Speaker 1: Hey, Daniel, I have a question for you, very important.
Speaker 1: All right, what is it? How close are we to
Speaker 1: having real life lightsabers? You're asking a physicist that question.
Speaker 1: I would ask the same question to my favorite engineer. Wait,
Speaker 1: do you think it's an engineering solution? Do we need
Speaker 1: like some kind of breakthrough in theoretical physics first? No,
Speaker 1: I mean the science fiction authors have done their job
Speaker 1: already and they passed it on to the physicists. Oh yeah,
Speaker 1: and the physicists I figured out how to do it. Well,
Speaker 1: you know, we've been smashing photons together to see what happens,
Speaker 1: and how does that do as a lightsaber? Well, so
Speaker 1: far it makes a really awesome sound, like but kind
Speaker 1: of cut through swords and deflect like guns. That's the
Speaker 1: engineering problem. Hi am or handy cartoonists and the creator
Speaker 1: of PhD comics. Hi. I'm Daniel. I'm a particle physicist
Speaker 1: and a professor at UC Irvine, and until a moment ago,
Speaker 1: I had never made a lightsaber sound with my mouth. Yeah,
Speaker 1: we could tell that was terrible, Daniel. All right, let's
Speaker 1: hear your lightsabers sound. Right, sounds a lot more accurate. Well,
Speaker 1: we'll let the listeners vote I think the coolest sound though,
Speaker 1: is when they clash, you know, because they're like woman,
Speaker 1: it's or something. When they hit that's even worse, Daniel,
Speaker 1: everyone knows it's oh, that was much better. All right,
Speaker 1: You're right, that's definitely better. And those movies are ingrained,
Speaker 1: are burned into my brain, for better or for worse,
Speaker 1: like somebody inscribed them with a lightsaber, like somebody was
Speaker 1: their hand and said I would only remember these movies
Speaker 1: for the rest of my life. It would be pretty
Speaker 1: awesome if the movies themselves were a Jedi mind trick,
Speaker 1: but I think they were. They certainly got a lot
Speaker 1: of my money out of my pocket. These are the
Speaker 1: movies you want to pay for. But anyways, welcome to
Speaker 1: our podcast. Daniel and Jorge explain the university production of
Speaker 1: My Heart Radio, in which we pull off the physics
Speaker 1: mind trick of attempting to understand the universe. We convince
Speaker 1: ourselves and hopefully convince you, that the crazy cosmic mysteries,
Speaker 1: the grandest questions of the existence of humanity, the things
Speaker 1: that philosophers have been wondering about for thousands of years,
Speaker 1: the very nature of our reality and its meaning, can
Speaker 1: be understood by tiny little squishy brains living on a
Speaker 1: little rock orbiting a very normal star. We talk about
Speaker 1: all of these questions and we explain all the answers
Speaker 1: to you. That's right. We used the force to understand
Speaker 1: the forces of the universe and to look out to
Speaker 1: galaxies far far away and actually also a long long
Speaker 1: time ago to understand how it's all put together and
Speaker 1: why it's all hanging there the way it is. Because
Speaker 1: everything around us presents mysteries. How do these things work?
Speaker 1: What happens when they bump into each other? And as
Speaker 1: a particle physicist, my favorite way to understand how things
Speaker 1: work is to do exactly that. Smash them into each other,
Speaker 1: or collide them into each other, or blow them up,
Speaker 1: whatever you prefer. Yeah, because the universe has a dark
Speaker 1: side and also a light side, and it seems to
Speaker 1: be in constant struggle with itself, bumping into each other,
Speaker 1: colliding fields, interacting with each other, all of it to
Speaker 1: create this amazing spectacle that we can see just by
Speaker 1: looking out into the night sky. And we've made remarkable
Speaker 1: progress in understanding the very nature of the universe by
Speaker 1: describing space itself and everything out there in terms of
Speaker 1: oscillating quantum fields, these things which fill the whole universe
Speaker 1: with their energy and slide and smush against each other
Speaker 1: to come together to describe the reality that you and
Speaker 1: I experience. Wait, Daniel, you mean it's not all made
Speaker 1: out of medic clorians, little tiny beings that you know,
Speaker 1: bind everything together. The medic Clorians were biological, not quantum mechanical.
