the host becomes very low and the bulk is coming from the intergalactic medium. So there are different ways to sort of try to mediate against this contribution coming from the host that we try to do. And another option is if we can see very well where our object is in the host galaxy, we could possibly extract a sort of golden set of fps all sitting at the edges of their host, and then we could ignore the role of the host. So the different ways to try and get around that problem but I want to just be honest that that is our big uncertainty here. But as we simulated a catalog we assumed would get 1000 fps. That seemed like a lot in 2018. Now it seems like few. So this is a field that's moving very fast. And not surprisingly we found that fps alone don't constrain things very well. But if you assume the price of existing cosmology. The CMB BAO supernova and H naught. And you add fps then you get sort of stronger constraints on omega barion which is the energy density and variants in the universe which is not surprising because you're probing the electrons out there so you're probing the variants directly. In terms of constraining the curvature. Again, you need to put everything in and it's only relative to the number of to the omega barion that you get the sort of improvement on your curvature constraints. It turned out that that the problem that I mentioned to you in my list of tensions this missing barrier on problem. It turns out that that is actually the right problem to solve and we was thinking of this upside down and Tony had this really great insight when he read more and realize that if I GM that I had told you about I'm just going back here you go it's sitting over there. It's the barion mass fraction. So it's how much. What is the basically how many Barion's are in the intergalactic medium what is the mass fraction of the intergalactic medium that is made up of Barion's. And we assume that was a fixed number given to us by astronomy, but it turns out that's a big unknown, because we expect the universe to have roughly, you know, close to 5% Barion's, but when we add up those observed we only see 70% of them. These were assumed to be missing and somewhere in the warm hot intergalactic mediums they were assumed to be in the IGM, but not yet observed. So Tony figured out that if we could keep F as an if I GM is a free parameter, and instead use cosmology as your prior. You could allow the FRBs to then constrain the best fit for FIGM, and then you go out and you you measure, and you could solve that missing Barion problem if you get the right value for FIGM. And so we published this in 2019 and early this year exactly that was done right led by by JP McCart and others. There was a publication earlier this year in nature, and they took four localized FRBs in host galaxies at reasonable redshift you can see there. And let me show you the video because it's so beautiful and dramatic how well it explains. So here's my fast radio burst, it's coming out of the galaxy that runs near the edge of the galaxy zooming in on the burst. You can start to see what happens to the different frequency components if the medium is empty if you're in vacuum, they all travel at the same speed. But if there's stuff in the way those electrons that I told you about the cold plasma, then the frequency of the photons determines how much they are slowed down and they are slowed down at different rates. The dispersion measure tells you about the what is in between us and the source. And so this missing Barion problem that was a problem for quite a while is essentially solved by fast radio burst observations. It's quite dramatic. And there's a host of other cosmology and fundamental physics problems that you can solve using fast radio burst. I've listed a few here. There are I've got slides of these that I've made that that you can talk through sort of slowly. I didn't want to dominate with one thing, but there are papers and papers and papers that are probing these sorts of questions. So there's a fortune that we can start to think about if we are able to see enough FOBs and each paper has priors that you need to think about. The first is if you want to probe helium realisation, you need enough of these bursts out to a redshift of five that's very far and, you know, very optimistic. If you want to be able to study dark energy, you need to be able to have enough FOBs at high enough redshift, or enough of them in very small redshift bins. You need to figure out a way to deal with a host, or you need to find a way to associate them with something else that you can associate them with a gamma ray burst. Then the FRB gives you the dispersion measure the gamma ray burst gives you the redshift. So you don't need to know necessarily the host together that gives you the equation of state. So there are really subtle ways to probe cosmology. If you have enough FOBs or enough FOBs with more information. We can probe dark matter using FRBs, because if there are FOBs in between a dark matter source and us, they would be lensed. And they would be lensed in such a way that we would observe the FRB, depending on the type of dark matter in a different way, there could be little double peaks. There could be substructure within those bursts that we have not yet well understood that is explained by dark matter along the line of sight. And for very simple pure fundamental physics very clear question like does the photon have mass, you could observe that as well. It would be very hard to do because a massive photon also gives you that one of a new squared behavior that you already see in the dispersion