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Speaker 1: Hey, Daniel, why do particle physicists obsessed so much about mass?

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Speaker 2: Well, mass is one of the basic properties of a particle.

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Speaker 2: It's like part of its identity.

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Speaker 1: Whoa is that? Healthy?

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Speaker 3: Though?

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Speaker 1: You think your mass should define who you are?

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Speaker 2: I don't think we have to worry too much about

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Speaker 2: like particle mental health.

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Speaker 1: Yeah, but shouldn't they be defined by their magnetism or

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Speaker 1: how colorful they are?

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Speaker 2: Well, we're all made of particles, so I guess we

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Speaker 2: can just decide for ourselves how to identify with them.

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Speaker 1: You are your particles, right, my particles are me? No,

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Speaker 1: I'm pretty sure it's the other way around.

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Speaker 2: It depends if you believe in strong or weak emergence.

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Speaker 1: That is a massive detail, right there. I am Poor Hamm,

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Speaker 1: a cartoonists and the author of Oliver's Great Think Universe.

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Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor

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Speaker 2: at UC Irvine, and I really wish there was more

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Speaker 2: we could know about each particle.

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Speaker 1: What do you want to know?

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Speaker 2: I want to get to know them. You know, particles

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Speaker 2: are kind of like black holes. There's a few things

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Speaker 2: you can measure about it, the spin, the mass, the charge,

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Speaker 2: et cetera. But otherwise they're all totally identical. It's not

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Speaker 2: like this particle is Bob and that one is Sam

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Speaker 2: and this one is Juanita. You know, all electrons are

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Speaker 2: the same.

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Speaker 1: What if they don't want to be known? What if

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Speaker 1: they're private particles?

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Speaker 2: I see they're all spartacles.

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Speaker 4: Huh.

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Speaker 1: Yeah, they have secrets. They don't want the Walsh out

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Speaker 1: there on the internet.

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Speaker 2: Well, like I've said before, I don't think the universe

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Speaker 2: deserves any privacy. You know, we are curious creatures and

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Speaker 2: we're part of the universe, so knowing ourselves is sort

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Speaker 2: of like knowing the universe.

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Speaker 1: Are you saying. Physicists then are sort of like professional boxers.

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Speaker 2: I like to think of as more as the detectives

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Speaker 2: maybe private snoops. Yeah, we are snoops for sure, and

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Speaker 2: we're out to solve the biggest mystery in the universe,

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Speaker 2: which is like, how does this whole thing all work?

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Speaker 1: Did you change your jaw title then to a particle

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Speaker 1: snooper particle investigator? I'm a PI a PPI. I guess

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Speaker 1: I don't like having PP in my title. Yeah, PP's

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Speaker 1: not good on many things. But yeah, anyways, welcome to

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Speaker 1: our podcast Daniel and Jorge Explain the Universe, a production

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Speaker 1: of iHeartRadio in which we.

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Speaker 2: Try to lift the level of discourse as best we can,

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Speaker 2: elevating your mind to the deepest, biggest, most ethereal questions

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Speaker 2: in the universe. How does it all work, what's it

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Speaker 2: all made out of? What are the rules of the game,

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Speaker 2: and how is the game played in such a way

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Speaker 2: to give us this crazy, amazing, visceral conscious experience of

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Speaker 2: such a real world, which in the end is made

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Speaker 2: up of tiny, little, almost massless particles.

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Speaker 1: Yeah, because it is a pretty awesome experience to exist

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Speaker 1: in the universe and to look out there and appreciate

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Speaker 1: all the wonders and amazing things that are happening out

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Speaker 1: there in the universe that we can see and also

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Speaker 1: that we can't see.

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Speaker 2: And as we drill down into the nature of reality,

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Speaker 2: taking things apart into molecules and atoms and nuclei and

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Speaker 2: protons and neutrons, we like to give names to these things.

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Speaker 2: We say, oh, this kind of thing is an electron,

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Speaker 2: and that kind of thing is a neutrino, and this

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Speaker 2: kind of thing as a quark. It's just part of

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Speaker 2: who we are to want to attach labels to bits

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Speaker 2: and pieces of the universe.

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Speaker 1: Yeah, it's all part of humans quests to understand what's

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Speaker 1: going on out there, to get a handle on how

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Speaker 1: things work and how to predict what's going to happen

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Speaker 1: in the future.

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Speaker 2: And as we look at these tiny little particles, we

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Speaker 2: want to describe them in ways that make sense to us.

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Speaker 2: You know, how much spin does it have? What can

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Speaker 2: it do? And maybe at the most fundamental level, part

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Speaker 2: of the identity of a particle is how much mass

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Speaker 2: does it have?

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Speaker 1: Yeah, some particles have a little bit of mass, some

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Speaker 1: particles have a lot of and some particles have no mass. Right,

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Speaker 1: some particles adheres to a very impressive diet.

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Speaker 2: Photons have no mass, while top quarks, the heaviest known

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Speaker 2: fundamental particle, have the mass of like one hundred and

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Speaker 2: seventy five protons. So there really is an extraordinary range,

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Speaker 2: which is something that we don't understand at all. But

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Speaker 2: mass is also part of how we tell which particle

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Speaker 2: is which. I think about an electron and a muon.

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Speaker 2: What are the differences there between the two? They're almost

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Speaker 2: identical particles, except that muons have more mass than electrons do.

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Speaker 2: And when we produce particles in our experiments. That's how

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Speaker 2: we tell what's what. We measure the masses of these

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Speaker 2: particles and we say, oh, this one's got to be

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Speaker 2: an electron because look at its mass. So it's not

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Speaker 2: just that we take the particles, we assign mass labels

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Speaker 2: to them. We use the mass to tell us who

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Speaker 2: is who.

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Speaker 1: Yeah, and there are lots of particles out there. Some

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Speaker 1: of them are not shy at all about how much

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Speaker 1: mass they have. Some of them are a little bit

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Speaker 1: shy and don't necessarily want to reveal how much mass

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Speaker 1: he has.

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Speaker 2: Some of the weirdest particles out there are neutrinos, these

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Speaker 2: ghostly little particles that are everywhere but very hard to spot.

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Speaker 2: And in the case of neutrinos, their identity is something

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Speaker 2: of a more complex story. They have sort of two

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Speaker 2: different kinds of clothing they can wear, who they talk to,

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Speaker 2: and how they move through the universe. And because their

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Speaker 2: mass is so weird and so hard to nail down,

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Speaker 2: it's not something we actually know very well.

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Speaker 1: It's all a big mystery. And so today on the

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Speaker 1: podcast we'll be asking the question how massive is a neutrino?

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Speaker 2: Or maybe we should have said, how massive isn't a neutrino?

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Speaker 1: Wait? What why shouldn't we have not said.

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Speaker 2: That because neutrinos have some masks, but they definitely aren't very.

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Speaker 1: Massive, or how very little massive nutrina is? Is that

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Speaker 1: what I mean?

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Speaker 2: How dainty is a neutrino?

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Speaker 5: Yeah?

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Speaker 1: I thought you meant, like, how significant in nutrino is?

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Speaker 1: Like how massive it is it in a universal scale

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Speaker 1: of awesomeness?

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Speaker 2: Yeah. It actually turns out neutrinos are quite important and

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Speaker 2: play a big role in the physics of the universe

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Speaker 2: despite being almost invisible. So from a consequential point of view, right,

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Speaker 2: neutrinos are massive. Dude.

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Speaker 1: Well, I think what you're saying is that the mass

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Speaker 1: of the neutrino is not known. We don't know how

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Speaker 1: much mass it has.

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Speaker 2: We do not know how much mass the neutrino has.

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Speaker 2: We've only known that it has mass for a couple

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Speaker 2: of decades, which was a big shocker and sent quakes

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Speaker 2: through the theoretical community when we figured that out, and

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Speaker 2: it's still something that is very hard to pin down

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Speaker 2: and not something we know.

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Speaker 1: It was a massive shock weighed heavily on the minds

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Speaker 1: of physicists for a long time.

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Speaker 2: They didn't take it lightly, that's for sure.

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Speaker 1: So yeah, this is an interesting question. How much maths

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Speaker 1: does and theatrino have. Apparently it's kind of tricky to

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Speaker 1: find out. So as usually, we were wondering how many

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Speaker 1: people out there had thought about this question or have

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Speaker 1: an idea about the mass of a nutrino.

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Speaker 2: So thanks very much to everybody who answers these questions

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Speaker 2: for this fun segment. If you'd like to hear your

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Speaker 2: voice speculating for everybody else's entertainment and education, please write

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Speaker 2: to us two questions at Danielandjorge dot com.

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Speaker 1: So think about it for a second. How massive do

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Speaker 1: you think a neutrino is? Here's what people have to say.

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Speaker 3: Not sure if the vibe was that there's more than

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Speaker 3: one type of neutrino. So maybe there's like some with

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Speaker 3: more mass. But I thought that neutrinos were like massless

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Speaker 3: or like had negligible mass and so like they travel

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Speaker 3: at the speed of light.

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Speaker 6: I think there's different types of neutrinos that are different sizes.

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Speaker 6: You talked about one of NASA finding another universe by

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Speaker 6: seeing neutrinos pass through Earth. So there's some massive ones

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Speaker 6: but not so massive. How big maybe like fifty protons

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Speaker 6: big or something, if that even makes sense, And maybe

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Speaker 6: neutrinos are also dark matters what you also said in

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Speaker 6: one of your earlier podcasts.

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Speaker 2: I would think that a neutrino is real light because't

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Speaker 2: interact with other particles, but it may interact with the

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Speaker 2: Higgs field. So I actually have no idea.

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Speaker 7: Well neutrino so eno means very small in Italian or smaller,

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Speaker 7: so I would assume that the mass of a neutrino

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Speaker 7: is much much much smaller than that of a neutron,

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Speaker 7: and I'm tempted to say that.

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Speaker 5: Neutrinos are massless.

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Speaker 4: Maybe mass is just I think the amount of energy

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Speaker 4: that's required to move something, so gravitational mass is just

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Speaker 4: a unique form of inertial mass, wherein it's the gravity

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Speaker 4: which is pulling you and that changes according to where

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Speaker 4: you are, whereas inertial mass is just independent of that.

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Speaker 4: I guess I.

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Speaker 5: Don't know how massive a neutrino is. I'm pretty sure

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Speaker 5: that I've heard that they have mass, and I think

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Speaker 5: it's extremely like neutrinos are very low mass, and it

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Speaker 5: would be great if they had the lowest amount of

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Speaker 5: mass allowed by quantum mechanics. That would be pretty.

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Speaker 1: Neat, right. I think a lot of people seem to

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Speaker 1: know it had very little mass.

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Speaker 2: I really like the linguistic analysis, reverse engineering the name

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Speaker 2: particle to infer what its mass has to be.

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Speaker 1: What do you mean it has neutral mass?

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Speaker 2: Well, you know, neutrino means little neutral particle. That was

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Speaker 2: the name given to it before we even really knew

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Speaker 2: what it was, because that's all we knew about it,

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Speaker 2: that it could be very massive and that it was

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Speaker 2: electrically neutral. So in that sense, you might even be

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Speaker 2: tempted to say that it's a well named particle.

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Speaker 1: They were going to say it has the mass of

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Speaker 1: a newt. But also you kind of have to know

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Speaker 1: Italian to know that the io ending, you know, know,

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Speaker 1: means small, don't you not everyone speaks Italian.

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Speaker 2: That's true. I guess if it had been named by

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Speaker 2: somebody who speaks Spanish, would be like nutrito.

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Speaker 1: Yeah exactly. Or in English, I guess, how would you

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Speaker 1: call it new trini neutral?

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Speaker 2: Do we have affectionate endings in English?

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Speaker 1: Tiny neutron? There you go, like tiny tim?

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Speaker 2: Or maybe we'd give it an ironic nickname you know,

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Speaker 2: like big.

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Speaker 1: Neutron, Yeah, neutronizer or something, or how about just neutron.

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Speaker 1: I mean that sounds pretty massive now in comparison to neutrino.

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Speaker 2: Neutron had already been discovered. Is the name of another particle?

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Speaker 1: Oh well, there you go, that one's misnaming them. All right, Well,

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Speaker 1: let's dig into this mystery. What is the massive a neutrino?

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Speaker 1: But I guess far as Daniel talk to us about

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Speaker 1: what a neutrino actually is.

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Speaker 2: Neutrino is a really fun particle because it's so weird

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Speaker 2: and yet so fundamental and so important and at the

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Speaker 2: same time not a part of the matter that's around us.

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Speaker 2: You know, if you take a part the stuff that

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Speaker 2: you're made out of, and that I'm made out of,

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Speaker 2: and that everything you've ever eaten is made out of,

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Speaker 2: you discover that it's made of atoms, and those atoms

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Speaker 2: are made of protons and neutrons and electrons. But the

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Speaker 2: protons and neutrons can be made out of quarks, up

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Speaker 2: quarks and down quarks. Specific that means that everything that

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Speaker 2: we know is made of two kinds of quarks, up

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Speaker 2: quarks and down corks, as well as electrons. So really

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Speaker 2: just three particles explain all of the matter that we know,

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Speaker 2: the stuff that the Earth is made out of, that

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Speaker 2: the Sun is made out of, that the visible matter

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Speaker 2: in the galaxy is made out of. Of course, put

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Speaker 2: dark matter aside because we don't know what that is

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Speaker 2: made out of. So those three particles sort of underlie

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Speaker 2: everything that exists. But there's another particle that's in the

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Speaker 2: same category as like one of the basic templates of

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Speaker 2: possible matter, and that's the neutrino. Because you notice that

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Speaker 2: the upcork and the down cork sort of have each other.

