Does dark matter have an anti-particle?

Published Jun 11, 2024, 5:00 AM

Daniel and Jorge talk about the relationship between matter, dark matter and anti-matter!

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Hey, Daniel, have you run out of ideas to explain dark matter yet?

You know, we're not even close.

None of them have worked out, you.

Know, also not even close to working out?

Are you close to having any ideas?

Oh? We have so many ideas.

Are they all going in the right direction? Though?

We'll never know until one of them works out?

Being what you need is like an idea that's an anti idea, you know, going in the opposite there.

Or maybe an anti idea will collide with all of our ideas and make pure podcast energy.

Maybe we'll finally blow.

Up, We'll annihilate our lack of understanding.

No, no, we don't want to annihilate our careers. We just want to blow up.

I wouldn't mind annihilating some ignorance.

Hi, I'm morehem, a cartoonist and the author of Oliver's Great Big Universe.

Hi. I'm Daniel. I'm a particle physicist, and I'm always wondering what crazy new idea is going to revolutionize physics.

You're wondering which idea or you're trying to come up with an idea to revolutionize physics. Wouldn't be more productive to do the latter.

I'm trying to do all of them. Man, I'm trying to come up with ideas. I'm looking forward to the ideas, and I also sometimes just enjoy fantasizing about some time in the deep future when those ideas have already been found and proven right, and humanity is just like marinating in the understanding.

Man.

M you seem to have like three brains here working at the same time, past, present, and future. I mean that's part of the problem, Daniel, hmm.

Maybe I need a better cooling system. I'm inn overheat.

Yeah or yeah, I'll just focus focus on the present and what ideas are there. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.

In which we focus on the past the present and the future of our understanding of the universe. We trace you through the history of human thought to show you why we think what we think in the present, and we try to sketch out for you the future of human understanding, the ideas that are being considered, the crazy ideas that are just over the horizon, and try to even anticipate what's past the edge of human imagination.

That's right, because science is the ultimate idea generator. Coming up with the explanations for how the universe works, what's going on in it, what are things made out of, and maybe what ideas themselves are made out.

Of the universe is sort of like a big cosmic mystery novel. We are gathering clues and trying to crack the case. We don't actually know if there's an answer. There's no guarantee that the universe does actually make sense and that it can be understood by us. But along the way it's going to take some creativity, some inventiveness, some openness to crazy new ideas that might rock our world.

I guess the mystery novel is better than science fiction for the universe genre.

I guess so science fiction to me is just like mystery novels about.

Science the size of get murdered or what.

Do you mean?

Nobody needs to get murdered, But it's always a mystery. Like when you're reading a science fiction novel, you're wondering, like, how does this universe work? What are the laws of that universe? Truly the same process we do in actual science for the real universe we're actually living in. We're trying to crack the case and figure out what are the rules? How does this little universe work?

I see, it's not a who done it? It's more of a what done it?

What's it doing? Yeah?

Exactly why done it? Or is that more philosophy?

Yeah? Maybe maybe more like how's it doing it?

How's it going? This is just stray a little far from the mystery genre here. Yeah, it is a big mystery. There are huge mysteries out there in the universe. How long will it be around? And what are the things in it made out of? We still don't really know.

There are so many questions that we don't have answers to, and so many ideas that we are considering. When you look back at the history of human physics and think about the progression of our understanding. It can seem like maybe it was linear, like we understood this and then that, and then this other idea came along. But the truth is that it's a multi branching tree of explorations, people going down dead ends all the time, and when you fast forward to the current forefront of human understanding and ignorance, you see that happening in real time. You see lots of different ideas being explored to explain the current mysteries of the universe.

Yeah, because science and exploration is a human process, and so like any human process, it's we're bound to make mistakes, we're bound to go down the wrong path, We're bound to be totally convinced that one idea is totally true, but then later we find out that maybe it's.

Not exactly And it all seems so painfully obvious in hindsight, Like, man if I was around back then, I totally would have figured that out and written that seminal paper. But it's so much harder when you're actually standing at the forefront of human understanding. And one of the biggest mysteries that we're trying to crack today is what is the universe made out of? What is all the stuff that's out there. We know that most of the universe is not made out of the kinds of particles that we are made out of, atoms, made of quarks and electrons, but something else, something much more mysterious, something we have not yet cracked.

Yeah, we've talked about in the podcast a lot. There's a whopping ninety five percent of the universe that we have no idea what it is, what it's made out of, where did it come from, how does it work. That's a pretty big percentage of the universe.

Yeah, we don't know what kind of books it likes to read, whether read science fiction or mystery or just romance novels. I mean, we basically know nothing about this stuff, that's right.

We don't know if it killed anyone, whether it's there was just circumstantial evidence.

Was it in the library with the candlestick or not. Nobody knows.

Yeah, no, I think it was in the particle collider with the proton accelerator.

Yeah. Maybe. And a big chunk of that ninety five percent is something we know is a kind of matter. It's stuff. It's something that's out there, but we can't see it or touch it, and so This mystery of dark matter is something that really preoccupies particle physicists in particular because we want to understand what is that dark matter made out of.

It's been one of the biggest mysteries in the last thirty forty years where we looked at into the cosmos and found that there are things holding galaxies together that are kind of invisible and intangible.