Speaker 1: They never described it in Star Wars. Maybe they are
Speaker 1: quantum mechanical. Maybe they are quantum biology. Yeah, maybe right, Well,
Speaker 1: it seems almost the same. I mean, you're saying that
Speaker 1: the universe made of these fields that are bound together
Speaker 1: with these little tiny things that bump around each other
Speaker 1: and somehow direct the cosmos. That's kind of what George
Speaker 1: Lucas was saying. That's kind of what everybody was saying.
Speaker 1: If you're going to say kind of and be really
Speaker 1: generous about it, you know, yeah, kind of. But I
Speaker 1: love this picture of the universe as all these different
Speaker 1: quantum fields. You have like a field for the photon,
Speaker 1: you have a field for the electron, you have a
Speaker 1: field for the corks and you know those fields we
Speaker 1: can think about is having particles in them would slide
Speaker 1: around and keep a little discrete blob of energy. And
Speaker 1: we've talked to the podcast about how particles are these
Speaker 1: little ripples in the quantum fields. But one of the
Speaker 1: most interesting things that these fields can do is talk
Speaker 1: to each other. The photon field in the electron field
Speaker 1: don't just fill the space of the universe and ignore
Speaker 1: each other. They interact, They touch, they bind together, they
Speaker 1: transfer energy back and forth. Yeah, and thankfully, I guess right,
Speaker 1: because if all the fields ignored each other, like nothing
Speaker 1: would ever happen. We wouldn't be here. We're here because
Speaker 1: of those interactions. In a way, every interaction between two
Speaker 1: different kinds of particles, the way the electron is bound
Speaker 1: to the nucleus of the atom, the way chemical bonds form.
Speaker 1: The reason you don't fall through your chair is all
Speaker 1: because those quantum fields don't ignore each other. It's because
Speaker 1: they interact with each other, because they pass energy back
Speaker 1: and forth. In some sense, it's a bit of an
Speaker 1: artificial distinction to say we have two different fields. Might
Speaker 1: want to think of them holistically, is one bundle of fields,
Speaker 1: one force with the dark side and the light side, right,
Speaker 1: I think you're kind of saying the same thing, one
Speaker 1: force to rule them all. Now I'm mixing our mythologies.
Speaker 1: We need to have like a Lord of the Rings
Speaker 1: Star Wars crossover event. Who would win? Oh my goodness,
Speaker 1: fan fiction writers get on it? Are those owned by
Speaker 1: like different corporate conglomerates, in which case will never happen.
Speaker 1: Not on the internet. Anything can happened on the Internet.
Speaker 1: That's true until Disney's lawyers come after, you know, Disney
Speaker 1: buys Lord of the Rings. Then we might get like
Speaker 1: a Marvel Star Wars Lord of the Rings for a
Speaker 1: crossover right, Oh my goodness, would throw iron Men in there,
Speaker 1: And I'm all in Gandolf versus iron Man. Well, who
Speaker 1: would win? Doctor Strange or Gandalf or the Wizards. I
Speaker 1: don't know who's got a better grasp on the quantum fields,
Speaker 1: but it is interesting and things like Star Wars they
Speaker 1: use lasers, right, laser guns to shoot at each other,
Speaker 1: and also lightsabers to cut through appendages, and also doors
Speaker 1: and walls. And it's interesting to think that light can
Speaker 1: interact with matter, Like if you shoot a laser, it's
Speaker 1: gonna burn a hole through your wall, right, And you
Speaker 1: can even use light to push a solar sale, to
Speaker 1: push a spaceship off of the solar system. Exactly. Light
Speaker 1: is really weird. It has energy, it has a momentum,
Speaker 1: but it doesn't have any mass, and yet of course
Speaker 1: it can influence our world because of that energy. In
Speaker 1: that momentum, A laser will deposit a lot of energy
Speaker 1: in a very small spot and burn right through it.
Speaker 1: And that exactly happens because those photons can interact with
Speaker 1: charged particles. The quantum field of photon and the quantum
Speaker 1: field of those electrons or muns or quarks can interact
Speaker 1: and pass energy back and forth. I always wondered when
Speaker 1: I watched those lightsaber battles. I thought, how does that work?
