Does anti-matter feel anti-gravity?

Daniel and Jorge talk about whether anti-matter falls down, or up!

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Episode Transcript

Speaker 1 (00:08):
Hey, Jorgey, do you have your antimatter snack yet? I
had a banana as usual. It's anti slip. Does that count? No?
But you do know that bananas give off antimatter radiation,
don't you wait? What that's bananas? Isn't that dangerous. It's
so little that it doesn't really matter. That's why you're

(00:29):
so matter of fact about it. That's why it annihilated
my taste for bananas. Well, the important thing is that
it annihilates your hunger. That's the whole point of eating food,
is the antimatter of hunger. Hi am or Handy, cartoonist

(00:55):
and the creator of PhD comics. Hi, I'm Daniel. I'm
a particle physicist and a professor at U C Irvine.
And it really has been years since I had a banana. Years.
Oh my gosh, I feel sorry for you. Why are
you depriving yourself and one of life's simplest pleasures. Although
I recently convinced my daughter to start eating bananas, so
now we have bananas around the house. Oh my goodness. Wait,

(01:18):
why are you recommending it to your daughter but not
having any yourself. You know, it's a very personal question,
person to person, I mean you brought it up, and
I'm just asking a fallow up question. I just mean
that it's subjective. You know, one person can love bananas,
another person can hate them. To slippery slope, some people
find them appealing. Welcome to a podcast Daniel and Jorge

(01:39):
Explained the Universe, a production of Our Heart Radio in
which we try to explain our subjective, our personal experience
of the universe the way that it seems to us.
All this data that we gather with our eyeballs, biological
and technological, the things that we see out there in
the universe, we want to understand all of them. We
want the whole universe to be a story that makes

(02:01):
sense to the human brain. This is part of course,
the long journey of science and trying to wrap up
the mysteries of the cosmos into something we understand. And
our goal on this podcast is to take you on
that journey and explain all of it to you. Yeah,
because it is a very mysterious universe, full of amazing
things that are happening in it, and a lot of
things that we don't understand, even things that we take

(02:23):
for granted on an everyday basis. Yeah, there are so
many basic questions about the universe that we do not
have answers to, which means that for you young folks listening,
you future scientists, there are plenty of discoveries left to
be made, lots and lots of open questions for you
to explore. These are big questions about the universe, about
our very existence, of why we're here and how it

(02:45):
is that we are here because there is a lot
of the things in the universe that matter, and also
a lot of things that antimatter, like bananas. I wasn't
joking that bananas produced antimatter. That's a real thing. Oh yeah,
But is an antimatter dangerous? Like if you touch antimatter,
you explode anti matter. When it hits real matter, it
will annihilate into photons. But bananas contain potassium, which is unstable.

(03:07):
It undergoes radioactive decay, emitting positrons, which are anti electrons,
and when those do hit your body, they will annihilate
and create a tiny little flash of light. But it's
such a tiny amount of antimatter that it doesn't really matter. Well,
that's why I eat bananas, because you know, it makes
me glow, makes me feel lighter too. There isn't potassium

(03:27):
in everything. I mean, it's all around us too, right,
It's not just bananas that have potassium. That's right. It's
not just bananas that have potassium. And it's all sorts
of other things that also radioactively decay. So it's actually
anti matter sort of all around us all the time.
It's also showering down on us from the atmosphere because
of cosmic ray impacts. Yeah, there are all kinds of
amazing things showering us at the moment right now and

(03:50):
enveloping us, and and for a lot of those things,
we still have big questions about them, even big things
like gravity. Anti matter is fascinating. It appears in science fiction,
but it's also some thing that's real. It's one of
these interesting hints that the universe is more complex than
just the stuff that we are made out of, that
the universe is capable of doing many more things than
can just be found out of the particles that we

(04:12):
are made of. There are all sorts of other weird
possible particles out there, and they all give us hints
about what the underlying rules are governing the universe itself.
And you're right, because ant matter is so rare. There
are basic questions we have about its properties, Yeah, including
something as basic as gravity, gravity, which you know we

(04:32):
kind of depend on every day of our lives to
stay on planet Earth. Without gravity, we'd all be floating
out there in space. That's not something I ever worry about,
but maybe I should start to do. We need to
like look at the gravity prediction every day as well
as the weather prediction. Well, I know it's a heavy
burden to be carrying around worrying about gravity, but it
seems to be pretty reliable. Right. We ever noticed any
change in your gravity? I mean, I don't want to

(04:55):
enquire about your weight or anything like that. That's also
personal information. That definitely explains it. Right, It's not that
I'm getting heavier and heavier. It's at the gravity of
the Earth itself is increasing. Sounds like you have an
amazing experiment in at hand here, But it does raise
a lot of interesting questions about gravity and antimatter, specifically

(05:16):
whether or not they are the same for everything in
the universe. That's right, antimatter seems to be like the
opposite of matter in so many interesting ways, and so
people also wonder whether or not antimatter falls down or
whether it might possibly fall up, like does antimatter fail upwards?

(05:37):
So today on the program we'll be tackling the question
does antimatter feel anti gravity? Interesting? Now, are you saying
it might feel anti gravity or it has anti feelings
against gravity? We should invite it onto the podcast to
ask it what its emotional response is to gravity. But

(06:00):
I think today we're focusing on a more physics question,
which is just like, when gravity does this thing, where
does antimatter go? Doesn't like run away from gravity? Is
that what you mean? Because antimatter is the opposite of
matter in so many interesting ways, Yet we also really
don't understand how gravity works for fundamental particles. We think

(06:21):
about gravity in terms of like boulders or basketballs, or baseballs,
or even little bits of sand, But once we get
down to the quantum level, those particles do things that baseball's,
basketballs and bits of sand can't do, and we don't
really know how to apply gravity to those situations, which
opens up all sorts of questions like maybe it does
the opposite of what it does for normal matter. Do

(06:43):
you think antimatter minds that we call it antimatter? Like
maybe it just has a different opinion about the universe.
You know, maybe it's just pro something else. Yeah, I
think in the antimatter galaxies that might be out there
in deep space. On their podcast, they're probably calling us
the antimatter yeah. Or maybe there's a third opinion, you know,
why does it have to be so adversarial these politics

