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April 15, 2021 44 mins

Daniel and Jorge talk about the result of the g-2 experiment at Fermilab and what it means!

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Speaker 1 (00:08):
Hey all, Hey, do you know what today is? Wednesday?
It's Wednesday, April seventh. Today is like Christmas for particle physicists. Really,
but what if you don't celebrate Christmas, Well, then it's
like Christmas and Hanukkah and Valentine's Day and your birthday
all rolled into one. Nice. Does that mean all particle
physicists get a special box of chocolates today? Kind of?

Today's a day we find out the answer to a
question we've been waiting twenty years for. Does that mean
the chocolate's are twenty years old? To let's just holl
him that particles and chocolates age like fine wine. Hi

amor handmad cartoonists and the creator of PhD Comics. I
am Daniel. I'm a particle physicist, and I like my
chocolates nice and fresh, fresh out the cocoa tree. I've
actually had cocoa beans themselves. They're pretty intense but tasty chocolate.
The Universe and so welcome to our podcast, Daniel and
Jorge Explain the Universe, a production of I Heart Radio

in which we take a bite out of everything in
the universe. We sample the flavors of corks, we talk
about the size and the speed of black holes. We
talk about how the universe got to be this way
and the way it will look in a billion, or
a trillion or a gazillion years. We have ambitions to
take the entire universe and explain every little bit of
it to you because there is a lot to understand

and to learn about the universe, and the scientists are
currently added trying to explore what things are made out
of and what things can be made out of. That's right,
when we're not taking a break to do a podcast,
we are trying to unravel the nature of the universe
by figuring out what are the smallest bits of it,
how do those bits fit together, what are the patterns
of those bits, and are there more bits we haven't

found yet. Yeah, because there has been a lot of
progress in physics and particle physics and understanding what matter
and the forces are all made out of in this universe,
but it's sort of an ongoing effort. There are still
nooks and crannies and corners we haven't explored, and possibly
big areas of physics that still remain totally unknown. Job

security for a particle physicists. More nooks and crannies to explore.
But no, you're absolutely right. We have found out a
lot about the sub atomic nature of matter, but there
are still lots of questions we don't know the answer to,
and that tells us that there's probably a lot going
on that we don't have any clue about. We don't
know if we figured out like most of the puzzle
and we have a few details to wrap up, or

if we're just looking at the tip of the particle iceberg.
But then what is that iceberg made out of tanuel?
And what does it float on? It's all questions embedded
in questions. It floats on a sea of confusion. Yeah,
and O cartoons are probably drowning in the scene there.
But it is a pretty exciting time to be in physics.
There are a lot of interesting results lately and coming

out of the physics community, and so recently there was
another big announcement. Yeah, that's right. We've had this mystery
that's been sort of outstanding for twenty years, the result
of an experiment that was quite surprising that didn't agree
with our theoretical calculations. It suggested that maybe something new
was going on, maybe it was being influenced by some
other kind of particle or force and we hadn't yet discovered,

but it wasn't really precise enough for us to know
for sure, for us to hang our hats on. So
people built a bigger, better, stronger, faster experiment to make
a more precise measurement, and those were the results that
were just recently revealed. Yeah, and so to be on
the podcast, we'll be talking about did Firmulab just discover

a new particle whatever? Fermilab just discovered they definitely figured
out how to trigger a lot of science headlines. Oh yeah,
it was this pretty big in the pressed. This was everywhere.
I don't think it's been a science event recently that
triggered as many emails from listeners saying, what is this?
Explained this to us, what's going on? I need to understand.
It was everywhere I saw. It was on the front

page in the New York Times, and people were tweeting
about it. So it's kind of interesting and maybe significant
result in physics. And for me, it was fascinating to
see the sort of variety of headlines that people took,
Like the New York Times was pretty stately and understated
about it, but other places like Vice that had a
headline that reads, government physics experiments suggests something unknown is

influencing reality. Wow, that sounds like a pretty good plot
for a movie. And I think it's technically true, isn't it.
You know, it's an interesting choice of vocabulary, but it
is technically Every word in that headline is true. Government
physics experiment suggests something unknown is influencing reality. There you go.

You know, I can fact check it. It's definitely accurate.
It was done by government physicists, and there is something
out there influencing that experiment. I don't know about all
of reality, but it's definitely true. With so kudos to
that headline writer. They definitely took this sort of like
movie trailer approach to writing that headline and how they
added government physics experiment, Like, first of all, are there
non government physics experiment? Not many? Second of all, it

just makes it more sinister, doesn't it. No, I don't
know they're going for sinister or like authoritative. You know,
this is not your friend Joe's physics experiment. This is
like people in lab coats getting salaries. You know, you
should believe this does still really have any friends. Let's
be honest, I think they were going for sinister, you know,
like the government is trying to do something crazy. Oh man,
I just totally misread this one. I thought it was like,

