June 1, 2023 • 49 mins
Daniel and Jorge talk about whether the Universe would make sense without antimatter.
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Speaker 1 (00:08):
Hey, Daniel, are you glad our universe has antimatter?
Speaker 2 (00:12):
No, I'm definitely pro our universe. So I guess I'm
not anti antimatter.
Speaker 1 (00:18):
That means your pro matter. But I guess the question is,
would you miss antimatter if we didn't have it?
Speaker 2 (00:24):
I mean, I like things the way they are, so
if we lost antimatter, the universe would be pretty different
and maybe worse. But what if it's better, or maybe
it couldn't exist without antimatter and it would disappear in
a puff of mathematical contradictions.
Speaker 1 (00:38):
Okay, then I would be anti antimatter. I would not
be pro antimatter.
Speaker 2 (00:43):
I'm just saying it matters. Hi.
Speaker 1 (01:00):
I'm Boria mccartoonist and the creator of PhD Comics.
Speaker 2 (01:03):
Hi. I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I love all the kinds of
matter out there, the matter and the antimatter and the
pro matter.
Speaker 1 (01:12):
What about the meh matter? Not pro, not anti, It's
it's just kind of there.
Speaker 2 (01:18):
You know. I will admit that there are some particles
I think they're exciting. In other particles, I'm like, yeah,
that's just a mess.
Speaker 1 (01:23):
About your favorite kind of matter is chocolate matters certainly
better than vanilla matter, karp matter, But anyways, welcome to
our podcast, Daniel and Jorge Explain the Universe, a production
of iHeartRadio.
Speaker 2 (01:35):
In which we dig deep into all kinds of matter
out there that matters. We talk about the things that
make you up. We talk about the things that make
nothing up, and things that seem to exist for which
we do not yet understand. The whole universe is like
a jigsaw puzzle with lots of weirdly shaped pieces, and
our goal is to find all those pieces, fit them
together to tell the whole story of our universe. And
(01:56):
on this podcast we'd like to do that and try
to explain all of it to you.
Speaker 1 (02:00):
That's right. It is a vast and complicated universe, full
of all kinds of crazy and interesting kinds of matter
and energy and concepts and mathematics that we like to
explore as human beings and ask questions about and then
explain it to you, or at least ask you the question,
what's the matter with you?
Speaker 2 (02:18):
We study all of these particles, we try to understand them,
and sometimes we even taste them to see if they're delicious.
But I wasn't joking when I said that some of
the particles out there are a little crazier and harder
to think about than others. I mean, there are so
many particles discovered in the era of the particle Zoo
that we almost ran out of silly Greek letters to
use to name all of them.
Speaker 1 (02:38):
Oh boy, what happens when you run out of Greek letters?
Speaker 2 (02:40):
Then you start using Hebrew letters? Okay, like the Gimmel
particle on the aleph particle. H interesting, But we've discovered
so many weird masons and baryons that we had to
use some of those weird Greek letters that nobody even
really knows how to write down.
Speaker 1 (02:55):
I guess we have done a pretty good job of
kind of looking out into the universe and basically talent
up all the different kinds of matter, all the different
kinds of particles that can't exist out there, because there
are a lot. As you're saying, there are.
Speaker 2 (03:06):
A lot, and it's sort of a two step process
to understand the universe. Like number one, just look out
and see what's there. Gather together all the puzzle pieces.
Number two, try to click them together to tell the
whole story. Are there pieces missing, do they fit together
into a puzzle or is it just a weird, disjointed
pile of confusion.
Speaker 1 (03:25):
Yeah, And I guess the history of it is that
we used to think that we knew what the building
blocks of the universe was, right. We thought the elements
of the periodic table were like the basic lego pieces
of the universe. But actually those turned to be made
of other things. And then those some of those things
turn to be made of other things.
Speaker 2 (03:42):
That's right. We revealed this sort of hierarchical structure of matter,
things made of smaller things, made of smaller things, but
the path to understand them in the history of science
was not so straightforward. We sort of like drilled down
and then got wider and weirder, and then drilled down
again and got wider and weirder. For example, when we
wanted to understand the nucleus, when we wanted to understand
(04:02):
protons and neutrons and what's inside them, we'd build bigger
atom smashers and higher energy colliders, but we didn't immediately
find out what was inside the proton. Instead, first we
discovered all sorts of weird other kinds of particles that
don't exist inside the atom, chaons and pions and rope
particles and omega particles and all sorts of other Greek letters.
I don't even know how to pronounce. Things got weird
(04:24):
before they got clearer.
Speaker 1 (04:26):
Yeah, no, I understand. It's all Greek to me.
Speaker 2 (04:30):
In the same way that we want to understand what's
inside the quarks that make up the proton, but first
we found more quarks along the way. Instead of figuring
out what's inside the upcork and the down cork, we
found the charm and the strange, and the top and
the bottom. So the universe gives us a big pile
of clues before it reveals its deepest secrets.
Speaker 1 (04:48):
Yeah, it is a weird universe full of surprises. And
one of the weirdest things about matter in the universe
is that it seems to have an opposite to it.
There seems to be a lot of antimatter in the universe.
Speaker 2 (05:00):
Every particle out there seems to have its weird twin.
And we don't know if this is a detour in
our path to finally understanding what is the fundamental nature
of matter, or if it's a crucial side quest to
get a clue that will help us unlock the deepest mystery.
We don't know if and of matter is necessary, we
don't know what role it plays, We don't really know
(05:20):
what clue it's giving us about the nature of the universe.
Speaker 1 (05:23):
And so to the other podcast, we'll be asking the
question why do we have anti particles? Feel like that's
a weird double negative question, like why don't we have particles?
Or why do we have anti particles? What's the correct
grammar here or is it in Greek?
Speaker 2 (05:46):
I think why do we have anti particles? Is the
deep question? You know, every time we see something in
the universe, we wonder like, hmmm, did it have to
be this way? Is this necessary? Is this a clue
as to the fundamental nature of the universe or just
sort of like a random accident.
Speaker 1 (06:00):
Well, so, as usual, we were wondering how many people
out there had thought about this question or have any
ideas about why we have anti particles.
Speaker 2 (06:08):
So thank you very much to everybody who answers these
questions for this fun segment of our podcast. If you
would like to play along next time, please don't be shy.
Write to me two questions at Danielandjorge dot Com.
Speaker 1 (06:20):
So think about it for a second. Why do you
think we have anti particles? Here's what people had to say.
Speaker 3 (06:25):
In general, antiparticles exist because particles exist and there's some
sort of balance that was broken at.
Speaker 1 (06:33):
The Big Bang.
Speaker 4 (06:34):
I don't know, but the universe seems to like symmetry,
and somehow antiparticles had to exist for some kind of
symmetry to be to be fulfilled. But I don't know.
It's kind of crazy.
Speaker 1 (06:51):
I think anti particles exist for the same reason you
don't get monopole magnets.
Speaker 2 (06:56):
But I'm got clear, so we'll say with me, well
maybe not.
Speaker 3 (06:59):
I feel like you need the antiparticles like cancel it out,
because you can't have like something from nothing. You need
to have something and then the opposite of it, so
that like overall nothing has changed.
Speaker 5 (07:13):
Any particles are probably like the ying and yang. For
every particle, there has to exist an anti particle in
order to balance the forces in the universe, similar to
matter and anti matter.
Speaker 6 (07:27):
I think the reason why antiparticles exist is because everything
in nature and physics seems to be balanced. So if
you sum up everything, it comes off like zero. But yeah,
for everything that exists, there needs to be an anti
thing Somemari like Ying and Young.
Speaker 1 (07:42):
All right, some very philosophical answers here, some of them
kind of zen.
Speaker 2 (07:47):
Yeah, there's a lot of philosophy in these questions, you know,
wondering whether the universe could have multiple explanations or just
one explanation, or whether it has any explanation at all,
whether it makes sense, and whether it's sensible to human minds.
All that stuff is tied up in this quest to
understand the universe.
Speaker 1 (08:04):
Do you think maybe there are anti particle scientists out
there and or cartoonists we're wondering why do we have particles?
What is this weird stuff?
Speaker 2 (08:12):
I don't know, but humans are capable of developing science
as well as antiscience. More recently, I'm.
Speaker 1 (08:18):
Just antiphysics, I like all the other sciences.
Speaker 2 (08:21):
Are you antiphysics or are you anti physicists?
Speaker 1 (08:23):
I'm anti answering that question and that's an answer to
that a position there. Well, let's dig into it, Daniel Water,
anti particles is it like antimatter exactly?
Speaker 2 (08:35):
Anti particles are what make up anti matter. So matter
is the stuff that we find around us that you
were made of. That I am made out of everything
you have ever eaten is made out of particles that
we call matter particles. So you and I are made
out of protons, neutrons, and electrons, and those protons and
neutrons are made up of quarks. Anti matter is made
(08:57):
up of anti particles, so you could have, for example,
anti hydrogen is made of an anti proton and an
anti electron, where the anti proton is then made of
anti quarks. So there's a close connection, of course between
anti matter and anti particles.
Speaker 1 (09:12):
I see. So particles are the little things that we're
all made out of, and some of them have anti
versions of them. Do all particles have anti versions or
only some of them? Like do the force particles have
anti force particles?
Speaker 2 (09:26):
Great question, sort of yes and no. All the particles
have anti particles, but some of them are their own
anti particles, so I'm not sure if that counts as
having an anti particle. So, for example, the electron has
an antiparticle the positron, and the muon has an anti
particle the anti muon, and the quarks have antiparticles the
(09:47):
anti quarks. Those are different particles, or you could think
of them as two parts of the same pair. But
they are distinct states. But then particles, like you said,
the force carrying particles like the photon, the photon is
its own anti particle, and so you might also say
it doesn't have an anti particle. But I'd like to
think about it as one particle playing two roles.
Speaker 1 (10:07):
What about some of the other force particles, do they
have anti versions?
Speaker 2 (10:10):
Well, there are two w bosons, and they are each
other's antiparticles. So you have the W plus and the
W minus for example. So those two force particles are
each other's anti particles, which is why we have two
of them. The Z boson is its own antiparticle, and
the gluon is actually eight gluons, all of different colors,
and some of them are each other's antiparticles. So you
(10:31):
can have like a red anti green gluon, which is
the antiparticle to the anti red green gluon. It gets
really colorful with gluons.
Speaker 1 (10:41):
Well, I feel bad for those particles that are their
own anti versions of themselves. It's like they're their own
worst enemies.
Speaker 2 (10:47):
Or maybe they're lonely. Right, one is the loneliest number.
Speaker 1 (10:50):
After all, this should hang out together.
Speaker 2 (10:53):
Some people confuse anti matter with dark matter, And there's
lots of mysteries in particle physics, right, lots of things
that we don't understand about the universe, But those are
two separate mysteries. Dark matter is the invisible matter that's
out there in the universe that we know is holding
galaxies together and shaping the whole development of the large
scale structure of the universe. We don't know what it is,
(11:15):
and if it's made of particles, that's a different idea
from antimatter. Antimatter is a real thing that we can make,
that we can study. We've seen it in our detectors.
We know for sure that it exists and it's made
of anti particles.
Speaker 1 (11:29):
Well, I guess maybe the question now is how do
you make antimatter? Can you make it or does it
exist in nature or is it just a matter of
like flipping the sign on some quantum property of regular particles.
Speaker 2 (11:40):
So sort of all of the above. Antimatter isn't very common.
The universe is almost entirely made of matter, meaning it's
made of particles instead of anti particles, but sometimes antimatter
is produced, though it doesn't last very long because it
runs into normal particles and annihilates but for example, the
discovery of anti I mapps, which led to the nineteen
(12:01):
thirty three Nobel Prize, was from naturally produced antimatter. So
a positron the opposite particle to an electron produced in
cosmic rays, meaning high energy collisions of particles from space
hitting the upper atmosphere and creating antimatter which then showered
down to the surface of the Earth.
