November 19, 2019 • 41 mins
This mysterious particle is part of our Universe, but not part of the atom
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Speaker 1 (00:09):
Hey, Orne, Hey, do you have a lot of cousins
in your family? Yeah, I've got a few. I have
maybe over thirty six cousins, maybeing around the number. Wow,
that's a big family. Well, would you be surprised to discover,
sort of late in life, a brand new cousin you'd
never even heard of before? That would be pretty amazing,
kind of weird, I guess, but maybe yeah, I would
(00:30):
be surprised, all right. And then what if that cousin
turns out to be exactly like you, like, look like
you in every single way. Okay, Yeah, that's that's getting
kind of weird, all right. And then what if this
cousin looks exactly like you? Accept there are two hundred
times more massive Dan, Hi, I'm Poor. Hey, I'm a
(01:07):
cartoonist and the creator of PhD comics. Hi I'm Daniel.
I'm a particle physicist, and I do not have thirty
six cousins. Welcome to our podcast, Daniel and Jorge Explore
your Family Tree, in which we examine all the amazing
and fascinating things about the universe, about the big things,
the small things, and about how things are related to
(01:28):
each other. Yeah. So, um no, that's not the name
of our podcast. It's actually Daniel and Jorge explain the
university production of My Heart Radio, in which we do
examine crazy things about the universe and we try to
make them relatable. We try to present them in a
way that you can understand them, so they connect to
topics that matter to you. Yeah, in a way, we
do sort of explore the family tree of the universe.
(01:49):
You know, how you came to be here, what what
sort of pairings and fusions occurred for you to be
here in this universe appreciating it and listening to funny podcasts.
H I think one of the reasons people are interested
in the origins of the universe and the creations of
our cosmos is because they want to understand how we
got here and what it means in the same way
(02:10):
people explore their family tree. They want to know where
did my family come from, what stories are in our past,
what is my personal context? And also I think it's
a useful way for us to sort of organize our thoughts.
You know, when we think about the the universe in
terms of particles, we sometimes think about how those particles
are related to each other, Like, do particles have families. Yeah,
(02:30):
and I think you know, every part of anyone's family
tree or origin tree kind of tells you a little
bit of the story of the of the whole thing, right,
like how you came to be, how things work, and
how things move about in life, and other ways your
life could have gone. Like if you have a very
successful cousin that's a gazillionaire, then you know, you wonder
(02:51):
could I have made different choices and been a gazillionaire?
Or if be people's paths in life diverge. Yeah, or
if you are that busile in our cousin, then good
for you. Please please contact us. We would love to
take your donations. That's right. It would be awesome to
have at least one gazillionaire listener. Who is our richest listener?
That's a good question. Pod. You have to send us
(03:12):
a check. Whoever sends it is the biggest check that
doesn't bounce. When's this little plaque here that I am
just now putting together. It's made of platinum? Right, Yeah,
well it's going to be once we get those checks. Yes,
you'll get a drawing of a plaque that's made of platinum.
Oh my gosh. Even more valuable from a well known
(03:35):
internet cartoonist exactly. But we do try to understand the
world around us, and sometimes that means putting things in
context and understanding what are the patterns, what are the
structures there, and what clues do those patterns give us
about that sort of fundamental nature of the universe. Yeah,
so to be on the podcast, we'll be talking about
(03:56):
a particle in nature that is maybe not the most
famous one um and maybe not the most well known
one or consequential in your existence, but which does I
think tell you a little bit about and told humanity
a little bit about how the universe works. Yeah, this
is the non gazillionaire cousin. This is the cousin that
(04:16):
ended up maybe sleeping under the overpast and wearing funny
clothes to the family reunion. I feel bad for this particle. Now,
this particle doesn't need your help. It's very massive. Yes,
So in today's episode, we'll be talking about the muan electrons, mysterious,
(04:36):
lesser known, much more massive cousin. And I'm biased, of
course because I'm a particle physicist, but I think it's
really fascinating to think about how we know each particle
is there. We talk about the standard model of particle
physics sometimes, but that's a theoretical construct. It's like our
idea for how these particles might relate to each other.
And that's fascinating. We'll dig into all that, but I
(04:58):
think it's also really important. Remember each of these were discovered.
There's a story behind each particle. Humanity didn't know it
existed and then boom, some experiment revealed it. And on
the podcast, we've talked about the first discovery of the particle,
how the whole concept of a particle was created, the electron.
Then we talked about how we know the photon is
a thing, how we know it's really a particle, the
(05:20):
photo electric effect, And so now we're gonna take the
next step and talk about the discovery of the muan. Yeah,
because you know, I think that every particle tells a story,
you know, and also every story is made out of particle.
So there's kind of this really weird, confusing loop there
that honestly, Yeah, this is like the Superhero Origin story
particle version. Yeah. So the muan is not a name
(05:43):
that rolls off the tongue. Makes me think of maybe cows,
mu muans, maybe uan Muan, Muan mu Off, muanmu Off.
I was thinking sort about karate kid thing there, but
it's back to the eighties reference. Yeah, back to the
age differences. And it's it's funny actually because the name
(06:04):
Uan is totally inappropriate. We'll dig into it later. But
they named it before they discovered it because they thought
it was going to be a different particle, and then
they sort of changed the name later. Um, it's not
a great history for naming particles. Boy, my favorite topic
in science. Yeah, and so I was wondering, how much
do people know about me once? Is it a famous
(06:26):
particle or is it sort of the darker cousin of
the electron that nobody really knows about, hasn't gotten the
same Instagram attention the black Sheep, the gotee wearing particle
of the family tree. Now you're setting enough to be
like the grumpy particle. It's going to come in with
some evil plan to finally get It's it's revenge, and
it's you already made this particle, the homeless particle that
(06:47):
lives under a bridge. So yeah, that was the sad
particle that deserves our love and compassion, not the one
that's been plotting its victorious return to the center of attention. Well,
you never know what these particles, you know, physics, there's
a lot of drama. But as usual, I walked around
and I asked people if they knew what the muan
(07:10):
was and how we knew it was a thing. Yeah,
So before you listen to these answers, think about it
for a second. If someone asked you what a mu
on is, would you know what it is? Have you
heard it before? Here's what people had to say. I'd
say it's a unit of measure. It's like one of
the fundamental elements or particle of what makes up everything.
Mu one. I believe this to be the name of
(07:31):
a sub atomic particle uh luans luans uh. I don't
remember what classification they follow under as far as the
naming conventions. Fundamental particle, some sort. It's real small subotomic particles.
I kind of represented what it does. How do we
(07:53):
know nuance exist um particle starts. So what's your opinion
of these answers today? Good? It sounds like most people
have heard of it or I heard of the word before.
You know, very only a few people said never heard
of it or think it was a unit of measure,
like a you know how much water? Would you like,
(08:13):
I'll have seven muans of water. I wonder that if
you pronounced it correctly, maybe they knew about it, but
just under a different pronunciation. Do you think I'm mispronouncing
the name of mu. I don't know. I mean, what's
the correct way? Is it muan or muan? Like you're
making it sound like a Disney movie, like, oh, my
favorite Disney princess is mulan. My favorite Disney princess muan muan. Oh.
(08:40):
That is a great way, though, to get more attention
for particles in the mainstream. We should get Disney to
name the next Disney Princess after a particle. Why not that?
Why it could be the next Pixure movie. What it's like?
What's the emotional roller coaster right of being a fundamental
particle of nature? Yeah? So much to explore there, and
I expect that will be getting checks from Pixar when
(09:01):
they make a billion dollar movie out of it. But
I was impressed with these answers, though, I want to
pick a bone about one thing. People say, yes, it's
a fundamental particle, totally cool. People also say it's a
sub atomic particle or it's one of the fundamental particles
that make up everything. And that's really a key idea
that I think people have not understood about muans, that
(09:22):
you can be a tiny particle and not be sub atomic,
not be part of the atom. Oh, I see, subotomic
doesn't just mean it's smaller than atom. You're saying that,
it means that you're part of the atom. Remember, fundamental
particles have no size, their dots, they're zero volumes, so
they're all smaller than the atom. In that sense of
(09:43):
being fundamental guarantees you'd be smaller than the atom. I
think to me, sub atomic means it's part of the atom,
like you break it up and you find it inside
the atom. Okay, so we'll get into that, but let's
bring it down for people. For us, what is a
muan and why does it sound like an electron? You
it ends with O N, but maybe, but it's not
the electron. Yeah, but it really is related to the electron.
(10:06):
It's sort of like the electrons cousin. And by that
I mean that it's identical to the electron in so
many ways. It has the same electric charge, it has
the same interactions with matter like it interacts via the
weak force and via the electromagnetic force, but it doesn't
feel the strong force, just like the electron. It has
(10:26):
a neutrino, just like the electron has its neutrino. So
in so many ways, it's exactly the same as the electron.
