Daniel and Kelly’s Extraordinary Universe - Does anti-matter feel anti-gravity?
Episode Date: January 17, 2023Daniel and Jorge talk about whether anti-matter falls down, or up!See omnystudio.com/listener for privacy information....
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No, Hey, Jorge, do you have your anti-matter 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. Is that why you're 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 anti-matter of hunger.
Hi, I'm Jorge McCartunist and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist and a professor at UC 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
of 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, 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 follow-up question i just mean that it's subjective you know one person can love bananas
another person can hate them hmm just slippery slope some people find them appealing welcome to our podcast
daniel and horhe explained the universe a production of our hard 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
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 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 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 is that we are here, because there is a lot of things in the universe that matter.
and also a lot of things that antimatter.
Like bananas.
I wasn't joking that bananas produce antimatter.
That's a real thing.
Oh, yeah, but isn't antimatter dangerous?
Like if you touch antimatter, you explode?
Antimatter, when it hits real matter, it will annihilate into photons.
But bananas contain potassium, which is unstable.
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, makes me glow.
Makes me feel lighter, too.
Isn't potassium 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.
It's all sorts of other things that also radioactively decay.
So it's actually antimatter 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 enveloping us. And for a lot of those things, we still have big questions about them.
Even big things like gravity. Antimatter is fascinating. It appears in science fiction, but it's also
something 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 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.
are governing the universe itself.
And you're right, because antimatter is so rare, there are basic questions we have about
its properties.
Yeah, including something as basic as gravity, gravity which, you know, we 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 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's
It seems to be pretty reliable, right?
Have you ever noticed any change in your gravity?
I mean, I don't want to inquire about your weight or anything like that.
That's also personal information.
That definitely explains her, right?
It's not that I'm getting heavier and heavier.
It's that the gravity of the Earth itself is increasing.
Sounds like you have an amazing experiment in Ed Hand here.
But it does raise a lot of interesting questions about gravity and antimatter,
specifically whether or not they are the same for.
everything in the universe.
That's right.
Anti-matter 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?
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 I think today we're focusing on a more physics question, which is just like, when gravity does its thing, where does antimatter go?
Does it 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 fear.
fundamental particles. We think 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 baseballs, 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 you think antimatter minds that we call it
anti-matter? 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 anti-matter galaxies that might be out there in deep
space on their podcast, they're probably calling us the anti-matter. Yeah, or maybe there's a third
opinion, you know, why does it have to be so adversarial these politics 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 had thought about anti-matter and
whether it feels gravity or whether it feels
anti-gravity or whether it feels gravity.
So thanks very much to everybody who participates in this segment 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.
Gravity, because anti-gravity might be things pushing each other apart.
What do you think? Gravity or anti-gravity?
Antigravity.
I feel like antimatter 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 there uncle gravity?
I think that antimatter feel gravity in the same way that normal matter feels gravity.
And anti-gravity, I think, is, we don't know if that even exists.
Well, if I remember your lessons on anti-matteryms.
matter, it should feel gravity because antimatter is just regular matter with opposite chart.
I know that matter feels gravity because of the bending of space time towards something with mass.
I don't really know what antimatter is and whether it exists in another field or spatial field than mass.
But I suppose in the fields that antimatter exists, maybe there's the bending of that field,
which would be called anti-gravity.
So I'd say it does feel anti-gravity.
a lot of very pro and anti-positions on this question.
I'd my emotions go up and down as I was listening 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 anti-matter feels negatively about a lot of things.
Yeah.
Anti-matter 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, first of all?
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 and protons and neutrons,
which are of course made of of quarks 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,
magnetic force and the glue on for the strong nuclear force. And so you and I are like this 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 quarks and
another type of quarks. And wait, a third type of quark, right? Three quarks? How many quarks are there?
There are six quarks that we have discovered. The up quark and the down quark, those two are the ones
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 quarks,
make protons and neutrons,
and you add electrons to complete the atom.
Right.
So we're made out of those kinds of particles,
and most of the stuff in the universe
is made out of those three particles, right?
Like the planets, the stars,
the comets out there, the asteroids,
whole galaxies are basically those three kinds of particles, right?
Yeah, we think that iron.
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 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, the 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. I know sometimes particle physicists distinguish between matter particles
and force particles. But when we're talking about matter 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 used to that. But also that's the stuff that
we're made out of, but there's also other stuff in the universe in this category of matter, right?
There's like heavier electrons and heavier quartz. Yes, there are other versions of
of these particles.
