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What are paraparticles? · Daniel and Kelly’s Extraordinary Universe

• 0:13
  Speaker 1: How does the universe work? What are the rules that
• 0:15
  Speaker 1: govern its most microscopic nature. For a few hundred years,
• 0:19
  Speaker 1: we've been making progress on this question, mostly by taking
• 0:22
  Speaker 1: things apart, and when we zoom into the universe at
• 0:25
  Speaker 1: the smallest level, it seems so far like there are
• 0:28
  Speaker 1: two different categories of particles, matter particles like quarks and electrons,
• 0:33
  Speaker 1: and force particles like photons and gluons. For a long time,
• 0:37
  Speaker 1: it seems like that has to be all there is.
• 0:40
  Speaker 1: What else could there possibly be? But experiments aren't the
• 0:44
  Speaker 1: only way to reveal the secrets of the universe. Another
• 0:47
  Speaker 1: very fruitful path is to follow the math. When we
• 0:50
  Speaker 1: ask what else the math allows, we sometimes get predictions
• 0:53
  Speaker 1: for very weird phenomena like antimatter, or black holes or
• 0:57
  Speaker 1: Higgs bosons, which turn out to be real in the universe.
• 1:02
  Speaker 1: So can the math show us another kind of particle?
• 1:05
  Speaker 1: A weird third way beyond matter and forces. Welcome to
• 1:10
  Speaker 1: Daniel and Kelly's Extraordinary mathematical Universe.
• 1:27
  Speaker 2: Hello, I'm Kelly Wiersmith. I study parasites and space, and
• 1:30
  Speaker 2: I think there are four kinds of particles.
• 1:35
  Speaker 3: Are parasites the fourth particle?
• 1:37
  Speaker 2: I mean if physics were any good, the answer would
• 1:39
  Speaker 2: be yes. See what I think is that y'all like symmetry,
• 1:44
  Speaker 2: and I think that if you decide there's three kinds
• 1:46
  Speaker 2: of particles, that will be an odd number and you'll
• 1:49
  Speaker 2: have to decide there's another kind, so that it's even Hi.
• 1:53
  Speaker 3: I'm Daniel.
• 1:53
  Speaker 1: I'm a particle physicist, not a paraparticle physicist or a
• 1:57
  Speaker 1: parasitical particle physicist or any.
• 2:00
  Speaker 3: Those other varieties.
• 2:01
  Speaker 1: But I do love understanding the nature of the universe
• 2:04
  Speaker 1: and finding symmetry in.
• 2:05
  Speaker 2: It all amazing. So are you one of those physicists
• 2:09
  Speaker 2: who feels like there needs to be symmetry in these
• 2:11
  Speaker 2: answers or does it just kind of depend on the topic?
• 2:14
  Speaker 1: Wow, what a deep question to drop on me at
• 2:15
  Speaker 1: the top of the episode. I think what we've learned
• 2:18
  Speaker 1: so far is that there is symmetry in the universe.
• 2:21
  Speaker 1: Like all the rules we've discovered about physics seem to
• 2:25
  Speaker 1: follow symmetric patterns. There's like reflections and translations, and you
• 2:29
  Speaker 1: can generalize this into abstract algebra called group theory. So
• 2:33
  Speaker 1: the universe seems to be well described by symmetries in mathematics.
• 2:37
  Speaker 1: Does that mean the universe is symmetric or that's just
• 2:40
  Speaker 1: the way we like to think about it. I mean,
• 2:42
  Speaker 1: that's a deep question in philosophy. We're not going to
• 2:43
  Speaker 1: answer it today. But I appreciate symmetry.
• 2:46
  Speaker 3: I love it. I love the mathematical beauty of what
• 2:49
  Speaker 3: we've learned about the universe.
• 2:51
  Speaker 2: Why should the universe be symmetrical instead of like just
• 2:53
  Speaker 2: a mess? Like as an evolutionary biologist, like it all
• 2:56
  Speaker 2: being held together with like duct tape and zip ties
• 2:59
  Speaker 2: makes more sense to me then it being beautifully symmetrical.
• 3:01
  Speaker 2: But why is it symmetrical?
• 3:04
  Speaker 1: I think I have a natural preference for explanations that
• 3:08
  Speaker 1: are simple, that are harmonious and parsimonious, right, Like we
• 3:13
  Speaker 1: think that the universe should be in the end described
• 3:17
  Speaker 1: by one simple idea, and so we're constantly looking for that,
• 3:21
  Speaker 1: and symmetry helps us restrain that. It helps us reduce
• 3:24
  Speaker 1: the number of options, you know, like instead of having
• 3:27
  Speaker 1: to come up with ten numbers, what if there's a
• 3:29
  Speaker 1: symmetry that tells you that those numbers are all related,
• 3:32
  Speaker 1: so there really is just one number that turns into ten.
• 3:35
  Speaker 1: But you might also ask the basic question like, well,
• 3:37
  Speaker 1: why do we expect the universe to be simple and parsimonious,
• 3:41
  Speaker 1: and I don't have an answer for that, you know,
• 3:43
  Speaker 1: just so far that seemed to work, you know, looking
• 3:46
  Speaker 1: for the simplest explanation so far has found us things
• 3:49
  Speaker 1: that work in the universe. They predict experiments, they describe
• 3:52
  Speaker 1: things we haven't seen yet. So many times in the
• 3:55
  Speaker 1: history of science we followed the symmetry in mathematics to
• 3:58
  Speaker 1: make discoveries like particles or like electromagnetism. You know, Maxwell
• 4:05
  Speaker 1: looking at these equations and seeing a lack of symmetry
• 4:07
  Speaker 1: and penciling in the piece he needs to make the
• 4:09
  Speaker 1: equation symmetrical, discovering something real in the universe, or Peter
• 4:14
  Speaker 1: Higgs finding a piece that clicks together with all the
• 4:17
  Speaker 1: other pieces to answer why symmetry is broken, so it
• 4:21
  Speaker 1: seems to work, is the only real answer I can
• 4:24
  Speaker 1: give you.
• 4:24
  Speaker 2: Interesting, you know, So I was I'm reading this book
• 4:27
  Speaker 2: called The Remedy right now, and it is about how
• 4:30
  Speaker 2: like Coch and Pasteur determined that microorganisms caused disease. And
• 4:35
  Speaker 2: the author was arguing that actually this kind of flew
• 4:38
  Speaker 2: in the face of we should look for the simplest answer,
• 4:41
  Speaker 2: because the simplest answer at the time was that bad
• 4:44
  Speaker 2: air causes all of these maladies, and so having one
• 4:47
  Speaker 2: cause that explained all of this stuff seemed much simpler
• 4:50
  Speaker 2: than you know, Tuberculosis is caused by this tiny organism,
• 4:54
  Speaker 2: and smallpox is caused by that tiny organism that we
• 4:56
  Speaker 2: can't even see. And so the fact that bad air
• 4:59
  Speaker 2: was simple a sort of made people cling to it
• 5:02
  Speaker 2: a little bit longer than this more complicated answer that
• 5:04
  Speaker 2: tended to be right. And so I think in almost
• 5:05
  Speaker 2: every case it makes a lot more sense to look
• 5:07
  Speaker 2: for the simplest explanation first, but you should not let
• 5:11
  Speaker 2: it close your eyes to the more complex answers that
• 5:13
  Speaker 2: might actually be the reality of the situation.
• 5:15
  Speaker 1: Yeah, you should choose the simplest answer that works, that
• 5:18
  Speaker 1: actually describes the universe. Yes, not the simplest answer that
• 5:22
  Speaker 1: doesn't describe the universe. But you're right, you don't know
• 5:25
  Speaker 1: in advance what's going to work and what isn't, And
• 5:27
  Speaker 1: so we often start from the simplest thing because why
• 5:30
  Speaker 1: not right, And if that doesn't work, then we move
• 5:32
  Speaker 1: on to something more complicated.
• 5:33
  Speaker 3: And that's how we get chemistry and biology and.
• 5:36
  Speaker 1: All sorts of other delicious, beautiful messes of science. Right,
• 5:41
  Speaker 1: that have yet to pull themselves together into a single
• 5:43
  Speaker 1: parsimonious explanation. And that's also one reason why I am
• 5:46
  Speaker 1: a physicist, because physics, I feel like, is closer to
• 5:50
  Speaker 1: getting to a single answer than chemistry is. For example,
• 5:53
  Speaker 1: I was always frustrated in chemistry, like this rule for
• 5:55
  Speaker 1: this thing, and this rule for that thing, and this
• 5:57
  Speaker 1: other rule except for this other scenario. Maybe I just
• 6:00
  Speaker 1: have a bad memory and it's hard to hold all
• 6:02
  Speaker 1: those things in my head. But I just really like
• 6:04
  Speaker 1: to look, here's one equation. Start from that you can
• 6:06
  Speaker 1: get to anything. That just always appealed to me.