measure. But if you were able to disambiguate the two, you would be able to really get quite far in ruling out massive photons. And this should be done just with FOBs. This is just one tiny slice of radio cosmology radio astronomy that's possible. In terms of localizing them, this is really important so that the missing variant problem that I mentioned, you have about five minutes left. But you can take a bit more if you need. No worries that problem. The problem solved by really localizing for FRBs also gave us the chance to understand these FRBs so they all seem to sit at the edge of their host galaxies. They all seem to come from massive galaxies that are still star forming very much like ours. And that gives you a chance to guess at what the progenitors are so some kind of merger is a very likely event something like a neutron star or a magnet or merger. It's slightly less likely that they may be living evenly distributed across the galaxy that's not certain it's possible that one on the inside of the galaxy is not able to reach us because there's so much dust in the galaxy. But there's sort of hints that we can start to get more excitingly is really this that these are all nature papers and the first one Tony and I wrote the nature news and reviews about these three beautiful papers where they essentially discovered and parametrized the first fast radio burst inside our own galaxy. So they localized it to this magnet are the soft scamera repeats a magnet are which is in our galaxy. It's a known magnet are so so we know now that magnet is can definitely produce FRBs, which was not known before you know it was this like weird puzzle that they're about 30 at magnet is now galaxy. Why haven't we seen an FRB from them yet they're just not these bright bursts. And so the brightness that we see them extra galactically and yet the lack of bright ones from our galaxy was a puzzle. Now that we're seeing them from the galaxy that actually tells us yes magnetals could be sources. And so it really does sort of solve that that piece of the puzzle. It's also our first counterpart as I mentioned before, and it was an x-ray. So just to kind of my skip some slides from me because I realized the time is a time crunch, but hyrax is really, in my opinion, our best bet locally to do absolutely phenomenal ground break breaking FRB science and this is the sort of plan for hyrax. We're building an array of parabolic dishes, and they will be in that 400 to 800 megahertz band, which is really perfect for FRBs. And it turns out to also be perfect for dark energy. So here are the forecasts for what we can do with cosmology, the one on the left was made by my student the one on the right is an update with different numbers of arrays and you can see we can even get very far with only 128 dishes. But the precision that we can get with 1024 is kind of exceptional. And the plan is for hyrax to be spread around South Africa with possible progenitors at various parts in Africa. So the core of the array will sit at the same site as the SKA. And the name comes from cat seven that's crew array telescope there were seven of them. So more of those became near cut, right, more of cat telescopes, and mere cuts are these very cute little animals that live in the crew. So hyrax are rock dusties or hyraxes turn out to be the nearest genetic relative to elephants, much to everybody's surprise. And they are also very much living in the same area of the crew. And so the name hyrax is for the telescopes that will live essentially near mere cat. So the frequency band here you can see has incredibly low radio frequency interference. So that's really what we want to be able to do beautiful radio astronomy. And so keeping that interference very low is important. And it's an act of government in South Africa, not to have radio interference in the crew area. And so you can see it's optimal that image on the left shows you it's optimal for dark energy, but it's also exceptionally good for finding fast radio bursts within that frequency band. In terms of studying dark energy what we're really doing is instead of observing, instead of observing galaxies in excruciating detail, we're observing the sort of zoomed out, averaged picture of them. So we're able to see a huge number of them in an unresolved way, but it's enough to get maps of the large scale structure which tells us about the barrier and acoustic oscillation. So in the early universe they were these oscillations and they picked out a preferential length scale, which is you see the slight over density of galaxies that are 150 megaparsecs apart. And that's that sort of characteristic scale that allows us to sort of like lever our way into understanding the expansion history of the universe. And so dark energy is very much probable using using the hierarchy experiment and here are the constraints that we can get as well for curvature. You can see they're spectacular the way better than what you'd be able to get for playing. So there's a lot, there's a lot to be done on the cosmology side, but of course my excitement right now is on the fast radio burst side. And here you see the different, the different sites that we are proposing. And the hope is that we will have our triggers which are sets of eight telescopes in other parts of Africa. You can see we have hopes to have one very close to, very close to where you are in Rwanda. And the idea essentially there is that you get a very, very large baseline for your observations. So, sorry, here's a picture of the eight element array. But essentially what that means is that instead of being able to, you know, a somewhat