Sound like when you discover a new particle and it's
totally different, like a cork or a gluon, it's just
completely different from the electron. This one is very very
similar to the electron. It's like weirdly similar, but then
with one important difference. Okay, so it's a particles. It's
(10:51):
not a cow, it's not a Disney princess. So it's
a particle, meaning like it's a it's one of these
things that you see nature in the universe, like things
that pop up and you can touch them and and
there it's a thing. Yes, muans are a thing. There
are a little thing. There are particles, and there are
little dots of matter. They have mass and they have
(11:11):
charge and they interact. Okay, so it's it's a particle
like the electron. But you're saying and you say it's
a cousin of the electron, not that they share like
not that their parents were siblings, but just like in
the sense that it's very similar to the electron. Yeah,
when we organize our knowledge, we look for patterns. We
look for similarities. Right like when we were a hundred
(11:33):
years ago, when the state of knowledge about the universe
was the periodic table. We didn't just have like a
pile of different elements and say here's an element. There's
an element. We said, oh, look, this one is similar
to that one. They're both really active, or these are
really similar because they're both really inactive, or this one
weighs a tiny bit more than that one. We notice patterns.
We put those patterns together in the same way we're
looking for patterns in the fundamental particles. So we try
(11:56):
to figure out which ones are related to each other.
And we have only a few handles on each particle.
Is only like a few things we can know about
a particle, right, And so is this a particle that
we can see in our everyday lives, like is it
floating around? Does it move around wires and electricity like
the electron, or is this kind of a weird one
(12:18):
of those weird particles And you know you don't ever
actually see Yeah, you don't see the muan because it
doesn't last for very long. It lives for two point
two microseconds and then it turns into an electron and
some neutrinos. But they are actually everywhere. There's ten thousand
muons going through a square meter of Earth every minute,
so there's a lots of muans everywhere, but you just
(12:39):
can't really see them very easily because they don't last
very long. Wait, what I mean? How can they be
everywhere but also only last two point to microseconds? Does
that mean that they're they're constantly coming into existence, lasting
for two point two microseconds and then disappearing and breaking up,
or what does that mean? How can they be all
around is but also evaporating at the same time. Well,
(13:00):
there's two things going on there. One is your right,
they're being created um when particles hit the atmosphere. So
protons hit the atmosphere and they create a shower of particles,
some which include muans, and those muans fly along a
little bit, but they don't last very long, just two
point two microseconds, and then they turn into electrons. But
they last for two point two microseconds according to their
(13:20):
clocks because they move really fast. There's a relativistic time dilation.
So the according to us that two point two microseconds
takes longer to click, and so for us it can
take like seconds or minutes from muans to decay. But
for them, if you're sitting on top of the muan,
it would only last You would only be alive for
(13:42):
two point two microseconds. Yeah, that's the half life of
a muan. So muon is not stable. It's not like
an electron you can just sit there for eons and
eons and just be itself. A muon is a heavy particle,
and heavy particles like to decay into lighter particles. In
this case, the muon turns into an electron very quickly
according to its clock. Oh, I see the ones that
we see. The ones coming from the atmosphere are moving fast,
(14:03):
so they last longer. But if I just created a
mew on here in front of me, it would last
only for two point two micro seconds, and it's not
going anywhere. If you could bake muans in your oven
and you take them out of the oven two point
two microseconds later, boom, they turn into a electro. Yeah,
you gotta eat them up real quick. Exactly. They're like
making fortune cookies or toss them really fast, have him
pop out of the toaster really fast, in which case
(14:25):
they would last longer technically, right, that's true. Yeah, exactly.
Somebody could shoot muans into your mouth and it would
last long enough to get there. I wouldn't recommend that.
That's that's not a suggestion for something somebody should do.
And actually, two point two microseconds it is kind of
a long time for a particle that's this massive to last.
And so what does it mean that it disappears or
breaks up like it? It's just unstable like it, just
(14:48):
it's made out of other things and it breaks up
or literally just kind of evaporates into energy and that
energy turns into something else. Yeah, that's a great question.
These are fundamental particles, so they're not made up of
anything else. As far as we know. The muon turns
into the electron. It's not like it has an electron
inside of it, and it breaks up into an electron
and other stuff it converts. It goes from a muan,
(15:12):
it turns via the weak force into a W particle
and a neutrino, and then the W particle turns into
an electron and another neutrino. So the muon turns into
an electron and two different neutrinos, but it didn't have
those bits inside of it. Remember, particle physics is like alchemy.
We can convert one kind of matter into another kind
of matter. Okay, so it's um. It doesn't break apart,
(15:35):
it's just somehow. It's it's very existence. The universe sort
of doesn't like it. Like it. It can just seesis
to exist and in favor of other things existing instead
of it. Yeah, and this is true for every particle
that is pretty massive. The universe doesn't like massive particles.
It's like putting a particle on the top of a hill.
Eventually it's going to roll down. And so the muon
(15:58):
is like the at the top of the on. The
electron is rolling down to the bottom of the hill.
Eventually the muon is going to turn into the electron.
And every particle in nature that that can do this
does this. The only reason the electron doesn't is that
there's no lighter particle for it to turn into. Oh,
and that's why we are able to exist, because the
(16:18):
universe does seem to like electrons and quarks which make
us up. And so that's why we were stable. But
if we were made out of me as, we would
disappear pretty quickly. Yes, exactly. We are made up of
the lightest particles out there, up corks and down corks.
Of the lightest corks. Electrons are the lightest version of
that kind of particle called a lepton. So the matter
(16:39):
that makes us up that's stable is made out of
stuff that can't turn into lighter stuff because there is
no lighter stuff for it to turn into. Right, Yeah,
there's nothing for it to turn into, so we we
stay where we are. But the muon is heavy and
could turn into something else. So it does precisely. And
for those of you wondering, like, well, what about a photon?
Why can't an electron turn into a photon? Of photon
(17:00):
is mass lists Remember that there are rules about how
these things happen, and one of those rules is conservation
of electric charge. An electron has a minus one charge,
so it can't turn into a photon which has zero charge,
because you have to somehow disappear that charge. The only
way for that to happen is for an electron to
hit a plus one positron, and then they can turn
into a photon together, but for a particle to just
(17:22):
spontaneously decay, it has to convert to another particle that
has all the same sort of quantum mechanical numbers. Okay,
so the muon is the electrons massive cousin or massive
sort of like alternate universe version of the electron. Right, Yeah,
it's two hundred times the mass of the electron. It's
really really massive. That's a lot. It's like crunched into
(17:43):
the same meat. Yes, exactly. It's like if you met
another version of you, but you weren't bigger, you were
denser or something. You're two hundred times as much mass,
but still fundamental. And it doesn't hang around existence very long,
and it usually breaks up into or not breaks up
into runs into lighter particles, so we don't really seed
around that much. But still it's sort of an important
(18:05):
part of the universe, and it seems that it's important
part of the universe and also tells us a lot
about the mysteries of how everything is put together. Yeah,
and it actually lasts a long time for a heavy particle.
Other particles that are heavy, like the Higgs boson, they
decay much more quickly. They decayed in like ten to
the minus twenty seconds, whereas this one decays very slowly,
(18:27):
it's just two point two microseconds. And the reason is
that it decays via the weak force, which is very weak.
To the weaker the force, the longer takes for that
decay to happen. M hmm. All right, let's get into
that a little bit more, and also how it was
discovered and why it is such an important particle. But
first let's take a quick break. All right, So the
(18:58):
meuan decays by the weak force. What does that mean?
How can something decay via a force like the force
makes a decay? Yeah, the fource sort of provides the
avenue for the decay to happen. Like, how does a
muon turn into an electron just just roll down a
hill and say, hey, now I'm an electron. It has
to has to be an interaction there. And so what
happens is the muon turns into a W particle and
(19:21):
a neutrino. And the W particle, remember, is the particle
of the weak force. It's like the weak force version
of the photon. And so that's what we mean when
we say uses the weak force to decay. It doesn't
just spontaneously happen. Something has to sort of carry that information,
so it has to make it happen. It's like a reaction,
and that reaction always includes one of the forces, and
in this case it uses the weak force, right, and
(19:43):
that weak force came out of just its own energy.
It uses the mass. Right. The muon is a huge
amount of energy in it because it has so much mass,
and that mass is turned into the energy of the
electron and the neutrinos that come out of it. So yeah,
the weak force turns the mass of the muan into
very small masses of these other particles and gives them
a lot of energy, right, and it ends up as
(20:04):
an electron and to neutrinos precisely. All right, Well, to
tell us Daniel, how was it discovered and why is
this an important particle? Well, it was discovered initially in
cosmic rays. Um. People saw these particles just sort of
shooting from the sky and they didn't understand what was
making them, and they thought, oh, well, you know, we
found a few particles, so these are probably electrons. This
(20:25):
is you know, in the early nineteen hundreds, we didn't
have a really deep understanding of how particles work. We
didn't have a good bench of particles, and so people thought,
you know, everything they saw they thought in terms of
the particles at the time. So you have to sort
of wind your mind back to what we knew at
the time. Back then, we knew about protons, we knew
about neutrons, we knew about electrons, and so people saw
(20:47):
these particles shooting from the sky. They didn't know what
made them, but what they saw was that they penetrated
really far into matter, much more than electrons could. We
saw the actual nuance and not the not what it
looks like after it decays or turns into something else.