• 6:09
  Speaker 2: That's so interesting. I think we live on very different
• 6:11
  Speaker 2: sides of this gradient. So like for me, you know,
• 6:14
  Speaker 2: you said biologists and chemists have yet to come up
• 6:17
  Speaker 2: with a simple theory. I don't feel like that's what
• 6:19
  Speaker 2: we're trying for at all.
• 6:20
  Speaker 1: Like why maybe that's why you haven't found one.
• 6:24
  Speaker 2: Why would you assume that there is one? Like life
• 6:26
  Speaker 2: is beautifully complex, you know, the it depends is where
• 6:29
  Speaker 2: all the fun lives. I think. You know, you're like, oh,
• 6:33
  Speaker 2: that's frustrating, and I'm like, no, that's that's the exciting part.
• 6:36
  Speaker 2: Like what it depends on what life is complicated and
• 6:39
  Speaker 2: messy and that's what makes it beautiful.
• 6:41
  Speaker 1: But isn't it beautiful when you find things that are
• 6:43
  Speaker 1: true across all of life? Right Like DNA, for example,
• 6:46
  Speaker 1: undergirds a lot of life on Earth, and that's really
• 6:48
  Speaker 1: powerful to discover that and to understand it. Right, Yeah,
• 6:51
  Speaker 1: it's not as fascinating as like this one kind of
• 6:54
  Speaker 1: frog does this one kind of thing on random tuesdays
• 6:58
  Speaker 1: in my opinion.
• 6:58
  Speaker 2: Well, I will politely disagree with you. I think what
• 7:02
  Speaker 2: the frogs are doing on tuesdays I am deeply interested in.
• 7:05
  Speaker 2: But yes, you know, I think it's beautiful that you know,
• 7:09
  Speaker 2: the blueprint for life is stored in the same material
• 7:13
  Speaker 2: no matter what organism you're looking at. But we all
• 7:16
  Speaker 2: do very different things with that material. You know, bacteria
• 7:19
  Speaker 2: do horizontal gene transfer. They're swapping genes back and forth,
• 7:22
  Speaker 2: and you know, we have to have sex to swap
• 7:25
  Speaker 2: genetic material, and we've got recombination and I don't know anyway,
• 7:28
  Speaker 2: that's where the it depends gets fun again.
• 7:31
  Speaker 1: Well, we have made a lot of hay in physics,
• 7:33
  Speaker 1: at least in looking for symmetries and then trying to
• 7:37
  Speaker 1: understand when there are holes, is there something to fill
• 7:40
  Speaker 1: that hole? Right the way we did with antiparticles and
• 7:43
  Speaker 1: the way we did with all the quarks, and so
• 7:45
  Speaker 1: often mathematical beauty really does lead us to new discoveries.
• 7:49
  Speaker 1: And that's what we're talking about today on the podcast.
• 7:51
  Speaker 1: Whether there is another bucket, another kind of thing out
• 7:56
  Speaker 1: there in the universe that we can use to describe
• 7:58
  Speaker 1: how everything works, maybe explains why those toads do that thing.
• 8:01
  Speaker 3: On Tuesday, at.
• 8:03
  Speaker 2: The end of all of our banters, I'm like, how
• 8:05
  Speaker 2: are we going to get back on track? And you
• 8:06
  Speaker 2: always get us there.
• 8:07
  Speaker 1: Okay, it's sometimes a bigger step than I expect.
• 8:11
  Speaker 4: But.
• 8:14
  Speaker 2: You're good at jumping that chasm. So all right. So
• 8:17
  Speaker 2: today we're talking about paraparticles and I had never heard
• 8:21
  Speaker 2: of para particles before, and so let's see if our
• 8:24
  Speaker 2: audience is on the same page as Kelly. So we asked,
• 8:29
  Speaker 2: what are para particles? And here are the answers we got.
• 8:32
  Speaker 4: I wonder if it's something to do with larger things
• 8:35
  Speaker 4: showing particle light behavior in certain circumstances. I'm so glad
• 8:40
  Speaker 4: there isn't. TONI exam at the end of the podcast.
• 8:43
  Speaker 2: Piece of a particle, like a very small part of
• 8:47
  Speaker 2: the particle, some sort of entity that exists alongside the
• 8:51
  Speaker 2: traditional particles.
• 8:53
  Speaker 3: Somewhere between a real particle and a ghost particle, like
• 8:57
  Speaker 3: a virtual particle, and then it's enabling interactions with others.
• 9:02
  Speaker 4: I think it's like a super superposition. And it's one
• 9:05
  Speaker 4: of those weird things about quantum mechanics that if you
• 9:08
  Speaker 4: look at it, it just disappears off.
• 9:11
  Speaker 2: I might be particles that we believe exist but haven't
• 9:15
  Speaker 2: I prayed for yet.
• 9:16
  Speaker 3: Kind of like a particle but not quite.
• 9:19
  Speaker 2: Something that acts like a particle when certain conditions are.
• 9:23
  Speaker 3: Met at something that's almost a particle. Paraparticles rely on
• 9:27
  Speaker 3: their neighboring particle for existence. I'm completely stunned by this one.
• 9:32
  Speaker 2: The virtual particle pairs that spring to existence in a vacuum.
• 9:37
  Speaker 2: Is a paraparticle something that lives off of or takes
• 9:41
  Speaker 2: advantage of another particle?
• 9:43
  Speaker 3: Is it a paralyzed particle?
• 9:45
  Speaker 2: So lots of playing with what para means in other contexts.
• 9:49
  Speaker 2: I like it got you all are very clever.
• 9:52
  Speaker 1: But they missed the obvious. Nobody went for the connection
• 9:55
  Speaker 1: to parasites.
• 9:56
  Speaker 2: Guys, Guys, I work so oft hard so hard. Oh wait, no, no, no,
• 10:03
  Speaker 2: that's not true. Somebody said, relying on their neighbors for existence,
• 10:07
  Speaker 2: that's their parasitical particles. That's right way to go, that
• 10:13
  Speaker 2: particular audience member. Thank you for paying attention all this time.
• 10:17
  Speaker 1: I was just glad that nobody went for the sort
• 10:19
  Speaker 1: of anti academic grifter line, the like academics are just
• 10:23
  Speaker 1: parasites on society and they're sucking money and scams and
• 10:27
  Speaker 1: don't really believe anything they're doing, all that bad faith
• 10:29
  Speaker 1: nonsense you sometimes see in various corners of the internet.
• 10:32
  Speaker 2: Oh wow, are you I feel like there's a bit
• 10:35
  Speaker 2: of insecurity today.
• 10:40
  Speaker 1: I just want to address the reality, you know, that
• 10:42
  Speaker 1: kind of stuff is out there in the universe. Anyway,
• 10:44
  Speaker 1: I was very happy to hear all these positive and
• 10:46
  Speaker 1: constructive answers. Thanks everybody. If you'd like to contribute your
• 10:50
  Speaker 1: ideas for future episodes, don't be shy right to us
• 10:52
  Speaker 1: two questions at Daniel and Kelly dot org. You can
• 10:55
  Speaker 1: hear your voice on the podcast.
• 10:57
  Speaker 2: Amazing. All right, So let's dig in. So what are
• 11:00
  Speaker 2: a particle? So you said in the introduction that there
• 11:02
  Speaker 2: are maybe three kinds of particles. Can we start by
• 11:06
  Speaker 2: reviewing the first two kinds, because I'm sure that you've
• 11:09
  Speaker 2: mentioned in the past that particles come in matter and
• 11:12
  Speaker 2: force flavors. But every once in a while, at the
• 11:15
  Speaker 2: end of an episode, I'll discover my brain has reached
• 11:17
  Speaker 2: capacity and maybe some stuff overflowed out the top, and
• 11:21
  Speaker 2: so remind me what are meta particles? What are force particles?
• 11:24
  Speaker 2: And then we'll get into this third kind.
• 11:26
  Speaker 3: Yeah, sure, no problem. I'd be careful with the word flavor.
• 11:29
  Speaker 1: Though flavor has a particular meaning in particle physics, it
• 11:32
  Speaker 1: means something else, and it's not like you know, cookie
• 11:35
  Speaker 1: dough and mint chocolate chip. It's like the difference between
• 11:38
  Speaker 1: electrons and muons and towels or different flavors of leptons.
• 11:42
  Speaker 2: Like that's an actual like physics jargon term is flavors.
• 11:46
  Speaker 1: Oh absolutely, And there's amazing the whole subfield of particle
• 11:49
  Speaker 1: physics called flavor physics. And then the people who work
• 11:52
  Speaker 1: on the flavor of particles that have a lot of mass,
• 11:54
  Speaker 1: that's called heavy flavor physics, which sounds like it should
• 11:57
  Speaker 1: be a hip hop group, but it really is a
• 11:59
  Speaker 1: bunch of nerds.
