Why do some particles die?

Find out why particles die with Daniel and Jorge

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Episode Transcript

Speaker 1 (00:08):
Or Hey, just starting a new decade? Make you feel
young or old? What? It's a new decade. It's gonna
be very soon when this podcast comes out, it will well,
you know, it makes me feel a little bit of both.
I guess I feel you old? You old? Is that
a quantum superposition of young and old kids? It's both

(00:28):
in neither. Well, here's something that might make you feel
kind of young. Oh, this is this invent the Fountain
of Youth. Still running a grand application for that project.
But I know it's more a sense of perspective. All right, well,
what is it? I'll take it. Well, did you know
that the particles in your body are more than thirteen
billion years old? Compared to that, you're like a baby. Wait,

(00:51):
you're telling me that I'm a billion years old and
that's supposed to make me feel young. Maybe it just
means you need a n APP. Sounds good, calculatory. Hi.

(01:15):
I'm Jorge. I'm a cartoonists and the creator of PhD Comics.
Hi I'm Daniel. I'm a particle physicist and I've seen
many many particles pass away. Welcome to a new decade
of our podcast. Daniel and Jorge explain the Universe, a
production of I Heart Radio, in which we venture forth
into a whole new decade and try to understand the universe,

(01:36):
a decade perhaps in which we will reveal new secrets
about the universe that nobody in human history has ever understood.
That's right. We like to talk about the planets and
the stars and the cosmos, but also the little tiny
things in the universe, the particles that we're all made
out of and that are all around us all the time.

(01:57):
I'm glad that you said we like to talk about
a particle. Sometimes I think it's just me. Well, I'm
using the Royal We, the Physicist podcast Arial We. But yeah, well,
I do like to talk about particles because I feel like,
in the end, we're all made of particles, and if
we want to understand the universe, we got to start

(02:19):
at the beginning, the smallest, the littlest nuggets. And if
we understand the way the universe works at these smallest scales,
then we have a chance to maybe understand the way
things work at larger scales. Yeah, you know, I think
that as human as we tend to kind of forget
that fact. You know, we're made out of tiny, little
molecules and atoms and tiny little particles. We I think

(02:39):
we love to think of ourselves as as these sort
of ethereal thinking beings, but really we're just like a
giant lego set of particles, right, Yeah, And ever since
I learned about quantum mechanics and the frothing vacuum and
how particles are popping in out of existence at all times,
it gives a different sense for what you are. You
are a collection of particles, but that set of particles

(03:00):
is changing, so you're more like a storm, like a cloud.
You're like an excitation of the space in which you
were living. He gives a different sense for what it
means to be you. And that's why I want to
understand the universe from the smallest scale, because it tells
us what it's like to be us, what it means
to be a thing. Well, I am definitely hopefully a thing,
and I'm definitely in a state of excitation. And I

(03:22):
have to say that I did get a fronting vacuum
for Christmas, so I'm glad you. Does that mean that
it makes phone for your coffee while it cleans the kitchen? Yeah,
it's it's it's a multitasker's dream. I'll have the cappuccino
vacuum please. Yeah. So, so today we'll be talking about
the things that everyone is made out of. You, me, this,

(03:44):
this um microphone that I'm speaking to, those speakers that
are broadcasting our voices. Everything is made out of particles.
And some people might be surprised, maybe or maybe not,
that particles don't last forever. That's right, particles are not
forever as far as we know. But there are kind
of two different kinds of particles. There's the particles that

(04:05):
make up me and you, and as we've talked about
in the podcast, those are mostly three different particles up quarks,
down quirks, and electrons. But then we talk about all
these other particles higgs bosons, top quarks, w bosons, and
those particles aren't around. You don't like find a pile
of them under rock somewhere, and that's because they don't

(04:26):
last very long. They flash into existence and then they
die very quickly. Hey, can I choose what kind of
quarks I'm made out of? Like? Can I be up
corks all the time. I don't know what kind of
special powers you have as a cartoonist, but if you're
made of protons and neutrons, and there's not a whole
lot of flexibility, so some of them disappear and some
of them are born all the time. Um, And so

(04:46):
to be on the podcast will be sort of tackling
that crazy phenomenon of what makes particles come into and
out of existence. Why is it that some particles were
born in the Big Bang and are still around, whereas
other particles only get to lie tend to the minus
twenty three seconds in our universe. So to be on
the podcast, we'll be talking about why do particles die?