Speaker 1: How do two lightsabers, two beams of light hit each other? Well,
Speaker 1: this is getting a little philosophical, Daniel. Our lightsabers beams
Speaker 1: of light actual like light that just stands there and
Speaker 1: sits there. Or are they like some kind of material, like,
Speaker 1: you know, like a plasma beam. Wouldn't they be called
Speaker 1: plasma sabers? Then? I mean they are called lightsabers, and
Speaker 1: I imagine George Lucas knows his quantum mechanics. Yeah, but
Speaker 1: maybe they're called lightsabers because they give off light. I
Speaker 1: guess that's a good point. You know, light bulbs are
Speaker 1: not made of light. As we're getting deep here, this
Speaker 1: is very stimulating, illuminating conversation here, well too, bright minds.
Speaker 1: You know, let's see what we can do. I guess
Speaker 1: we were talking about interacting things interacting, and you know,
Speaker 1: it's kind of interesting that electrons can definitely interact with
Speaker 1: other electrons, right, like an electron will repel another electron,
Speaker 1: and like a proton will repel no, the proton like
Speaker 1: things seem to be able to interact with it themselves,
Speaker 1: but not directly. Actually, electrons do not interact directly with
Speaker 1: other electrons. Electrons interact with photons, and photons interact with electrons,
Speaker 1: sort of like having an interpreter, and you can talk
Speaker 1: to the photon and the photon can talk to the
Speaker 1: other electron. But electrons don't interact with each other directly.
Speaker 1: I see, you gotta go through their agents, like talk
Speaker 1: to my people exactly. It's like electrons are celebrities. They
Speaker 1: don't just email you there people email your people. But
Speaker 1: I guess this brings up the an interesting question, which
Speaker 1: is what do photons interact with specifically? Yeah, exactly when
Speaker 1: these two lightsabers are about to cross, and to make
Speaker 1: that sound that I can't make what exactly is going
Speaker 1: on at the microscopic level in George Lucas's mind. Yea,
Speaker 1: so it's the On the podcast, we'll be asking the
Speaker 1: question do photons bump into each other? And Daniel this
Speaker 1: seemed a little risk a like, what do you mean
Speaker 1: bumping to each other? Like they bump and grind like casually,
Speaker 1: like oops, sorry, bumping to each other? Yeah. Well, you know,
Speaker 1: photons can do all sorts of things. They can be
Speaker 1: circularly polarized, so I guess they can do like spins
Speaker 1: on the dance floor. And you know, I'm not one
Speaker 1: to tell you what's appropriate and what's not appropriate. Talk
Speaker 1: to your parents about that. But this is more of
Speaker 1: a physics question. You know what happens when two beams
Speaker 1: of light cross each other? Do the photons ignore each other?
Speaker 1: Do they hit each other? Two photons push against each other?
Speaker 1: You know what happens when you cross the streams. Oh,
Speaker 1: and now we're getting to another mythology. Ghostbusters do not
Speaker 1: cross the streams exactly. I want to see bankman versus
Speaker 1: Gandolf versus a jedi. Now, oh, obviously Agreman would win.
Speaker 1: I mean, the smart engineer always wins. I don't know.
Speaker 1: I Bankman is quite the smart professor. Yeah, because I
Speaker 1: think this is something that I wondered about as a kid.
Speaker 1: Like if you take a flashlight and you take another
Speaker 1: flashlight and you point them not even at each other,
Speaker 1: but just like pointing them in the same direction, or
Speaker 1: cross their beams, Like, what's happening there? Like, what's happening
Speaker 1: to the Do the light beams ignore each other or
Speaker 1: do they kind of interfere or somehow scatter each other.
Speaker 1: So you're saying you wanted to understand light and so
Speaker 1: you make light collisions? Well, I don't know. Is it
Speaker 1: possible for light to collide? That's the question of today's episode.
Speaker 1: Can create a collite, a photon collider? So that's the
Speaker 1: big question we're asking today is can light bump into
Speaker 1: each other? Does light interact with itself? Because not every
Speaker 1: particle interact with other particles. Neutrinos, for example, ignore most
Speaker 1: of the matter in the universe, sliding right by as
Speaker 1: if it wasn't even there. Each particle, each ribble in
Speaker 1: the quantum field, can either see other fields or ignore
Speaker 1: the other fields. It's not like an option, it's not
Speaker 1: like it depends on its mood. Some of these fields
Speaker 1: couple with each other, and other fields just don't couple
Speaker 1: with each other at all. Well, it's kind of interesting
Speaker 1: because I know we've talked about this a lot before.
