What is Dark Matter and Why Does it Matter?

hi welcome to Fermilab it's my pleasure to introduce dr. dr. Dan Bauer he's one of the preeminent scientists working on dark matter in the world he's gonna lead us through a nice discussion on dark matter and why why it matters so Dan please okay thanks for coming to the ask of scientist program here as writer says I'm going to try to tell you some of what I know about dark matter and why why it matters to all of us so I'll try to talk a little bit about what is dark matter why do we believe it exists where might it be how can we look for dark matter particles when might we find them and what do we learn about the universe if we do find them all right so let's start with what is dark matter the basic definition is it's some form of matter that doesn't emit reflect or absorb electromagnetic radiation light and all the different variations of light like radio waves gamma rays so just picture that you have a source of light you have this cloud of dark matter you have an eyeball what happens the light just goes straight through it doesn't bounce off it doesn't interact in any way with the dark matter whereas normal matter which is everything that makes us up and everything we know about might appear dark to our eyes but that's because it does something different it absorbs a reflects light so the light didn't reach your eye and it looks dark but that's because that material interacted with light whereas dark matter didn't interact at all with light so it's maybe an unfortunate name maybe it would have been better named as invisible matter because it doesn't interact at all with light okay so when I first started working in this field my kids were much younger and when I mentioned dark matter they had a rather different interpretation of what it might be this is what they thought of unfortunately this guy is rather reflective and carries a lightsaber so that's that's definitely not what we're talking about in dark matter so what what could it be when you when you think about dark matter what what would you think of first well well you might think of as things like black stars stars that are dead or rogue planets that have lost their Sun and are wandering around even outside of the galaxy or dark nebulae the problem is all of those in some way or another admit to absorb or reflect light so they don't qualify as the type of dark matter that we're talking about there is a form of normal matter neutrinos we are now the neutrino lab we make a lot of these and people originally thought of these as possibly being the Dark Matter because they don't interact electromagnetically just like we said that dark matter shouldn't but they're in fact far too energetic and have way too little mass to make up the dark matter so they've already been ruled out as the source of dark matter perhaps there's a new kind of elementary particle this is what we do with framing that way we produce elementary particles and study their properties so maybe there's something that we haven't been able to make yet that has mass and therefore produces gravity and may interact with normal matter but only very weakly so that we wouldn't have seen it yet maybe that's what dark matter is where would it come from well it could have came from the same place all matter came from the Big Bang so from the early universe starts off here with the Big Bang and at that point dark matter particles could have been produced and in fact could be around from all that time if they're stable normal matter was also produced then so everything we we know was produced in everything you see in this time line up to the present day is charting what happened to normal matter what we don't know is what happened to the dark matter in that period of time all right so how does it differ from normal matter well we know one way it doesn't feel the electromagnetic force but let's let's stop and ask ourselves what is normal matter and this is the way we particle physicists think about normal matter there's a whole bunch of different elementary particles that make us up most of what makes us up is the electron and and light photon and the proton and neutron which are made out of these quarks we know all about their interactions we use that all the time and work we do at Remmy lab there's also the four forces we know about gravity electromagnet electromagnetism and the weak and strong nuclear forces so none of this accounts for dark matter we understand all this and it doesn't have the properties the dark matter has so we don't know what's over here on the side but there could be a standard model of dark matter there could be a table very much like this on this side with many different dark matter particles and maybe even dark forces that allow these particles to talk to one another that we would be completely unaware of what we're interested in and what we can measure possibly is how do the two different sectors interact so we know one way and I'll talk about this in a minute they both feel the force of gravity but there may be another way there may be a very weak form of interaction that allows us to sense this dark sector over here and allow us to know that there's dark matter interacting with us alright so over the period of time this has been studied and it's now close to twenty years I guess our particle theorists have been very busy coming up with possible explanations for dark matter this is a logarithmic scale on both scales so this vertical scale tells us how frequently dark matter interacts with normal matter from almost never to very often oh I keep hitting the wrong button sorry about that and the the horizontal scale is the mass of the dark matter so just to set a scale it's neutrino mass which is the lightest particle we know about the proton mass which is what makes up us along with the neutron and then a mass of a sand grain so you see this covers an enormous possible range of how often dark matter would interact with us and what its mass would be it's hard to study this bigger range this is the part that we've been able to study so far because it has moderate interactions with normal matter and masses that were familiar with and know how to detect in the laboratory and the one of the favorite candidates for a long time has been generically labeled wimp weakly interacting massive particle physicists love to give strange names to the particles and this is no exception so dark matter could be in the form of a wimp okay so I've outlined the properties of dark matter but you're probably asking yourself why don't we even talk about this why do we believe dark matter exists at all and that's because when