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November 28, 2019 44 mins

How did physicists lose trillions of neutrinos? 

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Speaker 1 (00:08):
Hey, jorgey, have you seen a particle lying around here? Um?
Why did you lose one? Yeah? I had this new trino,
actually more than one, and what happened? You lost him? Yeah?
It was here I turned around. You know exactly how
many particles are you missing? Daniel? Let's see I want
to it was about sex tillion. How do you lose

a sextillion particles? Well, actually it was one sextillion particles
per second. Daniel, you expect us to believe that you're
not going to destroy the world with your physics experiments. Hi,

I'm Jorge, I'm a cartoonists and the creator of PhD comments.
Hi I'm Daniel. I'm a particle physicist, and I have
not yet destroyed the world. And welcome to our new
true physics crime podcast. Daniel and Jorge uncover mysteries of
the universe and explain them, in which we hunt down

those responsible for the missing particles. That's right, And it's
always the last person you expect, or the last with
the last force, the last fundamental force you expect. That's right.
It was the butler in the library with the strong force.
It was the butler with a particle collider using the

strong force. But welcome to our podcast, in which we
explore everything that's amazing about the universe, from space physics
to particle physics and basically everything in between, including comics.
That's right, Welcome to Daniel and Jorge Explain the Universe,
a production of I Heart Radio that includes apparently even comics.
I guess comics are part of the universe. Comics are

made of particles, just like everything else, are they, though?
Are they more like an idea or an art? Is
art made out of particles? Art is just a concept
in your brain. Your brain is made of particles. So yeah,
basically it's math made out of particles. Okay, that's a
deeper question, but our philosophy. Daniel and Jorge expound ignorantly

on philosophy. Daniel Jorge get derailed in the first few
minutes of every podcast. Jorge can't get to the topic
of explaining the universe within ten minutes. Well, let's get
into its. So today's podcast, we'll be talking about a
big mystery in physics, apparently one of the biggest mysteries
in particle physics. For a long time, you guys were

wondering about this for a while. It seems. Yeah, we're
always looking for mysteries and particle physics, and a lot
of people in our field are focused on the heavy particles,
the new, the big, the fat stuff, the Higgs boson
the top cork, the kind of stuff you need a
lot of energy to make in particle colliders. But there
are also a lot of really interesting, fascinating puzzles about
the tiniest, the lightest, the weird, these little particles out there. Right, Yeah,

I'm not on a diet. I just need to decay
some some heavy particles in my body, that's right. So
this week we are cutting back on the rich diet
of heavy particles we've been feeding you, and we will
be sprinkling you some salad of light particles. So this
was a mystery for a long time that you guys
couldn't figure out, right, And it's a huge mystery. It's

like sixtialing of these particles are missing every second. Yeah,
I had to look that up. Sex tillion. That's ten
to the twenty and so ten to the twenty. It's
a big number. It's a hard number to even wrap
your head around, but that's the number of neutrinos that
hit the Earth every second, So then the podcast will
be tackling the topic the mystery of the missing neutrinos.

And this is a classic story in experimental physics when
people thought they understood something basically how many neutrinos the
Sun makes and how many we should see here on Earth,
and then they went out to measure it and they
didn't get the answer they expected, and so that was
a big puzzle for a long time. Right, I mean,
you guys basically deal with mysteries, right like when things
go missing. That's when you guys get it excited. Well,

I like to think that most of science is like
a detective story. You know, you're trying to put the
pieces together. You're looking for the evidence, you see if
it fits. Sometimes you think maybe somebody's lied to you,
and you have to try to understand did you miss here?
Is the evidence wrong? You need to re measure. So
a lot of science is sort of like trying to
unravel a detective story. That's what's fun about it for me. Now,

do you guys see yourselves more like you know, Humphrey
Boger type of detectives or more like a Jim Carrey
as Van Toura type of detectives more like the Woody
Allen um, you know, not really understanding, worrying about imposter syndrome,
you know, trying to pretend to think of yourself as
Humphrey Bogard, but you dressed like as Jim Carrey. Would

you look like Wooden? That kind of what I'm getting
from you, and I get paid like none of them. No,
but you're right, we are detectives of the universe. We
are trying to understand the story of the universe. How
this whole thing came together, how the holding fits together,
doesn't make sense. And you know, remember that science is

of the people, by the people, and for the people,
and so the things we work on are the things
that get us interested so that we can tell a story,
so that we can try to find an interesting mystery
to unravel, so that we can tell the story of
the universe. And so sometimes things go missing in this universe, right,
like you think that there's something or you you according
to your math or your theories, you think that there

should be something there or used to see a lot
of something, but you don't. And so that's a that
kind of throws everything into question. Yeah, and it's sort
of good news and bad news. And we do this
a lot in science. We say, well, we predict that
if we make some measurement, you know, we know what
we'll see. Like if you say, let's go count the
number of red stars versus white stars. We think we