trust us, we discovered something crazy, but instead you're suggesting
it's like government about to build doomsday device that will
ruin your weekend. I think that reveals your attitude towards government.
An you're like trusting of the government more government. Hey,
I'm a government physicist, so you know, I see you're
one of them. Do you wear like, you know, sunglasses

with your white lap coats and everything? Only when I'm
trying to influence reality, which is basically all the time.
Since I'm part of reality, this podcast is influencing reality,
is it though? We're just sound ways in the air, Daniel,
Unless you think our listeners aren't part of reality, you know,
hopefully they're real, but we don't have to be real.
You know. This podcast is generated by an algorithm, a

government physics algorithm. It's it's unreal. Anyways. It was a
pretty big result, a lot of impressive out there about it,
and I have to admit, Daniel, I didn't know about
this weeks before the actual announcement. Oh wow, is that
because you have a link into like the secret science
results kinda I was commissioned to to make a comic
about it by a journal, and so they sent me

the secret paper weeks ago, saying you can't share it
with anybody. Are you telling me you knew this answers
one of the biggest questions in particle physics for weeks
and didn't tell me a sworn of secrecy, Daniel. They
would have revoked my cartoon is license if I've had
told anyone. Plus also that they're like, they gave me
the paper and they're like, you can't tell anyone what
it says. And I'm like, I can't even read this paper.

I wouldn't be able to tell you tell anyone, but
my friend Daniel could read this paper. All right, Well,
I admire your integrity. Yeah, thank you. At least you
admire something about me. But it was a pretty exciting
thing in the physics community. And let's talk about whether
or not it lives up to the hype business, really
something that might influence our view of reality or is

it sort of another incremental result in the physics endeavor
of humans? Yeah, well, you know, it's an important moment
in particle physics because we have been desperate for a
discovery for quite a long time, you know, I would
say decades. We have known for a long time that
our theory isn't correct, that isn't complete, at least it
can't be the final answer, because there's so many unanswered

questions in it, so many parts of our theory which
just seems sort of like ad hawk or put in
by hand, or unexplained. So we've been cast thing about
for a new discovery to give us a clue as
to how to change our theory or what the new
vision of physics should be. And the main strategy for
doing that has been things like building big particle accelerators,
to trying to make new particles that we can add

to our table and give us a sense of the
larger patterns. But that's been coming up kind of dry.
We haven't found anything at the large age on collider
other than the Higgs boson, which we already believed existed.
So now we're sort of like looking under every rock.
Is there any experiment out there that can find something new?
Is there any measurement government physicists can do to find

some discrepancy between our theory and nature because we need
that kind of discrepancy in order to find something new.
So that's why this experiment is sort of like one
of the last best hopes for particle physics, that we
can figure out something new, find a clue that reveals
a new idea about the nature of reality. I guess
for some of our listeners who maybe we did not

see the headlines, let's just talk about the announcement. So
this was an announcement coming at a Fermi Lab, which
is a particle physics laboratory outside of Chicago, and they've
been around for forever, but and recently they announced that
some new results regarding the muan, which is a particle. Right,
that's right, So you're familiar with the electron. It's part
of you. It orbits all your atoms. The electron has

a heavy cousin. It's much heavier than the electron, but
it's otherwise totally identical. And the very existence of the
muan is sort of a mystery, like why do we
even have a muan. We don't know, but it's like
this copy of the electron, and it's a good place
to do precision measurements to try to like see if
there's anything weird going on, because the muan has this
little magnetic field, and that magnetic field is very sensitive

to the stuff going on all around the muan. Yeah,
so they've been studying this particle for a long time
and they just did a new measurement of its magnetic
moment and the results are what's kind of interesting with
regards to what it means for our view of the universe.
That's right, and you might be wondering, like, why does
the muan have a magnetic field? How does that even work?

We'll remember, a muan is this tiny fundamental particle. We
don't really know if it's made of anything smaller. We
sort of imagine it to be a tiny little dot.
But even though it's a tiny little dot, we also
think it has this thing called quantum spin, which means
that in theory, it has some angular momentum because it
has electric charge and angle momentum. That means it has
a little magnetic field. And that magnetic field is a

really nice way to probe what the particle is doing
as it flies through space. Is it just flying through
space or does it also shoot off other particles briefly?
And if it does shoot off other particles. Then, even
though these are virtual particles that only exist for a
fraction of a second, they can change the way the
muan's magnetic field works. And it's sort of a great

way to figure out what kinds of particles can exist,
what's out there on nature's menu. Because it's quantum mechanical,
every kind of particle that can be shot off the
muan will be created and influence the muan's magnetic field.
So don't thing of the particles out there waiting for
the muan. They are like possible particles that the muan
briefly creates as it flies. If you like fields instead

of particles, then another equivalent way to think about it
is that the muan is flying through a bunch of
quantum fields and its energy can slide briefly into those
fields and then come back. Since that influences the muan's
magnetic direction, you can tell when it happens, which gives
you a clue if there are fields and particles you
don't know about. And so what they do is they