we look out in the universe with telescopes and surface arrays and everything else we see effects that we can't account for and their gravitational effects so we've been looking in all sorts of different ways we look at galaxies we look at the Cosmic Microwave Background we look at the structure of the universe itself and so on and all of these are giving us a picture that there's roughly this this is what makes up the universe that they're most of the matter energy of the universe is actually dark energy which we won't talk about here but there's about five times more Dark Matter than there is this little sliver of normal matter so this is us this is what we believe dark matter is and this is dark energy where we're a very small part of it's out there in the universe in this picture so most of the matter is dark matter the only caveat here is that this relies on the belief that Einstein got it right with general relativity and that we completely understand gravity if there's something subtle we don't understand about gravity then this could be wrong okay so let's look at a few of these in a little more details so you can see some of the evidence some of the original evidence for dark matter came from studying how galaxies rotate or how galaxy clusters rotate and you you can measure the velocities of galaxies or stars in galaxies and what you see is something like this this is a typical rotation curve for a galaxy and what yours what you should see if if you're only detecting the stars and gas it's these sort of curves so the wrote the speed as you go farther out from the center of the galaxy should drop off what instead the data shows is it doesn't it stays level all the way out to the farthest extent you can see I'm gonna stop pushing these buttons so this tells you that there's something there's some form of matter that's keeping the speeds up all the way out as far as you can see and that's modeled here by this thing called halo that's actually what a Dark Matter halo a big sphere of dark matter would do so that tells you that there's something invisible there another way of understanding that there's dark matter is something called gravitational lensing so Einstein said the gravity makes a well essentially that can even bend light and so if you have a huge mass here then light from a galaxy behind that mask it's bent around and it can form rings or arcs when we look at it from this point of view and in fact that's what you see is this is a very pretty example of that where you see the this was actually a big cluster of galaxies and you see these blue arcs those are background galaxies that are that where the light is being bent around and appearing to us as this arc it's not quite a ring but it's close the problem is that when you look at the distances and the mass is involved there isn't enough matter here to do this and in fact when you calculate how much matter there should be you get a picture like this so the blue is the amount of matter it would take and the way it's distributed and in order to produce these arcs and you can see that blue well in some cases it overlaps with the bright shiny things in many cases that there's nothing there and so this is another reason why we believe there's a lot more math there than is producing light ok so here's one more type of evidence so what this is is a simulation of two clusters of galaxies colliding where dark matter is depicted in blue it's not actually shining blue we're just using that as a coloring for it and normal matter is in pink and what you saw there is that the the blue just passed right through the two clumps of blue passed right through didn't do anything whereas the pink got slowed down and because normal matter interacts with itself and in fact we see something exactly like that this is not a simulation anymore this is an example of it's called the bullet cluster it's an example of two clusters that have passed through one another the pink is is a coloring but it shows the x-ray emission from the gas that has interacted whereas the blue is is the coloring of the gravitational lensing like I showed you before how much mass there is in order to have produced the light behind it so again there's there's appears to be dark matter everywhere we look in the universe okay and finally people have developed supercomputer computer simulations where you just put in dark matter and gravity so there's no normal matter in what I'm going to show you here it's just dark matter and gravity and you start from the beginning of the universe the time index is shown up here that's billions of years and this scale is about the scale it's ten times larger than our galaxy and so what you see evolving here as time goes on is a big web where matter is clumping dark matter is clumping together on all different scales and forming what looks like a giant spider web with knots and many places and if I let this go all the way to the end you would see something that is very similar to what the next frame shows which is an actual observation with the telescope from Earth of the large-scale structure of the universe where they've mapped out all of the galaxies and clusters that can be seen as far out as you could see and you see exactly that sort of web but this is this is light here this is actually an actual observation so what that tells us is that what we're seeing in the universe producing light has a structure very much like what you would see if you had just dark matter and evolved the universe so what that means to us is that it was dark matter that actually clumped together and formed the seeds that led to the formation of galaxies so in that sense it's dark matter that's responsible for us being here at all because it enabled the galaxies to form okay so if you take that and apply it locally you know this is the Milky Way galaxy as we know it this is what we see when we look with telescopes but if you want to put it in context to what it actually is it's embedded in this huge cloud of dark matter again because the rotation curve shows you there's a lot of mass and because we believe that that dark matter actually was the seed that drew the normal matter in that formed the galaxy okay so I've talked a lot about the the evidence for dark matter let me tell you a bit about how we might go about finding such such particles this is an example of what physicists call a Fineman diagram you may have seen this sort of thing before it really is fairly simple it's just a diagram ik diagrammatic way of showing you how particles interact so here the dark matters is depicted by this Greek symbol Chi and normal matter by these forks and there's