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Speaker 2: There's like a pair of quarks. You might wonder like, well,

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Speaker 2: who's the electrons partner, And the electron does have a partner,

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Speaker 2: it's the new trino. So it sort of like completes

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Speaker 2: the quartette of the fundamental bits of matter, even though

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Speaker 2: the neutrino doesn't appear in the atom and isn't used

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Speaker 2: to make up your lunch or your dinner or anything

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Speaker 2: you've ever eaten.

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Speaker 1: Hmmm, I guess maybe the first question I would have

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Speaker 1: is why not why they aren't neutrino's part of the

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Speaker 1: matter that we're made at it, or why don't we have,

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Speaker 1: you know, neutrino bits inside of us.

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Speaker 2: Yeah, it's a great question. You know, the universe has

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Speaker 2: these bits and pieces, and they have rules for how

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Speaker 2: they can come together, and then you get complex structures

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Speaker 2: emerging from that. You know, you have quarks bind together

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Speaker 2: to make protons and neutrons, which then bind with the

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Speaker 2: electron to make atoms, to make all sorts of other

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Speaker 2: complex stuff. I scream and stars and black holes and

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Speaker 2: all that stuff. And really it's the interaction. They're the

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Speaker 2: binding that's crucial. While quarks and electrons all have electric charges,

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Speaker 2: and quarks have strong charges, so they can use the

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Speaker 2: more powerful forces to build complex matter. Neutrinos are different

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Speaker 2: from the other three kinds of basic fundamental bits of

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Speaker 2: stuff in that they only feel the weak force, so

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Speaker 2: they have no electric charge, they're neutral, and they also

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Speaker 2: have no color, so they don't feel the strong nuclear force,

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Speaker 2: which means they're only left to interact via gravity, which

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Speaker 2: is basically negligible for a particle and the weak force.

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Speaker 2: So in order to bi old something out of neutrinos,

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Speaker 2: you'd have to have them bound together by the weak force,

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Speaker 2: but the weak force is just too weak to do that.

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Speaker 1: Interesting, What do you mean too weak? Like you can't

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Speaker 1: stick to nutriinas together with the weak force.

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Speaker 2: The weak force can be used to interact, but it's

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Speaker 2: really very, very shockingly weak. That's why, for example, if

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Speaker 2: you shoot a photon at the wall, it'll splat against

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Speaker 2: the wall and interact with all the electrons inside of it.

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Speaker 2: But if you shoot a neutrino against the same wall,

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Speaker 2: it will fly right through. It's not like it's finding

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Speaker 2: holes in the wall. It's not like the wall is

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Speaker 2: a screen or a mesh that it's slipping through. It

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Speaker 2: ignores all those particles because it doesn't interact with them.

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Speaker 2: So it's really all about the strength of the interactions.

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Speaker 2: And if you wanted to like bind two neutrinos together

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Speaker 2: into a more complex object, that have to be in

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Speaker 2: a bound state in order to be trapped together by

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Speaker 2: an interaction that's so weak, they would have to be

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Speaker 2: almost motionless. It wouldn't take very much energy to break

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Speaker 2: it apart, So you'd have to have very cold bits

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Speaker 2: fall together to make a bound state and then be

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Speaker 2: very easy to break it apart. So it's basically not

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Speaker 2: possible to build more complex structure using the weak force.

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Speaker 1: I think you're saying that you can, but maybe matter

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Speaker 1: would have to be super duper cold to put together

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Speaker 1: things with the weak force.

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Speaker 2: Yeah, matter would have to be super duper cold, and

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Speaker 2: they would have to not be other stronger forces disrupting it.

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Speaker 1: Right, I don't know how does the weak force work.

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Speaker 1: Does it repel or attract or both? Does it have

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Speaker 1: positive negative charges to it?

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Speaker 2: So the weak force is quite complicated. We talked once

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Speaker 2: about whether the weak force can attract or repel. It

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Speaker 2: actually can do both. There are two different charges for it.

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Speaker 2: They're called isospin and weak hypercharge, and so it's a

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Speaker 2: complex combination of all these different numbers that tells you

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Speaker 2: what the weak force is going to do. But in short,

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Speaker 2: it can attract and it can repel. So it's very

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Speaker 2: similar to electromagnetism. Actually, electromagnetism and the weak force together

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Speaker 2: are part of a larger idea called electro week And

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Speaker 2: the reason that one of them is more powerful than

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Speaker 2: the other has to do with the Higgs boson, which

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Speaker 2: breaks the symmetry between the two forces, leaving one of

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Speaker 2: them very powerful and one of them very very weak.

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Speaker 1: So, like if I took two neutrinos, and I cooled

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Speaker 1: them down out there in space and I stuck them together.

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Speaker 1: Would they stick together due to the weak force?

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Speaker 2: You could put two neutrinos into a bound state if

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Speaker 2: they were very, very cold, so they didn't have enough

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Speaker 2: kinetic energy to escape these bonds and there was nothing

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Speaker 2: else bothering them. Yes, you could. And you could even

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Speaker 2: add more.

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Speaker 1: Yeah, you could add more. Maybe can you build a

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Speaker 1: whole planet out of neutrinos?

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Speaker 2: You could build larger, more complex structures, but it would

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Speaker 2: be very fragile, and it certainly wouldn't look like a planet,

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Speaker 2: and the whole thing could probably pass through the Earth

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Speaker 2: without even noticing, because neutrinos, again don't interact with normal matter.

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Speaker 2: So even if you build more complex structures out of neutrinos,

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Speaker 2: it exists sort of in parallel to us, the same

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Speaker 2: way that like dark matter does. Dark matter is here,

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Speaker 2: dark matters everywhere. Dark matter might make complex structures that

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Speaker 2: we can't see, but they passed right through us, and

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Speaker 2: we passed right through them because we don't have any

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Speaker 2: interactions with them, the same way a neutrino can pass

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Speaker 2: through like a light year thick wall of lead without

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Speaker 2: even interacting. And so a whole planet of neutrinos would

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Speaker 2: do the same thing. Like, right now, there's one hundred

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Speaker 2: billion neutrinos passing through every square centimeter of the surface

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Speaker 2: of the Earth every second, and yet we don't feel them.

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Speaker 2: So somebody could throw a planet of neutrinos at us

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Speaker 2: and we wouldn't even notice.

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Speaker 1: Would that neutrino planet break apart when it goes through

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Speaker 1: us or would it stay together?

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Speaker 2: A tiny fraction of those neutrinos would interact with us,

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Speaker 2: so those a little bonds would break up, but most

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Speaker 2: of it would totally ignore us. Neutrinos have a very

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Speaker 2: very tiny probability of interacting with electrons or with quarks.

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Speaker 1: So and then when you say weak, do you mean

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Speaker 1: like low probability or just that the force is weak?

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Speaker 2: We mean low probability, not small momentum exchange, but low probability.

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Speaker 2: Like you shoot a neutrino at another particle, it's very

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Speaker 2: unlikely to interact. If it does interact, it can impart

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Speaker 2: significant momentum, it's just a low probability of it happening.

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Speaker 1: Oh, that's interesting. So it's really called the weak force

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Speaker 1: because of its weak probability, not because like you wouldn't

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Speaker 1: feel it.

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Speaker 2: Yeah, exactly. The very strength of the forces are more

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Speaker 2: about the probability of that interaction, which, if you integrate

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Speaker 2: over all possibilities, does end up playing a role in

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Speaker 2: like its impact on the world, basically how massive is

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Speaker 2: its impact.

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Speaker 1: So then maybe like a better name for the weak

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Speaker 1: force would have been improbable for us, the unlikely.

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Speaker 2: Force, the unlikely force that makes it sound like it's

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Speaker 2: going to go on a hero's journey and in the

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Speaker 2: end it become the most powerful force in the universe.

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Speaker 1: That's right, the underdog for exactly What else do we

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Speaker 1: know about neutrinos.

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Speaker 2: We know that there are three kinds of neutrinos, the

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Speaker 2: way that there's like three different kinds of electron. There's

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Speaker 2: the more massive version that's the muon and the even

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Speaker 2: more massive version that's the tau, So there's three different

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Speaker 2: flavorers of electron. There's also three different flavors of neutrino.

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Speaker 2: So there's a neutrino associated with the electron, the electro

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Speaker 2: and neutrino, and one associated with the muon and one

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Speaker 2: associated with the taw.

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Speaker 1: What do you mean associated? What does that mean? They

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Speaker 1: signed a contract?

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Speaker 2: Well, these guys interact via the weak force, and so

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Speaker 2: for example, if you want to make an electron, you

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Speaker 2: can make it from a w boson. A W boson

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Speaker 2: can decate to an electron, but also decays to a neutrino.

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Speaker 2: And when you create an electron, you also create an

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Speaker 2: electron neutrino. You create a muon, then you also create

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Speaker 2: a muon neutrino. So when we say associated with, we

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Speaker 2: mean like grouped together with by the weak force. It

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Speaker 2: groups these guys together. Remember that we count the number

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Speaker 2: of eleptons in the universe and that's conserved. So for example,

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Speaker 2: you can't just like make more electrons. If you make

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Speaker 2: more electrons, you also have to make more anti electrons

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Speaker 2: to balance out the number of electrons in the universe.

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Speaker 2: But electron neutrinos fall into that category. So you can

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Speaker 2: make an electron and then you make an anti electron neutrino,

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Speaker 2: and the universe's books are all balanced.

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Speaker 1: Like an electron and a neutrino are sort of like twins,

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Speaker 1: like you can have you can make one without the other.

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Speaker 2: You can make an electron either with an anti electron

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Speaker 2: neutrino or with an anti electron, So like a boson

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Speaker 2: will de kate to an electron and an anti electron

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Speaker 2: neutrino together, or a z boson will dekate to an

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Speaker 2: electron and an anti electron. You can't just make an

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Speaker 2: electron by itself.

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Speaker 1: So there's it sounds like there are more electrons and

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Speaker 1: there are anti electrons and electron latrinos.

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Speaker 2: There's definitely more matter than antimatter. So yeah, they're more

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Speaker 2: electrons than anti electrons. But when it comes to the neutrinos,

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Speaker 2: like we have these pairings. So there's three different flavors

401
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Speaker 2: of neutrino, the muon, the electron, and the town neutrino.

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Speaker 2: Each one is connected to one of these leptons because

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Speaker 2: the weak force likes to make those together.

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Speaker 1: That's just something we've observed, right, Like we noticed that

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Speaker 1: the weak force, when it does things in the universe,

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Speaker 1: it creates these things in pairs. Like is there anything

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Speaker 1: else we know about them that associates them, Like do

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Speaker 1: they have the same quantum varible about it?

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Speaker 2: I like the way you say, that's just what we observed,

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Speaker 2: Like that's basically science, right. We observe the universe and

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Speaker 2: then we describe it, and then we try to boil

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Speaker 2: that description down to a couple a set of rules

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Speaker 2: as possible, and think about what that means. So, yeah,

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Speaker 2: that's just what we've observed. We've never seen this be violated.

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Speaker 2: So there's an asterisk there. We'll talk about neutrino oscillation

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Speaker 2: in a minute, but yeah, really that's the only difference

417
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Speaker 2: we know about it from these different kinds of neutrinos

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Speaker 2: that the weak force associates them with different leptons, with electron,

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Speaker 2: a muon, or a taw. The other question, of course,

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Speaker 2: is about their masses, like what are the masses of

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Speaker 2: these particles. We know that for normal matter, all the

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Speaker 2: quarks and the electron, the masses tend to increase as

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Speaker 2: you go to their copies, like the muon is heavier

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Speaker 2: than the taw. The upcork has heavier versions the charm

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Speaker 2: and the top. The down cork has heavier versions the

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Speaker 2: strange and the bottom. When it comes to the neutrinos,

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Speaker 2: we don't know so much about what their masses are

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Speaker 2: and how that's organized.

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Speaker 1: All right, it sounds like a good cue for us

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Speaker 1: to dig deeper into the mass of the neutrino and

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Speaker 1: talk about how we know it has mass and how

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Speaker 1: we measure that mass. So let's get into that, but

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Speaker 1: first let's take a quick break. All right, we're talking

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Speaker 1: about the mass of a neutrino specifically, what is its mass?

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Speaker 1: Is it a lot, is it a little? And why

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Speaker 1: is it the way it is? So we talked about

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Speaker 1: what a neutrino is. They are ghostly particles that fly

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Speaker 1: around the universe without really interacting with the rest of

439
00:21:25,240 --> 00:21:27,919
Speaker 1: the matter in the universe. Daniel a quick question. Do

440
00:21:27,960 --> 00:21:29,080
Speaker 1: they interact with dark matter?

441
00:21:29,400 --> 00:21:33,160
Speaker 2: Ooh, yeah, great question. We don't know. For a long

442
00:21:33,160 --> 00:21:36,399
Speaker 2: time we wondered if neutrinos were the dark matter, like

443
00:21:36,400 --> 00:21:38,800
Speaker 2: they kind of fit the bill because we can't really

444
00:21:38,840 --> 00:21:40,960
Speaker 2: see them and there's maybe a lot of them out there.