take this muan and they spin it in a certain direction,
so they know the way it's going, sort of like
a gyroscope and then they stend it around in a
circle a bunch of times until it decays into an
electron because muans don't actually last very long. They're unstable particles,
and based on the direction the electron came out, they
can tell how the muan was spinning. So now they
know how the muan spin change from when they created

it to when it decayed, and that tells them basically
how all the other little particles out there were pushing
on the magnetic field of the muan, which tells you
something about what particles are out there. And they're measuring
this magnetic field of the muan, and I guess maybe
a more basic question is like why do particles have
magnetic fields? Isn't that weird? Like our particles little magnets. Yeah,

it's kind of weird because you think of little particles
as these little dots, and you know they have like
spin and charge and mass and stuff. But anything that
has spin, quantum spin and has electric charge also has
a little magnetic field because remember that's where magnetic fields
come from, Like the magnetic field of your piece of
iron comes from electrons spinning inside of it, and so

muans also spin, so they also have a small, little
magnetic field. So then I guess the next question is
why is this magnetic field of this little particle important
and what could it tell us about other particles that
could be out there. It's really important because the magnetic
field tells us about the other particles that are out there,
because the magnetic field allows the muan to sort of
interact with those particles. As the muan is flying along,

then the magnetic field gets sort of touched by all
the other particles that are out there, you know. For example,
like this magnetic field is carried by photons, so the
way that magnetic field information is transmitted is through photons.
So muan can be flying along, it can like pop
off a little photon and then reabsorb it. And it
can pop off a photon and that photon can interact

with other particles that can come out of the vacuum,
you know, like pairs of electrons and positrons or any
other particle out there, and then get reabsorbed. So sort
of what happens to that photon when it gets shot
off the muan and then re absorbed can influence the
magnetic field of the muan and also can tell you
about the other particles that are out there that can
talk to this magnetic field. And remember that by particles

out there, we don't mean particles that are already existing
and are hanging out waiting for the muan, but possible
particles on nature's menu that can be created from the
Muan's energy. That's what we're looking to explore. Well, I
see you used sort of like the magnetic field of
the muon is kind of an antenna almost, like do
you use it to see how it gets influenced by

other particles that are out there in the universe exactly,
just like an antenna, because all those other particles also
can sort of like talk magnetic language to the muon.
And if you watch really carefully how the muan is
spinning in the direction of its magnetic field, you can
tell the signals that it's picking up from those other particles.
And it's sort of like a gyroscope. You know, you
start a gyroscope spinning, it should keep spinning the same

way unless something applies forth to it. You know, give
it a little push or a little twist or something.
If you've got a muan spinning and you know the
direction of its magnetic field, you can watch as that
magnetic field changes and you can measure the influence of
all the particles around it. Cool. So then that's what
this experiment did, is that it's basically like a large
tunnel or ring or like a tomb, and you have

these muons flying around and you're sort of measuring how
they get knocked around by the universe, basically how their
little magnetic field gets tweaked by you know, what could
possibly be out there in the universe. Yeah, it's a orcles.
The muans go around in this ring and as they
go around, they get tweaked by all these other particles,
and it's a really cool way to try to find

something new without knowing what's out there. Anything that interacts
with the muan's magnetic field will give a little effect.
So you add up all the different kinds of particles
that can give an effect, and you get like an
overall number, and you can compare that to what we
calculate from our theory, where we add up the effects
of all the particles we know about, and we can
compare what nature is doing with all the real particles

to what our calculations are doing. You know, with all
the particles we know about, and that can give us
a clue if there's any particles missing from our list. Cool. Yeah,
you use this sort of like a metal detector, kind
of like you're sensing what's out there. And if you
think you know what's out there, then you should be
able to predict what this little antenna will tell you.
But if there are new things out there, the disintenna

will not do what you expected to do. Yeah, and
the differences are very very small. People have been calculating
this stuff for decades and been measuring for decades, and
most things agree. But if you measure it really, really precisely,
then you can see the influence of like very rare,
potentially new heavy particles. So we're talking about one of
the most precisely known and most precisely measured quantities in

all of physics. And the more precise we can make it,
the better a test we can do to see if
there are any particles out there that we might be missing.
I guess you're looking super closely to see this little
antenna you know, deviates from your theory, because if it
deviates from your theory, that means your theory is not
complete or there's new things out there. Yeah, and the
experimental challenge is getting all the other sources of uncertainty

out of the way, any other transient magnetic fields, or
knowing exactly how you started this muan, or making sure
nothing else is influencing it. It's a lot of work
to set this experiment up and make it super duper precise.
It's like lots of other experiments like the gravitational wave experiment,
where they spent decades figuring out how to get those
mirrors to balance and be really really quiet. There's a

lot of just sort of like careful work in setting
up the experiment like this, and there's also a lot
of careful work in doing the calculation and making sure
you're correctly accounting for all the particles that we do know.
So it's like a huge project. It's not just like hey,
I have this idea, let's go check this out tomorrow afternoon.
You know, this takes decades to design and to organized
and like really iron out all the wrinkles. Right. You

get a wait for the chocolate to you know age,
and you get to wait for everyone to sign the
Valentine's Day card, and it just takes a long time,
all right, Well, let's get into the theory of this
experiment and also the experiment and how those two are
not quite the same and what that means for our
understanding of the universe. But first let's take a quick break.