Like we actually you can actually see and feel the muants.
You can't really feel them, but you can make particle
(21:08):
detectors that can detect them. You can actually do this
in your garage using something called the cloud chamber. They
were able to see them using detectors that they put together.
And these detectors were like a cubic piece of film,
like remember the old way films worked, where like light
was exposed on the film. You didn't have a digital
camera or anything, and that made some kind of chemical change.
You're saying, you can make like a solid cube of this. Yeah,
(21:29):
you just take a solid cube of it, you leave
it up on a mountain and you leave it there
for like six months, and then you cart it back
down or you guys your grad students to do that.
Then you slice it into pieces and then you can
develop each of those. And what you do is you
see all the particles that shot through it in those
six months, and so they can see and when they
did this, they saw all these particles shooting through this
(21:51):
film and they were surprised at how far they were going,
because electrons shouldn't get that far. Electrons penetrating a little
bit and then they stopped. But these particles were shooting
all the way through. It's kind of like a bull
in a china's shop universus, like a mouse in a
china shop. Yeah, And they didn't understand that. They thought, well,
you know, are there two kinds of electrons or there's
(22:11):
sometimes electrons can penetrate really far. It was really a
puzzle at the time. What made them think it was
an electron? Why couldn't it be like, uh, some kind
of new atom or something. We did know it had
negative charge, and so I think that's what made people
think it was more likely to be an electron or
something like an electron than something positive like inside the nucleus.
And remember, at the time, we only knew basically about protons, neutrons,
(22:33):
and electrons, and so everything we saw where like all
of a sudden, having this imagination that we could just
explain everything in the universe in terms of these particles,
and that was It was a great success of the
particle model at the time, right, like everything could be
built out of protons, neutrons, and electrons. What a wonderful simplification.
And so when we first saw these particles that penetrated
really far, we thought, well, it must be one of those, right,
(22:56):
But it was not. It was not, and people were
able to then later douce it in the laboratory using
collisions and and all sorts of other stuff, and they
discovered that if you put it in a magnetic field,
it didn't bend as much as an electron. And that's
when they decided, you know what, this must be a
different kind of thing. It's like a new version of
the electron, a different flavor of the electron, because it
(23:17):
must be more massive, which is why it doesn't bend
inside the magnetic field as much reflected as much because
it has so much mass, it that just has more inertia. Precisely,
it takes a stronger magnetic field to bend a mu
on than it does for an electron. And this was
kind of a scandal in particle physics at the time. Scandal. Yeah,
people were upset. They were like, what a mu on?
(23:39):
Who ordered that? Like, we don't need this. Get out
of here with your ridiculous new particle. We have this
beautiful description of the universe. We don't want more particles.
Up until then, everything that you knew about helped make
the universe. It's kind of what you're saying, like everything
you knew about at a purpose. Yeah, we had taken
apart the stuff around us and found the basic building blocks,
(24:00):
and then we didn't. Some people were like I don't
want to hear stories about other building blocks that could
be out there. It just sort of confuses the issue, right,
It's a shift in the question not just what are
we made out of? But what is the basic organizing
principle of the universe. It shows you all of a
sudden that there's a larger question you didn't even think
to ask. It's like you find something that you don't
know what to do with it, like it it doesn't
(24:22):
help you with what you knew about how things work. Yeah,
you're putting together jigsaw puzzle and all of a sudden,
somebody hands you like a really big piece that just
doesn't fit, and you're like, what I didn't ask for,
that I don't need. That doesn't help me with my problem. Like, well,
but okay, but this piece is here and it's not
going away, right, Yeah, And so it makes you think
that maybe there's another puzzle, or that the puzzle is
(24:44):
bigger than you think it is. Yes, all of a
sudden you realize this is a three dimensional puzzle and
you've been only playing on on two dimensions, and and
it just blows your mind. And so that's. Ah, it's
sort of an earthquake, an intellectual earthquake through the field
at the moment. But also it's a great opportunity. Those
are the kind of discoveries that make you realize, Wow,
(25:04):
there's a whole larger question to ask, and there's a
whole world of answers out there. And of course now
we know there's not just the meal one. There's also
the Tao, which is the even heavier version of it,
and that every particle has these cousins. Yeah. I like
how this counts as a scandal in physics, Like was
it on the front page of the Daily Physics News
or the National Enquiring Enquirer of Physics? Um newspapers, people
(25:31):
to tabloids. People had to give testimony about this and
there You know, physicists are not that exciting, so we
just got to create drama wherever we can. There was
even more drama because some people had predicted the existence
of a particle sort of similar to this. Mm hmm,
what do you mean predicted like just just guessing. Yeah. Well,
(25:52):
there was a famous physicist named Yukaba the Genius and
won a Nobel Prize for all sorts of fascinating stuff.
And he was trying to understand the strong force. He
was like, okay, the weak force, we have that one.
We have the photon for the electromagnetism um, but what
mediates the strong force? And he did some calculations that
he thought, I bet there's a particle out there about
(26:13):
two hundred times the mass of the electron and it
mediates the strong force. All right, So that's his prediction, right,
And back in the day, physics would just make predictions,
like here's my idea and here's what I predict, Like
we need this for this for what we know to
make sense. Yeah, just like with the Higgs Boson. Peter
Higgs said, this doesn't make sense to me, but if
you look at the universe in a new way, then
(26:34):
it makes more sense. And this new way predicts a
new particle, so you can test my theory. That was
what you Kala did, and he predicted a new particle
about two hundred times the mass of the electron. Then
they found this particle and you Kal was like, who
I was right, But it turns out this particle has
nothing to do with the strong force at all. So
it's just like a coincidence, right, And he still got
(26:56):
the Nobel Prize. He still got the Nobel Prize, but
not for this and um, not for this one. But
he's sort of the reason why this particle has a
strange name. Oh really, he he was a fan of Cows.
I don't know if he liked Kobe Beef, you know,
the guy's Japanese or anything, but he you know, we
had the electron, which is really really light, and we
(27:16):
had the proton, which is like two thousand times the
mass of the electron, and he predicted a particle sort
of an intermediate mass, and so he wanted it called
like the you know, the mazo tron something where mazing
means like middle, and so that was the sort of
the origin of this, like, let's call these particles here,
you know, in this mass region, we'll call the meso particles. Well,
(27:39):
what do you have to call it the messo on
or messing on or I feel like just to be
consistent here. And then later people were like, well, it's
not really have anything to do with these other particles
we found in the same mass, but we'll just keep
calling it the muon anyway, I bet he wanted to
call it the me on. I'm so smart. Yeah, but
(28:04):
this is where like, come on, dude, but it's a
it's a fascinating moment in physics because or the yuan
is the mean, or how about we calling muan done compromise.
That's exactly how these decisions get made, and that's why
we have such terrible names for particles. Yeah. So, but
(28:24):
now it's so it's a well known thing, like everyone
knows about muans. Did they know that they're there and
you can study them. You can. You can. They're coming
through going through our bodies right now at ten thousand
times per minute. Yeah, ten thousand muans per square meter
per minute, and you're right. At first it was totally
exotic and what is this weird thing? And now we
know it's a relative of the electron, but also created
(28:48):
another field, which is cosmic ray physics. It was the
first cosmic ray scene. And at first people weren't sure,
like where are these particles coming from? We know they're
coming down from the sky, but are they made in
the sky or whatever. And people did all these crazy experiments,
like balloon experiments with a shot detectors up into the
atmosphere with balloons and discovered that the higher up you go,
the more muans there are, and that tells you that
(29:10):
like muanes are being created in the upper atmosphere, and
then they're decaying as they sort of come down to Earth.
And finally people put together this picture like particles were
hitting the top of the atmosphere and creating these showers
of particles and we were just sort of picking up
the little last bits of the fireworks as they hit
the surface. Right. I bet they also try to shoot
a cow to the moon. That's where the inspiration. Well,
(29:34):
you know how the Russians put a dog in one
of their first attempts to go to space. I won't
comment as to whether particle physicists ever used a weather
balloon to launch a cow. Yeah, they're like, we gotta
up those Russians a dog. Anyone can launch a dog
into space. This is this is well before the space race.
This is the cow race. But I love thinking about
(29:56):
what it must have been to be a physicist at
that time, and too like crack in a whole new
era of discovery bye bye, you know, putting photographic plates
up on mountains and just seeing like what's up there.
There's so many amazing things to discover. Somebody like new
World were opened up. They discovered that all this invisible
stuff is happening around us. That's really wonderful to sort
(30:16):
of like crack open a new way of looking at
the universe. Yeah, all right, let's get into the last
bit here, which is what does the Muan teaches, what
does it tell us about how the universe is put together?
But first let's take another quick break, all right, I know,
(30:43):
so the muan is a thing. It's there. It's super massive,
looks just like the electron. We can feel it. It's
going through us right now. Why is it there? That's
the question that maybe a lot of people have. I mean,
we don't need the muan to make iPhones or ezas,
so why is it there? Is that the standard upon
(31:03):
which we judge things. Now, if we don't need you
for iPhones or pizzas, you don't need to exist. What
else is there? Daniel? That's my whole life basically, just personally.