Absolutely's back even more than thirty or forty years. We've been confused about it since the nineteen thirties. It's a long history of confusion about dark matter and many, many ideas about what it might be.

Yeah, and as you said, particle physicists are interested in it, but we don't even know if if it is a particle, right Daniel.

We indeed have no idea what it is, whether or not it's a particle, and if it's a particle, whether it's a new, weird kind of particle we have never seen before.

So today on the podcast we'll be tackling the question could dark matter be its own anti particle? Wait, wouldn't an anti dark matter particle be called a light matter particle?

A lot of people get confused about these two topics, or I got a lot of emails where people try to connect these two ideas. Dark matter antimatter are the two things the same, it's the missing anti matter action explanation for dark matter. These things are very confusing to hold in your head at the same time. So I thought it'd be fun to do an episode to explore the connections between dark matter and antimatter, because there really are some interesting cutting edge ideas about dark matter and anti matter.

You want to bring this topic into the anti.

Dark that's right. I want to illuminate dark matter, not anti illuminate it.

You want to explain it, not anti confused people, or you do want to anti confuse people.

I guess I'm confused about whether I want to do that or not.

Yeah, well this is an interesting question, and so as usual, we were wondering how many people out there had thought about the possibility that dark matter could be its own anti particle.

Thanks very much for everybody who plays for this segment of the podcast. If you'd like to hear your voice on the future episode, we would welcome you to participate. Please just write to me to questions at Danielanjorge dot com and I'll add you to the list.

So think about it for a second. Do you think dark matter could be its own anti particle or do you anti not think that the dark matter could not be its I think you just did your anti failed to do that.

Yeah, I'm gonna give that a dark anti chuckle.

There you go. Here's what people had to say.

Well, I would say that dark meta could be pretty much anything, because we have no idea what it really is.

But if it would be its.

Own antiparticle, wouldn't it annihilate itself on a large scale? If it's anything like Meta and Antimeta no idea, Well, then.

There would need to be a partner particle in the dark matter part antiparticle, and the dark matter particle would annihilate when they met dark matter antiparticles gone wild.

Well, I don't really see why dark matter couldn't be its own antiparticle. I think I remember you saying that photons are their own anti particle, But I really have no idea.

I think that dark meta can't be its own anti particle because if it was, it would annihilate and produce photons, which we would observe, and I don't think we've observed that.

Is documenta A particle is this shoe already. I don't know. To be honest, I don't understand the question really. So if it's a particle, how can it beat its own antiparticle?

All right, a lot of interesting, thoughtful answers. A lot of people seem to be a little bit confused about what do you even mean and whether dark matter is even a particle?

Like do we know that for sure or not?

Yeah? Yeah, all good questions, really great comments here.

Yeah, it might help I maybe explain the question to them a little more.

No, that's all the fun, man.

You enjoy airing their confusion.

I enjoyed trying to get a sense for what the average podcast listener will think when they see the topic of the episode.

Well, pretty awesome answers here, And so let's dig into it, Daniel, what do you know about what dark matter is made of?

It? Yeah, so, as you said earlier, we do know something about dark matter. We have a sort of precision ignorance, and that we know very well how much of this stuff there is. We look out into the cosmos, so we see evidence for it everywhere. All that evidence is gravitational, but it tugs on stuff and changes the whole ructure of the universe. As you say, it's the reason that galaxies can spin so fast and still hold themselves together. There isn't enough gravity from all the luminous matter, the stars and the gas and the dust to hold galaxies together as they spin so fast, and yet they don't like throw their stars into intergalactic space. Very often, we see evidence of dark matter in the very early universe from the light in the cosmic microwave background, which shows us ripples in that early universe plasma. Those ripples are affected by the density of dark matter as everything was sloshing around. So there's evidence for dark matter everywhere in the universe. We know that it's there, we know that it's stuff. It has gravity, but we don't know what it's made out of.

Is that technically what makes it matter the fact that it has gravity, or the fact that it has mass that then maybe has gravity to it, or can something you have gravity without mass.

Something could have gravity without mass, because remember gravity is actually connected to energy more deeply than it is to mass. Mass is just a kind of energy. So for example, you get enough photons into one spot in space, they will curve space and create effectively gravity. In principle, you can even make a black hole just out of photons, so you don't need mass in order to curve space and have gravity. One reason that we're convinced that dark matter is matter is because of how it behaves as the universe expands. Think about normal matter, atoms, protons, et cetera. As the universe expands, space gets bigger, that stuff gets more dilute. It gets less dense because you've got the same number of protons and now you've got more space, so the density of that stuff is decreasing. Dark matter acts exactly the same way as the universe expands. The density of dark matter changes exactly the same way the density of protons and electrons does, and that's different for other kinds of stuff like photons radiation. The density of photonic energy changes differently than for protons because photons also gets their wavelength stretched as the universe expands, and dark energy is something totally different. Its density doesn't decrease as the universe expands. But dark matter behaves exactly the same way other kinds of matter do, and so we're pretty convinced that dark matter is actually a kind of matter.

I guess what is it about dark matter that makes it dilute like regular atoms.

Is it's inertia, or it's mass or what.