(05:13):
It make it sound so sad, you know, Oh, I see?
Why do particles move on? We talk about why particles
are born and what they've accomplished in their brief, beautiful lives.
You know, why do particles go to Grandpa's farm where
they're running happily and jumping over streams streams of particles?
They go to the particle reserve where they're well taken

(05:36):
care of. And here's another example of where we're sort
of anthropomorphizing particles. Right, Particles definitely don't have feelings and
emotions and families and Thanksgiving dinners, but we talk about
them as if they are born and as if they die,
and I think it just helps us connect to them,
it helps us think about them. So some particles decay
and others don't. So some particles die and some of

(05:56):
them live forever? Is that true? Can some particles live
from the beginning of time till the end of time?
We can never say for sure. All we can say
is what we've seen and were in. Some particles, like electrons,
we have never seen them decay, so we can estimate
how long the lifetime of an electron is based on
never having seen any of them decay and having looked

(06:17):
at a lot of them, And the current estimate is
like seventeen ga jillion years. Now it might be is
that is that? The is? What that in a paper?
Actually I rounded up at six point nine gajillion years.
But the point is we make some statistical statement and
say it must be longer than this very very big number,
much longer than the age of the universe, or we
would have seen when decay. But we can never be sure.

(06:41):
And it's the same with a proton. They're pretty stable.
Like if you put an electron in a jar, it's
just gonna sit there. It's never gonna turn into anything.
It's never going to I guess collide with something and
turn into something else. Is that possible? Oh, it certainly
could actually could get absorbed and then disappeared. But an
electron in isolation could you to sit there forever, the

(07:01):
same way a photon can fly across the universe for
billions of years and still be a photon. But other particles,
you know, you put a neutron in a jar or
a top cork in a jar, and it will spontaneously decay,
will turn into other stuff. Some of the particles that
I am made out of might be zillions of years old,
and some of them could be, you know, three years old. Yeah, Unfortunately,

(07:24):
most of them are billions of years old. If you
were looking to feel young, that's not the way to
do it. I'd like to focus on the young part
of me, Daniel, I'm young inside. Yeah. And so in
particle physics, the technical term we use is that some
particles are stable. We think they just hang out forever,
they don't do anything, and other particles are unstable because

(07:44):
they decay into other particles. And so this is kind
of an interesting word, decay and particle using them for particles,
and so we were wondering, as usual, how many people
out there associate the two works together and know about
this process that all particles go through or don't go through. Yeah.
So I walked around campus a UC Irvine and I

(08:05):
asked people if they knew that heavier particles can decay
into lighter particles and why it happens. So think about
it for a second. How much do you know about
particle decay? And what would you be able to answer
if Daniel appros you on the street one day. Here's
what people had to say. Do you know that particles decay? No?
I didn't. Yes. Do you know why that happens? No? Yes?

(08:28):
Do you know why that happens? I'm gonna say energy emissions? Yes?
Do you know why that happens? A great active decay?
You know what is it? I just know that if
as too many neutrons and it's center, it's like unstable,
so they can't I'll stay they shut off. No, I
did not know that. I don't know because like there's

(08:49):
some kind of potentials high for them. I'm actually not sure.
Do you know why that happens? Uh? No, but I
do know, like the half life of particles, and so
all right, a couple of yes and no answers. None
of the answers changed, none of the answers decayed. They're
all stable in their ignorance of this question. You know,

(09:09):
some people said yes, and are you saying they maybe
they said yes, but they didn't really know. Some people
said yes, they know that it does happen, but they
weren't really clear on why. And when I pressed them,
they just sort of described the process that happens, you know,
like they have short lifetimes. That's like asking, you know,
why does something I have a short lifetime? Because it
has a short lifetime. There isn't really there wasn't really

(09:30):
much understanding for why it happens, Like why can these
heavy particles not just stick around forever? I see? Well,
some people said radioactive decay, But that's that's a little
bit different, right, that's when a whole atom sort of
breaks down, not a particular particle. Yeah, it's a little
bit different, but it's actually the same thing because what's
going on inside radioactive decay is just a particle decay.

(09:53):
It has an impact on the rest of the Atomate
changes the automate changes a neutron into a proton and
that changes what the atom is. But radioactive decay is
actually just an example of one of the particles inside
the atom decay. Oh wow, so it's like a Russian doll. Yeah, precisely.
Well that's what reality is. It's like Russian dolls, right,
you get these layers and layers of reality. Yeah, it

(10:14):
all leads back to Russia. We were going to try
to avoid politics on the show, but it's the new
in the New decade. We're not doing politics, all right,
So pretty good answers. And I have to admit I
don't know why particle decay. I know that they decay,
and they sometimes spontaneously trying to do other things, but
I also don't know why some of them don't decay.