Speaker 1 (12:21):
So when was this When was the first time we
saw antimatter?
Speaker 2 (12:24):
So it was first observed in the late nineteen twenties.
It was predicted by Paul Durack, the quantum physicist, who
saw the mathematical need for them in his equations, and
he said, hm, my equations predict there should be electrons
and should also be another particle with the opposite charge
as the electron. So he predicted it, and then Carl
Anderson saw it. We have a whole fun podcast episode
about the discovery of antimatter and the twists and turns
(12:47):
and the egos involved. It's a really fun story. Check
that out. We've known about it for almost one hundred
years now.
Speaker 1 (12:53):
It sort of involves cloud chambers, right, which is something
you can usually find in most science museums.
Speaker 2 (12:58):
Yeah, early particle physics didn't have fancy digital electronics and
the complicated detectors we have now. They had to use
techniques to observe the paths of these particles with the
technology they had. And one thing you can do to
illuminate what particles are flying through the air around you
is to create clouds of water vapor. If you have
air that's super saturated with water, meaning it actually has
(13:21):
more water in it than it likes to have, then
it's very easy to knock that water out of the air,
and a passing charge particle will do just that and
will create a string of droplets in the air. You
can actually create cloud chambers at home. Check out lots
of YouTube videos for how to do this. You can
build one in your garage. You can see them at
science museums and so you can see high energy particles
(13:43):
streaming through the air around you, muons and all sorts
of stuff. Carl Anderson proved that a fraction of these
are actually anti matter particles, and he did that by
showing how they curve differently in magnetic fields. Because magnetic
fields will change the path of a charge particle depending
on the charge. A positive charge will be in it
one way. A negative charge will bend it the other way.
(14:03):
So he saw particles that had the same mass as electrons,
but bend in the other.
Speaker 1 (14:07):
Direction like a positively charged electron. Is that basically what
an anti electron is, Just an electron with a charge flip.
Speaker 2 (14:16):
Yeah, that's what antiparticles are. They're just like their particle counterparts,
but they have the opposite charges, so the opposite electric charge,
the opposite weak charges, and the opposite color charges. So
in the case of the electron, it's basically a positively
charged electron.
Speaker 1 (14:31):
Right, because I guess an electron doesn't have the weak
charge and it doesn't have the strong charge.
Speaker 2 (14:36):
Right, Electrons do have the weak charge. Actually, remember, the
weak force is actually unified with electromagnetism into one force
we call electro week, and electrons can interact via the
weak force. They can emit w's for example, that's how
beta decay happens. So electrons interact with the weak force.
In fact, every particle we've ever seen interacts with a
weak force, which is fascinating because the other forces are
(14:58):
not so democratic. The strong force only interacts with quarks
and not at all with electrons or neutrinos, and electromagnetism
doesn't interact with neutrinos. But we've never found a particle
that doesn't have any kind of weak charge. Every particle
out there so far we discovered interacts with the weak force.
Speaker 1 (15:15):
Wait, what's the name of the week charge? If you
have a week charge, what is that called?
Speaker 2 (15:19):
Well, there's actually two different week charges. One of them
is called weak isospin and the other one is called
weak hypercharge. But you can combine them actually to make
electromagnetic charge. So there's two different charges for the electro
weak force, but one of them is really from electromagnetism.
Speaker 1 (15:34):
I'll pretend I totally understood that. But I guess when
you're trying to make an anti electron, which one do
you flip? Do you flip the electromagnetic charge like the
you know, plus and minds that we're all familiar with,
or do you flip one of these other sub charges?
And if you do, do I mean there are several
versions of an anti electron.
Speaker 2 (15:51):
Now you flip all the charges. So there's only one
version of a positron, and it has a positive electric charge.
It also has both of its weak charges flipped.
Speaker 1 (15:58):
But what if you flip one and the other you
can't do that, man, don't do that. They'll tell you
why not to do, tell you why I can't do it.
Then I can choose whether or not I can't.
Speaker 2 (16:07):
I will do it. It's not me, man, it's the
laws of the universe. No, we do not see particles
where only one charge is flipped and the other one
is not.
Speaker 1 (16:16):
Why not.
Speaker 2 (16:17):
Yeah, that's a very cool question, imagining particles that are
particles according to one force and anti particles according to
another force. Remember, we recently answered a question about whether
it even matters whether you're calling something matter or antimatter,
and turns out that's totally an arbitrary distinction. So it
doesn't really matter if one force considers a particle matter
(16:37):
and the other one considers a particle the anti matter.
But the forces do have to be consistent, and in
the case of the weak force and electromagnetism, for example,
they are tightly linked, so you can't just flip one
and not the other. The charges of the two forces
really are connected by the structure of the theory.
Speaker 1 (16:54):
I think what you're what you're saying, is this matter
anti matter distinction is really kind of arbitrary kind of right,
Like it's not as clear cut, like maybe there are
shades of gray or shades of antiness.
Speaker 2 (17:06):
Yeah, we definitely don't claim to understand everything there is
to know about antimatter. But I think you're right A
lot of this comes down to just like what do
you call matter and what do you call antimatter. A
crucial idea is that there are these symmetries that you
can flip these charges and the equations still work, that
the universe can do both of these things, and so
it does in some cases. We have like multiple ways
(17:27):
to categorize what is matter and what is antimatter.
Speaker 1 (17:30):
Well, I think the thing that most people probably remember
about antimatter, and that maybe is relevant here, is that
like a matter particle and it's antimatter particle, if they touch,
then they annihilate. They become pure energy. Right, We've talked
about that before they explode. That's one of the things
about antimatter.
Speaker 2 (17:47):
Particles and their antiparticles can annihilate into a force particle.
So for example, an electron and a positron can come
together to make a photon or a z boson and
a and an anti quark can come together to make
a glue on, and the opposite can happen. Also, a
photon can turn into a matter antimatter pair, or a
z boson can decay into a muon and its anti particle.
Speaker 1 (18:11):
But then I guess if anti nus is kind of
relative or there's a gray area there, or how does
that affect the annihilation? Like if I take a cork
and an antiquark, but I flip some other other signs,
do they still annihilate?
Speaker 2 (18:23):
They can annihilate if there is a particle that carries
their combined charges. So for example, an electron and a
positron can annihilate because in total they have zero electric
charge and the photon has zero electric charge. That's why
an electron cannot annihilate with another electron, because then you'd
have to have a particle with a minus two charge
in order to conserve electric charge. So the same thing
(18:46):
goes for the other charges.
Speaker 1 (18:47):
So like if I have a green cork and an
anti green cork, but a given different you know, regular charges,
what's gonna happen? Are they going to annihilate or repel
each other? Or what I'm just trying to get at,
Like what it means to be anti mime. Is it
depending on this annihilation thing or is it kind of random.
Speaker 2 (19:03):
It's a little bit more complicated for the color charge
because gluons themselves are colored. You know, the photons don't
have any charge for example, right, so it's simple plus
and minus annihilate to zero charge photons. In the case
of gluons, gluons do carry color. In fact, they carry
two colors, which is even more confusing. So for example,
a red anti green quark can combine to make red
(19:25):
anti green gluon. The glue on itself carries two of
those colors, but the gluons don't carry electric charge, so
this can only happen for quarks that have opposite electric
charges that can balance out to zero electric charge. So
one way to think about how to pair particles and
antiparticles is whether they can annihilate into these force particles.
Speaker 1 (19:46):
I see, So maybe one particle can have multiple anti
versions of itself.
Speaker 2 (19:50):
There are definitely multiple different versions of quarks that an
individual quark can annihilate with to create a gluon. Because
there are so many different kinds of gluons, they always
have to have opposite electric charges. Because the gluons don't
have electric charge, So yeah, it gets really complicated when
you're talking about the color charges because there's multiple different
color charges and the gluons carry them themselves, and so
(20:12):
the whole thing is a big mess.
Speaker 1 (20:14):
Is that how you end every physics paper? YadA YadA,
YadA YadA, And it's all a big mess.
Speaker 2 (20:19):
It's a big mess, and it's a glorious puzzle and
we're still working to try to figure it out. Yeah.
Speaker 1 (20:24):
Cool, Well, I guess the big question is still why
do we have anti particles at all? Why do they
exist in the universe? And so let's dig into that
question and some of the other open questions about antimatter.
But first let's take a quick break. All right, we're
(20:52):
talking about antimatter antiparticles and why do we need them
at all? Which sounds like a very insensitive question.
Speaker 2 (21:00):
What the deepest question we ask when we see something
in the universe, We ask like, why is it this
way and not some other way? Does it have to
be this way? Is the universe parsimonious, like it only
contains things that have to happen? Or is it sort
of like baroque that has all sorts of flourishes that
it doesn't really need, and it's just sort of beautiful.
We tend to think of the universe as parsimonious. We
try to take every piece that we find and fit
(21:21):
it into the puzzle to explain why the universe works
this way.
Speaker 1 (21:25):
Well, I guess one of the reasons we as we
talked about last time, that we call some things matter
and something's antimatter, is that we mostly see matter out
there in the universe, at least as far as we know.
Our planet, our Solar System, our galaxy is made out
of regular matter, and there's a big mystery about why
there isn't as much antimatter in the universe. But maybe
one question that you can ask is, like, is matter
(21:46):
and antimatter made at the same rate in the universe.
Like if you run a particle collision experiment and you
create some energy and some particles spill out to matter,
particles get made as much as antimatter particles.
Speaker 2 (22:00):
A little bit on what you start from. I mean,
if you start from particles of matter, then you're going
to get more matter particles than antimatter particles. If you
start from antimatter particles, then you're going to get more antimatter,
and we actually ran a whole collider that smashed matter
versus antimatter. Now, was the collider outside Chicago, the Tevatron,
collided protons with anti protons, and so there we got
(22:21):
even splits of matter and antimatter. Whereas the collider at Cerne,
the Large Hadron Collider, smashes protons with protons because antimatter
was such a big headache to produce for the other collider,
And so there we get more matter produced than antimatter
because we're starting from matter. But most of these processes
are symmetric.
Speaker 4 (22:39):
Right.
Speaker 2 (22:39):
If you just have a big pile of photons and
you wait for them to decay, they will produce an
equal number of positrons and electrons.
Speaker 1 (22:47):
I see. So I guess the big mystery is that
it sounds kind of like the universe is able to
make equal amounts of both kinds of matter, but what
we see in the universe is mostly only one kind
of matter.
Speaker 2 (22:58):
Yeah, we suspect that the very early universe, matter and
antimatter were created at the same rates that as the
universe cooled down from the frothing pile of quantum fields
and things got cold and isolated enough that you could
call things particles, that the particles and anti particles existed
at basically the same level. Then there was a huge
amount of annihilation, as you can imagine, and most of
(23:19):
the matter and antimatter went away and turned into radiation.
But a little bit more matter is left over than antimatter,
and we don't understand the source of that discrepancy, even
though it's the reason why we have matter galaxies and matter,
stars and matter, people and matter chocolate and not anti matter.
The universe seems to have some preference for matter over antimatter.
Speaker 1 (23:40):
Which makes me ask the question, is anti chocolate vanilla
or white chocolate or is it a case of having
multiple antiversities?
Speaker 2 (23:48):
I hope so, because neither of those things should be
categorized with chocolate.
Speaker 1 (23:51):
You're just pro chocolate. You just anti everything that's.
Speaker 2 (23:55):
I'm just anti calling things chocolate that aren't chocolate. Even
calling them anti chocolate somehow groups them to get they're
in that chocolate category where they don't belong.
Speaker 1 (24:02):
What about vegan chocolate, not chocolate.
Speaker 2 (24:05):
No, totally chocolate. It comes from the cocoa bean.
Speaker 1 (24:07):
Yeah, absolutely, all right, Well, the big question is why
does it exist? At all. Why do we have antimatter,
Like is it something that the equations of the universe
requires or is it just something that seems to happen.