We don't know. Right. If it's a particle, then that makes perfect sense because you can increase space, but you're not changing the number of particles, and so it will dilute in exactly that same way. If it's something else other than a particle, then you're not me. But this is something we notice, and it's a really big clue that tells us that dark matter really is matter. Obviously, it has energy, and it seems to contribute also gravitationally to those tenser equations the same way other kinds of matter does. But more importantly, I think it dilutes in the same way it matter does. Why that is we don't know, but it feels like a big clue that it's a kind of matter.

And if it's a kind of matter, does have to be a particle. Orking have matter without particles.

We've never seen matter without particles. That doesn't mean you can't, right, We've only ever studied a tiny fraction of all the energy in the universe. The kind of stuff that makes up atoms and gas and dust and ice cream and kittens is five percent of the universe, and our quantum field theory with these fundamental fields that ripple to make particles and all that stuff, that explains that very very well. But it's a little bit of a reach to say that everything else in the universe has to follow the same rules. Maybe it does, and it certainly would be nice and neat in a confirmation of quantum field theory if dark matter was described by quantum fields and the ripples in those fields were particles. But we don't know, right. Dark matter is a big chunk of the universe and it's not something we understand, so there's no guarantee that it's made of particles.

But the leading theory of it is that it is sort of quantum some kind of quantum particle, or is it not even that established, or it may it's the only thing you got.

I think it's something interesting about the way science is done.

Right.

We don't know that dark matter is particles, and yet most of the theories of dark matter are that it's a particle. Why is that? Mostly because that's the only thing we've got, right. It's so much easier to talk concretely about various kinds of new particles because we know how to do that. We had that toolkit already. It's much harder to be creative and be like, huh, what if dark matter or something else. We talked once on the podcast about whether dark matter was a kind of unparticle, something which looked the same no matter how much you zoomed in, you never like revealed its discrete quantum nature. But those theories are much more speculative and much harder to deal with, just because we've never seen that kind of matter, So you just really out there into the wilderness Intellectually. That doesn't mean that dark matter has to be a particle. But the reason that most of the theories of dark matter are particles is because we're all particle physicists trying to figure this out.

Particle physicists trying to get grant to study dark matter.

Perhaps, Yeah, I mean, if you invite a carpenter over to fix a hole in your house, what's he going to do? Suggest some carpenter. So that's what we're doing. We're patching up our lack of understanding the universe using the only tools we have.

Well, I guess, if it is a quantum particle, what do we know about it? We know that it would have mass and maybe inertia, but maybe it wouldn't feel the electromagnetic force or the strong force or the weak force.

But it does feel gravity.

That's right. We know that it feels gravity because everything feels gravity. Everything that has energy feels gravity. We're confident doesn't feel the strong force or the weak force or the electromagnetic force. There's a couple of asterisks though, that are really important. One is there could be more forces. There could be some new dark electromagnetism, and there could be like dark photons, so there could be all sorts of forces that only dark matter feels. Right, It doesn't mean that dark matter doesn't feel any force. It just might not feel our kinds of force. And also, the second really important caveat is that dark matter could contain multitudes. Right, our kind of matter is many kinds of particles. We got six quarks, we've got six leptons, we got all sorts of bosons. Why do we imagine dark matter is one particle. Well, that's just like the simplest first idea. Dark matter could be very complex. It could be lots of different particles with different masses and different kinds of interactions. Just like our kind of matter. So when we speak about dark matter, we shouldn't be like monolithic and say it does feel this, it doesn't feel that. There could be lots of different kinds that do and don't feel, various different kinds of forces.

It could be a day, not an it.

Yeah, exactly what are dark matter's pronouns? I don't know.

Well, I mean, like you're saying there might be different kinds of dark matters.

Yeah, exactly. You can imagine a whole different set of state of dark matter. And maybe most of it doesn't feel electromagnetism in the weak force and gravity, but maybe some tiny fraction of it does. Right, Maybe some tiny fraction of it isn't actually that dark.

Or maybe I wonder there could be an infinite number of kinds of dark matters.

Oh man, that blows my mind. Could there be an infinite number of kinds of particles?

Yeah?

I suppose, So there's no limit to the number of states. You could have, the number of kinds of quantum fields. Yeah, sure, let's have an infinite dark matter. Awesome, there's a new theory right there.

The infinite dark man, the infinite dark Yeah, theory of.

Cham cham's infinitely dark universe.

Right right, Like, maybe we feel some forces in common with dark matter, but maybe there's other kinds of matter out there that we have no relation to, but maybe dark matter does.

Yeah, absolutely, there could be. I think also, you should come up with a color palette, like a color called infinitely dark. You know, there's all these shades of black people invent hmmm, infinitely dark. Yeah, that'd be a good coat of paint right there.

All right, we'll copyright it and we'll make no money from it.

So your idea, man, don't give me any credit.

I'll take it, all right. Well, there's the as you said, there's this idea that maybe dark matter is something weird, and there's other kinds of weird stuff out there in the universe, and sometimes people are maybe quick to wonder if those two things are connected. And one weird thing in the universe is antimatter. And so let's talk about whether dark matter is related to antimatter or whether it's anti not related to antimatter, one of those two. But first, let's take a quick break.

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All Right, we're talking about dark matter, and we're posing the question whether dark matter is maybe related to anti matter, like is dark matter made out of antimatter? Or I guess specifically, is dark matter its own antimatter?