445
00:21:41,119 --> 00:21:44,040
Speaker 2: Turns out neutrinos can't be the dark matter because we

446
00:21:44,119 --> 00:21:47,320
Speaker 2: know the dark matter moves slowly, it's cold. We know

447
00:21:47,400 --> 00:21:50,080
Speaker 2: that from like how it's influenced the structure of the universe.

448
00:21:50,119 --> 00:21:52,880
Speaker 2: If dark matter moved faster, things would be less lumpy,

449
00:21:53,080 --> 00:21:56,520
Speaker 2: and neutrinos move really really fast, So neutrinos are too

450
00:21:56,560 --> 00:21:59,600
Speaker 2: hot to be the dark matter. Do neutrinos interact with

451
00:21:59,680 --> 00:22:01,880
Speaker 2: dark man? We don't think so, because we don't think

452
00:22:01,920 --> 00:22:05,280
Speaker 2: that dark matter feels the weak force or the improbable force,

453
00:22:05,320 --> 00:22:07,280
Speaker 2: as you'd like to call it, because if it did,

454
00:22:07,280 --> 00:22:08,919
Speaker 2: we would have seen it bump into some of our

455
00:22:08,960 --> 00:22:12,520
Speaker 2: big underground detectors. So because dark matter probably doesn't feel

456
00:22:12,520 --> 00:22:15,119
Speaker 2: the weak force, it probably doesn't interact with neutrinos.

457
00:22:15,560 --> 00:22:17,080
Speaker 1: Yeah, I feel the same way. I think I'm too

458
00:22:17,119 --> 00:22:18,200
Speaker 1: hot to be dark matter.

459
00:22:19,760 --> 00:22:20,920
Speaker 2: I'm always telling people that.

460
00:22:22,680 --> 00:22:24,160
Speaker 1: And ironically, I'm also pretty cool.

461
00:22:24,560 --> 00:22:26,080
Speaker 2: You're a paradox of physics.

462
00:22:26,400 --> 00:22:29,440
Speaker 1: Yes, I'm an enigma wrapped in a cartoonist. But talking

463
00:22:29,440 --> 00:22:31,280
Speaker 1: about the mass of a nutrino, I guess the first

464
00:22:31,320 --> 00:22:33,320
Speaker 1: question is like, first of all, how do you know

465
00:22:33,359 --> 00:22:36,320
Speaker 1: it has mass? Like, there are particles out there without mass, Right,

466
00:22:36,359 --> 00:22:38,280
Speaker 1: how do we know that neutrino has mass?

467
00:22:38,359 --> 00:22:40,720
Speaker 2: Yeah, you're right. There are particles out there that have

468
00:22:40,800 --> 00:22:44,040
Speaker 2: no mass, like the photon and the gluon. So it's

469
00:22:44,080 --> 00:22:47,280
Speaker 2: not impossible for the neutrino to have no mass, and

470
00:22:47,400 --> 00:22:50,760
Speaker 2: for a long time we assumed that it didn't. There's

471
00:22:50,800 --> 00:22:53,560
Speaker 2: even an argument about what we mean by the standard

472
00:22:53,600 --> 00:22:56,439
Speaker 2: model of particle physics, sort of our description of our

473
00:22:56,480 --> 00:22:59,280
Speaker 2: best understanding. Some people say that the standard model of

474
00:22:59,280 --> 00:23:03,479
Speaker 2: particle physics requires neutrinos to have no mass, though there

475
00:23:03,480 --> 00:23:05,879
Speaker 2: are extensions of it that allow them to have mass.

476
00:23:06,000 --> 00:23:08,400
Speaker 2: Some people say that's beyond the standard models. Some people

477
00:23:08,480 --> 00:23:10,960
Speaker 2: say that's the new standard model. As you might expect,

478
00:23:11,000 --> 00:23:13,000
Speaker 2: this big argument about how we name it. But for

479
00:23:13,040 --> 00:23:16,320
Speaker 2: a long time we assumed neutrinos had no mass. But

480
00:23:16,440 --> 00:23:18,520
Speaker 2: now we do know that they have mass, and we

481
00:23:18,600 --> 00:23:21,440
Speaker 2: know that in two different ways. We know that they

482
00:23:21,480 --> 00:23:24,479
Speaker 2: have mass even without knowing how much mass they have.

483
00:23:24,960 --> 00:23:27,520
Speaker 1: Interesting do you know because they I don't know, pass

484
00:23:27,720 --> 00:23:29,960
Speaker 1: around heavy objects, or because you've weight them.

485
00:23:30,040 --> 00:23:31,800
Speaker 2: So we know in a few different ways. Actually, one

486
00:23:31,800 --> 00:23:35,000
Speaker 2: of the first clues was looking at a supernova. There

487
00:23:35,040 --> 00:23:37,880
Speaker 2: was a supernova in nineteen eighty seven that was very,

488
00:23:38,000 --> 00:23:41,120
Speaker 2: very bright, and we saw a big flash of neutrinos

489
00:23:41,320 --> 00:23:44,440
Speaker 2: coming from that supernova. And the neutrinos actually arrived a

490
00:23:44,520 --> 00:23:48,000
Speaker 2: little bit before the photons because neutrinos come from the

491
00:23:48,040 --> 00:23:50,840
Speaker 2: center of the supernova and they aren't blocked by the

492
00:23:50,920 --> 00:23:53,480
Speaker 2: rest of the matter in the supernova, whereas the photons

493
00:23:53,520 --> 00:23:55,560
Speaker 2: come from the surface and it takes a while for

494
00:23:55,600 --> 00:23:58,359
Speaker 2: the energy to like propagate out and produce those photons.

495
00:23:58,560 --> 00:24:01,080
Speaker 2: But they looked at when the new trinos arrived and

496
00:24:01,119 --> 00:24:04,320
Speaker 2: realize that they don't all arrive at the same time.

497
00:24:04,920 --> 00:24:08,399
Speaker 2: We think they all leave the supernova basically the same moment,

498
00:24:08,480 --> 00:24:11,280
Speaker 2: but they don't all arrive at the same time. The

499
00:24:11,359 --> 00:24:15,520
Speaker 2: higher energy neutrinos arrive earlier than the lower energy once.

500
00:24:15,840 --> 00:24:19,080
Speaker 2: The higher the energy, the faster they go. That makes sense,

501
00:24:19,119 --> 00:24:22,400
Speaker 2: but it's actually a property you can only have if

502
00:24:22,440 --> 00:24:26,800
Speaker 2: you have mass. Massless particles like photons, all travel at

503
00:24:26,800 --> 00:24:30,439
Speaker 2: the same speed regardless of their energy. All photons travel

504
00:24:30,480 --> 00:24:34,399
Speaker 2: at the same speed because they're massless. Neutrinos have a

505
00:24:34,520 --> 00:24:37,920
Speaker 2: spread in their velocity, which means they have a mass.

506
00:24:38,800 --> 00:24:40,640
Speaker 1: But I guess it tells you that they're not as

507
00:24:40,680 --> 00:24:43,719
Speaker 1: fast as photons, which means they have mass. Right, because

508
00:24:44,440 --> 00:24:46,760
Speaker 1: anything that doesn't have mass would move at the speed

509
00:24:46,760 --> 00:24:47,520
Speaker 1: of light exactly.

510
00:24:47,600 --> 00:24:49,800
Speaker 2: Things that don't have mass always have to move at

511
00:24:49,840 --> 00:24:52,640
Speaker 2: the speed of light. There's no option there, right, Massless

512
00:24:52,640 --> 00:24:54,800
Speaker 2: objects always move at the speed of light.

513
00:24:55,040 --> 00:24:57,239
Speaker 1: Okay, so neutrinos don't move at this speed of light,

514
00:24:57,280 --> 00:24:59,480
Speaker 1: which means they have some mass. But then is that

515
00:24:59,560 --> 00:25:01,199
Speaker 1: the main way that we know they have mass?

516
00:25:01,200 --> 00:25:03,960
Speaker 2: So there's another really fascinating clue which comes from the

517
00:25:04,000 --> 00:25:07,040
Speaker 2: Big Bang. We think that a lot of neutrinos were

518
00:25:07,080 --> 00:25:09,560
Speaker 2: made in the Big Bang, Like all this energy was

519
00:25:09,600 --> 00:25:12,119
Speaker 2: hot and dense, and the quantum fields were frothing, and

520
00:25:12,160 --> 00:25:14,640
Speaker 2: as they cooled down, they sort of dribbled out into

521
00:25:14,680 --> 00:25:16,720
Speaker 2: all the different fields that are out there. So the

522
00:25:16,720 --> 00:25:18,480
Speaker 2: Big Bang made a lot of quarks and made a

523
00:25:18,480 --> 00:25:21,439
Speaker 2: lot of electrons, and made a lot of neutrinos as well.

524
00:25:21,640 --> 00:25:24,639
Speaker 2: And as those particles all mixed together, the amount of

525
00:25:24,640 --> 00:25:28,119
Speaker 2: photons and neutrinos and quarks determined like what kind of

526
00:25:28,119 --> 00:25:31,120
Speaker 2: stuff got made. Later as things cooled, like how much

527
00:25:31,160 --> 00:25:33,800
Speaker 2: hydrogen did you get and how much helium did you get?

528
00:25:33,840 --> 00:25:35,719
Speaker 2: And out of those things sort of sloshed together and

529
00:25:35,800 --> 00:25:38,920
Speaker 2: froth together in the Big Bang. So by studying the

530
00:25:38,960 --> 00:25:41,280
Speaker 2: relics of the Big Bang, the leftover bits of it,

531
00:25:41,480 --> 00:25:43,840
Speaker 2: we could actually get some clues as to like how

532
00:25:43,840 --> 00:25:46,600
Speaker 2: many neutrinos there were, and we can even figure out

533
00:25:46,640 --> 00:25:48,840
Speaker 2: something about the mass of those neutrinos.

534
00:25:49,000 --> 00:25:52,359
Speaker 1: But wait, I thought, neutrinos don't interact with regular mass,

535
00:25:52,600 --> 00:25:55,480
Speaker 1: So how can like regular mass relics tell you about

536
00:25:55,560 --> 00:25:57,360
Speaker 1: how many the trinos there were in the Big Bank.

537
00:25:57,440 --> 00:26:00,600
Speaker 2: Yeah, you're right. The neutrinos almost never interact with matter,

538
00:26:01,000 --> 00:26:03,200
Speaker 2: but if matter is dense enough, they will, Like the

539
00:26:03,320 --> 00:26:07,600
Speaker 2: probability is not zero, it's greater than zero. And actually,

540
00:26:07,680 --> 00:26:10,560
Speaker 2: back in the earlier times, when the universe was hotter,

541
00:26:10,680 --> 00:26:13,280
Speaker 2: when things were denser, the weak force was not as

542
00:26:13,359 --> 00:26:16,040
Speaker 2: weak as it is today. We think back in the

543
00:26:16,160 --> 00:26:19,560
Speaker 2: very early universe, the weak force and the electromagnetic force,

544
00:26:19,680 --> 00:26:22,040
Speaker 2: before the Higgs boson broke the symmetry, the two were

545
00:26:22,080 --> 00:26:26,080
Speaker 2: actually equally as powerful. So neutrinos used to interact with

546
00:26:26,119 --> 00:26:27,880
Speaker 2: normal matter more than they do today.

547
00:26:28,040 --> 00:26:29,800
Speaker 1: I think what you're saying is that our models of

548
00:26:29,880 --> 00:26:32,320
Speaker 1: the Big Bang tell us that there were a lot

549
00:26:32,359 --> 00:26:34,639
Speaker 1: of neutrinos at the Big Band, and that they have passed.

550
00:26:34,720 --> 00:26:36,719
Speaker 2: The models of the Big Bang tell us something about

551
00:26:36,920 --> 00:26:40,560
Speaker 2: how many neutrinos there were, like the number of neutrinos,

552
00:26:41,040 --> 00:26:44,080
Speaker 2: because neutrinos back then were moving really really fast, they

553
00:26:44,080 --> 00:26:46,640
Speaker 2: were very very hot, and so they helped like spread

554
00:26:46,720 --> 00:26:49,800
Speaker 2: energy out. They sort of acted like photons because everything

555
00:26:49,920 --> 00:26:52,880
Speaker 2: was so hot. And when we study the early universe

556
00:26:52,960 --> 00:26:56,240
Speaker 2: we can see these acoustic oscillations, like there were these

557
00:26:56,280 --> 00:26:59,879
Speaker 2: density waves. In the early universe. Things were hot and dense,

558
00:27:00,040 --> 00:27:03,000
Speaker 2: and the created pressure waves in the matter photons and

559
00:27:03,040 --> 00:27:05,840
Speaker 2: neutrinos helped us sort of smooth that out a little bit.

560
00:27:06,240 --> 00:27:10,320
Speaker 2: So by looking at those oscillations they're called baryon acoustic oscillations,

561
00:27:10,560 --> 00:27:13,240
Speaker 2: which make these ringing patterns in the early universe, we

562
00:27:13,280 --> 00:27:16,080
Speaker 2: can measure how many neutrinos and how many photons there were,

563
00:27:16,240 --> 00:27:18,800
Speaker 2: So that tells us something about the number of neutrinos.