(07:04):
of physics? Stop the polarization of physics exactly, it's all
just matter. Yeah, it's not helping our society for sure. Well,
as usual, we were wondering how many people have thought
about anti matter and whether it feels gravity, or whether
it feels anti gravity, or whether anti feels gravity. So
thanks very much to everybody who participates in this segment

(07:26):
of the podcast. If you would like to try answering
the question of the day, please feel free to write in.
We'll set you up and you can hear your voice
on the podcast. Think about it for a second. Do
you think antimatter falls down or up? Here's what people
had to say, pravity, because anti gravity might be things
pushing each other apart. What do you think gravity or

(07:47):
anti gravity? I feel like anti matter still has mass.
It doesn't have like anti mass, so I don't think
it feels anti gravity. Do we know if there's anti gravity?
Is their uncle gravity? I think that antimatter feel gravity
in the same way that normal matter feels gravity, and

(08:08):
anti gravity, I think is we don't know if that
even exists. Well, if I remember your lessons on anti matter,
it should feel gravity because any matter is just regular
matter with opposite chart. I know that matter feels gravity
because of the bending of spacetime towards something with mass.
I don't really know what anti matter is and whether

(08:29):
it exists in another field or spatial field than mass.
But I suppose in the field that anti matter exists,
maybe there's the bending of that field, which would be
called anti gravity, So I'd say it does feel anti gravity. Alright,
a lot of very pro and anti pocisitions on this question.
My emotions go up and down as I was listening

(08:51):
to those things. I like how people were anti knowing
an answer. What happens when knowledge collides with anti knowledge.
You probably get the current state of affairs right now
in the world. You get a physics podcast about the
mysteries of the universe. But it is an interesting question
whether antimatter feels anti gravity, because I guess antimatter feels

(09:12):
natively about a lot of things. Yeah, antimatter is one
of my favorite ideas in physics because it shows you
that our matter isn't the only kind of matter that
can be out there. There's like the opposite of our
kind of matter. Though, like what exactly opposite means is
a bit of a question philosophically, Right, Well, I guess
maybe start with the basics what is matter for of all?

(09:34):
Because I know there are matter particles and there are
force particles, right, I think the basic idea is that
the universe is filled with quantum fields, and some of
these are matter quantum fields. Right. Yeah, what we call
matter is what you and I are made out of.
We call it matter because it's the first thing we discovered,
and so we sort of named it the normal stuff.
And you and I are made of these particles electrons

(09:57):
and protons and neutrons, which are of course made up
of core works inside them. And as you say, they
are all bound together by forces, the electromagnetic force, the
weak nuclear force, the strong force, which all use particles
to communicate with each other. So there's like the photon
for the electromagnetic force and the gluon for the strong
nuclear force. And so you and I are like this

(10:18):
big complicated mesh of particles all weaving themselves together to
make me and you. Right, and we are made out
of the basic three kinds of matter particles, right, electrons,
and one type of forks, and another type of cork.
And wait, a third type of cork. Right, three courts?
How many quarks are there? There are six quarks that

(10:38):
we have discovered, the up cork and the down cork.
Those two are the ones that we find mostly in
the proton and the neutron, although there is a little
bit of other kinds of quirks sometimes appearing in the
proton and neutron, but for the most part, it's up
quarks and down corks make protons and neutrons, and you
add electrons to complete the atom. Right, So we're made
out of those kinds of icles, and most of most

(11:01):
of the stuff in the universe is made out of
those three particles, right, Like the planets, the stars, the
comments out there, the asteroids, the whole galaxies are basically
those three kinds of particles. Right. Yeah, we think that
our entire solar system, our entire galaxy, our cluster of
galaxy is all made out of this same kind of
basic stuff that these basic building blocks can be put

(11:21):
together in lots of different ways to make stars and
lava and weasels and peanut butter and all the stuff
that we know in the universe. And that's why we
call it matter. And on a semantic note, I would
include also the force particles, you know, the gluons and
the photons and things that tie them together to really
make them who we are. So we're not just like
a loose pile of particles as constituting matter in this case.

(11:43):
I know, sometimes particle physicists distinguished between matter particles and
force particles, but when we're talking about matter and versus antimatter,
I think it makes more sense to just lump it
all together as matter. Okay, shifting definitions here of basic
things like matter and force. I guess we're all a
little bit das to that. But also that's the stuff
that we're made out of. But there's also other stuff

(12:05):
in the universe in this category of matter, right, there's
like heavier electrons and heavier courts. Yes, there are other
versions of these particles. This is one of the really
fascinating things about particle physics is that the particles we know,
the electron, the upcork, and the down cork have these reflections.
That's what I meant earlier about the sort of philosophical
definition of opposite. Because with the particles we know, there

(12:27):
are several versions of them. So even before we talk
about antimatter, as you said, there are heavier versions of
these particles, so they're sort of reflected in this one
dimension along mass. So there's like a heavier version of
the electron it's called a muon, and a heavier version
of the up cork it's called a charm cork. And
then there's a second reflection, right, So there's the muan

(12:47):
and then the towel is the upcork, the charm cork,
and then the top cork. So each of these basic
particles of matter that we know, there's two more versions
of each of them. So it's this weird reflection of
the kinds of matter that we're familiar with along the
mass access they're heavier versions of each of these. Well,
not all the particles, right, the force particles don't have

(13:08):
heavier cousins, do they. Yeah, that's right. Only the fermions
have these heavier cousins. We're not aware of any heavier
version of the photon or the z boson. Okay, but
there is something called antimatter particles, which is like if
you take all of those particles you mentioned, the ones
we're made out of their heavier cousins. And also in
some ways, if you also take the force particles and

(13:30):
numpit amount in, there's a whole other version of all
of those particles that are called antimatter. That's exactly right.
So all these particles that were aware of, there's another
way they're reflected, not just like there's a heavier version
of them, but now there's like this opposite version of
them where we take all the charges, for example, and
we flip them, so the electron has charged minus one.