(10:35):
That's kind of puzzling to me. So let's get into
a Daniel. Well, let's maybe define for people first, what
is particle decay. Yeah, decay is a funny word because
it implies like you've died and your bits are sort
of falling apart and blowing away in the winds really dramatically, right,
But really, by decay, we just mean that a particle
turns into other particles like it's it was kind of

(11:00):
particle and then an instant later it's like it's broke apart.
Did break apart or does it transform? Yeah, that's exactly it.
It doesn't break apart. It transforms like when a higgs
boson turns into a pair of bottom corks, which it
likes to do. It's not like it was made out
of a pair of bottom quarks and it broke up

(11:20):
into those. This is not like you're taking a molecule
of water and splitting it into the hydrogen and the
oxygen that you can do. But when particles decay, they
transform from one kind of matter to another. It's really
it's alchemy. So the higgs boson was not made of
bottom quarks. It transformed from higgs boson into a pair
of bottom corks. It's kind of like when the Beatles

(11:42):
broke up. It's not that they it's almost up. Good,
I'm glad, I'm right, Okay. So it's not like a
case like it breaks down, but it's more like, um,
it just decide it to be something else totally. Yeah.
And it's not like it's making a decision, right, It's

(12:03):
like it's alive and his moods and it's like today
I'm not feeling it. I just want to be be
corks today. How do you know, Daniel, how do you
know his bosons? I've interviewed them. They're not very insightful.
You talk to them to find out that they don't talk.
Is that what you're saying. I try to interview them.
You know, their agent never calls me back, so you
know they're super important or they have nothing to say.

(12:25):
And we see the same process happened for lots of
other particles and not to the Higgs boson. Right, Really,
the neutron decays into a proton, and when it does so,
it kicks out an electron and some neutrino um. The
top cork decays into a W and a B corks.
This kind of stuff happens all the time. Like, what
do you mean It kicks out like it transformed into
one thing and another thing, but one of the things

(12:46):
flies away. Yeah, a particle can turns. We'll get into
this a little bit later. There are a lot of
rules for how particles decay, but one of the most
important one is that a particle cannot decay into one
other single particle. It can only decay into multiple particles.
So when a neutron decase, It decays into a proton
and an electron and an anti neutrino. And this is
what we called beta decay. This is actually what happens

(13:08):
inside the nucleus when an atom radioactively decays, is that
one of the neutrons is turned into a proton. And
this is all kind of that quantum mechanical magic. Don't
say magic, not magic, quantum mechanical wizardry. Science. Man's you
used to word alchemy? How is that any different? Alchemy
is science. For a long time people thought it was nonsense, impossible,

(13:31):
but then it turns out it's actually possible. We do
it all the time, so it's been brought back into science.
Well maybe he'll disabill happen for a wizardry. Okay, alright, alright,
I'll compromise. We'll call it quantum witching about that in
one way? Is that a compromise? I don't quite understand,
But all right, it's quantum something. Yes, yeah, yeah, yeah,

(13:52):
I guess what it's. What I mean is that it's
not like things are like you said. They don't break
apart into into the parts that they're made out of.
They literally sort of like become a ball of for
more deal energy, and then that energy transforms into other things. Yeah, precisely,
you're converting one kind of matter into another kind of matter.
And that seems really strange, right, like where did it go?

(14:14):
But remember all of these things are particles, and particles
are just excited states of the quantum fields. Space is
filled with these fields, and sometimes they ripple, and those
ripples are particles. So we're really talking about is moving
energy from one quantum field, like the Higgs field, into
another quantum field, like the field for bottom corks. It's
like the excitation passes from one field to the other. Yeah, exactly,

(14:38):
just like a wave can move from one kind of
fluid into another kind of fluid. Or when you strum
a guitar string, you're changing the shaking of the guitar
string into the shaking of the air. Interesting, and so
we go back to the Beatles because it's it is
sort of like the loneliest guitar. All right, Yeah, go
you win. You're right, it's just like the Beatles. But

(15:00):
that's kind of what we call particle decay or particle death.
I guess that. I mean, that's what we mean when
when we asked the question why do some particles die
because basically the elect the first particle that was there
basically stops existing, stops existing, and something else exists. Yeah,
and it's and it's bits are no longer there. We

(15:20):
don't know if the Higgs boson is made of smaller
bits right now we think of it. It's just fundamental.
But whatever it is is no longer around. It's not
just getting taken apart and rearranged like Jigsaw puscles into
something else, like Lego pieces into something else. It's really
getting transformed. And that's what we mean. You mean the
Higgs is not made out of little Higgy's um. I

(15:41):
think the Lego company has a copyrun on that name,
so we should avoid using it, all right, So that
and so it really dies, right, it's like it's no
longer in the universe. Yeah, it's gone. And so we
make particles like this in collisions all the time. We
collide protons together, we make some heavy particle z W
a top cork, Higgs boson, something else, and they live

(16:01):
for like ten to the minus twenty three seconds before
they turn into something else. And you know, that's what
makes it so hard to study these particles that they're
not around for very long, so it's hard to talk
to them. Wow. Well, it seems like some particles are
alive quote unquote for ten to the minus twenty three seconds,
and some of them are live for seven bizillion years.