Speaker 1: How there are two kinds of particles. There are matter particles,
Speaker 1: like the stuff that we think of the stuff, and
Speaker 1: then there are force particles. And so a photon is
Speaker 1: a force particle. And so the question, I guess maybe
Speaker 1: a larger question is to force particles interact with themselves.
Speaker 1: It is a really interesting and deep question. Some of
Speaker 1: the force particles can actually interact directly with themselves, and
Speaker 1: others interact indirectly with themselves. But as we'll learn today,
Speaker 1: there's several layers of nuance to the answer. All right, well,
Speaker 1: we'll get right on it. But as usual, we were
Speaker 1: wondering how many people have thought about this like question,
Speaker 1: this question of whether light can interact with itself? And
Speaker 1: so as usual, Daniel went out there into the internet, Daniel,
Speaker 1: or to your campus. These are questions from our cadre
Speaker 1: of Internet volunteers. So thanks very much for everybody who
Speaker 1: continues to participate and fill my inbox with these really
Speaker 1: fun answers. I greatly appreciate it, and if you'd like
Speaker 1: to hear your voice on the podcast, please don't be
Speaker 1: shy right to us. Two questions at Daniel and Jorge
Speaker 1: dot com. Yeah, so we ask folks, do you think
Speaker 1: that photons bounce off of each other? Here's what people
Speaker 1: had to say. Since photons do not have electric charge
Speaker 1: and mass, I think they do not bounce off each other.
Speaker 1: I think that photons should bounce off each other because
Speaker 1: in physics we learned that photons are particles that act
Speaker 1: as waves because they have a particle wave kind of
Speaker 1: duality to them. So if their particles, they should be
Speaker 1: able to bounce off each other. But also at the
Speaker 1: same time, they're very small, so the rate that they
Speaker 1: do bounce off each other so small because it's very
Speaker 1: hard to hit two very small particles together. I would
Speaker 1: think not. I think they pass right on by each other. Yes, yes, yes, yes?
Speaker 1: Why or how? Wait? Pick up? Oh? Maybe they don't
Speaker 1: wait protons? Maybe they need neutrons. Do you know what
Speaker 1: a photon is? A photon? What's a photon? Way? A
Speaker 1: photon will need to stick to a proton what is
Speaker 1: a photon? Wait? Is it too protons? I would say
Speaker 1: the photons can bounce off each other, because I know
Speaker 1: my understanding is the photons don't have mass. But I
Speaker 1: know the idea of a light sale requires bouncing photons
Speaker 1: off of them. So it's something about the momentum or
Speaker 1: energy of a photon can actually impart some momentum into
Speaker 1: an object. So I would say because of that, photons
Speaker 1: probably can bounce off each other if shot at each other,
Speaker 1: just right, if I remember rightly, you've said on some
Speaker 1: prior episode that photons do not bounce off each other,
Speaker 1: but just pass right through. One might think they would
Speaker 1: bounce off because of their particle nature, but they also
Speaker 1: have wave nature, and I guess that's what lets them
Speaker 1: pass right through each other. I don't believe photons can
Speaker 1: directly interact with each other, being waves as well as particles.
Speaker 1: They just passed through, uh, interfering or not on their
Speaker 1: way through, but then continuing on their happy ways. I
Speaker 1: really don't know. I suppose they could. I know, if
Speaker 1: they hit hard enough, they'll break into other things, all right.
Speaker 1: I like that kid's answer. That was pretty funny. Yes, yes,
Speaker 1: of course, Wait what I love hearing people think about
Speaker 1: it on the fly, their initial reaction and then their
Speaker 1: physics brain engages and they're like, hold on a second,
Speaker 1: is that really the way this works? Really? They have
Speaker 1: two brains. I have lots of small brains all wrapped
Speaker 1: up together. To my, oh boy, that's a weird picture.
Speaker 1: Like if we open your skull, we wouldn't find a brain,
Speaker 1: We just find a whole bunch of little brains. Yeah,
Speaker 1: I'm like nineteen little brains in a trench coat, not
Speaker 1: actually a full person. Boy, that's a bit disturbing. I
Speaker 1: guess you know, you've got different parts of your life
Speaker 1: and so you gotta engage like, oh I need dad brain,
Speaker 1: or I need husband brain, or it's physics brain time.