We're talking about Fermi labs recent announcement of a new
interesting result regarding the men which is one of the
fundamental particles, and they measured something about it and they
predicted something about it, and it's not quite the same, Daniel,
So maybe step us through what some of the theory
calculations are and what they're actually calculating. So what they're
trying to do is understand what happens when a muan

is flying through space. And this is a quantum mechanical particle,
and so you have to consider not just like the
boring option that a muan just like flies through space
and does nothing, but all the other possibilities. For example,
a muan might also fly through space but emit a
photon and then reabsorbed that photon. That's one possibility, it's
not very unlikely. In fact, we think the particles are

doing that all the time. And like we talked about
in the episode about renormalization and like what's the electrons
actual charge. What we measure is sort of like the
combination of all the possibilities that the muan can do
all at once. We don't just ever measure like a
single particle doing one thing. So this kind of stuff
is happening all the time. There's lots of different things
that muan can be doing when it goes from A

to B, and we try to consider like all those possibilities.
So possibility one is just going a straight line. Possibility
to is emit just a single particle and then reabsorb it.
Possibility three is emit two particles and reabsorbed them. Possibility
four is admit a photon and then that photon turns
into two other particles which then collapse back into a photon,

and then we can get reabsorbed by the muan. And
you can imagine how it's easy to imagine lots and
lots of different scenarios for what can happen for a
muon when it goes from A to B, and all
those scenarios affect the muan's magnetic moment just the same
way all these kind of quantum interactions with the vacuum
affect the electrons charge or its mass This is all
part of like what makes the muan. So when you're

calculating the overall magnetic moment of the muan, you need
to account for all the things that it could be doing,
including these little brief interactions it has where it interacts
with magnetic fields and creates other particles. Right, So it's
I guess it's kind of this idea that a particle
isn't just like a particle like alone in the universe.
It's like it's constantly doing stuff, doing quant the mechanical stuff.

It's constantly you know, maybe popping off other particles and
then reabsorming them, and it's not just like sitting there
and doing nothing. Yeah, there's this difference between like the
bare particle, which is sort of the simplest concept you
can have in theory, than the actual particle in reality,
which is part of the universe and interacting with all
these quantum fields around it. And that's sort of like
the thing we measured, the thing we observed. So the

bare particle really only sort of exists in our minds
like a single isolated particle doing nothing. In reality, the
particles are constantly buzzing with all sorts of other virtual particles.
And that's really what the muan is. Don't think of
it like a muan surrounded by a cloud of other particles.
The muan is that whole cloud. It's got like a
bare particle at its core, but the whole thing together

is the muan. And so it's sort of part of
what the muan is is to have this cloud of
other particles all part of it. Yeah, and it's kind
of like a quantum mechanical cloud of other particles. It's
constantly making right, Like, it's not just the bare particle,
it's also at the same time simultaneously existing as all
these other sort of with all of these other particles

that are created and virtually exists for tiny moments of time. Yeah,
And I think the quibble on the quantum mechanics of it,
it's not really true that they all simultaneously exist, but
that the possibilities of them all exist. And so there's
a superposition of all those wave functions for the particle
to be doing this or for the particle to be
doing that, and if you're not measuring it, then all
those options can exist at the same time. Doesn't really

have a philosophical meaning to say, like they all actually
do exist. But you know, that's a whole other digression.
We can talk about quantum wave functions another time. So
it's kind of like the cat, Like the cat is
both live and dead, and that's so that's usually put,
and so that me on is both alone and also
has all these other friends around it. Yeah, well you
might not be surprised to hear that I have an

objection to how it's usually put. I would say the
cat as a possibility of being alive and a possibility
being dead. I don't know what it means for it
to be alive and dead at the same time. That's
the whole idea of classical physics that somehow these wave
functions do collapse before we measure them. But in this case,
there's an infinite number of things that meant can do.
And the more particles you add, the more options, the
more times like a particle emits another photon or turns

into something else, the less likely those things are. So
the most likely thing to happen is that the muon
just sort of like goes from A to B. And
then you can like add a correction to that by
adding one particle, and you can add another correction to
that by adding two particles. If you want to get
like a rough idea, you just need to do a
few of these calculations. If you want to get it
like really really accurately, then you need to sum over
like thousands and thousands of these different possibilities. It's kind