This is one of the really fascinating things
about particle physics is that the particles we know,
the electron, the up quark, and the down quark
have these reflections.
That's what I meant earlier about the sort of philosophical definition
of opposite.
Because with these particles, we know there 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 other.
upcork. It's called a charm quark. And then there's a second reflection, right? So there's the muon and then the tau. There's 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 axis. They're heavier versions of each of these. Well, not all the particles, right? The force particles don't have 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 were made out of, they're heavier cousins. And also, in some ways,
if you also take the force particles and lump it a while 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 we're
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.
There's another version of the electron,
which we call the anti-matter version of the electron.
Sometimes we call it a positron,
which has charge plus one.
And so it's reflected in this like different direction.
And that's true also for the muon and for the upcork
and for the downcork and the top cork.
All these particles have their anti-matter versions.
So the anti-matter 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 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 and a positron are the same, except they react oppositely to these fields.
The same electromagnetic field, which pushes 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 quarks, they don't feel the electromagnetic force, right?
So they don't have electrical charge, right?
Quarks do have electromagnetic charge, but they're really weird.
They're like plus two thirds or minus 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, the strong nuclear force.
So they have the electric charge and they also have this color charge for the strong nuclear force.
Okay, so quarks feel the color charge and also the electric charge now then is an anti-quark, something that has both of those things.
flipped or just one of those things flipped?
Both of those things get flipped for an anti-quark, 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.
It's like there's a positive version and a negative version.
And one is the antiparticle 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.
But the way we think about in particle physics is like you take a particle, you apply the
anti-particle 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 a photon and you apply this operator to it.
You just get the photon back.
It's sort of like symmetric.
So the photon serves as its own antiparticle.
Because I guess 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 there's an electric field there, it does not bend
the path of the photon.
If you don't have anything to flip, then you can't have an antimatter cousin.
Is that kind of generally the rule?
That's generally the rule.
And that holds also, for example, for gluons,
gluons are the particle that transmit the strong nuclear force.
and they do carry color.
They carry this charge.
And so you can have anti-glu-ons.
You can take a glue-on and make the anti-version of it.
It has the opposite color.
All right.
So that's matter and anti-matter.
But one thing I guess all matter 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 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,
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 particles.
Yeah, all the fermions definitely do have mass.
Even the neutrinos 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 to interact with the Higgs boson,
you have to have an anti-matter 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 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 then 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, let's take a quick break.
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Jeopardy truthers who say that you were given all the answers believe in...
I guess they would be Kenspiracy theorists.
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Are there jeopardy truthers?
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Yeah, ever since I was first on, people are like...
They gave you the answers, right?
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They gave you the answers, and you still blew it.
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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 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 bed across the room or to ship stuff across the world or to launch stuff into outer space.
That would be pretty awesome.
Forget other stuff.
How about ourselves?
We could all be flying around.
Finally, you'd get that flying car.
Exactly, right?
It could be an anti-car.
Well, that's one of the exciting things about all of these open questions is that once you
understand the way the universe works, you might discover something really surprising.
That 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 years.
We're still waiting, Daniel.
What's the hold up?
Well, you know, anti-matter is not easy to study.
It's sort of all around us in 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 muons and anti-muons as well.
But it doesn't last very long because it smashes into stuff and annihilates.
And there just doesn't seem to be very much of it in the universe, which is one of the big
mysteries, right?
We talked 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 is it?
Isn't there more anti-matter in the universe?
Why is the universe matter and not antimatter?
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 its anti-matter 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.
the positron. This really is alchemy that we're talking about. You're transforming the energy from
one quantum field, the electron of the positron field, then into a photon field, and then into
something else. That photon can turn into quarks or into Ws 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
there's 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 couple 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 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 anti-particles.
Even if there aren't actually anti-particles around us, their fields are there.
The, 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 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 color and things like that.
And so one thing that regular matter particles we know have is something called mass,
like it's a property of regular matter particles.
And that's the thing that gives it, 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 sense of what mass is.
But when you dig into it theoretically, it turns out to be kind of complicated.
As you say, there's two different ideas of mass there.
One is 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 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 conceptually different from this other.
concept of mass, gravitational mass.
That's a mass that appears in like the gravitational force equation,
GMM over R squared,
that tells you like how strong gravitational force is 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 measure of how much it feels
the electromagnetic force.
mass is kind of like the measure of how much it feels gravity and inertia, 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 as like how much stuff the electron has or how much stuff the
top core has.
In our theory, these are all point particles.
They 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 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 it heavy. It just
sort of is that massive. There's another interesting level to dig into there, which is like, is this
mass actually 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 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 could just think,
I'm just going to put a label on these particles.
