Daniel and Kelly’s Extraordinary Universe - Daniel answers Listener Questions about dark matter, black holes and particle colliders

Episode Date: December 8, 2020

Daniel answers questions from listeners like you! Got questions? Come to Daniel's public office hours:https://sites.uci.edu/daniel/public-office-hours/ Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

This is an I-Heart podcast. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System

On the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate.

Maybe find out how it ends by listening to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hi, it's Honey German, and I'm back with season two of my podcast. Grazias, come again. We got you when it comes to the latest in music and entertainment with interviews with some of your favorite Latin artists and celebrities. You didn't have to audition? No, I didn't audition. I haven't auditioned in like over 25 years. Oh, wow.

That's a real G-talk right there. Oh, yeah. We'll talk about all that's viral and trending with a little bit of cheesement and a whole lot of laughs. And of course, the great bevras you've come to expect. Listen to the new season of Dresses Come Again on the Iheart Radio app, Apple Podcast, or wherever you get your podcast.

Sometimes my friends and my colleagues ask me, Daniel, why do you give out your email address? How can you promise to answer every listener email? Don't you worry that you're going to get too many emails or you might get some weird questions you don't know how to answer? Well, I'm a physicist at a public university. The public pays my salary. And I feel like my job is to help unravel the nature of the universe. and, and this is big, to teach physics to people. Now, I teach classes to students at UC Irvine,

but I also think that part of the job of being a publicly paid physicist is to be available to the public. So I want to teach everyone who wants to learn. So I answer all these emails not just because it's my job, but because I love doing it. And I'm not afraid that I won't know the answer to a question. Actually, I love when I don't know the answer because it gives me an excuse to go learn more about it.

Hi, I'm Daniel. I'm a particle physicist, and I really do love answering random physics questions from the internet. And welcome to the podcast, Daniel and Jorge Explain the Universe, a production of IHeartRadio. You'll notice that today on the podcast is just me, Daniel. My friend and co-host Jorge can't be here today. So I'm taking the opportunity to fill in and to talk about one of my favorite things on the podcast, which is answering listener questions. In our podcast, we try to explore all the amazing questions about the universe, all the things that science has figured out and all the things that science has yet to answer. And all those things that science is working on, those come from questions. Those are the questions asked by scientists who are paid to do science and by scientists like you,

who sit at home or sit in your car and just wonder about the nature of the universe. All of that is doing science, which makes all of us scientists. And that's why I love answering questions from listeners, because it means I get to include more people in this circle of science. So when Jorge's not around today, I'm going to use this opportunity to dig back into our backlog of listener, questions. I got a lot of wonderful questions I can answer sort of quickly over email, but sometimes people send me questions that take a little bit more explanation and that I think

everybody on the podcast might like hearing the answer to. So I save those up for listener questions episodes, but I'll admit we have a bit of a backlog. And so I'm going to dig into some of those today on the program. So today on the program, we'll be answering questions from the backlog. And I love these questions because they really show me what people are thinking. I mean, people write me questions, but they're not simple questions like, hey, tell me about black holes, or things that are well-discussed other places on the internet, like the double-slit experiment that you can just Google and find a really wonderful explanation. People write to me after they've done some thinking. They have some topic they're trying to

understand, they're trying to bring it together in their minds, and there's something that just doesn't quite fit. And that's really what physics is. Physics is trying to apply your mental model to the universe and seeing doesn't make sense. And often what you try to do is sort of climb the same mountain from two directions. Start from one side and then later start from the other side and see if you can get to the same place. And that's wonderful. And I love helping people sort of navigate the mountain of physics and get them to the top. It helps me also because I've climb the mountain from one direction and somebody else is trying it from another way and I wonder, hmm, why doesn't that work or is that possible or can you figure it out using those ideas?