• 12:00
  Speaker 2: Well, you know, nerds can have hip hop groups. You
• 12:03
  Speaker 2: don't have to be so judgy.
• 12:05
  Speaker 3: Yeah, heavy flavor flakes, let's hear it.
• 12:08
  Speaker 2: I love it.
• 12:10
  Speaker 3: All right.
• 12:10
  Speaker 1: So today we're talking about one way to distinguish particles,
• 12:14
  Speaker 1: and that's by their spin. So there are particles that
• 12:17
  Speaker 1: make up matter, me and you, and everything that's out
• 12:20
  Speaker 1: there and everything you've ever eaten are made out of
• 12:22
  Speaker 1: quarks and lectons. So the upcork and the down cork
• 12:26
  Speaker 1: make up protons and neutrons. You add electrons, which are
• 12:30
  Speaker 1: kind of lefton, and you can make any atom. Right
• 12:33
  Speaker 1: from that, you can make any molecule. And anything anybody
• 12:35
  Speaker 1: has ever seen or thrown at their sister is made
• 12:37
  Speaker 1: out of this kind of stuff, right, Okay, So this
• 12:40
  Speaker 1: is what we call matter particles. And all these particles
• 12:43
  Speaker 1: have something in common, which is their quantum spin has
• 12:46
  Speaker 1: units of one half, which means they can have spin
• 12:48
  Speaker 1: up one half or spin down one half. So all
• 12:51
  Speaker 1: these particles, which we call fermions after Enrico Fermi, these
• 12:55
  Speaker 1: are matter particles. They're particles with one half spin.
• 12:59
  Speaker 2: Can you help me like visualize that, like, are they
• 13:02
  Speaker 2: actually spinning?
• 13:03
  Speaker 1: M You know the answer to that question, Kelly is
• 13:06
  Speaker 1: nobody knows. Quantum spin is a super fascinating topic because
• 13:11
  Speaker 1: on one hand, it's very different from a real spin,
• 13:14
  Speaker 1: like normal spin, like you take a ball and you
• 13:17
  Speaker 1: spin it. We can talk about the angular momentum, we
• 13:19
  Speaker 1: can talk about the velocity on the surface. A classical
• 13:22
  Speaker 1: object has spin and it has angular momentum, right, And
• 13:25
  Speaker 1: we know that that angler momentum is important to the
• 13:27
  Speaker 1: universe because it's preserved. Like if you spin a ball
• 13:31
  Speaker 1: in space, it keeps spinning. And the reason that like
• 13:34
  Speaker 1: our galaxy is spinning is because of conservation of angular momentum.
• 13:37
  Speaker 1: The reason the solar system has the shape that it does,
• 13:40
  Speaker 1: it's like sort of flat. The way the galaxy is
• 13:43
  Speaker 1: a disc is because of angle momentum. Anglementum is a
• 13:45
  Speaker 1: really big important thing in the universe. Things really do spin.
• 13:49
  Speaker 1: Quantum particles don't spin in the same way because electrons
• 13:53
  Speaker 1: are not tiny little balls. And like one hundred years ago,
• 13:56
  Speaker 1: when they were thinking about this, they were like, well,
• 13:58
  Speaker 1: what if they spin, how fast would they be spin?
• 14:00
  Speaker 1: They try to calculate, like how fast the surface of
• 14:03
  Speaker 1: an electron is spinning, and you get an answer that's
• 14:05
  Speaker 1: like higher than the speed of light. So it's obviously nonsense.
• 14:09
  Speaker 1: Whenever you do physics and you get an answer that
• 14:11
  Speaker 1: doesn't make sense, like something has gone wrong along the
• 14:13
  Speaker 1: way right.
• 14:14
  Speaker 2: Or you've created a new field.
• 14:17
  Speaker 1: In this case, the answer is that these are quantum particles.
• 14:20
  Speaker 1: They're not classical, so you can think of them as
• 14:22
  Speaker 1: existing physically the same way, where every part of them
• 14:25
  Speaker 1: has a location every moment in time, so they don't
• 14:29
  Speaker 1: physically spin. You shouldn't think about these quantum particles as
• 14:32
  Speaker 1: like little balls that are spinning, and so you might ask, well,
• 14:35
  Speaker 1: if it's not spinning, why do you call it spin.
• 14:38
  Speaker 1: We call it spin because it has a lot of
• 14:40
  Speaker 1: the same properties as classical objects spin. For example, it's
• 14:44
  Speaker 1: conserved right, and it's conserved together with other kinds of
• 14:49
  Speaker 1: angular momentum, meaning that what the universe cares about is
• 14:52
  Speaker 1: the total angler momentum, including spin. So you can convert
• 14:56
  Speaker 1: like normal angler momentum like the Earth is spinning, into
• 14:59
  Speaker 1: quantum angle momentum spin, and back and forth. The universe
• 15:03
  Speaker 1: requires you to conserve the sum of those two, which
• 15:05
  Speaker 1: tells you they're like the same kind of thing the
• 15:08
  Speaker 1: same way that like energy is often conserved, but it's
• 15:11
  Speaker 1: the sum of kinetic and potential energies. Which tells you like, Okay,
• 15:14
  Speaker 1: these are two kinds of the same thing, because what
• 15:17
  Speaker 1: the universe cares about is the sum of them, not
• 15:19
  Speaker 1: the individual ones. So we know that quantum spin is
• 15:23
  Speaker 1: similar to real spin classical spin because the universe conserves
• 15:27
  Speaker 1: the sum of those things, and quantum spin has other
• 15:30
  Speaker 1: similar properties, like things that have quantum spin and electric
• 15:34
  Speaker 1: charge have little magnetic fields because charges in motion give
• 15:38
  Speaker 1: magnetic fields. So like an electron which is spinning, has
• 15:41
  Speaker 1: a little magnetic field, and that's why it's like bent
• 15:43
  Speaker 1: by magnetic fields, et cetera, et cetera. So we don't
• 15:47
  Speaker 1: really know what it is, but we know that it
• 15:49
  Speaker 1: acts a lot like spin, so we call it quantum spin,
• 15:53
  Speaker 1: which I think is a pretty good name, even though
• 15:54
  Speaker 1: it's not spinning.
• 15:57
  Speaker 2: Okay, all right, So I usually to hear things like
• 16:00
  Speaker 2: four times before they stick in my brain. I think
• 16:02
  Speaker 2: we're at like two, so be prepared to repeat that.
• 16:05
  Speaker 2: But so to try to help me, all right, So, fermions,
• 16:08
  Speaker 2: these are the mass or the matter particles. Yes, and
• 16:12
  Speaker 2: so I'm gonna think of fermions as like it's firm matter.
• 16:16
  Speaker 2: It makes us be although you know now you're gonna
• 16:19
  Speaker 2: misspell fermions from here on out because it's not spelled
• 16:22
  Speaker 2: like firm. But anyway, all right, that's how I'm remembering it.
• 16:24
  Speaker 2: And so now let's talk about force. And so I
• 16:27
  Speaker 2: always thought force was like a field, and I didn't
• 16:30
  Speaker 2: think of it as a particle anyway. So let's go on.
• 16:34
  Speaker 2: So the bosons are force particles.
• 16:38
  Speaker 1: Yes, And let me also liabrate on the comment you
• 16:40
  Speaker 1: made about field versus particles. There are two ways of
• 16:43
  Speaker 1: thinking about what stuff is and how it's pushed. One
• 16:46
  Speaker 1: is the field picture, which is really natural to a
• 16:49
  Speaker 1: lot of particle physicists. There's an electron field, and the
• 16:53
  Speaker 1: electron is actually just a ripple in that field, and
• 16:55
  Speaker 1: there's an electromagnetic field, and photons are ripples in that field.
• 16:59
  Speaker 1: And in that view, the fields are the fundamental thing,
• 17:02
  Speaker 1: and particles are just ripples in those things. They are
• 17:04
  Speaker 1: like emerging phenomena from the fields, and the fields can interact.
• 17:07
  Speaker 1: And we talk about that picture a lot on the podcast.
• 17:10
  Speaker 1: There's another way to think about things and say, you know,
• 17:13
  Speaker 1: fields are just like a construct in our minds. We
• 17:15
  Speaker 1: never see them directly. We only see them acting on particles,
• 17:19
  Speaker 1: and the particles are the things we can see. We
• 17:21
  Speaker 1: see dots on the screen, we see electrons moving through wires, etc.
• 17:25
  Speaker 1: So particles are the real things. And so from that
• 17:28
  Speaker 1: point of view, we have electrons and they're little particles,
• 17:31
  Speaker 1: and we have quarks and their little particles, and then
• 17:34
  Speaker 1: the forces we can talk about other particles. So we
• 17:36
  Speaker 1: have like the photon. What happens when two electrons repel
• 17:39
  Speaker 1: each other, they exchange photons. So this is the particle
• 17:43
  Speaker 1: picture of the universe. Everything is made out of little particles,
• 17:46
  Speaker 1: and it can explain matter. It's a little bit more awkward,
• 17:49
  Speaker 1: but it can also explain forces right in that picture,
• 17:52
  Speaker 1: like electrons exchange photons. That's the way they attract or
• 17:55
  Speaker 1: repel each other. And it's a little bit awkward because
• 17:58
  Speaker 1: like how exactly they do electrons and positrons attract each
• 18:01
  Speaker 1: other by exchanging photons.