(16:22):
It seems unfair, doesn't it. All right, so let's get
into why that is and what causes a particle to
decay or not. But first let's take a quick break,

(16:44):
all right, Daniel, So why does it happen? Why the
particles have to die? The key thing to understand is
that there's a difference in the mass of these particles.
So higher mass particles like the Higgs, like the top
they decay into lower mass particles. And this makes simple
sense because of conservation of energy. If you have a
high mass particle just at rest all of its energies

(17:06):
in its mass. If it turns into other particles, those
particles have to have lower mass, otherwise you'd be violating
conservation of energy. Oh, I see, And it's a it's
a spontaneous event, right, Like nothing triggers it. It's not
like it bumped into something and it broke up, or
you shot you shot a particle at it and then
that caused the transformation. It's like it was just sitting

(17:27):
there and because it had too much, too much mass,
it just suddenly breaks up. Yeah, it's spontaneous. It doesn't
need to be triggered from anything from the outside. And
it's also random. So if you have like a hundred
Higgs bosons and you have them all in an array
somewhere and you watch them, some of them would decay
very quickly and some of them would live a little
bit longer, and it's a distribution there. So we can

(17:49):
predict the probability of the Higgs boson decaying after a
certain time. You can't predict it for an individual one
because it's quantum mechanical. But we know, like what the
average lifespan is a Eiggs boson, where the average lifespan
is of a top cork, and it's totally random, Like
what what I guess? What triggers a death the death
of a particle. That's the deepest question in quantum mechanics, right.

(18:11):
We know that physics predicts the probability of things happening
at various times, but we don't know how the universe
makes a decision about what's going to happen when you
know in which Shortinger's boxes the cat alive or dead.
This is exactly that question, because the way the Shortinger's
box works, if you have an atom inside the box
that can decay or not decay, and it has a
certain lifespan, and if it's already decayed, that's killed the cat.

(18:33):
And if it hasn't decated, hasn't killed the cat. And
what makes a decision for an individual box We don't know.
The universe has some mysteriously not magical um which he
dies somewhere that makes those decisions. I see, it's not magic,
it's just mysterious. It is mysterious. Now. It's one of
my deepest questions about the universe is how it picks

(18:54):
random numbers. Where is the universe's random numbers generator? How's
that work? Um and and way. That's a deep fascinating question.
But the key thing to understand is that higher mass
particles decay into lower mass particles. Right that that you're saying,
that's like the Golden rule of particle decay. Yeah, there
is actually something called the Golden rule, and it helps
you sort of do that do onto other particles. As

(19:17):
other particles we do onto you. Yeah, I don't know
how particles behave and if they're nice to each other
or not, but firm me. The golden rule helps you
understand sort of why lower mass particles are more likely
to exist in the universe than higher mass Like, why
don't higher energy, lower mass particles turn into high mass
particles all the time. Why does it mostly go the
other way? Why do things sort of move down the

(19:39):
mass ladder? Well, to to make something heavier rooting, you
need to collide with something else and then from that
you can like join together. Yeah, and that's exactly what
we do in particle collisions. We make these heavy particles
very briefly by smashing lower mass particles with a lot
of energy together, So we have enough energy to create
these high mass particles. But then you might wonder, like,

(19:59):
why don't they just stick around? Why don't high mass
particles just sit there being high mass particles forever? Right?
And is that also a rule? I mean, so, the
one rule is that you can only decay do things
that are less massive than you, so kind of basically smaller,
lighter things. That's one rule. The other rule seems to

(20:20):
be that maybe the like the more mass you have,
the more the quicker you are you're going to decay.
Is there a correlation also in like if you have
more mass, the less life you have. Yes, that's certainly true.
The more mass you have, the more likely you are
to decay quickly. Also, the more ways you have to decay,
the more ways you're allowed to decay, the more rapidly

(20:43):
you're going to decay. So if you have a really
heavy particle but it can only decay via like the
weak force, then it's gonna be around for longer because
the weak force doesn't act for often. It's very weak.
Where if you can decay via the strong force hydronically,
then you can decay very very quickly because the strong
force is very powerful. Oh so it's kind of like

(21:03):
if it has a lot of options, then it's going
to take one of those options sooner or later precisely.
And the way I like to think about it is
that these particles sort of like to relax. They start
out in these very high mass states, and you think
of it like having a lot of tension, and it
wants to relax down to the lower mass the way
it's sort of water likes to flow downhill, right, and
everything in the universe likes to spread out and cool

(21:23):
down and and sort of smooth out, and being in
lower mass states is more smooth, has less energy sort
of concentrated in one place. So maybe we should rename
this episode why the particles like to relax? Why are
particles so smooth? All right? So what you're saying, um,
this death of this decay, this transformation is really just

(21:46):
like the universe kind of reverting or going towards the
lowest possible energy state. Yeah, imagine what happens, for example,
when you strum a guitar string, right, let's go back
to that. You have a lot of energy stored in
the guitar string. But then that guitar string interacts with
other stuff, right, It can bump into air molecules and
give it some of its energy, and then the sound