So first, let's just think about antimatter as a completely separate direction, like we're talking about matter versus dark matter, a completely separate question, is matter versus antimatter?

I like you're using versus feels like there's a there's gonna be a fight, like shark versus tornadoes, shark versus godzilla.

You know, can't cong versus godzilla? Yeah, there you go.

Consider first a completely separate kind of question, like if you're trying to get to know somebody. You might ask, you know, do they like mystery novels versus science fiction novels. That's one dimension. You might also ask, like, do they like Mexican food or Italian food? Matter? That's a separate kind of question.

No, it's the same thing.

People who like science fiction always like Mexican food.

Wow, there are plenty of pizza love and science section readers out there. I promise you.

That's they're fakes. I don't believe it.

So back to anti matter is this is like a subset of a kind of matter. Antimatter is a totally normal thing in our universe. We have particles like electrons and protons, and what we've noticed is that we also have other kinds of particles like the positron and the anti proton. These are very very similar to the particles we know and love. They just have the opposite charges. And so it turns out that like the quantum field that gives you an electron can also do something else. It can wiggle in another way that gives you a particle with the opposite electric charge, the positron, And the same is true for the quarks. The quark fields can also wiggle in a way to give you anti quark particles. And so what we notice is that the fields that give us matter have this capacity to also generate antimatter.

Well, this is a part that it's always confused me. I know that antimatters matter with the charges flip, but sometimes some particles have multiple charges, right, Like quarks can field multiple forces, like the electromagnetic force and also the strong force. So does that mean that an antiquark has all of its signs flip or some of it sigence flip? Are the different flavors of sign flippage.

Well, what you call matter and what you call antimatter is a little bit arbitrary. Like we could have called the electron matter and the positron antimatter, or we could have called the positron matter and the electron antimatter, and that's arbitrary from field to field. Also, like we could keep calling the electron matter and call the anti quarks matter. Also it's a little bit arbitrary. Really, what we're trying to get at is that there's a symmetry in these fields. These fields can do two different kinds of things, and so specifically, like anti quarks have the flipped electric charge, but they can also have a flipped color charge and a flipped weak charge. So if you have, for example, a red quark, it's antiquark as the opposite electric charge. It also has an anti red color for the strong force.

And what about the weak force.

Yeah, so the weak force actually is two different charges, which makes it very complicated, and those are also flipped. And that's one way to understand what happens when matter and antimatter meet. A lot of these properties that the quarks and the electrons have. These are conserved quantities like charge and color and whatever, and when matter and antimatter meat, they balance each other out in terms of those quantities. So you can take a particle that has electric charge and then another one that has the opposite electric charge. You can put them together to make a photon which is neutral, which has no electric charge. You can only do that because the accounting works out. They balance each other out to get you to zero.

But I guess what do you what do you call a cord that has the opposite electric charge, the opposite weak force charge, but the same strong force charge.

Is it still anti.

It's a little bit arbitrary, but that particle would have an anti particle with all of those charges flipped.

Oh, I see, So you use anti when all the charges are flipped. But if something he only hell, they has one thing flipped, you just call that like another particle.

It's more than we talk about this in terms of pairs, right, this is a particle antiparticle pair. But again, which one you call anti in which one you call not anti is totally arbitrary, So you can make up whatever rules you want. Really, the thing is that the fields can generate two different kinds of particles with opposite characteristics.

H Daniel, I'm starting to suspect here that maybe you just call this thing wrong.

I'm not anti against that.

Yeah, I mean I think you're saying that antimatters really just matter.

Yes, antimatter is just another kind of matter.

Yes, yeah, And the anti is just like if you pick one kind of matter and you flip all its signs and you call that it's antimatter, but not necessarily right.

Yeah. In the same way there are relationships between other bits of things we call matter, like the electron and the muon and the towel. These are all very very similar particles. They just have different masses. There's some relationship between them. We see lots of different kinds of these relationships, these patterns in our particle physics, and there's lots of different dimensions there. There's like the symmetries of the leptons. This is symmetries of matter and antimatter. This is the symmetry between the quarks and the leptons. There's all these like reflections and patterns we see in the particles, most of which we don't understand, and the names for them are terrible because they date back to when we understood it even less well.

I think I figured it out.

I think what you're saying is that it makes sense to call something an anti electron or an anti quark or an antiproton, but it doesn't really make sense to use the term antimatter. Like that term doesn't really apply to anything specific.

It does not really apply to anything specific. Really, what it does is tell you what kind of things we tend to not have in the universe, like matter really is like about the stuff that we see in the universe. We see lots of protons, we see lots of electrons, so we call those matter. It turns out there are other states which tend to not appear very often in the universe. They do sometimes, but not very often, and so that's why they get called antimatter.

So really there should be like matter, and then there should be anti the most common matter.

Really, matter contains multitudes, right, there's lots of different things that matter can do, right, and only a few of those states exist. In the same way with muons. Muons don't exist very often in the universe. They're created sometimes in collisions and then decay away. We don't call them antimatter because they're not around very often.

No, but do you know what I mean?

Like, I think what you're saying is what you call antimatter, typic you really what you mean is anti common matter? Yeah, sure, Like the term antimatter doesn't really exist.

