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

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

• 0:08
  Speaker 1: Sometimes my friends and my colleagues asked me, Daniel, why
• 0:12
  Speaker 1: do you give out your email address? How can you
• 0:15
  Speaker 1: promise to answer every listener email. Don't you worry that
• 0:19
  Speaker 1: you're gonna get too many emails or you might get
• 0:22
  Speaker 1: some weird questions you don't know how to answer. Well,
• 0:25
  Speaker 1: I'm a physicist at a public university. The public pays
• 0:29
  Speaker 1: my salary, and I feel like my job is to
• 0:32
  Speaker 1: help unravel the nature of the universe. And and this
• 0:35
  Speaker 1: is big to teach physics to people. Now, I teach
• 0:38
  Speaker 1: classes to students that you see Irvine, But I also
• 0:41
  Speaker 1: think that part of the job of being a publicly
• 0:43
  Speaker 1: paid physicist is to be available to the public. So
• 0:48
  Speaker 1: I want to teach everyone who wants to learn. So
• 0:51
  Speaker 1: I answer all these emails not just because it's my job,
• 0:54
  Speaker 1: but because I love doing it and I'm not afraid
• 0:57
  Speaker 1: that I won't know the answer to a question. Actually,
• 0:59
  Speaker 1: I love when I don't know the answer because it
• 1:01
  Speaker 1: gives me an excuse to go learn more about it. Hi,
• 1:19
  Speaker 1: I'm Daniel. I'm a particle physicist, and I really do
• 1:23
  Speaker 1: love answering random physics questions from the Internet. And welcome
• 1:27
  Speaker 1: to the podcast. Daniel and Jorge Explain the Universe, a
• 1:31
  Speaker 1: production of I Heart Radio. You'll notice that today on
• 1:34
  Speaker 1: the podcast just Just Me Daniel, my friend and co
• 1:37
  Speaker 1: host Jorge can't be here today, so I'm taking the
• 1:40
  Speaker 1: opportunity to fill in and to talk about one of
• 1:42
  Speaker 1: my favorite things on the podcast, which is answering listener questions.
• 1:47
  Speaker 1: In our podcast, we try to explore all the amazing
• 1:50
  Speaker 1: questions about the universe, all the things that science has
• 1:53
  Speaker 1: figured out, and all the things that science has yet
• 1:56
  Speaker 1: to answer, and all those things that science is working on.
• 2:00
  Speaker 1: Those come from questions. Those are the questions asked by
• 2:03
  Speaker 1: scientists who are paid to do science, and by scientists
• 2:07
  Speaker 1: like you who sit at home or sit in your
• 2:09
  Speaker 1: car and just wonder about the nature of the universe.
• 2:13
  Speaker 1: All of that is doing science, which makes all of
• 2:15
  Speaker 1: us scientists. And that's why I love answering questions from listeners,
• 2:20
  Speaker 1: because it means I get to include more people in
• 2:23
  Speaker 1: this circle of science. So when Jorge is not around today,
• 2:27
  Speaker 1: I'm gonna use this opportunity to dig back into our
• 2:30
  Speaker 1: backlog of listener questions. I got a lot of wonderful
• 2:33
  Speaker 1: questions I can answer sort of quickly over email, but
• 2:36
  Speaker 1: sometimes people send me questions that take a little bit
• 2:39
  Speaker 1: more explanation and that I think everybody on the podcast
• 2:42
  Speaker 1: might like hearing the answer to. So I saved those
• 2:45
  Speaker 1: up for listener Questions episodes, but I'll admit we have
• 2:48
  Speaker 1: a bit of a backlog, and so I'm gonna dig
• 2:50
  Speaker 1: into some of those today on the program. So today
• 2:54
  Speaker 1: on the program, we'll be answering listener questions from the backlog.
• 3:03
  Speaker 1: And I love these questions because they really show me
• 3:06
  Speaker 1: what people are thinking. I mean, people write me questions,
• 3:09
  Speaker 1: but they're not simple questions like hey, tell me about
• 3:12
  Speaker 1: black holes or things that are well discussed other places
• 3:16
  Speaker 1: on the internet, like the double slit experiment that you
• 3:19
  Speaker 1: can just google and find a really wonderful explanation. People
• 3:22
  Speaker 1: write to me after they've done some thinking. They have
• 3:25
  Speaker 1: some topic they're trying to understand, they're trying to bring
• 3:27
  Speaker 1: it together in their minds, and there's something that just
• 3:30
  Speaker 1: doesn't quite fit. And that's really what physics is. Physics
• 3:34
  Speaker 1: is trying to apply your mental model to the universe
• 3:37
  Speaker 1: and seeing doesn't make sense. And often what you try
• 3:40
  Speaker 1: to do is sort of climb the same mountain from
• 3:43
  Speaker 1: two directions. Start from one side and then later start
• 3:46
  Speaker 1: from the other side and see if you can get
• 3:48
  Speaker 1: to the same place. And that's wonderful and I love
• 3:51
  Speaker 1: helping people sort of navigate the mountain of physics and
• 3:54
  Speaker 1: get them to the top. It helps me also because
• 3:57
  Speaker 1: I've climbed the mountain from one direction and somebody else
• 4:00
  Speaker 1: is trying it from another way, and I wonder, why
• 4:02
  Speaker 1: doesn't that work, or is that possible? Or can you
• 4:05
  Speaker 1: figure it out using those ideas? And sometimes I have
• 4:08
  Speaker 1: to sort of back up and try to understand where
• 4:10
  Speaker 1: did somebody go wrong, and then help them navigate around
• 4:13
  Speaker 1: that crevass or whatever so they can get to the
• 4:15
  Speaker 1: top and they can get that understanding. But for me
• 4:18
  Speaker 1: it's a great mental exercise. It lets me go off
• 4:21
  Speaker 1: and learn about all sorts of stuff that I don't
• 4:23
  Speaker 1: get to think about necessarily on an everyday basis. And
• 4:26
  Speaker 1: that's why I'm excited to announce something else new, which
• 4:29
  Speaker 1: is my public office hours. If you have a question
• 4:32
  Speaker 1: about physics, but you don't really like writing emails or
• 4:35
  Speaker 1: sending me tweets, come to my public office hours where
• 4:38
  Speaker 1: you can come chat with me and ask me questions
• 4:40
  Speaker 1: about physics or just listen while other people ask me questions.
• 4:45
  Speaker 1: I'll have my first one December twenty at nine am
• 4:50
  Speaker 1: California time. That's noon Eastern time and six pm in Europe.
• 4:55
  Speaker 1: So that's December four, twenty at nine a m. California time.
• 5:00
  Speaker 1: And you can find the location online for connecting. If
• 5:03
  Speaker 1: you go to my website to site dot U c
• 5:06
  Speaker 1: I dot E d U slash Daniel, or maybe you
• 5:10
  Speaker 1: should just google it, you can find a link to it.
