 Thank you. Well, we're all terrified now. Thank you to both Rebecca and Taylor for inviting me to do this tonight. I have sort of a four-pronged thing I want to do this evening and I promise you there's going to be a whole bunch of interactivity. But in the first phase of this, I'm going to bore you to death in anticipation of what we're going to do later with the Nerf Canon, which I promise you may be life-threatening, at least eye-threatening, and fun because I'm going to have you running around the room. All right? So the first thing we're going to do tonight, and hopefully this will only take about 10 minutes, is we're going to talk a little bit about what does it actually mean to see the universe? What is really going on when you observe the universe around you? The next little phase of this that riffs off of the first one is that I want you to walk away tonight. If you're going to remember one thing besides, oh my God, oh my God, he put my eye out with that Nerf Canon, I want you to remember that everything is waves. If you thought that waves were just something that water did, or that air did, or that light does, if you already know that light is a wave, and we'll play with that a little bit tonight, I want you to walk away, at least with the basic idea, that it's not limited only to those things. And in fact, I'll show you some pictures tonight to convince you of the first steps toward understanding that fact. Then we're going to bust out the Nerf Canon, and we're going to start to think about what it means to see something that your eyes really have no hope of ever actually seeing. And we'll cover why that's the case in the first part here. And then at the end, I hope to share with you a tiny glimpse of the subatomic world. And that will involve, I think, people at the end cycling up and having a look in this black box that I have here up on the counter. So let's begin with what it means to see the universe. So let's just open this up. What do you think it means to see? What is seeing? Anderson, you're reliable. Yes, go ahead. Yeah, some dude who's talking at me right now. Yeah, no, that's a pretty good modern understanding of what seeing is. So to reiterate that, light is coming to our eyes. Our eyes are the organ in our body that converts the light into a chemical and electrical signal. The wet wear in our head is able to learn over a short period of time how to interpret those signals and reconstruct a three dimensional representation of the world around us using light. There are other ways we experience the world. There's touch, which is also electrical in nature. There's sound. And that's another way of converting a wave into an experience that the brain can interpret. We have a whole bunch of these senses, taste, smell or the other ones that we're all familiar with. So indeed, what does it mean to see the universe? Well, I like these photos. These are two of these are astronomy pictures of the day. And if you have never visited the APOD or astronomy picture of the day archive, I highly encourage you to bookmark it or get the mailing that's sent every day. You'll get amazing pictures in your inbox, in your Twitter feed, whatever. They have multiple ways of getting this stuff every day. And these are just two of them. And I picked these because they combine both the terrestrial and our local galactic neighborhood. So this is a beautiful waterfall captured at night. And then this is part of our Milky Way galaxy, our home galaxy, where one star among about half a trillion stars that make up this collection of stars. This is another collection of stars far from ours. This is, I forget exactly how far it's several hundred, several million light years away. That is, it takes the light from that object up there a few million years to get to Earth. We're not seeing that object as it exists now. We're seeing that object as it existed when the light left it, which is about two and a half million years ago. So think about what life on this planet was like two and a half million years ago. We're only seeing that thing as it looked then, now in that picture. This one's nice because it's got a person in it. So this is looking over a valley in Switzerland. And I work on an experiment in Switzerland, which is why I picked this. And again, you've got a meteorite here. You've got the Milky Way. It's got everything. It's got human light sources. So how do we see, well, we rely on light doing one of two things, either going straight from something that's emitting light, and that light strikes our eyes, or light coming from another source like the the bulbs in this room bouncing off of things in the room and then coming to our eye. And we're able to interpret all of that using our brains. So here's light reflecting off of things during the day in downtown Dallas. So at night, of course, this would be all lit up, like this valley is all lit up, and then there'd be sources of light for us to see. So Anderson captured it. This is the cartoon that kind of repeats what he says. Matter either scatters or emits