of like, these are all different possibilities of what it
can do, but somehow they all affect its magnetic field.
And so like if you know, like it could do
a B, C and D, you can add up a B,
C and D and to get sort of like what
the theory predicts what the magnetic field of me on
is going to be? Right, that's right, And we use
something called perturbation theory, which tells us that, like we

do the biggest contributions first, and then the more ones
that we add sort of we're just refining the smaller
and smaller decimal places. So it's not like when we
get to diagram number forty seven thousand, we're going to
find something that totally changes the answer in the first
decimal place. As we add diagrams that are more and
more complex, we're getting smaller and smaller corrections, and so
we're sort of like asthem tonically approaching what we think

is the true value. But these calculations get harder and
harder because the later diagrams have more particles, and they
have loops and they have crazy stuff, and most importantly,
some of these create particles that have the strong nuclear
force in them, and those calculations are particularly tricky to do.
And that's really at the heart of why this is
so hard, right, And I guess the problem is that
the neon it's not just doing a B, C and D.

It's doing like abc d dot dot dot to like
you know, infinite number of possibilities, right Like it it's
almost like a fractal I think it's like it can
be turned into a photon and then but then the
photon can turn into two food things, and then those
two things could turn into other things, and you know,
the effects get smaller, but like the possibilities are endless,
right Yeah. And there's a really interesting question. They're like,

does it really have an infinite number of possibilities or
is it just the way that we are organizing in
our minds requires an infinite number of ideas because in reality,
there's just a number. Like nature doesn't do an infinite
number of calculations. Every time a muan goes from A
to B, it just does its thing. So it could
be like that our mathematics isn't expressed in a way
that makes this kind of idea simple and compac Or

it could be that there really are an infinite number
of things possibly going on there, we just don't know.
It's a really fun philosophical question. Philosophy. Yeah, we need
a longer podcast for that, all right. So you can
sort of predict what the meos magnetic field is supposed
to be from all these other like virtual particles, and
then you can also go out and measure the magnetic
field using an experiment exactly. And that's what they did,

like twenty years ago at Brookhaven. They did this experiment
where they line up a bunch of muans, they get
them all spinning in the right direction, and then they
shoot them into their machine which zips them around in
a circle using a big magnetic field. So they build
this really big, very precise, very expensive magnet and they
did this measurement this is twenty years ago at Brookhaven,
and they found that the answer didn't really agree with

their theoretical calculations and that's sort of what's set up
what we're doing today. Because people were wondering about, like
why doesn't this agree? So they decided they needed to
do another experiment. They need to get more data, they
need to like, you know, refine this answer. So they
actually took that same magnet from Bookhaven and they shipped
it over to Fermi Lab where they set up a
whole new experiment using the same magnet, and they have

like much much more data and they've been analyzing that
and that's what the announcement was all about. Do you
think they used the regular like U S Mail or
did they fetexit or how does it want ship a
giant physics magnet? You just put a lot of stamps
on it and you hope that they pick it up.
You no, this have great pictures. They had to take
it on a boat for a while. They have it
on this like double wide trailer crawling across the Fermi Lab.

It was pretty cool. It's not an easy thing. The
ship is definitely some additional charges. And I think the
idea is that twenty years ago, like they found that
the theory and the experiment are not the same. But
it's sort of like borderline right, like it was three
point five sigma difference, meaning it's like it's different, but
it could be still kind of a statistical fluke. Right. Well,
it's funny because we do all these things really quantitatively.

We're very careful about the number when we're calculating it,
and that we're very careful about theoretical value that we
do really quantitative statistics to understand, like what's the probability
that these two numbers are actually different versus that we
just have like a random fluctuation in our experiment that
makes them look different, because we don't want to get
fooled by just like having a random fluctuation. So we
do all these really careful calculations and then in the

end it's still subjective because three point five sigma tells you,
like the probability for this to not have been just
a fluctuation, and it says it's pretty small, but it's
not convincing, Like particle physicists don't find that level of
discovery enough to believe the result. So three point five
sigma is kind of impressive but sort of not enough.
So I guess you could call it borderline. Yeah, it's

kind of like flipping a coin and trying to see
if it's like a loaded coin. And you get seven
or seventy five heads in a row or out of
a hundred, and you're like, does that mean that it's
a loaded coin or does that mean that I just
got lucky and got seventy five heads out of a hundred.
And that's where the subjective element comes in. At what
point do you declare this coin is fair? At what
point do you declare the coin is not fair? And

so in our field, we have this standard of five stigma,
which is like one in three and a half million
chants of it being a random fluctuation, And so three
and a half stigma sounds like it's close to five stigma,
but it's a whole gaussy entail kind of a thing,
and so it's actually not that close. All right, So
they put these muance inside of a magnetic ring and
they're growing around and they're spinning, and you're sort of

measuring also what happens to those muans, right, and kind
of what happens to them tells you the value of
the muance magnetic field. Yeah, so they get these muans
spinning a certain way, they shoot them around in this
ring this big magnet and the magnetic forces the spin
just change a little bit, because the spin will change
in the presence of a magnetic field, and they zoom
around a few hundred times, and only a few hundred times.

