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What if dark matter is more complicated? · Daniel and Kelly’s Extraordinary Universe

• 0:07
  Speaker 1: What is the universe made out of? This is the
• 0:10
  Speaker 1: central question that animates my research and my entire career,
• 0:14
  Speaker 1: and I've been working on it for decades. Humanity's been
• 0:17
  Speaker 1: working on it for centuries or even millennia. Why haven't
• 0:21
  Speaker 1: we figured it out yet? Well, turns out, like lots
• 0:23
  Speaker 1: of things, it's complicated. And just when we thought we
• 0:26
  Speaker 1: were getting our minds around what our kind of matter
• 0:30
  Speaker 1: is made out of, it turns out that our kind
• 0:32
  Speaker 1: of matter is unusual, it's weird, it's not the typical
• 0:35
  Speaker 1: thing in the universe. The problem is so much bigger,
• 0:38
  Speaker 1: so much broader than we even imagined. And understanding what
• 0:42
  Speaker 1: the rest of the universe is made out of is
• 0:44
  Speaker 1: gonna take some real creativity, not just in thinking about
• 0:48
  Speaker 1: what it might be made out of, but how we
• 0:50
  Speaker 1: actually search for it. Today on the episode, we'll talk
• 0:53
  Speaker 1: about a new quirky idea for what dark matter might
• 0:56
  Speaker 1: be made out of and how it inspired a whole
• 0:59
  Speaker 1: new technology to look for these kinds of quirky particles.
• 1:03
  Speaker 1: Welcome to Daniel and Kelly's Extraordinarily Quirky Universe.
• 1:21
  Speaker 2: Hello, I'm Kelly Wienersmith. I study parasites and space and
• 1:25
  Speaker 2: look forward to an episode where I repeatedly mix up
• 1:28
  Speaker 2: quarks and quarks. That's what's coming, friends.
• 1:34
  Speaker 1: It's quirks and quirks.
• 1:36
  Speaker 2: Are you serious? I didn't even get the two words right? Yes.
• 1:40
  Speaker 1: Nailed it.
• 1:42
  Speaker 2: Oh, man. Introduce yourself, dweeb.
• 1:46
  Speaker 1: All right. I'm Daniel Whiteson. I'm a particle physicist who
• 1:49
  Speaker 1: likes thinking about aliens. And I have actually looked for
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  Speaker 1: quirks out in the wild. Oh, yeah.
• 1:56
  Speaker 2: I'm excited that we're talking about your research today. But
• 1:59
  Speaker 2: my question for you, because I read the outline to
• 2:01
  Speaker 2: the end. Good job, Kelly.
• 2:05
  Speaker 1: I think you protest too much a little bit there.
• 2:07
  Speaker 1: I didn't doubt until you said that.
• 2:09
  Speaker 2: Oh, let's move on. So the question at the top
• 2:12
  Speaker 2: of your outline is, what if dark matter is complicated? Yes.
• 2:16
  Speaker 2: Which made me think. What do you mean, what if? Like,
• 2:20
  Speaker 2: when someone talks about a physics topic, I'm like, obviously
• 2:23
  Speaker 2: it's going to be complicated. So my question to you is,
• 2:26
  Speaker 2: what physics topic is not complicated? Wait, what topic should
• 2:34
  Speaker 2: you be like, oh, this is complicated? I'm surprised. I
• 2:36
  Speaker 2: didn't expect a physics topic to be complicated. This would
• 2:40
  Speaker 2: be like, you know, I would be like, oh, today
• 2:42
  Speaker 2: we're talking about biology. And the answer is going to be,
• 2:45
  Speaker 2: it depends. And like expecting people to be surprised. It's always,
• 2:49
  Speaker 2: it depends.
• 2:50
  Speaker 1: Well, a good example of something that turned out to
• 2:52
  Speaker 1: be kind of simple is the Higgs boson. You know,
• 2:55
  Speaker 1: before we discovered the Higgs, we had lots of different
• 2:58
  Speaker 1: theories to explain how particles got masses. And then we
• 3:01
  Speaker 1: also had lots of different Higgs theories. Like maybe there's
• 3:04
  Speaker 1: one Higgs, maybe there's four Higgs, maybe there's weird kinds
• 3:07
  Speaker 1: of Higgs. And so we went out and we looked
• 3:10
  Speaker 1: for it and we found the Higgs. And then we
• 3:13
  Speaker 1: studied it and we've been studying it. And so far,
• 3:16
  Speaker 1: the story is it's the simplest version of the Higgs
• 3:19
  Speaker 1: anybody imagined. We call it the vanilla Higgs because there's
• 3:23
  Speaker 1: nothing complicated about it, which is a little unfortunate because
• 3:27
  Speaker 1: we would love for it to be more complicated and interesting.
• 3:30
  Speaker 2: Okay, but A, didn't you have to build a super
• 3:33
  Speaker 2: complicated machine that costs like billions of dollars to find it?
• 3:37
  Speaker 2: Isn't that complicated?
• 3:40
  Speaker 1: I mean, in that sense, all of life is complicated, Kelly.
• 3:43
  Speaker 1: Putting on a podcast is complicated. Sometimes going to the
• 3:45
  Speaker 1: bathroom is complicated.
• 3:46
  Speaker 2: Oh, my.
• 3:47
  Speaker 1: But when I say what if dark matter is complicated,
• 3:50
  Speaker 1: I mean, what if it's not the simplest version of
• 3:52
  Speaker 1: the story? You know, what we do in physics all
• 3:55
  Speaker 1: the time is we say, here's a big question mark
• 3:58
  Speaker 1: we don't really know how to approach. Let's start by
• 4:01
  Speaker 1: just assuming that the answer is the simplest version we
• 4:04
  Speaker 1: can imagine, the simplest version that works. And we'll go
• 4:07
  Speaker 1: with that. And if the data say otherwise, we'll adapt it,
• 4:10
  Speaker 1: we'll develop it. Or if we just can't find the
• 4:12
  Speaker 1: simplest version, we'll make it more complicated. But it's sort
• 4:15
  Speaker 1: of like an Occam's razor approach, you know, start with
• 4:17
  Speaker 1: the simplest possible description and then add flourishes as you need.
• 4:22
  Speaker 2: Yes, right. If you hear the sound of hooves pattering
• 4:24
  Speaker 2: on the ground, assume horses, not zebras. Got it.
• 4:28
  Speaker 1: Exactly. So we're going to dig into dark matter and
• 4:31
  Speaker 1: all the various forms of it and the ideas of
• 4:33
  Speaker 1: what it might be. In a minute, but today's episode
• 4:36
  Speaker 1: is going to focus on a particular kind of weird
• 4:39
  Speaker 1: dark matter that's fairly popular these days, theoretically. And that's
• 4:43
  Speaker 1: this little particle called a quirk. And so on today's episode,
• 4:47
  Speaker 1: we are going to get quirky and talk about what
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  Speaker 1: quirks are and the quirky ways that we are looking
• 4:52
  Speaker 1: for them. But first, I wanted to know if this
• 4:54
  Speaker 1: particular weird little name for a hypothetical particle... had crossed
• 4:59
  Speaker 1: over into the pop-sci community. So I asked folks out
• 5:03
  Speaker 1: there if they knew what a quirk was. If you
• 5:07
  Speaker 1: would like to join this audience participation segment, we would
• 5:09
  Speaker 1: love to have you write to us to questions at danielandkelly.org.
• 5:14
  Speaker 1: In the meantime, here's what a bunch of extraordinaries thought
• 5:16
  Speaker 1: a quirk might be. Oh, they're odd little behaviors that
• 5:20
  Speaker 1: people express. I would imagine it's something similar to a quirk, maybe,
• 5:24
  Speaker 1: but of You know, maybe it's something that is kind
• 5:29
  Speaker 1: of interesting or funny about something. That's their quirk.
• 5:33
  Speaker 2: I'm pretty sure a quirk is a mutation that gives
• 5:36
  Speaker 2: the person who has it supernatural abilities. I love this.
• 5:40
  Speaker 2: So based on the answers that we've received so far,
• 5:42
  Speaker 2: it looks like they're falling into two categories, which are
• 5:45
  Speaker 2: weird human behaviors or very clever inferences where they're like, oh,
• 5:52
  Speaker 2: it sounds like quark. Yes. So maybe it's related to that.
• 5:56
  Speaker 2: And so I give you all a lot of credit
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  Speaker 2: for being clever.