If 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 as having.
this mass. You think of it as a kind of a label, like you said, that what particles just have
just like electric charge. And so the question is if antimatter is just regular matter with some
of the charges flip, 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 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
symmetric. It would follow the pattern if also mass was flipped for antimatter. Or is gravity
not a force? Is 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,
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 is 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 also kind of a question about like, what is gravity anyway?
But I guess the main picture we're trying to pin is that, you know, like if an electron has a negative charge and a negative electric charge and it weighs, you know, 0.000-000-something kilograms, does an anti-electron not just have positive electric charge, but does it also maybe weigh negative 0.000-000-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 would mean that if you push on it in one direction, it would accelerate the other direction.
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 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 meet, they might repel each other,
which 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.
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, the 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 the idea.
And like you said, it's kind of counterintuitive where you try to push something, but it actually
moves towards you. That would be weird, right?
That would be very weird and sort of counter to 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 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?
same for antimass?
It could be, 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 would be pretty strange.
Yeah, but I mean, if you think about it, like an electron repel.
is another electron, right? Because they 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, and I think what happens there is even weirder because the positron is repelled from the electron. But the electron is still attracted to the positron. 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 wouldn't that that be 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-inertion.
Yeah, anti-inertia would be really weird.
Negative inertial mass particles would behave very strangely.
And this is something we would 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 consider 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 version of an electron,
not just a positron, but 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, negative mass electron.
It's certainly possible that there are other reflections of the particles that we're not aware of, right?
We're not limited to just matter and antimatter or heavier versions.
You know, there are theories about like super symmetric versions of each of these.
particles and so it's totally possible to come up with another idea like a particle
that is just like the electron but with negative inertial mass and say maybe it could
exist in the universe then you have to answer questions like well why was it 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 you 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 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
and to manipulate, and we can see their behavior.
So, for example, the discovery of antimatter was seeing a positron move to a magnetic field
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 considered these things separate.
He said things have inertial mass and they have gravitational mass.
These are different ideas. If you're out in empty space where there's no gravity, an object 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 MA. People measured it and they always found these two things to be the same.
The mass that appears in those 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. That's not a proof that they are. It's just an
assumption at 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 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 antimatter 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 is it possible for 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
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.
Oh, I see.
So if something could have negative gravitational mass,
it would mean Einstein was wrong.
Or that general relativity needs to be maybe expanded.
Does it necessarily mean it's wrong?
Mark, 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 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 we really don't know whether we need to build on top of Einstein's
theory or whether we need to like reexamine 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 quite sure what you're saying are you
saying that, okay, so Einstein's theory assumes that gravitational mass and inertial mass are
the same, which means that you can't have negative gravitational 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, gravitational mass.
Einstein's theory says you can't have negative gravitational mass, that that just can't happen
because of the equivalence 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 mass,
then 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 doesn't have negative inertial mass.
So then general relativity would predict that it also has positive gravitational mass.
So 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 force would 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 the particle moving towards it.
So double bonkers.
Unless 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 it is possible maybe to have anti-gravity
from being an anti-matter particle,
to have an anti-inertial or anti-gravitational mass.
It 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.
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Yeah, mine's brown-olar, but with an H.
So it looks like brown-holer.
Okay, that's, okay, yours might be worse.
We can never get married.
Yeah.
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that you're on an airplane and all of a sudden you hear this attention passengers the pilot
is having an emergency and we need someone anyone to land this plane think you could do it it turns out
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We get to the bottom of questions like these.
Join us as we talk to the leading expert on overconfidence.
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Listen to no such thing on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.
All right, we are feeling a lot of anti-emotions here
talking about antimatter, anti-gravity, anti-mass, anti-everything.
It's a very contraring 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-anty?
Those would be your double-negative mass particles, right?
It'd be anti-anty-attracted to a black hole.
What would you call the anti-matter version of your parent's sister?
Your anti-ante?
These are tough questions we're asking today.
Assuming people are still listening,
are they left in an anti-hoff?
We're talking about whether or not anti-matter feels anti-gravity,
which is kind of turned out to be a pretty complicated question
because, first of all, you have to think about
whether antimatter has antinertial mass or anti-gravational mass
and whether or not if they're the same thing
according to Einstein or maybe they're not.