That's the big question, right.
Speaker 2 (24:22):
That's the question, and the short answer is we don't know.
But what's really fascinating is that without antimatter, some of
our basic theories of physics don't work very well together.
Like we have relativity and we have quantum mechanics, both
things that we think make sense in the universe, but
when we try to bring them together, we get some conflicts.
(24:43):
And it turns out that antimatter resolves those conflicts and
lets us bring special relativity and quantum mechanics together into
one theory.
Speaker 1 (24:52):
Wait, I thought those two things didn't like each other.
Speaker 2 (24:54):
So we have two different theories of relativity, special relativity,
which tells us about what happens and things move really
really fast near the speed of light, and then general relativity,
which tells us how space bends in the presence of mass.
General relativity and quantum mechanics we do not know how
to combine into a theory of quantum gravity. That's something
for a future physicist, maybe one of our listeners, to
(25:16):
figure out, but special relativity and quantum mechanics we do
know how to combine, and we've had that for many,
many decades. So that's basically relativistic quantum mechanics, and that
is something that we know how to do thinking about
quantum particles and moving near the speed of light, and
we do that all the time in our particle colliders, right,
it happens all the time that we have high speed particles.
(25:37):
So relativistic quantum mechanics we can do bend space, curved space.
Quantum mechanics we don't know how to do.
Speaker 1 (25:44):
Interesting. Okay, So you're saying somehow antimatter and antiparticles somehow
make quantum mechanics and special relativity work together. What does
that mean?
Speaker 2 (25:52):
So it all has to do with preserving causality, and
special relativity makes it really hard to think about causality,
to think about the order that things happen in the universe,
because it forces us to think about the order of
events in a very different way than like Newton thought
about things, and the way that we intuitively think about things.
You probably think about the universe happening as if there's
(26:13):
like a giant clock and the whole universe like ticks
forward and then the next thing happens, and the universe
ticks forward and the next thing happens. But you can
think of the whole universe as having like one clock,
so you can tell like one story about what happened
in the universe. Special relativity tells us that that's not
actually true, that there's lots of different clocks in the universe,
(26:34):
and how fast they tick depends on where you are
and how fast they're moving relative to you, So you
can actually tell lots of different stories about what happened
in the universe, even stories that conflict with each other,
that contradict each other about the order in which events happen.
Speaker 1 (26:51):
Yeah, I know. We've talked about this before and include
it in our book. It's kind of this idea that
if two people run a race, you think that whoever
wins would be clear, but it sort of depends on
how fast they're moving and how fast the judges moving,
or how fast you're moving as an observer.
Speaker 2 (27:08):
Right, Imagine two people running a race, but instead of
running alongside each other on a track the way people
typically do, imagine them starting in the same place but
running opposite directions. This makes it easier to think about
because they end up far apart from each other. If
you're standing at the starting line and you're not moving
relative to the starting line, imagine these two runners run
at the same speed relative to you. You call it
(27:30):
a tie. But if somebody else is flying along in
a spaceship alongside one of these runners, they see the
two runners moving at different speeds relative to them, and
moving clocks run slow, which means they see one of
these runners in slow motion relative to the other one,
So they'll think one of the runners wins the race
and the other one is slower. But another judge going
(27:50):
the opposite direction sees the same thing, but flipped. He
sees the first runner's clock running slow, so he thinks
the second runner wins the race. So who you think
wins the race depends on the speed you're going relative
to the runners. Like people can honestly disagree about the
order of events, did the first runner reach the finish
line first or did the second runner reach the finish
(28:12):
line first. This is not a case of like people
being confused or mistaken or getting things wrong. It means
that there are multiple true stories about what happened. In
the universe that conflict with each other.
Speaker 1 (28:24):
Well, there's sort of one story, right, It's just when
you transform it between points of views, the order of
events changes.
Speaker 2 (28:32):
Yeah. That sounds to me like multiple stories. But you're
right that we can link them together. Special relativity tells
us how to predict what any observer will see. And
what special relativity says is that different observers will see
the order in different events. The laws of physics are
consistent from frame to frame, and they predict the observers
tell different stories. Yeah, so you can think about that
(28:53):
as like one coherent understanding.
Speaker 1 (28:56):
Yeah, that's what I mean. It's not like there's two realities.
Nobody can ever figure this out. It's more like, you know,
everyone has to agree on which observer they're measuring your
race by.
Speaker 2 (29:07):
Right, that's right. It means that the order of events
is not universal, right, that it's dependent on the observer.
Speaker 1 (29:12):
Well, or it is universal, as you said, it changes
depending on what you ask.
Speaker 2 (29:17):
Yeah, it depends on the observer. Right, It's not something
everybody agrees on will happen from their point of view. Right,
Different points of view will see a different order of events,
and that's very confusing when you think about causality because
you think, like you know, there should be an order
two events, Like you can't finish the race before you
start it, you can't receive a message before you send it.
You can't die before you're born. There are some things
(29:39):
send in the universe where there's a causal link between them, right,
and so they have to happen in a certain order.
Speaker 1 (29:45):
All right, Well, what does that mean for causality and antimatter?
Speaker 2 (29:48):
Then well, you might think that this makes the universe nonsense,
because if different people can see events order different ways,
does not just break causality. Does that mean you can
eat an apple before it's grown? Does that mean you
can get a message before it's sent? This kind of stuff, Well,
special relativity has some protection built in for that, right,
It says this can only happen for things that are really,
(30:09):
really far apart, things that are so far apart that
light can't pass between them. We call these space like
events instead of timelike events. And so you can reorder
events that are really really far apart because they're already
not causally connected. If two things are so far apart
that light couldn't pass between them, then there's no way
(30:29):
for them to have a causal connection. You can't like
send a message from one to the other. And so
things that are already causally not connected. Those things you
can reorder by traveling at some crazy speed. Things that
are causally connected, Like if you turn on a flashlight
and then the beam arrive somewhere else, there's enough time
for light to get from one to the other. You
(30:51):
can't reorder those events just by going faster or.
Speaker 1 (30:54):
Slower, all right, So then how does that figure into antimatter?
Speaker 2 (30:57):
So these events that you can't reorder, those are things
we call inside our light cone. Light cone are things
that we can affect in our future, and there's things
that affected us from the past. So that special relativity,
and it has this nice causal connection for things inside
your light cone. Things outside your light cone, they can
get reordered by things going fast or slow. Quantum mechanics, however,
(31:18):
doesn't naturally obey this rule. Quantum mechanics has weird limitations
on how much you can know about objects momentums, and velocities. So,
for example, you measure a particle really really specifically. The
Heisenbergen certainty principle tells you you can't know anything about
its velocity, how fast it's going. So in principle, quantum
(31:39):
mechanics allows things to go faster than the speed of light.
That allows particles to move from one place to another
outside the light cone because they could be going faster
than the speed of light. Quantum mechanics doesn't have the
speed of light built into it naturally, it allows particles
to violate this speed limit. WHOA well.
Speaker 1 (32:01):
On they think quantum mechanics can break the speed of light.
That sounds a little bit too much, Daniel. I think
you mean maybe, like our math allows it to, but
we don't know if in reality it can go faster
than light. Doing If you just.
Speaker 2 (32:13):
Start from sort of low speed quantum mechanics, the original
quantum mechanics that was developed right, non relativistic quantum mechanics
for slow moving particles, then that theory with the Heisenberg
uncertainty principle doesn't respect the speed limit of the universe.
It's only when you try to bring quantum mechanics and
special relativity together to make a theory of relativistic high
(32:34):
speed particles that you have to answer this question like, uh, oh,
what happens if particles that quantum mechanics predicts can go
faster than the speed of light. What does special relativity
say about that? So it's you know, in trying to
bring the mathematics in harmony with the universe, that we
run into this problem. We're like, hold on a second.
Quantum mechanics has this problem with causality. It allows things
(32:54):
to move outside your light cone. What's going on and between?
You bring these two things together, that antiparticles save the
day and allow you to bring quantum mechanics and special
relativity together in a way that makes perfect sense.
Speaker 1 (33:08):
I think maybe what you mean is that antimatter says
physicism because their original theory made no sense.
Speaker 2 (33:17):
Yeah, you cannot bring quantum mechanics and special relativity together
without anti particles.
Speaker 1 (33:21):
Right, It's like the limitations of the theory would allow
things to move faster than light, but probably in reality
they don't.
Speaker 2 (33:29):
That's right. We think special relativity is the law of
the universe. Nothing moves faster than light. Original old school
quantum mechanics has this problem that allows things to move
faster than the speed of light, potentially breaking causality. And
you're right, we don't think that happens in reality, So
we need to patch up the theory, and it turns
out that we need antimatter in order to do that.
Speaker 1 (33:47):
All right, well, let's dig into how antimatter saves the day.
It's sort of like a plot to is the villain
actually turns out to be the good guy. So let's
dig into that, and what does it mean about our
understanding of matter, antimatter and all kinds of matters or
in the universe. But first, let's take another quick break.
(34:15):
All right, we're talking about antimatter antiparticles. Why do we
have them? Why do we need them? It turns out
that they're useful in making our theories work, which is
not really I guess an answer to the question.
Speaker 4 (34:28):
Is it?
Speaker 2 (34:28):
Well, it's sort of an answer to the question. You know.
It says that the universe needs this to be consistent,
or our theories need this in order to be consistent
description of the universe.
Speaker 1 (34:38):
Okay, so then you're saying that it somehow helps reconcile
special relativity and quantum mechanics. How does it do that?
Speaker 2 (34:44):
So let's think about how quantum mechanics breaks causality. Right,
Imagine you have like a particle that you emit right
here at this moment, and quantum mechanics predicts that it
has a probability to end up like in Andromeda ten
seconds from now. That would break causality because if be
outside your leg cone, it would be like getting to
Andromeda faster than the speed of light. Nothing that we
(35:05):
do right now should be able to affect Andromeda until
millions of years into the future, because Andromeda is millions
of light years away.
Speaker 1 (35:13):
I think you're saying, the quantum mechanics, we have a
description of a particle here, and because there's uncertainty about
where it can be, there's a certain probability that in
the next second it can be right where it is now,
or it can be a meter away or two meters away.
And there's a very very very small possibility that in
the next two seconds, according to the quantum mechanics, it
(35:34):
can then be in Andromeda. That's kind of how you
would describe it.
Speaker 2 (35:38):
Yeah, exactly if you have a lot of uncertainty on
its momentum, because you've narrowed down its position super duper well,
and Heisenbergen certainty principle tells you can't know both things
at the same time. So if you know the position
really really well, you don't know the momentum, and therefore
there's a possibility that it has some crazy high momentum
would be faster than the speed of light, getting it
(35:59):
too Andrama in just ten seconds instead of the millions
of years it should take. And this would be a
problem for causality because those two events are spacelike. It's
outside of our light cone, which means that somebody flying
by in a spaceship could see them happen. In the
other order, could see this particle arrive in Andromeda before
it leaves our galaxy, which is nonsense. Right, So anything
(36:22):
that moves faster than the speed of light breaks causality.
That's one reason why we don't think things can move
faster than the speed of light, because it would allow
you to reorder events that are causally linked. Right, so
make the universe nonsense.
Speaker 1 (36:35):
Well, it sort of sounds like quantum mechanics just breaks
causality anyways, right. Quantum mechanics say that particles can just
pop out of nowhere without any cause, So like quantum
mechanics says that a particle can suddenly disappear here and
appear in Andromeda.
Speaker 2 (36:50):
Why not now, I wouldn't say that quantum mechanics necessarily
breaks causality. It makes a different description of the universe.
It makes the universe probabilistic instead of deterministic. It says
weird things can happen, like a photon can turn into
an electron and a positron, or it could do something else.
It says that the laws of the universe only predict
what might happen instead of what does actually happen. But
(37:12):
there is still causality, Like in quantum mechanics, the wave
function right now is determined by the wave function in
the past. Right The wave function itself doesn't specify exactly
what will happen, only to probabilities, but the wave function
is still determined by the past wave function, so there
should still be logic in quantum mechanics.