(13:50):
There's another version of the electron, which we call the
antimatter version of the electron. Sometimes we call it a positron,
which has charged plus one. So it's reflected in this
like different direction. And that's true also for the muan
and for the up cork, and for the down cork
and the top cork. All these particles have their antimatter versions.

(14:10):
So the antimatter versions are when you flip their charges,
which is related to the kind of force they feel, right,
Like electrons feel the electromagnetic force, which means they have
a charge, and that's what you flip to get the
anti electron exactly. And we're talking here just about the
electric charge, which is a label that we put on
particles that feel the electromagnetic force. And a minus charge

(14:34):
means one thing, and a positive charge means something else.
And we know, for example that like positive negative charges
will pull on each other and similar charges will repel
each other. So that's a label we put on particles
to describe how they react to electromagnetic fields. And so
an electron an apostitron are the same, except they react
oppositely to these fields. The same electromagnetic field which pushes

(14:56):
an electron up will push a positron down, so it
has the same mass as an electron, but the opposite
electric charge. Right. And then other particles like the corks,
they don't feel the electromagnetic force, right, so they don't
have electrical charge. Right. Corks do have electromagnetic charge, but
they're really weird. They're like plus two thirds or minus

(15:16):
one third, so they definitely feel electromagnetic fields. You just
don't typically think of them as doing so because they
also have a charge for a much more powerful force,
a strong nuclear force. So they have the electric charge
and they also have this color charge for the strong
nuclear force. Okay, so of course feel the color charge
and also the electric charge. Now, then is an anti

(15:38):
cork something that has both of those things flipped or
just one of those things flipped. Both of those things
get flipped for an antiquark exactly. And I guess that's
true for all the other particles. But what about the
force particles. That's also true for their antimatter versions, So
that's really interesting. It actually depends on the force particle.
So for example, the W boson that actually carries electric charge,

(16:00):
it's like there's a positive version and a negative version,
and one is the anti particle of the other. So
the antiparticle of the W plus is the W minus. Okay. Yeah.
And then there's some interesting things about certain particles that
are their own antiparticle, like photons, right, that's right. For photons,
there is no other particle to serve as the antiparticle.
They are their own antiparticle, which is sort of weird.

(16:23):
But the way we think about in particle physics is
like you take a particle, you apply the antiparticle operator
to it, and say, what do you get? If you
start with an electron and you apply the antimatter particle
operator to it, you get a positron. You start with
the photon and you apply this operator to it, you
just get the photon back and sort of like symmetric.
So the photon serves as its own antiparticle. Because I guess,

(16:45):
does the photon have a charge. Photon does not have
an electric charge, right, the photon does not feel electromagnetic fields.
If a photon is flying through space and this electric
field there does not bend the path of the photon.
If you don't have anything to flip, then you can't
have an antimatter because is that kind of generally the rule.
That's generally the rule, and that holds also for example,
for gluons. Luonto the particle that transmit the strong nuclear force,

(17:08):
and they do carry color, they carry this charge, and
so you can't have anti gluons. You can take a
gluon and make the anti version of it as the
opposite color. All right, So that's matter and antimatter. But
one thing, I guess all matters seems to have in common,
whether or not it feels certain forces or not. Is
that everybody seems to feel gravity? Right, Well, we're not

(17:30):
exactly sure about what happens with antimatter and gravity, but
there is something we think that isn't flipped, which is
the mass. Like an electron we think has the same
mass as a positron, it's not like that mass then
goes negative. That suggests they probably have a similar relationship
to gravity as the original particle, but we just aren't sure. Well, yeah,
I guess that's what I was trying to get at,

(17:51):
which is that a lot of most of these particles,
the matter particles, have mass, right, that's one thing we
know about them, and almost in a way, that's kind
of what makes the matter part Yeah, all the fermions
definitely do have mass. Even the new trinos have mass,
even though they have a really tiny little bit of it,
and all of them get mass, we think from the
same process, which is interacting with the Higgs boson, And

(18:12):
to interact with the Higgs boson you have to have
an antimatter particle. Also, the Higgs boson requires particles to
interact like in pairs. It couldn't give the electron mass
if the positron didn't exist, for example, right, All right,
well then, I guess you know, we know that all
of these matter particles feel gravity, right because we feel gravity,
and all of the things on Earth feel gravity. And

(18:34):
we know that the stars and the planets out there,
and the galaxies and the galaxy clusters all feel gravity
and they're mostly made out of matter stuff. And so
the question that is, does antimatter also feel gravity or
does it feel something else, maybe the opposite of gravity.
And so let's get into that weighty question. But first

(18:55):
let's take a quick break. All right, we're anti talking
about not feeling anti gravity or is this a pro
gravity podcast? I'm definitely pro gravity. I don't want it

(19:18):
to pick up and move somewhere else, like I'd like
for it to stay pretty much where it is. I'm
relying on it every day. Oh really, I guess I'm
more morally flexible when it comes to gravity. I mean,
if I could, like, you know, ignore it for a
little bit, that'd be pretty cool to fly around, wouldn't
that be great? It would be nice to be able
to manipulate gravity, right If we had ways to create
like anti gravity somehow, it'd be easier to move your

(19:40):
bed across the room, or to ship stuff across the world,
or to launch stuff into outer space. That would be
pretty awesome. We forget other stuff. How about ourselves, we
could all be flying around. Finally, you get that flying
car exactly right. It could be an anti car. Well,
that's one of the exciting things about all of these

(20:00):
open questions is that once you understand the way the
universe works, you might discover something really surprising that's could
give you a handle for creating all sorts of new
crazy technologies. Yeah. I mean, we've been waiting for these
anti gravity flying cars for for years. We're still waiting, Daniel,
what's the hold? Well, you know, antime matter is not
easy to study. It's sort of all around us in

(20:23):
very very tiny amounts. It's made when cosmic rays hit
the atmosphere. Part of the shower of particles that comes
down to the surface is antimatter. There's like muans and
anti muans as well, but it doesn't last very long
because it smashes into stuff and annihilates, and it just
doesn't seem to be very much of it in the universe,
which is one of the big mysteries. Right. We talked