know the answer, let's just go check. And usually it's
a totally on You get the answer you expected, you
move on. But sometimes you don't get the answer you expected,
and that's either an amazing opportunity to learn something new
about the universe or a huge headache. Yeah, and so
the mystery that we're talking about here today is that
you guys were expecting there to be a lot of

neutrinos somewhere, but they're they're not there. You're missing, Yeah, exactly.
We know the Sun makes a huge number of neutrinos
and its fusion furnace, and a guy went out to
measure these things and they're really hard to spot, and
he saw a lot of neutrinos, but not nearly in
the number he expected. There was an enormous number of

neutrinos missing, and so that was a mystery for a
long time. Yeah, Like you had some physics, it's a
math about the Sun that it should be spewing out
a ton of neutrinos, but we where are they? That
was the mystery. That was the mystery, And so I
was wondering, are people aware of this mystery? Do people
know how this work? And you know here you see, Irvine,
we have a special relationship with a neutrino. Do you

know why? Um? I do, because I'm an avid listener
of Daniel and Horry explain the universe for those of
you who are, and maybe you should explain. Well, the
guy who discovered the neutrino, Fred Ryness, was a professor
at u C Irvine, and he won the Nobel Prize.
And the building you work in, Daniel, is called after this. Yeah,
it's called Ryness Hall. And I see a bust of

the guy in the lobby, and you know, there's a
huge picture of his experiment on the wall. And so
I figured, well, most folks that you see Irvine must
be aware. It's not like we're winning physics Nobel prizes
every week around here, and so you got one. You
should expect people to know, Yeah, exactly, And so I
thought people should know about this. Probably everybody around here

knows all about neutrinos. So I walked around campus to
ask people if they knew what a neutrino was and
if they knew about the mystery and then missing neutrinos. Yeah,
so before you listen to these answers, think about it
for a second. If someone asked you what a neutrino
is and whether you knew that a lot of them
are missing apparently, think about what you would answer. Here's

what people had to say. Do you know what a
neutrino is? No? No, I have not. You know they
were discovered by a professor here at you see your vine. No,
I didn't women about No, I've never heard of yeah neutrino. Yeah,
I heard about it. I read about it. I mean
I read something about that in a Physics Building US
lecture hall um, But I can't remember. I know I

read that someone discovered it from here as an anti
neutrino or something like that. I have not. I've heard
of it. Do what it is? I've I've heard of it.
I don't know the specifics of what it is I have.
Do you know whether neutrinos can turn into other kinds
of neutrinos? No? I don't. All right, Daniel sounds like
you need to do a lot more branding work there

at the university. I gotta say I was a little disappointed.
I mean, I love the fact that these dedans are
willing to answer or a a question, that their game for it,
total respect for that. But almost nobody had even heard
of a neutrino. There was one guy who was like
something in the physics building. Maybe I think I read
about it somewhere. Sounds like, you know, he was waiting
for the bathroom and killing time by reading a poster

or something. Oh, that's what you should do. You should
go around campus putting little like bumper stickers on the
inside of bathroom stalls. That's where people do the most reading,
probably if they look up from their phone, which is
kind of gross if you think about it. But let's
not think about that. Yes, so if you're listening to
this podcast in a bathroom stall, you know, hey, think

about neutrinos instead. But hey, actually you're listening to this
podcast abound netrinos, so you're doing both at the same time.
But yeah, maybe it would help if you change the
name of your building to the neutrino something like that.
You know, Yeah, perhaps perhaps Anyway, I apologize to fred
Ryness and the fred Ryness family because all the students
walk around campus have no idea about this incredible discovery

made by physicist here on campus. That's okay, we are
going to educate everybody today about the amazing particle that
is the neutrino and the mystery of why they went missing.
And don't feel too bad. I didn't. I don't think
I knew what a neutrina was until you know, I
started talking to you a couple of years ago. So
it's not it's not an essential part of your diet,
I guess. No. You can mostly get on with your

life without knowing when antrino is, that's true. But you
are sort of bombarded by them a lot. Yeah, they're
everywhere around you. There are a hundred billion neutrinos passed
through every square centimeter of the Earth per second. So
you hold out to your fingernail, that's like the size
of your thumbnail. It's a hundred billion per second. Wow,

that's a lot of neutrinos in my thumb. It is
a lot of neutrinos, and they're all pumped out from
the fusion in the sun, like the sun when it
does all that fusion. It combines all those elements to
make heavier and heavier elements. It pumps out a lot
of energy and a lot of that is in the
term of photons, but also neutrinos because this is fusion reaction,
so a lot of neutrinos are produced. Yeah, all right,

so let's get down into the details of it. So
let's talk about what a neutrino even is before and
then we'll talk about where why people thought they were
missing so many of them were missing. So, Daniel, what
what is it? Neutrino? How would you describe what it is?
It's a really weird little particle because it's an essential
part of our sort of periodic table of particles, but