And sometimes I have to sort of back up and try to understand where did somebody go wrong and then help them navigate around that crevasse or whatever so they can get to the top and they can get that understanding. But for me, it's a great mental exercise. It lets me go off and learn about all sorts of stuff that I don't get to think about necessarily on an everyday basis. And that's why I'm excited to announce something else new, which is my public office hours. If you have a question about physics, but you don't really like writing emails or sending me tweets, come to my public office hours where you can come, chat with me and ask me questions about physics or just listen while other people ask me questions.

I'll have my first one, December 14th, 2020 at 9 a.m. California time. That's noon Eastern time and 6 p.m. in Europe. So that's December 14th, 2020 at 9 a.m. California time. And you can find the location online for connecting. If you go to my website to cites.ucy.edu slash Daniel. Or maybe if you just Google it, you can find a link to it. So come and join me at my public office hours. Ask me a question about black holes or about tiny particles or about whatever is in your head that you can't quite figure out about the universe. So I'm excited to answer some listener questions. Let's dig in. First, we have a question about dark matter. Hi, Daniel and Jorge. It's Rocky from California.

I have a question about dark matter. How can dark matter exist if it cannot feel the strong force? I'm assuming dark matter is made up of atoms. And if that is the case, then how can it not feel the strong force when the strong force is necessary to keep the protons and neutrons in the nucleus of an atom together? Thanks in advance. All right. So that's a great question from Rocky from California.

He wants to know how can dark matter exist if it can't feel the strong force because he thinks the strong force is what's necessary to hold matter together. Now, first of all, you're totally right that protons and neutrons are held together by the strong force. They're made out of tiny little quarks and they're bound together by gluons. And it's a strong force that keeps these mostly positively charged particles together into the protons and neutrons that are familiar for us and are also the building blocks of atoms. However, dark matter is not made out of atoms. Dark matter is made out of something else, something weird, something new, something that is not the same kind of stuff that makes up our particles. How do we know that?

How can we possibly know what dark matter is not made out of if we don't know what it is made out of? Well, we can know that because we can see what dark matter can do and what it can't do. For example, everything that's made out of atoms has a temperature and it glows. Even really, really cold stuff glows in the infrared and really, really hot stuff glows in the visible light, like the sun or a rock in front of you. Everything that is made out of atoms has electrons and has temperatures and eventually will emit light. Also, everything that's made out of atoms has electrons in it, which means that it reacts to light. It either emits light on its own or it reflects light or it absorbs light. And dark matter we know does not

interact with light. That's why we call it dark. In fact, we have no way to interact with dark matter other than gravity. Remember that we've discovered dark matter because we've seen that it's there to hold galaxies together as they spin around really, really fast, where otherwise their stars would be thrown into intergalactic space. And we know that dark matter exists because we've seen this gravitational effects on the early universe. It's created these gravitational wells where normal matter has sort of fallen in, and that seeded the production of stars and galaxies in the early universe. Without the gravitational force of dark matter, we wouldn't have the universe that we see today. Galaxies would have taken billions of years longer to form. And we can also

study how dark matter moves around the universe. We know that dark matter is fairly cold. It doesn't move very, very fast. Dark matter moved very fast. It would have spread out more smoothly in the early universe, and we would see a universe with a very different structure. So we We think that dark matter is fairly cold, it's fairly slow moving, and that allows it to clump gravitationally and to cede all the structure that we see in the universe. So we know a lot about how dark matter moves and what it is, but we don't really know what it's made out of, right? We don't know if it's made out of a particle.

We don't know if it's made out of several particles. We think of it sort of as like a pressureless fluid because we don't think there's anything sort of holding it together other than its gravity. Rocky asked about how dark matter is held together without the strong force. Well, it's not really held together except for the gravity. And that's why dark matter, even though there's more of it than normal matter, it's much fluffier. It's much more diffuse. Like if you look at the distribution of stuff in our galaxy, the stuff that is normal matter that's made

out of me and you and hamsters and stars and everything else that we see in the universe, all the visible matter is made out of atoms and it clumps up very, very tightly, right? stars and rocks and stuff. Well, dark matter, we think, is much more diffuse. Even though there's more dark matter than everything else, it's really spread out. Like a volume of space, the size of the earth, has only about a squirrel's mass of dark matter. That's because the dark matter is not clumped together the way planets and stars are. It's spread out everywhere. And it extends far beyond where the visible galaxy ends. If you could see dark matter, you would see a huge halo surrounding the entire galaxy. And so that tells you that dark matter isn't tightly held together by a strong