Speaker 1 (37:30):
I guess that's weird because if you're saying that anything
might happen, I.
Speaker 2 (37:33):
Would say anything might happen, you know quantum mechanics, as
is the probability for things to happen. Some things are
impossible even in quantum mechanics, like you can't violate conservation
of electric charge right, Electrons have no probability to turn
into positrons directly, because I would violate conservation of electric charge,
which is built into our quantum mechanical theories.
Speaker 1 (37:54):
But haven't we talked about how like, according to quantum mechanics,
a pink elephant could certainly you're out of nowhere outside
of the Earth's orbit, right in space.
Speaker 2 (38:03):
Yeah, that's not impossible. That doesn't break any of the rules.
Speaker 1 (38:06):
But then we have no cause would it.
Speaker 2 (38:08):
Well, the cause would be that there's a distribution of
probabilities for what those particles in the vacuum could do.
They could sit there and do nothing. They could create
one electron, they could create ten electrons, they could create
forty two trillion electrons. They could create a Boltzmann brain,
they could create a pink elephant. Those things are probabilities.
What does our universe choose one particular probability and not another?
(38:30):
What does it choose one that's like really unlikely, like
a pink elephant in space, and not another that's more
likely that we don't understand. That's like a deep question
in quantum philosophy, whether all of them happen at once
in different universes, whether the universe collapses these wave functions
to choose one. Whether it even is truly random, That
is definitely not something we know. But I wouldn't say
(38:50):
there's no cause there's still like a distribution of probabilities
for what might happen.
Speaker 1 (38:54):
Well, let's get back to the antimatter particle. How does
that antimatter particle fit into this scenario.
Speaker 2 (38:59):
Then it turns out if you do these calculations, and
you calculate like, okay, what's the probability for my particle
to appear in and Drama in ten seconds from now,
and you include antimatter, then those probabilities vanish. Because the
probability for you to see a particle go to Andrama
in ten seconds, there's another probability for a particle to
go from Andromeda to here in ten seconds, for an
(39:21):
antimatter particle to come the opposite direction. And because matter
and antimatter have all the opposite properties, those two things
quantum mechanically cancel each other out. So the antimatter nonsense
cancels out the matter nonsense to make no nonsense. Whoa, whoa, whoa.
Speaker 1 (39:39):
Wait, we had this scenario of having one particle here
that suddenly appears in Andromeda in ten seconds. You're saying,
there's a different scenario in which an anti particle the
exact antiparticle of my particle is where my particle would appear.
That one disappears and appears where my current particle is
at the same time, and somehow that cancels it out.
(40:01):
But what are the chances that there's an antiparticle exactly
where my particle would go.
Speaker 2 (40:07):
Well, all of this stuff is very unlikely. But when
you do a quantum mechanical calculation, you sum over all
the possibilities, and these equations are wave equations, so you
can get like constructive interference and destructive interference and things
where the probabilities cancel out, those things just don't happen.
Like in the Devil's Slight experiment. You see interference places
where lots of particles and places with no particles, the
(40:28):
places where no particles land, and the interference on the
screen is because there's been destructive interference among the probabilities.
So when the probabilities cancel out, those things just don't
happen in the universe, And so the probability for a
particle to break special relativity and appear in Andromeda is
canceled out by the probability for an antiparticle to do
the opposite.
Speaker 1 (40:49):
Well, I guess what does it mean to cancel out
the probability? That means that it's never going to happen.
Speaker 2 (40:53):
It means that it's never going to happen. And so
if you bring quantum mechanics and special relativity together, you
include anti particles, then it all clicks together perfectly and
you get no violations of causality.
Speaker 1 (41:06):
But wait, the wouldn't that also cancel all movements like
even a meter distance?
Speaker 2 (41:13):
Yeah, great question. It doesn't happen for things inside the
light cone because things inside the light cone everybody agrees
on the order, whereas things outside the light cone you
can reorder them. So, for example, if I say, well, look,
my particle left here and ended up in a drama
in ten seconds, that's outside my light cone. So somebody
else flying by in a spaceship might see them happen
(41:33):
in the opposite order. Right. Seeing it happen in the
opposite order is like seeing a particle go backwards in time,
which is equivalent to the anti matter particle. Right, So
both probabilities exist, the particle and anti particle version, because
you can reorder them because they are outside your light cone.
Things inside your light cone, you can't reorder them. Their
(41:54):
order is fixed. Only things outside the light cone where
you could reorder them, where somebody could see it as
a part article and the other person could see it
as an anti particle. Only those things cancel out.
Speaker 1 (42:04):
It feels a little convenient, like maybe saying like, oh,
my theory breaks down after this limit. Let's just come
up with something totally different and ex sort it only
applies outside of this limit where my thing breaks.
Speaker 2 (42:16):
Yeah. Well, it's sort of convenient and sort of spooky, right.
It's sort of like if you didn't know antiparticles existed
and you were trying to bring quantum mechanics and relativity
together into relativistic quantum mechanics, You're like, huh, this is
a problem. This could be solved if, for example, there
were the existence of antimatter hmm, and then you went
out in the universe and you found it, You'd be like, wow,
that was pretty cool. Here it's sort of works the
(42:38):
opposite direction. We're like, no antimatter exists, and we can
use it to help bring these two theories together. It
is very convenient, but that's sort of like a glorious
moment when you're like, oh wow, look these things. They
sort of need to exist for the universe to be
self consistent.
Speaker 1 (42:53):
Now, you said something earlier that was kind of interesting.
You said, anti particles kind of go back in time.
What does that mean?
Speaker 2 (42:58):
Well, mathematically you can look at it a particle moving
forwards in time, and it's equivalent to an antimatter particle
moving backwards in time. And you can sort of see
that in this example we're talking about, where like, my
particle goes from here to Andromeda, and it does it
faster than the speed of light. Right. If it does
it faster than the speed of light, that means that
somebody else going by in a spaceship they could see
(43:18):
it happen in the opposite order. They could see it
arrive in Andromeda before it leaves my house in the
milky way, right, which means that it's started in Andromeda.
The first event is in Andromeda. So I could say, look,
this is a particle going forwards in time faster than
the speed of light. Somebody else could say, no, it
goes the other direction. They could say, no, it's going
from your future to your past. But I see it
(43:41):
as an antimatter particle because they could reorder the events,
and so they see it going from Andromeda to the
Milky Way, and they see it moving as an antimatter particle.
Speaker 1 (43:50):
But I guess maybe in order to measure my particle
here and there, don't I need to measure the particle,
wouldn't they collapse the wave function and make this all
kind of not really applicable.
Speaker 2 (44:00):
You would need to collapse the wave function absolutely, and
of course it wouldn't really happen, right. That probability is
actually zero. You can't collapse the wave function and make
this happen. What we're talking about really is just a
partial probability. There's another part to that calculation, the antimatter part,
that cancels it out. So you can't actually do this right.
You can't see a particle appear in Andromeda in ten seconds.
(44:21):
It would take millions of years to get there, and
the probability for that to happen is canceled out by
the anti matter version, So that's why it just doesn't happen.
Speaker 1 (44:28):
Is this sort of like one of those virtual particle
scenarios where like just a matter of fact that something
else can happen, actually in a way happens canceling out
other effects that are happening.
Speaker 2 (44:40):
Yeah, you can think about this the way other quantum
mechanical weirdness happens, where like particles can interfere with themselves.
Right again, like in the double slit experiment, if you
don't know which slit the particle went through, has a
probability to go through both, and those probabilities can actually
interfere with themselves, So single particle interferes with itself. This
is sort of the same deal. Like this single particle
(45:01):
that goes from here to Andromeda, you could also be
seen as an antimatter particle going the other direction, and
those two probabilities cancel, which is why it never actually happens.
Speaker 1 (45:10):
All right, Well, then what is the I guess main
takeaway is it that quantum mechanics does work with special activity,
and it's because antimatter particles exist or are a possibility
in the universe.
Speaker 2 (45:22):
That's exactly right. You need antimatter to bring quantum mechanics
and special relativity together and not break causality. If we
think the universe is causal, meaning that like there's a
logical flow to things, that the past influences the future
and not the deep past. Then you need antimatter in
order to have special relativity and quantum mechanics. We just
(45:43):
don't know how to do it without antimatter.
Speaker 1 (45:45):
Cool. All right, well, you've commissed me. I'm pro antimatter
or I'm not anti antimatter.
Speaker 2 (45:51):
Does that mean that you're pro anti vanilla, which means
you're willing to try some chocolate.
Speaker 1 (45:55):
I am pro anything with the word vanilla in it.
Speaker 2 (46:00):
Right, I'm part of the vanilla eradication project. How do
you feel?
Speaker 1 (46:03):
Oh my god? And that is how this podcast got canceled. Daniel.
Thank you, it's been a nice run. We're done.
Speaker 2 (46:13):
No, I love vanilla. Vanilla is wonderful.
Speaker 1 (46:15):
We've gone the way of Scott Adams and Dilbert.
Speaker 2 (46:19):
I'm not a flavorist. Okay, I'm definitely pro vanilla.
Speaker 1 (46:22):
I'm just more we think they're flavorists.
Speaker 2 (46:24):
Daniel, I need to go for some flavor sensitivity training.
Speaker 1 (46:29):
It sounds like, thank you, maybe you should examine those
anti FeAs.
Speaker 2 (46:37):
All right, well, between this and the next episode, I
will do a deep dive into my own internal flavor preferences.
Speaker 1 (46:43):
There you go examine your own anti matter. All right, Well,
another interesting bit of how we're trying to figure out
how the universe works, and how sometimes it's interesting how
our theories of the universe actually kind of turn out
to be true, which is kind of surprising, right.
Speaker 2 (46:58):
It is surprising sometimes, and that crazy little human brains
can come up with mathematical stories that do seem to
describe the universe, even in ways we didn't anticipate.
Speaker 1 (47:08):
All right, Well, thanks for joining us. We hope you
enjoyed that. See you next time.
Speaker 2 (47:14):
Hey, everyone, I want to take a moment and share
a personal message with you. When I record these podcasts,
there's no live audience here, and so I have no
idea really how they're going to be received. So I
love hearing that they have an impact on people's lives,
maybe inspiring you to think about the universe, or talk
to your kids about physics, or even just keep your
brain going on long drive or a boring shift at work.
(47:38):
That's what gives me the energy to keep making these
to put them out twice a week without fail for
five years now. So it really heartens me to hear
from you. But I realize that you all don't get
to know each other as much to hear about these experiences.
So I want to share a little bit with you,
including an example that made me smile and one that
frankly brought some tears to my eyes. First, a happy one,
(47:59):
someone writes and says, I don't have a question but
a compliment. Just wanted to let both of you know
that I greatly appreciate the way you both explain physics.
As a person who has no science background and barely
passed college algebra, it's refreshing to hear people explain things
without talking down to the listener. That's wonderful and it's
exactly what we're trying to do, make physics more accessible
to everybody without dumbing it down at all. But some
(48:22):
of the messages we get are a little bit harder
to hear. A woman wrote in that her brother is
a listener and an ultrarunner, but that at thirty nine
he had a massive stroke and faces a long recovery.
She writes that quote each night he makes sure his
phone is charged and loaded with enough Daniel and Jorgey
to get him through the night. It's without drama that
(48:42):
I say that your show is one of his lifelines,
right now, you guys are his intellectual support above all,
on behalf of our family. I want to thank you
for your podcast and being a comfort to him in
this season. Wow, it's hard to overstate how deeply that
touches me, and I want to send him our encouragement
on his road to recovery. I'm so glad that we
(49:05):
can be there to help in this small way, and
I want to say thank you to everyone out there,
those of you who are listening and writing back or
just enjoying silently. You're all the reason that I do this.