Um No, it's a good question. It's a question I'd
like to know the answer to. Why does the muan exist?
(31:23):
The short version of the answer is the title of
a great book I read last year. It's called We
Have No Idea? Because we really do have new idea.
Why the muan is there? Doesn't seem to be used
for anything, is what you're saying. Like neutrinos, I think
also are there, but we don't know why why they're
they're right, Yeah, neutrinos and muans and many of the
other particles are not part of the atom. You know,
(31:44):
build them, You don't use them to build up the
stuff that we're familiar with, but they sort of can
exist there on Nature's menu. You might ask the same
question about like some of the really heavy elements, like
why is plutonium a thing? Well, it turns out you
can assemble protons and new trons and electrons in this
way that's stable, and it hangs out and it does
this funny thing. We call it plutonium, and plutonium also
(32:05):
the case, right, it like breaks up. This one actually
breaks up into other things. But it's also kind of ephemeral,
like it's only there for so long before it becomes
something else. Precisely, and in the same way we organize
our list of particles, and we want to like, why
are these there? What does this tell us about maybe
one deeper layer of reality, Like maybe the muans and
(32:29):
electrons are made out of smaller particles and these are
just like different ways to assemble those little internal bits, right,
And there's a few ways to assemble them, the way
that there's a few ways to assemble protons and neutrons
to get different elements. Maybe there's a few ways to
assemble these little tiny ons. One way is to get
an electron, in other ways to get a muan, in
other ways to get a towel, which is the third
(32:50):
member of that family. We just don't know. We know
it's a clue, though, right, it's a tantalizing clue that
there's something going on here. We just don't know what
it means. It's a clue as to some sort of
hint that there's some sort of rule for how electrons exist.
Like if you can make an electron that's heavier, maybe
that tells you something about what makes an electron an
(33:11):
electron precisely, and why there are three of them tells
you something about how that rule has to play out.
Because there's three electrons, the electron, the muant in the towel,
there's three neutrinos. There's also three up corks is three
down quarks. Like there's something really fundamental going on there
we just don't understand. But it seems like an obvious clue.
You know. It's like you're doing your jigsaw puzzle and
(33:33):
you find this other weird piece. It turns out, oh,
that piece fits into a different jigsaw puzzle you didn't
even know about, and you know it's as you start
to get this larger picture right or you find it
like all of your pieces have three sides to them.
Then you start thinking, you know, whoever made this puzzle,
if it was made by somebody had a thing for threes, Yeah,
the universe has a thing for threes, and we don't
(33:55):
know why that is. The Muan was our first clue
that particles have copies at all, and now it turns
out every particle has three copies, and so that's a
huge open question. Is a kind of question people are
gonna look back in a hundred years and be like, man,
that was so obvious. Why couldn't they figure it out?
If I was a physicist in I would totally figured
(34:16):
it out. But it's not so easy when you don't
know the answer when you have to come up with it.
But it's important for people to understand it's not you know,
it's not part of the stuff that we are made of,
but it does answer this larger question. It's like what
is the sort of context of everything? That's why we're
trying to figure out, like what are all the particles?
Because the more particles you put into this table, the
more clues we get as to what the rules are
(34:38):
for making this table. And then maybe we can peel
back a layer and show how this table is put together, right,
or I guess maybe a question I would have is,
how do you even know it's a separate thing? Like
why isn't it just called the heavy electron? Could it
just be an electron that just gets a lot of
mass added onto it somehow through energy or something. That's
a deep question and goes sort of to like what
do we call a particle? Part of the idea entity
(35:00):
particle is its mass? Like that's how we identify what
particle we're talking about. We measure the mass and we say, well,
if it has this mass, it's an electron a sort
of semantics, but it's it's what we mean by an electron.
We mean quantum dot in space that has these properties,
and one of those is the mass. And there are
only a few. It's not like this, it's a there's
a knob you can't have halfway between ELECTRONO mu on
(35:20):
this like the electron mass, the muan mask, the town mass.
There's some notches there, right, And so this was the
first particle that kind of we found outside of the
ones that make up atoms. Is that what you're saying
that this was the first one that was weird? Yeah, precisely,
it's weird and cute. I'm glad you're finally putting positive
attributes on the on the muon you're trying to make it.
I said weird, I didn't say cute. I think somebody
(35:43):
has a particle fetish and it's not the cartoon is. Yes, well,
maybe the particle physicist has a particle fetish. I will
totally own up to that. I love you, particles. I
think we all love particles by necessity. We can't live
without you, like particles when they make up pizza and iPhones,
though otherwise you don't care about them. You objectify particles
(36:04):
and cartoon is cartoonists. Well, I think this particle is
interesting in that it also kind of hints, you know,
at the the universe is full, is full of these
small little details that people can't explain right now, and
then maybe tell us a little bit about that there
are other mysteries yet to discover. Yeah, and you know
(36:27):
the story of how the muan was discovered is also motivational, right,
people saw this weird stuff in these pictures and they
could have just shrugged it off. It could have been like,
I don't know, electrons are doing some weird that day whatever,
but instead of cracked open this whole other mystery, and
we are still doing that. We still don't totally understand
the muan. One thing we'd like to understand is the
muan's magnetic field. Oh, it's a it's odd. It has
(36:49):
a weird magnetic field. Yeah. These particles, remember, have quantum spin,
so they're doing something we like spinning. That's giving them
each a little magnetic field because they have electric charge
and spinning charges give magnetic fields. But when we predict
the magnetic field of the mu want from what we
know about it, and then we go when we measure
the magnetic field, it's a little bit different. It's not
exactly right, And that little difference we could say, I
(37:12):
don't know, shrug it off. Maybe mu want is doing
some weird that day, or it could be a clue.
It could be that the muant is like interacting with new,
weird heavy particles we haven't even seen before. It could
be the first evidence that there are more particles out
there that we haven't yet discovered. And also they help
us unravel ancient mysteries like maybe you heard about how
muans are used to take a picture of the inside
(37:34):
of pyramids. What do you mean, like we can make
an meon viewer, like like me on glasses. No, you
can use me on to like x ray a pyramid,
because what happens is muans, zillion muans shooting from the
sky through everything. And if you take a muan detector
and you put it on the other side of something,
you can tell sort of the density of that thing,
(37:56):
because muans will penetrate air differently than they'll penetrate raw,
for example. And so you take a lot of muans,
you shoot them through something, you can tell whether that
thing is full, is hollow or not hollow. And so
they did this recently by looking at muans that went
through the Great Pyramids, because we're curious, like what's inside
the Great Pyramid, but you don't want to take it apart,
(38:16):
and so they use it basically to x ray the
Great Pyramids, like you put a detector underneath the pyramid
or or what. Yeah, you take the detectors as far
underneath the pyramids as you can in some of those
rooms that do exist. And you know, you can't build
an x ray gun the size of the pyramids. But
the sky is a muan gun, right, The sky is
shooting muans at us all the time. The sky is
(38:38):
a muan gun. Oh my god. Yeah, put on your
tin hats, folks, because the sky really is shooting particles.
That was like, I need like a lead titanium head,
not a tin head. Maybe, you know, maybe the Pharas
have the right idea. Maybe that's why they have those
really weird head dresses. Well, that's what I was going
to ask, is how do you know what meal On
(39:01):
look like after they go through aliens? If there are
aliens inside the pyramid, you wouldn't know. Wow. I was
so ready with an answer to that question until you
went to aliens. And now I'm totally at all awesome.
That's why I'm here, Daniel, to ask the tough questions
that are on everyone's minds. Joking aside, they did find
(39:21):
something inside the pyramids. They think they may have found
a new empty room inside the pyramids that they didn't
know about before. Is the way the muans full of
cows before the cows are the aliens actually to wrap
it all up, then we're in deep trouble when they're
overlords coming and they're like, what are you guys doing?
(39:42):
And they say, welcome to our our leader, King muon
the first first of his name. No, they found that
inside the Great Pyramid there may be a new hollow
section that nobody knew about before. And it's only things
to Muans that we were able to Muan x ray
the p It's a new on chamber they found. Thanks. Yes,
(40:08):
so it may not be inside your iPhone and it
may not be inside your pizza, but it does help
unravel ancient mysteries about ancient civilizations. Al Right, well, with that,
we will wrap it up and we hope you enjoyed
that little discussion about this unknown but supermassive and mysterious
part of the universe, part of our family of cousins, particles, big, small,
(40:30):
massive or not. We'd love you all, at least I do.
Thanks for tuning in. See you next time. Before you
still have a question after listening to all these explanations,
please drop us a line. We'd love to hear from you.
You can find us on Facebook, Twitter, and Instagram at
(40:52):
Daniel and Jorge that's one word, or email us at
Feedback at Daniel and Jorge dot com. Thanks for listening,
and remember Daniel and Jorge explain the universe is a
production of i heart Radio. For more podcast from my
heart Radio, visit the i heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. Yeah.