• 5:12
  Speaker 1: So come and join me at my public office hours.
• 5:15
  Speaker 1: Ask me a question about black holes, or about tiny particles,
• 5:18
  Speaker 1: or about whatever is in your head that you can't
• 5:21
  Speaker 1: quite figure out about the universe. All right, so I'm
• 5:25
  Speaker 1: excited to answer some listener questions. Let's dig in. First,
• 5:28
  Speaker 1: we have a question about dark matter. Hi, Daniel and Jorge.
• 5:32
  Speaker 1: It's Rocky from California. I have a question about dark matter.
• 5:36
  Speaker 1: How can dark matter exist if it cannot feel the
• 5:38
  Speaker 1: strong force. I'm assuming dark matter is made up of atoms,
• 5:42
  Speaker 1: and if that is the case, then how can it
• 5:44
  Speaker 1: not feel the strong force when the strong force is
• 5:46
  Speaker 1: necessary to keep the protons and neutrons in the nucleus
• 5:49
  Speaker 1: of an atom together. Thanks in advance, all right. So
• 5:52
  Speaker 1: that's a great question from Rocky from California. He wants
• 5:55
  Speaker 1: to know how can dark matter exist if it can't
• 5:58
  Speaker 1: feel a strong force, because he thinks the strong forces
• 6:01
  Speaker 1: what's necessary to hold matter together. Now, first of all,
• 6:04
  Speaker 1: you're totally right that protons and neutrons are held together
• 6:08
  Speaker 1: by the strong force. They're made out of tiny little
• 6:10
  Speaker 1: quarks and they're bound together by gluons, and it's a
• 6:13
  Speaker 1: strong force to keep these mostly positively charged particles together
• 6:17
  Speaker 1: into the protons and neutrons that are familiar for us
• 6:19
  Speaker 1: and are also the building blocks of atoms. However, dark
• 6:24
  Speaker 1: matter is not made out of atoms. Dark matter is
• 6:27
  Speaker 1: made out of something else, something weird, something new, something
• 6:31
  Speaker 1: that is not the same kind of stuff that makes
• 6:33
  Speaker 1: of our particles. How do we know that? How can
• 6:37
  Speaker 1: we possibly know what dark matter is not made out
• 6:40
  Speaker 1: of if we don't know what it is made out of. Well,
• 6:42
  Speaker 1: we can know that because we can see what dark
• 6:44
  Speaker 1: matter can do and what it can't do. For example,
• 6:48
  Speaker 1: everything that's made out of atoms has a temperature, and
• 6:52
  Speaker 1: it glows. Even really really cold stuff glows in the infrared,
• 6:57
  Speaker 1: and really really hot stuff glows in the visible light.
• 7:00
  Speaker 1: Like the sun or a rock in front of you.
• 7:03
  Speaker 1: Everything that is made out of atoms has electrons and
• 7:06
  Speaker 1: has temperatures and eventually will emit light. Also, everything that's
• 7:11
  Speaker 1: made out of atoms has electrons in it, which means
• 7:14
  Speaker 1: that it reacts to light either emits light on its
• 7:17
  Speaker 1: own or reflects light, or it absorbs light. And dark matter,
• 7:21
  Speaker 1: we know does not interact with light. That's why we
• 7:23
  Speaker 1: call it dark. In fact, we have no way to
• 7:26
  Speaker 1: interact with dark matter other than gravity. Remember that we've
• 7:30
  Speaker 1: discovered dark matter because we've seen that it's there to
• 7:33
  Speaker 1: hold galaxies together as they spin around really really fast,
• 7:37
  Speaker 1: where otherwise their stars would be thrown into intergalactic space.
• 7:41
  Speaker 1: And we know that dark matter exists because we've seen
• 7:43
  Speaker 1: these gravitational effects on the early universe. It's created these
• 7:47
  Speaker 1: gravitational wells where normal matter has sort of fallen in,
• 7:50
  Speaker 1: and that seated the production of stars and galaxies in
• 7:53
  Speaker 1: the early universe. Without the gravitational force of dark matter,
• 7:56
  Speaker 1: we wouldn't have the universe that we see today. Galaxies
• 7:59
  Speaker 1: would have it can billions of years longer to form,
• 8:02
  Speaker 1: and we can also study how dark matter moves around
• 8:05
  Speaker 1: the universe. We know that dark matter is fairly cold.
• 8:08
  Speaker 1: It doesn't move very very fast. Dark matter moods very fast.
• 8:12
  Speaker 1: It would have spread out more smoothly in the early
• 8:14
  Speaker 1: universe and we would see a universe with a very
• 8:16
  Speaker 1: different structure. So we think that dark matter is fairly cold,
• 8:20
  Speaker 1: it's fairly slow moving, and that allows it to clump
• 8:23
  Speaker 1: gravitationally and to seed all the structure that we see
• 8:27
  Speaker 1: in the universe. So we know a lot about how
• 8:29
  Speaker 1: dark matter moves and what it is, but we don't
• 8:32
  Speaker 1: really know what it's made out of, right, We don't
• 8:35
  Speaker 1: know if it's made out of a particle. We don't
• 8:37
  Speaker 1: know if it's made out of several particles. We think
• 8:40
  Speaker 1: of it's sort of as like a pressureless fluid because
• 8:43
  Speaker 1: we don't think there's anything sort of holding it together
• 8:46
  Speaker 1: other than its gravity. Rocky asked about how dark matter
• 8:50
  Speaker 1: is held together without the strong force. Well, it's not
• 8:52
  Speaker 1: really held together except for the gravity. And that's why
• 8:56
  Speaker 1: dark matter, even though there's more of it than normal matter,
• 9:00
  Speaker 1: it's much fluffier. It's much more diffused. Like if you
• 9:03
  Speaker 1: look at the distribution of stuff in our galaxy, the
• 9:06
  Speaker 1: stuff that is normal matter that's made out of me
• 9:09
  Speaker 1: and you, and hamsters and stars and everything else that
• 9:12
  Speaker 1: we see in the universe. All the visible matter is
• 9:15
  Speaker 1: made out of atoms, and it clumps up very very tightly, right,
• 9:18
  Speaker 1: stars and rocks and stuff. Well, dark matter, we think,
• 9:21
  Speaker 1: is much more diffuse. Even though there's more dark matter
• 9:24
  Speaker 1: than everything else, it's really spread out like a volume
• 9:27
  Speaker 1: of space. The size of the Earth has only about
• 9:30
  Speaker 1: a squirrel's mass of dark matter. That's because the dark
• 9:33
  Speaker 1: matter is not clumped together the way planets and stars are.
• 9:36
  Speaker 1: It's spread out everywhere, and it extends far beyond where
• 9:40
  Speaker 1: the visible galaxy ends. If you could see dark matter,
• 9:43
  Speaker 1: you would see a huge halo surrounding the entire galaxy.