Thanks for listening, and remember that Daniel and Jorge explain
(49:26):
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Hey, Daniel, are you glad our universe has antimatter?
Speaker 2 (00:12):
No, I'm definitely pro our universe. So I guess I'm
not anti antimatter.
Speaker 1 (00:18):
That means your pro matter. But I guess the question is,
would you miss antimatter if we didn't have it?
Speaker 2 (00:24):
I mean, I like things the way they are, so
if we lost antimatter, the universe would be pretty different
and maybe worse. But what if it's better, or maybe
it couldn't exist without antimatter and it would disappear in
a puff of mathematical contradictions.
Speaker 1 (00:38):
Okay, then I would be anti antimatter. I would not
be pro antimatter.
Speaker 2 (00:43):
I'm just saying it matters. Hi.
Speaker 1 (01:00):
I'm Boria mccartoonist and the creator of PhD Comics.
Speaker 2 (01:03):
Hi. I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I love all the kinds of
matter out there, the matter and the antimatter and the
pro matter.
Speaker 1 (01:12):
What about the meh matter? Not pro, not anti, It's
it's just kind of there.
Speaker 2 (01:18):
You know. I will admit that there are some particles
I think they're exciting. In other particles, I'm like, yeah,
that's just a mess.
Speaker 1 (01:23):
About your favorite kind of matter is chocolate matters certainly
better than vanilla matter, karp matter, But anyways, welcome to
our podcast, Daniel and Jorge Explain the Universe, a production
of iHeartRadio.
Speaker 2 (01:35):
In which we dig deep into all kinds of matter
out there that matters. We talk about the things that
make you up. We talk about the things that make
nothing up, and things that seem to exist for which
we do not yet understand. The whole universe is like
a jigsaw puzzle with lots of weirdly shaped pieces, and
our goal is to find all those pieces, fit them
together to tell the whole story of our universe. And
(01:56):
on this podcast we'd like to do that and try
to explain all of it to you.
Speaker 1 (02:00):
That's right. It is a vast and complicated universe, full
of all kinds of crazy and interesting kinds of matter
and energy and concepts and mathematics that we like to
explore as human beings and ask questions about and then
explain it to you, or at least ask you the question,
what's the matter with you?
Speaker 2 (02:18):
We study all of these particles, we try to understand them,
and sometimes we even taste them to see if they're delicious.
But I wasn't joking when I said that some of
the particles out there are a little crazier and harder
to think about than others. I mean, there are so
many particles discovered in the era of the particle Zoo
that we almost ran out of silly Greek letters to
use to name all of them.
Speaker 1 (02:38):
Oh boy, what happens when you run out of Greek letters?
Speaker 2 (02:40):
Then you start using Hebrew letters? Okay, like the Gimmel
particle on the aleph particle. H interesting, But we've discovered
so many weird masons and baryons that we had to
use some of those weird Greek letters that nobody even
really knows how to write down.
Speaker 1 (02:55):
I guess we have done a pretty good job of
kind of looking out into the universe and basically talent
up all the different kinds of matter, all the different
kinds of particles that can't exist out there, because there
are a lot. As you're saying, there are.
Speaker 2 (03:06):
A lot, and it's sort of a two step process
to understand the universe. Like number one, just look out
and see what's there. Gather together all the puzzle pieces.
Number two, try to click them together to tell the
whole story. Are there pieces missing, do they fit together
into a puzzle or is it just a weird, disjointed
pile of confusion.
Speaker 1 (03:25):
Yeah, And I guess the history of it is that
we used to think that we knew what the building
blocks of the universe was, right. We thought the elements
of the periodic table were like the basic lego pieces
of the universe. But actually those turned to be made
of other things. And then those some of those things
turn to be made of other things.
Speaker 2 (03:42):
That's right. We revealed this sort of hierarchical structure of matter,
things made of smaller things, made of smaller things, but
the path to understand them in the history of science
was not so straightforward. We sort of like drilled down
and then got wider and weirder, and then drilled down
again and got wider and weirder. For example, when we
wanted to understand the nucleus, when we wanted to understand
(04:02):
protons and neutrons and what's inside them, we'd build bigger
atom smashers and higher energy colliders, but we didn't immediately
find out what was inside the proton. Instead, first we
discovered all sorts of weird other kinds of particles that
don't exist inside the atom, chaons and pions and rope
particles and omega particles and all sorts of other Greek letters.
I don't even know how to pronounce. Things got weird
(04:24):
before they got clearer.
Speaker 1 (04:26):
Yeah, no, I understand. It's all Greek to me.
Speaker 2 (04:30):
In the same way that we want to understand what's
inside the quarks that make up the proton, but first
we found more quarks along the way. Instead of figuring
out what's inside the upcork and the down cork, we
found the charm and the strange, and the top and
the bottom. So the universe gives us a big pile
of clues before it reveals its deepest secrets.
Speaker 1 (04:48):
Yeah, it is a weird universe full of surprises. And
one of the weirdest things about matter in the universe
is that it seems to have an opposite to it.
There seems to be a lot of antimatter in the universe.
Speaker 2 (05:00):
Every particle out there seems to have its weird twin.
And we don't know if this is a detour in
our path to finally understanding what is the fundamental nature
of matter, or if it's a crucial side quest to
get a clue that will help us unlock the deepest mystery.
We don't know if and of matter is necessary, we
don't know what role it plays, We don't really know
(05:20):
what clue it's giving us about the nature of the universe.
Speaker 1 (05:23):
And so to the other podcast, we'll be asking the
question why do we have anti particles? Feel like that's
a weird double negative question, like why don't we have particles?
Or why do we have anti particles? What's the correct
grammar here or is it in Greek?
Speaker 2 (05:46):
I think why do we have anti particles? Is the
deep question? You know, every time we see something in
the universe, we wonder like, hmmm, did it have to
be this way? Is this necessary? Is this a clue
as to the fundamental nature of the universe or just
sort of like a random accident.
Speaker 1 (06:00):
Well, so, as usual, we were wondering how many people
out there had thought about this question or have any
ideas about why we have anti particles.
Speaker 2 (06:08):
So thank you very much to everybody who answers these
questions for this fun segment of our podcast. If you
would like to play along next time, please don't be shy.
Write to me two questions at Danielandjorge dot Com.
Speaker 1 (06:20):
So think about it for a second. Why do you
think we have anti particles? Here's what people had to say.
Speaker 3 (06:25):
In general, antiparticles exist because particles exist and there's some
sort of balance that was broken at.
Speaker 1 (06:33):
The Big Bang.
Speaker 4 (06:34):
I don't know, but the universe seems to like symmetry,
and somehow antiparticles had to exist for some kind of
symmetry to be to be fulfilled. But I don't know.
It's kind of crazy.
Speaker 1 (06:51):
I think anti particles exist for the same reason you
don't get monopole magnets.
Speaker 2 (06:56):
But I'm got clear, so we'll say with me, well
maybe not.
Speaker 3 (06:59):
I feel like you need the antiparticles like cancel it out,
because you can't have like something from nothing. You need
to have something and then the opposite of it, so
that like overall nothing has changed.
Speaker 5 (07:13):
Any particles are probably like the ying and yang. For
every particle, there has to exist an anti particle in
order to balance the forces in the universe, similar to
matter and anti matter.
Speaker 6 (07:27):
I think the reason why antiparticles exist is because everything
in nature and physics seems to be balanced. So if
you sum up everything, it comes off like zero. But yeah,
for everything that exists, there needs to be an anti
thing Somemari like Ying and Young.
Speaker 1 (07:42):
All right, some very philosophical answers here, some of them
kind of zen.
Speaker 2 (07:47):
Yeah, there's a lot of philosophy in these questions, you know,
wondering whether the universe could have multiple explanations or just
one explanation, or whether it has any explanation at all,
whether it makes sense, and whether it's sensible to human minds.
All that stuff is tied up in this quest to
understand the universe.
Speaker 1 (08:04):
Do you think maybe there are anti particle scientists out
there and or cartoonists we're wondering why do we have particles?
What is this weird stuff?
Speaker 2 (08:12):
I don't know, but humans are capable of developing science
as well as antiscience. More recently, I'm.
Speaker 1 (08:18):
Just antiphysics, I like all the other sciences.
Speaker 2 (08:21):
Are you antiphysics or are you anti physicists?
Speaker 1 (08:23):
I'm anti answering that question and that's an answer to
that a position there. Well, let's dig into it, Daniel Water,
anti particles is it like antimatter exactly?
Speaker 2 (08:35):
Anti particles are what make up anti matter. So matter
is the stuff that we find around us that you
were made of. That I am made out of everything
you have ever eaten is made out of particles that
we call matter particles. So you and I are made
out of protons, neutrons, and electrons, and those protons and
neutrons are made up of quarks. Anti matter is made
(08:57):
up of anti particles, so you could have, for example,
anti hydrogen is made of an anti proton and an
anti electron, where the anti proton is then made of
anti quarks. So there's a close connection, of course between
anti matter and anti particles.
Speaker 1 (09:12):
I see. So particles are the little things that we're
all made out of, and some of them have anti
versions of them. Do all particles have anti versions or
only some of them? Like do the force particles have
anti force particles?
Speaker 2 (09:26):
Great question, sort of yes and no. All the particles
have anti particles, but some of them are their own
anti particles, so I'm not sure if that counts as
having an anti particle. So, for example, the electron has
an antiparticle the positron, and the muon has an anti
particle the anti muon, and the quarks have antiparticles the
(09:47):
anti quarks. Those are different particles, or you could think
of them as two parts of the same pair. But
they are distinct states. But then particles, like you said,
the force carrying particles like the photon, the photon is
its own anti particle, and so you might also say
it doesn't have an anti particle. But I'd like to
think about it as one particle playing two roles.
Speaker 1 (10:07):
What about some of the other force particles, do they
have anti versions?
Speaker 2 (10:10):
Well, there are two w bosons, and they are each
other's antiparticles. So you have the W plus and the
W minus for example. So those two force particles are
each other's anti particles, which is why we have two
of them. The Z boson is its own antiparticle, and
the gluon is actually eight gluons, all of different colors,
and some of them are each other's antiparticles. So you
(10:31):
can have like a red anti green gluon, which is
the antiparticle to the anti red green gluon. It gets
really colorful with gluons.
Speaker 1 (10:41):
Well, I feel bad for those particles that are their
own anti versions of themselves. It's like they're their own
worst enemies.
Speaker 2 (10:47):
Or maybe they're lonely. Right, one is the loneliest number.
Speaker 1 (10:50):
After all, this should hang out together.
Speaker 2 (10:53):
Some people confuse anti matter with dark matter, And there's
lots of mysteries in particle physics, right, lots of things
that we don't understand about the universe, But those are
two separate mysteries. Dark matter is the invisible matter that's
out there in the universe that we know is holding
galaxies together and shaping the whole development of the large
scale structure of the universe. We don't know what it is,
(11:15):
and if it's made of particles, that's a different idea
from antimatter. Antimatter is a real thing that we can make,
that we can study. We've seen it in our detectors.
We know for sure that it exists and it's made
of anti particles.
Speaker 1 (11:29):
Well, I guess maybe the question now is how do
you make antimatter? Can you make it or does it
exist in nature or is it just a matter of
like flipping the sign on some quantum property of regular particles.
Speaker 2 (11:40):
So sort of all of the above. Antimatter isn't very common.
The universe is almost entirely made of matter, meaning it's
made of particles instead of anti particles, but sometimes antimatter
is produced, though it doesn't last very long because it
runs into normal particles and annihilates but for example, the
discovery of anti I mapps, which led to the nineteen
(12:01):
thirty three Nobel Prize, was from naturally produced antimatter. So
a positron the opposite particle to an electron produced in
cosmic rays, meaning high energy collisions of particles from space
hitting the upper atmosphere and creating antimatter which then showered
down to the surface of the Earth.