Hey, Orne, Hey, do you have a lot of cousins
in your family? Yeah, I've got a few. I have
maybe over thirty six cousins, maybeing around the number. Wow,
that's a big family. Well, would you be surprised to discover,
sort of late in life, a brand new cousin you'd
never even heard of before? That would be pretty amazing,
kind of weird, I guess, but maybe yeah, I would
(00:30):
be surprised, all right. And then what if that cousin
turns out to be exactly like you, like, look like
you in every single way. Okay, Yeah, that's that's getting
kind of weird, all right. And then what if this
cousin looks exactly like you? Accept there are two hundred
times more massive Dan, Hi, I'm Poor. Hey, I'm a
(01:07):
cartoonist and the creator of PhD comics. Hi I'm Daniel.
I'm a particle physicist, and I do not have thirty
six cousins. Welcome to our podcast, Daniel and Jorge Explore
your Family Tree, in which we examine all the amazing
and fascinating things about the universe, about the big things,
the small things, and about how things are related to
(01:28):
each other. Yeah. So, um no, that's not the name
of our podcast. It's actually Daniel and Jorge explain the
university production of My Heart Radio, in which we do
examine crazy things about the universe and we try to
make them relatable. We try to present them in a
way that you can understand them, so they connect to
topics that matter to you. Yeah, in a way, we
do sort of explore the family tree of the universe.
(01:49):
You know, how you came to be here, what what
sort of pairings and fusions occurred for you to be
here in this universe appreciating it and listening to funny podcasts.
H I think one of the reasons people are interested
in the origins of the universe and the creations of
our cosmos is because they want to understand how we
got here and what it means in the same way
(02:10):
people explore their family tree. They want to know where
did my family come from, what stories are in our past,
what is my personal context? And also I think it's
a useful way for us to sort of organize our thoughts.
You know, when we think about the the universe in
terms of particles, we sometimes think about how those particles
are related to each other, Like, do particles have families. Yeah,
(02:30):
and I think you know, every part of anyone's family
tree or origin tree kind of tells you a little
bit of the story of the of the whole thing, right,
like how you came to be, how things work, and
how things move about in life, and other ways your
life could have gone. Like if you have a very
successful cousin that's a gazillionaire, then you know, you wonder
(02:51):
could I have made different choices and been a gazillionaire?
Or if be people's paths in life diverge. Yeah, or
if you are that busile in our cousin, then good
for you. Please please contact us. We would love to
take your donations. That's right. It would be awesome to
have at least one gazillionaire listener. Who is our richest listener?
That's a good question. Pod. You have to send us
(03:12):
a check. Whoever sends it is the biggest check that
doesn't bounce. When's this little plaque here that I am
just now putting together. It's made of platinum? Right, Yeah,
well it's going to be once we get those checks. Yes,
you'll get a drawing of a plaque that's made of platinum.
Oh my gosh. Even more valuable from a well known
(03:35):
internet cartoonist exactly. But we do try to understand the
world around us, and sometimes that means putting things in
context and understanding what are the patterns, what are the
structures there, and what clues do those patterns give us
about that sort of fundamental nature of the universe. Yeah,
so to be on the podcast, we'll be talking about
(03:56):
a particle in nature that is maybe not the most
famous one um and maybe not the most well known
one or consequential in your existence, but which does I
think tell you a little bit about and told humanity
a little bit about how the universe works. Yeah, this
is the non gazillionaire cousin. This is the cousin that
(04:16):
ended up maybe sleeping under the overpast and wearing funny
clothes to the family reunion. I feel bad for this particle. Now,
this particle doesn't need your help. It's very massive. Yes,
So in today's episode, we'll be talking about the muan electrons, mysterious,
(04:36):
lesser known, much more massive cousin. And I'm biased, of
course because I'm a particle physicist, but I think it's
really fascinating to think about how we know each particle
is there. We talk about the standard model of particle
physics sometimes, but that's a theoretical construct. It's like our
idea for how these particles might relate to each other.
And that's fascinating. We'll dig into all that, but I
(04:58):
think it's also really important. Remember each of these were discovered.
There's a story behind each particle. Humanity didn't know it
existed and then boom, some experiment revealed it. And on
the podcast, we've talked about the first discovery of the particle,
how the whole concept of a particle was created, the electron.
Then we talked about how we know the photon is
a thing, how we know it's really a particle, the
(05:20):
photo electric effect, And so now we're gonna take the
next step and talk about the discovery of the muan. Yeah,
because you know, I think that every particle tells a story,
you know, and also every story is made out of particle.
So there's kind of this really weird, confusing loop there
that honestly, Yeah, this is like the Superhero Origin story
particle version. Yeah. So the muan is not a name
(05:43):
that rolls off the tongue. Makes me think of maybe cows,
mu muans, maybe uan Muan, Muan mu Off, muanmu Off.
I was thinking sort about karate kid thing there, but
it's back to the eighties reference. Yeah, back to the
age differences. And it's it's funny actually because the name
(06:04):
Uan is totally inappropriate. We'll dig into it later. But
they named it before they discovered it because they thought
it was going to be a different particle, and then
they sort of changed the name later. Um, it's not
a great history for naming particles. Boy, my favorite topic
in science. Yeah, and so I was wondering, how much
do people know about me once? Is it a famous
(06:26):
particle or is it sort of the darker cousin of
the electron that nobody really knows about, hasn't gotten the
same Instagram attention the black Sheep, the gotee wearing particle
of the family tree. Now you're setting enough to be
like the grumpy particle. It's going to come in with
some evil plan to finally get It's it's revenge, and
it's you already made this particle, the homeless particle that
(06:47):
lives under a bridge. So yeah, that was the sad
particle that deserves our love and compassion, not the one
that's been plotting its victorious return to the center of attention. Well,
you never know what these particles, you know, physics, there's
a lot of drama. But as usual, I walked around
and I asked people if they knew what the muan
(07:10):
was and how we knew it was a thing. Yeah,
So before you listen to these answers, think about it
for a second. If someone asked you what a mu
on is, would you know what it is? Have you
heard it before? Here's what people had to say. I'd
say it's a unit of measure. It's like one of
the fundamental elements or particle of what makes up everything.
Mu one. I believe this to be the name of
(07:31):
a sub atomic particle uh luans luans uh. I don't
remember what classification they follow under as far as the
naming conventions. Fundamental particle, some sort. It's real small subotomic particles.
I kind of represented what it does. How do we
(07:53):
know nuance exist um particle starts. So what's your opinion
of these answers today? Good? It sounds like most people
have heard of it or I heard of the word before.
You know, very only a few people said never heard
of it or think it was a unit of measure,
like a you know how much water? Would you like,
(08:13):
I'll have seven muans of water. I wonder that if
you pronounced it correctly, maybe they knew about it, but
just under a different pronunciation. Do you think I'm mispronouncing
the name of mu. I don't know. I mean, what's
the correct way? Is it muan or muan? Like you're
making it sound like a Disney movie, like, oh, my
favorite Disney princess is mulan. My favorite Disney princess muan muan. Oh.
(08:40):
That is a great way, though, to get more attention
for particles in the mainstream. We should get Disney to
name the next Disney Princess after a particle. Why not that?
Why it could be the next Pixure movie. What it's like?
What's the emotional roller coaster right of being a fundamental
particle of nature? Yeah? So much to explore there, and
I expect that will be getting checks from Pixar when
(09:01):
they make a billion dollar movie out of it. But
I was impressed with these answers, though, I want to
pick a bone about one thing. People say, yes, it's
a fundamental particle, totally cool. People also say it's a
sub atomic particle or it's one of the fundamental particles
that make up everything. And that's really a key idea
that I think people have not understood about muans, that
(09:22):
you can be a tiny particle and not be sub atomic,
not be part of the atom. Oh, I see, subotomic
doesn't just mean it's smaller than atom. You're saying that,
it means that you're part of the atom. Remember, fundamental
particles have no size, their dots, they're zero volumes, so
they're all smaller than the atom. In that sense of
(09:43):
being fundamental guarantees you'd be smaller than the atom. I
think to me, sub atomic means it's part of the atom,
like you break it up and you find it inside
the atom. Okay, so we'll get into that, but let's
bring it down for people. For us, what is a
muan and why does it sound like an electron? You
it ends with O N, but maybe, but it's not
the electron. Yeah, but it really is related to the electron.
(10:06):
It's sort of like the electrons cousin. And by that
I mean that it's identical to the electron in so
many ways. It has the same electric charge, it has
the same interactions with matter like it interacts via the
weak force and via the electromagnetic force, but it doesn't
feel the strong force, just like the electron. It has
(10:26):
a neutrino, just like the electron has its neutrino. So
in so many ways, it's exactly the same as the electron.