• 9:48
  Speaker 1: And so that tells you that dark matter isn't tightly
• 9:51
  Speaker 1: held together by a strong force the way protons are
• 9:54
  Speaker 1: and the way neutrons are. It's really a very different
• 9:57
  Speaker 1: kind of stuff. And we know pretty well that it's
• 10:00
  Speaker 1: not made out of quarks, not only because we know
• 10:03
  Speaker 1: that doesn't build atoms which give off light, and it
• 10:06
  Speaker 1: doesn't have that kind of interaction, but because of other
• 10:09
  Speaker 1: really fascinating studies. For example, we've looked at the very
• 10:12
  Speaker 1: early universe, how atoms were formed, what made helium and
• 10:16
  Speaker 1: what made hydrogen, what made any lithium and this kind
• 10:19
  Speaker 1: of stuff, And the fraction you get of helium or
• 10:23
  Speaker 1: hydrogen or lithium depends really sensitively on the density of
• 10:28
  Speaker 1: quarks in the early universe. If you had a lot
• 10:31
  Speaker 1: more quarks sort of per cubic meter, then you've got
• 10:33
  Speaker 1: more heavy elements, and if you had fewer quarks per
• 10:36
  Speaker 1: cubic meter, you've got fewer heavy elements. And we can
• 10:39
  Speaker 1: measure the ratio of hydrogen to helium to lithium in
• 10:44
  Speaker 1: the early universe, and that tells us essentially what the
• 10:47
  Speaker 1: quark density was, how many quarks were around, and then
• 10:51
  Speaker 1: we can account for those. We can say, well, if
• 10:53
  Speaker 1: there were this many quarks around, then did they turn
• 10:56
  Speaker 1: into all the stars and planets and stuff that we
• 10:58
  Speaker 1: see and mostly that at up. So that tells us
• 11:01
  Speaker 1: basically that there aren't left over quarks from the early
• 11:04
  Speaker 1: universe that got turned into dark matter. So we know
• 11:07
  Speaker 1: that dark matter is not made out of quarks and
• 11:10
  Speaker 1: electrons and all this kind of familiar stuff. It has
• 11:13
  Speaker 1: to be made out of something different. And there's also
• 11:16
  Speaker 1: confirming evidence from the cosmic microwave background radiation that tells
• 11:20
  Speaker 1: us how different kinds of matter sort of slashed around
• 11:23
  Speaker 1: in the early universe. There's a kind of matter that
• 11:26
  Speaker 1: we're familiar with that we're made out of, interacts with itself,
• 11:29
  Speaker 1: it ties itself together very tightly, So it slashed around
• 11:32
  Speaker 1: in a different way from dark matter, which seems to
• 11:35
  Speaker 1: have no interaction other than gravity. And so it slashed
• 11:39
  Speaker 1: around differently and led to sort of different distributions matter
• 11:42
  Speaker 1: in the early universe, and we can see those in
• 11:44
  Speaker 1: the wiggles of the cosmic microwave background radiation. So the
• 11:48
  Speaker 1: picture is pretty clear and from lots of different directions.
• 11:51
  Speaker 1: It tells us two things. One that dark matter is
• 11:54
  Speaker 1: not made out of the kind of matter that we're
• 11:56
  Speaker 1: familiar with, the kind of matter you need to build
• 11:58
  Speaker 1: atoms where the strong un force holds itself together, and
• 12:01
  Speaker 1: that dark matter only feels gravity. There's no other interaction
• 12:06
  Speaker 1: that is participating in. However, there is a limit to
• 12:10
  Speaker 1: our knowledge, right We can tell that dark matter doesn't
• 12:13
  Speaker 1: have any very powerful interactions the kind that would help
• 12:16
  Speaker 1: it clump together and form objects and this kind of stuff,
• 12:19
  Speaker 1: But we can never really say that there's no interaction.
• 12:22
  Speaker 1: There might be there and just sort of fairly weak.
• 12:24
  Speaker 1: And people recently have been studying this in great detail
• 12:27
  Speaker 1: and trying to answer the question, is there some other
• 12:30
  Speaker 1: kind of force, some new kind of interaction that only
• 12:34
  Speaker 1: dark matter feels where dark matter can feel this with itself. Now,
• 12:38
  Speaker 1: if it exists, it can't be very very powerful. Otherwise
• 12:41
  Speaker 1: it would help dark matter pull together and it wouldn't
• 12:43
  Speaker 1: be as diffused. But it still might be there. There
• 12:46
  Speaker 1: might be some kind of new force that helps dark
• 12:48
  Speaker 1: matter pulled together or interact in some gentle way. So,
• 12:53
  Speaker 1: if dark matter is not made out of quarks, then
• 12:56
  Speaker 1: what is it made out of? What kind of stuff
• 12:59
  Speaker 1: is there out there in the universe that's not made
• 13:01
  Speaker 1: out of atoms and the kind of stuff that we
• 13:03
  Speaker 1: are familiar with. Well, it might be that dark matter
• 13:07
  Speaker 1: is made out of some new weird particle, something like
• 13:11
  Speaker 1: a whimp weakly interacting massive particle. It's just like a
• 13:15
  Speaker 1: generic idea, sort of like a placeholder idea. We don't
• 13:18
  Speaker 1: really have a great reason to believe that whimps exist,
• 13:22
  Speaker 1: but it's just sort of like an idea that fits
• 13:24
  Speaker 1: all the boxes, and so we go and we look
• 13:27
  Speaker 1: for it. And the basic idea is that maybe dark
• 13:29
  Speaker 1: matter is just made out of this new kind of particle,
• 13:32
  Speaker 1: a heavy, tiny little dot that carries a lot of mass,
• 13:35
  Speaker 1: and so it gives us the gravitational effects that we
• 13:38
  Speaker 1: see and has no other kinds of interactions except for
• 13:41
  Speaker 1: maybe some new weak interaction. When we say weakly interacting
• 13:45
  Speaker 1: massive particle, we don't mean weak like the week nuclear
• 13:49
  Speaker 1: force we're familiar with. We mean weak with a lower
• 13:51
  Speaker 1: case W. We mean sort of a feeble and not
• 13:54
  Speaker 1: very strong or not very powerful force. And it could
• 13:57
  Speaker 1: have some kind of self interaction. It would have some
• 14:01
  Speaker 1: kind of interaction with normal matter, but we don't think
• 14:04
  Speaker 1: that it feels the familiar strong force, the one that
• 14:06
  Speaker 1: binds atoms together. Then again, dark matter might be something
• 14:10
  Speaker 1: different from a whim. It might be several particles, and
• 14:13
  Speaker 1: maybe those particles can talk to each other and can
• 14:16
  Speaker 1: build interesting structures, but not very powerfully. Then again, there
• 14:20
  Speaker 1: are crazy ideas out there, like maybe dark matters made
• 14:23
  Speaker 1: out of primordial black holes, dense clumps of matter that
• 14:27
  Speaker 1: pulled together even before there were particles, even before there
• 14:30
  Speaker 1: were quirks pre corks, right in the very early universe.