it's not part of the atom. Like to make an atom,
you need quirks to make protons and neutrons, and then
you need an electron to go around it to balance it.
Then there's this neutrino particle. What is it for? We
don't really know why it exists. We found it, we
see that it's there. It's sort of bounces things out
a little bit, but it's not part of the atom,
like you are not made of neutrinos. You aren't. There

are no neutrinos in you. So it's something that can exist,
right basically, and does exist a lot in the in
the universe, but it doesn't really interact with anything that
we're made out of, right, Like, it doesn't. You can't
really feel them, that's right. Neutrinos are very snobby, and
so you remember that there are several ways for particles

to interact. They can interact via electromagnetism that's light, and
they can interact via the strong force that's gluons that
holds a nucleus together. And then there's this other force,
the weak nuclear force, which is really really weak. That's
the only force that neutrinos feel, right, And it's both
really weak and only really works if you're really really
close to it, right, Like if you're neutrina just happens

to pass very very near the nuclear of your atoms,
then it might react with you, right, yeah, And you
can think of the weak nuclear force is sort of
like another version of electromagnetism, but with a really heavy photon.
Like the photon, the real one, the one that makes
them light, has no mass. It flies across the universe,
it can go forever right, you shine a flashlight from here,

your photons can still be traveling billions and billions of
miles away. But the weak nuclear forces like a version
of that with a really heavy, slow photon. And and
so it's really think I've ever heard of that term before, Daniel,
A heavy photon. Yeah, it's like a heavy photon. And
in fact, the weak forces you can have a heavy light. Yeah,
I feel like that would be a great science fiction

novel title heavy light. Somebody out there copyr at that.
For us, it's like slow heavy light. And so it's weak,
and it's very short range. And so, as you were saying,
a neutrino can pass through an enormous amount of matter
without interacting, Like if it passes through a light year
of lead, that has a fifty percent chance of interacting.
Like you you send a hundred neutrinos through light year
of lead, you get about fifty of them coming out

the other side not even noticing. Right, it doesn't feel
the electromagnetic force, which is what you would sort of
need to feel in order to like push my particles
or even for me to feel really sort of feel
them in the traditional sense of the word of feeling
or touching something. That's right. If you shoot an electron
at a light year of lead, it will bounce off

the surface of it or get absorbed because they will
interact with the other electrons, or it will interact with
the atomic nucleus. And if you shoot a proton at
a piece of lead, it will interact with the atomic
nucleus via the strong force. But the neutrino doesn't feel
the strong force, and it doesn't feel electromagnetism too, so
they two strongest ways particles can interact. The neutrino doesn't

feel at all. It's like a little ghost particle flying
through the universe. And it's both a ghost and apparently
um a multifaceted ghost. Yeah. It comes in three flavors,
fruity ghosts and chocolate ghost and goes no, they're all
diet flavors. Remember this thing has no mass, right, it's heavy.

It's heavy. There's there's romaine, there's iceberg, and there's alfalfa
flavored calorie wise, it's the lettuce of particles. Yes, it's
the lettus of particles. Yeah, it's interesting because we have
we talked on the program once about how there's different
kinds of electrons. Is the electron, the one you know
and love, that's part of you that makes up electricity,

and then it has these cousins, the Muan and the tow.
So together there's three particles. We call them leapt the electron, Mwan,
and tow. The weird thing is the neutrinos also have
three versions, the electron neutrino, the muon neutrino, and the
town neutrino. So there's three kinds of neutrinos, just like
these three kinds of electrons. Now, why are they tied
to the electron and the meu on and the town.

Couldn't just just call them, you know, romaine neutrino between
you know, I was at the meeting and I totally
suggested that and I was shot down. You know, They're like,
you're just a lobbyist for big Salad, And hey, I
am a lobby salad. I am a big pro salad person,
all right, So but yeah, why are they sort of tied?
Why do we associate them with electrons? And that's really

fascinating because it turns out that each neutrino is a
different kind. And if you take a neutrino, we call
an electron neutrino and you interact with it using this
slow photon, the w boson. Then they can turn into
an electron, but a muon neutrino can only turn into
a muon and a town neutrino can only turn into
a towel. And so these two talk to each other.
They're like paired, like the electro on and the electron

neutrino come together somehow. Um, they're like part of a grouping.
You know, we're always looking at particle physics for patterns
and organizations, and it turns out that these two are related,
and the muon and the muon neutrino related in the
town the town neutrino related. There's something about the universe
that that requires them to be connected, right, And you
associated them with electrons because they can sort of turn

into electrons or they sort of come from electrons or something.
There's some something that ties them together as opposed to
like tying them to like corks or something. Yeah, precisely,
you can use a w boson to turn an electron
neutrino into an electron, but you can't turn it into
a muan neutrino. And and there's something really weird about this,
Like the universe keeps count. For example, you can't turn

a mu on into an electron. The universe like has
account like the number of muans in the universe the
number of electrons in the universe, And you can't just
like take one from here and put it in the
other column. The universe doesn't let you do that. You
can't mix a match. You can't make some match like
you might imagine, Hey, take a mu on and turn
it in to an electron and a photon. Get rid
of that extra mass. There's nothing physically wrong with that.