Yeah, but then how do you deal with particles that are never around anyway? Like we have top quarks, those things never exist except on their specialized conditions, and we have anti top quarks. Neither of those things really exist very often, So the whole thing's a mess. I totally agree.

Yeah, Like you can have anti top quarks, but it doesn't make sense to call it anti matter.

Yeah, exactly. Neither top quarks nor anti top quarks are ever around in the universe and any significant density, and it is arbitrary which one you call anti in which one you call not anti. The takeaway is that all these particles can do this really interesting thing where they can create two different states. Electrons really are cousins of positrons. The electron field can do this thing. It can wiggle in an electron way and in a positron way. So then we think about dark matter, where like, hmm, what about dark matter? Can dark matter do that? Also?

Well, the question is it can dark matter have it's an anti version of it? Or could dark matter be an anti version of some other particles?

Oh? I see, The question is does dark matter have its own anti dark matter? Right like, if dark matter is a particle, do the fields that generate those particles can they also make another kind of particle which we call anti dark matter and again totally arbitrary, which when you're call in dark matter, which when you call it anti dark matter, doesn't make any difference. The question is is it doing both things or is it some new weird kind of particle where it can't do that it is its own anti matter where like instead of a field that can generate pairs like positrons and electrons. It's some weird field that generates only one singular kind of particle. We're not considering the question whether anti hour matter is dark matter. Is dark matter made of positrons and anti quarks. That's not possible because we know it doesn't feel electromagnetism and all that stuff, and antimatter does.

Right.

Well, that's kind of the question I was wondering about. Could somehow maybe our understanding of our fields and charges is not quite complete, and so if you flip certain things in our kind of matter, maybe you get dark matter.

I don't know all the matter particles that we know about, except for neutrinos have charges, right, So electrons and muons and towels and quarks and all that stuff have charges, And so if you flip them and you make anti matter, then they still have charges. It's just the opposite charges, and so that means they really can't be the dark matter. There is a question about neutrinos. Neutrinos we don't understand very well, and it's possible the neutrino's actually a potential example of a particle that might be its own anti particle and it's one reason why people wonder about dark matter. Is dark matter like the electron where it has a particle and an antiparticle pair, or is dark matter like the way people might think the neutrino is where it is its own anti particle, right right. But here's where I win the Nobel price, Daniel. What if the electromagnetic cores that we know about, we think it only has plus or minus two charges, but what if it has a third charge? Well, there is a third charge. Zero neutrinos have zero electric charge.

Right right?

Well, okay, what if there's a fourth charge and somehow if you take like an electron and you flip it to this fourth charge, then we can no longer interact with it, And so it would sort of behave like dark matter, wouldn't it?

Love the creativity, totally willing to explore this with you, But it feels like electric charges are either zero or positive or negative, and if it's not zero, then it's got to be positive or negative, and then it's going to feel electricity, in which case it's not dark matter. So I don't know how to escape in that mathematics.

Well, it's sort of like, aren't some particle don't some particles have three charges.

So the strong force has three charges for example, red, green, and blue, instead of just plus and minus. Oh, I see, So you want to expand electromagnetism to say it's not just on a single number line, it's on some more complex structure.

Yes, that is my Nobel Prize proposition.

I guess I would say, why does it have to be electromagnetism. Why not just have these particles have no electric charge? Why change electromagnetism.

Well, we're trying to figure out if it could maybe explain dark matter. Right, it does have some other dimension of electromagnetism. Maybe it could be dark matter.

It's possible that electromagnetism is different from what we think it is. Although electromagnetism like the best tested theory out there, like to nine decimal places we understand electromagnetism, So that'd be a pretty tricky needles to thread.

That's why I would be awarded the Noble Price.

Yeah, or at least five or six. Absolutely for six Yeah, I mean swing for the fences, man, if you're going for it.

Absolutely, yeah, I'll take all of them for the next one hundred years.

All right, Yeah, we'll send them all to your infinitely black painted mansion. But I think it's more likely that dark matter just has zero electric charge. I mean, we have examples of particles with no electric charge, like neutrinos. That's not exotic or weird. So why can't dark matter just have no electric charge?

Okay, it sounds like you're not entertaining the notion that maybe dark matter is some sort of antiversion of our regular matter. And the question you actually want to ask today is is this sort of property of dark matter?

Right?

Like?

Does dark matter.

Behave like the other kinds of particles where it has an anti version of itself?

Or is it some weird thing named after mysterious Italian physicist at Torre Mayerana, where it is its own antiparticle somehow?

Now I guess why is this question more interesting than mine?

I think all questions are interesting. Of course, If the dark matter is somehow a reflection of our kind of matter, it would have to be a reflection in some new way we haven't even imagined. In that sense, it wouldn't be like antimatter. It'd be like yet another reflection the way we see patterns between electrons and muons and towels, and we see patterns between quarks and leptons. Say, for example, we discover dark matter, and we discover that every particle has a weird dark version of itself. There's a dark upcork and a dark top cork, and a dark electron, and that, like our kind of matter is like weirdly reflected into dark matter. Then you can make a connection between matter and dark matter and say, oh, there's some reflection here. It'd be a different relationship than the one described by matter and antimatter, but there would be some sort of symmetry there. I think maybe that's what you're going for. That would be possible, and that would be awesome. And if we discover dark matter and see that structure, I'll make sure that you get credit for it.