Be the muan doesn't live forever. Eventually mulan will decay
into an electron and a couple of neutrinos. But that's
good because that lets you measure the direction of the
magnetic field at the end, because the direction of the
electron tells you the direction of the muan spin and
its magnetic field. So when the muan sort of dies,
you can measure how much was it's been affected by

this magnetic field, and that tells you what the muans
magnetic field was by itself. They've spent twenty years sort
of refining this experiment just to get more and more precise,
and finally we got a numbers. So now we have
two numbers. We have the number that the theorists predict
based on all of the things that the muan can
do of what this magnetic field should be, and we
have a number that experimentally spent twenty years measuring. And

they're not the same. And you know, they did this
in a really cool way. They did it in a
blind search way because this is a very important number
and a lot of sort of careers rely on this.
Folks want the number to be interesting. They're hoping it's
going to deviate from the theory, but they definitely want
to get it right, and so they do this in
a blind way by sort of scrambling the data a

little bit. They add like a random offset to all
of the numbers that's sort of hidden. It's like a
hidden key to the data. So they don't buyas the
way they do the analysis to try to like push
it in the direction that they may be subconsciously want.
And so they held the key like in a secret
office until just six weeks ago. So even the people
working on this experiment for the last decade or so,
I didn't know the answer until six weeks ago when

they cracked open this key and they typed it in
and then they finally saw the answer. Wow, it sounds
like a spy novel, you know, like that there's a
hidden key and nobody knew the secret until the very end. Well,
I think it's actually really exciting because it makes it climactic.
There's a moment when you're asking Nature a question and
you're getting the answer right. Otherwise it sort of creeps

up on you and like when you actually learn or
here's a correction, oili's change this and the answer is
sort of like evolving as you're improving your techniques. It's
nice to have a definitive moment, a crisp time, when
you say, Nature, what is the answer to this question?
And then you get an answer back from the universe.
All right, Well, they announced this result which everyone got
very excited about recently, and so let's talk about what

the result was and what it could mean about the universe.
But first let's take another quick break. All right, so
did a government physics experiment? So just something unknown is

influencing reality, Daniel, The shady government physicists distrowed our understanding
of the universe and reality. I'm trying to influence reality
by eating boxes of chocolates. It seems to affect the
reality of the size of my Trying to increase your
magnetic field or decrease your magnetism just influenced my effect
on the universe, my personal gravity. It might be shrinking

your magnetism. Will have to ask your family. Yeah, so
they found that the theoretical and the experimental results do
are either different as it was sort of suggested twenty
years ago, but now we know kind of more for certain. Yeah,
these numbers have improved. Both theoretical numbers have been improved
and the experimental numbers have been improved. So the uncertainties

on these two numbers have shrunk, but the gap between
them has not. So there's still like this opening between
these two numbers. And you know, i'd read you this number,
but it's sort of crazy. It's just like a very
specific number, and the differences are in the last couple
of digits of the like this twelve digit number, but
you know, the scale of it is, like the theoretical
value is to ten thousands of one percent smaller than

the experimental value. That's like how precisely we've calculated and
measured these quantities. Wait wait, wait, so then you're saying
that the difference between the theoretical and the experimental is
to ten thousands of one percent. That's the difference. Yeah,
it's a really tiny difference. So you need really precise
experiment and really careful calculations to even be sensitive to this.

That's why it's so impressive that they can even ask
this question. It's almost like you flip the coin and
you've got heads, you know, fifty point oh oh one
times more than you've got tails, And normally that would
be like you know, in the noise, but maybe you
flip the coin like a gazillion times to know that
it's like, yeah, there's something a little bit biased about

this coin, that's right, And if you're gonna do that measurement,
you have to ask, well, do I expect I mean,
the shape of the heads is not exactly the shape
of the tails, and maybe that influences it with the
air currents. And you've got to be like really precise
about all of those calculations if you want to claim
that it's unfair or that it's fair. And so you know,
that's what they've done. They've done like a tour the

force of these theoretical calculations and the experimental calculations, and
so both of these results have changed, Like the experimental
result we now have a new number from Fermi Lab
as of yesterday, but also the theoretical results have changed.
For example, they found like a mistake at one point
where they made up the wrong sign, like they changed
a plus to a minus accidentally, and that changed the result.