light. Light, it turns out, is a wave. That was a hard fought thing. It took a long time to sort that out. And then there was lots of debate even once the evidence was in. And then it gets to our eyes and our eyes have a whole bunch of biological capabilities to focus the light and convert the light to other forms of energy that can be transmitted to, for instance, our brain. But one question you might ask yourself is, okay, cool, this eye, the eye is amazing, right? You go your whole life, hopefully with nearly perfectly functioning eyes, I have to wear corrective lenses, because my eyes are not that great. All right. But the eye is very limited for a variety of reasons. But one of them is that it just can't see all the kinds of light that exist in the universe, right? So the question of is there a limit to what humans can see, what you can see, what I can see is sort of a two-fold thing. If we had perfect optical systems, perfect lenses, really powerful magnification capabilities in our eyes to take, collect lots of light and feed it into our retinas, under those ideal conditions, is there anything we couldn't see? And the answer is, yeah, there's a lot we can't see. All right. So here are some rules of thumb for observing things with light. So first of all, because light is a wave, and I'll show you a movie in a second that will drive this home a little bit, that wave has to have certain properties in order for you to actually get information from the thing it's either emitted from or more importantly, scattered off of. So for instance, as a rule of thumb, the length of the wave that makes up a kind of light, roughly speaking, tells you the scale of sizes you can see. All right. So I'll come back to that idea in a moment, but basically any object that's smaller than the wavelength, the typical repetitive dimension of a light wave, anything that's smaller than that just doesn't affect the wave in a way that allows you to get information about the object. And that means you may be able to observe the light, but it's not going to tell you anything about what you're seeing. It's not scattering off of the object in a way that will give you any useful information. So what are some typical wavelengths of light? So a wavelength is, for instance, the distance from the crest of one light wave to the neighboring crest. So if you think of a wave as a regular undulating pattern like this, go from the tippy top to the tippy top of the next crest, and that's the wavelength of light. Red light, which is the longest wavelength we can see, has a length of about 750 billionths of a meter or 750 nanometers. The shortest wavelengths we can see are violet. So when you see something that's a deep purple color, it's right on the edge of the eye's ability to actually see anything. The eye is not really sensitive to any waves longer than this or shorter than this. So infrared, which is what's used in many TV remote controls to control the television set or other remote control things like that, that's just outside of our visible range. How many of you have mobile phones? Okay, and how many of you have cameras on your mobile phones? So here's a fun experiment you can do tonight. Find an infrared remote control in your house, all right? So take it and aim it at the camera and then start recording or just look through the, look at the screen at the image that's being shown. Push a button on the remote control and you'll see the sort of sickly green thing light up in the end of the remote. So cameras, it turns out are slightly sensitive to the infrared and they'll convert that infrared to a different color in the screen. And this is why you have to do all this color correction in mobile phone photography. In fact, any photograph taken with a CCD camera has this problem and has to be color corrected so that it doesn't get these funny greens in it that come from infrared. All right, so you can kind of see infrared with some help. And that's another theme of tonight. Instrumentation aids are eyes ability to see things. And we need that. Okay, so the smallest thing that we can actually see using the light that our eyes are directly sensitive to is of a size of about 350 nanometers. Now just off the top of your head, does anybody know the sizes of things like cells, plant cells, animal cells, cell membranes, things like that? Anderson? Yeah. Okay, so that we could probably see with visible light, right? Yeah. What about things in a cell like organelles in a cell or the cell membrane? Does anyone know what the cell membranes thickness is? Somebody other than Anderson? I should we should have done the bingo card tonight. No? Yeah. Yeah, exactly. It's about that order of magnitude. It varies on the cell type. But yeah, three ish 10 ish nanometers, something like that. Yep, perfect. So that the cell membrane, you're just not going to see directly unaided without some other kind of instrumentation that is probing smaller distances. So I did this, I filmed this earlier today just to show you this is a beaker floating in a bath of