Awesome. Thank you.

But it sounds like you want to explore this question of whether dark matter can be its own antimatter. And I didn't mean to minimize it. I was just wondering, why is this question interesting? Why does it matter if something is its own antimatter.

I think it's interesting because it's one of the few tools we have right We've been thinking about particle dark matter for a long time, and for a long time people have been assuming that, well, if dark matter is a particle, it's probably like the other ones, in which case there's some anti version of it, like people call the dark matter particle Kai. So maybe there's a Kai and an anti Ki, and the two things like both exist in our universe. That's sort of like the standard approach. Most dark matter theories have a particle and an anti particle for the dark matter, but we haven't found any of those things yet. We've been looking for this particle for a long long time and have seen it, So people are trying to be creative and people thinking, well, maybe it's a little different from what we imagined. Maybe it operates in a different way, and this field is a little bit different. And it's important also for how you look for it, because it changes how that particle gets mass. If the particle is its own anti particle, then it doesn't get its mass from the Higgs field the way our particles do. Has to get its mass in some other way, and that means you can't use the Higgs field to discover dark matter.

Wait wait, wait, let's maybe take a step back. So I think the scenario trying to paint for people, is that dark matter is out there, it's a particle, and it's subject to some certain forces. Definitely, not the electromagnetic force, perhaps definitely gravity, maybe some other kinds of forces out there. And the question is, could that dark matter have its signs flipped to where it becomes antimatter, but then it's its own antimatter as opposed to having dark antimatter just exists out there in the world.

Yeah, exactly right.

You're asking a very specific question, which is could it be its own antimatter, not just like does it have antimatter anti dark batter, but whether it's its own anti matter particle.

Yeah, saying something is its own anti particle, it's kind of weird. It's kind of just like saying there is no anti version of it. There's just one example. Another maybe a clear way to say it is like, does this field, the dark matter field that makes dark matter particles make two kinds that are paired in this way we've been talking about, like electrons and positrons, quarks and anti quarks, or does it just make one that just make a single solitary particle. And we do have some examples of particles that are their own anti particle or don't have antiparticles. However you want to say it, Like the photon, right, what's the anti particle of the photon. There isn't one. The photon already has zero and all those charges you flip them, you still get zero. The electromagnetic field can make a photon, doesn't make an anti photon.

Mmm.

So in the same way, are you saying that the question is whether dark matter has any charge at all in any of the force fields.

Really, that's kind of what you're asking, right.

That's a clever idea. But if dark matter is its own antiparticle, it's possible for it to still have some charge. It would just mean that there is no anti version of it.

Oh what do you mean?

Like if it had a charge in some kind of force field, could just flip it and wouldn't that be its anti matter version?

But that flipped version might not exist, right, Like take neutrinos for example, trios very concrete example, because we don't actually know if anti neutrinos even exist in the universe. We've seen particles we call them neutrinos. We talk about it as if there are neutrinos and anti neutrinos. But we're not even actually sure if anti neutrinos are a thing. It could be that all the neutrinos we've ever seen are just neutrinos, right, And so you might ask, well, but neutrinos have no charge, but they do have weak charges, right, They interact with the weak force. So there are those weird hypercharges and isospin and all those weird weak quantum numbers. But it could just be that there aren't the anti versions of them, Like you say, just flip the charge. But it's not like you can take a particle and just like flip a switch on it to make the anti version of it. The field has to be capable of generating that. Maybe the fields just don't, right. I mean, there's a different quantum mechanical math that describes fields that make one kind of particle and fields that make pairs of particles. And it's possible, and we've worked out all the mathematics to have particles that don't have antiparticles or are their own antiparticles, whichever way you want to say it.

Wait, so the neutrino doesn't have an anti neutrino, or we've never seen an anti neutrino, or it technically could have one, but we've never seen one.

We've seen lots of neutrinos. We don't know whether there are anti neutrinos.

But theoretically there could be, right, like, all, do you have to do this flip design?

There are versions of the theory of the universe in which neutrinos have anti neutrinos, and that makes neutrinos a specific kind of particle. They're called direct particles that can generate both the particle and the anti particle. But it could also be and it's totally consistent with everything we've seen in the universe so far and all experiments that neutrinos are their own antiparticle or have no antiparticle. There's another kind of mathematics for particles invented by Meyron that explains everything we've seen in the universe without anti neutrinos.

But what do you take that math and just flip the sign on the of the trino.

What do you get? Does it just explode?

Does it just break down the theory or what I'm trying to figure out what you mean?

Take the math and flip the sign, then you have another field, right, so instead of having one field that's generating the two particles, you can imagine there's another field out there that generates like a complimentary particle. So instead of a single field generating a pair of particles, now you are inventing two different fields, one for a neutrino and one for another particle, which is the trino with all of its charges flipped, which you'd be tempted to call an anti neutrino, But it's not generated from the same field, so it doesn't really have that particle anti particle relationship as.

Opposed to like an anti electron is not a different field or it is it the same field.

No, an anti electron and an electron are generated from a single quantum field. It's two things that a single field can do. Single field can ripple an electron like way, and it can ripple in an anti electron like way. There's no separate anti electron quantum field.

So why can't the neutrina do that.