(20:44):
a lot about how matter and antimatter are symmetric. It's
all the same, just with the flipped number. You might
wonder like, well, why isn't there more antimatter in the universe.
Why is the universe matter and not anti matter? What's
the difference in the end. Yeah, we have a whole
episode on that, and I think we also have a
whole episode on the annihilation of matter and antimatter. Right.
When a matter particle like an electron hits it's antimatter

(21:07):
version a positron, they like disappear and turn into pure energy, right, Yeah,
they can turn into a photon, they can turn into
a z boson, And you're right, they do disappear, right.
It's not like what comes out as a rearrangement of
the bits inside the electron and the positron. This really
is alchemy that we're talking about. You're transforming the energy
from one quantum field the electron of depositron field, then

(21:29):
into a photon field, and then into something else. That
photon can turn into corks or into w's or into
something else entirely. It really is pretty awesome. This annihilation
is like a conduit for transforming matter into something else.
And it's funny that you mentioned that it's all around us, right,
I mean, well, technically it is all around us, because
if there's an electron quantum field all around this, there's

(21:51):
also an anti electron quantum field all around this too. Right.
Is it a separate field or is it the same
field as the electron? Oh, good question, It is its
own field. There's another field there for the anti electron.
We tend to comple them together sometimes in the calculations,
although it gets complicated because there's like left handed versions
of them and right handed versions of them, and the

(22:11):
weak force treats those differently. Dig into our episode about
the weak force and symmetry to understand that more in detail.
But the short answer is, yes, we are surrounded by
quantum fields for antiparticles. Even if there aren't actually antiparticles
around us. Their fields are there, like parking spots are
there even if no cars are in them. Yeah, there's
negativity all around us these days, it seems. But as

(22:33):
we're saying, what's interesting about antimatter is that it's like
regular matter, but it has certain of its properties flipped,
like the charge of the electromagnetic force and charge and
also it's a color and things like that. And so
one thing that regular matter particles we know have is
something called mass, Like it's a little it's a property
of regular matter particles, and that's the thing that gives it,

(22:56):
you know, inertia, and it makes it feel gravity. Right,
it's kind of a measure of how much it feels
gravity or how hard it is to push or pull. Yeah,
mass is one of these amazing things that seems so simple.
We think we understand it. You have an intuitive stance
of what mass is, but when you dig into it theoretically,
it turns out to be kind of complicated. As you
say this, two different ideas of mass there. One is

(23:17):
inertial mass, which is like, when you push on something,
how much does it move? And that's the mass that
appears in Newton's equation F equals M A. Basically, it
relates F how hard you're pushing on something to A
how fast it accelerates when you push on it. And
Newton tells us that the relationship between those two quantities
is mass. That's sort of what inertial mass is. Something

(23:39):
with more inertial mass takes a larger force to get
the same acceleration. Something with almost no inertial mass. You
can accelerate pretty easily with a very small force. That's
conceptionally different from this other concept of mass, gravitational mass.
That's the mass that appears, and like the gravitational force
equation g mm over are squared that tells you, like

(24:01):
how strong gravitational forces between two objects, right, and so,
regular particles have this property that we call mass. I
mean we've called it before in this podcast. Like it's
almost like a label or it's almost like a charge
for the force of gravity, right, Like the electric charge
is kind of like it's a measure how much it
feels electromagnetic force. Mass is kind of like the measure

(24:22):
of how much it feels gravity and inertiap Right, It's
almost like it's like a little property of matter. Yeah,
it's like a little property of matter and you shouldn't
think of it. It's like how much stuff the electron has,
or how much stuff the top cork has. In our theory,
these are all point particles. I have no volume. This
is just like a property of the particle. If you're
comfortable assigning like quantum labels to things, like this thing

(24:44):
has a positive charge, and you don't have to like
figure out a physical place for that charge to live.
You should try to do the same thing with the
mass of the particle. Like the particle just has this mass.
You don't have to like have room to put enough
stuff into the top cork to make heavy. It just
sort of is that massive. There's another interesting level to
dig into there, which is like, is this mass actually

(25:07):
a property of the particle itself or is it a
property of the interaction of that particle with fields, Because
we think that like in a universe without a Higgs field,
all these matter particles, the top cork, the electron, they
would be massless, they would fly around like photons. It's
only because the Higgs field is there that these particles
have a mass. So sort of like a cloud of

(25:28):
Higgs bosons surrounding every particle changing the way it moves
so that it looks like as if it had mass.
So if you want to zoom out, you can just think,
I'm just gonna put a label on these particles. You
want to zoom in, you could think about, like, well,
this particle is sort of like a virtual cloud of
Higgs bosons around it that are changing it, and I'm
just going to label the whole cloud is having this mass.

(25:49):
Do you think of it as a kind of a
label like you said that particles just have just like
electric charge, And so the question is if antimatter is
just regular matter with some of the charges flipped, does
it also flip the label of mass, like does it
also flip how it feels gravity or how it feels inertia? Right,
that's the main question we're asking today. Yeah, and it

(26:09):
really comes down to this basic question about what is
gravity anyway? Is gravity a force the way the other
forces are, you know, the electromagnetic force and the strong force,
who have all their charges flipped for antimatter. If you
think about it that way, then gravity is just another
force and the charge for it is mass, as you say,
And then it would make sense. It would be like

(26:30):
sementric It would follow the pattern if also mass was
flipped for antimatter. Or is gravity not a force? If
gravity is something else? And we've been thinking about it
as a force because we just don't see the curvature
of space and time, and so we've created this fictitious
force to explain the effect of the bending of space
time on the motion of particles and If that's the case,

(26:52):
it would make sense for space time to treat everything
inside of it the same way. Antimatter and matter particles
are both just little bundles of energy and his energy
that bends that space, and so then it would make
sense for matter and antimatter to all have the same
relationship with gravity instead of the opposite relationship. So this
question about whether antimatter feels gravity or anti gravity is