water. This little video will repeat. So I set it up so that the beaker had some water in it and it was it's top was sitting very close to the level of the water, which is there. And I sent two waves in which had roughly the same energy in them. And don't ask how I guaranteed that it took me a little bit to get that all worked out. But basically, I used a ruler to push the water from one side and I either did a short sharp shock or a long shock over a bigger distance. The long shock over a bigger distance gives a big wave and you'll see when this goes back and cycles through again, it's about 20 seconds long. So the water's flat here, you'll see this big rise come through and the the length of the rise from one crest to the next is way wider than the beaker and the beaker just kind of rides it just surfs it. Not very exciting. Over here, the short sharp shock, however, nearly knocks the beaker all the way over. And this is just to illustrate to you the difference between seeing things with a wavelength that's too big, in which case you're just kind of jostling around things like atoms or hitting those small things with something of comparable size. And here I contrived the wave to be roughly the same width as the beaker. So it doesn't completely knock it over, but it really upsets the beaker on the right hand side far more than on the left. So watch the short wave coming in. It's right here. So that thing's about the same width as the beaker. And it really slams into it. I mean, look what it does to that thing. Okay. So that's observing with a short wavelength phenomenon and that's observing with a long wavelength phenomenon. You can't learn much about the beaker from the long wave. But from the short wave, all kinds of interesting things can happen to the short wave phenomenon. So you need small things to see small things. So here's some scales that you may be familiar with. All right, so a human hair is about 100 millions of a meter in thickness 100 microns. By the time you get down to roughly 10 microns, we're talking about the sizes of chromosomes, bacteria, animal cells and so forth, it spans a space. genes themselves are down here between one micron and 100 nanometers. And then we're getting down to you know, specific proteins, antibodies, viruses and things like that in the 10 nanometer range. And then down here around 0.1 nanometer, we're approaching the atomic scale. Alright, so 10.1 nanometers or so 10 to the minus 10 meters, and you're roughly at the size of atoms. There's no way we're going to see atoms if we can't see cell membranes with visible light. So how are we going to probe atoms and even more interestingly, how are we going to probe things that are smaller than atoms? Yeah, Anderson. Yep. Boy, spoiler alert on this kid. I tell you, all right. First, though, why don't we just make some smaller light waves, right? There's all kinds of light waves we could play with, we could do UV. Alright, UV is is capable of tearing electrons off of molecules and biological systems. It's why it can induce cancers. x rays, right, you're not supposed to get a lot of those, but they're great for imaging the body, they penetrate things and they scatter off of bones, and they're good for doing things like dental dental imaging and so forth. gamma rays, right, you definitely don't want to get exposed to too much of that because that'll take your electrons for a ride and never return them, which is not so good for DNA. But hey, it's got a really short wavelength. Alright, so human eyes are only sensitive to a small fraction of all possible light waves. We know that, right? So why not use these other things? Well, sure, we could do that. But it does come at this cost. I mean, you can shoot x rays and gamma rays at really tiny things. But the shorter the wavelength, the higher the energy of the light wave and the more energy that light wave carry, the more damage it does when it interacts with something. So yeah, I mean, sure, we can we can send a bullet at something to probe its size, but it might also do significant damage on its way through. And if you want to think about this, the x rays and gamma rays, they're the high speed bullets of the of the imaging world, you can use them. It can make it can cost tremendous energy to make them in any level of intensity. And I'll show you one of these facilities in a minute. But it does tremendous damage to the sample. So you're limited in what you can actually see with these things. Alright, so let me just show you a couple of things here. So some very famous techniques for seeing very small things or things like x ray crystallography. If you can get a sample and crystalline form and put it in an x ray beam, you can do imaging of it. And so one of the most famous examples of this is a picture I'll show you in a minute. But even x rays are too big to image things like atomic nuclei or the stuff inside of them, protons, neutrons. And if anything's rattling around inside of them. Alright, those things are only one times 10 to the or about one times 10 to the minus 15 