• 18:03
  Speaker 3: It's hard to imagine you.
• 18:04
  Speaker 1: Could like attract Zach by throwing a ball at him, right,
• 18:07
  Speaker 1: it feels like it would only push him away. But
• 18:09
  Speaker 1: you know, this is the quantum world, and you can
• 18:11
  Speaker 1: do weird things like you can throw a photon with
• 18:14
  Speaker 1: negative momentum, so when Zach catches it, he's pulled towards you.
• 18:18
  Speaker 1: It's like a tractor beam photon.
• 18:20
  Speaker 2: And biology is too complicated, doesn't make sense. What are
• 18:24
  Speaker 2: you guys thinking?
• 18:26
  Speaker 1: Yeah, yeah, And this is one reason why I think
• 18:28
  Speaker 1: the field picture is a little bit more natural.
• 18:31
  Speaker 3: But anyway, we can.
• 18:31
  Speaker 1: Talk about these forces as mediated by particles. And these
• 18:35
  Speaker 1: particles have a property which is that they don't have
• 18:38
  Speaker 1: half integer spin like one half or negative one half.
• 18:40
  Speaker 1: They have integer spin. So a photon, for example, can
• 18:43
  Speaker 1: have spin one, spin zero or spin negative one. And
• 18:47
  Speaker 1: the W boson and the Z boson, and the Higgs
• 18:49
  Speaker 1: boson and the gluons, all the particles that correspond to
• 18:52
  Speaker 1: the forces and how matter particles exchange momentum, they all
• 18:56
  Speaker 1: have the same property that their spin is integer values,
• 18:59
  Speaker 1: you know, half it's like plus two minus one, this
• 19:02
  Speaker 1: kind of stuff. So those are particles we call bosons.
• 19:06
  Speaker 1: So the fermions and the matter particles, the bosons are
• 19:09
  Speaker 1: the force particles in this picture.
• 19:11
  Speaker 2: All right, So now we've got through the two kinds
• 19:14
  Speaker 2: of particles, and let's bring a little bit of pep
• 19:16
  Speaker 2: into this conversation after the break, So we'll talk about
• 19:19
  Speaker 2: the Paul exclusion principle when we get back all right,
• 19:42
  Speaker 2: So we've established that we have two kinds of particles.
• 19:46
  Speaker 2: We've got the fermions, which are the matter particles, and
• 19:49
  Speaker 2: the bosons, which are the force particles. Why does it
• 19:53
  Speaker 2: matter that we divide them in this way? Why can't
• 19:55
  Speaker 2: they all just be particles.
• 19:58
  Speaker 1: They are all just partticles or fields equivalently, but they
• 20:02
  Speaker 1: have very different behaviors, and that behavior is really important. Specifically,
• 20:07
  Speaker 1: bosons can do something fermions will never ever ever do,
• 20:11
  Speaker 1: which is, bosons can be in the same quantum state
• 20:14
  Speaker 1: and fermions never will. So you made this joke about PEP.
• 20:18
  Speaker 1: The poly exclusion principle, named after Wolfgunning Poll says that
• 20:23
  Speaker 1: no two fermions can ever be in the same quantum state.
• 20:26
  Speaker 1: So if you have two identical particles like two electrons,
• 20:29
  Speaker 1: they can't have all the same quantum description, which would
• 20:33
  Speaker 1: be like their location, their momentum, their spin, their energy,
• 20:37
  Speaker 1: all this kind of stuff. They can't be identical. They
• 20:40
  Speaker 1: have to be unique. Every fermion has to have a
• 20:43
  Speaker 1: different quantum state.
• 20:44
  Speaker 2: Does it make sense to think of that? So our
• 20:46
  Speaker 2: fermions are our matter particles. Does it make sense to
• 20:49
  Speaker 2: think of it as like two pieces of matter can't
• 20:53
  Speaker 2: take up the same space. Or this is like a
• 20:55
  Speaker 2: totally different thing than thinking about it that way.
• 20:58
  Speaker 1: Two pieces of matter can't up the same space as
• 21:01
  Speaker 1: long as they have something to differentiate them. So, for example,
• 21:04
  Speaker 1: electrons have two possible spins right, spin up and spin down.
• 21:08
  Speaker 1: So in the ground state of an atom, for example,
• 21:10
  Speaker 1: you can have two electrons with exactly the same energy,
• 21:14
  Speaker 1: the same momentum, the same location, the same energy, the
• 21:16
  Speaker 1: same everything, but one is spin up and the other
• 21:19
  Speaker 1: is spin down. That's why you have two electrons in
• 21:22
  Speaker 1: the lowest state. That's where that two comes from. Because
• 21:26
  Speaker 1: there are two options for spin. You can't have two
• 21:28
  Speaker 1: electrons both spin up, and you can't have two electrons
• 21:31
  Speaker 1: both spin down.
• 21:32
  Speaker 3: Because of this poly.
• 21:33
  Speaker 1: Exclusion principle, it says you can never have two electrons
• 21:36
  Speaker 1: in the same state, and that's why you don't get
• 21:39
  Speaker 1: all of the electrons in the ground state. If you
• 21:41
  Speaker 1: already have two electrons in that ground state, it's full.
• 21:44
  Speaker 1: It can't take anymore. There's no third spin right, So
• 21:47
  Speaker 1: when another electron comes along, it has to have a
• 21:50
  Speaker 1: higher energy, has to be in the next energy level
• 21:52
  Speaker 1: because the lowest rungs are filled and it's one electron
• 21:55
  Speaker 1: per unique state, right, So the lowest energy level has
• 21:58
  Speaker 1: two of those. The next one, because has more energy,
• 22:01
  Speaker 1: has more options for like where the electron it is
• 22:05
  Speaker 1: around the atom this p state. Now we're getting deep
• 22:07
  Speaker 1: into chemistry, some beyond my expertise right away. But that's
• 22:12
  Speaker 1: why you can have more electrons in that second one,
• 22:14
  Speaker 1: and then more in the third level and more in
• 22:16
  Speaker 1: the fourth because there's more options for differentiating exactly which
• 22:20
  Speaker 1: version of that energy level you're in. And this is
• 22:23
  Speaker 1: why we have chemistry. This is why gold looks the
• 22:26
  Speaker 1: way it does. This is why we have water, this
• 22:28
  Speaker 1: is why atoms bind together. This is why our whole
• 22:32
  Speaker 1: universe looks the way that it does, because fermions cannot
• 22:36
  Speaker 1: be in the same state.
• 22:37
  Speaker 2: Now, is this an observation of what's happening or do
• 22:41
  Speaker 2: we understand why it has to be that way.
• 22:45
  Speaker 1: It's still a little bit mysterious, Like, it's definitely an
• 22:47
  Speaker 1: observation and we've never ever seen it violated. And if
• 22:51
  Speaker 1: it was violated, like the whole universe would look different,
• 22:53
  Speaker 1: Like if somebody turned this rule off and said, hey, fermeons,
• 22:56
  Speaker 1: no problem. You can now share a state. All of
• 22:59
  Speaker 1: matter would collapse.
• 23:00
  Speaker 2: Bad news exactly, it would.
• 23:03
  Speaker 1: Be bad news. So I don't recommend it. If you're
• 23:04
  Speaker 1: sitting in the Universe control room and you have your
• 23:06
  Speaker 1: finger on that knob, call me please before you do anything.
• 23:11
  Speaker 1: We do have some handwavy explanations for why it is.
• 23:14
  Speaker 1: We don't have a really full formal proof. We can't
• 23:17
  Speaker 1: go from like, here are the fields, here's how Fermions
• 23:20
  Speaker 1: will behave. What we can do is prove the negative,
• 23:23
  Speaker 1: like we can show why Fermions can't do this thing,
• 23:28
  Speaker 1: Like we can show that if Fermions did this thing,
• 23:30
  Speaker 1: it would lead to some contradictions. So I'm trying to
• 23:33
  Speaker 1: walk you through a handwavy version of that proof in
• 23:36
  Speaker 1: a minute. But we couldn't have started from scratch and
• 23:40
  Speaker 1: really shown how this happens. And Fineman famously said that
• 23:44
  Speaker 1: we don't have a full proof, and also it's really
• 23:46
  Speaker 1: challenging to give an intuitive explanation for this because quote,
• 23:50
  Speaker 1: we do not have a complete understanding of the fundamental
• 23:53
  Speaker 1: principle involved. Finan was big on this theory that like,
• 23:57
  Speaker 1: if you can't explain it simply, you don't really understand it,
• 24:00
  Speaker 1: which I think is really interesting as a hypothesis because
• 24:03
  Speaker 1: it kind of lines up with what we were talking
• 24:05
  Speaker 1: about earlier, and it touches on something we were talking about,
• 24:08
  Speaker 1: I think on the discord of like how on this
• 24:10
  Speaker 1: pod we're constantly trying to explain complicated stuff in an
• 24:13
  Speaker 1: intuitive way. Without all the math. You can't just be like,
• 24:15
  Speaker 1: here's a bunch of math. This math tells you what
• 24:18
  Speaker 1: the answer is. We want to tell a story that
• 24:20
  Speaker 1: connects with the ideas in your head, so you go, oh,
• 24:23
  Speaker 1: that makes sense.