We have no reason why that doesn't happen. We just
don't see it, right. We just we've never seen that happen.
And so for some reason, the universe likes to keep
the same number of electrons and muans. They just can't
turn into each other. And we thought for a long
time that the same was true of neutrinos, that if
you had an electron neutrino, it had to be an
electron neutrino forever. You couldn't just turn it into a

muon neutrino. We thought the same rule that applied to
electrons also applied to neutrinos. Oh, I see, because electrons
can't mix a match. You thought neutrinos couldn't mix a
match between these three different kinds that it can take
the form of yeah, And that's what we're doing all
the time in physics. We're saying, here's a rule. How
broadly does that rule apply? Right? This rule seems to

apply to electrons, mules, and taels for reasons we don't understand, Like,
we have no understanding for why you can't turn a
mu on into an electrono photon. We just don't see it.
It's just it's a descript and of what we haven't seen,
not like a deep understanding of the universe. Maybe someday
somebody will come up with an explanation like, oh, it
makes perfect sense because these things are built out of

different little you know, sub muans or something. I don't know.
But so we see that happening for electronic MUAs and towels,
and we thought maybe the same thing applied, right, all right,
So that's in a trino. It's this kind of snobby
particle that camp doesn't want to bother with us, apparently,
doesn't doesn't really like us, apparently, And so I just said,

it's kind of it's there in the universe, floating all
around us, but it doesn't really interact with us. And um,
I think if you want to learn more, we have
an episode on the neutrino. Right, if you kind of
scroll through, there are archives and you'll you'll find the
neutrino episode just on the neutrino. Yeah, sometime late last
year we put out a whole episode on the neutrino
and how it's discovered and what it means and how
it interacts and gory details about neutrinos. Right, all right,

so let's get into how you guys lost a six
stillion of them per second in this universe. It was
before my time, so I don't know why you're putting
the blame on me. That's sorry. We'll lay out the
clues and the hints of the spoilers um of this mystery,
but first let's take a quick break. Al Right, So

we're surrounded by neutrinos and they're all around those but
they don't they can't touch us. But at some point,
you guys physicists, you guys lost a lot of them,
like you didn't know where they were. I know, I
had them in my hand and then I put my
keys down and I turned around. You know, they were gone, Like,
doesn't happen to you? And it's totally reasonable, right, did
you guys try to put it pussing an ad in

the back of like milk cartons or something. Yeah, we
just drew a blank box. Have you seen these neutrinos?
Have you seen this? Actually you can't see them. Have
you detected any with some heavy water by any chance? Well,
it's funny because you know, we are surrounded by neutrinos,
but they're not just sitting around. It's not like we're
swimming through them. We're not like in a pool of neutrinos.

It's more like we're in a wind of neutrinos. Oh,
I see, we're they're going through us. You know, they're
not they're not even stopping relating, hanging out. Yeah. They're
produced by the Sun and they shot out a great energies.
Something like three percent of the energy of the Sun
is pumped out just in terms of neutrinos. So that's
a lot of energy. Right. The Sun is a big blob.

It produces a lot of energy, and these are shot
out from the Sun and you know, neutrinos are very
light the way almost nothing, and so they're traveling at
nearly the speed of light. Probably, like looking at the Sun,
even three is enough to blind you, you know. Yeah,
if neutrinos could interact with your eyeballs, that they would
blind you. So don't So one more reason to not

be like President Trump and look at the Sun, especially
on an eclipse. Okay, so you guys calculated that the
Sun should be making a lot in neutrinos a hundred
billion per square centimeter per second on Earth. But um,
but we didn't see that. Like that's how much your
model of the sun predicted should be pumping out of

the Sun. How many neutrinos should be pumping out of
the Sun. But you're saying that the mystery was that
we didn't see any neutrinos like that here on Earth. Yeah,
and this started from like do we understand the sun?
Like we think we understand what's going on. There's all
these different elements in there. They're fusing. The fusion process
produces this and that and heat and neutrinos. So if

we understand the Sun, we should be able to check
those calculations. We should be able to run a calculation
that says how many neutrinos does the Sun produced per
second and then go out and measure it. And this
is not because people were interested in like the deep
particle physics of neutrinos. People thought, oh, yeah, we understand atrinos.
They just want to understand the Sun. And so they
predicted how many neutrinos the Sun should produce those hundred

billion per square centimeter per second, and then like looking
at the chemistry of it, right, like you know that
it's fusing hydrogen, and so you know what comes out
of that fusion should have these percentages of stuff coming out. Yeah,
and there's different mixtures and each element produces neutrinos and
different energies and all this stuff. And so put that