Sound like when you discover a new particle and it's
totally different, like a cork or a gluon, it's just
completely different from the electron. This one is very very
similar to the electron. It's like weirdly similar, but then
with one important difference. Okay, so it's a particles. It's
(10:51):
not a cow, it's not a Disney princess. So it's
a particle, meaning like it's a it's one of these
things that you see nature in the universe, like things
that pop up and you can touch them and and
there it's a thing. Yes, muans are a thing. There
are a little thing. There are particles, and there are
little dots of matter. They have mass and they have
(11:11):
charge and they interact. Okay, so it's it's a particle
like the electron. But you're saying and you say it's
a cousin of the electron, not that they share like
not that their parents were siblings, but just like in
the sense that it's very similar to the electron. Yeah,
when we organize our knowledge, we look for patterns. We
look for similarities. Right like when we were a hundred
(11:33):
years ago, when the state of knowledge about the universe
was the periodic table. We didn't just have like a
pile of different elements and say here's an element. There's
an element. We said, oh, look, this one is similar
to that one. They're both really active, or these are
really similar because they're both really inactive, or this one
weighs a tiny bit more than that one. We notice patterns.
We put those patterns together in the same way we're
looking for patterns in the fundamental particles. So we try
(11:56):
to figure out which ones are related to each other.
And we have only a few handles on each particle.
Is only like a few things we can know about
a particle, right, And so is this a particle that
we can see in our everyday lives, like is it
floating around? Does it move around wires and electricity like
the electron, or is this kind of a weird one
(12:18):
of those weird particles And you know you don't ever
actually see Yeah, you don't see the muan because it
doesn't last for very long. It lives for two point
two microseconds and then it turns into an electron and
some neutrinos. But they are actually everywhere. There's ten thousand
muons going through a square meter of Earth every minute,
so there's a lots of muans everywhere, but you just
(12:39):
can't really see them very easily because they don't last
very long. Wait, what I mean? How can they be
everywhere but also only last two point to microseconds? Does
that mean that they're they're constantly coming into existence, lasting
for two point two microseconds and then disappearing and breaking up,
or what does that mean? How can they be all
around is but also evaporating at the same time. Well,
(13:00):
there's two things going on there. One is your right,
they're being created um when particles hit the atmosphere. So
protons hit the atmosphere and they create a shower of particles,
some which include muans, and those muans fly along a
little bit, but they don't last very long, just two
point two microseconds, and then they turn into electrons. But
they last for two point two microseconds according to their
(13:20):
clocks because they move really fast. There's a relativistic time dilation.
So the according to us that two point two microseconds
takes longer to click, and so for us it can
take like seconds or minutes from muans to decay. But
for them, if you're sitting on top of the muan,
it would only last You would only be alive for
(13:42):
two point two microseconds. Yeah, that's the half life of
a muan. So muon is not stable. It's not like
an electron you can just sit there for eons and
eons and just be itself. A muon is a heavy particle,
and heavy particles like to decay into lighter particles. In
this case, the muon turns into an electron very quickly
according to its clock. Oh, I see the ones that
we see. The ones coming from the atmosphere are moving fast,
(14:03):
so they last longer. But if I just created a
mew on here in front of me, it would last
only for two point two micro seconds, and it's not
going anywhere. If you could bake muans in your oven
and you take them out of the oven two point
two microseconds later, boom, they turn into a electro. Yeah,
you gotta eat them up real quick. Exactly. They're like
making fortune cookies or toss them really fast, have him
pop out of the toaster really fast, in which case
(14:25):
they would last longer technically, right, that's true. Yeah, exactly.
Somebody could shoot muans into your mouth and it would
last long enough to get there. I wouldn't recommend that.
That's that's not a suggestion for something somebody should do.
And actually, two point two microseconds it is kind of
a long time for a particle that's this massive to last.
And so what does it mean that it disappears or
breaks up like it? It's just unstable like it, just
(14:48):
it's made out of other things and it breaks up
or literally just kind of evaporates into energy and that
energy turns into something else. Yeah, that's a great question.
These are fundamental particles, so they're not made up of
anything else. As far as we know. The muon turns
into the electron. It's not like it has an electron
inside of it, and it breaks up into an electron
and other stuff it converts. It goes from a muan,
(15:12):
it turns via the weak force into a W particle
and a neutrino, and then the W particle turns into
an electron and another neutrino. So the muon turns into
an electron and two different neutrinos, but it didn't have
those bits inside of it. Remember, particle physics is like alchemy.
We can convert one kind of matter into another kind
of matter. Okay, so it's um. It doesn't break apart,
(15:35):
it's just somehow. It's it's very existence. The universe sort
of doesn't like it. Like it. It can just seesis
to exist and in favor of other things existing instead
of it. Yeah, and this is true for every particle
that is pretty massive. The universe doesn't like massive particles.
It's like putting a particle on the top of a hill.
Eventually it's going to roll down. And so the muon
(15:58):
is like the at the top of the on. The
electron is rolling down to the bottom of the hill.
Eventually the muon is going to turn into the electron.
And every particle in nature that that can do this
does this. The only reason the electron doesn't is that
there's no lighter particle for it to turn into. Oh,
and that's why we are able to exist, because the
(16:18):
universe does seem to like electrons and quarks which make
us up. And so that's why we were stable. But
if we were made out of me as, we would
disappear pretty quickly. Yes, exactly. We are made up of
the lightest particles out there, up corks and down corks.
Of the lightest corks. Electrons are the lightest version of
that kind of particle called a lepton. So the matter
(16:39):
that makes us up that's stable is made out of
stuff that can't turn into lighter stuff because there is
no lighter stuff for it to turn into. Right, Yeah,
there's nothing for it to turn into, so we we
stay where we are. But the muon is heavy and
could turn into something else. So it does precisely. And
for those of you wondering, like, well, what about a photon?
Why can't an electron turn into a photon? Of photon
(17:00):
is mass lists Remember that there are rules about how
these things happen, and one of those rules is conservation
of electric charge. An electron has a minus one charge,
so it can't turn into a photon which has zero charge,
because you have to somehow disappear that charge. The only
way for that to happen is for an electron to
hit a plus one positron, and then they can turn
into a photon together, but for a particle to just
(17:22):
spontaneously decay, it has to convert to another particle that
has all the same sort of quantum mechanical numbers. Okay,
so the muon is the electrons massive cousin or massive
sort of like alternate universe version of the electron. Right, Yeah,
it's two hundred times the mass of the electron. It's
really really massive. That's a lot. It's like crunched into
(17:43):
the same meat. Yes, exactly. It's like if you met
another version of you, but you weren't bigger, you were
denser or something. You're two hundred times as much mass,
but still fundamental. And it doesn't hang around existence very long,
and it usually breaks up into or not breaks up
into runs into lighter particles, so we don't really seed
around that much. But still it's sort of an important
(18:05):
part of the universe, and it seems that it's important
part of the universe and also tells us a lot
about the mysteries of how everything is put together. Yeah,
and it actually lasts a long time for a heavy particle.
Other particles that are heavy, like the Higgs boson, they
decay much more quickly. They decayed in like ten to
the minus twenty seconds, whereas this one decays very slowly,
(18:27):
it's just two point two microseconds. And the reason is
that it decays via the weak force, which is very weak.
To the weaker the force, the longer takes for that
decay to happen. M hmm. All right, let's get into
that a little bit more, and also how it was
discovered and why it is such an important particle. But
first let's take a quick break. All right, So the
(18:58):
meuan decays by the weak force. What does that mean?
How can something decay via a force like the force
makes a decay? Yeah, the fource sort of provides the
avenue for the decay to happen. Like, how does a
muon turn into an electron just just roll down a
hill and say, hey, now I'm an electron. It has
to has to be an interaction there. And so what
happens is the muon turns into a W particle and
(19:21):
a neutrino. And the W particle, remember, is the particle
of the weak force. It's like the weak force version
of the photon. And so that's what we mean when
we say uses the weak force to decay. It doesn't
just spontaneously happen. Something has to sort of carry that information,
so it has to make it happen. It's like a reaction,
and that reaction always includes one of the forces, and
in this case it uses the weak force, right, and
(19:43):
that weak force came out of just its own energy.
It uses the mass. Right. The muon is a huge
amount of energy in it because it has so much mass,
and that mass is turned into the energy of the
electron and the neutrinos that come out of it. So yeah,
the weak force turns the mass of the muan into
very small masses of these other particles and gives them
a lot of energy, right, and it ends up as
(20:04):
an electron and to neutrinos precisely. All right, Well, to
tell us Daniel, how was it discovered and why is
this an important particle? Well, it was discovered initially in
cosmic rays. Um. People saw these particles just sort of
shooting from the sky and they didn't understand what was
making them, and they thought, oh, well, you know, we
found a few particles, so these are probably electrons. This
(20:25):
is you know, in the early nineteen hundreds, we didn't
have a really deep understanding of how particles work. We
didn't have a good bench of particles, and so people thought,
you know, everything they saw they thought in terms of
the particles at the time. So you have to sort
of wind your mind back to what we knew at
the time. Back then, we knew about protons, we knew
about neutrons, we knew about electrons, and so people saw
(20:47):
these particles shooting from the sky. They didn't know what
made them, but what they saw was that they penetrated
really far into matter, much more than electrons could. We
saw the actual nuance and not the not what it
looks like after it decays or turns into something else.
