 So is this live? Yeah. Oh good. We're live. We're live on video or good. Okay, so well I'm very happy to introduce Nicholas. He's gonna be talking to us about dark dark matter and physics. So here you are Nicholas Okay, so Hello, everyone. I'm really happy to be here today and excited to be talking to you about something different Which is physics the source of a lot of technological advancement, but this talk will mostly focus on The motivation behind it. So we're gonna be talking about the big concepts We're gonna be talking about the big questions. So I'm gonna try to to feed the information a bit slower Okay, so to start out with my name is Nicholas I am a PhD student and researcher at the University College London and This is my first emf camping festival super excited If you want to contact me or want to look into my research read more about dark matter You can try my web page and the way to remember The link is by thinking about the word Schrodinger spelled backwards Got it. Got it Right so I Chose to present this slide and to Keep coming back to it for for a specific reason. So this slide represents my universe But it also represents the universe in some respects So I chose the the ratios of the different colors on this slide to correspond to physical Things in the universe so the white background Cover 70% of the slide and represents the amount of dark energy that exists in the universe The only thing we know about dark energy is that it's a mysterious quantity It's a mysterious physical Object that currently dominates the universe and drives the expansion of the of the the close by Local neighborhood of stars. So if we if we look at the sky Everything is moving away and the further away it is the faster it moves away from us So that's that dark energy and that corresponds to 70% of Everything in the universe now we come to to the red outline of the matter text That corresponds to everything we interact with matter normal matter normal stuff chemicals atoms light everything that you may think of every worry every Thing memory happy happiness sadness is contained within that red outline and corresponds to only five percent of the observable universe the rest is what we call dark matter and is Just shown as a cat out in this picture and I just chose to put it as a cat out because that's that's what we're gonna Be exploring where we're trying to find to see behind this quantity today That is 25% of the observable universe this idea that There's five times more matter in the universe that we don't have access to Really frustrates me and drives a lot of my motivation into my research Just just to put that into perspective Try to put down six Features that define yourself. So I am a Gay hard-working physicist. I like creative things I love hanging out with friends and I spend a lot of time contemplating life Now picture of people walking into the room could only see only one thing They could only see me as a workaholic or just somebody that hangs out with friends all the time I'd be really frustrated That's what the universe is feeling right now. We only have access to five percent of it We only have access to a fifth of What we could have access to there's so much more to know Conversely picture your favorite canceled series imagine if somebody was holding five more seasons of it somewhere in their basement How much would you want to hunt that person down and watch those five seasons? Right so dark matter. It's Really hard to interact with it's really elusive. So how did we come up with this idea? How do we even know that it's there? We can owe that to these two people On the left we have Austrian astrophysicist Fritz wiki really interesting character His research pioneered the field of dark matter and he's the person coining The definition so he originally called it non luminous matter for its characteristics of just being not not there or not not emitting any light on the right we have Vera Rubin amazing American astrophysicist who Brought the idea of dark matter back to life and also Made the the subject of dark matter as one of the outstanding questions in modern physics So the way these two people Managed to prove that there's something in the universe. We don't quite understand is by looking at how things move so in the background of this slide I have I Chose to present two revolving systems of objects on the left We have a system that revolves slower there's less stuff in it and For it to be revolving at that speed there doesn't need to be a lot of gravity holding it together on The other hand on the right hand side. We see a system that's moving a lot faster This is quite similar to how When you were younger you would hold hands and spin around really fast the faster you would spin the stronger You would need to hold on so if things are spinning really fast that implies that there must be some really strong force holding it together and in the cosmic scales that force is gravity To have a stronger force this implies having more stuff in your in your system So what they did was they just studied the way galaxies moved and how things within galaxies moved and Then they kept getting wrong numbers. They the numbers didn't end up They saw how fast things moved they observed how many things are in the system and Suddenly they were coming up with numbers that were five times smaller that what would justify the velocities at which these objects were moving and Then at some point somebody gave up and said what if there's something that we can't see what if there's something that's so non-interactive Transparent to light that is there, but we can't quite put our hands on it yet and that Gave birth to this idea of dark matter something that is non-luminous something that is present yet inaccessible We are also able to know a lot about dark matter by just looking at the stars so this is one of the main examples of The people show to to demonstrate how dark matter is known to be very weakly interacting This shows the aftermath of a cosmic collision So imagine these two giant clouds of galaxies passing through each other like two water balloons As they as they do that as they pass through each other The the stuff in it will start colliding and will start recoiling of each other producing this Giant recoil gas and we see that in red in this picture. We see Just after the the two clusters pass through each other all the light emitting stuff does resemble the aftermath of a collision However, if we try to look at the same picture and count Or measure where most of the mass lies We find something different most of the mass actually has gone through the collision and