• 14:34
  Speaker 1: If they were these spots of over density that collapsed
• 14:37
  Speaker 1: into little black holes. They might still be around. Nobody's
• 14:41
  Speaker 1: ever seen a primordial black hole, and so it's hard
• 14:43
  Speaker 1: to say that they explained the dark matter, but we
• 14:45
  Speaker 1: haven't been able to rule them out as well. And
• 14:48
  Speaker 1: then on the podcast last week, we talked about an
• 14:51
  Speaker 1: even crazier idea, which is maybe dark matters not even
• 14:55
  Speaker 1: made out of particles. Maybe it's made out of some
• 14:58
  Speaker 1: new kind of stuff, some un particle which isn't broken
• 15:01
  Speaker 1: up into little bits of definitive mass but acts really differently.
• 15:05
  Speaker 1: Remember that dark matter is much more prevalent in the
• 15:08
  Speaker 1: universe than normal matter. Our normal matter is actually quite abnormal.
• 15:13
  Speaker 1: So everything we've learned about normal matter might be generally
• 15:16
  Speaker 1: true about the rest of the universe, but it's a
• 15:19
  Speaker 1: bit dangerous to extrapolate from five per cent of the
• 15:23
  Speaker 1: energy density of the universe that's what normal matter is
• 15:25
  Speaker 1: responsible for to the rest of the universe. It might
• 15:28
  Speaker 1: very well be that we're making an error in generalizing
• 15:32
  Speaker 1: and the thinking that the rules that apply to this
• 15:34
  Speaker 1: five percent also apply to the rest of the universe.
• 15:37
  Speaker 1: So it could be something new, something weird, something totally
• 15:40
  Speaker 1: crazy and bonders and that's what makes it so exciting
• 15:43
  Speaker 1: because we know there's something out there new, something we
• 15:47
  Speaker 1: do not yet understand, something when we do figure it out,
• 15:50
  Speaker 1: is guaranteed to teach us something new about the universe.
• 15:53
  Speaker 1: And that's why physics is exciting. Alright, So thank you
• 15:57
  Speaker 1: to Rocky for that wonderful question about what a dark
• 16:00
  Speaker 1: matter feels a strong force. No, it cannot feel the
• 16:03
  Speaker 1: strong force. It's not made out of atoms. It's made
• 16:06
  Speaker 1: out of something new, something weird, which feels gravity, and
• 16:09
  Speaker 1: maybe something else, but we're not sure. All right, I
• 16:12
  Speaker 1: want to answer some more questions, but first it's time
• 16:15
  Speaker 1: to take a quick break. Okay, we're back and it's
• 16:30
  Speaker 1: just Nanuel today and I'm answering listener questions from the backlog.
• 16:34
  Speaker 1: Thank you to everybody who's sent in these questions, and
• 16:36
  Speaker 1: apologies if it's been several months since you sent them
• 16:39
  Speaker 1: in and you've been waiting for an answer. I hope
• 16:41
  Speaker 1: late is better than never. And this next question is
• 16:44
  Speaker 1: one of my favorites because it comes from a seven
• 16:47
  Speaker 1: year old listener. So thank you to everybody who listens
• 16:50
  Speaker 1: to the podcast, and extra thank you to everybody who
• 16:52
  Speaker 1: listens with your kids and answers their questions. And if
• 16:56
  Speaker 1: your kids ask you a question about physics and the
• 16:58
  Speaker 1: universe that you can't, just send it on to us
• 17:01
  Speaker 1: will take care of it for you. So here's a question,
• 17:04
  Speaker 1: for example from Bradley who's seven years old. Hi, my
• 17:08
  Speaker 1: name is Bradley Stuff. I am seven years old. I
• 17:12
  Speaker 1: am from out A Loma, California, and my question is
• 17:16
  Speaker 1: why do black holes slow down time? What a wonderful question,
• 17:20
  Speaker 1: a deep question about the nature of the universe and
• 17:22
  Speaker 1: some of the weirdest things in it. So Bradley is
• 17:25
  Speaker 1: wondering why do black holes slow down time? Now? Time
• 17:31
  Speaker 1: slowing down? Time dilation is sort of a famous result
• 17:34
  Speaker 1: in physics. Most people think of time dilation is what
• 17:38
  Speaker 1: happens when you move really, really fast on a spaceship,
• 17:41
  Speaker 1: and that's the famous result of one of Einstein's theories,
• 17:44
  Speaker 1: special relativity. Special relativity tells us what happens when you
• 17:48
  Speaker 1: move near the speed of light, and it shows us
• 17:51
  Speaker 1: how time and space are sort of enttangled. And it's
• 17:54
  Speaker 1: worth stepping through how it happens in special relativity because
• 17:57
  Speaker 1: there's a lesson for us there, and how it happens
• 18:00
  Speaker 1: in general relativity, which is what we'll need to talk
• 18:03
  Speaker 1: about why time slows down near a black hole. So
• 18:06
  Speaker 1: if you get on a spaceship and you travel really
• 18:09
  Speaker 1: really really fast compared to the Earth, then your time
• 18:12
  Speaker 1: doesn't actually seem to slow down for you. Remember that
• 18:16
  Speaker 1: speed is always relative, and time slows down for people
• 18:20
  Speaker 1: moving fast relative to an observer. So if you jump
• 18:24
  Speaker 1: on a spaceship and you travel really really fast, you
• 18:27
  Speaker 1: might expect to see your clocks slow down. Right wrong.
• 18:31
  Speaker 1: Clocks only slow down when they are moving. So if
• 18:34
  Speaker 1: you see a clock going really really fast, then it
• 18:37
  Speaker 1: slows down. If you're on a spaceship and you're holding
• 18:41
  Speaker 1: a clock, then it always ticks at the normal rate
• 18:44
  Speaker 1: relative to you, because it's not moving relative to you.
• 18:48
  Speaker 1: Time only seems to slow down for somebody else watching you,
• 18:52
  Speaker 1: for somebody else for whom that clock is moving really
• 18:55
  Speaker 1: really fast. So, for example, you jump on a spaceship,
• 18:59
  Speaker 1: you travel really really fast relative to the Earth. On
• 19:03
  Speaker 1: board the spaceship, you see the clock taking at a
• 19:05
  Speaker 1: normal rate. Somebody back on Earth using a telescope to
• 19:09
  Speaker 1: look at your clock, they will see your clock ticking slowly.