(22:07):
spreads out through the air and you enjoy the music
of the Beatles. This is just energy dissipating, right. Why
it is energy dissipated. It dissipates because of entropy, because
things like to spread out, things like they get more smooth,
and so in the same way, you can think of
a particle sort of like as the strumming of a
quantum field, it's like a field that's oscillating, and if
that field can talk to other fields, like the Higgs

(22:29):
field can talk to the bottom core field, that it
has a way to sort of spread out into those
other fields. It's like it's louder and so it it
can reach other fields better. Yeah, Or it's like, you know,
it's in a box and there are more holes in
the box, so it can spread out. If there are
lots of really big holes in the box, that it
can get out, whereas if you put it in a
box and there's almost no holes and it's gonna take

(22:51):
a long time for that energy to leak out. And
so the lower the mass, then the more stable you are. Precisely,
and if there's no particle with or mass than you,
than your stable because you can't spread out anymore. So
the particles at the bottom of the rungs that have
no particles below them, then they can't decay to anything
else and so they are stuck. And that's the situation

(23:12):
with the electron, because there's nothing with a less mass
then you or or do you have to do also
with the rules of particles, like an electron can just
turn into a super light I don't know, quark or
higgs or something. Yeah, there has to be something with
less mass than you that you are also allowed to
decay into. So, for example, a muan can decay into

(23:35):
an electron, it also has to create two neutrinos at
the same time for other rules, but the opposite can't happen.
Electrons don't decay into muans because muons are heavier than
electrons and the electrons are the are the lightest ones,
right Tows and muans can both decay into electrons electrons
the bottom of the ladder, but electrons can't decay into
corks and whatever. And there's all sorts of rules preventing

(23:57):
some kind of decays from happening. So um, as long
as you're not breaking one of the rules, you always
decay into the lightest particle around. Oh I see. So,
like a muon can't decay into something that's not an electron,
muans almost always decay into electrons. Sometimes a particle will
have several things that can decay into. So for example,
the higgs can decay into a pair of bottoms, but

(24:18):
it can also decay into a pair of photons or
a pair of w bosons or something else, or a
pair of charm corks or even a pair of electrons.
So sometimes a particle will have lots of different places
it can go, all right, So there are sort of
rules to these decays, but generally they follow that rule,
like if you decay, you're going to decay into lower
mass particles until you hit the bottom, until you're like

(24:41):
the gopher, and then working in the mail room. You
can't get fired demoted more than that. Yeah, it's just
like that. It's like getting fired down the hierarchy. And
once you're at the bottom, you know, um, then you
can hang on forever. I guess it's not like having
a job, because you could get kicked down this street.
But I guess maybe stable particles are the unemployed ones

(25:02):
in this analogy. Right, Oh, there you go. You don't
have a job, so you can't get fired, all right.
And so then that's why some particles never never decay
like electrons. You're saying, they can't decay in to anything lighter,
and so they just hang around forever. As far as
we know, they hang around forever. I mean, we don't
know that we know all the list of particles that

(25:22):
are out there but for the electron to decay into
a lighter particle, there would have to be another particle
out there that we hadn't heard it before, and it
would have to interact with the electron. So it has
to be some force that couples the electron to this
particle to allow to decay, to create sort of that
hole in the box, to let the electron turn into
that other particle. Um. And you know, there are other

(25:42):
particles like neutrinos, but electrons can't decay into neutrinos because
that violates one of the rules, like electrons have a charge,
neutrinos don't. So you can't turn electron into a neutrino
because then where does the charge go. There has to
be conservation not just of mass, but also all these
other quantum magical quantities. Yeah, and we have this whole

(26:03):
list and we'll go into it in a minute for
all the rules of particles have to follow in the decay.
And the things to understand about that is that this
is just a list of rules we invented um to
sort of describe the things that don't happen. We're like, well,
this doesn't happen. Why not, Well, let's make a rule
that says it can happen. That doesn't mean we know
why the rule is there, right, It's just we've noticed
this never happens, and so there must be a reason.

(26:26):
We just don't know yet. It's not it's not so
it's not it's less rules, but more like trends or
you know, things we've never seen happen. Yeah, and our
goal is to make the sort of minimal set of trends,
like what's the minimal set of rules you need to
describe everything we've seen. And then we look at those
and we say, well, do this makes sense? And what
does it mean about the universe? And can we find

(26:49):
a reason why these rules have to exist and stuff
like that, And so what are some of the other
particles that also live forever? The quarks lift forever. The
up corks and the down corps do live forever. Yes,
there are no lighter quarks, right. The charm cork and
the strange cork, those are heavier, and so they decay
into the up and the down and the top cork.

(27:09):
In the bottom cork they're even heavier, so they decay
also down the ladder to charm and strange and then
into up and down. So literally every particle in my
body then is is as old as time itself. All
the particles in your body are just three different kinds
of particles up quarks, down quirks, and electrons. And I
think that those particles have been around since just after

(27:30):
the Big Bang. None of my particles have were created
more recently than that. It's not because you can create
those particles. You know, if for example, one of the
electrons in your body hits a piece of antimatter coming
from a cosmic ray, it can get annihilated into a photon,
and then that photon lives very briefly and turns back
into an electron and positron, so then it's been reborn.