force the way protons are and the way neutrons are. It's really a very different kind of stuff. And we know pretty well that it's not made out of quarks, not only because we know that it doesn't build atoms which give off light and it doesn't have that kind of interaction, but because of other really fascinating studies. For example, we've looked at the very early universe, how atoms were formed, what made helium and what made hydrogen, what made any lithium, and this kind of stuff. And the fraction you get of helium or hydrogen or lithium depends really sensitively on the density of quarks in the early universe. If you had a lot more corks sort of per cubic meter, then you got more heavy elements. If you had fewer corks per cubic meter, you got fewer

heavy elements. And we can measure the ratio of hydrogen to helium to lithium in the early universe and that tells us essentially what the quark density was how many quarks were around and then we can account for those we can say well if there were this many corks around then did they turn into all the stars and planets and stuff that we see and mostly that adds up so that tells us basically that there aren't left over quarks from the early universe that got turned into dark matter so we know that dark matter is not made out of corks and electrons and all this kind of familiar stuff it has to be made out of something different. There's also confirming evidence

from the cosmic microwave background radiation that tells us how different kinds of matter sort of sloshed around in the early universe. There was a kind of matter that we're familiar with that we're made out of interacts with itself. It ties itself together very tightly. So it's sloshed around in a different way from dark matter, which seems to have no interaction

other than gravity. And so it sloshed around differently and led to sort of different distributions matter in the early universe. and we can see those in the wiggles of the cosmic microwave background of radiation. So the picture is pretty clear and from lots of different directions, it tells us two things. One, that dark matter is not made out of the kind of matter that we're familiar with, the kind of matter you need to build atoms where the strong force holds itself together,

and that dark matter only feels gravity. There's no other interaction that is participating in. However, there is a limit to our knowledge, right? we can tell that dark matter doesn't have any very powerful interactions, the kind that would help it clump together and form objects and this kind of stuff, but we can never really say that there's no interaction there. It might be there and just sort of fairly weak. And people recently have been studying this in great detail and trying to answer the question, is there some other kind of force, some new kind of interaction that only dark matter feels where dark matter can feel

this with itself? Now, if it exists, it can't be very, very powerful. Otherwise, it would help dark matter pull together and it wouldn't be as diffuse. But it still might be there. There might be some kind of new force that helps dark matter pull together or interact in some gentle way. So if dark matter is not made out of quarks, then what is it made out of? What kind of stuff is there out there in the universe that's not made out of atoms and the kind of stuff that we are familiar with? Well, it might be that dark matter is made out of some new weird particle, something like, something like a wimp, weakly interacting massive particle.

It's just like a generic idea. It's sort of like a placeholder idea. We don't really have a great reason to believe that wimps exist, but it's just sort of like an idea that fits all the boxes, and so we go and we look for it. And the basic idea is that maybe dark matter is just made out of this new kind of particle, a heavy, tiny little dot that carries a lot of mass, and so it gives us the gravitational effects that we see,

and has no other kinds of interactions except for maybe some new weak interaction. When we say weakly interacting massive particle, we don't mean weak like the weak nuclear force we're familiar with. We mean weak with a lowercase w. We mean sort of a feeble, a not very strong or not very powerful force. And it could have some kind of self-interaction. It could have some kind of interaction with normal matter. But we don't think that it feels the familiar strong force, the one that binds atoms together.