meters in size or one femtometer. Alright, so if you didn't know that unit before tonight femtometer 10 to the minus 15 meter, these are 10s of 1000s of times smaller than the atom itself, or their abouts. Well, millions of times smaller than the atom itself. Alright, so this is one of the most famous x ray images that was ever taken. And this is a whole story in and of itself, you can get a historian of science to tell you about this. This is a chemist and x ray crystallographer Rosalind Franklin, who was the very first person to actually take an x ray crystallographic image of what became known as the double helix structure of DNA. So this is in fact the image that revealed that it's this double helix intertwined structure. It was taken by her and a colleague, R.G. Gosling. Without her knowledge, Gosling showed it to Crick and Watson, and it was Crick, Watson and Gosling who got the Nobel Prize for this, not not Rosalind. Yeah, she was passed over, she died at about age 38. So since they don't do the Nobel posthumously, she was never really honored for this work. It's only really rather recently that this has come to light. Okay, but that funny image there, which was taken with x rays has a lot of information packed into it. And if you know how to read that information, you can figure out that DNA has this double helix structure that that is so common now that we all learn about. But nobody knew that before her. You want a modern x ray facility to do industrial, biological and chemical work. This is one of them. There's only a few of these in the world. This is known as an x ray free electron laser. It is two kilometers long. It gets a whole bunch of electrons up to really high speed and then it wiggles them. And it turns out when you wiggle electrons, they emit light. And if you wiggle them really fast at high speed, they emit x rays. And in fact, if you wiggle them all at the same time, you get an x ray laser out of this. So the laser beam comes down this long beam line here to several facilities with research capabilities. There's various experimental halls. The experiment where I got my PhD used to be right there, but it's all gone now. All of this replaced the old particle physics facilities that are here at this lab. This is the Slack National Accelerator Laboratory, one of about a dozen or so federally funded basic research laboratories in the United States. Its primary mission now is light source science. So it serves academia and industry. They've done all kinds of fascinating things with this. And there's this goal of doing something known as femtosecond chemistry, where they do x ray images x ray movies of chemical reactions happening in real time. And those processes happen on the scale of femtoseconds 10 of the minus 15 seconds. So lots of facilities are racing to try to see that for the first time. But this is huge, right? Three kilometers from the end to end, only about two of it are being used right now. The upgrade will use that remaining kilometer of capability back there. Why does light get to have all the fun? Okay, why does light get to have all the fun? And in fact, Louis de Broglie for his thesis work back in 1924 thereabouts 1920, 1924, made a postulate. If if lights having all the fun of being a wave, and having energy and momentum which are particle like properties. So if light can be wave like, but also when it's short enough in wavelength crash into things as if it's a particle, why does matter have to then be confined to only have particle like nature to it. So he postulated that if lights a wave, why not also matter? So let's look at light waves. I promise you these are the only equations I have in here tonight. Alright, there are some really easy equations. If you want to know the energy of a light wave, you just need to take a well defined physical constant and multiply it by the frequency of the wave. That's the rate at which crests of the wave pass you in time. Okay, so the equation is simple e equals hf and h is that constant. I'll come back to that in a second. If you want to know the momentum of that wave, you just take the constant and you divide it by the wavelength. That's not so bad. So if you know the wavelength but you don't know the frequency, no problem, you can get the momentum of that wave and you can figure out other things from it. So the equation for that would be p equals h the constant over this funny letter. It's Greek lowercase lambda. Okay, for wavelength. That constant is Planck's constant, one of the most fundamental constants in the universe. It essentially tells you what the smallest amount of momentum is in the universe. And it's got these units. So the number is 6.626 times 10 to the minus 34 kilogram meters per second, worst units in the world. This is a bit more approachable. 