(27:52):
Right in that sense, These particles are always having interaction
and and sometimes they get they disappear and come back.
So some of these electrons have been born more recently,
but it's possible for an electron to stick around the
whole lifetime in the universe. Yeah, every particle that I
am made out of was made at the Big Bang,
or you know, it was there when it all happened.
It's got stories to tell around. Yeah. Oh, if you

(28:15):
could interview particles, if only they could talk. Part If
these particles could talk, these particles could talk, they probably
tell stories like in old folks homes, you know, while
when I was a kid and I have an onion
on my belt and the universe was young. You think
you have it bad now? We had to live through

(28:35):
the hot plasma. Yeah, I think. I think about what
it was like in the Big Bang. We have to
walk up hill both ways, all right, So that is
kind of what happens is when particles die. And so
let's get into a little bit more of what these
rules are in more detail and what they mean for
us as billion of year old beings. But first let's

(28:59):
take a quick break. Yeah, all right, Daniel. So particles die, unfortunately,
is just the way of the universe. Uh. And then,
and that means that particles sometimes, if they're too heavy,

(29:20):
they will transform into lower energy particles until you get
to a certain types of particles which apparently never decay,
like quorcs and electrons. Yeah, and not just lower energy particles,
lower mass particles or lighter particles. As we have this
rung of particles and they decay down, down down the rung,

(29:41):
and they get to the bottom of the ladder, and
they can't decay any further. And the particles ever spontaneously
go up the ladder. Absolutely they do. If they get
a burst of energy, they absorb some energy, then they
can go up the ladder. And that's exactly the kind
of thing we do in particle collisions, is that we
bring particles together with a lot of energy and low mass,
and we create we push them up the ladder briefly,

(30:02):
because our question is like what particles are on the ladder,
how far up the ladder can you go. It's like
we're swimming in very cold, cold universe and we're trying
to climb up the ladder to see like what could exist,
what used to exist. So we create these pockets, momentary
pockets of density to push a particle up the ladder
to see like, oh look you can make top quarks.

(30:22):
Oh look you can make Higgs bosons. Yeah, And so
that kind of answers the question why the particles die
is that that's just kind of the way of the universe.
Nothing heavy last forever. That's the kind of caveat right,
like something's last forever. But if you're too heavy, you're
not gonna last for a long time. I feel like
that should be on your tombstone. Nothing heavy lads forever,

(30:44):
or maybe the you know, the motto of the universe
would be like only electrons and quarks last wherever. Yeah,
it's true that nothing heavy last forever. It's a deep
principle of the universe that things spread out. You know,
it's connected to entropy that things tend to like to
transform into more relaxed states and the ones with more disorder,
and the things that lower mass particles, they just have

(31:06):
a lot of different ways to be. Like a higher
mass particle, it can basically just sit there. It's used
up all of its energy to create this particle. But
if it decayed into lower mass particles, then there's a
zillion different arrangements for it, and the universe prefers that.
It prefers configurations with lots of different arrangements. It's more disorder,
and so that's just the way the universe flows. Even

(31:28):
for an electron. I guess I'm curious. Even for an electron,
you're saying, we'll probably never decay, but but it can,
Like can is one of its possibilities that it just
one day disappears for no no reason and transform into
I don't know, fluton or something. Yeah, potentially, I mean,
electrons are stable. But again, all these statements that we
make are statistical. We've never seen an electron decay and so,

(31:51):
and there are a bunch of rules that prevented from
turning into the particles that are lighter than it, things
like charge conservation and electron number concert ration, all sorts
of other rules we invented just to sort of describe
the fact that we never see them decay. But in principle,
there could be some lighter particle of the electron that's
connected to the electron with some very very weak force

(32:13):
that we haven't discovered yet, and eventually, after sixty two
chillion years, electrons will decay into those other particles. It's possible.
Was that time you used their chillion chilion just invented it.
But it's technically like the Chilian it's it represents the
flow of the universe. Man, Oh dude, yeah, alright, So

(32:34):
I let's getting through these rules because I feel like
that's where the meat of this is, right, Like, it's
not like any particle can just die spontaneously. It has
to follow some rules that the universe seems to follow
or maybe not rules. Are these more like we've never
seen these things happen, but maybe they but they they're

(32:55):
not absolute rules. Maybe. Well, it's that way with all
the physics. We see stuff happen. We write down rules
that we think describes what happens, and that we hope
those rules are fundamental to the universe. But we could
be wrong. There could be exceptions to these rules we
just haven't observed yet. So in the same way, we're like,
you know, let's write down all the results of particle
physics experiments, and then let's try to simplify that into