• 6:01
  Speaker 1: Yeah, I had nothing to do with naming this particle
• 6:04
  Speaker 1: and it's not my favorite name, but it's true that
• 6:06
  Speaker 1: it does sound related to a quark and it is
• 6:09
  Speaker 1: related to a quark. So good job, Marcus, for naming
• 6:13
  Speaker 1: this particle.
• 6:14
  Speaker 2: Wait, well, you know the guy who named the particle?
• 6:16
  Speaker 1: I do. He's a physics professor at UC Davis and
• 6:19
  Speaker 1: a friend of mine.
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  Speaker 2: Oh, well, hi, Marcus. Does Marcus listen to the show?
• 6:24
  Speaker 1: I guess we'll find out. Marcus, let me know if
• 6:26
  Speaker 1: you listen to the show.
• 6:27
  Speaker 2: All right. So you were getting quirky. I'm going to
• 6:33
  Speaker 2: get quirky. Let's start by defining what a quark is. Yeah.
• 6:39
  Speaker 1: So quark with an A is the thing that we
• 6:41
  Speaker 1: already know exists, and it's the foundation of matter. So
• 6:46
  Speaker 1: remember that we are made out of molecules, those molecules
• 6:49
  Speaker 1: are made out of atoms, of the elements, hydrogen, oxygen, carbon, etc.
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  Speaker 1: Those elements all have the same structure, those electrons surrounding
• 6:57
  Speaker 1: a nucleus, and inside the nucleus you have protons and neutrons.
• 7:01
  Speaker 1: Those protons and neutrons are then made out of quarks,
• 7:04
  Speaker 1: in particular, two kinds of quark. There's the up quark
• 7:08
  Speaker 1: and the down quark. And if you add two up
• 7:11
  Speaker 1: quarks together and a down or two down quarks together
• 7:13
  Speaker 1: and up, you get the proton and the neutron. So
• 7:17
  Speaker 1: that's as far as we know so far. The quarks
• 7:19
  Speaker 1: might have structure within them. They might be made out
• 7:22
  Speaker 1: of tiny squiglions or something. But as far as we know,
• 7:24
  Speaker 1: that's the fundamental layer of matter so far.
• 7:28
  Speaker 2: Okay. And I am getting hung up on pronunciation. So
• 7:31
  Speaker 2: you say it. Cork like the cork for a bottle
• 7:34
  Speaker 2: of wine is how it sounds like you're saying it.
• 7:38
  Speaker 1: Well, I think that would be cork and I'm saying quark.
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  Speaker 1: So it's like K-W-A-R-K. Quark.
• 7:44
  Speaker 2: Quark. All right. I'm still not, I'm going to, I'll
• 7:47
  Speaker 2: keep trying. I'll keep trying.
• 7:48
  Speaker 1: Is this an unfamiliar word for you years into the podcast?
• 7:52
  Speaker 1: You're uncomfortable saying the word quirk?
• 7:55
  Speaker 2: No, it's just now that we've thrown quirk in there,
• 7:59
  Speaker 2: it's now my, you know, my head gets, I get
• 8:01
  Speaker 2: it too in my head sometimes. Anyway.
• 8:04
  Speaker 1: Plus you got your little East Coast accent going on
• 8:06
  Speaker 1: there to distort everything a little bit.
• 8:08
  Speaker 2: Makes everything a little bit more complicated, but a lot cooler.
• 8:10
  Speaker 1: Meanwhile, I have the totally neutral West Coast accent, you know,
• 8:15
  Speaker 1: the way English is meant to be spoken.
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  Speaker 2: Super boring.
• 8:18
  Speaker 1: Super boring. Okay.
• 8:19
  Speaker 2: So we think this is a fundamental particle that makes
• 8:22
  Speaker 2: up everything else. Where do we go from there?
• 8:26
  Speaker 1: And there are other kinds of quarks. There's the charm
• 8:29
  Speaker 1: and the strange, the top and the bottom, the six
• 8:31
  Speaker 1: quarks in total. But the lightest quarks are the stable ones,
• 8:35
  Speaker 1: the ones that hang around and you can use to
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  Speaker 1: build matter. So that's a lot of fun. It's a
• 8:39
  Speaker 1: really interesting puzzle. Like, why are there these quarks? What
• 8:41
  Speaker 1: are they made out of, et cetera? But that's the
• 8:43
  Speaker 1: structure of matter at the lowest scale. And again, we
• 8:46
  Speaker 1: treat it as fundamental because that's the simplest version of
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  Speaker 1: the story, but probably it's more complex. Probably they're made
• 8:52
  Speaker 1: out of something internal that we'll see when we build
• 8:55
  Speaker 1: the super duper collider, et cetera. But for now, we
• 8:57
  Speaker 1: can just think of them as fundamental because that story
• 9:00
  Speaker 1: kind of works. And they're named from a poem, Finnegan's Wake.
• 9:05
  Speaker 1: There's a line in there that says, three quarks from Mr. Mark.
• 9:08
  Speaker 1: And so this is like a word I think invented
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  Speaker 1: by James Joyce and Murray Gell-Mann, who named the quarks
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  Speaker 1: as a concept. He pulled that line from the poem.
• 9:18
  Speaker 2: What? I didn't know that. Wait, I thought your friend
• 9:20
  Speaker 2: Maurice named the– what was it?
• 9:25
  Speaker 1: My friend Marcus, who I will now call Maurice because
• 9:29
  Speaker 1: he's a space cowboy and a particle physicist. No, he
• 9:33
  Speaker 1: named Quirks. But Quirks, the thing we actually know exists,
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  Speaker 1: that we're trying not to confuse people about the difference
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  Speaker 1: between these two, even though their names are very similar,
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  Speaker 1: which is the frustrating thing. Quirks were named by Murray Gell-Mond,
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  Speaker 1: who won the Nobel Prize for coming up with the idea.
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  Speaker 2: Got it. Okay. And you really should have gotten a
• 9:49
  Speaker 2: different co-host for today's show, because if pronunciation is going
• 9:53
  Speaker 2: to be something that trips us up, we are doomed
• 9:55
  Speaker 2: from the start. Okay.
• 9:56
  Speaker 1: And the crucial feature of quarks is how they stick together, right?
• 10:00
  Speaker 1: Because we don't see quarks out in the wild. We
• 10:02
  Speaker 1: see pairs of quarks or we see triplets of quarks.
• 10:05
  Speaker 1: Like you take three quarks, you make a proton or
• 10:07
  Speaker 1: a different mixture, you get a neutron. You can also
• 10:10
  Speaker 1: do pairs of quarks to make like a pion or
• 10:12
  Speaker 1: a kaon, all sorts of the whole zoo of particles
• 10:15
  Speaker 1: that are made out of pairs or triplets of these quarks.
• 10:19
  Speaker 1: And the way they stick together is with the strong force.
• 10:22
  Speaker 1: Same way that like the nucleus of the atom and
• 10:24
  Speaker 1: the electron are bound together using electromagnetism. That's the way
• 10:27
  Speaker 1: they attract and the reason they're held together. The way
• 10:30
  Speaker 1: the earth and the sun are bound together using gravity.
• 10:33
  Speaker 1: Quarks are bound together using the strong force, the strong
• 10:36
  Speaker 1: nuclear force, which is the most powerful force we know of.
• 10:39
  Speaker 2: And that's, is that true for all six types of them?
• 10:43
  Speaker 1: All six types of them feel the strong force. And
• 10:46
  Speaker 1: the other particles, electrons, neutrinos, They don't feel a strong
• 10:49
  Speaker 1: force at all. Okay. For those people who think about
• 10:51
  Speaker 1: quantum field theory, they are not charged in the strong force.
• 10:55
  Speaker 1: So they're just like neutral. The way that like a
• 10:57
  Speaker 1: neutrino has no electric charge and so it can fly
• 11:00
  Speaker 1: through an electric field without feeling it, electrons have no
• 11:03
  Speaker 1: strong charge. So they can just fly through a color field,
• 11:07
  Speaker 1: we call it, without feeling it. Okay. But the strong
• 11:10
  Speaker 1: force is also much different from the other forces. Like
• 11:13
  Speaker 1: electromagnetism and gravity... When things get further apart, the bond
• 11:18
  Speaker 1: between them weakens, right? Yep. And you're used to that.
• 11:21
  Speaker 1: And it even follows a cool geometric pattern, one over
• 11:23
  Speaker 1: the distance squared. Just like if you shine a light,
• 11:26
  Speaker 1: the intensity of that light gets weaker with distance. You
• 11:29
  Speaker 1: get further away from a star, it gets weaker and weaker.