4.136 times 10 to the minus 15 electron volt seconds for the chemists in the audience. If you prefer electron volts, as a particle physicist, I prefer electron volts. So that one works for me. So de Broglie's hypothesis was why does light get to have all the fun? So he made a postulate. Why aren't there matter waves? Why can't matter behave like a wave too? And so he said, if that's true, we should expect the wave like properties to be related to the momentum of a particle. Momentum is a particle property. So he just imposed this. And then this was used to make a bunch of predictions. And it turned out he was right. So if you take light waves, for instance, and make them do the things that waves do, and Taylor, I'll need your help with this one. Okay, then you can have all kinds of fun with this stuff. So let me show you a wave behavior that light does. And then I'm going to show you some pictures and we'll take a look at that. All right. So you're going to kill those lights. And what I'm going to do is I've turned a laser on here. It's a red, red visible light laser beam. And we're going to zoom in over here. That's the dot from the laser beam. Okay, so I've just zoomed in with the camera here on the little spot that the laser beam is making on the wall. Alright, so it's this rather intense but fuzzy circular beam. Okay, nothing particularly exciting going on. But because light is a wave, it does the things that waves do. So if you imagine a whole bunch of waves coming in toward the shore on a lake like on the Great Lakes or in the ocean, and then imagine that there's a rock wall between the waves and the beach. And that rock wall has a little hole in it. The waves that pass through that hole will start to spread out and they'll start to overlap with each other. And wherever the crests are lie on top of each other, the waves will get taller. And wherever the troughs overlap with each other, the waves will get lower. And if crests overlap with troughs, the waves will cancel out. This is something known as interference. And an interference pattern is a pattern of intense, bright things, tall things and dark places where there's no wave at all. And so if we kill the lights here, I'll show you an interference pattern. I'm going to make this light pass through a hole in a breakwall. This is just a little slit in a piece of material. And when you do this, what do you see? You see a pattern of light and dark spots. Let's see if I can stop shaking. So where there was a spot before, all right, bright spots and dark spots. All right, do lights again. Cool. So let me set this back here. All right, so that's one of the things that waves can do. And so let me show you some pictures. So again, here are some bright spots and some dark spots. These are images that are taken of waves interfering with themselves as they are forced to scatter through some kind of structure. Sometimes the wave peaks add up, and sometimes the peaks and the troughs intersect, and then they cancel each other out. So the bright spots are where they add up. And the dark spots, the dark gaps in between are where they cancel each other out. One of these is the interference pattern from a laser beam. And one of these is the interference pattern an electron wave makes with itself. One of these is a matter wave interference. One of these is a light wave interference. Which one do you think is which? Yeah. All right, so laser electron. Okay, turns out it's the other way around. So that's the electron beam interfering with itself, single beam going through a crystal structure, it can scatter off two places in the crystal structure. And depending on how shifted the scattered bait beams are, they interfere and give you light spots and light spots and dark spots, where it places where there are electrons, places where there are not electrons, as if they canceled each other out. That one's the red laser beam over there, I made a black and white so that you couldn't tell. It used to be a color image. Okay, hard to tell is the point, right? Because they're both wave like things, and they exhibit wave like behaviors. Okay, so for example, just to give you some some some feel for this, an electron in a very common instrument, a transmission electron microscope or TEM may be accelerated through a 10 like kilovolt electric potential to get the electrons in the beam up to speed. So that that gives the electrons about 10 kilo electron volts of energy kinetic energy due to that acceleration. And if you run that through the de Broglie wavelength calculation, it turns out those electrons have a wavelength of 0.015 nanometers 0.015 nanometers. Now that is absolutely small enough to see for instance the cell membrane. If you use that to make an image of a cell, you'd see much more structure in the cell. Now compare that to x rays at the same energy, which are light waves, they only have a wavelength of 0.2 nanometers. So if you had two equally, you know, energy costing ways of making waves, the electrons win over the x rays hands down, no problem. And it's much easier to make transport and accelerate electrons than it is to control x rays x ray optics are insanely difficult to do because they blast through conventional mirrors. So how do you focus an x ray beam when it rips your mirrors apart? There's a whole engineering