Speaker 1 (12:21):
So when was this When was the first time we
saw antimatter?
Speaker 2 (12:24):
So it was first observed in the late nineteen twenties.
It was predicted by Paul Durack, the quantum physicist, who
saw the mathematical need for them in his equations, and
he said, hm, my equations predict there should be electrons
and should also be another particle with the opposite charge
as the electron. So he predicted it, and then Carl
Anderson saw it. We have a whole fun podcast episode
about the discovery of antimatter and the twists and turns
(12:47):
and the egos involved. It's a really fun story. Check
that out. We've known about it for almost one hundred
years now.
Speaker 1 (12:53):
It sort of involves cloud chambers, right, which is something
you can usually find in most science museums.
Speaker 2 (12:58):
Yeah, early particle physics didn't have fancy digital electronics and
the complicated detectors we have now. They had to use
techniques to observe the paths of these particles with the
technology they had. And one thing you can do to
illuminate what particles are flying through the air around you
is to create clouds of water vapor. If you have
air that's super saturated with water, meaning it actually has
(13:21):
more water in it than it likes to have, then
it's very easy to knock that water out of the air,
and a passing charge particle will do just that and
will create a string of droplets in the air. You
can actually create cloud chambers at home. Check out lots
of YouTube videos for how to do this. You can
build one in your garage. You can see them at
science museums and so you can see high energy particles
(13:43):
streaming through the air around you, muons and all sorts
of stuff. Carl Anderson proved that a fraction of these
are actually anti matter particles, and he did that by
showing how they curve differently in magnetic fields. Because magnetic
fields will change the path of a charge particle depending
on the charge. A positive charge will be in it
one way. A negative charge will bend it the other way.
(14:03):
So he saw particles that had the same mass as electrons,
but bend in the other.
Speaker 1 (14:07):
Direction like a positively charged electron. Is that basically what
an anti electron is, Just an electron with a charge flip.
Speaker 2 (14:16):
Yeah, that's what antiparticles are. They're just like their particle counterparts,
but they have the opposite charges, so the opposite electric charge,
the opposite weak charges, and the opposite color charges. So
in the case of the electron, it's basically a positively
charged electron.
Speaker 1 (14:31):
Right, because I guess an electron doesn't have the weak
charge and it doesn't have the strong charge.
Speaker 2 (14:36):
Right, Electrons do have the weak charge. Actually, remember, the
weak force is actually unified with electromagnetism into one force
we call electro week, and electrons can interact via the
weak force. They can emit w's for example, that's how
beta decay happens. So electrons interact with the weak force.
In fact, every particle we've ever seen interacts with a
weak force, which is fascinating because the other forces are
(14:58):
not so democratic. The strong force only interacts with quarks
and not at all with electrons or neutrinos, and electromagnetism
doesn't interact with neutrinos. But we've never found a particle
that doesn't have any kind of weak charge. Every particle
out there so far we discovered interacts with the weak force.
Speaker 1 (15:15):
Wait, what's the name of the week charge? If you
have a week charge, what is that called?
Speaker 2 (15:19):
Well, there's actually two different week charges. One of them
is called weak isospin and the other one is called
weak hypercharge. But you can combine them actually to make
electromagnetic charge. So there's two different charges for the electro
weak force, but one of them is really from electromagnetism.
Speaker 1 (15:34):
I'll pretend I totally understood that. But I guess when
you're trying to make an anti electron, which one do
you flip? Do you flip the electromagnetic charge like the
you know, plus and minds that we're all familiar with,
or do you flip one of these other sub charges?
And if you do, do I mean there are several
versions of an anti electron.
Speaker 2 (15:51):
Now you flip all the charges. So there's only one
version of a positron, and it has a positive electric charge.
It also has both of its weak charges flipped.
Speaker 1 (15:58):
But what if you flip one and the other you
can't do that, man, don't do that. They'll tell you
why not to do, tell you why I can't do it.
Then I can choose whether or not I can't.
Speaker 2 (16:07):
I will do it. It's not me, man, it's the
laws of the universe. No, we do not see particles
where only one charge is flipped and the other one
is not.
Speaker 1 (16:16):
Why not.
Speaker 2 (16:17):
Yeah, that's a very cool question, imagining particles that are
particles according to one force and anti particles according to
another force. Remember, we recently answered a question about whether
it even matters whether you're calling something matter or antimatter,
and turns out that's totally an arbitrary distinction. So it
doesn't really matter if one force considers a particle matter
(16:37):
and the other one considers a particle the anti matter.
But the forces do have to be consistent, and in
the case of the weak force and electromagnetism, for example,
they are tightly linked, so you can't just flip one
and not the other. The charges of the two forces
really are connected by the structure of the theory.
Speaker 1 (16:54):
I think what you're what you're saying, is this matter
anti matter distinction is really kind of arbitrary kind of right,
Like it's not as clear cut, like maybe there are
shades of gray or shades of antiness.
Speaker 2 (17:06):
Yeah, we definitely don't claim to understand everything there is
to know about antimatter. But I think you're right A
lot of this comes down to just like what do
you call matter and what do you call antimatter. A
crucial idea is that there are these symmetries that you
can flip these charges and the equations still work, that
the universe can do both of these things, and so
it does in some cases. We have like multiple ways
(17:27):
to categorize what is matter and what is antimatter.
Speaker 1 (17:30):
Well, I think the thing that most people probably remember
about antimatter, and that maybe is relevant here, is that
like a matter particle and it's antimatter particle, if they touch,
then they annihilate. They become pure energy. Right, We've talked
about that before they explode. That's one of the things
about antimatter.
Speaker 2 (17:47):
Particles and their antiparticles can annihilate into a force particle.
So for example, an electron and a positron can come
together to make a photon or a z boson and
a and an anti quark can come together to make
a glue on, and the opposite can happen. Also, a
photon can turn into a matter antimatter pair, or a
z boson can decay into a muon and its anti particle.
Speaker 1 (18:11):
But then I guess if anti nus is kind of
relative or there's a gray area there, or how does
that affect the annihilation? Like if I take a cork
and an antiquark, but I flip some other other signs,
do they still annihilate?
Speaker 2 (18:23):
They can annihilate if there is a particle that carries
their combined charges. So for example, an electron and a
positron can annihilate because in total they have zero electric
charge and the photon has zero electric charge. That's why
an electron cannot annihilate with another electron, because then you'd
have to have a particle with a minus two charge
in order to conserve electric charge. So the same thing
(18:46):
goes for the other charges.
Speaker 1 (18:47):
So like if I have a green cork and an
anti green cork, but a given different you know, regular charges,
what's gonna happen? Are they going to annihilate or repel
each other? Or what I'm just trying to get at,
Like what it means to be anti mime. Is it
depending on this annihilation thing or is it kind of random.
Speaker 2 (19:03):
It's a little bit more complicated for the color charge
because gluons themselves are colored. You know, the photons don't
have any charge for example, right, so it's simple plus
and minus annihilate to zero charge photons. In the case
of gluons, gluons do carry color. In fact, they carry
two colors, which is even more confusing. So for example,
a red anti green quark can combine to make red
(19:25):
anti green gluon. The glue on itself carries two of
those colors, but the gluons don't carry electric charge, so
this can only happen for quarks that have opposite electric
charges that can balance out to zero electric charge. So
one way to think about how to pair particles and
antiparticles is whether they can annihilate into these force particles.
Speaker 1 (19:46):
I see, So maybe one particle can have multiple anti
versions of itself.
Speaker 2 (19:50):
There are definitely multiple different versions of quarks that an
individual quark can annihilate with to create a gluon. Because
there are so many different kinds of gluons, they always
have to have opposite electric charges. Because the gluons don't
have electric charge, So yeah, it gets really complicated when
you're talking about the color charges because there's multiple different
color charges and the gluons carry them themselves, and so
(20:12):
the whole thing is a big mess.
Speaker 1 (20:14):
Is that how you end every physics paper? YadA YadA,
YadA YadA, And it's all a big mess.
Speaker 2 (20:19):
It's a big mess, and it's a glorious puzzle and
we're still working to try to figure it out. Yeah.
Speaker 1 (20:24):
Cool, Well, I guess the big question is still why
do we have anti particles at all? Why do they
exist in the universe? And so let's dig into that
question and some of the other open questions about antimatter.
But first let's take a quick break. All right, we're
(20:52):
talking about antimatter antiparticles and why do we need them
at all? Which sounds like a very insensitive question.
Speaker 2 (21:00):
What the deepest question we ask when we see something
in the universe, We ask like, why is it this
way and not some other way? Does it have to
be this way? Is the universe parsimonious, like it only
contains things that have to happen? Or is it sort
of like baroque that has all sorts of flourishes that
it doesn't really need, and it's just sort of beautiful.
We tend to think of the universe as parsimonious. We
try to take every piece that we find and fit
(21:21):
it into the puzzle to explain why the universe works
this way.
Speaker 1 (21:25):
Well, I guess one of the reasons we as we
talked about last time, that we call some things matter
and something's antimatter, is that we mostly see matter out
there in the universe, at least as far as we know.
Our planet, our Solar System, our galaxy is made out
of regular matter, and there's a big mystery about why
there isn't as much antimatter in the universe. But maybe
one question that you can ask is, like, is matter
(21:46):
and antimatter made at the same rate in the universe.
Like if you run a particle collision experiment and you
create some energy and some particles spill out to matter,
particles get made as much as antimatter particles.
Speaker 2 (22:00):
A little bit on what you start from. I mean,
if you start from particles of matter, then you're going
to get more matter particles than antimatter particles. If you
start from antimatter particles, then you're going to get more antimatter,
and we actually ran a whole collider that smashed matter
versus antimatter. Now, was the collider outside Chicago, the Tevatron,
collided protons with anti protons, and so there we got
(22:21):
even splits of matter and antimatter. Whereas the collider at Cerne,
the Large Hadron Collider, smashes protons with protons because antimatter
was such a big headache to produce for the other collider,
And so there we get more matter produced than antimatter
because we're starting from matter. But most of these processes
are symmetric.
Speaker 4 (22:39):
Right.
Speaker 2 (22:39):
If you just have a big pile of photons and
you wait for them to decay, they will produce an
equal number of positrons and electrons.
Speaker 1 (22:47):
I see. So I guess the big mystery is that
it sounds kind of like the universe is able to
make equal amounts of both kinds of matter, but what
we see in the universe is mostly only one kind
of matter.
Speaker 2 (22:58):
Yeah, we suspect that the very early universe, matter and
antimatter were created at the same rates that as the
universe cooled down from the frothing pile of quantum fields
and things got cold and isolated enough that you could
call things particles, that the particles and anti particles existed
at basically the same level. Then there was a huge
amount of annihilation, as you can imagine, and most of
(23:19):
the matter and antimatter went away and turned into radiation.
But a little bit more matter is left over than antimatter,
and we don't understand the source of that discrepancy, even
though it's the reason why we have matter galaxies and matter,
stars and matter, people and matter chocolate and not anti matter.
The universe seems to have some preference for matter over antimatter.
Speaker 1 (23:40):
Which makes me ask the question, is anti chocolate vanilla
or white chocolate or is it a case of having
multiple antiversities?
Speaker 2 (23:48):
I hope so, because neither of those things should be
categorized with chocolate.
Speaker 1 (23:51):
You're just pro chocolate. You just anti everything that's.
Speaker 2 (23:55):
I'm just anti calling things chocolate that aren't chocolate. Even
calling them anti chocolate somehow groups them to get they're
in that chocolate category where they don't belong.
Speaker 1 (24:02):
What about vegan chocolate, not chocolate.
Speaker 2 (24:05):
No, totally chocolate. It comes from the cocoa bean.
Speaker 1 (24:07):
Yeah, absolutely, all right, Well, the big question is why
does it exist? At all. Why do we have antimatter,
Like is it something that the equations of the universe
requires or is it just something that seems to happen.
That's the big question, right.