(27:13):
also kind of a question about like what is gravity anyway?
But I guess the main picture of trying to pain
is that you know, like if an electron has a
negative charge, the negative electric charge, and it weighs, you know,
point zero zero zero zero zero something kilograms, doesn't anti
electron not just have positive electric charge, but does it

(27:33):
also maybe way negative through a point zero zeros there
zero something kilograms? And what would that mean for the
anti electron? Yeah, that would be super fascinating, right, And
because we have two different concepts of mass, we have
to think about them sort of individually. Like if a
positron had negative inertial mass, what would that mean? It

(27:54):
would mean that if you push on it in one direction,
it would accelerate the other direction, right, Remember force equals
mass times acceleration. These are vectors, So if mass is negative,
that means that acceleration of force are pointing in different directions.
So you like give it a shove to the left
and it moves to the right. That's what having negative

(28:15):
inertial mass would mean. That's like really counterintuitive. Negative gravitational
mass would be different. It would allow for gravitational repulsion.
Gravity attracts things that both have positive mass. But if
two particles, one with positive gravitational mass and one with
negative gravitational mass meat, they might repel each other, which

(28:35):
would be really interesting because that's not something we've ever seen.
Gravitational repulsion. Yeah, super fascinating. And so let's maybe talk
more about each of these scenarios one at a time.
And so, first of all, let's say that antimatter doesn't
just flip the charges electrical charges of the forces in
regular matter particles, but let's say it also flips its
inertial mass, so it has anti inertia. I guess is

(28:58):
the idea, And like you said, it's kind of kind
of intuitive where you try to push something but it
actually moves towards you. That would be weird, right, That
would be very weird instead of counter through everything we've
understood and everything we've experienced in the universe, that would
be a very strange experience for us to shove somebody
and then have them slam into you. But I guess
maybe it does make sense if you just think about

(29:21):
it as it being antimatter, and where you think you're
pushing it, you're actually pulling it because it feels you're
pushing force the opposite way, So it's almost like you're
just pulling on something, right, Like an electron attracts a
positively charged particle, right, so it doesn't push it when
it gets near it, it actually pulls it. So couldn't
that just be the same for anti mass? It could be,

(29:44):
although it's a bit more general than that. We're talking about.
Any force applied to a positron would then move it
in the opposite direction of that force, whether it's a
gravitational force or electromagnetic force, or the weak force, which
positrons also feel. It's a little bit deeper than just
saying electromagnetism can attract and repel, so what's the big deal.
Now it's applied to every force on this positron, it

(30:07):
would be pretty strange. Yeah, but I mean if you
think about it, like an electron repels another electron, right,
because they have both have negative charge. Now, if you
have an electron and a positron, they would normally attract
each other because they have opposite charges. But then if
it has negative inertial mass, then it actually maybe flips
that force and it does repel. Yeah. I think what

(30:28):
happens there is even weirder because the positron is repelled
from the electron, but the electron is still attracted to
the positron, right, It's still attracted to that positive charge,
and so they sort of like chase each other. Like
the positron gets pushed away from the electron, but the
electron gets pulled along with the positron, So you get
this sort of like weird runaway effect. Yeah. I guess

(30:50):
when that is kind of a way to prove that
antimatter doesn't have anti inertial mass is that, you know,
if you have an electron, it gets attracted to an
anti electron, which means that it doesn't have anti inertia. Yeah,
anti inertia would be really weird. Negative inertial mass particles
would behave very strangely, and this is something we would

(31:11):
have seen because we do see positrons in the world.
We see them in cosmic rays, we can bend them
with magnets. We don't see them doing this sort of
weird behavior of being pushed in the opposite direction of
the force. So negative inertial mass is not something anybody
really considers seriously. When it comes to antimatter. It would
be really bizarre. We haven't seen it, but I wonder
if it's possible, Like could you have maybe a third

(31:34):
version of an electron, not just a positron, with something
that has its opposite charge, but also has negative inertia,
which would act just like another electron to an electron,
Like you would think it was an electron, but really
it's an antimatter electron with a flip inertial mass. Yeah,

(31:56):
negative mass electron. It's certainly possible that there are other
reflect actions of the particles that we're not aware of.
Our we're not limited to just matter and antimatter or
heavier versions. You know, there are theories about like supersymmetric
versions of each of these particles, and so it's totally
possible to come up with another idea like a particle
that it's just like the electron, but with negative inertial mass,

(32:16):
and say maybe it could exist in the universe. Then
you have to answer questions like, well, why was made
in the Big Bang? Where are these? If they do exist,
why haven't we seen them? And if you haven't seen them,
they have to come up with an explanation for why
they don't seem to appear in our universe. But it
doesn't mean that it couldn't possibly exist in the universe.
But I guess you're saying that the antimatter that we

(32:38):
have seen so far, like the anti electrons that we've seen,
seem to have regular inertial mass. Yeah, and this is
not so challenging to observe because we can apply pretty
powerful forces like electromagnetic forces to antimatter particles, which are
rare but not impossible to make into manipulated and we
can see their behavior. So, for example, the discovery of
antimatter was seeing a positron moved through a magnetic field

(33:02):
and bending in a way that an electron doesn't. So
we're pretty sure that antimatter has inertial mass the same
way that normal matter does. All right, Well, now let's
tackle this idea of having anti gravitational mass. Now, is
there such a thing as gravitational mass? I thought gravity
wasn't really a force, It was really kind of a
bending of space. This idea has some interesting history. Newton

(33:24):
considered these things separate. He said, things have inertial mass
and they have gravitational mass. These are different ideas. If
you're on an empty space where there's no gravity, and
objects still had inertia, right, and the force of gravity,
the mass that appears in there didn't necessarily have to
be the same as the mass in F equals m A.
People measured it, and they always found these two things
to be the same. The mass that appears in those

(33:45):
equations were the same, and so people thought, well, that's weird,
what a crazy coincidence of these things really are separate
concepts and yet always managed to be exactly the same.
So that was sort of an unexplained mystery for a
long time. Einstein, when he developed his theory of relativity,
he said, well, let's just assume that these things are
the same. He baked that in to his theory of relativity.