564
00:27:19,080 --> 00:27:20,960
Speaker 2: Then we can do a second thing to figure out

565
00:27:21,000 --> 00:27:23,199
Speaker 2: how massive the neutrinos had to be. Like we know

566
00:27:23,480 --> 00:27:26,920
Speaker 2: how many neutrinos there were, and then we can figure out, well,

567
00:27:27,240 --> 00:27:30,119
Speaker 2: how much mass could the neutrinos have without causing the

568
00:27:30,320 --> 00:27:33,560
Speaker 2: universe to collapse? Right, We know that the universe has

569
00:27:33,600 --> 00:27:36,240
Speaker 2: been expanding since it was very very young, and that

570
00:27:36,320 --> 00:27:38,800
Speaker 2: tells us something about like how much matter and radiation

571
00:27:38,960 --> 00:27:41,520
Speaker 2: and energy there is in the universe, because if there

572
00:27:41,560 --> 00:27:44,600
Speaker 2: was too much, then gravity would pull everything back together

573
00:27:44,680 --> 00:27:47,160
Speaker 2: very quickly into a big bang. So we know something

574
00:27:47,160 --> 00:27:49,560
Speaker 2: about how many neutrinos there were, we could put an

575
00:27:49,640 --> 00:27:52,679
Speaker 2: upper limit on how massive they could be without collapsing

576
00:27:52,720 --> 00:27:53,360
Speaker 2: the universe.

577
00:27:54,240 --> 00:27:56,280
Speaker 1: But I think the two are sort of tied together, right.

578
00:27:56,320 --> 00:27:59,040
Speaker 1: The number of neutrinos and how massive they are, right,

579
00:27:59,440 --> 00:28:01,359
Speaker 1: I mean you have to assume they have mass in

580
00:28:01,440 --> 00:28:03,840
Speaker 1: order for them to matter at the Big Bang, right.

581
00:28:03,840 --> 00:28:06,119
Speaker 2: Well, they don't have to have mass in order to matter.

582
00:28:06,320 --> 00:28:09,640
Speaker 2: It's funny that we use matter because remember, general relativity

583
00:28:09,640 --> 00:28:12,280
Speaker 2: is sensitive to energy density, whether it's in the form

584
00:28:12,320 --> 00:28:15,480
Speaker 2: of radiation or in the form of matter. It really

585
00:28:15,520 --> 00:28:18,160
Speaker 2: is just sensitive to energy density. So the Big Bang

586
00:28:18,160 --> 00:28:21,679
Speaker 2: analysis tells us the number of neutrinos totally independently of

587
00:28:21,720 --> 00:28:24,160
Speaker 2: their mass. And the second step is to say, well,

588
00:28:24,200 --> 00:28:27,120
Speaker 2: if neutrinos do exist, how much mass could you give

589
00:28:27,160 --> 00:28:30,720
Speaker 2: them without causing the universe to collapse? So that tells

590
00:28:30,800 --> 00:28:34,199
Speaker 2: us something about how massive they could be. Like an

591
00:28:34,280 --> 00:28:37,120
Speaker 2: upper limit, Yes, exactly, it's an upper limit. That number

592
00:28:37,160 --> 00:28:39,680
Speaker 2: is actually really really low. The number is less than

593
00:28:39,680 --> 00:28:41,720
Speaker 2: the tenth of an electron volt.

594
00:28:41,680 --> 00:28:44,240
Speaker 1: Which I guess to give us some context, how much

595
00:28:44,640 --> 00:28:45,720
Speaker 1: mass does an electron have?

596
00:28:45,960 --> 00:28:50,400
Speaker 2: So an electron has like five hundred thousand electron volts.

597
00:28:50,760 --> 00:28:54,320
Speaker 2: It's half of an MeV half of a mega electron bolt,

598
00:28:54,840 --> 00:28:58,040
Speaker 2: and so five hundred thousand electron vaults. That's not very much, right,

599
00:28:58,040 --> 00:29:01,200
Speaker 2: Electrons are very very low mass. Particles compared to like

600
00:29:01,240 --> 00:29:04,600
Speaker 2: a proton. A proton has like one giga electron bolts

601
00:29:04,600 --> 00:29:08,600
Speaker 2: one billion electron bolts. So we know from the Big

602
00:29:08,640 --> 00:29:12,440
Speaker 2: Bang that all neutrinos added together have to have less

603
00:29:12,440 --> 00:29:14,960
Speaker 2: than a tenth of an electron bolt, less than one

604
00:29:15,040 --> 00:29:17,320
Speaker 2: ten billionth of the mass of a proton.

605
00:29:17,640 --> 00:29:19,760
Speaker 1: You mean all the different kinds of neutrinos, not all

606
00:29:19,800 --> 00:29:22,200
Speaker 1: of the individual neutrinos in the universe.

607
00:29:22,280 --> 00:29:24,880
Speaker 2: Right, Yeah, that's exactly right. There are three neutrinos. When

608
00:29:24,920 --> 00:29:26,880
Speaker 2: you add up all their mass together, it has to

609
00:29:26,880 --> 00:29:29,479
Speaker 2: be less than a tenth of an ev where an

610
00:29:29,520 --> 00:29:33,080
Speaker 2: electron is five hundred thousand ev and a proton is

611
00:29:33,120 --> 00:29:35,000
Speaker 2: about a billion ev m.

612
00:29:35,640 --> 00:29:39,000
Speaker 1: Interesting, so then pretty light, very very light, Like how

613
00:29:39,080 --> 00:29:39,760
Speaker 1: much is a quark.

614
00:29:39,840 --> 00:29:41,560
Speaker 2: It depends a lot on which cork you're talking about.

615
00:29:41,600 --> 00:29:44,000
Speaker 2: The lowest mass quarks have like a few MeV a

616
00:29:44,040 --> 00:29:48,200
Speaker 2: few million electronvolts. The most massive ones, like the top quark,

617
00:29:48,560 --> 00:29:51,960
Speaker 2: is like one hundred and seventy five billion ev. So

618
00:29:52,040 --> 00:29:55,680
Speaker 2: these neutrinos have mass much much closer to zero than

619
00:29:55,720 --> 00:29:59,480
Speaker 2: anything we've ever seen before. They're like shockingly low mass.

620
00:30:00,040 --> 00:30:01,720
Speaker 1: Okay, so we have a sort of an upper limit.

621
00:30:01,800 --> 00:30:05,240
Speaker 1: You said for how much the three kinds of neutrinos

622
00:30:05,320 --> 00:30:08,080
Speaker 1: can add up together, But then how do we resolve

623
00:30:08,120 --> 00:30:09,400
Speaker 1: how much each one of them weighs?

624
00:30:09,480 --> 00:30:12,120
Speaker 2: So then we have another really fascinating clue which tells

625
00:30:12,200 --> 00:30:15,320
Speaker 2: us about the mass difference between the neutrinos. So so

626
00:30:15,440 --> 00:30:17,560
Speaker 2: far we know something about the sum of their masses.

627
00:30:17,600 --> 00:30:20,280
Speaker 2: We know it's less than point one ev. We also

628
00:30:20,320 --> 00:30:22,760
Speaker 2: know there are three neutrinos, when we're wondering, like, well,

629
00:30:22,800 --> 00:30:25,040
Speaker 2: they all have the same mass, is it like with

630
00:30:25,080 --> 00:30:27,239
Speaker 2: the other particles, where there's one low mass and then

631
00:30:27,240 --> 00:30:29,280
Speaker 2: another one and then another one. So we can do

632
00:30:29,320 --> 00:30:32,400
Speaker 2: another kind of experiment to measure the differences between the

633
00:30:32,480 --> 00:30:35,360
Speaker 2: masses of the neutrinos. And this comes from how they

634
00:30:35,400 --> 00:30:39,760
Speaker 2: actually change their identities. Neutrinos are weird compared to the

635
00:30:39,760 --> 00:30:43,920
Speaker 2: other particles. In even another way. They're different from the electron,

636
00:30:44,000 --> 00:30:46,800
Speaker 2: the muon, and the towel, and that they can change flavor.

637
00:30:46,960 --> 00:30:49,520
Speaker 2: Like if you create an electron neutrino and shoot it

638
00:30:49,560 --> 00:30:52,400
Speaker 2: through space and then wait like a light year two

639
00:30:52,520 --> 00:30:54,800
Speaker 2: light years and try to measure it, you might discover

640
00:30:54,920 --> 00:30:58,760
Speaker 2: it's no longer an electron neutrino. It's now a muon

641
00:30:58,880 --> 00:31:03,120
Speaker 2: neutrino or a neutrino. This is called neutrino oscillation.

642
00:31:03,720 --> 00:31:06,480
Speaker 1: M yeah, I think usually if you shoot anything the space,

643
00:31:06,560 --> 00:31:10,400
Speaker 1: no change flavor. But I guess how do we know this? Like,

644
00:31:10,520 --> 00:31:12,560
Speaker 1: how would we know if it changed flavors? And again,

645
00:31:12,600 --> 00:31:14,600
Speaker 1: flavor is kind of the charge of the weak force?

646
00:31:14,680 --> 00:31:14,840
Speaker 4: Right?

647
00:31:14,920 --> 00:31:17,840
Speaker 2: Flavor is actually which of these generations of particles? It

648
00:31:17,880 --> 00:31:21,720
Speaker 2: is like is it electron, is it muon? Is it tau? Right,

649
00:31:21,760 --> 00:31:23,040
Speaker 2: that's what we mean by flavor.

650
00:31:23,200 --> 00:31:25,520
Speaker 1: Oh, is there a charge the weak force or is

651
00:31:25,560 --> 00:31:26,440
Speaker 1: it just the weak charge?

652
00:31:26,480 --> 00:31:28,240
Speaker 2: The weak force does have a charge member, it's two

653
00:31:28,240 --> 00:31:31,800
Speaker 2: different charges. There's the isospin and the weak hypercharge, so

654
00:31:31,880 --> 00:31:34,760
Speaker 2: both of those count as weak charges. But the neutrinos

655
00:31:34,800 --> 00:31:37,720
Speaker 2: all have the same week charges where they have different

656
00:31:37,800 --> 00:31:41,880
Speaker 2: is this flavor? This different identity, But that identity actually

657
00:31:41,920 --> 00:31:44,120
Speaker 2: turns out to be different. When you create the neutrino

658
00:31:44,240 --> 00:31:46,640
Speaker 2: and when the neutrino flies through space, they have like

659
00:31:46,680 --> 00:31:49,960
Speaker 2: two different sets of identities. There's the identity we talked

660
00:31:49,960 --> 00:31:52,200
Speaker 2: about when a neutrino is made, like the weak force,

661
00:31:52,240 --> 00:31:54,480
Speaker 2: when it makes an electron, it makes an electron neutrino,

662
00:31:54,600 --> 00:31:56,760
Speaker 2: or if it makes a muan, it makes a muon neutrino.

663
00:31:56,800 --> 00:31:59,640
Speaker 2: But when neutrinos fly through space, they have three different

664
00:31:59,680 --> 00:32:03,600
Speaker 2: ideas entities, and those are their masses. So there's three

665
00:32:03,600 --> 00:32:06,240
Speaker 2: different kinds of neutrinos for the weak force, and there's

666
00:32:06,280 --> 00:32:09,040
Speaker 2: three different kinds of neutrinos for the masses. But those

667
00:32:09,040 --> 00:32:11,760
Speaker 2: are not the same. They're like a mixture of each other.

668
00:32:12,520 --> 00:32:14,760
Speaker 2: So if you imagine this like M one, M two,

669
00:32:15,000 --> 00:32:18,040
Speaker 2: M three are the three neutrino masses. When you create

670
00:32:18,040 --> 00:32:21,400
Speaker 2: an electron neutrino, it's not like it's M one. It's

671
00:32:21,440 --> 00:32:24,960
Speaker 2: some weird mixture of all the masses of the three neutrinos.

672
00:32:25,200 --> 00:32:27,280
Speaker 1: You mean some kind of weird quantum mixture. Is that

673
00:32:27,320 --> 00:32:27,720
Speaker 1: what you mean?

674
00:32:28,080 --> 00:32:30,880
Speaker 2: Yeah, it's a superposition. So you create an electron neutrino,

675
00:32:31,320 --> 00:32:35,560
Speaker 2: it's a quantum superposition of the three different neutrino masses.

676
00:32:35,960 --> 00:32:38,920
Speaker 2: You create a mule on neutrino, it's a different superposition

677
00:32:38,960 --> 00:32:41,280
Speaker 2: of those masses. It's like having two different set of

678
00:32:41,360 --> 00:32:44,920
Speaker 2: axes that are not aligned. It's like a rotation between

679
00:32:45,000 --> 00:32:46,000
Speaker 2: your set of axes.

680
00:32:46,160 --> 00:32:48,920
Speaker 1: I guess maybe the question I have is so there's

681
00:32:48,960 --> 00:32:52,560
Speaker 1: three types of neutrinos, electronion, and town neutrinos, and the

682
00:32:52,600 --> 00:32:54,600
Speaker 1: only difference between them is the mass.