• 11:32
  Speaker 1: And it makes sense. It's because the same amount of
• 11:34
  Speaker 1: light is now going through the surface of a larger sphere.
• 11:38
  Speaker 1: And the surface area of a sphere depends on the
• 11:40
  Speaker 1: radius squared. So very cool geometric argument. The strong force
• 11:44
  Speaker 1: ignores all of that. The strong force follows a different rule.
• 11:47
  Speaker 1: It doesn't weaken with distance. After you get past a
• 11:51
  Speaker 1: little distance, the force is constant. So things get further apart,
• 11:55
  Speaker 1: but the force doesn't weaken. It's really, really weird.
• 11:58
  Speaker 2: Whoa. I'm trying to think about the implications for that.
• 12:01
  Speaker 2: I feel like that would make all of the quarks
• 12:02
  Speaker 2: kind of like pull in on each other? That's exactly right.
• 12:06
  Speaker 1: Like collapse in?
• 12:07
  Speaker 2: Okay.
• 12:08
  Speaker 1: It means that, for example, it takes an enormous amount
• 12:10
  Speaker 1: of energy to have two quarks really far apart because
• 12:13
  Speaker 1: they're far apart and the force between them is still
• 12:15
  Speaker 1: fairly strong. And the energy in that bond is the
• 12:19
  Speaker 1: force times the distance. And so as they get further apart,
• 12:21
  Speaker 1: the energy in that bond is huge. So it takes
• 12:24
  Speaker 1: an enormous amount of energy to have two quarks and
• 12:26
  Speaker 1: have them be far apart. And so it just doesn't happen.
• 12:30
  Speaker 1: In fact, we've never seen a quark by itself because
• 12:33
  Speaker 1: quarks just like to be together. What happens if you
• 12:35
  Speaker 1: take two quarks and you pull– yes, cozy, right?
• 12:39
  Speaker 2: Yeah.
• 12:41
  Speaker 1: What happens if you take two quarks that are all
• 12:43
  Speaker 1: snuggled up next to each other nicely and you pull
• 12:45
  Speaker 1: them apart is that it takes a lot of energy.
• 12:49
  Speaker 1: And the universe doesn't like high-energy configurations. It likes lower-energy configurations.
• 12:53
  Speaker 1: It relaxes into lower-energy configurations, like things cool down and
• 12:57
  Speaker 1: balls roll down hills. Well, what it does here is
• 13:01
  Speaker 1: it realizes that there's a lot of energy in this
• 13:04
  Speaker 1: bond and quarks themselves, the particles, are very, very low mass.
• 13:08
  Speaker 1: So they're very easy to make out of energy. So
• 13:11
  Speaker 1: the universe prefers to pop new quarks out of that energy,
• 13:15
  Speaker 1: to turn that energy into new quarks to shorten the distance.
• 13:19
  Speaker 1: So for example, if you take a quark and an
• 13:21
  Speaker 1: anti-quark and you pull them apart, then what will happen
• 13:24
  Speaker 1: is a new quark-anti-quark pair will appear in between them.
• 13:28
  Speaker 1: shortening the distances between the quark pairs.
• 13:31
  Speaker 2: Where do they come from?
• 13:32
  Speaker 1: They just come from the energy of that bond. It
• 13:35
  Speaker 1: takes a huge amount of energy to pull a quark-antiquark apart,
• 13:38
  Speaker 1: and that energy just gets converted to mass because it's
• 13:41
  Speaker 1: a lower energy configuration. It's actually higher entropy configuration, to
• 13:45
  Speaker 1: be precise.
• 13:46
  Speaker 2: Nothing about physics is uncomplicated, Daniel.
• 13:50
  Speaker 1: No, and you're right. The strong force is like the
• 13:52
  Speaker 1: most complicated thing in physics. It's so powerful, it makes
• 13:55
  Speaker 1: it really hard to do any calculations, and anything involving
• 13:58
  Speaker 1: the strong force is a big mess. But it's sort
• 14:01
  Speaker 1: of like if you have a magnet, you have a
• 14:03
  Speaker 1: north and a south, and you cut it in half,
• 14:05
  Speaker 1: then you get a new north and a new south,
• 14:08
  Speaker 1: where the big magnet is now broken into two, right? Okay.
• 14:12
  Speaker 1: And so what happens in practice when we create quark-anti-quark pairs,
• 14:16
  Speaker 1: like the collider- is that you have a lot of
• 14:19
  Speaker 1: energy between them, and they don't just pop out one
• 14:21
  Speaker 1: new pair of particles, they pop out like 10 or 100,
• 14:23
  Speaker 1: so you get like a whole stream of particles. So
• 14:26
  Speaker 1: this is what we call jets, and you might see
• 14:28
  Speaker 1: this if you're reading about particle colliders, is that we
• 14:30
  Speaker 1: get these jets of particles produced. So when you create
• 14:34
  Speaker 1: a quark in a particle collider, you don't see a
• 14:36
  Speaker 1: single particle, you don't see a top quark or an
• 14:38
  Speaker 1: up quark or a charm quark, you see a spray
• 14:41
  Speaker 1: of particles produced from the energy of those bonds.
• 14:45
  Speaker 2: That's kind of fun.
• 14:45
  Speaker 1: Yeah, it's pretty cool.
• 14:47
  Speaker 2: That's sort of like festive of you all to name
• 14:49
  Speaker 2: and describe things that way.
• 14:53
  Speaker 1: And so we know the quarks exist and we've seen them.
• 14:55
  Speaker 1: In fact, we're drowning in them. We make them all
• 14:58
  Speaker 1: the time in the Large Hadron Collider. They like get
• 15:00
  Speaker 1: in the way of other discoveries because they're made so copiously.
• 15:03
  Speaker 1: Jets are everywhere. But we want to understand the universe
• 15:07
  Speaker 1: more deeply. And it turns out that quarks are a
• 15:10
  Speaker 1: way to explain our kind of matter. So protons and
• 15:13
  Speaker 1: neutrons and atoms. But most of the universe is not
• 15:16
  Speaker 1: made out of that kind of matter. So if you
• 15:17
  Speaker 1: want to actually understand what is the universe made out of,
• 15:20
  Speaker 1: what are the rules it follows, what is its fundamental nature,
• 15:23
  Speaker 1: you got to think bigger.
• 15:25
  Speaker 2: But I've got a question first. Do you get jets
• 15:27
  Speaker 2: of particles outside of like the Large Hadron Collider or
• 15:33
  Speaker 2: do you only get them in particle colliders?
• 15:35
  Speaker 1: You only get them in particle collisions when you break
• 15:38
  Speaker 1: up particles, but that happens outside of the particle collider.
• 15:41
  Speaker 1: Like the highest energy collisions on earth are not made
• 15:44
  Speaker 1: by humans. They're made when cosmic rays smash into the atmosphere.
• 15:49
  Speaker 1: And those cosmic rays are just really, really high energy
• 15:51
  Speaker 1: particles shot out from like the centers of other galaxies
• 15:55
  Speaker 1: at insane energies, much higher than we can muster. And
• 15:59
  Speaker 1: so you get these same kind of jets created in
• 16:01
  Speaker 1: the atmosphere.
• 16:02
  Speaker 2: Awesome. Yeah. Man, describing it that way makes it sound
• 16:05
  Speaker 2: like maybe you don't want to live in space where
• 16:07
  Speaker 2: you could get hit with galactic cosmic radiation. But I'm
• 16:10
  Speaker 2: not going to bang on that drum too long. Yeah.
• 16:13
  Speaker 1: You do not want a particle jet in the face.
• 16:15
  Speaker 1: Trust me.
• 16:15
  Speaker 2: No, no, that does not sound fun at all. OK,
• 16:18
  Speaker 2: let's take a break. And when we get back, we
• 16:20
  Speaker 2: will stop talking about quarks and start talking about the
• 16:24
  Speaker 2: other thing. So And we're back and we're going to
• 16:47
  Speaker 2: talk about our space cowboys discovery of quirks. Thanks, Maurice.
• 16:56
  Speaker 1: He didn't discover quirks. We don't know if quirks exist.
• 16:59
  Speaker 1: They're just an idea, Kelly.
• 17:01
  Speaker 2: Oh, all right. Well, let's talk about the idea of quirks.