Then again, dark matter might be something different from a wimp. It might be several particles. Maybe those particles can talk to each other and can build interesting structures, but not very powerfully. Then again, there are crazy ideas out there. Like maybe dark matter is made out of primordial black holes, dense clumps of matter that pulled together even before there were particles, even before there were quarks, pre quarks, right? In the very early universe, if there were these spots of overdensity that collapsed into little black

holes, they might still be around. Nobody's ever seen a primordial black hole. And so it's hard to say that they explain the dark matter, but we haven't been able to rule them out as well. And then on the podcast last week, we talked about an even crazier idea, which is maybe dark matter's not even made out of particles. Maybe it's made out of some new kind of stuff, some unparticle, which isn't broken up into little bits of definitive mass, but acts really differently. Remember that dark matter is much more prevalent in the universe than normal matter. Our normal matter is actually quite abnormal. So everything we've learned about normal matter might be generally true about the rest of the universe, but it's a bit dangerous to extrapolate from 5% of the energy density of the universe.

That's what normal matter is responsible for to the rest of the universe. It might very well be that we're making an error in generalizing. And the thinking that the rules that apply to this 5% also apply to the rest of the universe. So it could be something new, something weird, something totally crazy and bonkers. And that's what makes it so exciting because we know there's something out there new, something we do not yet understand, something when we do figure it out, is guaranteed to teach us something new about the universe. And that's why physics is exciting. All right, so thank you to Rocky for that wonderful question about whether dark matter feels a strong force. No, it cannot feel the strong force. It's not made out of

It's made it of something new, something weird, which feels gravity, and maybe something else, but we're not sure. All right, I want to answer some more questions, but first, it's time to take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances.

Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight that's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the iHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week. on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up.

Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both the meat. So do we find out if this person's boyfriend really cheated with his professor or not?

To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Your entire identity has been fabricated. Your beloved brother goes missing without a trace. You discover the depths of your mother's illness, the way it has echoed and reverberated throughout your life, impacting your very legacy. Hi, I'm Danny Shapiro. And these are just a few. few of the profound and powerful stories I'll be mining on our 12th season of Family Secrets. With over 37 million downloads, we continue to be moved and inspired by our guests and their courageously told stories. I can't wait to share 10 powerful new episodes with you, stories of tangled up identities, concealed truths, and the way in which family secrets almost

always need to be told. I hope you'll join me and my experience. extraordinary guests for this new season of Family Secrets. Listen to Family Secrets Season 12 on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Okay, we're back, and it's Giz Daniel today, and I'm answering listener questions from the backlog. Thank you to everybody who's sent in these questions, and apologies if it's been several months since you sent them in. you've been waiting for an answer. I hope late is better than never. And this next question is one of my favorites because it comes from a seven-year-old listener. So thank you to everybody who listens to the podcast. An extra thank you to everybody who listens with your kids and answers their

questions. And if your kids ask you a question about physics and the universe that you can't answer, just send it on to us. We'll take care of it for you. So here's a question, for example, from Bradley, who's seven years old. Hi, my name is Bradley Starr. I am seven years old. I am from Outta Loma, California. My question is, why do black holes slow down time? What a wonderful question, a deep question about the nature of the universe and some of the weirdest things in it. So Bradley is wondering, why do black holes slow down time? Now, time slowing down, time dilation is sort of a famous result in physics. Most people think of time dilation as what happens when you move really, really fast on a spaceship. And that's a famous result of one of Einstein's theories, special relativity.

Special relativity tells us what happens when you move near the speed of light. And it shows us how time and space are sort of intertangled. And it's worth stepping through how it happens in special relativity because there's a lesson for us there and how it happens in general relativity, which is what we'll need to talk about why time slows down near a black hole. So if you get on a spaceship and you travel really, really, really fast compared to the earth, then your time doesn't actually seem to slow down for you. Remember that speed is always relative. And time slows down for people moving fast relative to an observer. So if you jump on a spaceship and you travel really, really fast, you might expect to see your clock slow down,

right? Wrong. Clock's only slow down when they are moving. So if you see, see a clock going really, really fast, then it slows down. If you're on a spaceship and you're holding a clock, then it always ticks at the normal rate relative to you because it's not moving relative to you. Time only seems to slow down for somebody else watching you, for somebody else for whom that clock is moving really, really fast. So, for example, you jump on a spaceship, you travel really, really fast relative to the earth. On board the spaceship, you see the clock ticking at a normal rate. Somebody back on Earth, using a telescope to look at your clock, they will see your clock

ticking slowly. So your clock moves slowly only for somebody who sees that clock moving quickly, right? Moving clocks run slow. If you're holding your clock, you're on the spaceship, that doesn't tick slow for you. For you, time always moves at the normal speed. And the thing that's sort of hard to get your mind around there is that time is not universal. time moves differently on the spaceship than it does for you. You have a clock, they have a clock, and they don't agree.