683
00:32:54,920 --> 00:32:57,640
Speaker 2: The only difference between the electron, muon, and town neutrino

684
00:32:57,760 --> 00:33:00,280
Speaker 2: is how they interact with the weak force. Three different

685
00:33:00,320 --> 00:33:02,720
Speaker 2: kinds of neutrinos. There's two different ways to break them down.

686
00:33:02,800 --> 00:33:04,920
Speaker 2: One is how do they interact with the weak force?

687
00:33:05,200 --> 00:33:08,040
Speaker 2: The other is what are their masses? So you get

688
00:33:08,160 --> 00:33:11,120
Speaker 2: two different ways to categorize the three neutrinos.

689
00:33:11,440 --> 00:33:13,240
Speaker 1: What do you mean how it interacts with the weak force?

690
00:33:13,360 --> 00:33:17,920
Speaker 1: Like like it's probability of interaction or its strength of interaction?

691
00:33:18,080 --> 00:33:18,840
Speaker 1: What do you mean by that?

692
00:33:19,080 --> 00:33:21,760
Speaker 2: Like what it's made in association with? Like, if you

693
00:33:21,840 --> 00:33:24,440
Speaker 2: make an electron, what kind of neutrino do you make? Well,

694
00:33:24,520 --> 00:33:27,240
Speaker 2: you make an electron neutrino. If you make a tow

695
00:33:27,400 --> 00:33:29,120
Speaker 2: what kind of neutrino do you make? You make a

696
00:33:29,120 --> 00:33:29,880
Speaker 2: town neutrino.

697
00:33:30,000 --> 00:33:31,960
Speaker 1: But if you already made it, does it matter or

698
00:33:32,120 --> 00:33:34,040
Speaker 1: does it matter in like what it can do later?

699
00:33:34,240 --> 00:33:36,800
Speaker 2: It matters in the accounting of the number of electrons

700
00:33:36,880 --> 00:33:38,440
Speaker 2: or muons or towels in the universe.

701
00:33:38,520 --> 00:33:40,520
Speaker 1: Yeah, But like if you just catch one in space.

702
00:33:40,560 --> 00:33:42,720
Speaker 1: How do you know what it is because you weren't

703
00:33:42,760 --> 00:33:44,040
Speaker 1: there when it was made.

704
00:33:44,160 --> 00:33:46,640
Speaker 2: Yeah, good question. Well, electron neutrino is more likely to

705
00:33:46,720 --> 00:33:49,440
Speaker 2: make electrons and a muon neutrino will make a muon,

706
00:33:49,520 --> 00:33:51,640
Speaker 2: and a town neutrino will interact and make a tow.

707
00:33:51,920 --> 00:33:54,680
Speaker 2: One of our neutrino experiments can see electrons, it can

708
00:33:54,720 --> 00:33:56,960
Speaker 2: also see muons, and it can also see tows And

709
00:33:56,960 --> 00:33:59,400
Speaker 2: so you can tell which kind of neutrino it was

710
00:33:59,600 --> 00:34:02,080
Speaker 2: by how how it interacts. Does it create an electron,

711
00:34:02,120 --> 00:34:03,960
Speaker 2: does it create a muon, Does it created.

712
00:34:03,680 --> 00:34:06,920
Speaker 1: A taw What it can do in the future kind.

713
00:34:06,800 --> 00:34:08,520
Speaker 2: Of yeah, what it can do in the future, because

714
00:34:08,520 --> 00:34:11,320
Speaker 2: the universe keeps track of this, accounting how many electrons

715
00:34:11,320 --> 00:34:13,400
Speaker 2: are there, how many muons are there, how many towels

716
00:34:13,400 --> 00:34:15,879
Speaker 2: are there. But again, that's just one way to see

717
00:34:15,880 --> 00:34:18,680
Speaker 2: these things. Another way to see these things is how

718
00:34:18,760 --> 00:34:21,640
Speaker 2: much mass do they have? And for most particles it's

719
00:34:21,640 --> 00:34:24,160
Speaker 2: the same thing. The weak force creates an electron, the

720
00:34:24,160 --> 00:34:26,479
Speaker 2: electron has a mass. All electrons have the same mass.

721
00:34:26,480 --> 00:34:28,880
Speaker 2: It's just a number. And if you ask, like what

722
00:34:28,920 --> 00:34:31,160
Speaker 2: are the masses of the eleptons, you get three different numbers,

723
00:34:31,160 --> 00:34:33,920
Speaker 2: those align with the flavors of the e leptons, but

724
00:34:33,960 --> 00:34:36,279
Speaker 2: when it comes to the neutrinos, they don't. So when

725
00:34:36,280 --> 00:34:38,719
Speaker 2: you create an electron neutrino, it's a weird mixture of

726
00:34:38,719 --> 00:34:42,040
Speaker 2: these different masses, and as it flies through space, those

727
00:34:42,120 --> 00:34:44,719
Speaker 2: that mixture can change because mass tells us how things

728
00:34:44,840 --> 00:34:47,920
Speaker 2: move through space. So these electron neutrinos and mew neutrinos

729
00:34:47,920 --> 00:34:50,640
Speaker 2: and town neutrinos, because they're made of three different masses,

730
00:34:50,680 --> 00:34:53,560
Speaker 2: and those masses are different, those masses like fly through

731
00:34:53,600 --> 00:34:57,160
Speaker 2: space slightly differently, and they can turn from one into another.

732
00:34:57,320 --> 00:34:59,279
Speaker 1: I think what you're saying is that, like, if you

733
00:35:00,120 --> 00:35:02,799
Speaker 1: make an electron neutrino like in the center of the

734
00:35:02,800 --> 00:35:05,520
Speaker 1: Sun and it's flying to us, and it has the

735
00:35:05,600 --> 00:35:08,320
Speaker 1: identity of an electron neutrino, it might have that identity,

736
00:35:08,360 --> 00:35:10,560
Speaker 1: but it might not necessarily have a particular mass, like

737
00:35:10,600 --> 00:35:13,759
Speaker 1: it might have one of three different masses exactly. Or

738
00:35:13,840 --> 00:35:16,319
Speaker 1: if you like find a neutrino during space with like

739
00:35:16,800 --> 00:35:19,719
Speaker 1: one of the masses, like the highest mass for neutrinos,

740
00:35:19,760 --> 00:35:22,840
Speaker 1: then that could still be either an electron neatrino or

741
00:35:22,920 --> 00:35:25,040
Speaker 1: town latrino or a unutrino.

742
00:35:25,440 --> 00:35:28,279
Speaker 2: Yes, that's exactly right. In mathematical terms, if you have

743
00:35:28,400 --> 00:35:31,520
Speaker 2: a weak eigen state, if you have an electron neutrino,

744
00:35:31,600 --> 00:35:34,200
Speaker 2: that's something produced by the weak force. In a pure

745
00:35:34,200 --> 00:35:37,040
Speaker 2: electron state, it's a mixture of the mass states. If

746
00:35:37,040 --> 00:35:39,440
Speaker 2: you have a pure mass state, it's a mixture of

747
00:35:39,480 --> 00:35:40,440
Speaker 2: the flavor states.

748
00:35:41,200 --> 00:35:44,840
Speaker 1: I think basically nutrino's kind of have an identity crisis

749
00:35:44,840 --> 00:35:48,760
Speaker 1: going on, both a mass crisis and an identity crisis,

750
00:35:48,760 --> 00:35:50,520
Speaker 1: Like it doesn't quite know what it is, or it

751
00:35:50,520 --> 00:35:53,160
Speaker 1: could be different things, but it could also weigh different things,

752
00:35:53,160 --> 00:35:55,520
Speaker 1: and it could also call itself different things. And it's

753
00:35:55,520 --> 00:35:57,759
Speaker 1: sort of like up in the air, like it can

754
00:35:57,840 --> 00:36:00,400
Speaker 1: change its fluid between these identities exactly.

755
00:36:00,560 --> 00:36:03,560
Speaker 2: Neutrinos have two different kinds of identities, and they do

756
00:36:03,600 --> 00:36:06,640
Speaker 2: not align. For most particles, these things align very well

757
00:36:06,760 --> 00:36:07,440
Speaker 2: for neutrinos.

758
00:36:07,520 --> 00:36:10,000
Speaker 1: They don't like an electron. For example, if it's born

759
00:36:10,040 --> 00:36:12,320
Speaker 1: an electron, it's going to have the mass of an electron.

760
00:36:12,360 --> 00:36:14,040
Speaker 1: It's not somethingly going to have the mass of a

761
00:36:14,160 --> 00:36:15,920
Speaker 1: Taue electron or a Newon electron.

762
00:36:16,040 --> 00:36:18,200
Speaker 2: Right, Yeah, And this calls in the question what I

763
00:36:18,239 --> 00:36:20,040
Speaker 2: was saying at the very beginning of the podcast about

764
00:36:20,120 --> 00:36:22,920
Speaker 2: mass being part of the identity of a particle, because

765
00:36:22,960 --> 00:36:25,839
Speaker 2: neutrinos can't really be defined by their mass, Like, well,

766
00:36:25,880 --> 00:36:27,680
Speaker 2: it depends are you talking about who I interact with

767
00:36:27,800 --> 00:36:30,200
Speaker 2: or how I fly through space? Because the same neutrino

768
00:36:30,280 --> 00:36:32,800
Speaker 2: can give you two different answers to that question.

769
00:36:33,360 --> 00:36:36,480
Speaker 1: Interesting, all right, Well, let's dig into how we actually

770
00:36:36,640 --> 00:36:40,120
Speaker 1: measure the mass of a neutrino and what those results

771
00:36:40,120 --> 00:36:55,759
Speaker 1: have found. But first, let's take another quick break. Right

772
00:36:55,840 --> 00:36:58,720
Speaker 1: we're talking about the mass of a neutrino. How massive

773
00:36:58,920 --> 00:37:01,760
Speaker 1: is this ghostly part of that flies through space, barely

774
00:37:01,800 --> 00:37:05,719
Speaker 1: interacting with everybody else in the universe, ignoring everyone. It's

775
00:37:05,800 --> 00:37:06,880
Speaker 1: kind of a snobby particle.

776
00:37:06,960 --> 00:37:08,640
Speaker 2: It's just got its own stuff to do, you know.

777
00:37:08,680 --> 00:37:10,680
Speaker 2: It just can't stop and chat with everybody. It's got

778
00:37:10,719 --> 00:37:11,600
Speaker 2: its list of barrens.

779
00:37:12,239 --> 00:37:13,080
Speaker 1: It's very aloof.

780
00:37:14,320 --> 00:37:16,080
Speaker 2: It's just busy, man, It's just busy.

781
00:37:16,440 --> 00:37:19,480
Speaker 1: Just more neutral, has less opinions. I guess it's not

782
00:37:19,560 --> 00:37:23,759
Speaker 1: as interesting, all right. And so we're talking about how

783
00:37:23,800 --> 00:37:26,280
Speaker 1: much mass it has, and we know from the Big

784
00:37:26,320 --> 00:37:29,239
Speaker 1: Bang models that we have that it nutrina has very

785
00:37:29,280 --> 00:37:32,359
Speaker 1: little mass, and the different kinds of nutrino thos can't

786
00:37:32,400 --> 00:37:35,560
Speaker 1: have a lot of masks combined. We talked about how

787
00:37:35,600 --> 00:37:38,120
Speaker 1: the nutrina kind of has an identity crisis, doesn't quite

788
00:37:39,280 --> 00:37:42,200
Speaker 1: knows for real what kind of neutrino it is and

789
00:37:42,200 --> 00:37:45,000
Speaker 1: how much it weighs. It's so sort of fluid and quantumy,

790
00:37:45,160 --> 00:37:48,000
Speaker 1: kind of complex and superposition. So then I guess the

791
00:37:48,000 --> 00:37:50,200
Speaker 1: big question is what can you do with that? How

792
00:37:50,200 --> 00:37:54,959
Speaker 1: do you measure these masses if the neutrino so wishy washing?

793
00:37:55,280 --> 00:37:58,080
Speaker 2: Yeah, So the fact that neutrinos can change flavor was

794
00:37:58,120 --> 00:38:01,200
Speaker 2: a big mystery in particles physics for many decades. Like

795
00:38:01,200 --> 00:38:03,759
Speaker 2: we count the number of neutrinos we see from the

796
00:38:03,800 --> 00:38:06,319
Speaker 2: Sun electron neutrinos, and we don't see as many as

797
00:38:06,360 --> 00:38:08,640
Speaker 2: we thought we should, which is a big puzzle. For

798
00:38:08,680 --> 00:38:10,920
Speaker 2: a long time, we predicted a certain number of electron

799
00:38:10,960 --> 00:38:13,479
Speaker 2: neutrinos being created in the Sun, and we just didn't

800
00:38:13,520 --> 00:38:15,359
Speaker 2: see as many. We saw like a third as many

801
00:38:15,400 --> 00:38:18,640
Speaker 2: as we expected. Now we understand that's because they're oscillating.

802
00:38:18,680 --> 00:38:21,160
Speaker 2: They're changing from electron neutrino to something else, and so

803
00:38:21,200 --> 00:38:24,400
Speaker 2: we're not seeing them because they're not interacting with our electrons.