art to that. And it's still not perfect. It's much more fun and productive to work with particles that can be more easily controlled. Okay. Now those electrons that I showed you before from the Linux Coherent Light Source, the big x ray laser, those have even smaller wavelengths. So if you in the old days before the Slack National Accelerator Lab was a light source facility, it actually took those electrons and smashed them into things to see what was going on inside those things. And you know, in the old days back in the 1960s when this facility first came into existence, the typical beam energy was about, you know, 10 billion electron volts. And if you run that through the de Broglie wavelength calculation, you find out that that corresponds to a size of point 000012 nanometers or about 1.2 femtometers in size. Now that is approaching the scale of the nucleus of the atom. And in fact, this is how we figured out what the structure of the nucleus of the atom is. What is it that's rattling around inside the nucleus? Is it just protons and neutrons acting like little billiard balls all glued together? Or is there something else going on in there that's more complicated? And so these experiments were done in the 60s and 70s and definitively revealed the character of the proton and the neutron. And to this day, we're still reeling from that discovery, we're still trying to make sense of what's going on down there. So this is just to show you the kinds of things you can do with matter waves. So this is an image of a very close up of a cell membrane here, using a one of these transmission electron microscopes or TEMs. These are things you can in principle buy off the shelf these days and install in a laboratory. So here we have mitochondria, individual mitochondria. Okay, and they're big on this picture. This is roughly a micron scale this black line down here. This is the cell membrane here. And that's about 10 nanometers thick. Alright, so exactly consistent with what we heard earlier, that's about 10 meters on this scale, 10 nanometers on this scale. This is remarkable imaging, you can't really do this with x-rays, you just rip these samples apart, cells are just too sensitive for this kind of exposure to x-rays. Okay, so I think I've repeated myself here. That's what I get for doing cut and paste to write a talk. Oh, yeah, look at that. And we're discovering I'm Oh, wow, so exciting. Either that or time is repeating itself. This is all very fun. Okay. Alright, so let's have some fun. Let's play around with this idea of sending very small wavelength probes at tiny structures and try to understand what it was that Rosalind Franklin was doing and what it is that particle physicists did to understand the structure of the nucleus of atoms. So for this, I'm going to have my helper come on down. This is Abraham. Abraham has never taken one of my classes. Never. But he was a regular visitor to my office to talk about the physics of his special skill set that we'll use today. Okay, so let me get let me get the lights going here. Alright, cool. So he's going to put that face shield on. And what we're going to do is in miniature, we're going to do a scattering experiment. Now, this is the part of the class where one of you is likely to lose an eye. So I apologize in advance. Okay, but I'm sure that the health planet SMU is outstanding. So this is a Nerf gun, about 40 bucks or so on Amazon. And just to give you a sense of how dangerous this is. Okay, so can I have that? Oh, great. Perfect. Look at that. It's like I planned it, right? Like I planned it. Yes. Oh, I'll have to cross off the days since Anderson made a pun in class sign. So Alright, so Abraham's going to hold out this ball. This ball is kind of standing in for a model of the proton or the neutron circa 1940, 1950, something like that. Okay, now here's it before your arms are going to get tired. So why don't you save yourself? What I want people to do is I want people to spread out a little bit more in the room. So I want a few more people if some people could come from the center section, go over here if the folks in the left section could kind of spread out. Because what I want you to do is I want you to try to catch or mark where the projectiles land when they scatter. And we're going to do this as an experiment and Taylor or Rebecca, if you guys are taking pictures, could you grab some photos of people doing this great. And then similarly here, if we could kind of spread out a little bit. Alright, I should have done like a bingo card for this like will Dr. Sikul a backscatter one of these right in his face, which is a good possibility. Okay, let's hope not but but but but really let's hope so. So Oh, sure. Okay. So now I'm serious, these things bounce really fast. So I'm just going to caution people to maybe like protect their eyes a little like this or something like that. Alright, so I'm going to fire about 10 of these things at that sphere. And we're going to make a prediction based upon what we see about what scattering off of a proton or a