Speaker 2 (24:22):
That's the question, and the short answer is we don't know.
But what's really fascinating is that without antimatter, some of
our basic theories of physics don't work very well together.
Like we have relativity and we have quantum mechanics, both
things that we think make sense in the universe, but
when we try to bring them together, we get some conflicts.
(24:43):
And it turns out that antimatter resolves those conflicts and
lets us bring special relativity and quantum mechanics together into
one theory.
Speaker 1 (24:52):
Wait, I thought those two things didn't like each other.
Speaker 2 (24:54):
So we have two different theories of relativity, special relativity,
which tells us about what happens and things move really
really fast near the speed of light, and then general relativity,
which tells us how space bends in the presence of mass.
General relativity and quantum mechanics we do not know how
to combine into a theory of quantum gravity. That's something
for a future physicist, maybe one of our listeners, to
(25:16):
figure out, but special relativity and quantum mechanics we do
know how to combine, and we've had that for many,
many decades. So that's basically relativistic quantum mechanics, and that
is something that we know how to do thinking about
quantum particles and moving near the speed of light, and
we do that all the time in our particle colliders, right,
it happens all the time that we have high speed particles.
(25:37):
So relativistic quantum mechanics we can do bend space, curved space.
Quantum mechanics we don't know how to do.
Speaker 1 (25:44):
Interesting. Okay, So you're saying somehow antimatter and antiparticles somehow
make quantum mechanics and special relativity work together. What does
that mean?
Speaker 2 (25:52):
So it all has to do with preserving causality, and
special relativity makes it really hard to think about causality,
to think about the order that things happen in the universe,
because it forces us to think about the order of
events in a very different way than like Newton thought
about things, and the way that we intuitively think about things.
You probably think about the universe happening as if there's
(26:13):
like a giant clock and the whole universe like ticks
forward and then the next thing happens, and the universe
ticks forward and the next thing happens. But you can
think of the whole universe as having like one clock,
so you can tell like one story about what happened
in the universe. Special relativity tells us that that's not
actually true, that there's lots of different clocks in the universe,
(26:34):
and how fast they tick depends on where you are
and how fast they're moving relative to you, So you
can actually tell lots of different stories about what happened
in the universe, even stories that conflict with each other,
that contradict each other about the order in which events happen.
Speaker 1 (26:51):
Yeah, I know. We've talked about this before and include
it in our book. It's kind of this idea that
if two people run a race, you think that whoever
wins would be clear, but it sort of depends on
how fast they're moving and how fast the judges moving,
or how fast you're moving as an observer.
Speaker 2 (27:08):
Right, Imagine two people running a race, but instead of
running alongside each other on a track the way people
typically do, imagine them starting in the same place but
running opposite directions. This makes it easier to think about
because they end up far apart from each other. If
you're standing at the starting line and you're not moving
relative to the starting line, imagine these two runners run
at the same speed relative to you. You call it
(27:30):
a tie. But if somebody else is flying along in
a spaceship alongside one of these runners, they see the
two runners moving at different speeds relative to them, and
moving clocks run slow, which means they see one of
these runners in slow motion relative to the other one,
So they'll think one of the runners wins the race
and the other one is slower. But another judge going
(27:50):
the opposite direction sees the same thing, but flipped. He
sees the first runner's clock running slow, so he thinks
the second runner wins the race. So who you think
wins the race depends on the speed you're going relative
to the runners. Like people can honestly disagree about the
order of events, did the first runner reach the finish
line first or did the second runner reach the finish
(28:12):
line first. This is not a case of like people
being confused or mistaken or getting things wrong. It means
that there are multiple true stories about what happened. In
the universe that conflict with each other.
Speaker 1 (28:24):
Well, there's sort of one story, right, It's just when
you transform it between points of views, the order of
events changes.
Speaker 2 (28:32):
Yeah. That sounds to me like multiple stories. But you're
right that we can link them together. Special relativity tells
us how to predict what any observer will see. And
what special relativity says is that different observers will see
the order in different events. The laws of physics are
consistent from frame to frame, and they predict the observers
tell different stories. Yeah, so you can think about that
(28:53):
as like one coherent understanding.
Speaker 1 (28:56):
Yeah, that's what I mean. It's not like there's two realities.
Nobody can ever figure this out. It's more like, you know,
everyone has to agree on which observer they're measuring your
race by.
Speaker 2 (29:07):
Right, that's right. It means that the order of events
is not universal, right, that it's dependent on the observer.
Speaker 1 (29:12):
Well, or it is universal, as you said, it changes
depending on what you ask.
Speaker 2 (29:17):
Yeah, it depends on the observer. Right, It's not something
everybody agrees on will happen from their point of view. Right,
Different points of view will see a different order of events,
and that's very confusing when you think about causality because
you think, like you know, there should be an order
two events, Like you can't finish the race before you
start it, you can't receive a message before you send it.
You can't die before you're born. There are some things
(29:39):
send in the universe where there's a causal link between them, right,
and so they have to happen in a certain order.
Speaker 1 (29:45):
All right, Well, what does that mean for causality and antimatter?
Speaker 2 (29:48):
Then well, you might think that this makes the universe nonsense,
because if different people can see events order different ways,
does not just break causality. Does that mean you can
eat an apple before it's grown? Does that mean you
can get a message before it's sent? This kind of stuff, Well,
special relativity has some protection built in for that, right,
It says this can only happen for things that are really,
(30:09):
really far apart, things that are so far apart that
light can't pass between them. We call these space like
events instead of timelike events. And so you can reorder
events that are really really far apart because they're already
not causally connected. If two things are so far apart
that light couldn't pass between them, then there's no way
(30:29):
for them to have a causal connection. You can't like
send a message from one to the other. And so
things that are already causally not connected. Those things you
can reorder by traveling at some crazy speed. Things that
are causally connected, Like if you turn on a flashlight
and then the beam arrive somewhere else, there's enough time
for light to get from one to the other. You
(30:51):
can't reorder those events just by going faster or.
Speaker 1 (30:54):
Slower, all right, So then how does that figure into antimatter?
Speaker 2 (30:57):
So these events that you can't reorder, those are things
we call inside our light cone. Light cone are things
that we can affect in our future, and there's things
that affected us from the past. So that special relativity,
and it has this nice causal connection for things inside
your light cone. Things outside your light cone, they can
get reordered by things going fast or slow. Quantum mechanics, however,
(31:18):
doesn't naturally obey this rule. Quantum mechanics has weird limitations
on how much you can know about objects momentums, and velocities. So,
for example, you measure a particle really really specifically. The
Heisenbergen certainty principle tells you you can't know anything about
its velocity, how fast it's going. So in principle, quantum
(31:39):
mechanics allows things to go faster than the speed of light.
That allows particles to move from one place to another
outside the light cone because they could be going faster
than the speed of light. Quantum mechanics doesn't have the
speed of light built into it naturally, it allows particles
to violate this speed limit. WHOA well.
Speaker 1 (32:01):
On they think quantum mechanics can break the speed of light.
That sounds a little bit too much, Daniel. I think
you mean maybe, like our math allows it to, but
we don't know if in reality it can go faster
than light. Doing If you just.
Speaker 2 (32:13):
Start from sort of low speed quantum mechanics, the original
quantum mechanics that was developed right, non relativistic quantum mechanics
for slow moving particles, then that theory with the Heisenberg
uncertainty principle doesn't respect the speed limit of the universe.
It's only when you try to bring quantum mechanics and
special relativity together to make a theory of relativistic high
(32:34):
speed particles that you have to answer this question like, uh, oh,
what happens if particles that quantum mechanics predicts can go
faster than the speed of light. What does special relativity
say about that? So it's you know, in trying to
bring the mathematics in harmony with the universe, that we
run into this problem. We're like, hold on a second.
Quantum mechanics has this problem with causality. It allows things
(32:54):
to move outside your light cone. What's going on and between?
You bring these two things together, that antiparticles save the
day and allow you to bring quantum mechanics and special
relativity together in a way that makes perfect sense.
Speaker 1 (33:08):
I think maybe what you mean is that antimatter says
physicism because their original theory made no sense.
Speaker 2 (33:17):
Yeah, you cannot bring quantum mechanics and special relativity together
without anti particles.
Speaker 1 (33:21):
Right, It's like the limitations of the theory would allow
things to move faster than light, but probably in reality
they don't.
Speaker 2 (33:29):
That's right. We think special relativity is the law of
the universe. Nothing moves faster than light. Original old school
quantum mechanics has this problem that allows things to move
faster than the speed of light, potentially breaking causality. And
you're right, we don't think that happens in reality, So
we need to patch up the theory, and it turns
out that we need antimatter in order to do that.
Speaker 1 (33:47):
All right, well, let's dig into how antimatter saves the day.
It's sort of like a plot to is the villain
actually turns out to be the good guy. So let's
dig into that, and what does it mean about our
understanding of matter, antimatter and all kinds of matters or
in the universe. But first, let's take another quick break.
(34:15):
All right, we're talking about antimatter antiparticles. Why do we
have them? Why do we need them? It turns out
that they're useful in making our theories work, which is
not really I guess an answer to the question.
Speaker 4 (34:28):
Is it?
Speaker 2 (34:28):
Well, it's sort of an answer to the question. You know.
It says that the universe needs this to be consistent,
or our theories need this in order to be consistent
description of the universe.
Speaker 1 (34:38):
Okay, so then you're saying that it somehow helps reconcile
special relativity and quantum mechanics. How does it do that?
Speaker 2 (34:44):
So let's think about how quantum mechanics breaks causality. Right,
Imagine you have like a particle that you emit right
here at this moment, and quantum mechanics predicts that it
has a probability to end up like in Andromeda ten
seconds from now. That would break causality because if be
outside your leg cone, it would be like getting to
Andromeda faster than the speed of light. Nothing that we
(35:05):
do right now should be able to affect Andromeda until
millions of years into the future, because Andromeda is millions
of light years away.
Speaker 1 (35:13):
I think you're saying, the quantum mechanics, we have a
description of a particle here, and because there's uncertainty about
where it can be, there's a certain probability that in
the next second it can be right where it is now,
or it can be a meter away or two meters away.
And there's a very very very small possibility that in
the next two seconds, according to the quantum mechanics, it
(35:34):
can then be in Andromeda. That's kind of how you
would describe it.
Speaker 2 (35:38):
Yeah, exactly if you have a lot of uncertainty on
its momentum, because you've narrowed down its position super duper well,
and Heisenbergen certainty principle tells you can't know both things
at the same time. So if you know the position
really really well, you don't know the momentum, and therefore
there's a possibility that it has some crazy high momentum
would be faster than the speed of light, getting it
(35:59):
too Andrama in just ten seconds instead of the millions
of years it should take. And this would be a
problem for causality because those two events are spacelike. It's
outside of our light cone, which means that somebody flying
by in a spaceship could see them happen. In the
other order, could see this particle arrive in Andromeda before
it leaves our galaxy, which is nonsense. Right, So anything
(36:22):
that moves faster than the speed of light breaks causality.
That's one reason why we don't think things can move
faster than the speed of light, because it would allow
you to reorder events that are causally linked. Right, so
make the universe nonsense.
Speaker 1 (36:35):
Well, it sort of sounds like quantum mechanics just breaks
causality anyways, right. Quantum mechanics say that particles can just
pop out of nowhere without any cause, So like quantum
mechanics says that a particle can suddenly disappear here and
appear in Andromeda.
Speaker 2 (36:50):
Why not now, I wouldn't say that quantum mechanics necessarily
breaks causality. It makes a different description of the universe.
It makes the universe probabilistic instead of deterministic. It says
weird things can happen, like a photon can turn into
an electron and a positron, or it could do something else.
It says that the laws of the universe only predict
what might happen instead of what does actually happen. But
(37:12):
there is still causality, Like in quantum mechanics, the wave
function right now is determined by the wave function in
the past. Right The wave function itself doesn't specify exactly
what will happen, only to probabilities, but the wave function
is still determined by the past wave function, so there
should still be logic in quantum mechanics.