And that's one of the most awesome things about relativity is that it unshackles us from this sort of universal clock that tells us the whole universe ticks forward at the same moment and tells us that how time flows depends on where you are and on how fast you are moving. Now, general relativity adds something to that. It says that how time ticks forward doesn't just depend on where you are and how fast you're moving,

but also what you are nearby. And so Bradley's question is about a black hole. And he's exactly right. If you took a spaceship, and even if you never went very, very fast, but if you went near a black hole, say, for example, you went to orbit around a black hole. You stay at a safe distance so you're not going to fall in.

You can orbit a black hole just the same way you can orbit any other object with mass. If you're far enough away and you're moving fast enough and you don't get too close to the event horizon, you can orbit a black hole. Now, if you orbit a black hole for a year and you're pretty close, you might come back and discover that the rest of the universe, time has moved forward much more quickly. So time has slowed down. On the spaceship, time seemed to travel normally for you. It was a year according to you.

But somebody else far away looking at your clock would have seen your clock running slowly, which means their clocks are running faster than your clocks. And if you come back away from the orbit in the black hole, you might have discovered that a hundred years, years that passed on earth, or a thousand years, or a million years, depending on how close you came to the black hole. So Bradley's question is, why does that happen? You're not moving very fast. The velocity from special relativity is not what's slowing down your clock. Why is that time slows down near a black hole? Well, the important thing to understand is that time doesn't slow down just near black holes. It actually slows down near any massive object. That's right. That means that time is slower, for example, on the surface of the Earth than it is 100 meters above the Earth or 1,000

meters above the Earth. And this is precisely why general relativity plays an important role in our global positioning system. These satellites that orbit the Earth and tell us where we are and what time it is, they have to account for the fact that gravity changes time as you move closer to the Earth. So any massive object will slow down time. Now, black holes, of course, slow down time much more than anything else because they are much more massive, but every massive object will slow down time. The sun, the earth, even that huge boulder. You get closer to that big boulder, time slows down a tiny little bit. Now, why is it, though, that being near a massive object slows down time? The thing you have to understand is that gravity here is best understood, not as a force,

not that's something that's pulling on you, but as the curving of space. It's changing what it means to move in a straight line, for example. And I think the best way to understand the relationship between gravity as a force and gravity as a curvature of the space we're moving through is to think about what happens to somebody moving on a 2D surface. Say, for example, you have two people on the earth, which seems flat to them, right? And they're starting at the equator, but in different places, and they're walking north. If we say to them, all right, everybody walk north, then it seems to them like, well,

we're moving in a parallel line, right? we're both moving due north. Now, you know that if you start the equator and you walk due north, then eventually you'll reach the north pole. Think about how weird that is for the people on the surface, right? They're moving in parallel. They're separated by distance. They're moving in parallel.

And yet their paths cross. From their point of view, it's like there's something pulling them together, something bringing them closer and closer together, something like a force. From our point of view, if we understand that they're on a curved surface, then it makes sense for their motion to naturally bring them together because their motion is on a curved surface, even if we see no force there. And that's what gravity is. It takes a bit of a mental jihitsu, but you have to then extrapolate to three dimensions. Remember that gravity is not the bending of space relative to some other higher dimensional space in four dimensions or in