something that leads to an interaction between them you could look at this diagram in many different ways so if you look down on this diagram you're you're looking at I hate this thing you're looking at dark matter colliding with another dark matter particle and producing normal matter so you could look for that by looking out in space you know I said that the Milky Way is embedded in this huge Dark Matter halo so they're dark matter particles out there they should find them each other and collide and produce normal matter so you could look where you expect to see a lot of dark matter and see the these normal matter particles that's called indirect detection because you're not directly detecting the dark matter particle in that case if you look sideways at this diagram then you're talking about a dark matter particle scattering off a quark or a nucleus and the dark matter particle goes on and you see energy given to the nucleus or or electron that's called direct detection because the dark matter has directly interacted in your detector and then finally if you look from the bottom up you could collide normal matter particles and produce dark matter particles so you could use Fermilab or now CERN to collide together quarks well really protons and together and form Dark Matter so we'll talk about each of these a little bit more let me start with direct detection in the laboratory so this is a view of a crystal the little black things are nuclei and the rods in between you're supposed to represent the electrons that bind them together so in comes the Dark Matter particle ironically enough in white I don't know why they colored it that way and out it goes but what it did is to scatter off this nucleus right here and it produced some byproducts and in this case what it produced is ionization which is just kicking electrons out of an atom or heat which is this blue wiggling of the crystal so that's the sort of way you would look for it is to just look for evidence that something has entered your detector and produced a signature that's a little bit of heat and a little bit of charge okay so how do you go about designing an experiment to take advantage of that well that's a very small amount of energy being deposited there it's just a tiny little scattering off a nucleus so you have to build an extremely sensitive detector to see that small and energy it's roughly a billion times lower than the energy that the accelerators generate around here so we call it high-energy physics but this is actually low energy physics here secondly there's a lot of normal matter particles that are bouncing in that crystal all the time - and they they far outnumber any dark matter interactions so you're gonna have to find a way to to recognize them and suppress them and you need a lot of detector mass and a lot of patience because the we believe the dark matter density the amount of dark matter that's passing through us is so low that with current experiments you might affect a few of those per year so it's a long way to look for your Dark Matter particle interacting okay so let me tell you about an example it's not a random example it's the experiment I work on which is what I'm telling you about this one it's called super CTMS it stands for cryogenic Dark Matter search we've been through several phases of this so I won't go into all the details of this sort of apparatus but there are germanium and silicon detectors that are cooled very low temperature inside this that's huge massive cryostat so that they're sensitive to very small energies and I'll talk in a minute about how that works and then you have to surround that with a bunch of shielding of various types to get rid of those background particles that are all around us and I'll talk more about that too and then you have to cool it down with a special refrigerator and you have to go deep underground because there's a lot of particles coming from space in the form of cosmic rays that also can be a background let's talk about each of those individually so here's my thermometer going from room temperature down to absolute zero your typical home refrigerator works with a fluid that can be expanded and condensed so you can take heat away from the inside and expel it to the outside and it works very well but it only gets you down to about here freezer I'll get you a bit lower and you know coldest winter you can imagine is is still way up here a dilution refrigerator which is how we do these experiments works in a very similar way but with a very special set of helium isotopes that's the working fluid but you're again just expanding a gas out of a fluid and condensing it back in but here you you're now able to reach almost down to absolute zero and that's crucial to make these sort of detectors work okay so why is that why is that so important let me step over here and ask for a couple of volunteers if anybody would like to come up okay so you get to do the that one come on up okay so what we have here is a heavy dark matter particle I'm going to use you two and a light dark matter particle and what I have here is a crystal so these tennis balls are the nuclei and these Springs are the electrons that hold them together now I'm gonna have you wiggle this alright what is that that's heat that's a normal room temperature crystal keep wiggling I need a lot of energy here so that crystal is jiggling all over now if he throws that Dark Matter particle in here go ahead and toss it in didn't see anything right because the thing is wiggling too much now stop wiggling but wiggle just a little bit yeah just a little bit okay throw it in again okay so if you cool it down if you reduce most of the heat from the system then a single particle interacting and the crystal releases enough heat to be visible now this I said was a heavy dark matter particle so it generated a pretty good wiggle go ahead and wiggle a little bit again all right toss that little light Martin does he a thing right because it's still wiggling too much it's still too warm so to be sensitive to really light dark matter particles we have to cool this thing down so it doesn't do anything I have to give a really good toss all right so you see a little bit of wiggle here that's the principle we're working honest thank you all for your your help I appreciate it [Applause] so that's why the cold temperatures so to allow us to be sensitive to very small amounts of heat this was a much better demo than my my slide transition so we'll get rid of that one alright so another thing I mentioned is backgrounds we have to be able to recognize and suppress backgrounds so let me take my detector in my shielded volume in