didn't even care It's as if the balloons went through each other without really realizing they were there so This is again great proof that dark matter does exist it exists around us It frames galaxies and galaxy clusters, but it's also proof that it's extremely weakly interacting It's just not doing anything So how does one That wants to study dark matter Go about trying to find something that's so difficult to find Well, there's one thing that we know about dark matter and that's that in the early universe It once participated or it was part of this High-energy plasma it was once At an active component to the interactions happening but back then otherwise it wouldn't be part of the universe at all So we try really hard to see if we can simulate conditions That will allow us to to observe this very very weak interaction Which takes us to the text of this picture, so there's three Distinct ways in which we try to investigate the nature of dark matter on the top We have dark matter dark matter interactions, so dark matter may be able to interact with itself Then we're we look for ways that dark matter interacts with normal matter that are non gravitational so on on smaller scales and lastly we we look at Ways matter interacts with itself that may produce dark matter So in in either way the observable and what we have access to is the real matter stuff and In each category. We're trying to infer from what we can see the existence of dark matter Right, so so starting from the top. How do we go about? Trying to see dark matter dark matter interactions Well, we do that by looking for the products So imagine the the idea that dark matter particles when they collide They might produce lights or they might produce high-energy particles like neutrinos Which we can detect But how do we how do we look for places where dark matter does collide does interact? We do that by looking at really really dense areas in in the sky and that's Why we point telescopes at the center of the galaxy so the center of the galaxy is a place in state in space time where Gravity is really strong things tend to pull towards it and as they do they speed up It's as if things are free falling towards there. They're all heading towards the central spot and once they are there their Energy is extremely extremely high So we point telescopes there as is shown here. So on the on the slide. We have the Chandra telescope Which is a giant x-ray antenna and what it is trying to see is Flashes of light that are emitted from the center of the galaxy that can't be attributed to anything else So this is an exit search so that implies that you really have to know what's happening around the Local area that you're studying. So it's a quite challenging job to be able to distinguish whether or not Something that was observed can be attributed to known physics or whether it is dark matter causing it In the one of the other alternatives dark matter matter interactions We look for Interactions that could happen between the two directly So to do this we take advantage of the fact that dark matter is so weakly interacting That it goes through Everything it goes through the entirety of the planet that would stop many other particles So what we do is take huge very very clean very very Radiopure detectors in this case the LZ experiment Which is a seven-ton target of liquid xenon cooled to low temperatures and purified so much that there's absolutely Mine-newed amounts of radioactivity in it and we place it so far underground that cosmic radiation or radiation coming from the surroundings the The universe the atmosphere does not affect it so by lowering The amount of interaction this device has with its surroundings by placing it as such a clean environment We can become sensitive to such weak interactions as dark matter would be prone to In this detector we have Hundreds of cameras pointed into this volume and they're just expecting to see this instance where a collision occurs within the material and it is all the specific Signature and Specific magnitude that could only be attributed to dark matter This requires as I said extremely low background materials. So often what what has to be done is sourcing of ancient titanium Purification through extremely long processes But also very very low noise electronics And then the the final way in which we we tried to probe dark matter is using matter interactions So as I mentioned previously dark matter at some point was part of the whole so at some point it was interacting with everything else in the universe and What we know is that was very very close to the beginning when Temperatures and pressures were so high that it was inevitable for dark matter to come into contact with real matter so one way to try to force it out and Study it is by simulating those conditions the large Hadron Collider simulates the energies and pressure That we're present in the early universe by smashing particles together at Extremely high speeds as this is done extremely high energies are released and Multiple other types of particles are generated Then what can be done is looking at the output of such a collision using a detector such as the atlas detector and Sifting through the data trying to look for inconsistencies So you can't really look for something that didn't leave a signature But you can look for things that don't make sense So if a dark matter particle is produced within your detector that would result in You observing some sort of physics that is not standard so that would result in missing energy and things just not adding up to to the correct number by Adding all these effects together one can say with confidence whether or not a Dark matter particle was produced or not so in In conclusion, this is the general approach to to studying dark matter something so elusive that is essentially Making fun of the scientific community trying to to study it Something that we know is there we know a lot about it yet We can't really study it in a way that would allow us to prove its existence and study its features If in the future we do manage to prove and we do in some way managed to interact with it I I'm not sure whether or not it could be used for For something quite so exciting So every time a new scientific discoveries made everybody accepts and expects and anticipates The applications it might have in the case of dark matter because of the difficulty in its in its handling We wouldn't really be able to utilize it for information transfer We wouldn't be able to utilize it for energy transfer But we can use it to study extremely early periods of our universe and if possible Because it is composed