804
00:38:24,760 --> 00:38:28,080
Speaker 2: But we can also use that to measure the differences

805
00:38:28,120 --> 00:38:31,160
Speaker 2: in the masses of the neutrinos. It's because there's a

806
00:38:31,239 --> 00:38:34,640
Speaker 2: mass difference between the neutrinos because they fly differently through

807
00:38:34,640 --> 00:38:38,040
Speaker 2: space that they're changing their identity as they go. So

808
00:38:38,080 --> 00:38:41,040
Speaker 2: what we can extract from this are two numbers, the

809
00:38:41,080 --> 00:38:43,600
Speaker 2: mass differences. Like you imagine this M one, M two,

810
00:38:43,760 --> 00:38:46,680
Speaker 2: M three. We can measure the separation between those three.

811
00:38:46,760 --> 00:38:49,200
Speaker 2: We can't tell the overall mass, but we can tell

812
00:38:49,239 --> 00:38:52,040
Speaker 2: how different they are. But the gaps are between the

813
00:38:52,120 --> 00:38:53,120
Speaker 2: neutrino masses.

814
00:38:54,520 --> 00:38:57,400
Speaker 1: I guess the question is can we why can we

815
00:38:57,400 --> 00:38:59,560
Speaker 1: measure the absolute value of these masses.

816
00:38:59,200 --> 00:39:01,799
Speaker 2: Because this oscillatetiontion doesn't depend on the absolute value. It

817
00:39:01,880 --> 00:39:04,600
Speaker 2: only depends on the difference. Like if all the neutrinos

818
00:39:04,600 --> 00:39:07,200
Speaker 2: had the same mass, then there wouldn't be any oscillation.

819
00:39:07,480 --> 00:39:09,719
Speaker 2: If the mass differences were really really large, they would

820
00:39:09,719 --> 00:39:12,840
Speaker 2: oscillate more. So by measuring how much they oscillate, we

821
00:39:12,880 --> 00:39:16,080
Speaker 2: can measure this mass difference, but the oscillation doesn't depend

822
00:39:16,200 --> 00:39:18,600
Speaker 2: on the total mass. This's a separate experiment we'll talk

823
00:39:18,640 --> 00:39:21,000
Speaker 2: about in a minute, called the Caturing experiment, which is

824
00:39:21,040 --> 00:39:23,920
Speaker 2: going to try to measure the overall mass of the neutrino.

825
00:39:24,280 --> 00:39:27,359
Speaker 2: But this oscillation, something which is quite well established, gives

826
00:39:27,440 --> 00:39:30,760
Speaker 2: us a precise measurement only of the differences between the masses.

827
00:39:31,160 --> 00:39:33,120
Speaker 1: I guess maybe I didn't quite understand why we can

828
00:39:33,120 --> 00:39:34,560
Speaker 1: only measure the differences.

829
00:39:34,160 --> 00:39:36,719
Speaker 2: Because the oscillation comes from the differences, Like if there

830
00:39:36,760 --> 00:39:39,640
Speaker 2: weren't any differences, you would see no oscillation. And the

831
00:39:39,719 --> 00:39:42,560
Speaker 2: larger the difference, the more the oscillation. It's kind of

832
00:39:42,640 --> 00:39:46,880
Speaker 2: like measuring interference between two laser beams. If they're in sync,

833
00:39:47,040 --> 00:39:49,600
Speaker 2: you see no interference. If one of them is delayed,

834
00:39:49,960 --> 00:39:52,359
Speaker 2: then they're out of phase and they interfere with each

835
00:39:52,400 --> 00:39:55,200
Speaker 2: other and giving an effect you can measure. But all

836
00:39:55,239 --> 00:39:58,360
Speaker 2: you can measure from the interference is the difference between

837
00:39:58,400 --> 00:40:02,480
Speaker 2: the beams, because that's what causes the interference. And neutrino

838
00:40:02,719 --> 00:40:05,040
Speaker 2: is a mixture of different masses, and each of those

839
00:40:05,040 --> 00:40:08,920
Speaker 2: masses flies through space differently, and it's that difference that

840
00:40:09,040 --> 00:40:11,080
Speaker 2: causes them to change flavor to oscillate.

841
00:40:11,280 --> 00:40:13,319
Speaker 1: But then how do we measure the oscillations, Like we

842
00:40:13,320 --> 00:40:16,359
Speaker 1: can only measure one neutrino at a time, we don't

843
00:40:16,400 --> 00:40:18,839
Speaker 1: know what it was before. How do we know what

844
00:40:18,880 --> 00:40:19,880
Speaker 1: it was after.

845
00:40:20,000 --> 00:40:22,759
Speaker 2: Well, we don't measure oscillations for an individual neutrino, You're right.

846
00:40:22,760 --> 00:40:24,520
Speaker 2: What we do is measure them statistically. So we have

847
00:40:24,560 --> 00:40:26,480
Speaker 2: like a bunch of neutrinos made in the Sun, and

848
00:40:26,520 --> 00:40:28,799
Speaker 2: we know those are all electron neutrinos because the Sun

849
00:40:28,800 --> 00:40:31,480
Speaker 2: has electrons in it and not muons and towels, So

850
00:40:31,520 --> 00:40:33,839
Speaker 2: we can measure how many of those have disappeared by

851
00:40:33,880 --> 00:40:35,560
Speaker 2: the time they get to Earth. We can also make

852
00:40:35,560 --> 00:40:38,080
Speaker 2: a bunch of muon neutrinos and a particle beam on

853
00:40:38,200 --> 00:40:41,279
Speaker 2: Earth and then see how often they disappear. So we

854
00:40:41,320 --> 00:40:43,960
Speaker 2: can make a bunch of these measurements of neutrino oscillation,

855
00:40:44,239 --> 00:40:46,840
Speaker 2: not by looking at an individual neutrino and seeing it oscillate,

856
00:40:46,920 --> 00:40:49,560
Speaker 2: but by making a huge number of neutrinos and seeing

857
00:40:49,760 --> 00:40:52,759
Speaker 2: how many of them disappear from their original identity.

858
00:40:53,320 --> 00:40:55,560
Speaker 1: Because you're saying, like the way you measure them, when

859
00:40:55,560 --> 00:40:57,600
Speaker 1: you catch a neutrino, you sort of know what it was,

860
00:40:58,480 --> 00:41:00,480
Speaker 1: or at least the detectors can only as you're one

861
00:41:00,560 --> 00:41:02,040
Speaker 1: kind of neutrino at a time.

862
00:41:02,000 --> 00:41:03,920
Speaker 2: Exactly, and all you can do is measure is flavor.

863
00:41:03,920 --> 00:41:06,040
Speaker 2: That's the way we detect them is we interact with them.

864
00:41:06,080 --> 00:41:07,680
Speaker 2: The only way to interact with them is through the

865
00:41:07,680 --> 00:41:10,840
Speaker 2: weak force, and that means using electrons, viuans, and towels.

866
00:41:11,080 --> 00:41:12,520
Speaker 2: That's how we interact with them.

867
00:41:12,560 --> 00:41:15,600
Speaker 1: And then how does that tell us their mass differences?

868
00:41:15,640 --> 00:41:17,920
Speaker 1: Like if I catch in the trino, can I just

869
00:41:18,200 --> 00:41:20,440
Speaker 1: infer its mass from like how much energy it has

870
00:41:20,760 --> 00:41:21,919
Speaker 1: and how fast it was going.

871
00:41:22,000 --> 00:41:23,680
Speaker 2: So there are experiments that are going to try to

872
00:41:23,719 --> 00:41:25,560
Speaker 2: do exactly that, which we can talk about in a minute.

873
00:41:25,600 --> 00:41:29,480
Speaker 2: The oscillation experiments are just counting how many neutrinos have disappeared.

874
00:41:29,800 --> 00:41:33,080
Speaker 2: Neutrinos have such low mass that's very, very difficult to

875
00:41:33,120 --> 00:41:36,520
Speaker 2: measure them individually on a per neutrino basis. But there

876
00:41:36,680 --> 00:41:38,719
Speaker 2: is an experiment in Germany which is trying to do

877
00:41:38,800 --> 00:41:39,480
Speaker 2: exactly that.

878
00:41:40,239 --> 00:41:42,480
Speaker 1: Okay, so then you're saying that we have measured kind

879
00:41:42,480 --> 00:41:45,440
Speaker 1: of the differences between the masses. So what are those numbers?

880
00:41:45,520 --> 00:41:48,160
Speaker 2: Those numbers are really small. There's two numbers there. One

881
00:41:48,200 --> 00:41:50,800
Speaker 2: of them is ten mili electron volts. A milli electric

882
00:41:50,800 --> 00:41:53,440
Speaker 2: bolt is one thousands of an electron volts. The other

883
00:41:53,480 --> 00:41:56,600
Speaker 2: one is fifty milli electron volts. So some of them

884
00:41:56,600 --> 00:41:58,560
Speaker 2: has to be less than one hundred and twenty milli

885
00:41:58,640 --> 00:42:01,719
Speaker 2: electron volts. We know that the gaps between them are

886
00:42:01,800 --> 00:42:02,840
Speaker 2: ten and fifty.

887
00:42:03,760 --> 00:42:07,880
Speaker 1: This feels like a fourth grade logic problem, like Sally, Paul,

888
00:42:08,080 --> 00:42:12,239
Speaker 1: and John money in their pockets and it adds up

889
00:42:12,280 --> 00:42:15,080
Speaker 1: to a dollar twenty. But the difference between Sally and

890
00:42:15,080 --> 00:42:18,880
Speaker 1: Paul is fifty cents, and between Sally and John is

891
00:42:18,960 --> 00:42:22,280
Speaker 1: Paul sense how much does Sally have exactly?

892
00:42:22,320 --> 00:42:24,920
Speaker 2: And so we know that there's two possible solutions. We

893
00:42:25,000 --> 00:42:26,960
Speaker 2: know that two of the neutrinos are close to each other.

894
00:42:27,000 --> 00:42:29,359
Speaker 2: This is a small gap ten MeTV. We also know

895
00:42:29,400 --> 00:42:32,760
Speaker 2: that the third one is further away, it's fifty MeTV away.

896
00:42:32,920 --> 00:42:34,960
Speaker 2: We don't know if the two ones that are closer

897
00:42:35,040 --> 00:42:38,080
Speaker 2: are heavier or lighter, So like are the two ones

898
00:42:38,120 --> 00:42:39,480
Speaker 2: that are near each other at the top of the

899
00:42:39,480 --> 00:42:41,680
Speaker 2: spectrum or the bottom of the spectrum. We don't know.

900
00:42:42,040 --> 00:42:44,680
Speaker 2: There's two possible answers there. We also don't know quite

901
00:42:44,800 --> 00:42:47,239
Speaker 2: how it adds up, like the number we have from

902
00:42:47,239 --> 00:42:49,759
Speaker 2: the early universe is an upper limit, and they could

903
00:42:49,800 --> 00:42:52,520
Speaker 2: all still be very very low values. So there's a

904
00:42:52,560 --> 00:42:54,360
Speaker 2: lot of open questions there. We'd love to know the

905
00:42:54,440 --> 00:42:56,520
Speaker 2: sum of the masses of all the neutrinos.

906
00:42:57,280 --> 00:42:59,279
Speaker 1: Well, you sort of just need to know one of

907
00:42:59,280 --> 00:43:01,279
Speaker 1: the masses right, and then that would click the other

908
00:43:01,320 --> 00:43:01,960
Speaker 1: ones in place.

909
00:43:02,080 --> 00:43:04,279
Speaker 2: Well, there's still two possible solutions if you just know

910
00:43:04,360 --> 00:43:05,480
Speaker 2: one of them. You don't know if you have like

911
00:43:05,520 --> 00:43:08,759
Speaker 2: the inverted hierarchy where the two close ones are the top,

912
00:43:08,880 --> 00:43:10,279
Speaker 2: or if you have the other hierarchy where the two

913
00:43:10,320 --> 00:43:11,400
Speaker 2: close ones are at the bottom.

914
00:43:11,719 --> 00:43:14,120
Speaker 1: Oh, I see, but you're saying, we know this very precisely.

915
00:43:14,560 --> 00:43:17,000
Speaker 1: Like our models of the neutrino. When you shoot a

916
00:43:17,000 --> 00:43:19,040
Speaker 1: bunch of them out and you see how many transform

917
00:43:19,040 --> 00:43:22,080
Speaker 1: into different kinds, dat somehow tells you the difference in

918
00:43:22,120 --> 00:43:24,879
Speaker 1: their masses because it, I guess it affects the probability

919
00:43:24,880 --> 00:43:26,160
Speaker 1: of these transformations.

920
00:43:26,280 --> 00:43:29,640
Speaker 2: Yeah. And we've been doing these neutrino oscillation experiments for decades,

921
00:43:29,719 --> 00:43:31,400
Speaker 2: and we've done them in all sorts of ways, with

922
00:43:31,440 --> 00:43:34,160
Speaker 2: all sorts of different combinations. Make this kind of neutrino

923
00:43:34,280 --> 00:43:36,520
Speaker 2: disappear that kind of trino, make this kind of measure

924
00:43:36,560 --> 00:43:39,840
Speaker 2: the appearance of the other one. We've triangulated that whole matrix,

925
00:43:39,880 --> 00:43:42,120
Speaker 2: and we know exactly how these numbers work out. What

926
00:43:42,160 --> 00:43:45,160
Speaker 2: we don't know is the overall mass, only the differences.