all together, it's called the standard Solar model. That's a
model for like what's cooking in the Sun and what's
what it's pumping out. A guy named John Bacall calculated
that he had his model of the Sun and he
predicted a hundred billion per square centimeter per second, and
then his colleague Ray Davis said, well, I'm gonna go check,
and so he built an experiment to go see neutrinos

and try to measure these things and calculate how many
neutrinos were actually flying into the earth. And he found
what a bloody knife for He has this crazy experiment
which involved a hundred thousand gallons of dry cleaning fluid.
And you know, when you're physicists, you have to sort

of make do, Like there's the experiment you wish you
could do, and then there's the experiment you can afford
to do. And usually what you can afford to do
relies on what's commercially available cheap. And you know, Americans
use a lot of dry cleaning fluid, so it's not
that expensive to buy a lot. Is not that expensive
to buy a big volume of dry cleaning fluid which
contains a lot of chlorine. Oh, the chlorine was important, yes,

because when an electron neutrino hits a chlorine atom, it
turns it into argon. This is like alchemy, right. There's
a neutron inside the chlorine nucleus, and when the neutrino
hits it, it turns it into a proton and an electron,
and the proton stays behind the chlorine turns into argon.
So if you have a huge vat of this dry
cleaning fluid. Then very occasionally one chlorine atom will get

turned into argon. Wait, so a hundred thousand gallons of
dry cleaning fluid was not his first choice. He had
in mind something even crazier. Oh man, it's super toxic.
You want to imagine working with that stuff. You probably
killed off a bunch of grad students and that experiment,

but they, you know, the body's worth resolved. Yeah, and
the living ones never had children. So, um, what do
you mean dry cleaning fluid? Is it like chloral chlorophy
phil what if? What if? Yes, it's chlorophyll exactly. It's
a pyro chloro floro carbon. No, No, I'm not sure

exactly what it was, but it's some hydrocarbon that has
a lot of chlorine in it and it's used typically
in commercial applications for dry cleaning. Um. But he just
had this enormous vat of it, a hundred thousand. And
remember that neutrinos. There's a lot of them, but each
one is a very small chance of interacting. So the
bigger your volume, the more likelihood you are to get
one of these chlorine atoms to turn into argon. So

he was just looking at a handful of things a
year of these events. Yeah, it's not like, you know,
you turn this thing on and you got chlorine popping
into argon every two seconds. You know, It's more like
once a month maybe if you're lucky. It's kind of
like a laying out a giant net, right, That's what
these giant vad was, right, which just like like a
catcher's mid for neutrinos, because neutrinos don't really interact with

the walls or the you know, the ground of the earth,
of the clouds of the atmosphere, but they do interact
kind of with chlorine atoms in a way that you
can observe. Yeah, they interact with all that other stuff too,
but just really rarely and chlorine atoms. You can get
a really pure sample that has almost no argon in it,
and the only way to turn chlorine into ar gon

basically is to hit it with a new trino. So
any are gone in there you can mostly assume came
from neutrinos. So that's why he chose that substance, and
then he could bubble it out every once in a
while and see if he found ar gone in there.
And how do you think he's sourced that hundred thousand
gallons of dry I think he had a front. He
just called the local local fashion cleaners and worlds like, hey,

can you do this tomorrow? No, he probably just drove
around to the dumpster behind the local dry cleaners and
just used theirs, you know, all right, So that's how
you that's how you measured. He measured. He put out
a giant vat of it try to catch them, and
he didn't see enough. He didn't catch enough to kind
of justify the model of the sun that we had. Yeah,
John McCall's calculation predicted a hundred billion per square centimeters

per second, and he did his calculation and integrated it
all and he got about a third of that value.
So he was so two thirds of the neutrinos were missing,
like an enormous number, sixty six billion per square centimeter
per second. We're just gone, just missing, just not there,
just not there. And so he went back to his
friend and said, did you check your calculations? Are you

sure the sun is pumping all those numbers out? Were
they friends? Were they? Yeah? They were friends? There they
were you know, this is a scientific collaboration. And they
both ended up with Nobel prizes, so everybody's happy. But
they he went back to checked his numbers, and you know,
with the sun, there are things you can observe the
solar model predicts also light and other things, and so
there's a lot of ways to check that his model

of the sun was right. And he went back and
he double checked everything, and he's like, you know, I'm
pretty sure my model of the Sun is correct. And
we had a pretty solid understanding of solar physics and
astrophysics at the time. So the question was then, see then,
like did you did you take did you make a
mistake in your um how many grad students did you
dissolve in the drug cleaning fluid did you use did

you use dry cleaning fluid or brand new dry cleaning fluid?
You know, well, that's why it's sometimes an amazing opportunity,
but also sometimes the headache, like sometimes the explanation is prosaic,
you know, like oops, you jiggled the cable and it
wasn't connected correctly and that's the source of every problem.
Or remember that new Trino experiment that thought they discovered
new trina is going faster than light. And then the