(34:05):
That's not a proof that they are, that's just an
assumption of the foundation of general relativity. He said that
gravity and inertia are basically the same thing. Okay, and
so then what does that mean for having negative gravitational
mass or anti gravitational mass. Well, it means that general
relativity makes a very strong prediction that anything with energy

(34:25):
bends space the same way. And so we think that
antimatter probably feels gravity the same way that matter does.
So Einstein and general relativity say antimatterer should feel gravity,
it shouldn't feel anti gravity, and that's a strong prediction
from general relativity. Well, that's a strong you're saying assumption
about general relativity, right, But it is it possible for

(34:46):
something to have negative gravitational mass, so that if I
throw it at a black hole, it's actually going to
run away from the black hole and not towards the
black hole. I mean, it's possible in the sense that
like anything is possible in the universe, and we don't
know if general relativity accurately describes everything in the universe,
and specifically, we don't know how to apply general relativity
to particles. So it's possible that antimatter breaks general relativity

(35:10):
and that quantum gravity allows for other weird forces on
antimatter particles like anti gravity. But if you just say
we believe in general relativity, then it's not possible for
antimatter to have anti gravity. I see, So if something
could have negative gravitational mass, it would mean Einstein was wrong,

(35:30):
or that general grotivity needs to be maybe expanded. Doesn't
necessarily mean it's wrong, or would you just need to
like add something to Einstein's theory. Well, that's an interesting
philosophical question. I mean, we're pretty sure that Einstein is wrong,
not in the sense that any of his predictions have
been proven wrong, but we don't know how to extend
his theory to quantum particles. It definitely needs some sort

(35:50):
of adaptation, and that might mean that it needs to
be like tossed out and completely replaced with the theory
of quantum gravity. That's a completely different picture of how
space gets bent using like quantum gravitons. Or it might
be that we take Einstein's theory and we quantize it
that we like say, space itself is made of quantum
bits that are woven together, and general relativity emerges from that.

(36:11):
We really don't know whether we need to build on
top of Einstein's theory or whether we need to like
re examine the very foundations of it. But we do
know that can't work in the quantum realm, so it
needs some sort of update. It might be that we
discovered failing only when we see inside black holes, or
it might be that we discovered failing when we examine
the gravitational properties of antimatter. Well, I guess I'm not

(36:32):
quite sure what you're saying. Are you saying that? Okay?
So eince science theory assumes that gravitational mass and inertial
mass are the same, which means that you can't have
negative rotational mass anti gravitational mass, or that you still
could or like, if you have negative inertial math anti
inertial mass, then that would also mean you have anti
gravity irrotational mass. Einstein's theory says you can't have negative

(36:56):
gravitational mass, that that just can't happen because of the
equip into principle. But we don't know that that's true, right,
We don't know what the universe actually does. So if
we discover antimatter with negative gravitational mass, that means general
relativity is wrong in some important way. But maybe wouldn't
that just mean that it has negative inertial mass. Like,
if something has a negative inertial in them mass, then

(37:18):
in in Einstein's formulation, they would also have negative gravitational mass. Yeah,
that's a really cool thought. You're right that general relativity
just requires that they have the same inertial and gravitational mass,
which I suppose would allow for them to both be negative.
But again, we haven't seen particles with negative inertial mass.
So the antimatter we know and we are familiar with

(37:39):
doesn't have negative inertial mass, so then general relativity would
predict that it also has positive gravitational mass M. So
it's then it is possible to have a particle out
there that if you throw at a black hole, it's
going to run away from the black hole. But if
it has both negative and gravitational mass, it would have
the opposite force on it, and then that worse would

(38:00):
push it in the opposite direction, and two opposites resulted
in going the same way. WHOA, So it would still
go towards the black hole. It would still go towards
the black hole, Yes, because they would cancel each other out. Yeah, exactly.
Black hole's force would technically be away from it, and
that would result in a particle moving towards it. So

(38:20):
double bonkers unless um, somehow Einstein's theory is wrong and
they're sort of not the same thing, right exactly, the
possibility that Einstein is wrong and that antimatter particles have
positive inertial mass and negative gravitational mass. All right, well,
it seems like, um, it is possible maybe to have
anti gravity from being an antimatter particle, to have an

(38:42):
anti inertial or anti gravitational mass seems possible. But I
guess then the question is does it actually happen? What
are some experiments we've done to try to find the
answer to this question. So let's get into that, But
first let's take another quick break. All right, we are

(39:11):
feeling a lot of anti emotions here talking about antimatter,
anti gravity, anti mass, anti everything. It's a very contrary episode.
We're going up, we're going down. We're going anti up
and anti down all at the same time. Can you
go anti anti? Those would be your double negative mass particles, right,

(39:32):
be anti anti attracted to a black hole? What would
you call the antimatter version of your parents, sister, your
anti anti These are tough questions we're asking today, assuming
people are still listening or the left in an anti huff.
All right, we're talking about whether or not antimatter feels
anti gravity, which is kind of turned out to be

(39:54):
a pretty complicated question because, first of all, you have
to think about whether antimatter has anti inertia mass or
anti gravitational mass, and whether or not if they're the
same thing according to Einstein, or maybe they're not. I
don't know. I don't know. I feel like from all
this theoretical discussion, it seems like you're saying that it's
not possible to have anti gravity. I think it's very
unlikely that antimatter has anti gravity just because general relativity

(40:19):
is so successful. The YadA YadA YadA, dot dot dot.
On the other hand, why do we do experiments. We
don't do experiments just to like yawn and check the
boxes off of theoretical predictions. We do experiments because we
want to explore the universe. We want to find crazy,
shocking things that we can't explain that let us pull
the rug out of everything we thought we knew and

(40:40):
build up new ideas about the universe. So this is
definitely something we should check. We should go and see
whether antimatter follows our expectations or anti follows them. I
think I see what you're saying. You're saying you're anti
anti gravity, but you're pro the government giving you more
money to run experiments. Is that kind of what I'm
sensing here. I it's a little um contradictory position here.