It's possible that it does, right, we just don't know. Is a neutrino direct like in which case there is a neutrino and an anti neutrino generated by one field, or is a neutrino mayerna, in which case it can only generate one particle. We just don't know which is which. And the same question applies for dark matter. Is dark matter it's own antiparticle? Is it like that way the neutrino might be, or is it the way the electrons and quarks are.

I guess I'm losing a little bit of tra here because it seems like the question of whether dark matter can have an anti version. I think what you're saying is that it could have its own and antiversion, or we could just ignore it that it can have an its anti version.

It's a question about like what is the nature of the particle dark matter? Is it like electrons and positrons? Are there particles out there that are paired and dark you know, the kai and the anti kai? Or is dark matter a different kind of particle, not like electrons and positives, made in a different kind of way.

Whose field doesn't work both ways? Is what you're saying.

Yeah, exactly, that's the difference. Like some particles fields work both ways and can generate matter and anti matter versions of them, but some for some reason don't. And you're saying it sounds like the reason is like, we just don't include it in the math.

There's a way to write the mathematics where that doesn't happen. You can write it in a way that doesn't. You can write it in a way that doesn't for the trio. The jury is still out about which is the correct mathematics for dark matter also.

But for like the photon, what we know that it can't or what?

So the photon is different. It's neither direct nor myrona because it's not a matter particle. Photon is radiation, right, It's a wiggle in the electromagnetic field. So it's not a fermion at all. It's a boson. It's a totally different kind of particle. That's why the photon and the z boson these don't have anti particles. They're a different kind of ripple in a different kind of field.

It sort of feels like we're asking is dark matter an apple or an orange? We've never seen an apple or an orange. We don't even know if apples or oranges exist.

I mean, if you want to make the frend analogy, no, if you want to make the fruit analogy, that's awesome. It's like saying everything we've ever seen as an apple, except maybe neutrinos are oranges. Is dark matter an apple or an orange? Well, we've never seen an orange, but we also never seen dark matter, so who knows that's the fruit analogy?

Well, right, isn't that what I said? Like, we're saying, but we have seen apples, is dark matter and apple and orange? We don't know if oranges even exist.

Yes, that's right, but we do know apples exist, yes, but we have this mathematics for oranges. We're like, oh, that's.

Interesting, suggest that maybe oranges exist, but we don't know for sure, and we don't know for sure any seems to be an arbitrary choice. Well, the universe is kind of arbitr The universe picks we have two options. We don't know which it is. We're close to figuring out if the neutrino is an apple or an orange.

We don't know, but we have these two competing kinds of mathematics, and we want to be creative about dark matter because we're worried, frankly, that we've been too close minded, that we're too focused on the kinds of matter we're familiar with. So trying to break out of that box a little bit and consider other kinds of fruits.

So then the question we're really asking here today is is dark matter an orange or an apple?

Right?

Sure?

I want to dig into what it would mean for dark matter to be either of those fruits, and what that means about what it's made out of. Possibly, So let's dig into that for first, Let's take a quick break.

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All right, so then the question we're really asking here today is is dark matter an apple or an orange apple means that it can have its an antimatter version of it, and orange means it cannot.

I love first of all that the vocabulary for particle physics is so bad that we have to borrow it from fruits. Now, yeah, that makes it clearer somehow.

Yeah, it does to me.

I mean, you know, when you use jargon, it just kind of for the last mind.

Apples and oranges are also jargon. It's just different.

But I know apples and I know orangines. That of our listeners know apples and oranges. We're really asking if dark matter is an apple or an orange, and so what would it mean for it to be an apple? What would it mean for dark matter to have anti matter versions of itself as opposed to it being an orange, which would mean it cannot have an anti version of it if.

It's an apple. If there's an antimatter and a matter version of dark matter, that means something important. It means that it interacts with the Higgs boson and it gets its mass from the Higgs field. In order to get your mass from the Higgs field, you have to be a particle anti particle pair. That's absolutely essential. The Higgs field will not interact with you if you don't have a matter and an antimatter version of yourself.

How do you know, though, how has the Higgs boson.

It's part of the way the Higgs mechanism works, you know. As an electron is flying through space, it interacts with the Higgs field and it makes momentarily positrons. Like the mathematics of the interaction between particles and the Higgs field just doesn't work without the antimatter as well.

Wait, it doesn't work as well, but it does work, or it doesn't work at all.

No, sorry, it just does not work if you don't have matter and antimatter in addition.

Or at least the possibility of having an anti version of yourself.

Right, Yeah, those fields have to be able to do both things. Has to be an apple field in order to interact with the Higgs field.

And if it cannot, then you don't feel mass. You don't have mass.

Or what if it cannot, then you do not feel the Higgs field, which has two important consequences. One, it means if we can't use the Higgs boson to discover it. If dark matter has a matter and antimatter version, then that means that it interacts with the Higgs field. That means if we make a bunch of Higgs bosons, sometimes those Higgs bosons will turn into a dark matter an anti dark matter pair. We could like make a bunch of Higgs bosons at a large hadron collider and some of them could turn into dark matter. That would be very exciting. The other thing is, if you don't interact with the Higgs field, it means you don't get your mass from the Higgs field. Means you can't make this kind of matter from Higgs bosons. It means you have to get your mass from some other mechanism. Right. Remember, the Higgs field is one way to get mass, but not the only way that things get mass. It's just one example. If there are particles out there that are oranges that are their own antimatter, then if they have mass, they don't get it from the Higgs field, and that might be the case for neutrinos. That might even explain why neutrinos are so crasy, low mass, much lower mass than everything else in the.