large dish will allow us to see where the, that the FRB is in this galaxy. But a huge baseline will give us exceptional resolution sub-oxic and resolution so we could say where an FRB is in a particular galaxy. And so we can really pinpoint its exact location and get, you know, far more accuracy that will allow us to do really top level cosmology with them. And so there's immense, immense potential coming with Hierarchs and it's really a South Africa led project with a lot of international partners and we're hoping to build also with many African partners. The timeline is, you know, mapped out over there, you can see that over the next sort of two years we should be up to the 256th element array and there is the Karoo site. It's such a brilliant image I had to include it. So for some parting thoughts, I think there's a lot to be learned from studying FRBs, not just about our universe but also about how we think about things. So the fact that they were discovered without any technological innovation but just an attitude shift, I think it's something to take back into our everyday work. There may be great discovery awaiting us if we can just look at our problems in a different way. And the tech innovation is needed for us to revolutionize the next step. That's no doubt. But we never would have even thought to have that revolution if we hadn't really looked at our data in a different way. That's quite important. The next important thing is that the first one that we observed or the first few are not representative of the total sample. And it's often that you study something and you think you studied it so well, you know, you have a dog growing up and you assume all dogs are like the dog you had growing up, you know, but that's not at all true. And having that open mind and sort of trying to resist the confirmation bias that is introduced by only studying the limited resources available to us is really critical. And I think that's a lesson to take us into other fields. And of course the importance of searching, even if you see nothing, I think, you know, we know that already from discovering the Higgs after so many years, but we knew it was there. There may be other things that we're missing because we give up just a little too early. For me that it's really important to be able to bring together different wavelengths, different messengers, different parts of the sky. So it's really critical that we have telescope like observations on sky observations from different parts of the earth. Can't just have one array doing the science, the discovery that I just talked about from a couple of weeks ago. It was three radio telescopes and multiple gamma ray x-ray telescopes. There were multiple collaborations, countries, partnerships involved in really being able to make this discovery. One is not enough. They needed each other to calibrate against what they've done and make sure it was correct. If we can't set aside our biases, we'll always find what we're searching for. I think that's sort of critical and maybe obvious. And if you want to worry about 5G, which a lot of people seem to be this year, you should worry about how it ruins our radio astronomy. Our verified contributes is not good. And I think sort of, you know, if I if I just leave with one thought, it's that there's a real beauty in collaboration across fields and continents. You know, I started my life as my scientific life as a string theory high energy theorist, and I'm really enjoying learning every day about radio astronomy and cosmology. It's an absolute privilege to be able to take our heads out of the everyday world and stick them up in the stars. And so I thought I'd end with this beautiful artwork and quotes, just as some sort of inspiration. Thanks. Thank you. Thank you, Amanda, for the nice and inspiring talk. So we have one question from the audience, which was a more general question about the current tensions in our understanding of the universe. Do you think that these tensions are getting better? So are we are we going towards closing the gap in our understanding? No, I think they're getting worse. And it's good because they'll be like something will break and something good will happen, I think. More work for everyone. Thanks. And I think there's a revolution coming. Very good. Do we have more questions? I have a question. Go ahead. Yeah, question is thank you for all for the, for the lecture. A question is, is general relativity a physical theory? The question is, is general relativity a physical theory? Yeah, yeah. As opposed to it's a physical theory, I think, you know, physical theory well tested every every experiment has done it has passed. I mean, is that can we, can we, can we, can we see that does it pass through the, the, the correspondence principle? Like, every physical theory must, must converge. Can you, can you, can you, is there any convergence between the relativity and that theories? No, I mean general relativity doesn't yet fit with quantum gravity that with quantum field theory or quantum mechanics even. And that's just not understood. You know, those problems are slightly hidden by the fact that the very high energy regime or the very short distance regime are hidden from view they're inside a black. Very high energy. Microphones that are differing. Sorry. Certainly not yours. Have a question please. Okay. First of all, I think this is a really great job. I'm a double man made and team. So honestly, this is very impressive for me. Okay, we know that from the big down theory universe was born 13.7 billion years ago. And if you look at the inflation theory. We tell us