• 24:24
  Speaker 3: I get it.
• 24:25
  Speaker 1: Why it's this way and not the other way. And
• 24:27
  Speaker 1: that's very different from the mathematical explanation or concepts that
• 24:31
  Speaker 1: we often have in academia and we teach in college
• 24:34
  Speaker 1: and in graduate school, and that most physicists have in
• 24:36
  Speaker 1: their minds. This is like an intuitive grasp of something
• 24:40
  Speaker 1: you have to develop in order to explain it and
• 24:42
  Speaker 1: find me is saying that without that extra piece, this
• 24:45
  Speaker 1: like parallel explanation, that's intuitive, you don't really understand it.
• 24:49
  Speaker 1: And I think that's fascinating and maybe correct. But it's
• 24:52
  Speaker 1: a pretty strong statement of philosophy for a guy who
• 24:54
  Speaker 1: was famously against philosophy.
• 24:56
  Speaker 2: Yeah, and how do you think he would feel about
• 24:59
  Speaker 2: the current state of things today. Although I'm gonna go
• 25:02
  Speaker 2: ahead and admit that I hate questions where they're like,
• 25:04
  Speaker 2: what do you think Benjamin Franklin would think about blah
• 25:06
  Speaker 2: blah blah. It's like, I'm not Benjamin Franklin, and if
• 25:09
  Speaker 2: he was raised in our time, you might feel totally
• 25:11
  Speaker 2: different about things.
• 25:12
  Speaker 1: Yeah, Feineman is a complicated character because, on one hand,
• 25:15
  Speaker 1: super genius dude, lots of important insights, also lots of
• 25:19
  Speaker 1: great explanations, and he did something which I think is
• 25:23
  Speaker 1: really impressive that I've never seen before, which is he
• 25:26
  Speaker 1: came up with an explanation of or a concept in
• 25:27
  Speaker 1: this case Nuther's theorem in one of his popular books,
• 25:30
  Speaker 1: like for a popular Audience, and that explanation then got
• 25:35
  Speaker 1: transformed into a full rigorous proof, which is now the
• 25:38
  Speaker 1: go to rigorous proof you find in like formal physics books.
• 25:42
  Speaker 1: Usually things go the other way, you like, start with
• 25:44
  Speaker 1: a full rigorous proof and then you develop the intuitive explanation.
• 25:47
  Speaker 1: But he actually came up with it for the general
• 25:49
  Speaker 1: public and then it turned into a rigorous proof, So
• 25:52
  Speaker 1: that's pretty cool. Like, the guy definitely had talents and
• 25:55
  Speaker 1: lots of different directions. He's also famously kind of a jerk,
• 25:59
  Speaker 1: and so it's sort of a problematic figure in that sense.
• 26:02
  Speaker 1: I think if finally we're a lot today, he probably
• 26:04
  Speaker 1: would feel grumpy that people had come up with stuff
• 26:06
  Speaker 1: without him.
• 26:09
  Speaker 3: Great, I don't know Hardy.
• 26:12
  Speaker 2: Well, he's in our past. He's in the rear view mirror. Okay.
• 26:15
  Speaker 2: So we have observed that fermions don't occupy the same state.
• 26:19
  Speaker 2: We kind of understand why it would be nice to
• 26:21
  Speaker 2: understand better.
• 26:22
  Speaker 1: And we've observed that bosons can, right. We see this
• 26:26
  Speaker 1: all the time. Like you put two photons in a box,
• 26:29
  Speaker 1: they're very happy to sit right on top of each
• 26:31
  Speaker 1: other to be in exactly the same state. And this
• 26:34
  Speaker 1: lets you do things like make Bose Einstein condensates and
• 26:38
  Speaker 1: macroscopic objects that have quantum properties because all the photons
• 26:42
  Speaker 1: are in the same state, and you can't do that
• 26:44
  Speaker 1: with electrons. You put too many electrons together, they get
• 26:46
  Speaker 1: this degeneracy pressure. They don't want to be in the
• 26:48
  Speaker 1: same lowest state, so some of them have to be
• 26:51
  Speaker 1: in a higher energy state, and that's where you get
• 26:53
  Speaker 1: like pressure. That's why like white dwarves don't collapse because
• 26:57
  Speaker 1: the electrons inside them if they collapse would have to
• 27:00
  Speaker 1: end up being in the same lower energy state, and
• 27:02
  Speaker 1: they resist that they can't do it, and so like,
• 27:04
  Speaker 1: this has real impact in the universe, and it affects
• 27:07
  Speaker 1: how we do experiments and all sorts of stuff. And
• 27:09
  Speaker 1: so this is definitely real and we have some understanding
• 27:13
  Speaker 1: of how it.
• 27:13
  Speaker 3: Works, all right.
• 27:14
  Speaker 2: So fermions are our introverts and the bosons are our extroverts.
• 27:22
  Speaker 1: Electrons just want to be in their own house, like
• 27:24
  Speaker 1: watching their own TV show at night by themselves, and
• 27:27
  Speaker 1: photons are always up for a party.
• 27:29
  Speaker 2: Okay, So now we have a pretty good understanding of
• 27:32
  Speaker 2: fermions and bosons and what they can and can't do.
• 27:35
  Speaker 2: How do we get from here to paraparticles?
• 27:37
  Speaker 3: All right?
• 27:37
  Speaker 1: So to understand how paraparticles might fit into this picture,
• 27:41
  Speaker 1: because it sounds like there are only two options. Either
• 27:44
  Speaker 1: you have half into your spin, you know, one half,
• 27:47
  Speaker 1: three halves, five halves, or you have into your spin
• 27:50
  Speaker 1: zero one, two, three, whatever. What's another option? How could
• 27:53
  Speaker 1: you possibly have a third category?
• 27:55
  Speaker 3: Right?
• 27:55
  Speaker 1: And that was the prevailing wisdom for a long long
• 27:57
  Speaker 1: time until very recently. But to understand where the loophole is,
• 28:01
  Speaker 1: we've got to dig one level deeper into understanding why
• 28:05
  Speaker 1: fermions behave this way and why bosons behave the other way.
• 28:09
  Speaker 1: So we're going to go through this sort of rough
• 28:11
  Speaker 1: and imperfect proof of the poly exclusion principle to explain
• 28:15
  Speaker 1: why fermions behave one way and bosons the other way.
• 28:18
  Speaker 2: Daniel's got pep, All right, let's do that.
• 28:22
  Speaker 1: All right, So imagine two particles, particle one and particle two.
• 28:26
  Speaker 2: In typical physicist fashion. Those are very boring names for them, but.
• 28:29
  Speaker 1: Okay, okay, let's make them exciting names.
• 28:34
  Speaker 3: What would be exciting names for these particles? Now?
• 28:36
  Speaker 2: Feeling if we name them like Frank and Rita, it's
• 28:38
  Speaker 2: gonna be hard to keep track. Maybe one and two
• 28:41
  Speaker 2: was a good idea.
• 28:43
  Speaker 1: Okay, wow, that doctor criticism pretty quickly there. Alright, alright, alright,
• 28:48
  Speaker 1: so particle boring one in particle boring.
• 28:50
  Speaker 2: Two, all right.
• 28:51
  Speaker 1: Now, each of them can do one thing, right now,
• 28:53
  Speaker 1: They have two different options. They can be in state
• 28:55
  Speaker 1: A or state B. Okay, so particle A can do
• 28:59
  Speaker 1: two things. It can be in state A or it
• 29:01
  Speaker 1: can be in state B. Particle two can also be
• 29:03
  Speaker 1: in state A or state B. And then we can
• 29:06
  Speaker 1: describe the full quantum state of the pair of the
• 29:08
  Speaker 1: particles as saying like one A two B. That means
• 29:12
  Speaker 1: particle one is in state A, in particle two is
• 29:15
  Speaker 1: in state B.
• 29:16
  Speaker 2: Right, you could also have one B and two A, right,
• 29:19
  Speaker 2: and I.
• 29:19
  Speaker 1: Understanding absolutely exactly, And so let's do that. Let's take
• 29:23
  Speaker 1: our particles one A to B and let's swap them.