927
00:43:45,200 --> 00:43:48,520
Speaker 2: So the differences are very precisely known. The overall mass

928
00:43:48,800 --> 00:43:51,960
Speaker 2: is limited by this Big Bang cosmology stuff to less

929
00:43:51,960 --> 00:43:54,879
Speaker 2: than one hundred and twenty mili electron bolts. But now,

930
00:43:54,880 --> 00:43:58,640
Speaker 2: this is really cool experiment in Germany called the Katrine experiment,

931
00:43:58,640 --> 00:44:01,000
Speaker 2: which is going to try to measure the mass of

932
00:44:01,040 --> 00:44:03,640
Speaker 2: the electron neutrino as precisely as possible.

933
00:44:03,760 --> 00:44:05,920
Speaker 1: All right, let's talk about this experiment, and now what

934
00:44:06,040 --> 00:44:07,719
Speaker 1: is it? How does it work?

935
00:44:07,800 --> 00:44:11,600
Speaker 2: So this experiment is called the Carlsrua tritium neutrino experiment,

936
00:44:11,680 --> 00:44:14,040
Speaker 2: which is a tortured way to make catrin as an

937
00:44:14,080 --> 00:44:16,000
Speaker 2: acronym to.

938
00:44:15,880 --> 00:44:17,040
Speaker 1: Say the least.

939
00:44:17,200 --> 00:44:21,160
Speaker 2: But it starts from tritium and tretium decays two helium,

940
00:44:21,320 --> 00:44:24,080
Speaker 2: which is like two protons a neutron, and then it

941
00:44:24,160 --> 00:44:27,200
Speaker 2: also produces an electron and a neutrino.

942
00:44:26,960 --> 00:44:29,200
Speaker 1: And tretium is just an element, right.

943
00:44:29,080 --> 00:44:32,239
Speaker 2: Yeah, Tritium is two neutrons and a proton, so it's

944
00:44:32,280 --> 00:44:34,719
Speaker 2: like an isotope of hydrogen. Basically, what happens is one

945
00:44:34,760 --> 00:44:37,600
Speaker 2: of those neutrons turns into a proton and then emits

946
00:44:37,640 --> 00:44:40,200
Speaker 2: an electron. And a neutrino, And this is a nice

947
00:44:40,200 --> 00:44:43,320
Speaker 2: way to measure the neutrino mass because the electron neutrino

948
00:44:43,600 --> 00:44:46,080
Speaker 2: don't have a lot of energy. The comp moving really

949
00:44:46,120 --> 00:44:49,160
Speaker 2: really slow, and so basically you can see the effect

950
00:44:49,200 --> 00:44:52,480
Speaker 2: of the mass of these particles on how fast they're moving.

951
00:44:52,840 --> 00:44:54,920
Speaker 2: It's like, not a whole lot of energy made in

952
00:44:54,960 --> 00:44:58,040
Speaker 2: this reaction, so not a lot of despair. So if

953
00:44:58,040 --> 00:45:00,200
Speaker 2: the electron and the neutrino have a lot of mass,

954
00:45:00,200 --> 00:45:02,799
Speaker 2: they'll come out moving slower. They have less mass will

955
00:45:02,800 --> 00:45:06,080
Speaker 2: come out moving faster, And so we can't see the

956
00:45:06,080 --> 00:45:09,399
Speaker 2: neutrino directly, but we can measure the electron energy very

957
00:45:09,560 --> 00:45:12,640
Speaker 2: very precisely. So that's why this experiment does. It measures

958
00:45:12,680 --> 00:45:15,760
Speaker 2: those electrons really really precisely, and if it sees electrons

959
00:45:15,800 --> 00:45:18,920
Speaker 2: moving with more energy, it means that the neutrino mass

960
00:45:18,960 --> 00:45:21,520
Speaker 2: hasn't taken up some of that energy budget. And if

961
00:45:21,520 --> 00:45:24,080
Speaker 2: it doesn't see electrons moving with sort of near the

962
00:45:24,120 --> 00:45:27,840
Speaker 2: maximum possible energy that this decay can make, it means

963
00:45:27,840 --> 00:45:30,400
Speaker 2: that the neutrino has used up some of the energy

964
00:45:30,440 --> 00:45:33,320
Speaker 2: budget that otherwise could have made the electron go faster,

965
00:45:33,600 --> 00:45:36,279
Speaker 2: and that means the neutrino has some mass, so it's

966
00:45:36,320 --> 00:45:38,600
Speaker 2: sort of like a way to measure the neutrino mass

967
00:45:38,600 --> 00:45:42,080
Speaker 2: by seeing how much energy it slurps out from this reaction.

968
00:45:43,200 --> 00:45:44,680
Speaker 1: Okay, so let me see if I got this straight.

969
00:45:45,239 --> 00:45:48,040
Speaker 1: You start with an isotope of hydrogen called tritium, which

970
00:45:48,080 --> 00:45:51,080
Speaker 1: is two neutrons in the nucleus surrounded by an electron,

971
00:45:51,400 --> 00:45:53,240
Speaker 1: and then you just let it hang out and eventually

972
00:45:53,280 --> 00:45:56,200
Speaker 1: it's going to decay into a hydrogen atom like right,

973
00:45:56,280 --> 00:45:58,400
Speaker 1: Like one of those neutrons is just going to disappear,

974
00:45:58,640 --> 00:46:01,280
Speaker 1: transformed to something else. And you're saying that this reaction

975
00:46:01,360 --> 00:46:05,120
Speaker 1: shoots out an electron and an antineutrino, and the electron

976
00:46:05,200 --> 00:46:09,520
Speaker 1: we can measure its mass and speed because it's an electron,

977
00:46:09,840 --> 00:46:12,920
Speaker 1: and so whatever's left because we I guess you assume

978
00:46:13,000 --> 00:46:14,560
Speaker 1: a certain amount of energy at the beginning.

979
00:46:14,920 --> 00:46:17,360
Speaker 2: We know very well how tritium decays and how it

980
00:46:17,400 --> 00:46:20,080
Speaker 2: turns into helium and how much energy is available. Yeah,

981
00:46:20,440 --> 00:46:22,080
Speaker 2: and we know that energy has to go to the

982
00:46:22,080 --> 00:46:23,839
Speaker 2: electron and the neutrino, and.

983
00:46:23,840 --> 00:46:26,440
Speaker 1: So the difference between what you started with and how

984
00:46:26,520 --> 00:46:28,600
Speaker 1: much you measure the electron is the energy that goes

985
00:46:28,640 --> 00:46:31,520
Speaker 1: into the neutrino exactly, But then how does that tell

986
00:46:31,520 --> 00:46:33,399
Speaker 1: you the mass? It could just be like something light

987
00:46:33,480 --> 00:46:35,320
Speaker 1: moving fast or something heavy moving slow.

988
00:46:35,520 --> 00:46:37,920
Speaker 2: Yeah, So there's a spectrum of possibilities, and what we're

989
00:46:37,960 --> 00:46:41,759
Speaker 2: looking for is the maximum scenario, Like are there any

990
00:46:41,880 --> 00:46:44,880
Speaker 2: cases where the electron takes all of the energy available?

991
00:46:44,880 --> 00:46:48,040
Speaker 2: There's like a certain energy budget for producing this subtract

992
00:46:48,040 --> 00:46:50,839
Speaker 2: out the electron mass, and then we wonder like, are

993
00:46:50,880 --> 00:46:53,720
Speaker 2: there scenarios where the electron takes all of the energy.

994
00:46:53,920 --> 00:46:56,080
Speaker 2: If we see cases where the electron takes all of

995
00:46:56,080 --> 00:46:58,920
Speaker 2: the energy, that means the neutrino hasn't taken any So

996
00:46:58,920 --> 00:47:00,640
Speaker 2: it's sort of like a budget. You have a budget

997
00:47:00,640 --> 00:47:03,160
Speaker 2: for the whole thing. The electron mask gets taken out,

998
00:47:03,560 --> 00:47:06,200
Speaker 2: then we wonder like does the neutrino take a cut?

999
00:47:06,239 --> 00:47:08,560
Speaker 2: If the neutrino takes a cut, that leaves a smaller

1000
00:47:08,560 --> 00:47:11,400
Speaker 2: budget for the electron, and you'll never see an electron

1001
00:47:11,760 --> 00:47:15,359
Speaker 2: having energy higher than that limit. The neutrino doesn't take

1002
00:47:15,400 --> 00:47:17,880
Speaker 2: a cut, it leaves more energy for the electron and

1003
00:47:17,880 --> 00:47:20,480
Speaker 2: you'll see faster moving electrons. So you look at the

1004
00:47:20,520 --> 00:47:23,239
Speaker 2: tail of the distribution, like what's the fastest electron you

1005
00:47:23,280 --> 00:47:25,640
Speaker 2: ever see, and that'll tell you how much the neutrino

1006
00:47:25,800 --> 00:47:26,880
Speaker 2: is taken from the budget.

1007
00:47:27,120 --> 00:47:29,400
Speaker 1: M I think I get it. So, like you start

1008
00:47:29,440 --> 00:47:32,200
Speaker 1: with let's say one hundred units of energy, and you

1009
00:47:32,239 --> 00:47:35,600
Speaker 1: measure how much energy electron that comes out has, and

1010
00:47:35,640 --> 00:47:38,000
Speaker 1: you look for, like, what's the maximum energy that the

1011
00:47:38,040 --> 00:47:40,000
Speaker 1: electron can take away from this? And let's say it's

1012
00:47:40,000 --> 00:47:42,399
Speaker 1: like ninety nine out of a whole bunch of times,

1013
00:47:42,400 --> 00:47:44,759
Speaker 1: did you do this? Ninety nine is the maximum, which

1014
00:47:44,800 --> 00:47:47,799
Speaker 1: means like the minimum amount of energy the neutrino can

1015
00:47:47,880 --> 00:47:53,040
Speaker 1: take is one, which, since it's the maximum for the electron,

1016
00:47:53,120 --> 00:47:55,440
Speaker 1: it must mean that it's like it created a neutrino

1017
00:47:55,480 --> 00:47:56,440
Speaker 1: that wasn't moving at all.

1018
00:47:56,520 --> 00:47:59,200
Speaker 2: Maybe, And so they're looking for those scenarios like when

1019
00:47:59,200 --> 00:48:02,439
Speaker 2: you make a motionless neutrino and the electron takes all

1020
00:48:02,480 --> 00:48:06,120
Speaker 2: of its energy, that reaction reveals the mass of the

1021
00:48:06,160 --> 00:48:08,960
Speaker 2: neutrino in the energy of the electron.

1022
00:48:09,520 --> 00:48:12,200
Speaker 1: It reveals I guess, the mass of an electron neutrino.

1023
00:48:12,440 --> 00:48:15,239
Speaker 2: Yes, it's revealed the mass of a neutrino created with

1024
00:48:15,280 --> 00:48:17,760
Speaker 2: an electron. What does that really mean? Remember, the electron

1025
00:48:17,880 --> 00:48:21,319
Speaker 2: neutrino doesn't have a definite mass, So actually what it's

1026
00:48:21,360 --> 00:48:25,480
Speaker 2: measuring is a combination of all the masses of the neutrinos.

1027
00:48:25,880 --> 00:48:30,040
Speaker 2: It's just like incoherent some of the distinct neutrino mass

1028
00:48:30,120 --> 00:48:33,600
Speaker 2: values weighted by how much of each one is in

1029
00:48:33,640 --> 00:48:37,440
Speaker 2: that electron neutrino. So remember electro neutrinos don't have a

1030
00:48:37,480 --> 00:48:40,840
Speaker 2: definite mass, So you're measuring this like weird average mass

1031
00:48:40,880 --> 00:48:41,560
Speaker 2: of a neutrino.

1032
00:48:42,200 --> 00:48:44,200
Speaker 1: If you're going to sort of for like the minimum

1033
00:48:44,200 --> 00:48:46,360
Speaker 1: amount of mass that the neutrino has, then must be

1034
00:48:46,360 --> 00:48:48,600
Speaker 1: giving you the minimum mass for one of them. Right.

1035
00:48:48,680 --> 00:48:51,040
Speaker 2: Yes, it's a bit of a subtle point of quantum mechanics.

1036
00:48:51,320 --> 00:48:54,879
Speaker 2: The mass of that neutrino is not actually determined, right,

1037
00:48:54,920 --> 00:48:56,640
Speaker 2: It's not like it has a certain number and we

1038
00:48:56,680 --> 00:48:59,880
Speaker 2: don't know it. What we know is it's an electron neutrino,

1039
00:49:00,000 --> 00:49:03,480
Speaker 2: which means we don't know what its mass is. And

1040
00:49:03,560 --> 00:49:07,719
Speaker 2: so overall, on average, what you'll be sensitive to is

1041
00:49:07,760 --> 00:49:11,799
Speaker 2: the average mass of those neutrinos. But you're right, what

1042
00:49:11,800 --> 00:49:15,680
Speaker 2: we're doing is looking for the most energetic electron, which

1043
00:49:15,719 --> 00:49:18,160
Speaker 2: means we'd be sensitive to the lower end of the

1044
00:49:18,200 --> 00:49:21,160
Speaker 2: neutrino masses of that electron neutrino.

1045
00:49:21,040 --> 00:49:22,920
Speaker 1: Which would maybe give you like the lightest of the

1046
00:49:23,000 --> 00:49:24,160
Speaker 1: three neutrino masses.