Speaker 1: I find having split personalities is a bit of a problem.
Speaker 1: I see. So everybody's always just getting the same cartoon
Speaker 1: is braining all the time. Everyone's just getting the whole brain.
Speaker 1: There's no menu option. You get what you get and
Speaker 1: you don't get upset. But yeah, pretty interesting answers here
Speaker 1: from people. Some people think they yes, definitely they do,
Speaker 1: and some people think they definitely don't. And here's an
Speaker 1: interesting answer. Because they're waves. Can two waves interact with
Speaker 1: each other, yes, right, no reason why not. Like, two
Speaker 1: waves definitely can interact with each other. If you've seen
Speaker 1: waves in the ocean, you know they can add up together,
Speaker 1: they can even cancel each other out. So waves can
Speaker 1: definitely interact with each other. And photons can do that
Speaker 1: as well. You know, we've seen like the double slit experiment,
Speaker 1: is interference between photons, and so waves can definitely interact
Speaker 1: with each other. That's not an issue. But I guess
Speaker 1: in water in the ocean, if you get like one
Speaker 1: wave going one way and another way of going the
Speaker 1: other way, they do sort of mix in the middle,
Speaker 1: but afterwards they just keep going as if they hadn't interacted, right, Yeah.
Speaker 1: The effect that you see is a superposition of the
Speaker 1: two waves, and so there isn't necessarily direct coupling between
Speaker 1: the waves, but what you see is the addition of
Speaker 1: the two waves. In that sense, you experience the combination
Speaker 1: of them. But the individual waves can still be thought
Speaker 1: of as individual waves. Yeah, but then they keep going
Speaker 1: as if they hadn't interacted, right, Yeah. No, that's a
Speaker 1: good point. They don't interact with each other the way
Speaker 1: they would interact with for example, a boundary or a
Speaker 1: wall where they really would reflect. Yeah, they just sort
Speaker 1: of ignore each other. I mean in the moment, if
Speaker 1: you're setting in the middle, you would experience both waves
Speaker 1: and they would add or substract, but they eventually the
Speaker 1: waves keep going right. Yeah, that's true. And so the
Speaker 1: question is does the same happen to photons? That is
Speaker 1: indeed the question of the episode, And what happens when
Speaker 1: two photons getting near each other? Do they ignore each
Speaker 1: other or do they bounce off each other? Or do
Speaker 1: they do something else? All right, well, let's diget into it, Daniel,
Speaker 1: I guess, first of all, what does bouncing off actually mean? Like,
Speaker 1: what does it mean for one particle to bump into
Speaker 1: another particle? Do they actually bump? Yeah, so the microscopic
Speaker 1: view of bumping into things on the dance floor or
Speaker 1: sitting in your chair or whatever is sort of the
Speaker 1: conceptual view that you might have. You know, you probably
Speaker 1: imagine that the reason that you don't pass through a
Speaker 1: wall is that like the surface of your body is
Speaker 1: touching the surface of the wall and it's pushing back. Right,
Speaker 1: But what do we really mean by touching? Like microscopically?
Speaker 1: Zoom in? What's happening. Well, you know, the surface of
Speaker 1: your body is a bunch of atoms, and those have
Speaker 1: electrons around them. So really the tip of your finger,
Speaker 1: for example, is a bunch of electrons, and the edge
Speaker 1: of the wall, the surface of the wall, is also
Speaker 1: a bunch of electrons. And what happens when you push
Speaker 1: one against the other. The electrons themselves don't have to touch, right,
Speaker 1: They can repel each other without actually touching. So this
Speaker 1: microscopic view of the world from a physics point of view,
Speaker 1: there's no actual contact between these particles. It all happens
Speaker 1: via the fields between them, or equivalently, the particles that
Speaker 1: they're passing between each other. So when your finger pushes
Speaker 1: against the wall, it's ripples in the electromagnetic field or equivalently,
Speaker 1: photons that are transmitting that information that are pushing back
Speaker 1: back on you. Yeah, but you know, I think we
Speaker 1: have everyone has this intuitive feeling that things touch each
Speaker 1: other because like, my finger has a volume and the
Speaker 1: table has a volume, and that two objects can't sort
Speaker 1: of occupy the same space at the same time. And
Speaker 1: so if I press my finger against the table, like
Speaker 1: somehow the universe is resisting my finger being in the
Speaker 1: same place as the table, But two things can occupy
Speaker 1: the same place at the same time. Your body is
Speaker 1: full of neutrinos right now as well, and they're passing
Speaker 1: right through you and ignoring you. They are taking up
Speaker 1: your volume. The only reason you perceive a volume, the
Speaker 1: reason you think there's a boundary between your particles and
Speaker 1: the other particles is when there's a force between them.