(41:03):
I think it's just exciting to go out and ask
basic questions, like, hey, does antimatter of f all up
or down? And it's incredible to me that almost a
hundred years after we've discovered anti matter, we still don't
really know the answer to that. Like, experimentally, it turned
out to be surprisingly tricky to do experiments with antimatter, right,
And specifically, you're talking about measuring I guess, the gravity

(41:25):
of a particle, right, I mean, you can measure the
gravity of a planet, of a person, of a banana,
but it's hard to kind of talk about the gravity
of tiny little particles because they feel very little gravity.
It's hard to even measure the gravity of a banana.
Like you can measure the weight of a banana, you
put it on a scale, but there you're measuring the
gravity of the Earth. Right. The Earth is pulling on
the banana. If you have two bananas in the room

(41:47):
next to you, it's pretty hard to measure their attraction
between themselves because gravity is so weak. It's like ten
to the thirty times as weak as electromagnetism, So it's
something we typically ignore. Right, you have two bananas on
your table, you don't expect to see them like creep
towards each other if you leave them alone. But they
would in space, Right, that's the idea. If you were

(42:08):
floating out there in space and you have two bananas,
eventually they would become a bi banana. Banana na na. Yeah.
But even doing that experiment in space would be hard
because the gravity is so weak that it might get
swamped by other stuff like the solar wind would probably
blow on those bananas, pushing on them harder than the
force of gravity between the bananas. Or if the bananas

(42:29):
have like a little bit of residual positive and negative charge,
like you rubbed one on your pants accidentally and giving
it some static electricity, then those forces, even a few
electrons on the surface of each one, would be more
powerful than gravity. So gravity is super hard to measure
for small things because it's so weak, it's swamped by
everything else. It's like trying to listen to a whisper

(42:50):
during a really loud concert. But I guess if you
said the experiment the right way and make sure everything
doesn't have a charge, the two bananas would come together eventually,
because that is what happens out there in space, right,
That's how planets get formed and asteroids and the sun. Right. Yeah,
we think that's the basic process for forming all of
the structure in the universe. And we've done some really

(43:11):
pretty awesome virtuoso experiments measuring the gravity of like little things,
things about the size of a centimeter and involves isolating
them from everything else and seeing very very small motion,
which people observe by like attaching a mirror to the
object and shining a laser on the mirror and seeing
the laser spot like move a tiny little bit so
that you see that the object has moved. These are

(43:33):
really super precise experiments, very very difficult to do, but
still there. With macroscopic objects, we're talking about like things
the size of a millimeter or centimeter, not individual particles,
so we can measure the mass of tiny, regular matter
of things. But I guess it's hard to do it
with antimatter, right, because that's really the question we're asking
today is like, if you have something made out of

(43:54):
or a whole bunch of antimatter in one spot, would
it feel anti gravity? That's the experiment. That's also hard
to do it because it's hard to put together a
lot of antimatter. It is. We can make antimatter at CERN,
for example, we smash matter into targets and the whole
spray of stuff comes out, including some antimatter, and we
can filter it out and do experiments with it, and
we do that kind of thing. But we make like

(44:15):
pico grams of antimatter every year it's CERN. So you
want to make like a bananas amount of antimatter, it
would cost zillions of dollars and take years and years
and years. So instead of making really big objects out
of antimatter, we try to do really precision experiments with
much smaller amounts of antimatter. Also, would be super dangerous
to come to make like a even a piece size

(44:36):
or raisin size amount of antimatter, because then if it
touches regular matter, it's it's going to destroy the Earth basically, right,
It's one of the most efficient ways to release the
energy inside matter, which is a huge amount, right equals
mc squared. C is a really big number. The speed
of light C squared is a really big number. Is squared.
So as you say, like a raisin's worth of antimatter

(44:59):
combined with the reason but have as much energy is
like a nuclear detonation. So yes, if you are making
antimatter in your kitchen, be very careful. Yeah, we're very
anti that kitchen. A recipe there, But I think what
you're saying is that you can make antimatter in your
colliders and certain, but you haven't made enough to really
do gravitational experiments to see whether antimatter feels anti gravity.

(45:22):
We actually have done a few experiments with antimatter that
do ask this question about the effects of gravity on
these particles, but they're very, very difficult to do and
not as sensitive as we'd like yet. What I mean,
so you did the experiments but didn't reach a conclusion
or what couldn't get the data. So they've done the experiments.
They take anti protons and they combine them with anti
electrons to make anti hydrogen. And the reason they do

(45:45):
that is you need neutral antimatter. You don't want any
electric or magnetic fields affecting your antimatter. You want to
measure only the gravitational force on these objects. So they
make neutral anti hydrogen, which is super awesome anyway, because
then they can do things like study the spectral properties
of it and see if anti hydrogen behaves the same
way as hydrogen, which this whole other really fascinating field

(46:07):
of science to try to figure out what is the
difference between matter and antimatter. But because they have a
collection of these anti hydrogen atoms, they can also see
like what happens when they float there, Like do they
drift down or do they drift up? Well, I guess,
first of all, how do you hold a bunch of
anti hydrogen? So you create this I guess by bringing
together anti electrons and anti protons, and then they make

(46:30):
answer hydrogen and then you get a little cloud of
anti hygen. What do you do with that? Do you
keep it inside of a bottle? It's really challenging to contain.
You're absolutely right. What we do is we keep it
in a magnetic bottle. It doesn't work very well. A
magnetic bottle is good at holding charged particles. Because magnetic
fields bend the path of charged particles. So, for example,
the beams and the large hadron collider are kept moving

(46:50):
in a circle because of very powerful magnets or plasma,
and a fusion reactor is kept in a magnetic bottle
to keep it from escaping because it's filled with charge particles.
It doesn't work very well all on neutral particles, but
even anti hydrogen has a magnetic moment because the spins
the particles, they do feel magnetic fields a little bit,
so we can keep them in like a very very