an underground cavern and walk you through what are some of the backgrounds so there's cosmic rays they're high-energy particles from space generated from supernovae and and active galaxies at the surface there's about one per hand per second passing through us so they're passing through all the time most of them don't harm us but in fact this is a source of radiation so pilots get a higher dose of radiation because they they are higher in the air and the flux of cosmic rays is higher so we go underground to avoid this even the underground it's not completely negative negligible problem because one of these cosmic rays can come in hit the rock and make a particle that goes into the detector or it can come in and hit the shielding and make a particle that goes into the detector so we really have to be deep underground to get rid of most of these cosmic rays the other main source of background is radioactivity so you don't think of things around you or even your body being radioactive but all of us and all the materials around us have a tiny amount of radioactivity if you eat a banana you increase your radioactivity from from a potassium isotope that tiny amount of radioactivity actually is a huge background for these experiments so it can be in the rock or it can actually be in the material you're using for shielding yeah it's hard to get materials that are free of radioactivity so it's crucial that we minimize that that we get the ultra pure materials and we have detectors that can recognize any backgrounds that that can get into the detector volume okay so we say we go deep and I mean deep so we did the previous version of our experiment a half mile underground and in an old iron mine in Sudan in northern Minnesota and we're gearing up to go mile and a half underground at a active nickel mine and in Sudbury Ontario why because of the cosmic-ray rates so at the surface it's ridiculous you have like I say one per hand per second at Sudan we had one per minute in our experiment still too much we ran there for many years and that was ultimately a background it's one per day and the new lab at Sudbury so that's why we're going there also you have to have as clean a lab space as possible because you know you make clean materials but if if you're working on experiment you yourself can carry the lab environment and and contaminated so it's no lab where we're going the entire underground lab is a cleanroom it's ironic you think mine is a very dirty place this is one of the cleanest places around and it's an inactive mind but it's crucial to minimize this radioactivity problem oh what's it like working underground I'll give you a few snapshots from Sudan and if there's time at the end I'll show you a snow lab so it's really nice to go underground at Sudan in January because that that's minus 40 you spend most of the day in clean suits because you're trying to minimize the radioactivity that you're bringing to the experiment you meet some interesting creatures that's a little brown bat and he made it half a mile underground at Sudan and he didn't like me being there and we get to also talk to people so Sudan was operated as a state park and they would bring people down they'd say what the heck are you guys doing down here you know and so it was fun to tell them about it you get to work with really cool detectors in both senses of the word so this is a photo of one of the detectors that we use it's a germanium detector that's a model of it later so if you want to look more closely you can you'll be able to look at that you can see the scale and that shows you as well this is not very big it's a little bit bigger than this sized when we were in Minnesota we called him hockey pucks but they're a little bigger now but they're specially designed so that I said before the particles hitting these crystals liberate charged and produce these crystal vibrations heat or phonons we pattern onto the surface of these detectors little tiny thermometers and when you look closely on that one you'll see there's thousands of them on there and they're at a very cold temperature and they're right at the point where they could go superconducting or normal so they can either lose resistance totally or they can go normal and have their normal resistance if you hold them right there and push the right button a little bit of heat in the crystal will drive that normal until you'll be able to see that tiny little signal it's a very clever technology that was developed for this and is being used for many other things other than Dark Matter searches now and if you look at the ratio of ionization or charge to phonons as well as the position of the event and that crystal remember I said there's lots of sensors there so you can get some indication of where it happened in the crystal then you can use that to tell you where or what what type of interaction it was so you can see a typical view of one of our data sets where these are events where something hit the nucleus and rattled it these are events where something hit the electron and rattled it and these are events on the surface of the detector the power of the technology is to be able to separate that and that's crucial because almost all the backgrounds come from the surface they come from the environment outside of the detector these germanium and silicon crystals are ultra pure because the semiconductor industry needs to have them that way okay so what is the raw data look like would look like much to you we take some time to absorb this but let me point out that here was a particle hitting a detector and so you can see that these things which are sort of flatlined and wiggling and jumping around a little bit here's a signal and it's seen in MIT and several different sensors on the detector this was the heat or phonons this was the charge showing that signal there's some other interesting things here too but they're not interesting for dark matter this is a detector that's very sensitive to noise in the environment in this case vibration and so this thing sits and Wiggles around all the time and it's pretty useless for dark matter so you have to have crystals that are very little noise very little vibrational noise in order to make this work as well okay so when you go to the 15th floor you'll see this model for real that I just wanted to to show you this this is what particle interactions would look like so these little things here are sort of models of our detectors like that and we've just taken our data this is real data and we've converted it from the very high frequencies that you saw in the previous thing to - light and sound frequencies that you can see so