neutron would look like if it was a hard ball. Okay, ready, Abraham in three, two, one. Okay. Exciting, right? Alright, so let's let's find those here. I've got one here. Alright, everyone who's got one of these hold it up. We'll need to know 10 ish people to find them. All right. Okay, great. So you've got three great. You just hold up both hands them. That'll be great. Alright, so let's take a look at the results of this experiment. Right now. So did anybody over did anybody over here catch a nerve bullet? No, okay. So what do we observe about this scattering experiment? What is it like to scatter off of a solid sphere? Yeah, since you have your hand up. But I'm yes. Yeah. Yeah. Yeah, I'm not going to get through that thing. It's solid, right? So I'm expecting if it really is solid, I'm expecting stuff to bounce off come straight back at me. If I go straight out the ball, I was kind of I did get a few of those, right? They kind of basically came back at me as well as able to get one of these. Right? Nobody over there saw any excitement. All right. Okay, great. So let's pick these up and let's get them out of the field of play. We can you can put them down here on this tray on this cart so that where they're not in play. Geez, tough crowd. Alright, so now this is where Abraham skill set comes in. So Abraham has the ability to juggle. And what he's going to do for us is he's going to create a model of the neutron or a proton that turns out to be much more realistic based on what we now know about scattering electrons off of neutrons and protons. Okay. All right. So whenever you're ready, and then the audience be ready to catch again, because this is coming at you. All right. Good. All right, in three is Chris, I don't know why you're sitting there in three, two, one. We'll give the neutron a chance to reset. Cool. Okay, think we've already got a lot of data here. So a couple of things. Thank you, Abraham. I had round of applause for Abraham on that one. Awesome. Yeah. Well, in fact, it was liquid hydrogen that was used to do these experiments originally because it's a rich source of protons and also deuterated. So deuterated water was used as well. So you can attach a neutron to those protons. Alright, so most of the bullets went straight through but a couple of them winged off of the balls as he juggled them, right? So there's structure in there. But it's possible that you can go straight through it and not hit any of the things that are inside of it. And yet, when he was juggling, the volume of the space he was taking up was roughly the same size as that moon globe he was holding before. All right. And the pattern is very different. Right. Most of the bullets went straight through a few of them winged off at funny angles as they smacked into the stuff inside of our little model proton or neutron. This is the kind of pattern that emerged from using these scattering experiments in the 1960s and 70s. So alright, Abraham, you're all set. Thank you very much. Yep. Awesome. Okay, great. I shouldn't aim that at you. So what's remarkable about all of this is that by playing around with beams of particles scattering off of targets, and then taking different kinds of target structures into account, you can predict, well, what would a solid sphere look like if I were scattering off that? Or what would a perfect point of electric charge look like if I were scattering off that? Or what if it really isn't a perfect point of electric charge? What if it looks from a distance like a point? But as I get closer, it's actually things dancing around bound to each other by another force that also has a total electric charge. And it turns out that's what was really going on. The proton and the neutron are made from these little things called quarks. And the quarks have funny fractions of electric charge because thanks to Ben Franklin, we assign negative charge to go with the electrons now. He didn't know about electrons then that came out later. But what was eventually found to be the fundamental electric charge was associated with the electron. But it turns out there are things in nature that have less electric charge than an electron and they are the quarks. So because we're stuck with this historical feature that we assigned the fundamental electric charge before we discovered the truly fundamental electric charges in nature, the quarks have charges of two thirds and one third, the fundamental electric charge, which is that carried by the electron or the proton. So it takes three quarks to make up a proton, their charges add up to make a positive electric charge. And it takes three different kinds of quarks to add up and make a neutron all of the charges cancel out and the neutron is electrically neutral. And the quark picture took a long time. It took decades to cement. But by the 1980s, it was extremely well established that all the competing hypotheses were dead. And to this day, we're still using the existence of quarks and their cousins like the electron to try to understand the universe at its smallest scale. So