• 17:04
  Speaker 1: Yeah. So the idea of quirks is connected to the
• 17:07
  Speaker 1: much bigger question of dark matter. Like we have been
• 17:11
  Speaker 1: studying matter for hundreds or thousands of years. but only
• 17:15
  Speaker 1: recently discovered that most of the universe is not this
• 17:17
  Speaker 1: kind of stuff, right? Atomic matter is about 5% of
• 17:22
  Speaker 1: the energy density of the universe. Stuff made out of
• 17:24
  Speaker 1: quarks and electrons and stuff is unusual in the universe.
• 17:28
  Speaker 1: Most of the universe is not this. You know, if
• 17:31
  Speaker 1: the universe was a cupcake, dark energy would be the
• 17:33
  Speaker 1: cakey part, dark matter would be the frosting, and we
• 17:36
  Speaker 1: would be like the sprinkles on top.
• 17:38
  Speaker 2: Okay. I'm hungry now.
• 17:42
  Speaker 1: And so the biggest chunk of that pie, dark energy,
• 17:45
  Speaker 1: huge mystery. We talked about that on a recent episode.
• 17:48
  Speaker 1: But today we're going to focus on dark matter because
• 17:50
  Speaker 1: dark matter is something we know is out there. And
• 17:52
  Speaker 1: the question about dark matter is, what is it made
• 17:55
  Speaker 1: out of? We've studied normal matter, atomic matter. We've drilled
• 17:58
  Speaker 1: down into it. We understand what it's made out of,
• 18:00
  Speaker 1: made out of quarks, et cetera. But we don't know
• 18:03
  Speaker 1: anything about what dark matter is made out of. And
• 18:05
  Speaker 1: yet we know that it's out there.
• 18:07
  Speaker 2: And we know it's not a fudge factor.
• 18:09
  Speaker 1: And we know it's not a fudge factor because- We
• 18:12
  Speaker 1: have overwhelming, independent, multi-pronged evidence for dark matter as matter. Remember,
• 18:18
  Speaker 1: it was originally discovered because we were looking at galaxies,
• 18:21
  Speaker 1: how they rotate, and wondering, like, hey, is there enough
• 18:23
  Speaker 1: gravity in that galaxy to hold it together? Because it's
• 18:26
  Speaker 1: spinning pretty fast. And then they measured the amount of
• 18:28
  Speaker 1: gravity they could see from everything that glows, all the
• 18:31
  Speaker 1: stars and the gas, and there wasn't nearly enough gravity
• 18:33
  Speaker 1: to hold it together. But galaxies are not tearing themselves apart.
• 18:38
  Speaker 1: So that suggested there might be some new kind of
• 18:40
  Speaker 1: invisible matter holding them together. And then we also saw
• 18:44
  Speaker 1: some new kind of invisible matter bending how light moves
• 18:47
  Speaker 1: through the universe. That's gravitational lensing. And we see evidence
• 18:51
  Speaker 1: for a huge amount of invisible matter at the beginning
• 18:54
  Speaker 1: of the universe because it left an imprint on the
• 18:56
  Speaker 1: cosmic microwave background radiation. We see collisions between clusters of
• 19:01
  Speaker 1: galaxies that separate this new kind of invisible matter from
• 19:05
  Speaker 1: the luminous matter. And we can see the invisible matter
• 19:08
  Speaker 1: is there and separated from the luminous matter. It's its
• 19:11
  Speaker 1: own kind of thing. And we look at the structure
• 19:14
  Speaker 1: of the universe and how that's formed over time. And
• 19:16
  Speaker 1: we can only explain that if there's a huge amount
• 19:19
  Speaker 1: of invisible matter pulling gas together to make stars and galaxies.
• 19:25
  Speaker 1: And that structure only forms if dark matter is matter.
• 19:28
  Speaker 1: If it acts like matter, meaning that as the universe expands,
• 19:32
  Speaker 1: it gets diluted in the same way that matter does.
• 19:35
  Speaker 1: So we know it's there. We know there's a lot
• 19:37
  Speaker 1: of it. We know it makes gravity. We know it's matter.
• 19:39
  Speaker 1: The question is, what is it? Is it made out
• 19:43
  Speaker 1: of atoms of a different kind? Is it made out
• 19:45
  Speaker 1: of quarks of a different kind? Is it made out
• 19:47
  Speaker 1: of squiglions? We don't know. That is the deepest biggest
• 19:50
  Speaker 1: question in modern particle physics.
• 19:53
  Speaker 2: Okay, so we're like super confident it exists. We can
• 19:57
  Speaker 2: only measure it indirectly. We can't like look at it
• 20:00
  Speaker 2: and pull it apart.
• 20:02
  Speaker 1: That's right.
• 20:03
  Speaker 2: Does it make sense to assume that it should mirror
• 20:05
  Speaker 2: the matter that we know exists in any way? Because
• 20:09
  Speaker 2: I'm going to assume that the similarity of the names
• 20:11
  Speaker 2: suggests that we are assuming that dark matter has similar
• 20:15
  Speaker 2: things that make it up.
• 20:16
  Speaker 1: Yeah, great question. Well, I think the right approach is
• 20:20
  Speaker 1: let's come up with the simplest description we can that
• 20:24
  Speaker 1: matches the observation and start there. And if that doesn't work,
• 20:28
  Speaker 1: we'll add bells and whistles. And so the simplest thing
• 20:31
  Speaker 1: to do is to say, well, look, all of our
• 20:34
  Speaker 1: kind of matter is made of particles and described by
• 20:37
  Speaker 1: quantum field theory. So what if dark matter is also
• 20:40
  Speaker 1: made of particles, just a different kind of particles, and
• 20:43
  Speaker 1: also described by quantum field theory? And that could be wrong.
• 20:47
  Speaker 1: That's just a guess. We have no evidence that dark
• 20:50
  Speaker 1: matter is made of particles. It could be something totally
• 20:53
  Speaker 1: new and different. We know that it gravitates. That's about it, right?
• 20:58
  Speaker 1: We know that it clumps and it moves, so it's matter.
• 21:02
  Speaker 1: But we don't know if it's actually made of particles.
• 21:04
  Speaker 1: It could be made out of something else, which isn't atomic,
• 21:07
  Speaker 1: like in the sense that it's not made out of pieces, right?
• 21:10
  Speaker 1: It could be that, like, as you zoom in on
• 21:12
  Speaker 1: dark matter, no new structure resolves. It just always looks
• 21:16
  Speaker 1: the same, you know?
• 21:17
  Speaker 2: It's hard to wrap your head around.
• 21:19
  Speaker 1: It is, right? And so we start with maybe it's
• 21:22
  Speaker 1: like the kind of thing we know, which again could
• 21:24
  Speaker 1: be wrong, right? But it's just a place to start.
• 21:27
  Speaker 1: And so I think it's important in physics, especially in
• 21:30
  Speaker 1: popular science, to be clear about what we know and
• 21:32
  Speaker 1: what we don't know. So we're assuming that just so
• 21:34
  Speaker 1: that we have something to do, something to look for.
• 21:38
  Speaker 2: Somewhere to start, not just something to do implies that
• 21:42
  Speaker 2: you're happy spinning your wheels, but you're actually, you're trying
• 21:44
  Speaker 2: to make some progress with this starting point.
• 21:46
  Speaker 1: Well, we want to go out and look for something.
• 21:48
  Speaker 1: And so you need a specific idea of what you're
• 21:50
  Speaker 1: going to look for. You can't just, you know, sit
• 21:53
  Speaker 1: on your roof and smoke banana peels and hope dark
• 21:56
  Speaker 1: matter lands in your lap.
• 21:57
  Speaker 2: Oh, all right.
• 21:58
  Speaker 1: I mean, you can.
• 21:59
  Speaker 2: I mean, smoking banana peels and doing science doesn't have
• 22:01
  Speaker 2: to be mutually exclusive, but okay.
• 22:03
  Speaker 1: Yeah. So one idea, the simplest idea is what if
• 22:08
  Speaker 1: dark matter is one kind of particle? And what if
• 22:11
  Speaker 1: it has some kind of interaction with our matter, some
• 22:16
  Speaker 1: new kind of force? And we haven't seen it before
• 22:18
  Speaker 1: because it's a very, very weak force. Not weak with
• 22:21
  Speaker 1: a capital W as in the weak force, but weak
• 22:24
  Speaker 1: with a lowercase w as in like it's feeble. And
• 22:27
  Speaker 1: we say that it has that kind of force only
• 22:29
  Speaker 1: because that would make it possible for us to discover it.