1047
00:49:24,320 --> 00:49:26,560
Speaker 2: Yeah, And what we're looking to do is combine this

1048
00:49:26,640 --> 00:49:30,040
Speaker 2: with our measurements from neutrino oscillation, which tells very precisely

1049
00:49:30,360 --> 00:49:33,600
Speaker 2: the separation between the neutrinos, and now we want to

1050
00:49:33,600 --> 00:49:36,440
Speaker 2: anchor the overall scale and slide it up or slide

1051
00:49:36,480 --> 00:49:36,920
Speaker 2: it down.

1052
00:49:38,040 --> 00:49:39,719
Speaker 1: But I guess even if you do, like you said,

1053
00:49:39,719 --> 00:49:43,120
Speaker 1: there's two possibilities for the other two, right, so like

1054
00:49:43,239 --> 00:49:45,920
Speaker 1: you might know the massive one one of the masses,

1055
00:49:45,920 --> 00:49:49,000
Speaker 1: but you wouldn't necessarily know the mass of the other two.

1056
00:49:49,000 --> 00:49:51,160
Speaker 1: But I guess you would narrow it down to two possibilities.

1057
00:49:51,239 --> 00:49:53,200
Speaker 2: Yeah, we'd narrow down to two possibilities. You're right, This

1058
00:49:53,239 --> 00:49:56,440
Speaker 2: would still leave ambiguity for which higherarchy we have, Like

1059
00:49:56,480 --> 00:49:58,440
Speaker 2: are the two close ones the top? Were the two

1060
00:49:58,440 --> 00:50:01,040
Speaker 2: close ones at the bottom. So this experiment's been running

1061
00:50:01,040 --> 00:50:03,800
Speaker 2: for a couple of years and they have some preliminary results.

1062
00:50:03,920 --> 00:50:07,200
Speaker 2: Their measurement says that this mass they're measuring is less

1063
00:50:07,200 --> 00:50:10,960
Speaker 2: than eight hundred milli electron bolts. Now that's not much

1064
00:50:11,000 --> 00:50:13,239
Speaker 2: information because we already know from the Big Bang that

1065
00:50:13,280 --> 00:50:15,319
Speaker 2: it's less than one hundred and twenty. This is just

1066
00:50:15,360 --> 00:50:18,080
Speaker 2: sort of like their first result. They're going to keep

1067
00:50:18,120 --> 00:50:20,360
Speaker 2: running the collecting more data, and they hope they'll be

1068
00:50:20,400 --> 00:50:21,960
Speaker 2: able to measure this thing more precisely.

1069
00:50:22,200 --> 00:50:24,080
Speaker 1: Wait, so we know that they can be more than

1070
00:50:24,120 --> 00:50:26,600
Speaker 1: one hundred and twenty, but the first measurements say it's

1071
00:50:27,000 --> 00:50:28,160
Speaker 1: less than eight hundred.

1072
00:50:28,320 --> 00:50:30,799
Speaker 2: Yeah, so this is not as sensitive as the Big

1073
00:50:30,840 --> 00:50:32,000
Speaker 2: Bang measurement so far.

1074
00:50:32,239 --> 00:50:33,880
Speaker 1: But it would be really weird if they found that

1075
00:50:34,080 --> 00:50:36,560
Speaker 1: the mass in the try now is eight hundred million

1076
00:50:36,640 --> 00:50:38,439
Speaker 1: electron bolts, because that's way too much.

1077
00:50:38,760 --> 00:50:41,319
Speaker 2: Yeah, exactly, this sets an upper bound of less than

1078
00:50:41,360 --> 00:50:43,600
Speaker 2: eight hundred. We already know they're less than one twenty,

1079
00:50:43,840 --> 00:50:45,360
Speaker 2: so it'd be pretty weird to measure it at like

1080
00:50:45,480 --> 00:50:48,120
Speaker 2: six hundred or five hundred, you know. But these are

1081
00:50:48,239 --> 00:50:50,920
Speaker 2: very very different measurements, right, the Big Bang versus like

1082
00:50:51,000 --> 00:50:53,320
Speaker 2: experiments we're doing here on Earth. So it's not always

1083
00:50:53,360 --> 00:50:55,040
Speaker 2: the case that they're going to agree. There's a lot

1084
00:50:55,080 --> 00:50:57,480
Speaker 2: of theoretical assumptions that go into both of them. But

1085
00:50:57,560 --> 00:50:59,680
Speaker 2: the good thing about this one is we keep running,

1086
00:50:59,719 --> 00:51:02,480
Speaker 2: and so we can keep getting more and more precise measurements,

1087
00:51:02,920 --> 00:51:05,520
Speaker 2: and so they're hoping by twenty twenty four twenty twenty

1088
00:51:05,520 --> 00:51:07,879
Speaker 2: five they can get their sensitivity down to like two

1089
00:51:08,000 --> 00:51:10,960
Speaker 2: hundred MEB and then they can push even further.

1090
00:51:11,600 --> 00:51:14,319
Speaker 1: Because I guess it's all statistical, right, and so just

1091
00:51:14,360 --> 00:51:16,600
Speaker 1: the longer you run it, the more accurate you can

1092
00:51:16,640 --> 00:51:17,799
Speaker 1: say what the minimum is.

1093
00:51:18,000 --> 00:51:20,880
Speaker 2: And this experiment is also super fun because it involves

1094
00:51:20,960 --> 00:51:25,480
Speaker 2: this huge metal container. They shoot these electrons into this

1095
00:51:25,640 --> 00:51:29,320
Speaker 2: mammoth vacuum chamber to measure their energy super duper precisely

1096
00:51:29,719 --> 00:51:32,760
Speaker 2: this spectrometer. It required a really specialized shop to build

1097
00:51:32,800 --> 00:51:35,120
Speaker 2: this thing. You should go online and google a picture

1098
00:51:35,120 --> 00:51:38,560
Speaker 2: of this thing. It's like a big steel blimp basically,

1099
00:51:38,960 --> 00:51:41,040
Speaker 2: and it was so big that it was really hard

1100
00:51:41,080 --> 00:51:43,799
Speaker 2: to transport from the factory where they built it, like

1101
00:51:43,840 --> 00:51:47,040
Speaker 2: three hundred kilometers to the experimental site. They actually had

1102
00:51:47,080 --> 00:51:49,400
Speaker 2: to put it on a boat and float it down

1103
00:51:49,520 --> 00:51:53,719
Speaker 2: river through the Mediterranean, out through the Atlantic over to

1104
00:51:53,960 --> 00:51:57,799
Speaker 2: the Netherlands, and then up another river to the experiment.

1105
00:51:58,360 --> 00:52:00,759
Speaker 2: So it's only like three hundred fifty twolometers away, but

1106
00:52:00,760 --> 00:52:03,520
Speaker 2: I have to take like a nine thousand kilometer long

1107
00:52:03,640 --> 00:52:06,120
Speaker 2: detour because it was too big to like put on

1108
00:52:06,160 --> 00:52:07,880
Speaker 2: a flatbed truck and drive around.

1109
00:52:08,160 --> 00:52:10,680
Speaker 1: Wow, sounds like they should have thought about it before

1110
00:52:10,680 --> 00:52:14,520
Speaker 1: they built it. I mean they have built it on site.

1111
00:52:14,280 --> 00:52:17,200
Speaker 2: Yeah exactly. But you know, you take specialized techniques just

1112
00:52:17,200 --> 00:52:19,600
Speaker 2: to build this thing, and then specialized techniques just to

1113
00:52:19,640 --> 00:52:22,480
Speaker 2: move this thing. There's some awesome videos of it making

1114
00:52:22,520 --> 00:52:26,040
Speaker 2: its last seven kilometer journey across land from the docks

1115
00:52:26,040 --> 00:52:29,960
Speaker 2: to the laboratory. They like squeezed it through these old villages,

1116
00:52:30,280 --> 00:52:32,560
Speaker 2: you know, with like a centimeter to spare on each side.

1117
00:52:32,560 --> 00:52:34,439
Speaker 2: It's pretty awesome, all right.

1118
00:52:34,520 --> 00:52:37,880
Speaker 1: Well, again, a neutrino is part of our standard model

1119
00:52:37,880 --> 00:52:39,840
Speaker 1: of denvers and so, and it's also kind of like

1120
00:52:39,880 --> 00:52:42,120
Speaker 1: one of the last frontiers in terms of what we

1121
00:52:42,200 --> 00:52:44,120
Speaker 1: know about the standard model, right, Like, once we found

1122
00:52:44,160 --> 00:52:47,200
Speaker 1: the Higgs boson and we know about all the matter particles,

1123
00:52:47,560 --> 00:52:49,959
Speaker 1: the neutrino is sort of one of the last big

1124
00:52:50,080 --> 00:52:52,440
Speaker 1: questions we have about it, right, and which means it

1125
00:52:52,640 --> 00:52:56,480
Speaker 1: sort of helps complete our understanding of matter particles in

1126
00:52:56,480 --> 00:52:56,920
Speaker 1: the universe.

1127
00:52:57,000 --> 00:52:59,799
Speaker 2: Yeah, you're absolutely right. It's the frontier particle physics, and

1128
00:52:59,800 --> 00:53:03,319
Speaker 2: the US specifically has decided to double down on neutrinos.

1129
00:53:03,560 --> 00:53:06,400
Speaker 2: We didn't build the next greatest best particle collider to

1130
00:53:06,440 --> 00:53:09,280
Speaker 2: compete with CERN. Instead, the US has decided to build

1131
00:53:09,320 --> 00:53:12,040
Speaker 2: big neutrino experiments to measure these masses, to measure the

1132
00:53:12,080 --> 00:53:16,240
Speaker 2: neutrino interactions, to understand this weird sector of the universe

1133
00:53:16,320 --> 00:53:18,839
Speaker 2: in more detail. We think there's probably a lot more

1134
00:53:18,840 --> 00:53:19,960
Speaker 2: interesting hints.

1135
00:53:19,640 --> 00:53:21,960
Speaker 1: There, and so learning more about the nutrino what would

1136
00:53:22,000 --> 00:53:23,080
Speaker 1: that tell us about the universe.

1137
00:53:23,200 --> 00:53:26,000
Speaker 2: Well, understanding the neutrino mass will help us understand the

1138
00:53:26,000 --> 00:53:27,880
Speaker 2: Big Bang and like what was going on and the

1139
00:53:27,920 --> 00:53:30,799
Speaker 2: neutrino contributions there. We also don't really know how the

1140
00:53:30,880 --> 00:53:33,520
Speaker 2: neutrino gets mass, like does it get mass from the

1141
00:53:33,600 --> 00:53:36,719
Speaker 2: Higgs boson the way other particles do, or does a

1142
00:53:36,760 --> 00:53:39,399
Speaker 2: neutrino give itself mass? Like it might be that there

1143
00:53:39,480 --> 00:53:42,520
Speaker 2: is no anti neutrino, that the neutrino is its own

1144
00:53:42,560 --> 00:53:45,040
Speaker 2: anti particle. This is a fun story about a physicists

1145
00:53:45,040 --> 00:53:48,439
Speaker 2: called Mayorana who thought about these Mayorana particles that might

1146
00:53:48,480 --> 00:53:51,360
Speaker 2: be their own anti particles and give themselves mass in

1147
00:53:51,360 --> 00:53:53,239
Speaker 2: this weird way. So it might even teach us about

1148
00:53:53,239 --> 00:53:55,160
Speaker 2: what mass is for a particle.

1149
00:53:55,800 --> 00:53:59,200
Speaker 1: HM cool, And that's very important because it it would

1150
00:53:59,200 --> 00:54:00,520
Speaker 1: tell us why we have right.

1151
00:54:00,719 --> 00:54:02,880
Speaker 2: Yeah, absolutely, it would tell us more about what the

1152
00:54:02,920 --> 00:54:05,880
Speaker 2: meaning of mass is. They might also give us some

1153
00:54:05,880 --> 00:54:08,160
Speaker 2: clues about the nature of dark matter. We know that

1154
00:54:08,239 --> 00:54:11,440
Speaker 2: these three neutrinos are not the dark matter, but there

1155
00:54:11,520 --> 00:54:14,960
Speaker 2: might be a fourth kind of neutrino, hysterile neutrino that

1156
00:54:15,040 --> 00:54:17,560
Speaker 2: could be out there, and understanding the neutrino masses and

1157
00:54:17,600 --> 00:54:20,080
Speaker 2: how they mix and interact with each other might clear

1158
00:54:20,160 --> 00:54:23,360
Speaker 2: up some nagging questions about whether there are other flavors

1159
00:54:23,360 --> 00:54:24,600
Speaker 2: of neutrinos out there.

1160
00:54:25,640 --> 00:54:30,080
Speaker 1: That would be massive. All right, well, we hope you

1161
00:54:30,160 --> 00:54:33,480
Speaker 1: enjoyed that. Thanks for joining us, see you next time.

1162
00:54:41,280 --> 00:54:44,040
Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain

1163
00:54:44,120 --> 00:54:48,120
Speaker 2: the Universe is a production of iHeartRadio. For more podcasts

1164
00:54:48,120 --> 00:54:52,800
Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever

1165
00:54:52,840 --> 00:54:54,560
Speaker 2: you listen to your favorite shows.