in this case what we've done is put a radioactive source near the detector and you see the detectors are going off like crazy because there's just a huge and they're going off and it's hard to see it here you'll see it better on the 15th floor but they're going off at different patterns around the detectors if you take cosmic rays muons you see that they come straight through and interact in a line in the detector so you see a flash going through all of them that's a signature you can recognize and discard you know it's not dark matter what we normally would be doing it's sitting there and occasionally something happens and it's almost always the background particle but this is what we see we had a Dark Matter particle we would see just a little flash in it sound a very high frequency sound but okay so how do we analyze that data so I showed you those signal traces what we do is - we understand what what it ought to look like because we understand our detectors well enough so we put a we fit a shape to this and say what is the amount of phonon or charge under that and that's a measure of the energy deposited and by looking at the different sensors we can tell something about the position of the event but in order to calibrate that in order to really be sure what the energies are you have to put in something that you know the energy of and so we have radioactive sources where we know the energy of the particle coming in and within where you can say all right let me see what my fit would have said about that and that you know I'll pin the energy to that energy okay there's a problem when you're looking for a very rare events that if you're trying to analyze the data and you know where the event should be you're tempted to keep events in that region because you know that's where they ought to be and you'd really like to find Dark Matter so that's a bias and it it can unconsciously affect anybody even scientists that are trying to not be affected so in order to avoid that we insert fake events so somebody in the collaboration is designated as the person who throws in the fake events and only he or she knows where they're at but they put in enough of them so that it would blind you to the presence of a small amount of signal and therefore you can't just tune on on the signal events so then the game of foot is to use all the information you have to reject events for background sources finally at the end once you're done you remove the fake events opening the box and you see what's left and you see whether there's any excess that might be dark matter so let's just look at a recent result to show how that works these colored bands are a model of the background sources that we know about in the experiment so we know how they're distributed in energy and position we make a model and we add up all those sources and then we compare to these black points which is the data and say well you know looks like the background is pretty good representation of the data where is this pink band or lavender band is what a Dark Matter signal should have looked like so from that you can see already that we're not seeing dark matter we're seeing just the background because the data didn't follow what what we would expect to dark matter signal to be another way of looking at it is this way where I've added those fake events in and you see why that's important if you'd allowed yourself to only look at the real event you might have said oh I'm gonna tune my analysis so I keep all of those events but if I have a whole bunch of them in there I'm not going to be able to do that so there's a particular range and and this heat energy versus ionization where we know dark matter ought to appear the gray points are outside of that Dark Matter band and we do all our analysis we remove the fake events and we see what's left now did we detect dark matter here no because you see all these gray points they're still a background in the signal region so we didn't do as good a job as we would have liked to get rid of the background here and so we can't say but there could be dark matter there but we can't say that there is because they're still background there as well so what do we do in that case well when you make a plot like this where we're plotting the measured the rate of interaction of dark matter with normal matter versus mass again and okay we say we found events but they're consistent with background they're not a dark matter signal so that allows us to draw this curve on here and what it's doing it's called an upper limit it's saying dark matter is not found at rates of interaction with normal matter that are that high and with that mass so this region up here we've ruled out we say we didn't find dark matter there but dark matter could still be here and we wouldn't have noticed it because we had too big a background that in fact is what's happened with all of the current Dark Matter experiments so far as they said upper limits we we haven't found it yet ah takes a lot of people to do these experiments so it's not just me it's roughly a hundred people and super CMS and all of the collaborations have between 30 and 150 people doing this sort of work and you see you know we're we're all over the world all over the US and in Canada and and some other parts of the world as well like I say there's a lot of similar experiments worldwide using different technologies so some some groups use liquids liquids enon or liquid argon to detect dark matter others use bubble chambers which is an old technology that was pioneered here but as was resurrected for Dark Matter searches there's people who use scintillating crystals and other old technology and there's people that use C CDs like in cameras to look for dark matter so we're trying every possible technology we can we can do to find this there is another technique that one could use so we're moving through the galaxy and I said there's a Dark Matter halo so from our point of view you could think of that as the Dark Matter wind you know here we are moving through this and generating a wind blowing at us if only we could feel it but the earth is also rotating around the Sun and different times of the year the Earth's velocity either adds a little bitter or subtracts a little bit from the motion of the solar system around the galaxy what that does is create a small difference in the rate the dark matter would interact with with normal matter because it's really just the dark matter particle with a velocity that it has bumping into a nucleus well if it's a little less it gives us a little bit less energy if it's a little more it bumps it a little harder that's an effect that in