(33:17):
a set of rules that we think describes all those experiments,
and then we try to understand those rules, like do
they make any sense? And why this rule and why
of that other rule? Er what are the patterns among
the rules. That's sort of the stage we're ad in
particle physics. So it's it's interesting to think about what
these rules are and what they might mean. I see.
So it's kind of like you if you dropped an
egg and it broke on the floor, and you dropped
an egg again, and it broke on the floor, and

(33:39):
you dropped another egg and it's broken the floor, and
so and your mom is like, why did I have
an experimentalist as a kid? And so you made a
rule that set if you drop an egg it'll break. Yeah,
and that describes what you've seen and and then of
course you should test your prediction and try dropping eggs
in other people's houses and tom toomps the mountains and

(33:59):
to see if it is a deep rule of the
universe or just something specific like if you drop an
egg on the space station doesn't break. So it turns
out your rule needs to qualifier, right, I see this
is a special egg breaking rule only in whore his kitchen,
or only on Earth, or only near objects with gravity.

(34:19):
If you drop egg, does this break? Yeah, there's a
difference between general eggcticity and special eggticity. All right, So
what are some of the rules that govern particle decay
and just I guess real quickly here. Yeah. Well, one
of them we talked about already is that they have
to decay from heavier particles in the lighter particles because
of conservation of energy. The other is that electric charge

(34:41):
has to be conserved, so electrons, for example, can't decay
into neutrinos um muans have to decay into electrons. They
can't decay into positrons. You have to conserve because the
universe can't do anything with that extra charge. Is that
it it's like it has to do thing with it. Yeah, precisely,

(35:01):
electric charge is conserved. The universe cannot create or just
destroy electric charge. It sticks around, and that's not something
we understand why. But we've noticed that that it's the
case that electric charge is always conserved. I guess my
question is where did all this charge come from? Ymtanu
the Big Bang? And you know electric charge comes in
positive and negative, right, So you can create a positive

(35:22):
charge if you also create a minus or photon can
turn into an electron and a positron, because the total
electric charge is then conserved, all right, So that's a
that's another rule you have to concern And that also
works for the other charges I imagine, right, like the
color charge and the the smelly charge and all the

(35:42):
other charges. Yeah, for the other charges, there are similar
conservation rules. And you know these charges also are important,
for example, because the photon can only interact with charge particles.
So for example, the photon can turn into a electron impositron,
but it can't decay into neutrinos and interact with neutrinos
at all because it only talks to the electron and

(36:04):
the positron. Can it kind of do like a three
point turn like kind of decay into an electron which
then decase into a neutrino. Well, remember electrons are stable,
so if a photon decase and electrons, it can't then
turn into neutrinos. But if a photon decayed into like
a muon and an anti muon, that muant an antimu
and could then turn into a pair of electrons and

(36:24):
positrons and produce neutrinos at the same time. So yeah,
photons can eventually produce neutrinos, but not directly. I think
what I'm getting here is that if you are a
person who likes rules and memorizing rules, then particle physics
is for you. And we've got fewer rules than like
organic chemistry. You know, we're trying to keep it simple.

(36:45):
That's true that organic chemistry is all rules, and that
it's just a list of rules that nobody understands and
it's an exception for every single case. That's that's why
I didn't do organic chemistry. Didn't see what I mean
because the list is shorter. That's the only difference. Actually,
totally Pegg, dude, I'm interested in particle physics because it
has the smallest list of things to memorize. Did I

(37:05):
ever tell you why I became an engineer? No, because
you wanted to work with cockroaches. Because my dad said
to me in high school, He's like, engineering is the best. Man.
You don't have to memorize anything. If anyone asks you
a question, you just look it up in a book.
And I was like, that's for me when your classes
or when your homeworkers due or no to turn out,

(37:27):
you don't need those things either. Um, but maybe we
should just round it up with my favorite rule of
particle decay. Okay, okay, you have a favorite favorite is
that a particle cannot decay into one other particle has
to decay into at least two. Yeah. You can't just
have like a Higgs Boson decay into a bottom cork,
or you can't even just have like a Muon decay

(37:50):
into an electron. Why not? We're not exactly sure why not,
but we know that if it could happen, it would
break another rule, which is conservation of momentum. Imagine you
have a heavy particle it's just sitting there, has no momentum,
and it turns into a lower mass particle. Now, now
that energy that from the difference in mass has to
go somewhere, and usually that goes into the motion of

(38:12):
the particle. Okay, So if a muon, for example, turned
into an electron, there's extra energy there from the mass difference,
so the electron is moving. But then that violates conservation
the momentum because the muon originally had no momentum and
now the electron has momentum. So you have to create
another particle to balance out the momentum that the electron
is getting to go the other direction. But wait, what

(38:33):
if the muan, the first one, was moving a little bit,
can it decay to a smaller particle that's moving faster,
because then you can still conserve momentum. They can't because
there's some of potentially some observers moving to the same
speed as the muan, and they also need to see
something that makes sense. And so that's true for all
particles that have mass, that there's always the potential to