five dimensions. It's an intrinsic bending. It changes the relationship between points in space. It changes the relative distance between things, but it has the same effect. You can think of gravity as a force, but it's much more natural to think of it as the curving of space, which changes the path that you move on, even if there are no forces. And so what happens near a massive object? Well, anything with mass or actually anything with energy will bend space a little bit, but it doesn't just bend space. It also bends time. Because remember, we learned from special relativity that time and space are connected. Time ticks differently depending on where you are and how fast you are moving. And so the curvature of space is also the curvature of space time. And where

this is more curved, time slows down even more. And it gets pretty crazy. Like the curvature of space gets so intense that if you go inside a black hole, then space moves only in one direction. It's so intensely curved that every direction of space is now pointing towards the singularity. So there's another connection there between space and time. Outside the black hole, time only moves forwards, and space can go in every direction. Inside the black hole, space becomes one directional, the same way time is outside a black hole. It only points towards the black hole. There is no outwards direction. The reason you can't escape a black hole is because literally there is no direction in which to escape.

It doesn't matter how fast you go. And so that curvature of space is very intense and it also curves time. And now the other lesson we learned from special relativity is that it's a different experience to go really fast and to watch somebody going really fast. Right? The person who's going really fast, they think time is flowing normally. The person who's watching them move really fast relative to the earth, they see time slowing down. Well, the same effect happens for the curve.

curvature of space. If you and your friend come nearby a black hole and your friend approaches it and orbits the black hole, you will see her clock slowing down. But she will experience time normally. For her time is taking very normally, but for you, her time is moving very, very slowly. And in fact, if she fell into the black hole, you would never actually see her cross the event horizon because time and space is so distorted that her time would slow down so dramatically as she got closer to the black hole that you would never actually see her cross. It takes an infinite amount of time for you to see her cross. But from her perspective, time is flowing normally and she can pass over the event horizon and into the black hole and towards the singularity. So, Bradley,

great question. Why does time slow down near a black hole? It's because time and space are connected and black holes bend space time like every massive object. And so that curvature not only makes the weird feature that we call a black hole, it also affects the passage of time in the same way that moving at high velocities also affects the passage of time. All right, great question from Bradley, loved it. I'll be back in a moment to answer another question, but first, let's take another break. rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled

metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit.

Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age.

And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast.

A foot washed up a shoe with some bones in it. They had no idea who it was. Most everything was burned up pretty good from the fire that not a whole lot was salvageable. These are the coldest of cold cases. But everything is about to change. Every case that is a cold case that has DNA right now in a backlog will be identified in our lifetime. A small lab in Texas is cracking the code on DNA. Using new scientific tools, they're finding clues in evidence so tiny you might just miss it.

He never thought he was going to get caught. And I just looked at my computer screen. I was just like, ah, got you. On America's crime lab, we'll learn about victims and survivors. And you'll meet the team behind the scenes at Othrum, the Houston Lab that takes on the most hopeless cases to finally solve the unsolvable. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Okay, I'm back. This is Daniel answering listener questions, digging, into the backlog and trying to find the fun as most interesting, most exciting questions to answer

it for all of you. So here's another question. This one's about particle physics. Hey guys, I was wondering, what would it take to make a fundamental particle accelerator like an electron collider? What new things would we see from colliding fundamental particles like leptons and quarks? And would it be different than what we have today? All right, well, this is a wonderful question. And I think the motivation for this question comes from understanding that the large Hedron Collider is not a collider that shoots fundamental particles. Instead, it shoots protons. And remember, protons are not tiny little dots in our theory.

They are made of smaller particles. They're composite particles. They have quarks in them, and then a bunch of gluons to hold them together. And so I think this is what's motivating his question. He's wondering, what would it be like to build a collider made from actually tiny fundamental particles instead of tossing little bags of particles at each other? Well, first let's think about why the Large Hadron Collider is a Proton Collider. What are the pros and cons of that?

And then we'll talk about fundamental particle colliders. So the reason that we build a Large Hadron Collider out of protons is, number one, there are protons everywhere. Like, it's not hard to find protons. Everything around us is made of protons. But also because heavier particles are easier to accelerate. The more mass a particle has, the less it will radiate that energy when you accelerate. When you accelerate a particle, if it's very low mass like an electron, it will give off a lot of that energy in the form of photons. So the heavier particle is, the less it radiates.