Speaker 1 (37:30):
I guess that's weird because if you're saying that anything
might happen, I.
Speaker 2 (37:33):
Would say anything might happen, you know quantum mechanics, as
is the probability for things to happen. Some things are
impossible even in quantum mechanics, like you can't violate conservation
of electric charge right, Electrons have no probability to turn
into positrons directly, because I would violate conservation of electric charge,
which is built into our quantum mechanical theories.
Speaker 1 (37:54):
But haven't we talked about how like, according to quantum mechanics,
a pink elephant could certainly you're out of nowhere outside
of the Earth's orbit, right in space.
Speaker 2 (38:03):
Yeah, that's not impossible. That doesn't break any of the rules.
Speaker 1 (38:06):
But then we have no cause would it.
Speaker 2 (38:08):
Well, the cause would be that there's a distribution of
probabilities for what those particles in the vacuum could do.
They could sit there and do nothing. They could create
one electron, they could create ten electrons, they could create
forty two trillion electrons. They could create a Boltzmann brain,
they could create a pink elephant. Those things are probabilities.
What does our universe choose one particular probability and not another?
(38:30):
What does it choose one that's like really unlikely, like
a pink elephant in space, and not another that's more
likely that we don't understand. That's like a deep question
in quantum philosophy, whether all of them happen at once
in different universes, whether the universe collapses these wave functions
to choose one. Whether it even is truly random, That
is definitely not something we know. But I wouldn't say
(38:50):
there's no cause there's still like a distribution of probabilities
for what might happen.
Speaker 1 (38:54):
Well, let's get back to the antimatter particle. How does
that antimatter particle fit into this scenario.
Speaker 2 (38:59):
Then it turns out if you do these calculations, and
you calculate like, okay, what's the probability for my particle
to appear in and Drama in ten seconds from now,
and you include antimatter, then those probabilities vanish. Because the
probability for you to see a particle go to Andrama
in ten seconds, there's another probability for a particle to
go from Andromeda to here in ten seconds, for an
(39:21):
antimatter particle to come the opposite direction. And because matter
and antimatter have all the opposite properties, those two things
quantum mechanically cancel each other out. So the antimatter nonsense
cancels out the matter nonsense to make no nonsense. Whoa, whoa, whoa.
Speaker 1 (39:39):
Wait, we had this scenario of having one particle here
that suddenly appears in Andromeda in ten seconds. You're saying,
there's a different scenario in which an anti particle the
exact antiparticle of my particle is where my particle would appear.
That one disappears and appears where my current particle is
at the same time, and somehow that cancels it out.
(40:01):
But what are the chances that there's an antiparticle exactly
where my particle would go.
Speaker 2 (40:07):
Well, all of this stuff is very unlikely. But when
you do a quantum mechanical calculation, you sum over all
the possibilities, and these equations are wave equations, so you
can get like constructive interference and destructive interference and things
where the probabilities cancel out, those things just don't happen.
Like in the Devil's Slight experiment. You see interference places
where lots of particles and places with no particles, the
(40:28):
places where no particles land, and the interference on the
screen is because there's been destructive interference among the probabilities.
So when the probabilities cancel out, those things just don't
happen in the universe, And so the probability for a
particle to break special relativity and appear in Andromeda is
canceled out by the probability for an antiparticle to do
the opposite.
Speaker 1 (40:49):
Well, I guess what does it mean to cancel out
the probability? That means that it's never going to happen.
Speaker 2 (40:53):
It means that it's never going to happen. And so
if you bring quantum mechanics and special relativity together, you
include anti particles, then it all clicks together perfectly and
you get no violations of causality.
Speaker 1 (41:06):
But wait, the wouldn't that also cancel all movements like
even a meter distance?
Speaker 2 (41:13):
Yeah, great question. It doesn't happen for things inside the
light cone because things inside the light cone everybody agrees
on the order, whereas things outside the light cone you
can reorder them. So, for example, if I say, well, look,
my particle left here and ended up in a drama
in ten seconds, that's outside my light cone. So somebody
else flying by in a spaceship might see them happen
(41:33):
in the opposite order. Right. Seeing it happen in the
opposite order is like seeing a particle go backwards in time,
which is equivalent to the anti matter particle. Right, So
both probabilities exist, the particle and anti particle version, because
you can reorder them because they are outside your light cone.
Things inside your light cone, you can't reorder them. Their
(41:54):
order is fixed. Only things outside the light cone where
you could reorder them, where somebody could see it as
a part article and the other person could see it
as an anti particle. Only those things cancel out.
Speaker 1 (42:04):
It feels a little convenient, like maybe saying like, oh,
my theory breaks down after this limit. Let's just come
up with something totally different and ex sort it only
applies outside of this limit where my thing breaks.
Speaker 2 (42:16):
Yeah. Well, it's sort of convenient and sort of spooky, right.
It's sort of like if you didn't know antiparticles existed
and you were trying to bring quantum mechanics and relativity
together into relativistic quantum mechanics, You're like, huh, this is
a problem. This could be solved if, for example, there
were the existence of antimatter hmm, and then you went
out in the universe and you found it, You'd be like, wow,
that was pretty cool. Here it's sort of works the
(42:38):
opposite direction. We're like, no antimatter exists, and we can
use it to help bring these two theories together. It
is very convenient, but that's sort of like a glorious
moment when you're like, oh wow, look these things. They
sort of need to exist for the universe to be
self consistent.
Speaker 1 (42:53):
Now, you said something earlier that was kind of interesting.
You said, anti particles kind of go back in time.
What does that mean?
Speaker 2 (42:58):
Well, mathematically you can look at it a particle moving
forwards in time, and it's equivalent to an antimatter particle
moving backwards in time. And you can sort of see
that in this example we're talking about, where like, my
particle goes from here to Andromeda, and it does it
faster than the speed of light. Right. If it does
it faster than the speed of light, that means that
somebody else going by in a spaceship they could see
(43:18):
it happen in the opposite order. They could see it
arrive in Andromeda before it leaves my house in the
milky way, right, which means that it's started in Andromeda.
The first event is in Andromeda. So I could say, look,
this is a particle going forwards in time faster than
the speed of light. Somebody else could say, no, it
goes the other direction. They could say, no, it's going
from your future to your past. But I see it
(43:41):
as an antimatter particle because they could reorder the events,
and so they see it going from Andromeda to the
Milky Way, and they see it moving as an antimatter particle.
Speaker 1 (43:50):
But I guess maybe in order to measure my particle
here and there, don't I need to measure the particle,
wouldn't they collapse the wave function and make this all
kind of not really applicable.
Speaker 2 (44:00):
You would need to collapse the wave function absolutely, and
of course it wouldn't really happen, right. That probability is
actually zero. You can't collapse the wave function and make
this happen. What we're talking about really is just a
partial probability. There's another part to that calculation, the antimatter part,
that cancels it out. So you can't actually do this right.
You can't see a particle appear in Andromeda in ten seconds.
(44:21):
It would take millions of years to get there, and
the probability for that to happen is canceled out by
the anti matter version, So that's why it just doesn't happen.
Speaker 1 (44:28):
Is this sort of like one of those virtual particle
scenarios where like just a matter of fact that something
else can happen, actually in a way happens canceling out
other effects that are happening.
Speaker 2 (44:40):
Yeah, you can think about this the way other quantum
mechanical weirdness happens, where like particles can interfere with themselves.
Right again, like in the double slit experiment, if you
don't know which slit the particle went through, has a
probability to go through both, and those probabilities can actually
interfere with themselves, So single particle interferes with itself. This
is sort of the same deal. Like this single particle
(45:01):
that goes from here to Andromeda, you could also be
seen as an antimatter particle going the other direction, and
those two probabilities cancel, which is why it never actually happens.
Speaker 1 (45:10):
All right, Well, then what is the I guess main
takeaway is it that quantum mechanics does work with special activity,
and it's because antimatter particles exist or are a possibility
in the universe.
Speaker 2 (45:22):
That's exactly right. You need antimatter to bring quantum mechanics
and special relativity together and not break causality. If we
think the universe is causal, meaning that like there's a
logical flow to things, that the past influences the future
and not the deep past. Then you need antimatter in
order to have special relativity and quantum mechanics. We just
(45:43):
don't know how to do it without antimatter.
Speaker 1 (45:45):
Cool. All right, well, you've commissed me. I'm pro antimatter
or I'm not anti antimatter.
Speaker 2 (45:51):
Does that mean that you're pro anti vanilla, which means
you're willing to try some chocolate.
Speaker 1 (45:55):
I am pro anything with the word vanilla in it.
Speaker 2 (46:00):
Right, I'm part of the vanilla eradication project. How do
you feel?
Speaker 1 (46:03):
Oh my god? And that is how this podcast got canceled. Daniel.
Thank you, it's been a nice run. We're done.
Speaker 2 (46:13):
No, I love vanilla. Vanilla is wonderful.
Speaker 1 (46:15):
We've gone the way of Scott Adams and Dilbert.
Speaker 2 (46:19):
I'm not a flavorist. Okay, I'm definitely pro vanilla.
Speaker 1 (46:22):
I'm just more we think they're flavorists.
Speaker 2 (46:24):
Daniel, I need to go for some flavor sensitivity training.
Speaker 1 (46:29):
It sounds like, thank you, maybe you should examine those
anti FeAs.
Speaker 2 (46:37):
All right, well, between this and the next episode, I
will do a deep dive into my own internal flavor preferences.
Speaker 1 (46:43):
There you go examine your own anti matter. All right, Well,
another interesting bit of how we're trying to figure out
how the universe works, and how sometimes it's interesting how
our theories of the universe actually kind of turn out
to be true, which is kind of surprising, right.
Speaker 2 (46:58):
It is surprising sometimes, and that crazy little human brains
can come up with mathematical stories that do seem to
describe the universe, even in ways we didn't anticipate.
Speaker 1 (47:08):
All right, Well, thanks for joining us. We hope you
enjoyed that. See you next time.
Speaker 2 (47:14):
Hey, everyone, I want to take a moment and share
a personal message with you. When I record these podcasts,
there's no live audience here, and so I have no
idea really how they're going to be received. So I
love hearing that they have an impact on people's lives,
maybe inspiring you to think about the universe, or talk
to your kids about physics, or even just keep your
brain going on long drive or a boring shift at work.
(47:38):
That's what gives me the energy to keep making these
to put them out twice a week without fail for
five years now. So it really heartens me to hear
from you. But I realize that you all don't get
to know each other as much to hear about these experiences.
So I want to share a little bit with you,
including an example that made me smile and one that
frankly brought some tears to my eyes. First, a happy one,
(47:59):
someone writes and says, I don't have a question but
a compliment. Just wanted to let both of you know
that I greatly appreciate the way you both explain physics.
As a person who has no science background and barely
passed college algebra, it's refreshing to hear people explain things
without talking down to the listener. That's wonderful and it's
exactly what we're trying to do, make physics more accessible
to everybody without dumbing it down at all. But some
(48:22):
of the messages we get are a little bit harder
to hear. A woman wrote in that her brother is
a listener and an ultrarunner, but that at thirty nine
he had a massive stroke and faces a long recovery.
She writes that quote each night he makes sure his
phone is charged and loaded with enough Daniel and Jorgey
to get him through the night. It's without drama that
(48:42):
I say that your show is one of his lifelines,
right now, you guys are his intellectual support above all,
on behalf of our family. I want to thank you
for your podcast and being a comfort to him in
this season. Wow, it's hard to overstate how deeply that
touches me, and I want to send him our encouragement
on his road to recovery. I'm so glad that we
(49:05):
can be there to help in this small way, and
I want to say thank you to everyone out there,
those of you who are listening and writing back or
just enjoying silently. You're all the reason that I do this.
Thanks for listening, and remember that Daniel and Jorge explain
(49:26):
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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