answer was wiring. Yeah, they didn't jiggle the cable correctly.
So often the mistake is just that there's simple as
a calculation or some other small bug. But sometimes it's
a big clue that that gives you insight into how
the universe works. And what do you think that moment was? Like?
You know, like if you expect to see you know,
if you expect your three kids to go home one day,

when only one of them comes home, you know, that's
a big well, it depends on which kid. I guess,
not your favorite one. Um no, I think it must
have been exciting. I think probably the first of his frustraants.
Ah man, something's wrong, you know. But we are detectives
in me and we like to unravel this stuff. We

like to think about ways to double check your answers,
and let's check this, and let's check that, and let's
check this other thing and everything. Everybody double checked it.
And then other people did experiments, you know, not just
this one guy with his vada experiment with his Vada fluid.
Other people did experiments with other substances, and everybody agreed.
We were seeing about one third of the neutrinos that
we expected to see. So somewhere between the Sun that

you know, spewing out all of these neutrinos and your
vat of dry cleaning fluid, two thirds of those neutrinos
go missing, disappear exactly, have no alibi, all right. So
that so that was a big mystery in physics, and
it was it was a big deal, right, because it's
sort of you know, there's a lot in in this theory,

in this prediction, right, there's your understanding of the sun,
there's your understanding of particles, there's your understanding of how
particles interact with other particles, and so like, if this
is not jiving, then that's that's kind of a big deal. Yeah,
And it was an outstanding mystery for decades. It was like,
here's something we don't understand. Maybe somedays somebody will figure
it out, um, and so decades really for decades. Yeah,

Davis started his experiments in the sixties, and so this
is something which was an outstanding problem in physics for
a while. And you know, we have those problems today,
like a list of things we don't understand, like what
is dark matter. Eventually that will be a history problem,
all right, we'll know the answer and we'll look back,
but at the time it's just a question mark. And
so this was an open question for a long time.
I feel like it's one of those primetime specials, you know,

years later, the mystery still bothers him. I wish sometimes
we could just like fast forward, do a musical montage,
like like a musical montage my way to the answer
what is dark matter? She has some physicist hitting the
boxing um what we called the boxing ball, putting on
a lab coat, standing at the chalkboard, looking confused, having
a moment of inspiration running Philadelphia Courthouse guests exactly, low,

please provide the sound music for that musical montage. But yeah,
and then finally the mystery was solved. Right, finally, you
guys figured it out. They found the missing nutrinas we
did find the missing neutrinos. All right, let's get into
how they found these missing neutrinos. But first let's take
another quick break. All right, Daniels, how did they find

the missing six dillion neutrinos per second that were somehow
misplaced by physicists. Well, they had this idea. They thought, well,
maybe then trinos aren't missing, maybe they're just hiding, and
maybe they're hiding because they turned into other types of neutrinos.
And we talked earlier about how there's three kinds of
neutrinos electrons, muans, and towels, and they thought, well, what

if some of these are turning into muan neutrinos or
some of these are turning into town neutrinos. Oh my god,
they faked their death. That is such a standard opera
plot points. Should have been the first thing we thought of, Right,
did you look for neutrino with a weird mustache on it,
check to see if they had they had any large
outstanding debts or something. Yeah, Well, we thought, remember, well,

we're sure that electrons and muans can't turn into each other.
We know that doesn't happen. We don't know why, but
we've never seen it happen. Dedicated experiments looking for that
haven't seen it. But people thought, you know, we could
explain this mystery if if electron neutrinos were turning into
muans and tows wouldn't another kind of neutrino interact with chlorine? Also, like,

how does that explain? No, it wouldn't. So a muan
neutrino that comes and hits the chlorine, doesn't turn it
into argon. What does it do something different or it
just doesn't interact with the chlorine. It doesn't interact with
the chlorine in a way that turns into argons. You
can't measure muan neutrinos or town neutrinos um by looking
at chlorine. And so what people did was they built

another experiment, one that was sensitive to muans and one
that was sensitive to town neutrinos. So there's an experiment
called the Snow experiment. It was at Submarine Neutrino Observatory
and it could detect separately the rates of electron muan
and town neutrinos. And then they found them. And then
they found them, They're like, uh, there they are. We
saw them, these neutrinos. So you use your credit card.