And so they're constantly like improving and doing these things
better because neither of these things are easy. It's a
pretty tough thing. Like even the theory that it takes
like supercomputers to compute these numbers. Yeah, well, there's actually
a big controversy about how to do that theoretical calculation.
And some folks are using supercomputers to try to calculate
this thing from scratch out of all of these diagrams
and include what happens when the hedraumic particles that feel

the strong force are created out of the vacuum and
all this kind of stuff. And there's another group that
are trying to just like not do those calculations explicitly,
but take them from other measurements, like other experimental results,
and extrapolate from there to figure out like what are
the bits and pieces and then use theory to sort
of glue them together into a measurement. So the sort

of two different approaches to doing this calculation, and there's
some controversy there because the sort of traditional approach where
we extrapolate from other experimental measurements and use theoretical glue.
That's the one that has the discrepancy with the observed value.
But there's a new result that uses like pure computation
san and these crazy supercomputers in Europe, and it actually

agrees with the experimental result pretty closely. All right, But
we're talking about this result from Fermulab and they sort
of confirmed that it's the theory and the experiment are different.
And so, you know, assuming that they're right, or that
it gets further confirmed and all the theory checks out,
what could it mean about our model of the universe. Well,
you're right that the Fermulab experimental result is the new

shiny thing, and nobody is suggesting that it's wrong. But
it's only interesting and it's only suggestive of new physics
if it's different from the prediction. And we have two predictions,
one that agrees with the Fermulab result and one that doesn't.
And that's what the four point two sigma is. So
the picture is a big cloudy on the theoretical side.
As usual, there's a spectrum of possibilities, you know, from

like the most boring to the more interesting to the
totally crazy and potentially bonkers. Idea. As you said, the
most boring possibility is that it's just a mistake somewhere.
You know, maybe one of these theoretical groups has made
an error or they've forgotten to include something as the
minus signed wrong. You know, this is really really hard.
So I personally I like this calculation done by the
European supercomputers because it was done by the collaboration called

BMW because they're in Budapest, Marseille and whipper Toll, and
it's sort of like independent. They like start from scratch
and they're just doing the calculation, so we'll just have
to see what progress has made there in the future.
But they're comparing to the same experimental results. So it
really is sort of like a blow to this discrepancy
to have a new theoretical calculation that doesn't show the discrepancy. Interesting, so,
like they used some supercomputers and they found that there

is no discrepancy with the experimental result. Yeah, the prediction
they made, which came out well before the experimental result,
is bang on to the new experimental result. So we
don't know which of these two theoretical calculations is correct.
But sort of muddies the water it's harder to claim
that this discrepancy is the side of new physics new
particles influencing reality when we don't exactly know if it's correct,

all right, So that's the vanilla possibility. What's the chocolate
chip possibility chocolate chips is that they're are some new
particles out there influencing reality. You know, we strongly believe
that there must be more particles out there. The story
can't be complete. We look at the particles that we've
discovered so of our in nature, and they just don't
answer all of our questions, and we suspect that there

are lots more really heavy particles out there. The problem
with really heavy particles is that it takes a lot
of energy to make them. You've got to smash particles
together at the Large Hadron Collider with enough energy to
actually create these things so you can study them and
explore them. But if we don't have enough energy in
our machines, that doesn't mean those particles don't exist. It
just means we can't make them at the Large Hadron Collider,

and the only way to study them is to see
these little hints. So it's possible that this is a
hint of those new particles that are out there that
are influencing the Muance magnetic field because they appear in
some of these diagrams, some of these calculations that change
the Muans magnetic field. But that doesn't mean we know
what they are, right, It's sort of like unspecific. It's
like saying we know there's something out there, we just

don't know what it is. It's a more indirect way
of looking for a new part of right, because you're
sort of like seeing how they influence other particles, which
is not a direct measurement. All right, So then that's
the chuckle chip possibility. Maybe there are new particles or
heavier versions of our particles out there, and maybe the
Mean is going through space and it sometimes creates these

heavy particles which kind of tweak its magnetic field. Right,
that's the idea, And then there's some even crazier ideas.
People have specific theories for what might be influencing the
Muan's magnetic field, and these other theories we can test
because they're very specific. For example, my friend Dan Hooper
at Fermulab, he has this idea for a new particle.
It's called a z prime prime because it's sort of

like the existing Z particle, but it's different. So it's
a little bit of a twist on the Z particles,
like the Z particles. Evil twin like Z would flare
like the Z particles with little tail or something. It's
a spicy version of the Z particle, and it's sort
of like the Z but he would influence the muan's
magnetic moment in just this way, because when the muan
is flying along, it doesn't just create photon sometimes it

creates z s and ws and all sorts of other particles.
So it would also create the Z prime. It would
explain this discrepancy. But the cool thing about it is
that if this Z prime is real, it also would
have been created in the early universe. It would have
changed how the universe expanded, specifically because this Z prime,
if you create it would probably decay mostly into these
neutrino particles, which would boost the energy density of the

radiation portion of the universe. And right now, there's a
lot of questions about how the universe expanded in the
early days. You can check out our podcast about the
Hubble tension. This question of like how fast was the
universe expanding we have all these measurements that again don't agree.
So this z prime theory would explain not only the
Muan's magnetic moment, but also this weird question about the