the experiment that some of us in the room here work on, the Large Hadron Collider, we're smashing protons together. And it's sort of a funny historical twist. We're now taking these bags of quarks and smashing them into each other and seeing what stuff comes out. By getting protons up to extremely high energies, we're probing even smaller scales than those old experiments did. We're looking at 10 to the minus 18, 10 to the minus 19, 10 to the minus 20, 10 to the minus 21 meters in size. What's down there? And so far, we haven't seen any surprises. It seems to be its quarks and their cousins and no new surprises. But the thing about going into a frontier is you never know what you're going to find when you go there, right? So if you want, if you're like a hardcore physicist and you're like, this is dumb, I want the nitty gritty physics details about what these scattering experiments did. I don't know if the slides will be available afterward, but I put a link into the Science Magazine article by Michael Reardon, who's a bit of a historian of particle physics. And he talks about the discovery of the quarks, right, which was a very controversial discovery. It was a controversial proposal, and it took, like I said, decades to sort that all out, okay? So what I want to close with tonight, and for this, it's probably going to be best if everybody just kind of comes up here at the end after I wrap up my yammering. I'm going to give you a glimpse of the subatomic. And let me see how this thing's doing. Okay, cool. So let me kill these lights. Actually, we'll do this. We'll see if this works. Okay. So this thing up here, this box, is what's known as a cloud chamber. And what I'm going to do now is show you a video of it, okay? So it's a little hard to see with the glare and so forth, and that's why it'll be best if people just come up here at the end and take a look for themselves. But there's some things I can show you in this. So it'll be more obvious when you get up here, right? But look for little wispy lines in the video, all right? As I'm talking, just look around, pick a place and look. It's like spotting a meteor. Look for a trail that looks like a little comet has passed through the picture. Those aren't comets. Those are actually electrons and what are called alpha particles and the cousins of the electron known as the muon, smashing into alcohol molecules in the vapor in the bottom of the chamber. And these particles all have electric charge. And so when they blast through the alcohol vapor, they suck electrons off of the atoms and the molecules, which then causes the alcohol molecules in the vicinity to suddenly all get kind of yanked into the wake of this ionization that's going on. And so what you'll see are these little lines that zing through the cloud. And those lines are a trail of ionized atoms left over by a particle that's just buzzing around in the room right now. They're doing this all the time, but you can't see them. They're too small. Your eyes can't see these things. But with an instrument, we can reveal that they're just there like little ghosts all the time. So I'm really going to make this thing dance. I have a 40,000 volt power supply and I have this little tube up here. And when I crank this thing on, it's going to make a really strong electric field inside of this chamber and watch what happens to the vapor. Okay? Don't worry about the sound this thing's going to make because it sounds dangerous. Alright? Watch the vapor. What does it look like to make all the electrons and a bunch of molecules all suddenly move in one direction? That's what it looks like. We'll let it reset. It's got to reneutralize. It takes a few seconds and then we crank the field up again and they dance for us. So what you're seeing there are the little electrons and those alcohol molecules suddenly getting yanked out of their parent alcohol molecule and then dragged across the vapor by the electric field. And they leave those tiny little trails as they ionize. And then you have to wait a moment for it to neutralize and then you can do it again. Okay? So humans have learned over the last century how to make this kind of technology work for us. You'll find this technology in basically every hospital, every major hospital in the nation, using subatomic particles to image the human body non-invasively without having to make a single scalpel mark. You'll also find beams of particles used to treat particularly nasty cancers in places where it's really not safe to operate. So these are so-called proton beam therapies or carbon-ion beam therapies. Particle accelerators are just about everywhere now in medical treatment. And while they still haven't come to their maturity level, they've come a long way and we'll have to kind of see how that all shakes out. Okay? So at this point I'm going to close up my part of the talk and I'm going to invite you all to come on down and stare at the cloud chamber if you like and see if you can spot little particles naturally zinging through it in the room. Thank you very much.