• 19:13
  Speaker 1: So your clock moves slowly only for somebody who sees
• 19:16
  Speaker 1: that clock moving quickly. Right, moving clocks run slow. If
• 19:21
  Speaker 1: you're holding your clock, you're on the spaceship, that doesn't
• 19:24
  Speaker 1: take slow for you. For you, time always moves at
• 19:27
  Speaker 1: the normal speed. And the thing that's sort of hard
• 19:29
  Speaker 1: to get your mind around there is that time is
• 19:31
  Speaker 1: not universal. Time moves differently on the spaceship than it
• 19:35
  Speaker 1: does for you. You have a clock, they have a clock,
• 19:37
  Speaker 1: and they don't agree. And that's one of the most
• 19:39
  Speaker 1: awesome things about relativity is that it unshackles us from
• 19:43
  Speaker 1: this sort of universal clock that tells us the whole
• 19:46
  Speaker 1: universe ticks forward at the same moment, and tells us
• 19:49
  Speaker 1: that how time flows depends on where you are and
• 19:52
  Speaker 1: on how fast you are moving. Now, general relativity adds
• 19:55
  Speaker 1: something to that. It says that how time ticks forward
• 19:58
  Speaker 1: doesn't just depend on where you are are and how
• 20:00
  Speaker 1: fast you're moving, but also what you are nearby. And
• 20:04
  Speaker 1: so Bradley's question is about a black hole, and he's
• 20:07
  Speaker 1: exactly right. If you took a spaceship, and even if
• 20:10
  Speaker 1: you never went very very fast, but if you went
• 20:12
  Speaker 1: near a black hole, say for example, you went in
• 20:15
  Speaker 1: to orbit around a black hole, you stay at a
• 20:17
  Speaker 1: safe distance. So you're not going to fall in. You
• 20:20
  Speaker 1: can orbit a black hole just the same way you
• 20:22
  Speaker 1: can orbit any other object with mass. If you're far
• 20:25
  Speaker 1: enough away and you're moving fast enough, and you don't
• 20:27
  Speaker 1: get too close to the event horizon, you can orbit
• 20:30
  Speaker 1: a black hole. Now, if you orbit a black hole
• 20:32
  Speaker 1: for a year and you're pretty close, you might come
• 20:35
  Speaker 1: back and discover that the rest of the universe time
• 20:37
  Speaker 1: has moved forward much more quickly. So time has slowed down.
• 20:41
  Speaker 1: On the spaceship. Time seemed to travel normally for you,
• 20:44
  Speaker 1: it was a year according to you. But somebody else
• 20:48
  Speaker 1: far away looking at your clock, what is seeing your
• 20:50
  Speaker 1: clock running slowly? Which means their clocks are running faster
• 20:54
  Speaker 1: than your clocks. And if you come back away from
• 20:57
  Speaker 1: the orbit in the black hole, you might have discovered
• 21:00
  Speaker 1: that a hundred years have passed on Earth, or a
• 21:02
  Speaker 1: thousand years or a million years, depending on how close
• 21:06
  Speaker 1: you came to the black hole. So Bradley's question is
• 21:09
  Speaker 1: why does that happen? You're not moving very fast. The
• 21:12
  Speaker 1: velocity from special relativity is not what's slowing down your clock.
• 21:16
  Speaker 1: Why is that time slows down near a black hole? Well,
• 21:21
  Speaker 1: the important thing to understand is that time doesn't slow
• 21:24
  Speaker 1: down just near black holes. It actually slows down near
• 21:27
  Speaker 1: any massive object. That's right. That means that time is slower,
• 21:31
  Speaker 1: for example, on the surface of the Earth than it
• 21:34
  Speaker 1: is a hundred meters above the Earth or a thousand
• 21:37
  Speaker 1: meters above the Earth. And this is precisely why general
• 21:40
  Speaker 1: relativity plays an important role in our global positioning system.
• 21:43
  Speaker 1: These satellites that over the Earth and tell us where
• 21:46
  Speaker 1: we are and what time it is, they have to
• 21:48
  Speaker 1: account for the fact that gravity changes time as you
• 21:51
  Speaker 1: move closer to the Earth. So any massive object will
• 21:55
  Speaker 1: slow down time. Now, black holes, of course slow down
• 21:58
  Speaker 1: time much more than anything else because they are much
• 22:01
  Speaker 1: more massive. But every massive object will slow down time,
• 22:04
  Speaker 1: the Sun, the Earth, even that huge boulder. You get
• 22:07
  Speaker 1: closer to that big boulder, time slows down a tiny
• 22:11
  Speaker 1: little bit. Now why is it, though, that being near
• 22:14
  Speaker 1: a massive object slows down time. The thing you have
• 22:17
  Speaker 1: to understand is that gravity here is best understood not
• 22:21
  Speaker 1: as a force, not that's something that's pulling on you,
• 22:24
  Speaker 1: but as the curving of space. It's changing what it
• 22:28
  Speaker 1: means to move in a straight line, for example. And
• 22:31
  Speaker 1: I think the best way to understand the relationship between
• 22:33
  Speaker 1: gravity is a force and gravity as a curvature of
• 22:37
  Speaker 1: the space we're moving through. Is to think about what
• 22:39
  Speaker 1: happens to somebody moving on a two D surface. Say,
• 22:42
  Speaker 1: for example, you have two people on the Earth, which
• 22:45
  Speaker 1: seems flat to them, right, and they're starting in the equator,
• 22:48
  Speaker 1: but in different places, and they're walking north. If we
• 22:51
  Speaker 1: say to them, all right, everybody walk north, then it
• 22:54
  Speaker 1: seems to them like, while we're moving in a parallel line, right,
• 22:57
  Speaker 1: we're both moving due north. Now you know that if
• 23:00
  Speaker 1: you start the equator and you walk due north, then
• 23:03
  Speaker 1: eventually you'll reach the north Pole. Think about how weird
• 23:06
  Speaker 1: that is for the people on the surface, right, they're
• 23:09
  Speaker 1: moving in parallel, they're separated by a distance. They're moving
• 23:12
  Speaker 1: in parallel, and yet their path cross. From their point
• 23:16
  Speaker 1: of view, it's like this something pulling them together, something
• 23:20
  Speaker 1: bringing them closer and closer together, something like a force.
• 23:24
  Speaker 1: From our point of view, we understand that they're on
• 23:26
  Speaker 1: a curved surface, then it makes sense for their motion
• 23:29
  Speaker 1: to naturally bring them together because their motion is on
• 23:33
  Speaker 1: a curved surface. Even if we see no force there
• 23:36
  Speaker 1: and that's where gravity is. It takes a bit of
• 23:38
  Speaker 1: a mental jiu jitsu. But you have to then extrapolate
• 23:41
  Speaker 1: to three dimensions, and remember that gravity is not the
• 23:44
  Speaker 1: bending of space relative to some other higher dimensional space
• 23:48
  Speaker 1: and four dimensions or in five dimensions. It's an intrinsic bending.
• 23:52
  Speaker 1: It changes the relationship between points in space, it changes
• 23:56
  Speaker 1: the relative distance between things, but it has the same effect.