expansion of the universe in its early days. So it's
sort of like really nice because it would solve both
of these problems at the same time. That's a new
proposed particle. But would it also explained the difference between
the theoretical and experimental measurements of the muan. Absolutely would, Yeah,
it would solve both of those problems simultaneously. That doesn't
mean that it's real, you know, but it's nice if
there's another handle you can have on it. Because remember

the Muans matagnetic field is very indirect. It sounds like
a clear way to know what's responsible. So what you
want to do is have like another way to test
these things. Say, if it really is a Z prime,
can I see it somewhere else to get confidence that
it's a Z prime and not like a G prime
or a D prime or some other weird particle. So
he has a more specific prediction for another way we

can test this particle. But that doesn't mean that it's right.
Could it also be? Because I've heard it in the
news and from some of the scientists that you know.
This could maybe also point to maybe explain things like
dark matter or why the Higgs boson has them as
it has, like it could maybe even open it up
further to like crazy new kinds of other particles. Yeah,
it's harder to know whether it can tell us something

about dark matter because we don't know whether dark matter
interacts at all with the muan. It's true that this
method can tell us about any particle that will interact
with the muan, but it might be that dark matter
only feels gravity. Now, the dominant theory of dark matter
has a sort of interaction between dark matter and muans
and other particles at a very very low level. So

for some theories of dark matter, yes, this could explain it,
but again, we don't really know what would be doing this.
It just tells us there's some new particle out there
that does interact with the muan. It doesn't tell us
what that is. So dark matter is a favorite idea
because it's another big unexplained mystery. Well, I think maybe
the overall big headline is that maybe what we think

can happen in the universe is not what is actually
happening in the universe, like maybe there are things that
we have an accounted for, or that maybe it makes
our theory incomplete that we are seeing in this muon
magnetic field that is not in our theory. That's I
think that's sort of the general exciting part, right, Yeah,
it's always exciting to find a place where our theory

does not predict our experiments because it means it's a
place to learn, it's a place to improve our theory,
it's a place to add some thing new to our
understanding of the universe. For a long time, all the
experiments we do, like all the ones that the large
Hadron collider, are very very well predicted by our theory,
which means that it's working, which is exciting, but also
means that there doesn't provide any clues for how to

improve it, or expand it, or go to the next
level of the theory. So any discrepancy like this is
a wonderful clue that points us to maybe figuring out
a deeper idea by the nature of the universe. But
now let me maybe toss a bit of cold water
on that. Remember that this is only exciting if the
theory is right, and that's a bit of a fuzzy
picture still. I actually think the other discrepancy in the

B particles with Penguin diagrams at the Large Hadron Collider
is much more promising and exciting because the theoretical issues
are better controlled and there are several other experimental results
that suggest the same thing. So if I had to
put my money on something, I guess that this discrepancy
in the formula nuance will turn out to be a
problem in how the theory calculations were done, not actually

a new particle. And I'm more excited that the LHC
Penguin diagrams could be showing us new particles. So it
was good to double check, you know, Like if you
think this twenty year old chocolate it's gonna taste good,
maybe you should try it for us, right, Yeah, and
you should keep trying it. And that's what they're gonna
be doing. This is just the first batch of results
from this formulab experiment. They actually have a lot more

data that they've already taken. It's like on a computer somewhere.
They just haven't finished analyzing it, and they have ideas
for how to improve the quality of their measurement to
make it more precise, to shrink these errors even on
the data they already have analyzed. So we should expect
to see sometime in three more announcements about even more

precise measurements of these quantities, and also progress on the
theoretical side, as these two different groups try to figure
out like why they're getting different answers and who is
correct and maybe they can learn from each other. So
this is a story we should keep following. Yeah, because
this big announcement, as big as it was, it's really
just like the first bun out of the oven, right,
Like this is like their first batch of data. Uh,

and they're expecting to get like, you know, twenties sixteen
times more you know, me on spins detections, and that
their estimates are just going to get better. Yes, absolutely,
As they get more data, these statistical uncertainty will fall.
And in this case, the statistical uncertainty just from like
not having an infinite number of measurements is still the

dominant source of uncertainty. As they get more data, they're
gonna have to worry about other sources of uncertainty, systematic
uncertainties and things about like how they're calibrating their experiment.
But again, these are clever experimentalists and they have ways
of reducing those things. So as time goes on, all
the uncertainties will shrink and our knowledge of this quantity
will improve, and maybe it will reveal something new in

the universe influencing reality awesome, like maybe a new flavor
of ice cream or that chocolate. Al Right, well, I
guess as always, the answer is stay tuned. If you're
still a little bit confused about this whole topic, you
can read the comic that I drew for Physics the
APS Journal at PhD comics dot com, slash me on

m U O N and checked it out. But we
hope you enjoyed that. Thanks for joining us, see you
next time. Thanks for listening, and remember that Daniel and
Jorge explain the Universe is a production of I Heart Radio.
Or more podcast from my Heart Radio visit the I

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Jorge Cham

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