• 22:32
  Speaker 1: If dark matter only feels gravity, then we have no
• 22:36
  Speaker 1: chance of ever discovering what particle it's made out of
• 22:39
  Speaker 1: because an individual particle has basically no gravity. Gravity already
• 22:44
  Speaker 1: is 10 to the 30 times weaker than everything else.
• 22:47
  Speaker 1: Particles are super duper tiny. So measuring the gravity of
• 22:51
  Speaker 1: a particle seems impossible. So we say, all right, what's
• 22:54
  Speaker 1: the simplest thing we could actually find? And that's dark
• 22:57
  Speaker 1: matter made out of one kind of particle that has
• 23:00
  Speaker 1: a little bit of a force to it that could
• 23:02
  Speaker 1: bump into our kind of particles and we could maybe
• 23:05
  Speaker 1: see that. So there's a big program of research in
• 23:08
  Speaker 1: that direction, like huge, quiet chambers of xenon underground waiting
• 23:13
  Speaker 1: for dark matter to come and bump into one of
• 23:15
  Speaker 1: the xenon nuclei and we could see it. Really cool experiments.
• 23:19
  Speaker 1: Really amazing. Seen nothing so far.
• 23:22
  Speaker 2: Isn't dark matter everywhere? So wouldn't you expect it to
• 23:25
  Speaker 2: be running into xenon like all the time if that was...
• 23:29
  Speaker 2: You've explained this experiment on the show before.
• 23:31
  Speaker 1: Yeah.
• 23:32
  Speaker 2: And I am asking you to do it again.
• 23:35
  Speaker 1: Yeah, you're right. We expect dark matter to be everywhere.
• 23:37
  Speaker 1: We think that we are in the middle of a
• 23:40
  Speaker 1: dark matter ocean. Actually, because it's flying through us, it's
• 23:43
  Speaker 1: more like a dark matter wind. The problem is that
• 23:46
  Speaker 1: the interaction between dark matter and matter has to be really,
• 23:49
  Speaker 1: really small, or we would have seen it already. If
• 23:52
  Speaker 1: the interaction between dark matter and matter was like other
• 23:55
  Speaker 1: kinds of interactions, like electromagnetism or the strong force... It'd
• 23:58
  Speaker 1: be happening all the time. It'd be obvious around us.
• 24:00
  Speaker 1: We would have seen it forever ago. But for us
• 24:03
  Speaker 1: to not have seen it has to be very, very weak.
• 24:05
  Speaker 1: So even though dark matter is everywhere, the chances of
• 24:09
  Speaker 1: a dark matter particle going through a xenon atom and
• 24:12
  Speaker 1: actually interacting and bumping it are very, very small. For
• 24:15
  Speaker 1: the most part, it is phased right through. There are
• 24:17
  Speaker 1: a lot like neutrinos from that point of view.
• 24:20
  Speaker 2: How would you tell the difference between a neutrino that
• 24:22
  Speaker 2: bumped into your xenon particle and dark matter that bumped
• 24:25
  Speaker 2: into your xenon particle?
• 24:26
  Speaker 1: Yeah, really hard to do. And that's one of the
• 24:28
  Speaker 1: things that makes that search much more complicated is that
• 24:31
  Speaker 1: neutrinos are everywhere. And we were hoping for a while
• 24:35
  Speaker 1: that dark matter would have a higher rate of interacting
• 24:37
  Speaker 1: with xenon than neutrinos. And so they would like sit
• 24:41
  Speaker 1: above that, but we haven't seen them, which means that
• 24:43
  Speaker 1: if dark matter does exist, it interacts less often than neutrinos.
• 24:47
  Speaker 1: So then it becomes even harder to spot. You have
• 24:49
  Speaker 1: to see more interactions than you expect from just neutrinos
• 24:53
  Speaker 1: and make a statistical argument. So it's getting pretty tough.
• 24:57
  Speaker 2: Good news is we're a clever species and I think
• 24:59
  Speaker 2: we'll figure it out. But we haven't yet. Okay.
• 25:01
  Speaker 1: And one thing to do is to keep doing those
• 25:04
  Speaker 1: experiments and make them bigger and bigger and more sensitive
• 25:06
  Speaker 1: and try to make it more refined. Another thing to
• 25:08
  Speaker 1: do is to go back and say, hmm, what if
• 25:11
  Speaker 1: one of our assumptions was wrong? Maybe dark matter isn't
• 25:14
  Speaker 1: the simplest possible thing, right? Maybe dark matter is more complicated.
• 25:18
  Speaker 1: And I'm sure a bunch of folks out there are saying, well,
• 25:20
  Speaker 1: how do you know dark matter isn't just made out
• 25:22
  Speaker 1: of quarks? And it's not like, tied up in some
• 25:24
  Speaker 1: particles you haven't seen. And we have an answer to that.
• 25:28
  Speaker 1: We know that dark matter can't be made of quarks
• 25:30
  Speaker 1: because we know a lot about how many quarks there
• 25:32
  Speaker 1: are in the universe. It's an incredible bit of science.
• 25:36
  Speaker 1: But basically, as the universe was cooling very, very early on,
• 25:40
  Speaker 1: there was a moment when the universe was about the
• 25:43
  Speaker 1: density of the center of the sun. And during that moment,
• 25:46
  Speaker 1: it can do what the center of the sun can do,
• 25:48
  Speaker 1: which is fuse to make heavier stuff. And it did.
• 25:52
  Speaker 1: It made helium and a little bit of lithium. And
• 25:55
  Speaker 1: the amount of helium that it made is very sensitive
• 25:58
  Speaker 1: to the density of quarks at that moment. And so
• 26:01
  Speaker 1: because we can measure how much helium there is, and
• 26:04
  Speaker 1: we can tell how much was made in the early universe,
• 26:06
  Speaker 1: we know how many quarks there were billions of years ago.
• 26:10
  Speaker 1: And there's not nearly enough to explain dark matter. So
• 26:13
  Speaker 1: dark matter can't be made out of quarks. But my
• 26:17
  Speaker 1: friend Marcus, who you call Maurice, had another idea. He said, well,
• 26:23
  Speaker 1: what if dark matter is more like our matter? Instead
• 26:26
  Speaker 1: of imagining that it's just made of one particle... What
• 26:29
  Speaker 1: if there's a whole bunch of particles with complicated interactions,
• 26:32
  Speaker 1: like more like a mirror of the kind of matter
• 26:34
  Speaker 1: we know and love? And so he said, well, what
• 26:36
  Speaker 1: if there's a version of quarks, but dark? So like
• 26:38
  Speaker 1: dark quarks. And so instead of calling them dark quarks,
• 26:42
  Speaker 1: which I think is pretty cool, he called them quirks.
• 26:45
  Speaker 2: The Goth in me likes dark quarks.
• 26:47
  Speaker 1: Yeah, right? It makes you feel like black lipstick or something.
• 26:50
  Speaker 2: That's right.
• 26:51
  Speaker 1: So dark quarks or quirks are quark-like particles that that
• 26:56
  Speaker 1: have a dark strong force that binds them together. And
• 27:00
  Speaker 1: so it's a different interaction, it's a different force, but
• 27:03
  Speaker 1: it has the same sort of mathematical structure, et cetera.
• 27:05
  Speaker 1: So you take the idea of quarks bound together by
• 27:08
  Speaker 1: the strong force, you just copy and paste it over
• 27:11
  Speaker 1: to the dark sector and say, we got dark quarks
• 27:13
  Speaker 1: bound together with the dark strong force.
• 27:16
  Speaker 2: OK, but just to be clear, so you said we
• 27:18
  Speaker 2: know that they're not quarks because we know from the
• 27:21
  Speaker 2: beginning of the universe we've got that totally figured out.
• 27:24
  Speaker 2: And so what does it I think I still don't
• 27:25
  Speaker 2: understand what it means to have a dark version of
• 27:29
  Speaker 2: it if it's definitely not a quark.