Speaker 1: Neutrinos don't feel force, so they're just trapes right through
Speaker 1: the edge of Jorge and then out the other side,
Speaker 1: No big deal. The reason the table and the chair
Speaker 1: doesn't is because there's a force that prevents them. So
Speaker 1: it's really all about the force you can imagine things
Speaker 1: is sort of like with virtual springs between them, preventing
Speaker 1: them from getting too close, but there's no actual contact.
Speaker 1: Contact doesn't really mean anything. All there is is forced
Speaker 1: between particles, right. I think that's what you're saying, is
Speaker 1: that this idea that my finger can't occupy the same
Speaker 1: space as the table is really just kind of an illusion, right,
Speaker 1: because they could, I guess. But something is I'm not
Speaker 1: preventing my cluster of atoms in my finger from somehow
Speaker 1: being or you know, penetrating or infringing upon the volume
Speaker 1: of the atoms cluster together on the table. Yeah, and
Speaker 1: I wouldn't say the volume is an illusion. You know,
Speaker 1: people talk about like atoms being mostly empty space, and
Speaker 1: I think that's cool to give you the sense that
Speaker 1: like it's made of tiny particles, But it's also a
Speaker 1: little bit misleading that space isn't empty. It's filled with
Speaker 1: fields or with virtual photons that are zooming around and
Speaker 1: keeping everything in its position. You can define what your
Speaker 1: volume is, but that volume, the edge of it, is
Speaker 1: not defined by like the stuff that you're made out of,
Speaker 1: but the fields from that stuff, the forces of that stuff,
Speaker 1: And the volume also depends on what you're touching. Right,
Speaker 1: you want to touch a blob of neutrinos, then your
Speaker 1: volume is different. Then you want to touch something like
Speaker 1: a table or a chair. Right, So, because the volume
Speaker 1: depends on the fields, and not everything feels those fields,
Speaker 1: then the volume is a little bit dependent on what
Speaker 1: you're touching. Right. I think you're saying that, you know,
Speaker 1: instead of thinking of our fingers or at the table
Speaker 1: as collections of stuffy particles, maybe it's better to think
Speaker 1: of them as like clusters of ripples in the fields
Speaker 1: of the universe, Like my finger is not really a finger,
Speaker 1: is just a whole bunch of ripples kind of tightly
Speaker 1: cluster together. And so this whole bunch of ripples doesn't
Speaker 1: want to just um go through the bunch of ripples
Speaker 1: of the table. There's are forces that push my group
Speaker 1: of ripples against the tables group of ripples. That's right,
Speaker 1: And I like the sound of the word ripples, And yeah,
Speaker 1: you are made of little matter ripples, right, your particles,
Speaker 1: And you can think of as like little ripples in
Speaker 1: quantum fields of matter. And the way those things stay
Speaker 1: apart again is not that they are physically touching each
Speaker 1: each other, but that they exchange other kinds of ripples,
Speaker 1: these force ripples between them. So you can think of
Speaker 1: yourself as like a cloud of these little matter ripples
Speaker 1: that are maintaining their distance from each other by passing
Speaker 1: back and forth these other little ripples, and also maintaining
Speaker 1: their distance from other things. But there's no microscopic equivalent
Speaker 1: of touching. The surfaces are not like actually coming into contact, right,
Speaker 1: but in a way sort of like my ripples, like
Speaker 1: my way functions of my ripples are touching the way
Speaker 1: functions of the other ripples, and so that's that's kind
Speaker 1: of like touching, right, They're getting into each other's business.