• 24:01
  Speaker 1: You can think of gravity as a force, but it's
• 24:02
  Speaker 1: much more natural to think of it as the curving
• 24:05
  Speaker 1: of space, which changes the path that you move on,
• 24:08
  Speaker 1: even if there are no forces. And so what happens
• 24:11
  Speaker 1: near a massive object, Well, anything with mass, or actually
• 24:14
  Speaker 1: anything with energy will bend space a little bit. But
• 24:17
  Speaker 1: it doesn't just bend space. It also bends time because
• 24:22
  Speaker 1: remember we learn from special relativity that time and space
• 24:26
  Speaker 1: are connected. Time ticks differently depending on where you are
• 24:30
  Speaker 1: and how fast you are moving, and so the curvature
• 24:33
  Speaker 1: of space is also the curvature of space time. And
• 24:37
  Speaker 1: where this is more curved, time slows down even more,
• 24:41
  Speaker 1: and it gets pretty crazy, like the curvature of space
• 24:44
  Speaker 1: gets so intense that if you go inside a black hole,
• 24:48
  Speaker 1: then space moves only in one direction. It's so intensely
• 24:52
  Speaker 1: curved that every direction of space is now pointing towards
• 24:56
  Speaker 1: the singularity. So there's another connection there between space and time.
• 25:00
  Speaker 1: Outside the black hole, time only moves forwards, and space
• 25:04
  Speaker 1: can go in every direction. Inside the black hole, space
• 25:08
  Speaker 1: becomes one directional, the same way time is outside a
• 25:11
  Speaker 1: black hole, it only points towards the black hole. There
• 25:15
  Speaker 1: is no outwards direction. The reason you can't escape a
• 25:18
  Speaker 1: black hole is because literally there is no direction in
• 25:21
  Speaker 1: which to escape. It doesn't matter how fast you go.
• 25:25
  Speaker 1: And so that curvature of space is very intense, and
• 25:27
  Speaker 1: it also curves time. And now, the other lesson we
• 25:31
  Speaker 1: learned from special relativity is that it's a different experience
• 25:34
  Speaker 1: to go really fast and to watch somebody going really fast. Right,
• 25:38
  Speaker 1: the person who's going really fast, they think time has
• 25:40
  Speaker 1: flown normally. Person who's watching them move really fast relative
• 25:44
  Speaker 1: to the Earth, they see time slowing down. Well, the
• 25:47
  Speaker 1: same effect happens for the curvature of space. If you
• 25:50
  Speaker 1: and your friend come nearby a black hole, and your
• 25:53
  Speaker 1: friend approaches it and orbits the black hole, you will
• 25:56
  Speaker 1: see her clock slowing down, but she will experience time normally.
• 26:00
  Speaker 1: For her time is taking very normally, but for you,
• 26:04
  Speaker 1: her time is moving very very slowly, and in fact,
• 26:07
  Speaker 1: if she fell into the black hole, you would never
• 26:10
  Speaker 1: actually see her cross the event horizon because time and
• 26:13
  Speaker 1: space is so distorted that her time would slow down
• 26:16
  Speaker 1: so dramatically as she got closer to the black hole
• 26:19
  Speaker 1: that you would never actually see her cross. It takes
• 26:21
  Speaker 1: an infinite amount of time for you to see her cross,
• 26:25
  Speaker 1: but from her perspective, time is slowing normally, and she
• 26:28
  Speaker 1: can pass over the event horizon and into the black
• 26:31
  Speaker 1: hole and towards the singularity. So, Bradley, great question. Why
• 26:36
  Speaker 1: does time slow down near a black hole? It's because
• 26:38
  Speaker 1: time and space are connected, and black holes bend space
• 26:43
  Speaker 1: time like every massive object, and so that curvature not
• 26:46
  Speaker 1: only makes the weird feature that we call a black hole,
• 26:49
  Speaker 1: it also affects the passage of time in the same
• 26:52
  Speaker 1: way that moving at high velocities also affects the passage
• 26:55
  Speaker 1: of time. All Right, great question from Bradley. Loved it.
• 26:59
  Speaker 1: I'll be back in a moment to answer another question,
• 27:02
  Speaker 1: but first let's take another break. Okay, I'm back. This
• 27:18
  Speaker 1: is Daniel answering listener questions, digging into the backlog and
• 27:22
  Speaker 1: trying to find the funnest, most interesting, most exciting questions
• 27:25
  Speaker 1: to answer for all of you. So here's another question.
• 27:28
  Speaker 1: This one's about particle physics. Hey, guys, I was wondering
• 27:32
  Speaker 1: what would it take to make a fundamental particle accelerator
• 27:35
  Speaker 1: like an electron collider. What new things would we see
• 27:38
  Speaker 1: from colliding fundamental particles like leptons and quarks, and would
• 27:42
  Speaker 1: it be different than what we have today? All right, well,
• 27:45
  Speaker 1: this is a wonderful question, and I think the motivation
• 27:48
  Speaker 1: for this question comes from understanding that the large hadron
• 27:51
  Speaker 1: collider is not a collider that shoots fundamental particles. Instead,
• 27:55
  Speaker 1: it shoots protons. And remember, protons are not tiny little
• 27:59
  Speaker 1: dots in our theory. They are made of smaller particles.
• 28:02
  Speaker 1: They are composite particles. They have quirks in them, and
• 28:05
  Speaker 1: then a bunch of gluons to hold them together. And
• 28:08
  Speaker 1: so I think this is what's motivating his question. He's
• 28:10
  Speaker 1: wondering what would it be like to build a collider
• 28:13
  Speaker 1: made from actually tiny fundamental particles instead of tossing little
• 28:17
  Speaker 1: bags of particles at each other. Well, first, let's think
• 28:20
  Speaker 1: about why the large change on collider is a proton collider.
• 28:23
  Speaker 1: Where are the pros and cons of that and then
• 28:26
  Speaker 1: we'll talk about fundamental particle colliders. So the reason that
• 28:30
  Speaker 1: we build a large change on collider out of protons
• 28:32
  Speaker 1: is number one, there are protons everywhere, like it's not
• 28:35
  Speaker 1: hard to find protons. Everything around us is made of protons.
• 28:39
  Speaker 1: But also because heavier particles are easier to accelerate, the
• 28:43
  Speaker 1: more massive particle has, the less it will radiate that
• 28:47
  Speaker 1: energy when you accelerate it. When you accelerate a particle,
• 28:50
  Speaker 1: if it's very low mass, like an electron, it will
• 28:53
  Speaker 1: give off a lot of that energy in the form
• 28:56
  Speaker 1: of photons. So the heavier particle is the less it radiates.
• 29:00
  Speaker 1: So it's actually possible to get protons up to higher
• 29:03
  Speaker 1: speeds more easily than it is to get electrons. And
• 29:07
  Speaker 1: remember we want these protons to have a lot of energy.
• 29:10
  Speaker 1: The more energy you pour into your particle collider, the
• 29:12
  Speaker 1: higher energy state you can create, and the more massive
• 29:16
  Speaker 1: objects you can create. And the goal of particle colliders
• 29:20
  Speaker 1: is to explore the universe by discovering new massive particles,
• 29:24
  Speaker 1: by creating energy densities that are so high that it
• 29:26
  Speaker 1: becomes possible to make new weird particles that haven't existed
• 29:30
  Speaker 1: since the Big Bang and The awesome thing about these colliders, remember,
• 29:34
  Speaker 1: is that you don't have to know what you're looking for.