• 27:31
  Speaker 1: It's definitely not a quark. It's just another idea for
• 27:34
  Speaker 1: what dark matter might be made out of. And this
• 27:36
  Speaker 1: particular theory has one more tweak to it. He says, well,
• 27:40
  Speaker 1: what if we take these dark quarks, these quarks, and
• 27:44
  Speaker 1: we make them heavy? We make them fairly massive. We
• 27:47
  Speaker 1: make them like 5 or 10 or 20 times the
• 27:50
  Speaker 1: mass of a proton. Much, much heavier than the quarks
• 27:53
  Speaker 1: we know and love. What he discovered is that something
• 27:56
  Speaker 1: interesting happens. Let's remember what happens when you produce a
• 27:59
  Speaker 1: pair of quarks. Mm-hmm. in the collider. You pull them apart. Remember,
• 28:02
  Speaker 1: there's a huge amount of energy in that bond, but
• 28:05
  Speaker 1: because quarks are very low mass, they're cheap to make
• 28:08
  Speaker 1: out of energy. What happens is you pop a bunch
• 28:10
  Speaker 1: of them out of that bond. You've got to spray
• 28:12
  Speaker 1: these particles. All right, so now back to the dark sector,
• 28:16
  Speaker 1: the dark quarks, the quirks. What if the quirks are
• 28:19
  Speaker 1: really massive? So when you pull these two particles apart,
• 28:22
  Speaker 1: you don't have the energy to make new ones. There's
• 28:25
  Speaker 1: not enough energy in that bond to make new quirks
• 28:28
  Speaker 1: because quirks cost too much. Well, what's going to happen
• 28:31
  Speaker 1: is that they're going to come back together. So this
• 28:34
  Speaker 1: is really interesting because if you did make a quirk
• 28:38
  Speaker 1: and an anti-quirk at the Large Hadron Collider, what would
• 28:41
  Speaker 1: happen is that they would be produced, they would start
• 28:44
  Speaker 1: moving apart, and then they would come back together and
• 28:46
  Speaker 1: they would oscillate back and forth and back and forth.
• 28:50
  Speaker 1: So this would look very, very different from the kinds
• 28:53
  Speaker 1: of particles we're used to seeing.
• 28:55
  Speaker 2: And because they're massive, should we be able to measure that?
• 28:59
  Speaker 1: Because they're massive, they're too expensive to make out of
• 29:01
  Speaker 1: the energy in their bonds. Their bond remains. And so then, yes,
• 29:05
  Speaker 1: their mass means that we can see them oscillating. Instead
• 29:08
  Speaker 1: of spraying it a bunch of other particles, like we
• 29:10
  Speaker 1: never see quarks by themselves because they're so low mass
• 29:14
  Speaker 1: compared to the energy of their bond that they're surrounded
• 29:17
  Speaker 1: by sprays of other quarks that pull themselves together to
• 29:20
  Speaker 1: make other particles. like we see protons and neutrons and kaons,
• 29:24
  Speaker 1: but quarks are very expensive to make. And so when
• 29:27
  Speaker 1: you do make them, you can see them by themselves.
• 29:30
  Speaker 1: We think that it's possible to see individual quarks if
• 29:33
  Speaker 1: we make them at the collider, and the predictions are spectacular.
• 29:36
  Speaker 1: You know, they have these simulations of what a quirk
• 29:38
  Speaker 1: would look like, and it makes this, like, zigzag almost, this, like,
• 29:42
  Speaker 1: oscillatory pattern in the detector, which looks like nothing else
• 29:46
  Speaker 1: you would ever see in your collider.
• 29:48
  Speaker 2: Do we see that?
• 29:50
  Speaker 1: So I decided to ask that question, and it turns
• 29:51
  Speaker 1: out to be harder to answer than I expected.
• 29:54
  Speaker 2: Because physics!
• 29:56
  Speaker 1: Yeah.
• 29:58
  Speaker 2: Let's take a break. And when we get back, we
• 30:00
  Speaker 2: will have the rare treat of hearing about research that
• 30:03
  Speaker 2: Daniel has done. And we're back and we are talking
• 30:25
  Speaker 2: about Daniel's search for dark quarks. And Daniel, is Maurice
• 30:30
  Speaker 2: a co-author on this paper since you guys are friends?
• 30:34
  Speaker 2: Or does Marcus? Marcus was not part of this study.
• 30:38
  Speaker 1: Marcus, the space cowboy slash physics professor, wrote the original
• 30:41
  Speaker 1: paper on quarks. And there's been a whole bunch of
• 30:43
  Speaker 1: papers following up on this idea because it's theoretically reasonable.
• 30:48
  Speaker 1: Like all you need is dark matter to have interesting
• 30:51
  Speaker 1: particles with interesting interactions. like the strong force and for
• 30:54
  Speaker 1: them to be kind of massive. That turns out to
• 30:56
  Speaker 1: be like not a lot to ask theoretically. So the
• 30:59
  Speaker 1: theorists are like, oh yeah, this could be real. And
• 31:02
  Speaker 1: it makes a kind of spectacular prediction, which would be
• 31:05
  Speaker 1: really fun to see. And so the experimentalists were like, ooh,
• 31:08
  Speaker 1: that sounds like fun. Let's look for it. So it's
• 31:10
  Speaker 1: become sort of popular in the community and a bunch
• 31:12
  Speaker 1: of people have written papers about it. The problem is
• 31:15
  Speaker 1: that though it sounds spectacular and obvious, it actually turns
• 31:18
  Speaker 1: out to be quite hard to find these things.
• 31:21
  Speaker 2: And what makes it so hard? Shouldn't those zigzags be
• 31:24
  Speaker 2: easy to see in the data?
• 31:25
  Speaker 1: I think those zigzags would be easy to see in
• 31:27
  Speaker 1: the data if you knew where to look. Like if
• 31:30
  Speaker 1: I showed you data from the collider that produced quirks,
• 31:34
  Speaker 1: I think you could look at it and be like,
• 31:36
  Speaker 1: oh my gosh, look at that. That's something. Whoa, let's
• 31:38
  Speaker 1: go to Stockholm. The problem is that we have lots
• 31:41
  Speaker 1: and lots and lots of data. You know, we collide
• 31:44
  Speaker 1: particles every 24 nanoseconds and produce these sprays of particles
• 31:48
  Speaker 1: and analyze it. So There's just zillions and zillions of events.
• 31:53
  Speaker 1: And so 50 years ago, we used to analyze this
• 31:56
  Speaker 1: data with trackers. Trackers were people. They would look at
• 31:59
  Speaker 1: an image of a collision and say, oh, here I
• 32:02
  Speaker 1: see a particle. Oh, here I see a particle. Oh,
• 32:05
  Speaker 1: there I see a particle. Wow. And you can find
• 32:07
  Speaker 1: these pictures of these mostly ladies- who sat there analyzing
• 32:10
  Speaker 1: physics data and like finding tracks. And that was cool
• 32:14
  Speaker 1: back in the day when, you know, you just had
• 32:17
  Speaker 1: like a big piece of emulsion and a mountaintop and,
• 32:20
  Speaker 1: you know, collected it once a year and sliced it
• 32:22
  Speaker 1: up and found the tracks. But when you're collecting data
• 32:25
  Speaker 1: at 40 megahertz, you know, there's just not enough tracker
• 32:29
  Speaker 1: ladies in the world to do this. And so we
• 32:32
  Speaker 1: had to move to computerized tracking. And computers, you know,
• 32:35
  Speaker 1: they're very powerful, but they also just follow your instructions.
• 32:38
  Speaker 1: They do what you ask, which means if you don't
• 32:41
  Speaker 1: tell them to look for quirks, then they're not going
• 32:43
  Speaker 1: to find quirks. And the way that we've written our
• 32:46
  Speaker 1: computer programs to find particle tracks makes it impossible for
• 32:51
  Speaker 1: them to ever see quirks.
• 32:53
  Speaker 2: Oh, all right. And so you just need to tell
• 32:55
  Speaker 2: your computer programs, go see dark quirks, and then they will.
• 33:00
  Speaker 1: Exactly. Exactly right. It's that simple. No, it's a fascinating
• 33:05
  Speaker 1: puzzle because it's actually quite hard to write a computer
• 33:08
  Speaker 1: program that will find these particle tracks and do it
• 33:11
  Speaker 1: in a reasonable amount of time. And the reason is
• 33:14
  Speaker 1: that you don't actually see the whole particle. Our detector
• 33:17
  Speaker 1: is like a layer of cameras and each one takes
• 33:19
  Speaker 1: a picture of particles that are going by. And so
• 33:22
  Speaker 1: you never see like a smooth trajectory for a particle.