So it's actually possible to get protons up to higher speeds more easily than it is to get electrons. And remember, we want these protons to have a lot of energy. The more energy you pour into your particle collider, the higher energy state you can create and the more massive objects you can create. And the goal of particle colliders is to explore the universe by discovering new massive particles, by creating energy densities that are so high that it becomes possible to make new weird particles that haven't existed since the Big Bang. And the awesome thing about these colliders, remember, is that you don't have to know what you're looking for. You don't have to know that those particles are out there. As long as you pour enough energy into your collider, if you're above the threshold,

if you have enough energy in the collision to make these heavy particles, they will eventually appear, which is pretty cool, and that's what motivates us to have higher and higher energy. If you double the energy in your collider, you can make particles twice as massive. It's sort of like getting to explore on a whole other Earth-like planet. The possibilities for a discovery are amazing, and nobody's ever built a collider at these energies before. So if you could double the energy of your collider, you could see things for the first time that nobody has ever seen. Now, the disadvantage of using protons or any particle that's not a fundamental particle is that it's less precise, right? You can't control the energy of the interaction nearly as tightly as if you were shooting tiny little pinprick particles.

What happens when you collide protons together is that the energy holding the protons together is kind of negligible compared to the energy of the protons moving. So when they come near each other, the fact that the corks are bound together into a proton, becomes kind of irrelevant. You have this little sort of flimsy bag holding these corks together, but it's really the corks from one proton that interact with the corks from the other proton, or sometimes even the gluons. And then you get multiple interactions. You get two corks smashing into each other or two gluons smashing into each other or multiple things happening at once. And it's not just that multiple things happened, but that you can't control the energy. You can't say, I want cork collisions at a very specific energy. You can control the energy of

protons, but you never know how much of the proton's energy is going into each core. And in one collision, the corks you collide could have a tiny fraction of the energy of the protons. In another one, they could have a huge fraction of the energy of the protons. So you lose a very precise control over the energy that you're putting into your collision. But what you're gaining is the ability to have a huge amount of energy in that collision. So proton accelerators are really good for discovering stuff, for figuring out new stuff because they can explore a big range of energy.

One, because the proton can hold a lot of energy without radiating it off. And two, because the quarks get a different fraction of the proton's energy every time. So you can very naturally explore a lot of different energy ranges in your collisions. Now, can we make colliders out of fundamental particles? Yes, absolutely. And we have. One great example, are electron colliders. In the same tunnels that now hold the LHC 20 years ago, we had LEP, large electron

positron collider. And it made some great discoveries. And it used electrons in one direction and positrons in the other direction and it smashed them together. And the advantage here is that it's much more precise. You can control the energy. So if you're looking for a particle that requires an exact amount of energy to make it, you can tune your collider very precisely to put just that much energy into the collisions because you're now dealing with fundamental particles, not bags of particles. So you know exactly how much energy you've put into your accelerator and the magnets and all that energy is just going into that one fundamental particle. Then you have the other fundamental particle coming from the other direction. So things are very tightly controlled. And there's

been examples in history when this has been very important when you only make some new heavy particle when you have exactly the right energy to go into the collisions. And so you can tune the energy of your collider very precisely sort of scan up and down and see, oh, look, we're making a new particle at exactly this energy. An example is the discovery of the J-P-Sai, and people, if you're interested in the crazy story of the particle that has two names, go check out our podcast episode about that discovery. There's a lot of crazy stuff in the history of particle physics. Now, of course, the cons, the disadvantage of using an electron collider is that you can't

make electrons go as fast as protons very easily because they give off a lot of their energy. They radiate away their energy because electrons don't have very much mass. mass. And so if you want to go to high energy, it's better to use protons. And if you want really precise control of the energy, it's better to use electrons. The people also have other crazy ideas because the electron is not the only fundamental particle we can consider using, right? What about the muon? The muon is just like the electron in lots of ways. It's like the electron's cousin, but it has more mass. And what that mass means is that it doesn't radiate energy as quickly as electrons. So you could create a muon collider where you create muons, accelerate them, smash them