• 29:26
  Speaker 1: These are identical particles, okay, there's nothing different about them.
• 29:30
  Speaker 1: Every electron in the universe, for example, is the same.
• 29:32
  Speaker 1: And so let's just swap them. So we go from
• 29:35
  Speaker 1: one A to B to one B two A. Right now,
• 29:39
  Speaker 1: the quantum field theory of fermions, the math of fermions,
• 29:42
  Speaker 1: because they have spin one half. When you do this,
• 29:46
  Speaker 1: you get a minus sign. So you can't go from
• 29:49
  Speaker 1: one A to B just to one B two A.
• 29:52
  Speaker 1: You go to minus one B two A. You get
• 29:55
  Speaker 1: a negative sign in front of the quantum state. And
• 29:59
  Speaker 1: this has to do with what happens when you're swapping
• 30:01
  Speaker 1: them and you're making a face that tells me I
• 30:04
  Speaker 1: need to pause so you can ask a question.
• 30:06
  Speaker 2: Okay, So we said that you can have one A
• 30:10
  Speaker 2: to B as one state, and you can have one
• 30:14
  Speaker 2: B two A as another state. Yes, but I thought
• 30:17
  Speaker 2: that you were saying that, actually, you can't have one
• 30:19
  Speaker 2: B two A. It has to be negative one B
• 30:22
  Speaker 2: two A.
• 30:22
  Speaker 1: You can have one B two ah. Okay, but if
• 30:25
  Speaker 1: you start with one A two B and then you
• 30:27
  Speaker 1: swap them, you don't end up at one B two A,
• 30:29
  Speaker 1: which you end up with is negative one B two A.
• 30:32
  Speaker 2: Okay.
• 30:33
  Speaker 1: That's like saying, you know, take your driver's license and
• 30:36
  Speaker 1: or flip it around right, you don't necessarily get it
• 30:39
  Speaker 1: in this exactly the same orientation depending on how you
• 30:41
  Speaker 1: spin it.
• 30:42
  Speaker 3: Right.
• 30:43
  Speaker 1: Some things like a sphere, doesn't matter how you spin it,
• 30:45
  Speaker 1: you end up with exactly the same sphere as perfect symmetry.
• 30:48
  Speaker 1: Other things have like a handedness or an orientation right,
• 30:51
  Speaker 1: like or take your left hand and turn it around.
• 30:54
  Speaker 1: It doesn't look exactly like your right hand. Right, maybe
• 30:56
  Speaker 1: it looks like a mirror image of your right hand.
• 30:59
  Speaker 1: It's like negative of your right hand. So this is
• 31:02
  Speaker 1: the part where we're being like a little bit fuzzy
• 31:04
  Speaker 1: and sloppy. But fermions, because they spin one half when
• 31:07
  Speaker 1: you swap them, you get a negative sign in the
• 31:10
  Speaker 1: quantum state.
• 31:11
  Speaker 2: Okay, So that only happens with fermions, not with bosons.
• 31:15
  Speaker 1: Only with fermions, not with bosons. And that's what makes
• 31:19
  Speaker 1: this impossible. That's where we have a contradiction, right, because
• 31:22
  Speaker 1: say you have these two particles in the same state.
• 31:25
  Speaker 1: Say you started with one A two A, right, both
• 31:28
  Speaker 1: particles in the same state.
• 31:29
  Speaker 2: Can't do that, Okay, Oh no, you can with bosons.
• 31:32
  Speaker 1: You can with bosons. Well, let's say we have fermions
• 31:33
  Speaker 1: and we try to do that. Let's try to do
• 31:35
  Speaker 1: that and see what happens. Okay, so we have one
• 31:38
  Speaker 1: A two A where like we put two fermions in
• 31:40
  Speaker 1: the same place, in the same state. Okay, Well, now
• 31:44
  Speaker 1: let's swap them. Well, what happens. Quantum field theory says
• 31:47
  Speaker 1: we get negative one A two A. Okay, right, because
• 31:50
  Speaker 1: when we swap fermions we get a negative sign. But
• 31:52
  Speaker 1: these are supposed to be indistinguishable particles, so if you
• 31:55
  Speaker 1: swap them, you shouldn't get any change because there's no
• 31:58
  Speaker 1: real difference. You're swapping one A to two you have
• 32:01
  Speaker 1: to get one A two A. But quantum field theory says, no,
• 32:03
  Speaker 1: you have to get negative one A two A. So
• 32:06
  Speaker 1: we have two different rules. One that says if you
• 32:09
  Speaker 1: have particles in the same state and they're indistinguishable, and
• 32:12
  Speaker 1: you swap them, nothing happens. And the other rule from
• 32:15
  Speaker 1: field theory that says if they're fermions and you swap them,
• 32:18
  Speaker 1: you get a negative sign. Boom, that's a contradiction. So
• 32:22
  Speaker 1: that tells us you just can't do this. You can't
• 32:24
  Speaker 1: have fermions in the same state because then if you
• 32:27
  Speaker 1: swap them, you get a contradiction. Quantum field theory says
• 32:30
  Speaker 1: you're supposed to get a negative sign. Common sense says
• 32:33
  Speaker 1: you can't get a negative sign if you swap things
• 32:35
  Speaker 1: that aren't different.
• 32:36
  Speaker 2: Okay, So the Pauly exclusion principle is the result of
• 32:40
  Speaker 2: what happens with quantum field theory.
• 32:42
  Speaker 1: Yes, exactly. And you might think, well, what's this negative sign?
• 32:45
  Speaker 1: What is going on there? Remember that this negative sign
• 32:48
  Speaker 1: is part of the quantum state. It's not something we observe, right,
• 32:52
  Speaker 1: a negative sign and a quantum state is not observable
• 32:54
  Speaker 1: because every observable you make is only sensitive to the
• 32:56
  Speaker 1: quantum states squared. Remember quantum state. It can also be
• 33:00
  Speaker 1: like complex numbers. You can have like a wave function
• 33:03
  Speaker 1: has like four plus two I in it, and you
• 33:05
  Speaker 1: can't observe those things, but when you square it, the
• 33:08
  Speaker 1: imaginary part goes away, so we can't observe this. It's
• 33:11
  Speaker 1: like a hidden internal part of the quantum state. We
• 33:13
  Speaker 1: can't observe. And yet the math is there and it's real,
• 33:16
  Speaker 1: and it tells us that fermions cannot do this thing
• 33:19
  Speaker 1: because it leads to an inherent contradiction. Now, spin one particles,
• 33:22
  Speaker 1: bosons are different. Their rules when you swap them are different.
• 33:27
  Speaker 1: If you swap one A two B, and now you're
• 33:29
  Speaker 1: talking about bosons, you don't get the negative sign. You
• 33:32
  Speaker 1: just get one B two A. Everybody's happy. So if
• 33:36
  Speaker 1: you started with one A two A and you swap them,
• 33:38
  Speaker 1: quantum field theory says you get one A two A.
• 33:41
  Speaker 1: Common sense says you get one A two A, no contradiction.
• 33:44
  Speaker 1: Everybody's cool. It's that negative sign, that unobservable negative sign
• 33:48
  Speaker 1: in the quantum state that appears for fermions when you
• 33:51
  Speaker 1: swap them. That causes them to never be allowed to
• 33:54
  Speaker 1: be in the same quantum state if they're indistinguishable fermions.
• 33:58
  Speaker 2: Okay, so just to make sure that I'm under so
• 34:00
  Speaker 2: like negative one and one, they cancel each other out
• 34:03
  Speaker 2: when you add them together.
• 34:04
  Speaker 3: Or when you square them you get the same answer.
• 34:06
  Speaker 2: Okay, And so I should be keeping that in my head.
• 34:09
  Speaker 2: This isn't like we arbitrarily identified that some state is
• 34:13
  Speaker 2: negative one, and you could have called the states A, B,
• 34:16
  Speaker 2: and C. Like there is actually something about negative one
• 34:20
  Speaker 2: and one that is different in an important mathematical.
• 34:24
  Speaker 1: Way, exactly. And the important thing here is fermions have
• 34:28
  Speaker 1: a different kind of spin, and that changes what happens
• 34:30
  Speaker 1: when you swamp them and introduces this negative sign.
• 34:33
  Speaker 3: Okay.
• 34:33
  Speaker 1: And if you're curious about why that is exactly, this
• 34:36
  Speaker 1: is the bit that's famously impossible to explain with intuition.
• 34:39
  Speaker 3: We have math for it.
• 34:40
  Speaker 1: It's called the spin statistics theorem. And even Richard Meineman
• 34:43
  Speaker 1: couldn't come up with an intuitive explanation for it. So
• 34:46
  Speaker 1: I hope you're gonna excuse me for not having one either.