(38:55):
catch up to it and see it motionless. And so
you have to have a rule that works also for
those observers. You can always look at it in a
way that had that it has zero momentum because it's
not moving. And in that frame where has no momentum,
it can't just spontaneously turn into an electron that's moving,
because then you've created momentum. And conservation momentum is another

(39:17):
one of those rules about the universe. We don't know
why it exists. Um, we don't know why it's there.
We show a whole podcast episode about these rules because
they're really fascinating, and they highlight a famous woman in
physics who has long been overlooked, Emily Nurther, who invented
sort of the symmetry that that describes all these things.
H interesting. Well, I feel like you're saying that every

(39:39):
particle is that a stand still for somebody, every particle
that has mass. Yes, photons are never to stand still
because they have no mass and if they were to
stand still, they'd be nothing. Okay, So you always need
to decay to two particles because everything is particles, right,
even sort of like energy? Whoa man? That was deep?

(40:01):
Did I tell you I didn't have a banana today?
So I am running on fubes man, everything is energy
and energy particles. Let's go with that. You're like, let
me take a puff here? Yeah, man, what did you said?
Go for it? I'm smoking my banana appeals. But it's
I think it's fascinating that every particle when it decays

(40:23):
has to turn into two others. It can't just turn
into one. That means that the number of particles increases,
so there's no conservational rule and like the overall number
of particles in the universe, that's not a problem, all right,
Maybe just to wrap it all up then, um, you know,
I feel like we started off with the question why
do particles die? And I feel like I feel like

(40:44):
we arrived at a good answer. You know, I feel
like it what is the meaning of last of particles
or two? It's it's like, that's the way the universe is,
you know, nothing, Um, most particles don't last forever. You know.
That's just the way. That's a constant truth truth of
the universe, unless you're you get to the bottom rung,

(41:06):
in which case you can last forever. You can last, right,
you can hang on forever at that bottom rung. But yeah,
the universe just likes to spread out. That's what it
means for time to move forwards in some sense is
that pockets of energy density spread out and diffused themselves
across the universe. The whole universe is spreading out and
getting colder and more dilute, and so the same thing

(41:26):
happens on the particle level. So in that way, we
have that in common with particles. And I think it's
amazing to think about that, the idea that every particle
in my body, like every single one potentially or most
of them, they were all there at the Big Bang, right,
and maybe part with the Big Bang? Is that true? No,
we think they were. That matter was created just after

(41:48):
the Big Bang. Oh, I see, okay, so it was
there in the Big Bang. All of these particles that
are made out of the journey fourteen billion years just
for the privilege of being part me. And I hope
they're not disappointed. Yeah, I hope this is not their
peak moment here. You know, they've been in the heart

(42:08):
of stars, they've flown through the universe, but this is
where it is, This is where it's good. Maybe maybe
the answer to why particles eyes that they realized they
travel all this way just to be part of For
here sously the aspultaneously decay, because why even go on? Man. Yeah,

(42:29):
but it's cool, even if this is not their peak.
It's cool to think that every particle in my body
may be here until the end of time, right like it.
It was there the Big Bang, and now it's part
of me and it they'll still be around buzillions of
years into the future most likely. Yeah, because, like we've
talked about on this podcast several times, the thing that
is you is not the things that make you up.

(42:51):
It's the arrangement of those bits. Because you could take
your bits and rearrange them and to make a star
or lava or kittens. It's all the same stuff when
the same proportions. It's just how it's put together, so
you can put it together to make a whorehey, or
a Daniel or you know, BMW or whatever you like.
It's all the same stuff, and it's been around for
a long time, and it's gonna be here for sixty

(43:13):
two chillion years. I think what you're saying, Daniel is
that my particles are old, but I can be as
young as I want to be. That's right, That's exactly
what I'm saying. Your particles are fourteen billion years old,
but you're as fresh as a breath of air. But
then that that air is also made out of old particles. Yeah, precisely,
but we don't know, and we can tell where it's
been based on how it smells. All right, Well, we

(43:35):
hope you enjoyed that discussion about death, the death of particles,
the death and birth and rebirth sometimes of particles, and
the eternal life of other particles, and all the rules
in between. And we are struggling to understand these rules.
And the more we smash particles together and see the
rules for new particles, the more we can understand why
we have these rules and not those rules. And are
these rules really universal? And do they only exist in

(43:56):
our part of the universe or for for the particles
that we have seen so far. And one day we
hope to have a very simple, concise set of rules
that we totally describe everything in one line, and hopefully
we'll be around to explain that line. So stay tuned,
keep listening, subscribe and follow us on Instagram and Twitter,
and have a great twenty everybody. See you next time.

(44:23):
Before you still have a question after listening to all
these explanations, please drop us a line. We'd love to
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Thanks for listening, and remember that Daniel and Jorge Explain
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(44:45):
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