You're still alive. Precisely, they were able to spot them
into those neutrinos are they're They're just a different flavor.
So there's a bunch of neutrinos coming from the Sun.
Some of them turned into different kinds of neutrinos, and
then they go through us and the Earth. And you're
saying that they were only missing because we weren't looking

for the right kind of neutrino precisely. And it's important
to understand the Sun only makes electron neutrinos. There's three
different kinds where the Sun just makes electron it's like
a pure source of electron neutrinos because you have electrons
and fusion, right, the electrons with the lightest ones, and
so electrons are the thing that's in the atom, and
so electron neutrinos or what's made in the sun. So

the Sun produces all these electron neutrinos. But then there's
three kinds, and so by the time they get here,
they sort of sloshed around and some of them become
muns and some of them become town neutrinos. Right, And
they do this randomly or is it like a their
decay from like an energy high energy state to a
lower energy state or is it just kind of random?
Like do they I want to? I feel like more

like a towel. Is that how you get dressed every day?
So sort of randomly quantum mechanical wardrobe to I feel
like the working cartoon is tomorrow. I don't know if
you just invented quantum fashion. Jorge, Yeah, um, though it's
not entirely random, there's some random element to it, but
it's actually really fascinating and reveals something really deep about neutrinos.

You see, the weak force the thing that can interact
with neutrinos. It sees neutrinos differently than the Higgs boson does.
So those w bosons and the Higgs bosons are sort
of disagreeing about how to talk to the neutrinos. Wait,
what what do you mean? Yeah, well, so the weak
force says, okay, there's three kinds of neutrinos. There's electron neutrinos, mionutrinos,

and town neutrinos. And like I said earlier, the difference
between those is that the weak force can turn an
electron neutrino into an electron or a muon neutrino into
a muon. That's how the weak force sees neutrinos. But
the Higgs boson comes along and it says, no, no, no,
there's three neutrinos. There's numbers one, two, and three, the
lightest one, the medium one, and the heaviest one. And

you're like, okay, that's cool, which one is which? But
it turns out they don't overlap. It's not like neutrino
number one is the electron neutrino, and two number two
who is the muon neutrino the Higgs boson. What it
says electron number one, it means a weird mixture of electron,
muon and taw, and the Higgs boson neutrino number two
is a different mixture of electron, muon and tao. So

it's like these things look at it totally differently. They
see a different mixture. Are they still different things or
does it depend on who's interacting with them. It depends
on who's interacting with it. So if you're just flying
through space, what you need is to have a certain mass,
Like for a particle to fly through space, you need
to be a thing. You need to have a fixed mass.
Your mass can be zero or whatever, like for a photon,

but for any particle to propagate through space, it needs
to have its mass specified. Remember that's how you get
masses by moving through the Higgs field. So the Sun
makes you using the weak interaction. You're an electron neutrino,
you're flying through space, you have mass because of the
Higgs boson, and then you're either electron one, two or three, right,

But the electron neutrino is a weird mixture of one, two,
and three. So as it's flying through ace, these things
fly through space differently. The electron one, electron two, electron
three parts of the electron neutrino fly through space differently,
So by the time they get to Earth, you have
a different mixture of electron one, two, and three. And
maybe you're amuan neutrino or maybe your town neutrino. Wow,

that makes no sense, Daniel. So I start off as
one kind of netrino and you're saying that on the way,
the universe just kind of like looks at me differently.
And by the time I get to my destination and
two different things. Say your family goes on a trip together,
and one of you is thirsty and one of you
is hungry, and one of you is totally satisfied. Now
along the way, maybe you get some food and drink.

So by the time you get your location, the different
people in your family are feeling different than when they
left because the trip has been a different experience for
each of you. So by the time you get there,
it's kind of like you're a different family. But that's
because like time has passed and maybe I got thirstier
or hungrier, or I drank some water on the way.
Is there something actually happened on the way for these

neutrinos or is it just kind of like a the
universe sort of corrects itself, and the different parts of
the electron neutrino fly through space differently because they have
different masses. The electron neutrino doesn't actually have like a
mass like you can say with the mass of the
electron is but the electron neutrino doesn't have a mass.
It's a weird mixture of three neutrinos that do have masses.

So there's a different categorization, like a different set of
names based on the Higgs. Yes, there's different ways to
categorize neutrinos, and the Higgs boson categorizes them one way
and the weak force categorizes them differently. They don't agree.
And the Higgs force decides how you get mass, and
so it says you get this mass, you get that mass,
you get this other mass, and the weak force decides

what particle you turn into, like you turn into electron,
you turn into new and you turn into a tow
and because they don't agree, you get these really weird behaviors.
But then what comes out the other what arise here
on Earth is actually two different Is it still the
same electron neutrino or is it now something that's been
changed because of the what happens when you go through

the actual universe, it's something that's been changed. And so
electron neutrina starts out with some mixture of of neutrino one, two,
and three, and then those fly through space differently because
they have different masses, and by the time it gets here,
it's a different mixture, and that different mixture can be
more likely to be a muan neutrino. So then when
it gets to Earth it can be like, oh you
know what, now I'm the meu and neutrino. But when

it interacts with like argone than it does care whether
it's precisely then it does care. And so when they
it cares at the beginning at the end. But the
suwhere in the middle of the universe is like no, no, no, no, no,
I don't I don't like what you're starting out with.
I'm gonna change up your identity. Yeah, it's like it
spins all the knobs in flight, and then when you
get here you're like, huh, you're totally different. You know.