• 34:49
  Speaker 1: But if you take us out a word for that,
• 34:51
  Speaker 1: the fermions, when you swap them, you get a negative
• 34:53
  Speaker 1: sign that's not observable, but it does prevent them from
• 34:56
  Speaker 1: ever being in the same quantum state. Then you can
• 34:58
  Speaker 1: go from there to understand why the Fermi exclusion principle happens.
• 35:02
  Speaker 1: And it's going to lead us to think about the
• 35:04
  Speaker 1: third way that paraparticles might behave And if.
• 35:07
  Speaker 2: You are excited about that, then stick with us, because
• 35:11
  Speaker 2: we're gonna get to it after the break. Okay, so
• 35:33
  Speaker 2: we teased you before the commercial break that we're going
• 35:36
  Speaker 2: to explain to you how para particles behave. Your weight
• 35:39
  Speaker 2: is over, Daniel tell us about paraparticles and how they behave.
• 35:43
  Speaker 1: So for a long time, decades and decades, people thought
• 35:47
  Speaker 1: that fermions and bosons were the only options, not only
• 35:51
  Speaker 1: because hey, look, spin one half and integer spins seemed
• 35:54
  Speaker 1: like the only choices because like spin one third or
• 35:57
  Speaker 1: spin two thirds is impossible, but also in terms of
• 35:59
  Speaker 1: the explanation we just gave, it feels like there are
• 36:02
  Speaker 1: two options. Either you add a negative sign when you
• 36:04
  Speaker 1: swap them, like fermions, which means you can't be in
• 36:06
  Speaker 1: the same quantum state, or you don't like bosons, which
• 36:10
  Speaker 1: means you can be in the same quantum state. So
• 36:12
  Speaker 1: it seems like there's no crack there. It seems like
• 36:14
  Speaker 1: there's no room for another direction. And in the nineteen
• 36:18
  Speaker 1: seventies somebody went to a bunch of math to prove
• 36:21
  Speaker 1: that there is no third option under certain conditions. So
• 36:24
  Speaker 1: like if you live in a universe where space has
• 36:27
  Speaker 1: three dimensions, then there is no other option. You have
• 36:30
  Speaker 1: fermions and you have bosons, and that's its zip and period.
• 36:33
  Speaker 1: So people sort of put this away for a long time.
• 36:35
  Speaker 1: They were like, yeah, well that's done. Somebody proved it
• 36:38
  Speaker 1: dot dot dot. Nobody should ever spend time thinking about
• 36:41
  Speaker 1: it again. And that's like a famous place to make
• 36:43
  Speaker 1: a big discovery, because I'm sure this happens in biology. Also,
• 36:48
  Speaker 1: you have a paper which makes a big advance and
• 36:51
  Speaker 1: then it gets sort of summarized in a shorthanded sort
• 36:54
  Speaker 1: of way that ignores some of the assumptions that went
• 36:57
  Speaker 1: into it, and the conclusions just sort of get broaden
• 37:00
  Speaker 1: a little bit, and then people treat the lore as
• 37:02
  Speaker 1: if it was real and complete, and people rarely go
• 37:05
  Speaker 1: back and read the original paper to discover ooh, actually
• 37:08
  Speaker 1: there are coveyats here. So there are loopholes, and people
• 37:11
  Speaker 1: who do and discover those loopholes and then explore them
• 37:14
  Speaker 1: can like crack open a whole new area of physics.
• 37:17
  Speaker 3: Sometimes.
• 37:17
  Speaker 2: That's why it is so critical to read and to
• 37:19
  Speaker 2: read the original papers.
• 37:21
  Speaker 1: And for those of you wondering what that sound is
• 37:23
  Speaker 1: in the background. That's a big rainstorm in Virginia right now.
• 37:27
  Speaker 2: I love rain. Was that a dig on Virginia?
• 37:30
  Speaker 3: Why do you assume that's a dig? That's definitely not
• 37:32
  Speaker 3: a dig.
• 37:33
  Speaker 2: This is because I know you.
• 37:36
  Speaker 1: This week I'm an Aspen for the Aspen Center for Physics,
• 37:39
  Speaker 1: and it rains every afternoon and I love it. The
• 37:41
  Speaker 1: smell of it in the mountains is just wonderful. The
• 37:45
  Speaker 1: thing I do love about mountain rain is that it
• 37:47
  Speaker 1: ends also quickly.
• 37:48
  Speaker 2: Yeah, well, well those are rainstorms don't last very long.
• 37:52
  Speaker 2: And I am the reason you can hear it is
• 37:54
  Speaker 2: because I converted the tech room in the barn, the
• 37:57
  Speaker 2: horse barn that we have on our property to my office,
• 38:00
  Speaker 2: and so there's a metal roof above me, and so
• 38:03
  Speaker 2: the metal roof really makes the sound of rain much louder,
• 38:06
  Speaker 2: which I love when I'm sleeping up here at night.
• 38:09
  Speaker 2: Every once in a while I have sleepovers up here
• 38:10
  Speaker 2: with my daughter on Friday nights. But anyway, sorry about
• 38:13
  Speaker 2: the background noise, everyone, no problem.
• 38:16
  Speaker 1: And we now have enough background to understand paraparticles because
• 38:19
  Speaker 1: very recently two physicists at Rice University, which we both
• 38:23
  Speaker 1: know and love found some loopholes in this nineteen seventies
• 38:28
  Speaker 1: no go theorem, the one the famously said it's impossible
• 38:31
  Speaker 1: to have anything but a fermion and a boson. And
• 38:34
  Speaker 1: the loophole is, what if you give these particles some
• 38:37
  Speaker 1: other kind of properties, things that like a minus sign,
• 38:41
  Speaker 1: are not observable directly and disappear when you square it right.
• 38:46
  Speaker 1: So like a minus sign is a great example, because
• 38:48
  Speaker 1: you square it, you have plus one. If you didn't
• 38:50
  Speaker 1: have a minus sign, you can't tell plus one squared
• 38:53
  Speaker 1: and minus one squared have the same answer. But they
• 38:55
  Speaker 1: came up with another thing you can add to this particle,
• 38:58
  Speaker 1: like another category, another part of the description, not a
• 39:01
  Speaker 1: minus sign, but like a new dimension to this quantum field,
• 39:06
  Speaker 1: a new attribute, a new label you can give it,
• 39:08
  Speaker 1: and this kind of thing. Also when you square it,
• 39:12
  Speaker 1: it goes away. So there's some technical details here, but
• 39:15
  Speaker 1: the sort of way to understand it intuitively is that
• 39:18
  Speaker 1: these internal states depend on the observer a little bit.
• 39:22
  Speaker 1: So like you and I might see this electron differently
• 39:27
  Speaker 1: because we're different observers and we might make different observations.
• 39:31
  Speaker 3: So it's a little bit of like relativity there. So
• 39:33
  Speaker 3: if you.
• 39:34
  Speaker 1: Add this to some particle states in a weird mathematical way,
• 39:38
  Speaker 1: you can create a new kind of behavior. So it
• 39:41
  Speaker 1: sort of like fuzzes up a little bit, this notion
• 39:44
  Speaker 1: of indistinguishable particles. Are the particles indistinguishable or not? So
• 39:48
  Speaker 1: you might be wondering, well, we have electrons and we
• 39:51
  Speaker 1: have photons. Are there things out there in the universe
• 39:54
  Speaker 1: that follow this new weird quantum math. The answer is,
• 39:58
  Speaker 1: we don't know, not yet. What they've done is show
• 40:02
  Speaker 1: that there is another mathematical description of fields and particles
• 40:07
  Speaker 1: that you can construct that has like a third kind
• 40:10
  Speaker 1: of behavior. It's not a fermion and it's not a boson,
• 40:13
  Speaker 1: but it is self consistent and mathematical. Nobody's built one,
• 40:18
  Speaker 1: but they just sort of like mathematically shown that as
• 40:21
  Speaker 1: far as we know, the rules of the universe don't
• 40:24
  Speaker 1: disallow this.
• 40:25
  Speaker 2: So I don't want to ever question the amazing research
• 40:28
  Speaker 2: that comes out of Rice University. But it sounds like okay,
• 40:31
  Speaker 2: So they're like, well, there's this one thing we can't
• 40:33
  Speaker 2: see and can't measure, and so let's add another thing
• 40:37
  Speaker 2: we can't see or we can't measure. It's just like fire,
• 40:40
  Speaker 2: you know, like biologists can't be like, well, what if
• 40:41
  Speaker 2: the viruses we're wearing hats, maybe we should look for
• 40:46
  Speaker 2: what's a good combination of hat and viruses?
• 40:49
  Speaker 3: Right.
• 40:50
  Speaker 1: This is like taking the quantum particles and saying, hey,
• 40:52
  Speaker 1: we've only been thinking about them wearing cowboy hats.
• 40:55
  Speaker 3: What if they wear other kinds of hats?