of matter. Maybe one day we can even Use it to produce energy, but that I assume that that could be very far in the future Right, so this is this is all I had to say. Thank you very much Yeah, so we've got time for a couple questions about any questions. Go ahead. It's got me. Oh, yeah They're good. Yeah, so pardon migrants but it's it seems like from the start of this the description that it's an effect almost like The the rotation occurs because of an effect I presume something that big bang caused planets or a mass in the universe to move right or you mentioned that It's and where we detect things moving away from each other faster than we expect that to be the case So so if I simplify that and go to sort of my sort of childhood Physics, if I think of a spring atop or throwing something And if I look at that if I take a snapshot in time and I look at that earlier Then when that starts to slow down turn sort of normal parabola or normal bit of time if I the sooner I look at it They're still accelerating or still moving further apart than we'd expected to so what what makes us infer that We're not just we haven't just got the calculation long wrong of when the big bang took place or when the effect took place That we see this momentum or this motion Taking place at a greater rate than what we currently see that that makes sense what I'm trying to ask Let me see so Are you so the question is with regards to whether or not we can say That with confidence whether the the observations Do represent a an expansion of the universe that is currently happening and not an earlier instance Yeah, I guess so so for if you just take the rotation of the objects round Let's say I don't know black hole or whatever that whatever the mass was in the middle, right? Mm-hmm, and so I kind of got the impression that Poverting is the rotating and faster than we would expect them to be and so the gravity of the Piece in the center must be greater to hold them in those positions That's that's correct. Yes, and so if I think of a spinning top with some let's say strings and Masses weights on the outside of that I spun it if I use great force to spin that and then I might see a greater acceleration Initially, then what it would sort of normal out and over time and so I might expect in maybe 10 seconds would be quite slow But one point five seconds after I used a lot of energy to start the rotation It'd be a lot higher and so I might see the similarity. So my question really is what if the energy being applied to? Objects in the universe moving away from each other or bodies rotating around each other The energy is greater than our calculation is and so we see those moving faster than we originally anticipated So it's always possible for calculations to be wrong And what we can do is keep cross-checking all the measurements that that we have What I can say is that through multiple independent measurements so far the inconsistencies remain so General relativity was recently a hundred years from its proposal being proven correct by gravitational waves That was a huge milestone in science because that confirms our trust in general relativity Which is the ground works for most of this These concepts are built on We can have a longer conversation Later over a drink. Thank you much. Thanks. Yeah There's somebody just behind you Talking to this a bit louder. Hello. Yeah. Yeah, okay. So as I understand it Dark matter is kind of a fudge factor, right? It's we don't know what it is But we know there must be something there We have to there must be this much of it for the the numbers to work out against what we observe, right? and then You talk very briefly about this other fudge factor. We've got which is dark energy because one fudge factor wasn't enough, right? So my question is Why are there two fudge factors? You know, what what is it that makes us think though these two distinct things dark matter dark energy rather than One thing that we don't know about how do we distinguish those two fudges? No, that's that's that's a really good question but what what motivates really the distinction between the two is The understanding of the very similar like the very different effects They each have and the scales at which they are acting so dark matter would be holding galaxies together So in our own galaxy, there's a halo of dark matter Its effects can be quantified to be very local In in the way they filament so a lot of the pictures that I use in the background display simulations that are Created to represent Observations that what that we see and this Agrees to to a great enough significance that we understand that dark matter must be a physical fluid in the universe When it comes to the idea of dark energy The expansion that we see and can study does not follow the same trends so Dark energy behaves in different ways with respect to Tearing the universe apart rather than holding it together, which is what dark matter is doing The two are really hard to Compile into one theory There is no standing theory that I know of that tries to solve This cosmological type of fudge situation using one quantity or one parameter So that's if that if that satisfies your yeah, that gives me an idea Hi there you talking about the main way you know about stock matter even being there is from gravity and we also know because Relativity doesn't predict quantum mechanics the vice versa that both must be wrong at some level or incomplete at the very least How well proven is it that it's actually something physical and not a correction on relativity itself? so To reiterate your question, how do we know that it is It is necessary to introduce more matter and not a Subject of just correcting relativity to the scales corresponding to the problem Corrects or unknown bits of relativity More distance this there's actually a huge chapter in in dark matter known as modified gravity Which studies these effects What it tries to introduce is the idea of scale dependence on the way gravity acts It is usually not the most graceful of theories because It is it is trying to introduce many more parameters than than simpler models, so They are often not presented as the most most elegant ones in addition Most of them were killed recently with the detection of gravitational waves. So the the speed At which gravitational waves travel and the the frequency at which they're observed Would not be the same given modified gravity was in effect It is still on the table some theories survived the the release of the gravitational wave results But they're heavily disfavored Thank you. Thank you. Thank you very much indeed for a very interesting talk