principle you could detect and there is one experiment that says they've seen it this nice little sinusoid is a seasonal variation of the rate that's seen in that detector over many many years and their claim is oh yeah we've seen dark matter because it follows that expectation the effect is very small it's only about two percent change in rate over a year and it's not the only thing that changes seasonally so it's hard to accept and the biggest problem is no other experiment is seeing the effect and other experiments should have been sensitive enough including ours to have seen it so this is way science works we don't believe it's Dark Matter because only one experiment is seeing it there are other possible explanations and you really have to verify it in order to believe that something is astounding as dark matter has been seen you could take that concept a little further so there's another rotation you could think about which is the daily rotation of the earth so if you have a detector sitting on the Earth's surface and you have this galactic wind from dark matter then as it hits the detector at different times of the day it could cause the recoils from dark matter hitting it to go in different directions so if you could sense that direction difference I would be in good shape you'd think the problem is you have to see several dark matter particles per day in order to make that work and we haven't seen one and looking for twenty years so this may be a technique that would be used if we start to see dark matter particles but you have to envision something the size of Wilson halt to get that sort of rate detectors that big are being built in fact you'll hear a bit more about the neutrino detectors that are determined to have is building in South Dakota so it's not impossible but it would be a challenge let's talk briefly about the other ways of detecting dark matter so I stocked about indirect detection at the beginning the idea here is that dark matter particles may be sitting there in the center of the galaxy finding each other colliding annihilating and producing normal matter particles some of which get to us the problem is other things are sitting in the center of the galaxy like pulsars that can also produce such particles that come to us so the challenge is to try to say am I seeing more such things than I should have there's lots of different ways of looking for this there's a detector in space sitting on the International Space Station that's trying to detect antimatter there's a satellite trying to detect gamma rays you're looking for interactions that produce photons or electrons you can put telescopes or detectors on the Earth's surface and look for protons or gamma rays that make showers and you can see the showers or you can bury detectors in ice or water like at the South Pole ice for example or the Mediterranean there are detectors in both places there you're looking for neutrinos but in all cases you're looking for particles where there's an excess of them coming from some place where you believe there's a big concentration of dark matter and you don't believe that there's a lot of other things that could produce those particles that's the game of foot is modeled model all the sources you can think of and see if there's excess events it's as good as your modeling if you don't understand the distribution of pulsars for example then you're not going to know that you've detected Dark Matter there's lots of different ones I'm just going to flash these up because I don't want to completely run out of time but there's many different collaborations looking from space from the South Pole from the desert in Africa to this International Space Station looking for this sort of thing finally you can make dark matter on earth so you could collide we used to collide protons and antiprotons here and you could make dark matter and normal matter particles coming out of that or you could take a beam of protons and shoot it into a target and again you could potentially make dark matter particles and normal matter particles but how do you detect the dark matter particles if you do that because this is a typical I think this is the Higgs event actually but this is what happens in a Collider you produce this enormous swarm of normal matter particles how are you gonna know and all of that that you've also produced the Dark Matter particle well you can't see it it's not gonna interact at least very rarely but what its gonna do is carry away some of the momentum or the energy and so you have to look for something missing you have to add up all of this swarm of particles here and say that doesn't add up to what I put in what I used to to collide the event in the first place and then you have to say okay if I do enough of these and I find something missing in a lot of them does that mean I've detected dark matter it's as good as your detector and your analysis so it's it's not a straightforward thing by any means but they're doing it we did it here when we were a Collider and answering is doing it with the two big collider experiments this is a typical result it's a very similar sort of scheme where you modeled in these color bands or models of all the different normal processes that would produce that signature and then you look at the data and say mmm follows that color band pretty well doesn't it I don't see anything excess I don't see anything missing here so we didn't find Dark Matter in this case but they're continuing to look at CERN and you may have to just run a lot longer or produce higher beam energy in order to find it okay so what will we learn if we detect dark matter particles well so in particle physics we'll answer the question do dark matter particles exist yes if we find it yeah we found a new particle that we didn't have in our standard model are they stable well they must have been if they were produced in the Big Bang and we're detecting and now they must have been stable for 13.8 billion years so that's pretty stable what theory would would you construct to fit that well the theorists would go crazy they would come up with all sorts in fact they do already but they would go even crazier but you'll have to have a lot of particles before you can really tease out fully what they found but in the end it's going to lead to a more complete theory of particle physics there's something beyond the standard model that we will learn about cosmology so you know what is this missing piece that we call dark matter if we detect it in the lab we know it's an elementary particle that's because that's what we're looking for what is it imply about the early universe well we'll understand