Like we actually you can actually see and feel the muants.
You can't really feel them, but you can make particle
(21:08):
detectors that can detect them. You can actually do this
in your garage using something called the cloud chamber. They
were able to see them using detectors that they put together.
And these detectors were like a cubic piece of film,
like remember the old way films worked, where like light
was exposed on the film. You didn't have a digital
camera or anything, and that made some kind of chemical change.
You're saying, you can make like a solid cube of this. Yeah,
(21:29):
you just take a solid cube of it, you leave
it up on a mountain and you leave it there
for like six months, and then you cart it back
down or you guys your grad students to do that.
Then you slice it into pieces and then you can
develop each of those. And what you do is you
see all the particles that shot through it in those
six months, and so they can see and when they
did this, they saw all these particles shooting through this
(21:51):
film and they were surprised at how far they were going,
because electrons shouldn't get that far. Electrons penetrating a little
bit and then they stopped. But these particles were shooting
all the way through. It's kind of like a bull
in a china's shop universus, like a mouse in a
china shop. Yeah, And they didn't understand that. They thought, well,
you know, are there two kinds of electrons or there's
(22:11):
sometimes electrons can penetrate really far. It was really a
puzzle at the time. What made them think it was
an electron? Why couldn't it be like, uh, some kind
of new atom or something. We did know it had
negative charge, and so I think that's what made people
think it was more likely to be an electron or
something like an electron than something positive like inside the nucleus.
And remember, at the time, we only knew basically about protons, neutrons,
(22:33):
and electrons, and so everything we saw where like all
of a sudden, having this imagination that we could just
explain everything in the universe in terms of these particles,
and that was It was a great success of the
particle model at the time, right, like everything could be
built out of protons, neutrons, and electrons. What a wonderful simplification.
And so when we first saw these particles that penetrated
really far, we thought, well, it must be one of those, right,
(22:56):
But it was not. It was not, and people were
able to then later douce it in the laboratory using
collisions and and all sorts of other stuff, and they
discovered that if you put it in a magnetic field,
it didn't bend as much as an electron. And that's
when they decided, you know what, this must be a
different kind of thing. It's like a new version of
the electron, a different flavor of the electron, because it
(23:17):
must be more massive, which is why it doesn't bend
inside the magnetic field as much reflected as much because
it has so much mass, it that just has more inertia. Precisely,
it takes a stronger magnetic field to bend a mu
on than it does for an electron. And this was
kind of a scandal in particle physics at the time. Scandal. Yeah,
people were upset. They were like, what a mu on?
(23:39):
Who ordered that? Like, we don't need this. Get out
of here with your ridiculous new particle. We have this
beautiful description of the universe. We don't want more particles.
Up until then, everything that you knew about helped make
the universe. It's kind of what you're saying, like everything
you knew about at a purpose. Yeah, we had taken
apart the stuff around us and found the basic building blocks,
(24:00):
and then we didn't. Some people were like I don't
want to hear stories about other building blocks that could
be out there. It just sort of confuses the issue, right,
It's a shift in the question not just what are
we made out of? But what is the basic organizing
principle of the universe. It shows you all of a
sudden that there's a larger question you didn't even think
to ask. It's like you find something that you don't
know what to do with it, like it it doesn't
(24:22):
help you with what you knew about how things work. Yeah,
you're putting together jigsaw puzzle and all of a sudden,
somebody hands you like a really big piece that just
doesn't fit, and you're like, what I didn't ask for,
that I don't need. That doesn't help me with my problem. Like, well,
but okay, but this piece is here and it's not
going away, right, Yeah, And so it makes you think
that maybe there's another puzzle, or that the puzzle is
(24:44):
bigger than you think it is. Yes, all of a
sudden you realize this is a three dimensional puzzle and
you've been only playing on on two dimensions, and and
it just blows your mind. And so that's. Ah, it's
sort of an earthquake, an intellectual earthquake through the field
at the moment. But also it's a great opportunity. Those
are the kind of discoveries that make you realize, Wow,
(25:04):
there's a whole larger question to ask, and there's a
whole world of answers out there. And of course now
we know there's not just the meal one. There's also
the Tao, which is the even heavier version of it,
and that every particle has these cousins. Yeah. I like
how this counts as a scandal in physics, Like was
it on the front page of the Daily Physics News
or the National Enquiring Enquirer of Physics? Um newspapers, people
(25:31):
to tabloids. People had to give testimony about this and
there You know, physicists are not that exciting, so we
just got to create drama wherever we can. There was
even more drama because some people had predicted the existence
of a particle sort of similar to this. Mm hmm,
what do you mean predicted like just just guessing. Yeah. Well,
(25:52):
there was a famous physicist named Yukaba the Genius and
won a Nobel Prize for all sorts of fascinating stuff.
And he was trying to understand the strong force. He
was like, okay, the weak force, we have that one.
We have the photon for the electromagnetism um, but what
mediates the strong force? And he did some calculations that
he thought, I bet there's a particle out there about
(26:13):
two hundred times the mass of the electron and it
mediates the strong force. All right, So that's his prediction, right,
And back in the day, physics would just make predictions,
like here's my idea and here's what I predict, Like
we need this for this for what we know to
make sense. Yeah, just like with the Higgs Boson. Peter
Higgs said, this doesn't make sense to me, but if
you look at the universe in a new way, then
(26:34):
it makes more sense. And this new way predicts a
new particle, so you can test my theory. That was
what you Kala did, and he predicted a new particle
about two hundred times the mass of the electron. Then
they found this particle and you Kal was like, who
I was right, But it turns out this particle has
nothing to do with the strong force at all. So
it's just like a coincidence, right, And he still got
(26:56):
the Nobel Prize. He still got the Nobel Prize, but
not for this and um, not for this one. But
he's sort of the reason why this particle has a
strange name. Oh really, he he was a fan of Cows.
I don't know if he liked Kobe Beef, you know,
the guy's Japanese or anything, but he you know, we
had the electron, which is really really light, and we
(27:16):
had the proton, which is like two thousand times the
mass of the electron, and he predicted a particle sort
of an intermediate mass, and so he wanted it called
like the you know, the mazo tron something where mazing
means like middle, and so that was the sort of
the origin of this, like, let's call these particles here,
you know, in this mass region, we'll call the meso particles. Well,
(27:39):
what do you have to call it the messo on
or messing on or I feel like just to be
consistent here. And then later people were like, well, it's
not really have anything to do with these other particles
we found in the same mass, but we'll just keep
calling it the muon anyway, I bet he wanted to
call it the me on. I'm so smart. Yeah, but
(28:04):
this is where like, come on, dude, but it's a
it's a fascinating moment in physics because or the yuan
is the mean, or how about we calling muan done compromise.
That's exactly how these decisions get made, and that's why
we have such terrible names for particles. Yeah. So, but
(28:24):
now it's so it's a well known thing, like everyone
knows about muans. Did they know that they're there and
you can study them. You can. You can. They're coming
through going through our bodies right now at ten thousand
times per minute. Yeah, ten thousand muans per square meter
per minute, and you're right. At first it was totally
exotic and what is this weird thing? And now we
know it's a relative of the electron, but also created
(28:48):
another field, which is cosmic ray physics. It was the
first cosmic ray scene. And at first people weren't sure,
like where are these particles coming from? We know they're
coming down from the sky, but are they made in
the sky or whatever. And people did all these crazy experiments,
like balloon experiments with a shot detectors up into the
atmosphere with balloons and discovered that the higher up you go,
the more muans there are, and that tells you that
(29:10):
like muanes are being created in the upper atmosphere, and
then they're decaying as they sort of come down to Earth.
And finally people put together this picture like particles were
hitting the top of the atmosphere and creating these showers
of particles and we were just sort of picking up
the little last bits of the fireworks as they hit
the surface. Right. I bet they also try to shoot
a cow to the moon. That's where the inspiration. Well,
(29:34):
you know how the Russians put a dog in one
of their first attempts to go to space. I won't
comment as to whether particle physicists ever used a weather
balloon to launch a cow. Yeah, they're like, we gotta
up those Russians a dog. Anyone can launch a dog
into space. This is this is well before the space race.
This is the cow race. But I love thinking about
(29:56):
what it must have been to be a physicist at
that time, and too like crack in a whole new
era of discovery bye bye, you know, putting photographic plates
up on mountains and just seeing like what's up there.
There's so many amazing things to discover. Somebody like new
World were opened up. They discovered that all this invisible
stuff is happening around us. That's really wonderful to sort
(30:16):
of like crack open a new way of looking at
the universe. Yeah, all right, let's get into the last
bit here, which is what does the Muan teaches, what
does it tell us about how the universe is put together?
But first let's take another quick break, all right, I know,
(30:43):
so the muan is a thing. It's there. It's super massive,
looks just like the electron. We can feel it. It's
going through us right now. Why is it there? That's
the question that maybe a lot of people have. I mean,
we don't need the muan to make iPhones or ezas,
so why is it there? Is that the standard upon
(31:03):
which we judge things. Now, if we don't need you
for iPhones or pizzas, you don't need to exist. What
else is there? Daniel? That's my whole life basically, just personally.