• 33:24
  Speaker 1: What you see is like a blip here and a
• 33:26
  Speaker 1: blip there and a blip somewhere else. It's like if
• 33:29
  Speaker 1: you saw Bigfoot running across your backyard, but you don't
• 33:32
  Speaker 1: have a video, you have like a strobe light and
• 33:35
  Speaker 1: it takes a picture here and a picture there and
• 33:36
  Speaker 1: a picture there. And then later you put it together
• 33:38
  Speaker 1: into like, okay, here was Bigfoot's trajectory. And so we
• 33:42
  Speaker 1: have that, but we have like 2000 particles all at
• 33:45
  Speaker 1: the same time. And so the job of the computer
• 33:48
  Speaker 1: program is to go through all those little blips and
• 33:50
  Speaker 1: to say, oh, hey, this set of blips, this was
• 33:53
  Speaker 1: a particle. That set of blips, that was a particle.
• 33:55
  Speaker 1: This set of blips over here, this was a particle.
• 33:58
  Speaker 1: And to do that, it has to consider all the
• 34:00
  Speaker 1: possible arrangements. Like what if it's this set of blips?
• 34:03
  Speaker 1: What if it's that set of blips? And when you
• 34:05
  Speaker 1: have thousands and thousands of blips, the number of possibilities
• 34:08
  Speaker 1: is overwhelming. It's just too much, even for very powerful
• 34:11
  Speaker 1: computers to consider all the possibilities. So what we do
• 34:16
  Speaker 1: is what we always do in physics, which is we
• 34:18
  Speaker 1: make simplifying assumptions, right? We start with the simplest version.
• 34:21
  Speaker 1: We say, well, what if we knew something about the
• 34:24
  Speaker 1: shapes of those trajectories, about how they move through space?
• 34:28
  Speaker 1: That would make it easier to find them because we
• 34:30
  Speaker 1: wouldn't have to consider all sorts of weird stuff. So
• 34:32
  Speaker 1: years and years ago, when people were first solving this problem,
• 34:35
  Speaker 1: they said, let's only consider one trajectory, which is a helix,
• 34:40
  Speaker 1: which is how particles move through a magnetic field when
• 34:43
  Speaker 1: they have an electric charge. And that's what these particles are.
• 34:46
  Speaker 1: They're moving through an electric field. And so they said,
• 34:48
  Speaker 1: let's only look for a helix. And so that made
• 34:51
  Speaker 1: the problem solvable. It's still expensive. And a huge fraction
• 34:54
  Speaker 1: of our computing budget at CERN is dedicated to just
• 34:57
  Speaker 1: finding particle tracks. Even if you assume it's a helix,
• 35:01
  Speaker 1: it's still hard and it's still expensive. And so that's
• 35:05
  Speaker 1: the way we find particles now. But if there was
• 35:07
  Speaker 1: a quirk in our data, our computers would ignore it
• 35:10
  Speaker 1: and say, that's not a helix. I'm not looking for that.
• 35:12
  Speaker 1: So trash. And so that's like exciting, but frustrating because
• 35:18
  Speaker 1: it means that On one hand, there could be quirks
• 35:21
  Speaker 1: and they could be in our data and they could
• 35:24
  Speaker 1: be ready to be discovered right now. If you only
• 35:26
  Speaker 1: knew which collision of the zillions and zillions to look at,
• 35:29
  Speaker 1: to put on your screen, your brain could probably pull
• 35:32
  Speaker 1: it out and be like, buy my ticket to Stockholm.
• 35:35
  Speaker 1: But it's frustrating because there's zillions and zillions of collisions
• 35:39
  Speaker 1: and no human could look through all of them. And
• 35:42
  Speaker 1: so we needed to find a way to find tracks
• 35:45
  Speaker 1: that were not helices, find tracks that were other shapes.
• 35:49
  Speaker 2: And is there a particular shape you'd be looking for?
• 35:51
  Speaker 2: So you said they go apart and then they pull
• 35:53
  Speaker 2: back together. Would you be looking for like a detector
• 35:56
  Speaker 2: to get triggered and then triggered again as the particle
• 35:58
  Speaker 2: comes like back together on the way back? Does that
• 36:01
  Speaker 2: make sense?
• 36:02
  Speaker 1: Yeah. Yeah. So that's exactly right. We were looking for
• 36:05
  Speaker 1: a very particular striking kind of pattern for it to
• 36:08
  Speaker 1: move in this oscillatory way for the particles to go
• 36:11
  Speaker 1: out and then come back in and then go out
• 36:14
  Speaker 1: and come back in and oscillate. Or sometimes when they're produced,
• 36:17
  Speaker 1: it produces a pair and they move out together through
• 36:19
  Speaker 1: the detector, but they zigzag sideways. So there's all these
• 36:23
  Speaker 1: really spectacular trajectories happening. that we were looking for. And
• 36:27
  Speaker 1: Marcus came up with this idea for quirks like more
• 36:29
  Speaker 1: than 10 years ago. And there were some folks at
• 36:31
  Speaker 1: Berkeley who had an idea for like how to do
• 36:33
  Speaker 1: a shortcut to maybe find hints that there were quirks,
• 36:36
  Speaker 1: but I wanted to do it a little bit more deeply.
• 36:38
  Speaker 1: I wanted to actually find trajectories of these quirks. And
• 36:41
  Speaker 1: so we used a recent machine learning algorithm to train
• 36:44
  Speaker 1: a computer to find specifically this kind of trajectory. There's
• 36:48
  Speaker 1: a machine learning algorithm that knows how to find particle
• 36:51
  Speaker 1: tracks and you never have to specify exactly what shape
• 36:54
  Speaker 1: you're looking for. like lots of AI or machine learning,
• 36:57
  Speaker 1: you just train it. So we gave it a bunch
• 36:59
  Speaker 1: of examples of quirks that we simulated and we said, hey,
• 37:03
  Speaker 1: here's something you should look for. Hey, learn to look
• 37:05
  Speaker 1: for this thing. We trained it over and over and
• 37:07
  Speaker 1: over again. And then we gave it new data that
• 37:09
  Speaker 1: hadn't seen before that had quirks in it that we
• 37:12
  Speaker 1: just simulated and it was able to find them. And
• 37:15
  Speaker 1: so this was our first paper. We said, okay, it
• 37:18
  Speaker 1: turns out that thanks to machine learning, You can find
• 37:22
  Speaker 1: particle paths that are not the simple helix that most
• 37:25
  Speaker 1: particles move in. You can learn to find other kinds
• 37:28
  Speaker 1: of trajectories. And so now we have a tracker that's
• 37:32
  Speaker 1: able to find quirks that we can run on the
• 37:35
  Speaker 1: data from CERN. And if the quirks are in it,
• 37:38
  Speaker 1: it will pull them out.
• 37:39
  Speaker 2: Well, when are you going to start doing that? Why
• 37:41
  Speaker 2: are you talking to me, Daniel?
• 37:45
  Speaker 1: Well, the challenge is that it's expensive to run because
• 37:48
  Speaker 1: CERN has a lot of data. And running an algorithm
• 37:51
  Speaker 1: over that data costs a lot of computing time. And
• 37:54
  Speaker 1: there's lots of people who think they have great ideas
• 37:56
  Speaker 1: for how to spend that computing time. And they're all right.
• 37:58
  Speaker 1: Everybody's correct. There are a lot of great ideas. So
• 38:01
  Speaker 1: we have to argue that this is worth CERN's computing
• 38:04
  Speaker 1: time to give us access to the data to run
• 38:06
  Speaker 1: over it. And one reasonable objection is like, well, you know,
• 38:11
  Speaker 1: What if it's not quarks? What if there's something else
• 38:13
  Speaker 1: in the data that you didn't expect? What if it's
• 38:16
  Speaker 1: not some helix, but it's something else new? Why just
• 38:19
  Speaker 1: look for quarks? And, you know, this was my concern also.
• 38:22
  Speaker 1: I was like, you know, I don't actually care about quarks.
• 38:25
  Speaker 1: Quarks are cool. They would explain dark matter. Maybe they're real.
• 38:28
  Speaker 1: But the more fascinating idea is what if there's something
• 38:32
  Speaker 1: in our data that's unexpected? Not quarks, but like schmurks or,
• 38:36
  Speaker 1: you know, blurks or whatever. Something that doesn't move as
• 38:39
  Speaker 1: a helix.
• 38:40
  Speaker 2: I hope you get to name something.