(47:11):
bad magnetic bottle, and it works best if those anti
hydrogen atoms are slow, if they're cold, they're not like
flying around with high velocity, then this very weak bottle
tends to contain them. But that's a challenge because making
anti hydrogen that's moving slowly is hard because you have
to combine the positrons and the anti protons which come

(47:32):
in in beams, so you have to have like slow beams,
like gases of these things like merge together. The whole
thing is experimentally very tricky. Yeah, it sounds pretty hard,
but they have done this kind of and what did
they find. Did they find that it falls at the
bottom of this bad bottle, or does it flow it
up to the top of the bad bottle. So there's
a very cool experiment at CERN. It's called the Alpha experiment,

(47:53):
which stands for anti hydrogen laser physics apparatus. Is a
terrible acronym or really awesome experiment. And they do not
see anti matter falling upwards very fast. I mean, some
of these hydrogen atoms do float up and some of
them do float down. And because the difficulty of measuring gravity,
it's not a very precise measurement. What they can do

(48:14):
is they can say that anti hydrogen doesn't have a
negative gravitational mass of sixty five times the inertial mass.
So if anti hydrogen had a negative gravitational mass of
like a hundred or a million times the inertial mass,
they would have seen it because they would have flown
upwards really fast. They don't see them flying upwards really fast,

(48:34):
so they can say if it does have a negative
gravitational mass, it's not that big. So it's like very imprecise.
So far, if they had a lot more anti hydrogen
or more time, they can make more precise measurements. They
could sort of narrow this down statistically, all they can
do right now is like rule out a really crazy
result where anti hydrogen has a negative gravitational mass that's

(48:57):
also much bigger in magnitude in the inertial mass. But
could it have a varying different gravitational mass in magnitude
than than it's inertial mass. I mean, we're exploring the
bonkers universe theory out here, so maybe right. And this
is also sort of like just the way that they
can express their results. Even if the theoretical options are well,
it either has a positive gravitational mass or negative one

(49:20):
times the inertial mass. We can't tell the difference between
those two. Experimentally, all we can do is tell the
difference between negative sixty five and positive one. So we
can rule out negative sixty five, we can't yet rule
out negative one. M I see. So they done the
experiment and they don't have a clear result, but it's
not an anti result either. It's not. And they're just

(49:41):
getting started, right, and so they're going to make more
anti hydrogen and they're gonna do more precise experiments. There
are other experiments coming online at CERN to measure this
in other ways and so in the next few years
we hope to get more precise measurements of the gravitational
properties of antimatter. All right, Besides cern are there other
experiment is that we've done or are going to do

(50:02):
to measure the gravity of antimatter. These kind of particle
physics experiments are really the most direct way to probe this.
You can also do other sort of thought experiments to
think about the effects of antimatter. For example, like the
protons that are inside me and you, we talked earlier
about how they have quarks inside them, Well, they also
have antimatter inside them. Like the gluons that are inside

(50:25):
the protons, they sometimes turn into cork anti cork pairs
like very briefly before going back to being a gluon
the way like a photon will turn into a particle
antiparticle pair briefly and go back to being a photon.
So that means that like you and I are partially
made of anti matter. If antimatter had anti gravity in
some weird way, then we would see the effect of

(50:47):
that on protons. And we don't see any weird behavior
of protons. They don't seem to have any sort of
like deviation between their inertial and gravitational mass. So that's
a strong hint that antimatter probably has normal. Yeah, we
all have a little bit of negativity inside of us,
a little bit of a contrarian inside of us. But
I think you're saying that we all are made a

(51:08):
little bit of antimatter and it doesn't seem to be
affecting the regular matter. But at the same time, it's
a very tiny amount, isn't Isn't it like super duper
negligible the amount of antimatter inside of us? Yeah, so
it would be pretty negligible. All right. Well, maybe to
wrap up here, I think we've sort of maybe a
little bit debunked the idea of anti gravity for antimatter particles.
I mean, theoretically, it seems like it's not really possible,

(51:30):
or I mean it's possible, but we would mean we
would see a very different universe. And also these experiments
that you describe kind of rule it out as well.
So if that's true, then if you can't have anti gravity,
what does that mean about our theories of the universe.
I think I agree mostly with what you say, but
I always hold out a little bit of hope for

(51:51):
the crazy result. You know, even if the theory very
strongly says that can't happen, that just makes me more
excited to go and discover it that way, because it
means undermining that whole theory and starting from scratch, and
to me, those are the most exciting moments in science.
So I think you're right that the theory very strongly
suggests that antimatter doesn't have anti gravity, But that still
makes me hopeful. Wait, what makes you hopeful that maybe

(52:14):
one of these experiments will get a shocking result and
discover antimatter fluting up in a gravitational field and give
us a clue about the next direction we should take
for gravity, for understanding whether it is a quantum field
or whether space itself is quantized, and how to get
to quantum gravity. All right, well, I think what you're
trying to say is keep giving you money to run
these experiments just to make sure that the universe is

(52:37):
not actually crazy. I'd say, we never know where the
next surprise, where the great big learning moment about the universe,
will come, and so it makes a lot of sense
to go out there and do careful experiments and see
if the universe is the way we expect or not?
Where is to the anti way we expect? All right,
we'll stay tuned, as I guess we keep exploring this
idea of antimatter and what gravity actually is. I guess

(53:00):
it's hard to prove that there's such a thing as
anti gravity if we don't actually kind of know what
gravity is. That's a good point. We anti know gravity,
right like, It's still kind of up for the babe
whether general relativity, which is Einstein's theory, is right or not,
and how it matches up with quantum mechanics. It's one
of the deepest questions at the heart of modern physics,

(53:20):
how to unify these two pillars of our understanding of
the universe. All right, well, I guess we'll keep waiting
for news from the fringes of physics. We'll keep funding
those experiments. You mean it's above my pay grade? All right? Well,
we hope you enjoyed that or anti enjoyed that. Thanks
for joining us, See you next time. Thanks for listening,

(53:47):
and remember that. Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast from
My Heart Radio, visit the I Heart Radio app Apple
podcasts or wherever you listen to your favorite shows. No.