It's like if everybody got an airplane and then in
flight you like swapped heads and legs of all the passengers, right,
and then when you got the other to the flight,
you'd be like, wow, I don't recognize anybody. That is
both disturbing and also confusing. It's is it more like
kind of like you know, like um, like shooting light

through a prism or something like somehow going through the
medium separates out the nature of it. Yeah, it's it's
a lot like that. Um. And for those people who
are like really good with linear algebra, it's essentially what
you're doing is you're rotating the basis set. You have
a different eigenvectors that describe the sort of space of particles,
and the Higgs boson uses one set of eigenvectors and

the weak forces a different set, and they don't agree,
so you can rotate from one to the other. And
why is there such a discrepancy between what the universe
sees or things and what the math and the physics
and the collisions all predict. We don't know. We don't
know why the weak force and the Higgs boson see
these things differently. It's fascinating. We just don't know why
they don't agree. They're very different forces, right, and so

they I guess they have the right to make whatever
choice they like, But we don't know. We don't know.
I um they're rotated in this way, like why neutrinos one, two,
and three are not aligned with the electron, muon and
town neutrinos because it's not the case for the other particles,
like the EMU and tao. The weak force interacts with
them the same way the Higgs boson does. Like the
electron has a specific mass, the muon has a specific mass,

and so does the too. So it's a weird twist
that only happens for neutrinos. It's like in the Murder Mystery,
it's like, no, actually turned out nobody killed Mr Green.
Actually he turned into Mrs Mrs Plum. Turns out Mr
Green has two identical twins or a member of identical triplets,
and they all speak weird accents, and due to some
magical or unexplainable quantum phenomenon of the universe that's what happened. Yeah,

and it's not something we understand, and we actually don't
even understand how the neutrinos talked to the Higgs boson,
Like most particles get their mass from the Higgs boson,
but we don't actually know the neutrinos do, because that
to get your mass from the Higgs boson, you have
to have a particle and an antiparticle, like the electron
and the anti electron. But we don't know if neutrinos
have antiparticles or if they are their own antiparticles the

way a photon is. So there's a lot of mysteries
about neutrinos. I feel like we started out with such
an um simple mystery where are they? And we've turned
out like turning into a fundamental mystery of the universe
that we don't know precisely. And that's what's amazing about
these experimental checks. You know, they go out there like, yeah,
we think we understand this, let's just go double check.
Huh didn't work. I wonder what that means? Dot dot

dot crack open deep mystery of the universe. Right, that's
the possibility every time you're about to do a boring
experiment is that it could be the thread that unravels
your entire understanding of something fundamental about the universe. And
you wouldn't maybe think that was the case, just because
these particles are so inconsequential to our everyday lives, right,
so non interactive with everything else. But it turns out

then maybe cracking them open what tell us a lot
about the universe. Yeah, they are. There are a lot
of them, and they ignore, but they have a lot
of tiny little clues and when you add them all up,
they tell you something really fascinating about how the universe works.
And there's a lot of mysteries there. We still don't
know the answer to um. There might be CP violation
in neutrinos, to all sorts of weird stuff. But they're

really challenging to measure because they mostly ignore you, and
so you have to build really big detectors and wait
a long time just to do anything basically with neutrinos.
Is this going to drive out the price of my
drug cleaning? Daniel? Is what I is? How I wouldn't know.
Let's bring this back to me, right. I have seen
sort of a lot of like a lot of particle physics.

I know in your field is sort of turning towards
neutrinos because it is sort of like a place where
there are still a lot of big open questions. Yeah,
the entire United States high energy community is turning towards neutrinos,
focusing their energy on these questions because we think that
there are a lot of mysteries there that might be open.
In fact, there probably are still questions we don't even
know how to ask about neutrinos. It's like the beginning

of a field uh neutrino physics. So there's a bright future.
There's a lot of people working on it, a lot
of really fascinating questions, and I think in ten years
will know a lot more about the way the whole
universe works, just from these tiny, little ghostly particles. All Right,
so we we figured out the mystery, Daniel, we will
take credit. What fraction the Nobel Prize did we get
I don't remember, as John Renes with the weak fours

in the in the Mysterious Force, in the Underground lab
the Unknown, Deep Mystery of the Universe. It was Ray
Davis with a hundred thousand gallons of dry cleaning underground.
So the next time you look out into the universe
or see will not see this time, but be out
on a sunny day and look the sunlight all around you.
Maybe think about all the mysterious little neutrinos that are

going through you and everything else, and what secrets of
the universe they are hiding. We hope you enjoyed that.
Thanks for joining us, See you next time. Before you
still have a question after listening to all these explanations,
please drop us the line. We'd love to hear from you.

You can find us on Facebook, Twitter, and Instagram at
Daniel and Jorge That's one Word, or email us at
Feedback at Daniel and Jorge dot com. Thanks for listening
and remember that Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast from
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