Universe, because they don't interact with the Higgs field. They get their mass from something else.

That's the idea, right, That's one reason why people are suspicious that maybe neutrinos don't have anti particles because neutrino mass is super tiny. It's like a billion times lower than the masses of electrons and quarks and these other particles. It's very very small. It suggests that maybe they're getting their mass in another way.

So then the question, the repercussions of this question then is whether or not dark matter interacts with the Higgs field or that's one of the repercussions.

Yeah, that's one of the repercussions. And that's an important one because it means if dark matter gets mass. I remember, the mass of dark matter is the thing that like shapes the universe and bends space times that we get galaxies like this is an important consequential thing. Where does the mass of dark matter come from? If not the Higgs field, But it also has consequences for how we see it. If dark matter interacts with the Higgs field, that means we can make it in colliders. It means fundamentally it also has to feel the weak force in some way. Some part of dark matter at least has to, which means that we could maybe interact with it and our detectors and all these millions of dollars we spent building quiet tanks underground looking for dark matter, might see a signal. But if dark matter is not, if it's an orange and it doesn't get its mass from the Higgs boson, then something else is making most of the mass in the universe, and it means it's much less likely we can use our particle physics experiments to discover dark matter.

Well, that's a pretty big bed on apples. Well, it sounds like you're saying like, if it can interact with the Higgs, then we can maybe see it in our colliders, because in our colliders we can make higgs, and so you could use those higgs to make dark matter. But we haven't so far, Right, we have not so far. Isn't that evidence towards saying maybe dark matter is it orange?

Yeah? Exactly. Well it rules out some versions of the apple. There's always ways to escape these bounds. Maybe it's a different kind of apple, or maybe it's a really low mass apple or something. But yeah, we have never seen Higgs boson turned into dark matter so far. That's one reason to motivate this kind of creativity, to think outside of the apple box and imagine, you know, maybe dark matter is actually a banana. Who knows?

Sounds like you're getting on top of your apple box here poizing about fruit collisions.

Maybe dark matter is just a smoothie after all.

Yeah, there you go.

It's a quantum mechanical smoothie superposition of all the possible fruits.

Right right, And this episode is brought to you by Jump a Juice.

And Sherman Williams Infinitely dark Pace.

I feel like we just spent an hour trying to ask a question of whether a dark matter interacts with the Higgs field or not.

Yeah, we have just started with that question.

Yeah, let's go back in time.

Let's pull another fruit from the either and let's use that to go back in time. No, but do you know what I mean, Like, does it all just come down to that one question, does dark matter interact with the Higgs field or not? And the second question I guess would be how will we find out?

I don't think that's the only question. I think more fundamentally, we're just curious about the nature of dark matter. That's a consequence of it. But we're wondering, like how many different kinds of matter can there be in the universe? Is dark matter an example of a new kind of matter, or is it a weird version of the neutrino? Is it actually neutrinos? Fundamentally, we just want to know, like what kinds of stuff can the universe do? Because the more kinds of ways we can see the universe wiggle, the more clues we might get about simplifying that, about drilling down to the next layer of reality and understanding why we have all these weird reflections. Why are there electrons and muons and towels and matter and antimatter and quarks and leptons. Aren't they all just like putting together tiny little squiggly bits of the deeper theory. The more we gain and understanding the kinds of ways quantum fields can wiggle, the closer we are to figuring out what's underneath it all. So I think there's a deeper mystery there just about the nature of dark matter, not just whether it interacts with the Higgs field. That's an important consequence and effects whether we can see it.

We just want to know if dark matter is an apple or an oinge, or even if oranges exist.

Apparently we don't.

We don't, but we do have experiments coming online pretty soon to try to figure out if neutrinos are their own particle or not. We have a whole episode about this, and also about the fantastically mysterious life of Ettore Mayorana, who disappeared strangely on a sea voyage and nobody ever heard from him again. So check out the episode about whether neutrinos are Mayorana particles. That might give us a clue about whether the universe allows matter particles to be their own anti particles, or whether oranges exist.

Do we have an episode coming up about colliding apple or what? Have you collided with an orange?

We didn't before, but now we do.

Just make apple pie, all right?

Well, another interesting exploration into the ideas that particle physicists are considering about what the nature of matter out there is, including dark matter, maybe the biggest kind of matter there is in the universe.

Some day in the future, somebody will listen to this podcast and think, Man, those folks had no idea. The answer was right in front of them all along.

It was a banana.

The whole time plot twist from the first episode, we've been saying it's a banana.

We've been definitely laying the pipe for that plot twist.

Yeah, yeah, we've been peeling away at the plot twist for a long time. All right, Well, we hope you enjoyed that. Thanks for joining us, See you next time.

For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, Discord, Instant, and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is us dairy tackling greenhouse gases? Many farms use anaerobic digesters to turn the methane from maneure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.

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Daniel and Jorge Explain the Universe

A fun-filled discussion of the big, mind-blowing, unanswered questions about the Universe. In each e 
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