Um No, it's a good question. It's a question I'd
like to know the answer to. Why does the muan exist?
(31:23):
The short version of the answer is the title of
a great book I read last year. It's called We
Have No Idea? Because we really do have new idea.
Why the muan is there? Doesn't seem to be used
for anything, is what you're saying. Like neutrinos, I think
also are there, but we don't know why why they're
they're right, Yeah, neutrinos and muans and many of the
other particles are not part of the atom. You know,
(31:44):
build them, You don't use them to build up the
stuff that we're familiar with, but they sort of can
exist there on Nature's menu. You might ask the same
question about like some of the really heavy elements, like
why is plutonium a thing? Well, it turns out you
can assemble protons and new trons and electrons in this
way that's stable, and it hangs out and it does
this funny thing. We call it plutonium, and plutonium also
(32:05):
the case, right, it like breaks up. This one actually
breaks up into other things. But it's also kind of ephemeral,
like it's only there for so long before it becomes
something else. Precisely, and in the same way we organize
our list of particles, and we want to like, why
are these there? What does this tell us about maybe
one deeper layer of reality, Like maybe the muans and
(32:29):
electrons are made out of smaller particles and these are
just like different ways to assemble those little internal bits, right,
And there's a few ways to assemble them, the way
that there's a few ways to assemble protons and neutrons
to get different elements. Maybe there's a few ways to
assemble these little tiny ons. One way is to get
an electron, in other ways to get a muan, in
other ways to get a towel, which is the third
(32:50):
member of that family. We just don't know. We know
it's a clue, though, right, it's a tantalizing clue that
there's something going on here. We just don't know what
it means. It's a clue as to some sort of
hint that there's some sort of rule for how electrons exist.
Like if you can make an electron that's heavier, maybe
that tells you something about what makes an electron an
(33:11):
electron precisely, and why there are three of them tells
you something about how that rule has to play out.
Because there's three electrons, the electron, the muant in the towel,
there's three neutrinos. There's also three up corks is three
down quarks. Like there's something really fundamental going on there
we just don't understand. But it seems like an obvious clue.
You know. It's like you're doing your jigsaw puzzle and
(33:33):
you find this other weird piece. It turns out, oh,
that piece fits into a different jigsaw puzzle you didn't
even know about, and you know it's as you start
to get this larger picture right or you find it
like all of your pieces have three sides to them.
Then you start thinking, you know, whoever made this puzzle,
if it was made by somebody had a thing for threes, Yeah,
the universe has a thing for threes, and we don't
(33:55):
know why that is. The Muan was our first clue
that particles have copies at all, and now it turns
out every particle has three copies, and so that's a
huge open question. Is a kind of question people are
gonna look back in a hundred years and be like, man,
that was so obvious. Why couldn't they figure it out?
If I was a physicist in I would totally figured
(34:16):
it out. But it's not so easy when you don't
know the answer when you have to come up with it.
But it's important for people to understand it's not you know,
it's not part of the stuff that we are made of,
but it does answer this larger question. It's like what
is the sort of context of everything? That's why we're
trying to figure out, like what are all the particles?
Because the more particles you put into this table, the
more clues we get as to what the rules are
(34:38):
for making this table. And then maybe we can peel
back a layer and show how this table is put together, right,
or I guess maybe a question I would have is,
how do you even know it's a separate thing? Like
why isn't it just called the heavy electron? Could it
just be an electron that just gets a lot of
mass added onto it somehow through energy or something. That's
a deep question and goes sort of to like what
do we call a particle? Part of the idea entity
(35:00):
particle is its mass? Like that's how we identify what
particle we're talking about. We measure the mass and we say, well,
if it has this mass, it's an electron a sort
of semantics, but it's it's what we mean by an electron.
We mean quantum dot in space that has these properties,
and one of those is the mass. And there are
only a few. It's not like this, it's a there's
a knob you can't have halfway between ELECTRONO mu on
(35:20):
this like the electron mass, the muan mask, the town mass.
There's some notches there, right, And so this was the
first particle that kind of we found outside of the
ones that make up atoms. Is that what you're saying
that this was the first one that was weird? Yeah, precisely,
it's weird and cute. I'm glad you're finally putting positive
attributes on the on the muon you're trying to make it.
I said weird, I didn't say cute. I think somebody
(35:43):
has a particle fetish and it's not the cartoon is. Yes, well,
maybe the particle physicist has a particle fetish. I will
totally own up to that. I love you, particles. I
think we all love particles by necessity. We can't live
without you, like particles when they make up pizza and iPhones,
though otherwise you don't care about them. You objectify particles
(36:04):
and cartoon is cartoonists. Well, I think this particle is
interesting in that it also kind of hints, you know,
at the the universe is full, is full of these
small little details that people can't explain right now, and
then maybe tell us a little bit about that there
are other mysteries yet to discover. Yeah, and you know
(36:27):
the story of how the muan was discovered is also motivational, right,
people saw this weird stuff in these pictures and they
could have just shrugged it off. It could have been like,
I don't know, electrons are doing some weird that day whatever,
but instead of cracked open this whole other mystery, and
we are still doing that. We still don't totally understand
the muan. One thing we'd like to understand is the
muan's magnetic field. Oh, it's a it's odd. It has
(36:49):
a weird magnetic field. Yeah. These particles, remember, have quantum spin,
so they're doing something we like spinning. That's giving them
each a little magnetic field because they have electric charge
and spinning charges give magnetic fields. But when we predict
the magnetic field of the mu want from what we
know about it, and then we go when we measure
the magnetic field, it's a little bit different. It's not
exactly right, And that little difference we could say, I
(37:12):
don't know, shrug it off. Maybe mu want is doing
some weird that day, or it could be a clue.
It could be that the muant is like interacting with new,
weird heavy particles we haven't even seen before. It could
be the first evidence that there are more particles out
there that we haven't yet discovered. And also they help
us unravel ancient mysteries like maybe you heard about how
muans are used to take a picture of the inside
(37:34):
of pyramids. What do you mean, like we can make
an meon viewer, like like me on glasses. No, you
can use me on to like x ray a pyramid,
because what happens is muans, zillion muans shooting from the
sky through everything. And if you take a muan detector
and you put it on the other side of something,
you can tell sort of the density of that thing,
(37:56):
because muans will penetrate air differently than they'll penetrate raw,
for example. And so you take a lot of muans,
you shoot them through something, you can tell whether that
thing is full, is hollow or not hollow. And so
they did this recently by looking at muans that went
through the Great Pyramids, because we're curious, like what's inside
the Great Pyramid, but you don't want to take it apart,
(38:16):
and so they use it basically to x ray the
Great Pyramids, like you put a detector underneath the pyramid
or or what. Yeah, you take the detectors as far
underneath the pyramids as you can in some of those
rooms that do exist. And you know, you can't build
an x ray gun the size of the pyramids. But
the sky is a muan gun, right, The sky is
shooting muans at us all the time. The sky is
(38:38):
a muan gun. Oh my god. Yeah, put on your
tin hats, folks, because the sky really is shooting particles.
That was like, I need like a lead titanium head,
not a tin head. Maybe, you know, maybe the Pharas
have the right idea. Maybe that's why they have those
really weird head dresses. Well, that's what I was going
to ask, is how do you know what meal On
(39:01):
look like after they go through aliens? If there are
aliens inside the pyramid, you wouldn't know. Wow. I was
so ready with an answer to that question until you
went to aliens. And now I'm totally at all awesome.
That's why I'm here, Daniel, to ask the tough questions
that are on everyone's minds. Joking aside, they did find
(39:21):
something inside the pyramids. They think they may have found
a new empty room inside the pyramids that they didn't
know about before. Is the way the muans full of
cows before the cows are the aliens actually to wrap
it all up, then we're in deep trouble when they're
overlords coming and they're like, what are you guys doing?
(39:42):
And they say, welcome to our our leader, King muon
the first first of his name. No, they found that
inside the Great Pyramid there may be a new hollow
section that nobody knew about before. And it's only things
to Muans that we were able to Muan x ray
the p It's a new on chamber they found. Thanks. Yes,
(40:08):
so it may not be inside your iPhone and it
may not be inside your pizza, but it does help
unravel ancient mysteries about ancient civilizations. Al Right, well, with that,
we will wrap it up and we hope you enjoyed
that little discussion about this unknown but supermassive and mysterious
part of the universe, part of our family of cousins, particles, big, small,
(40:30):
massive or not. We'd love you all, at least I do.
Thanks for tuning in. See you next time. Before you
still have a question after listening to all these explanations,
please drop us a line. We'd love to hear from you.
You can find us on Facebook, Twitter, and Instagram at
(40:52):
Daniel and Jorge that's one word, or email us at
Feedback at Daniel and Jorge dot com. Thanks for listening,
and remember Daniel and Jorge explain the universe is a
production of i heart Radio. For more podcast from my
heart Radio, visit the i heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. Yeah.
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Daniel Whiteson
Kelly Weinersmith
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