• 29:37
  Speaker 1: You don't have to know that those particles are out
• 29:39
  Speaker 1: there as long as you pour enough energy into your collider,
• 29:42
  Speaker 1: if you're above the threshold, if you have enough energy
• 29:45
  Speaker 1: in the collision to make these heavy particles, they will
• 29:48
  Speaker 1: eventually appear, which is pretty cool, and that's what motivates
• 29:52
  Speaker 1: us to have higher and higher energy. If you double
• 29:55
  Speaker 1: the energy and your collider, you can make particles twice
• 29:57
  Speaker 1: as massive. It's sort of like getting to explore and
• 30:00
  Speaker 1: a whole another Earth life planet. Right. The possibilities for
• 30:03
  Speaker 1: a discovery are amazing, and nobody has ever built a
• 30:06
  Speaker 1: collider at these energies before. So if you could double
• 30:10
  Speaker 1: the energy of your collider, you could see things for
• 30:12
  Speaker 1: the first time that nobody has ever seen. Now. The
• 30:16
  Speaker 1: disadvantage of using protons or any particle that's not a
• 30:19
  Speaker 1: fundamental particle is that it's less precise. Right, you can't
• 30:23
  Speaker 1: control the energy of the interaction nearly as tightly as
• 30:27
  Speaker 1: if you were shooting tiny, little pin prick particles. I mean,
• 30:30
  Speaker 1: what happens when you collide protons together is that the
• 30:34
  Speaker 1: energy holding the protons together is kind of negligible compared
• 30:37
  Speaker 1: to the energy of the protons moving, so when they
• 30:40
  Speaker 1: come near each other, the fact that the corks are
• 30:43
  Speaker 1: bound together into a proton becomes kind of irrelevant. You
• 30:46
  Speaker 1: have this little sort of flimsy bag holding these corks together,
• 30:50
  Speaker 1: but it's really the quarks from one proton that interact
• 30:53
  Speaker 1: with the corks from the other proton, or sometimes even
• 30:55
  Speaker 1: the gluons, And then you get multiple interactions. You get
• 30:59
  Speaker 1: two corks mat shing into each other, or to glue
• 31:01
  Speaker 1: on smashing into each other, or multiple things happening at once.
• 31:05
  Speaker 1: And it's not just that multiple things happened, but that
• 31:08
  Speaker 1: you can't control the energy. You can't say I want
• 31:11
  Speaker 1: core collisions at a very specific energy. You can control
• 31:14
  Speaker 1: the energy of the protons, but you never know how
• 31:17
  Speaker 1: much of the protons energy is going into each cork.
• 31:20
  Speaker 1: And in one collision, the quarks you collion could have
• 31:22
  Speaker 1: a tiny fraction of the energy of the protons. In
• 31:25
  Speaker 1: another one that could have a huge fraction of the
• 31:27
  Speaker 1: energy of the protons. So you lose a very precise
• 31:29
  Speaker 1: control over the energy that you're putting into your collision,
• 31:33
  Speaker 1: but what you're gaining is the ability to have a
• 31:35
  Speaker 1: huge amount of energy in that collision. So proton accelerators
• 31:39
  Speaker 1: are really good for discovering stuff, for figuring out new
• 31:43
  Speaker 1: stuff because they can explore a big range of energy.
• 31:46
  Speaker 1: One because the proton can hold a lot of energy
• 31:48
  Speaker 1: without radiating it off. And two because the quarks get
• 31:51
  Speaker 1: a different fraction the protons energy every time. So you
• 31:54
  Speaker 1: can very naturally explore a lot of different energy ranges
• 31:57
  Speaker 1: in your collisions. Now, can we make colliders out of
• 32:00
  Speaker 1: fundamental particles, Yes, absolutely, and we have when great example
• 32:05
  Speaker 1: are electron colliders in the same tunnels that now hold
• 32:08
  Speaker 1: the LHC. Twenty years ago we had leapt large electron
• 32:13
  Speaker 1: positron collider and it made some great discoveries, and it
• 32:16
  Speaker 1: used electrons in one direction and positrons in the other direction,
• 32:19
  Speaker 1: and it smashed them together. And the advantage here is
• 32:23
  Speaker 1: that it's much more precise. You can control the energy,
• 32:26
  Speaker 1: and so if you're looking for a particle that requires
• 32:29
  Speaker 1: an exact amount of energy to make it, you can
• 32:31
  Speaker 1: tune your collider very precisely to put just that much
• 32:36
  Speaker 1: energy into the collisions. Because you're now dealing with fundamental particles,
• 32:40
  Speaker 1: not bags of particles, so you know exactly how much
• 32:43
  Speaker 1: energy you put into your accelerator and the magnets and
• 32:47
  Speaker 1: all that energy is just going into that one fundamental particle,
• 32:50
  Speaker 1: and you have the other fundamental particle coming from the
• 32:52
  Speaker 1: other direction. So things are very tightly controlled. And there's
• 32:56
  Speaker 1: been examples in history when this has been very important,
• 32:59
  Speaker 1: when you only makes some new heavy particle when you
• 33:01
  Speaker 1: have exactly the right energy to go into the collisions,
• 33:04
  Speaker 1: and so you can tune the energy of your collider
• 33:07
  Speaker 1: very precisely, sort of scan up and down and see, oh, look,
• 33:10
  Speaker 1: we're making a new particle at exactly this energy. An
• 33:13
  Speaker 1: example of the discovery of the Jape side and people
• 33:16
  Speaker 1: who are interested in the crazy story of the particle
• 33:19
  Speaker 1: that has two names go check out our podcast episode
• 33:22
  Speaker 1: about that discovery. There's a lot of crazy stuff in
• 33:25
  Speaker 1: the history of particle physics. Now, of course, the cons
• 33:28
  Speaker 1: the disadvantage of using an electron collider is that you
• 33:32
  Speaker 1: can't make electrons go as fast as protons very easily
• 33:35
  Speaker 1: because they give off a lot of their energy. They
• 33:38
  Speaker 1: radiate away their energy because electrons don't have very much mass,
• 33:42
  Speaker 1: and so if you want to go to high energy,
• 33:44
  Speaker 1: it's better to use protons, and if you want really
• 33:46
  Speaker 1: precise control of the energy, it's better to use electrons.