a lot better the interplay of dark matter and this other mysterious thing called dark energy if we understand if we detect dark matter well we'll know more about what was there in the early universe so that's really the what we gained in cosmology and finally in astrophysics we'll learn about the Dark Matter distribution in our galaxy although that will take a lot of events to tease out and we'll understand better how dark matter exactly played into galaxy formation so we'll understand how we got here basically okay so in the end why do we do these experiments the physics I find is fascinating and I can't imagine a more fundamental question than trying to tease out what's most of the matter in the universe that we can't see by light really challenging detector technology so in high-energy physics we live for this we love to build placated detectors and make them work and it's certainly complicated detectors to do this physics and it's hard to beat working in deep underground mines or the South Pole or in space although Fermilab and Cerner are cool places too so and finally it's just fun to tell people about at least it has been for me so let me just end with the fact that on October 31st is dark matter day it's the second International Dark Matter day and you should take advantage of that look for events around you here's the the website if you want to look for that and here's some more websites you can look if you want to learn more about this subject so I'll stop there and call for questions thank you Dan [Applause] do we have any questions we have one right here forgive me because you probably said it but I'm still I'm not clear why how you know 75 90 percent of the matter in the universe is dark matter is it because of the motion of the galaxies no it's a good question and I didn't cover it because it's it's a bit of a long story so you piece together all those different pieces of information the rotation curves what you see in the Cosmic Microwave Background and then you add all those up and you you make a model that says what would what amount of dark matter compared to normal matter would it take to explain all those as a whole that's how we come up with the fact that 85 percent of the matter is dark matter so you said towards the beginning that dark matter maybe excuse me provided the seed for matter to come together as galaxies but I thought by definition they didn't interact no that's also an excellent question so the way that work is that dark matter does feel gravity right so there were tiny little fluctuations after the Big Bang that that left small amounts of matter clumped including dark matter dark matter provided the gravity that started to grow those clumps like that simulation I showed you that made the big web the reason the dark matter is good at that and fast at that is that it it's only feeling gravity as far as we know normal matter if you try to pull it together will scatter and you know throw a pieces of it off and it isn't very good at cooling down and collapsing dark matter just feels gravity so it collapses down and once it collapses enough to make it gravity well then it pulls a normal matter that's the way but we believe it worked yes if gravitational effects are the only things we've observed in dark matter how can we predict these particle interactions that you showed in the Fineman diagrams that's another excellent question and the honest answer is we can't so it's been guided by the fact that all the particles we know have other types of interactions and so we presuppose the Dark Matter may have them too but in the end we could be wrong we could there could be no other interaction between dark matter and normal matter other than gravity and so these experiments could in fact never find what we're looking for that is a possibility the reason we're optimistic is that there are theories of particle physics where the particles would would high-energy particles would constitute the dark matter like you may have heard of supersymmetry that's the theory of particle physics that says every normal matter particle has a partner one of those partners the partner of the the photon is a natural candidate for dark matter it would have all the properties that we expected to have and it would interact with normal matter so there are some theories that say you know we're not completely wasting our time looking for this but you know it's it's always a gamble in this sort of game you don't know what you're looking for and you're guided by theory you're guided by past experience to try to make these experiments yes I'm the distinction between dark matter and dark energy yeah I didn't really explain that so dark matter is actually matter it feels gravity dark energy the only thing we know about it is it's some sort of repulsive force that's accelerating the universe faster than it should so we don't think there's any connection between dark matter and dark energy despite the names yeah we want to get this on tape is there a way to predict what type of particle would be created from a dark matter in a normal matter collision a dark matter particle colliding with normal matter normally wouldn't produce any other particles because dark matter is not moving very fast and so it doesn't really have enough energy to produce other particles if you made the Dark Matter particle in a Collider it might have enough energy to make another particle but the type of things that we're looking for the dark matter is moving along at a relatively slow speed first of all thank you for sharing what you shared I all new to me I'm not a physicist or a scientist in any way he is so my question is how get based on the progress that you and all these other scientists all over the world are making how far away do you think it is before we do identify dark matter yeah that's an excellent question when we ask ourselves a lot I'm not getting any younger the the theory I mentioned supersymmetry would have indicated we should already have seen Dark Matter so in that sense we were all disappointed not to have seen it in the previous generation of experiments and they're equally disappointed at the LHC where they expected to produce it already that doesn't mean it's not there it just may mean that that's not the theory that that is reality there is a region just below us right now but where we're about to reach where other theories say it ought to be there and those theories are equally viable so that gives us some belief that it's just around the corner but we're optimists you know we we like to think that we're going to find what we're looking for one last question Thanks I'm just clarification