• 38:41
  Speaker 1: Something that doesn't move in a weird oscillating pattern. Just
• 38:44
  Speaker 1: something that moves weirdly. Something new and striking. Because in
• 38:48
  Speaker 1: the same way, if you saw that in our data,
• 38:50
  Speaker 1: you'd be like, whoa, that's something new and weird. Your eyes,
• 38:53
  Speaker 1: your brain could identify it. Even if you didn't have
• 38:57
  Speaker 1: a theory yet to motivate it. Because, you know, not
• 39:00
  Speaker 1: all experimental discoveries have to be anticipated, right? It's not
• 39:04
  Speaker 1: like somebody says, I propose particle X, go look for it.
• 39:08
  Speaker 1: We can actually, as experimentalists, discover new things about the nature, right?
• 39:12
  Speaker 1: Without knowing that they exist. And that's my personal scientific
• 39:15
  Speaker 1: fantasy is to find something new and unexpected that when
• 39:19
  Speaker 1: you see people are like, what? That makes no sense.
• 39:22
  Speaker 1: Those are the best discoveries. So we thought about how
• 39:26
  Speaker 1: to take our machine learning quirk tracker and generalize it,
• 39:31
  Speaker 1: make it be able to find anything new, anything weird.
• 39:34
  Speaker 1: And we were able to do it because the way
• 39:37
  Speaker 1: the machine learning algorithm works is you never have to
• 39:39
  Speaker 1: specify the thing you're looking for. You just have to
• 39:42
  Speaker 1: train it. So we took another machine learning code and
• 39:45
  Speaker 1: we trained it to find helices and we trained it
• 39:48
  Speaker 1: to find quirks. And then we just generated a bunch
• 39:50
  Speaker 1: of weird stuff, like all sorts of crazy trajectories. And
• 39:54
  Speaker 1: we trained it to find those. So we showed it
• 39:56
  Speaker 1: all sorts of insane examples. And then we asked, well,
• 39:59
  Speaker 1: is it able to find unexpected stuff? So we came
• 40:03
  Speaker 1: up with even crazier trajectories and it was able to
• 40:06
  Speaker 1: find those. So now we have a machine learning based
• 40:09
  Speaker 1: tracker that's able to find trajectories of particles we haven't
• 40:13
  Speaker 1: even anticipated, for which there is no theory, which if
• 40:17
  Speaker 1: we find it, Some theorist is going to have to go, what?
• 40:19
  Speaker 1: How is that possible? I'm going to have to go
• 40:21
  Speaker 1: back to the chalkboard and figure out how to explain that,
• 40:24
  Speaker 1: which would be amazing. And the other advantage is that
• 40:27
  Speaker 1: now we don't have to just look for quirks. We
• 40:29
  Speaker 1: can look for anything new and weird in the data. So,
• 40:33
  Speaker 1: you know, maybe the data has something new and exciting
• 40:35
  Speaker 1: in it and maybe our tracker is going to find it.
• 40:38
  Speaker 1: I certainly hope so.
• 40:40
  Speaker 2: So as I thought I understood it, LHC, like, gives
• 40:43
  Speaker 2: out its data to anyone whenever, like, or any of
• 40:45
  Speaker 2: the scientists that are associated with the LHC. You can just, like,
• 40:47
  Speaker 2: download the data. What you're saying is that it's not
• 40:50
  Speaker 2: actually how it works. You need to use their computers
• 40:54
  Speaker 2: to run your algorithm to analyze the data because it's
• 40:57
  Speaker 2: just so much data. It's not like they can just, like,
• 40:59
  Speaker 2: send it to you through a tube onto your computer.
• 41:02
  Speaker 1: Okay. I mean, the internet is just a series of tubes,
• 41:05
  Speaker 1: so that is how it works. Yes and no. I
• 41:08
  Speaker 1: can download all the data. I have most of the
• 41:10
  Speaker 1: LHC data here on my laptop, but it's in a
• 41:13
  Speaker 1: very reduced form. It doesn't have all the little blips.
• 41:16
  Speaker 1: It's very, very simplified. And so the access I need
• 41:20
  Speaker 1: is to rerun a really basic initial part of the
• 41:23
  Speaker 1: data processing, which needs the data in like kind of
• 41:26
  Speaker 1: its raw form, which is really, really big and way
• 41:29
  Speaker 1: too big to put in my laptop or even a
• 41:31
  Speaker 1: transfer anywhere. And so the ethos at CERN is bring
• 41:35
  Speaker 1: the job to the data because the data are so big.
• 41:38
  Speaker 1: And so there's a bunch of computers that do have
• 41:40
  Speaker 1: access to that data. And so you need to argue
• 41:42
  Speaker 1: for time on those computers that have access to like
• 41:45
  Speaker 1: the ERP early raw version of the data that has
• 41:48
  Speaker 1: all these blips in it. So we can rerun this
• 41:50
  Speaker 1: particle tracking and maybe see quirks or schmurks or blurks.
• 41:54
  Speaker 2: So when do you think you're going to get an
• 41:56
  Speaker 2: answer on if they're going to let you run it?
• 41:59
  Speaker 2: I need to know the answer now, Daniel. I'm excited.
• 42:02
  Speaker 2: You got me excited about dark quirks.
• 42:07
  Speaker 1: There have been some initial conversations about how to do
• 42:09
  Speaker 1: this inside the collaboration and people are interested and excited
• 42:12
  Speaker 1: and we've got a little team that we're putting together.
• 42:14
  Speaker 1: And so, yeah, I'm hopeful that we'll be able to
• 42:17
  Speaker 1: run this and, you know, maybe something new will pop out.
• 42:20
  Speaker 2: Oh, and are you going to tell us first? Like,
• 42:22
  Speaker 2: don't publish it. Don't publish it. Tell DKEU first.
• 42:26
  Speaker 1: All right. We'll break the news here. If we discover something,
• 42:29
  Speaker 1: you'll be the first to know.
• 42:30
  Speaker 2: I cannot wait till that day comes.
• 42:35
  Speaker 1: So we're trying to understand the nature of matter in
• 42:37
  Speaker 1: the universe, and we figured out what about 5% of
• 42:40
  Speaker 1: it is made out of, though we still have lots
• 42:42
  Speaker 1: of open questions. And we're trying to understand what the
• 42:45
  Speaker 1: dark matter is made out of. Is it made out
• 42:48
  Speaker 1: of some particle? Is it made out of WIMPs? Is
• 42:50
  Speaker 1: it made out of something else? Maybe it's made out
• 42:52
  Speaker 1: of something weird like quarks, these new dark quarks that
• 42:55
  Speaker 1: have a dark, strong force. Or maybe it's made out
• 42:58
  Speaker 1: of something else, something we can't even anticipate. And one
• 43:01
  Speaker 1: of the big challenges is knowing how to look for
• 43:03
  Speaker 1: something new, especially when you have so much data. But
• 43:07
  Speaker 1: machine learning is really changing how we can analyze our
• 43:09
  Speaker 1: data and make things that used to be impossible now possible.
• 43:13
  Speaker 2: Well, you know, I really enjoyed this episode, not just
• 43:15
  Speaker 2: because we got to hear about what Daniel is working on,
• 43:17
  Speaker 2: but because we got to hear about, like, cutting edge,
• 43:20
  Speaker 2: what people are thinking about and how they're trying to
• 43:22
  Speaker 2: solve it right now. And I had a lot of
• 43:25
  Speaker 2: fun today. Awesome.
• 43:26
  Speaker 1: Well, thanks for coming on this quirky journey, everybody. Thanks, everybody,
• 43:36
  Speaker 1: for listening. Please go and do us a favor and
• 43:39
  Speaker 1: rate the show on whatever podcast app you're using. It
• 43:41
  Speaker 1: really helps people find us.
• 43:43
  Speaker 2: Daniel and Kelly's Extraordinary Universe is edited by the amazing
• 43:47
  Speaker 2: Matt Kesselman.
• 43:48
  Speaker 1: He really is a wizard. You can also find us
• 43:52
  Speaker 1: online on Blue Sky, Instagram, and XDNK Universe. Come engage
• 43:58
  Speaker 1: with us.
• 43:58
  Speaker 2: You can email us at questions at danielandkelly.org. We really
• 44:02
  Speaker 2: do want to hear from you.
• 44:04
  Speaker 1: And you can find our website, www.danielandkelly.org, where you'll also
• 44:09
  Speaker 1: find an invitation to join our Discord, where everybody comes
• 44:12
  Speaker 1: and talks about the amazing universe.
• 44:15
  Speaker 2: And we also have the most amazing moderators. This is
• 44:19
  Speaker 2: an iHeart Podcast. Thanks for joining us.