I don't know, Daniel, 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 is
so successful, yada, yada, yada, 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 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-antagravity, but you're pro, the government giving you more money to run experiments. Is that
kind of what I'm sensing here? I sense a little, um, contradictory.
position here. I think it's just exciting to go out and ask basic questions like, hey, does
antimatter fall up or down? And it's incredible to me that almost 100 years after we've discovered
antimatter, we still don't really know the answer to that like experimentally. It turns out to be
surprisingly tricky to do experiments with antimatter. Right. And specifically, you're talking about
measuring, I guess, the gravity 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 next to you,
it's pretty hard to measure their attraction between themselves
because gravity is so weak.
It's like 10 to the 30 times as weak as electromagnetism.
So it's something we typically ignore, right?
You have two bananas on your table.
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 floating out there in space and
you had two bananas, eventually they would become a by banana, a banana, nana. 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 have like a little bit of
residual positive and negative charge, like you'd rubbed one in your pants accidentally and
given 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 during a really
loud concert. But I guess if you set the experiment up 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 pretty awesome virtuoso experiments measuring the gravity of like little things,
things about the size of a centimeter.
It 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 really super precise experiments, very, very difficult to do.
But still, they were with macroscopic objects.
We're talking about, like, things the size of a millimeter or a centimeter, not individual
particles.
So we can measure the mass of tiny regular matter 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, or a whole bunch of antimatter in one spot, would it?
feel anti-gravity. That's the experiment that's also hard to do 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 a whole spray of stuff comes out, including some antimatter. We can filter it out
and do experiments with it and we do that kind of thing. But we make like picograms of
antimatter every year at 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, it would be super dangerous to make even a P size or raisin size amount of antimatter
because then if it touches regular matter, it's going to destroy the earth, basically, right?
Yeah, it's one of the most efficient ways to release the energy inside matter, which is a huge
amount, right?
E equals MC squared, C is a really big number, the speed of light.
C squared is a really big number squared.
So as you say, like a raisin's worth of antimatter combined with a raisin, but have as much energy as like a nuclear detonation.
So yes, if you are making antimatter in your kitchen, be very careful.
Yeah, we're very anti-that kitchen recipe out there.
But I think what you're saying is that you can make antimatter in your colliders and CERN,
but you haven't made enough to really do gravitational experiments to see whether antimatter feels anti-gravity.
We actually have done a few experiments with antimatter that do ask this question.
But the effects of gravity on these particles, but they are very, very difficult to do and not as sensitive as we'd like yet.
What do you 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 antiprotons and they combine them with anti-electrons to make anti-hydrogen.
The reason they do 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, but this whole other really fascinating field 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 could 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 anti-hydrogen, and then you get a little cloud of anti-hydrogen.
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 in a circle,
because of very powerful magnets or plasma in a fusion reactor is kept in a magnetic bottle to
keep it from escaping because it's filled with charged particles it doesn't work very well 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 into like a very very 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
antiprotons, which come 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 had done this kind of. And what did they find? Did they find that it falls to 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, which stands for anti-hydrogen laser physics apparatus.
This is a terrible acronym for a really awesome experiment.
I mean, they do not see antimatter falling upwards very fast.
I mean, some of these hydrogen atoms do float up and some of them do float down.
And because of the difficulty of measuring gravity, it's not a very precise measurement.
What they can do is they can say that anti-hydrogen,
doesn't have a negative gravitational mass of 65 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 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 measure.
is 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 also much bigger in magnitude than the inertial mass.
But could it have a varying different gravitational mass in magnitude
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 result.
Even if the theoretical options are, well, it either has,
as a positive gravitational mass or negative one times the inertial mass, we can't tell the difference
between those two. Experimentally, all we can do is tell the difference between negative 65 and
positive 1. So we can rule out negative 65. We can't yet rule out negative 1.
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 getting started, right? And so they're going to make more anti-hydrogen
and they're going to 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 experiments that we've done or are going to do 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 corks inside them, while they also have antimatter inside them.
Like the gluons that are inside 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 you and I are partially made of antimatter.
If antimatter had anti-gravity in some weird way, then we would see the effect of 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 gravity.
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 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 it?
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 big debunked the idea of
anti-gravity for antimatter particles.
I mean, theoretically, it seems like it's not really possible.
Or, I mean, it's possible, but it 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 could,
can 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 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's still.
still makes me hopeful.
Wait, what makes you hopeful?
That may be one of these experiments will get a shocking result
and discover antimatter floating 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 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.
Or it's the anti-way we expect.
All right.
Well, stay tuned.
As I guess we keep exploring this idea of antimatter and what gravity actually is.
I guess 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.
Yeah, that's a good point.
We anti-know gravity.
Right? Like, it's still kind of up for debate, 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.
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 and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio.
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