• 33:50
  Speaker 1: The people also have other crazy ideas because the electron
• 33:53
  Speaker 1: is not the only fundamental particle we can consider using. Right,
• 33:57
  Speaker 1: what about the muan. The muan is just like the
• 34:00
  Speaker 1: electron in lots of ways. It's like the electrons cousin,
• 34:04
  Speaker 1: but it has more mass. And what that mass means
• 34:08
  Speaker 1: that it doesn't radiate energy as quickly as electrons. So
• 34:12
  Speaker 1: you could create a muon collider where you create muans,
• 34:16
  Speaker 1: accelerate them, smash them into each other. In theory, it
• 34:19
  Speaker 1: would be easier to get those muans to go to
• 34:21
  Speaker 1: higher energies than it is for electrons because they don't
• 34:24
  Speaker 1: radiate as much. Now, the disadvantage is that there aren't
• 34:28
  Speaker 1: as many muans around like electrons. They are everywhere. You
• 34:32
  Speaker 1: take an atom, you heat it up, boom, you got
• 34:34
  Speaker 1: a bunch of electrons. Muans are much harder to produce
• 34:37
  Speaker 1: right there, produced in cosmic rays, or you can make
• 34:39
  Speaker 1: them in collisions, but you don't have a natural supply
• 34:41
  Speaker 1: of muans. The other disadvantage of muans, and this is
• 34:44
  Speaker 1: kind of a big one, is that they don't last
• 34:46
  Speaker 1: very long. Sure, they don't radiate energy as much as
• 34:49
  Speaker 1: electrons when they move fast, but they also don't live
• 34:52
  Speaker 1: forever like electrons do. An electrons sitting by itself will
• 34:56
  Speaker 1: sit there to the end of the universe. It's a
• 34:58
  Speaker 1: stable particle. I you on, on the other hand, last
• 35:01
  Speaker 1: two point two micro seconds. So if you have a
• 35:04
  Speaker 1: muan sitting by itself in space, it will spontaneously decay
• 35:08
  Speaker 1: to an electron and a couple of new trinos. So
• 35:11
  Speaker 1: that's pretty tough. Now, you can make the muans live
• 35:14
  Speaker 1: longer by getting them to go really fast because time
• 35:17
  Speaker 1: dilation happens. The muan lives two point two microseconds by
• 35:21
  Speaker 1: its clock right in its frame of reference if it
• 35:25
  Speaker 1: had a tiny little clock. If you can get them
• 35:27
  Speaker 1: to go really really fast, like moving around an accelerator,
• 35:30
  Speaker 1: then their clocks go slower and they last for much
• 35:33
  Speaker 1: longer seconds, minutes, as long as you want, depending on
• 35:37
  Speaker 1: how fast they are going. So there are some ways,
• 35:40
  Speaker 1: and people are talking seriously about building muan colliders for
• 35:44
  Speaker 1: future experiments. Now, what you can't do is build a
• 35:47
  Speaker 1: cork collider. We'd love to have a cork collider because
• 35:50
  Speaker 1: it would let us study all sorts of crazy awesome things.
• 35:53
  Speaker 1: But quarks, remember, cannot be by themselves. The strong force
• 35:57
  Speaker 1: to hold the proton together. It's very very wrong, and
• 36:00
  Speaker 1: it has a really weird feature, the strong force which
• 36:03
  Speaker 1: holds the corks together in the proton. As you pull
• 36:07
  Speaker 1: those two corks apart, the energy in that bond actually increases,
• 36:11
  Speaker 1: the force increases. This is the opposite than all of
• 36:15
  Speaker 1: the other forces, like the electromagnetic force between two electrons
• 36:19
  Speaker 1: decreases as the electrons get further apart. For quarks, the
• 36:23
  Speaker 1: strong force grows stronger as the corks get further apart,
• 36:26
  Speaker 1: which means this more and more energy in that bond
• 36:30
  Speaker 1: as they get further apart. And that's why quarks can't
• 36:33
  Speaker 1: ever be alone, because a cork far away from all
• 36:36
  Speaker 1: the other corks would require so much energy that that
• 36:40
  Speaker 1: space would be so unstable that that energy would very
• 36:43
  Speaker 1: rapidly turn into new particles. And that's exactly what happens
• 36:46
  Speaker 1: if you break up a proton into a bunch of
• 36:49
  Speaker 1: quarks and send them flying off in different directions than
• 36:51
  Speaker 1: they create new matter out of the vacuum using the
• 36:55
  Speaker 1: energy held in that strong force, and they bind those
• 36:57
  Speaker 1: corks together to these new corks that created out of
• 37:00
  Speaker 1: the vacuum, so you can't ever see a cork by itself,
• 37:03
  Speaker 1: which means you can't build a collider out of corks,
• 37:07
  Speaker 1: which is too bad. But right now in particle physics,
• 37:09
  Speaker 1: we happen to be thinking about the future of the
• 37:11
  Speaker 1: field and what kind of collider we want to build
• 37:14
  Speaker 1: in the next ten or twenty years. So people are
• 37:16
  Speaker 1: doing these kind of exercises and wondering like, what kind
• 37:19
  Speaker 1: of question can we ask with an electron collider? What
• 37:22
  Speaker 1: kind of science can we learned with the mun collider?
• 37:24
  Speaker 1: Should we build a photon collider? Or all sorts of
• 37:27
  Speaker 1: crazy stuff. So it's a really fun and exciting time
• 37:29
  Speaker 1: in the field to be thinking about the five, ten
• 37:32
  Speaker 1: fifty year trajectory. Can we come up with new ways
• 37:35
  Speaker 1: to accelerate particles so it doesn't cost ten billion dollars
• 37:38
  Speaker 1: and require loops underground that are thirty kilometers around. It's
• 37:42
  Speaker 1: a fun time and we're all thinking about the crazy
• 37:45
  Speaker 1: kind of discoveries that might be coming our way. All right, everybody,
• 37:50
  Speaker 1: that's all the time we have for today. Thank you
• 37:52
  Speaker 1: to everybody who sends them listener questions, and thank you
• 37:55
  Speaker 1: for your patients in getting to them. I plan to
• 37:57
  Speaker 1: keep doing these listener question catch up episodes until I've
• 38:00
  Speaker 1: answered every single one of your questions. And remember those
• 38:04
  Speaker 1: of you who have questions but don't want to write
• 38:06
  Speaker 1: in via email. I'll be having public office hours on
• 38:10
  Speaker 1: December four, Team twenty twenty. Go to my website sites
• 38:14
  Speaker 1: dot U, c I, dot E, d U slash Daniel
• 38:17
  Speaker 1: to get all the details. Come ask me questions, or
• 38:20
  Speaker 1: just listen to other people ask questions, or come talk
• 38:22
  Speaker 1: to me about physics. Thanks everyone, Thanks to everybody who's
• 38:26
  Speaker 1: sent in a question. I hope you enjoyed the conversations
• 38:28
  Speaker 1: about dark matter and black holes and future particle colliders.
• 38:33
  Speaker 1: Tune in next time. Thanks for listening, and remember that
• 38:43
  Speaker 1: Daniel and Jorge Explain the Universe is a production of
• 38:46
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  Speaker 1: visit the I heart Radio app, Apple Podcasts, or wherever
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