that we tell us that we have a theory of exponential expansion of space in the early universe. Could we say that there is a small correlation between inflation and dark energy. Yeah, so they behave completely the same. They behave the same I mean your spot on, and people have tried very hard to try and get the same particle to be at fault for both. So to try, you know, one, one possible thing is that you could have a particle a scalar field that tracks the background dominant energy form. And so it starts its life as inflation. And then you know we tried this with chameleon gravity for what it's worth and it doesn't quite work. But it starts its life as the inflaton and then it dumps all its energy into other particles tracks radiation tracks matter and then later on dominates to become dark energy. People have tried it's just very hard to do it with one field, but they behave exactly the same. They behave the same you're exactly right. The physics is the same. Okay, I have one more question please. The way that studying theoretically black holes, especially rotating case rotating black hole could help us to understanding. First, say that again, could studying black holes help us understand what is there a way that studying theoretically black hole especially retouching retouching case or teaching black holes. Yeah, to understanding this kind of burst. Since rotating black holes in the kind of matter around it. Oh, right, right. So there are some theories that come from there are some black hole neutron star merger theories that that could drive these bursts. So the difficulty is seeing a gravitational wave and a fast radio burst coincidence that we haven't managed to do yet. But if we did then yes, that that would be very compelling. It's one of the paths to multi messenger astronomy I think that's worth following up. And so you know we do. There's the sort of coordination where when one interesting astronomical event happens on the one hand nobody tells anybody because it's sort of under embargo, but the telescopes talk to each other so that they can look. And so the fast radio bursts, we did look for not myself personally but the community look for fast radio bursts at the gravitational wave events and none have been seen yet. So it's possible though that I mean we've only seen a few right it's possible that that's yet to come. Yeah, it's a great question. Thank you. So we have a few great questions from the audience, which I'm trying to summarize, because I think we are running a bit out of time. The first question is. So are there enough constraints from fast radio birds and so maybe another way of formulating is how competitive competitive are the arrow bars from fast radio birds. So what are the standard, like supernovae or anything for instance. You mean for dark energy. For the different, different dark energy and that matter. I don't think so I mean not at this stage so that at this point at this stage the their forecasts. There's not enough fast radio bursts to actually do an analysis and give error bars. Yeah, but today forecast to what they're what the. Yeah, so if we get enough of them where we want to see them then we should be competitive. Okay, but it's, you know, are we going to get 10,000 at range of three. You know it's like how realistic is that forecast we just don't know. Okay. Yeah. And the question is, is the frequency of the of the burst the only distinction between the fast radio burst or the conventional gamma reverse. No, so I think the fact that they're so bright and we see them extra galactically to quite far out I mean I don't know that I don't know how bright gamma ray bursts are. But yeah, I think that's the main sort of difference but it's possible that they're coming from similar sources, but it's possible that one source can produce both. Does that make sense. It doesn't make sense to me, I think. Thanks. Thank you. Sorry, if I may extend on the question so. So, it's like you define the gamma ray buzz and FRB is so for example, if our bees are from 30 Hertz to a few thousand Hertz and gamma reverse are higher frequency. And then you. Okay. So, can gamma ray buzz be taken to be like the background for, for, for our bees. I don't know what you mean by background. I mean to identify the source, if you have like, I mean, how would you tell that. Let's say that the frequency is very is to was a tour of the high side. How would you identify whether it's the gamma ray buzz or. Oh, you would see them with different telescopes you wouldn't see a gamma ray burst. Okay. So you'd see the different telescope but they seems to be lots more fast rate bursts and gamma ray bursts. Yeah, they just seem to be different objects so they may they may have some relationship. And if we can use gamma reverse as an anchor to learn about fast rate but fast radio burst that would be great. Just because we've understood gamma ray bursts a bit longer. All right, thank you. Thank you. So I think we already have had a bit of questions. Should for thank Amanda for her nice talk. And we can have a we have still some time before the next, the next talk right. Thank you. Thank you very much Amanda. So, should we keep going with questions or should we take a break before, before the next talk starts. According to the schedule. The next talk is five minutes ago so we should probably move on to the next talk. Yes, so we should move to the next talk. Right. And I think she will share the session here. Okay. Thank you very much Amanda. Thank you. Thank you very much. Thank you. So, Amanda, we can have your slides right. Yes. Okay. Thank you. Okay. So. No, we move to.