when you say that Dark Matter feels gravity do you mean that it is subject to gravity and that it also has its own gravity yes it has both it produces gravity and it feels gravity so it is mass just like other mass and it interacts with gravity just like normal matter if there's a few minutes could I play the snow lab we do I think this would be interesting to you because it gives you a very keen sense of what it's like to do these experiments underground in the early morning at Creighton mine near Sudbury Ontario the surface building hosts offices laboratories and support services it's here where you begin to gear up the process starts in the dry a name given to the shower and change rooms this is what it's here then you change into your clothes for underground normally shorts and a t-shirt as the temperature underground can easily reach the mid 30s Celsius you must wear a set of 19 in Quebec waterproof safety boots a hardhat safety glasses and a mining belt all this gear is required to travel safely down into the mine everyone entering the mine must tag in so that there is a record on surface of who's underground at all times the final piece of equipment you need before heading underground is a Kaplan the battery pack attaches to the mining belt and the light attaches to the front of the hardhat you join other snow lab staff to wait for the cage the large elevator that brings people and materials to and from the surface this is a it's a tight squeeze as you over 2 kilometers in just a few minutes you experience 25 to 30 percent more air pressure at that depth and the descent feels similar to flying in an airplane pop [Music] 15 psi snow lab is located at this deck to shield sensitive experiments from the cosmic radiation at the Earth's surface [Music] 6,800 peace pilot pence arriving at the 6800 level watch your step as you enter the drift the drift is the main part of the mine it's important to keep your cap lamp on and to watch your step during the two kilometer walk from the cage to SNOLAB mile walk ninety degrees fahrenheit overall SNOLAB is a clean lab meaning dust and dirt must be kept to a bare minimum mine dust in particular can interfere with experiments if it gets into the lab area car wash for these reasons strict cleanliness protocols are in place everything that enters the lab must be thoroughly cleaned that includes people the first step is to wash the mud and dust off your boots before entering the lab doors as you step into the lab you notice a temperature change immediately the conditions in the lab are well-regulated to keep a constant temperature and humidity at this point everyone must remove their hard hats and belts and hang them on the hooks along the wall remove your boots and safety glasses and place them on the shelves remember where you've placed your boots and everything else the next step is to head to the underground dry upstairs for women downstairs for men there is a dirty side and a clean side to the dry separated by showers anything that has been in the drift must remain on the dirty side to ensure the lab stays as clean as possible everyone showers to remove any remaining dust that may linger on skin or hair [Music] you are provided with safety boots a t-shirt and cleanroom suit following your shower these outfits remain underground and are washed in laundry facilities in the lab to eliminate the possibility of getting contaminated by mine dust and traveling to and from the surface we literally can't bring anything also need to wear a hairnet safety glasses and hardhat in the lab as you leave the dry to the lunchroom everyone must tag in again to keep track of who is in the lab the lunchroom is the heart of snow lab and also functions as a labs of refuge station in case of an emergency staff and visitors would congregate here scientists staff and visitors will spend eight hours underground working on experiments building the newest areas of the lab and maintaining the facility [Music] that's the form of shotcrete at the end of the day the flaming head back to surface this whole lab is maintained as the cleaner with a delighted support staff that wiped down we don't really come out the snow lab crew will be back prepared to do the same thing all over again tomorrow they're the original experiment at snow lab is called the Sudbury neutrino Observatory and it was looking for solar neutrinos click the more data you can use the got that YouTube just plays the next thing okay so I hope you enjoyed that yes and you not suffer the bends but people have fainted in the hoist and it's because of the air pressure difference although it's not well understood why but it's very rare you just don't go down there like I am you wouldn't go down there now because I have a congestion and so I would probably not make it I mean I know like you faint and you're alright but you have to be careful going to that depth and it's physically very tiring because you see the overhead involved you it's not just going into a lab here you know you've got a kilometer and a half walk in the hot environment you change everything then you get to work for eight hours and you get to come all out through that again long days it's so eight-hour working down there if you're lucky you're down there ten hours but if you're lucky you can get eight it's probably closer to six or seven so tacked on to that is the preparation the cleaning and the show correct yes all right let's think Dan and you

Channel: Fermilab

Views: 160,110

Rating: 4.8037806 out of 5

Keywords: Fermilab, Physics, Dark Matter, Matter, Dark Energy

Id: o79szJBtQ5E

Length: 64min 30sec (3870 seconds)

Published: Tue Oct 30 2018

Reddit Comments

[u/ProfessorMegamind]

............Dark Matter ! What the yell !? Seriously though , we sure as heck don't know what it is . The only thing we know is that it has mass , which we can only measure indirectly . We cannot perceive it in any way , save for it's influence on matter/energy in outer space . The best particle theories and experiments have failed miserably, excepting perhaps , an absurdly slick particle way beyond even neutrinos in slipperyness . This basically leaves distortion and condensation theories ; in otherwords , DM is an invisible aspect or product of the space-time matrix itself . Distortion would be from gravitational or other forces/energies . This relates to wave distortions in the S-T matrix ( EMR ) gaining mass , or creation of an alternate form of S-T , which differs from the norm by having mass . Bottom line : DMs creation process , and physical specifications are a complete mystery at present , and are likely to be so for quite some time . ........P.M.