• 40:56
  Speaker 1: What if choice of hats is another like degree of
• 40:59
  Speaker 1: freedom for describing these particles. And it turns out if
• 41:03
  Speaker 1: you do that, it cracks this open a little bit
• 41:05
  Speaker 1: and it lets you have another category. And so that's
• 41:07
  Speaker 1: interesting mathematically. It's only interesting physically if it describes the universe.
• 41:12
  Speaker 1: If the universe does this in the same way that
• 41:15
  Speaker 1: like DrAk looked at the solutions to the Shortener equation
• 41:18
  Speaker 1: and he was like, oh, this is interesting. This allows
• 41:21
  Speaker 1: you to have electrons but also allows you to have
• 41:23
  Speaker 1: positively charged particles. That doesn't mean the universe does it, right.
• 41:28
  Speaker 1: It could have just been like a mathematical oddity like, oh,
• 41:31
  Speaker 1: the math allows this, but does the universe choose it?
• 41:33
  Speaker 1: And turns out yes, the universe does choose to make antiparticles,
• 41:37
  Speaker 1: and the universe in many other cases chooses to explore
• 41:41
  Speaker 1: all the avenues of symmetries. We don't know if it does.
• 41:44
  Speaker 3: In this case.
• 41:45
  Speaker 1: What we've shown is that the mathematics of our description
• 41:48
  Speaker 1: of the universe do allow for our third category particles paraparticles,
• 41:52
  Speaker 1: but we don't know if they do ever exist in
• 41:54
  Speaker 1: the universe, and if they do, we don't think they
• 41:57
  Speaker 1: would be fundamental particles the way like photons and electrons are,
• 42:01
  Speaker 1: because there are no fundamental particles we know of that
• 42:04
  Speaker 1: fall into this category. You'd have to make like quasi
• 42:07
  Speaker 1: particles the way you make like anions or plasmons or phonons.
• 42:12
  Speaker 1: These are things that follow the math of particles. But
• 42:16
  Speaker 1: our waves not in a fundamental field like the electromagnetic
• 42:20
  Speaker 1: field or the electron field, but a wave in something else,
• 42:23
  Speaker 1: like a wave in air, or a wave in water,
• 42:26
  Speaker 1: or a wave in electron gas in some weird meta
• 42:30
  Speaker 1: material that solid state physicists cook up in their dark
• 42:33
  Speaker 1: little labs. And so it might be something that people
• 42:36
  Speaker 1: can create in the labs someday in the future and show, oh, look,
• 42:39
  Speaker 1: we've created this new quasi particle that has a different
• 42:43
  Speaker 1: kind of mathematical behavior than fermions or bosons. So that
• 42:47
  Speaker 1: would be cool and something nobody had seen before. Doesn't
• 42:50
  Speaker 1: mean we can make hoverboards or we can make wormholes
• 42:53
  Speaker 1: or anything like that yet, But you never know with
• 42:56
  Speaker 1: fundamental physics, like what's this going to lead to?
• 42:58
  Speaker 3: It's very deep.
• 42:59
  Speaker 1: It's very much at the foundation of quantum field theory
• 43:02
  Speaker 1: and our understanding of like the mathematics of it. So
• 43:04
  Speaker 1: it's exciting when anybody makes any progress in that area.
• 43:08
  Speaker 1: And it's a great example to push back on the
• 43:10
  Speaker 1: nonsense you might hear online that like physics hasn't made
• 43:13
  Speaker 1: any progress since the nineteen seventies. Like, dude, we're making
• 43:16
  Speaker 1: progress all the time. And here's a great example.
• 43:19
  Speaker 2: So are people currently working on experiments to try to
• 43:21
  Speaker 2: find these particles?
• 43:23
  Speaker 3: Yeah, more create than find. People are trying to engineer weird.
• 43:28
  Speaker 1: Exotic materials that might have these behaviors. And this is
• 43:31
  Speaker 1: the kind of stuff solid state physicists love to do,
• 43:34
  Speaker 1: you know. They're like, what if we made super thin
• 43:36
  Speaker 1: layers of graphene and then super thin layers of this,
• 43:40
  Speaker 1: and could we force the electrons to act as if
• 43:42
  Speaker 1: they're in a two D universe? Or can we see
• 43:45
  Speaker 1: superconductivity or whatever. So they're very clever at engineering materials
• 43:51
  Speaker 1: to make quantum states behave in new ways, and that's
• 43:54
  Speaker 1: the most promising way. We might see something that's a paraparticle,
• 43:57
  Speaker 1: you would be an emergent phenomenon, a quad particle that
• 44:00
  Speaker 1: comes out of the behavior of these weird exotic systems
• 44:06
  Speaker 1: and not exotic and like impossible or wrong in any way,
• 44:10
  Speaker 1: just like not something we find in nature usually. But
• 44:13
  Speaker 1: that's the cool thing about being humans. We're like constantly
• 44:16
  Speaker 1: pushing the boundaries and saying, hey, can the universe do this?
• 44:18
  Speaker 1: What happens if we do that? And it teaches us
• 44:21
  Speaker 1: things about the universe. This is how we learn where
• 44:23
  Speaker 1: the boundaries are by pushing them, right, yeah.
• 44:26
  Speaker 2: Yeah, So when we have a guest on our show,
• 44:28
  Speaker 2: you usually end the interview by asking them if an
• 44:32
  Speaker 2: alien were to visit our planets from an advanced civilization,
• 44:36
  Speaker 2: and you ask them if their thing exists on their
• 44:39
  Speaker 2: home planets. That's your way of testing how confident they
• 44:41
  Speaker 2: are that the thing actually exists. So, Daniel, if aliens
• 44:45
  Speaker 2: from an advanced civilization landed on Earth, do you think
• 44:48
  Speaker 2: they would know about paraparticles and would think that paraparticles existed?
• 44:52
  Speaker 1: This is a great question and a fair one, since
• 44:54
  Speaker 1: I just wrote a whole book on how aliens might
• 44:56
  Speaker 1: think about the universe. Y'all should check it out. It's
• 44:59
  Speaker 1: coming out in November. It's called Do Aliens Speak Physics.
• 45:02
  Speaker 1: I'm really excited about it.
• 45:03
  Speaker 2: Two sums way up.
• 45:05
  Speaker 1: My personal suspicion is that particle physicists are too up
• 45:10
  Speaker 1: in their own heads and they think that the whole
• 45:13
  Speaker 1: universe uses their mathematical description of how things work. And
• 45:17
  Speaker 1: that's just like too self centered to put ourselves at
• 45:20
  Speaker 1: the heart of the understanding of the universe. And likely
• 45:24
  Speaker 1: there's a bunch of arbitrary assumptions we've made, and probably
• 45:27
  Speaker 1: aliens have a completely different description of how the universe works,
• 45:30
  Speaker 1: and they're like, what, why are we even using quantum fields?
• 45:33
  Speaker 1: That makes no sense. Here's a much simpler way. But
• 45:36
  Speaker 1: if they are using quantum fields, then I think this
• 45:39
  Speaker 1: is an inevitable discovery.
• 45:41
  Speaker 3: They would make.
• 45:41
  Speaker 1: And they might have even found other ways, like there
• 45:43
  Speaker 1: might be four, seventeen or ninety two different kinds of
• 45:46
  Speaker 1: particles and they're like, what y'all have only found three?
• 45:49
  Speaker 1: Come back to us. You can join the cosmic society
• 45:51
  Speaker 1: when you're up to ten.
• 45:53
  Speaker 2: When you found particles, Then if they talk to us exactly.
• 45:59
  Speaker 1: Yeah, and maybe they'll listen this podcast and ooh, particles
• 46:01
  Speaker 1: and parasites.
• 46:02
  Speaker 3: Maybe these guys are on the right track.
• 46:03
  Speaker 2: Oh my gosh. Yeah, at least they'll think that we're interesting.
• 46:07
  Speaker 1: Aliens, if you are listening, please don't zap ups from
• 46:10
  Speaker 1: outer space.
• 46:10
  Speaker 2: Come talk to us, tell us about your secrets, and
• 46:12
  Speaker 2: tell us about your parasites, but keep it to yourselves,
• 46:17
  Speaker 2: all right.
• 46:18
  Speaker 1: Thanks everyone for going on this journey with us into
• 46:20
  Speaker 1: the heart of particle physics, how it works, what we know,
• 46:23
  Speaker 1: what we don't know, and the hints that mathematics is
• 46:26
  Speaker 1: giving us about what we might learn about the fundamental
• 46:28
  Speaker 1: nature of space and time and matter and energy and aliens.
• 46:33
  Speaker 2: See y'all next time. Daniel and Kelly's Extraordinary Universe is
• 46:43
  Speaker 2: produced by iHeartRadio. We would love to hear from you,
• 46:46
  Speaker 2: We really would.
• 46:47
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• 46:50
  Speaker 1: Extraordinary Universe.
• 46:52
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• 46:55
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• 46:59
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• 47:05
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