into each other. In theory, it would be easier to get those muons to go to higher energies than it is for electrons because they don't radiate as much. Now, the disadvantage is that there aren't as many muons around. Like electrons, they are everywhere. You take an atom, you heat it up, boom, you get a bunch of electrons. Muons are much harder to produce, right? They're produced in cosmic rays or you can make them in collisions, but you don't have a natural supply of muons. The other disadvantage of muons, and this is kind of a big one, is that they don't last very long. Sure, they don't radiate energy as much as electrons when they move fast, but they also don't live forever like electrons do. An electron sitting by itself will sit there till the end of the universe.

It's a stable particle. A muon, on the other hand, lasts 2.2 microseconds. So if you have a muon sitting by itself in space, it will spontaneously decay. to an electron and a couple of neutrinos. So that's pretty tough. Now, you can make the mouons live longer by getting them to go really fast because time dilation happens. The muon lives 2.2 microseconds by its clock, right, in its frame of reference, if it had a tiny little clock.

If you can get them to go really, really fast, like moving around an accelerator, then their clocks go slower and they last for much longer, seconds, minutes, as long as you want, depending on how fast they are going. So there are some ways and people are talking seriously about building muon colliders for future experiments. Now, what you can't do is build a quark collider. We'd love to have a quark collider because it would let us study all sorts of crazy awesome things. But quarks, remember, cannot be by themselves. The strong force to hold the proton together, it's very, very strong. And it has a really weird feature. The strong force, which holds the quarks together in the proton, as you pull those two corks apart, the energy in that bond

actually increases. The force increases. This is the opposite than all of the other forces, like the electromagnetic force between two electrons decreases as the electrons get further apart. For quarks, the strong force grows stronger as the corks get further apart, which means this more and more energy in that bond as they get further apart. That's why quarks can't ever be alone. because a cork far away from all the other corks would require so much energy that that space would be so unstable that that energy would very rapidly turn into new particles. And that's exactly what happens. If you break up a proton into a bunch of corks and send them flying off in different directions, then they create new matter out of the vacuum using the energy held in that strong force. And they bind those corks together to these new corks that you've created out of the vacuum.

So you can't ever see a quark by itself, which means you can't build a collider out of quarks, which is too bad. But right now in particle physics, we happen to be thinking about the future of the field and what kind of collider we want to build in the next 10 or 20 years. So people are doing these kind of exercises and wondering like, what kind of question can we ask with an electron collider? What kind of science can we learn with a muon collider? Should we build a photon collider or all sorts of crazy stuff? So it's a really fun and exciting time in the field to be thinking of. about the 5, 10, 50-year trajectory? Can we come up with new ways to accelerate particles

so it doesn't cost $10 billion and require loops underground that are 30 kilometers around? It's a fun time, and we're all thinking about the crazy kind of discoveries that might be coming our way. All right, everybody, that's all the time we have for today. Thank you to everybody who sends them listener questions, and thank you for your patience in getting to them. I plan to keep doing these listener question catch-up episodes

until I've answered every single one of your questions. And remember those of you who have questions but don't want to write in via email, I'll be having public office hours on December 14th, 2020. Go to my website, sites.ucy.edu slash Daniel, to get all the details. Come ask me questions or just listen to other people ask questions or come talk to me about physics. Thanks to everyone. Thanks to everybody who sent in a question. I hope you enjoyed the conversations about dark matter and

black holes and future particle colliders. Tune in next time. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of IHeart Radio. For more podcasts from IHeart Radio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys.

Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged. terrorism. Listen to the new season of law and order criminal justice system on the IHeart radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota,

luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate.

Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. I'm Dr. Scott Barry Kaufman, host of the psychology podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation,

you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome. Avoidance is easier. Ignoring is easier. Denials is easier. Complex problem solving takes effort. Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.