Speaker 1: Another way to say, instead of saying there is no
Speaker 1: touching is to say, that's exactly what touching is. That's
Speaker 1: how touching works. Your experience of touching means these particles
Speaker 1: are communicating with the other particles, but they don't have
Speaker 1: to be on top of each other. And this is
Speaker 1: something that physicists struggle to understand for a long time.
Speaker 1: They call this spooky action at a distance, because we
Speaker 1: like to think of physics as local, that you only
Speaker 1: affect things that are right next to you. You can't like,
Speaker 1: do something here and instantly affects things in andromeda. We
Speaker 1: like to think of physics is only happening in like
Speaker 1: a very close vicinity to an object. And so this
Speaker 1: idea that like an electron could push another electron without
Speaker 1: actually touching it was a little bit weird for physicists
Speaker 1: for a while. And then they invented this concept of
Speaker 1: a field that the electron creates this field around it,
Speaker 1: which then pushes on other electrons. Right, And like you said,
Speaker 1: it's sort of all depends on which fields you're talking about.
Speaker 1: Like some fields do interact with each other and some don't,
Speaker 1: Like there could be a whole house made of neutrinos
Speaker 1: falling on top of me right now, but it'll just
Speaker 1: keep going and won't touch or interact with any of
Speaker 1: my ribbles. Exactly in, each particle that's out there has
Speaker 1: a different set of ways to interact. Like the electron
Speaker 1: can interact via photons. It can also interact with the
Speaker 1: weak force, so you can interact using ws and interact
Speaker 1: using zs for example. So it's got like two ways
Speaker 1: to talk to other particles. You can speak two different languages,
Speaker 1: whereas the corks they can speak a third language. Right,
Speaker 1: they can interact via gluons because they feel the strong force,
Speaker 1: and the neutrino only speaks one language, just the weak force.
Speaker 1: So depending on which kind of particle you are, you
Speaker 1: see the universe very differently. Right. Either it's filled with
Speaker 1: stuff that wants to talk to you, or it's filled
Speaker 1: with people speaking gobbledygook that you can't understand and mostly
Speaker 1: just ignore. All right, well, let's touch on this a
Speaker 1: little bit more and we'll speak to what some of
Speaker 1: these forces are up to. But first let's take a
Speaker 1: quick break all right, we're talking about the question of
Speaker 1: what's going on in Star Wars when a lightsaber hits
Speaker 1: another lightsaber, Daniel, is the light actually touching it itself?
Speaker 1: Is is it colliding? Or is that actually something that's
Speaker 1: impossible in the universe. Did George Lucas make all that
Speaker 1: stuff up? Then? You know, he has a huge budget,
Speaker 1: so I'm sure he did all the R and D
Speaker 1: necessary to make sure that Star Wars is realistic. But actually,
Speaker 1: didn't Star Wars happen a long time ago? So in
Speaker 1: principle all this stuff has already and developed. Yeah, well,
Speaker 1: it depends on who the movies for, you know, like
Speaker 1: that the movie could be for aliens who are really
Speaker 1: far away, in which case it will have happened a
Speaker 1: long time ago from them. I see. Wow. I wonder
Speaker 1: if he wrote that into his contracts, you know, future
Speaker 1: kinds of revenue from alien galaxies. He was pretty savvy,
Speaker 1: I heard. I'm sure those contracts say everywhere in the
Speaker 1: known universe, and some lawyer out there is like, oh,
Speaker 1: what if we discover a new universe? Does this contract
Speaker 1: extend to merchandise sold in the multiverse? Yeah, although actually
Speaker 1: George look has sold everything Star wars did Disney try?
Speaker 1: So Disney owns the universe, that's right. Yeah, Well, we're
Speaker 1: talking about whether photons interact with photons, whether light can
Speaker 1: hit light, I guess, or interact with itself. And so
Speaker 1: we talked about what it actually means for particles to
Speaker 1: interact with each other, and it sort of all depends
Speaker 1: on what fields are in and how they interact with
Speaker 1: each other. One thing I think that's interesting that you
Speaker 1: said is that sometimes particles don't actually interact with each other,
Speaker 1: but they have sort of intermediary feels they talk through.
Speaker 1: Like an electron doesn't actually interact with another electron exactly.
Speaker 1: Electrons can interact with a very small number of particles directly.
Speaker 1: They can interact with photons, ws and zs, and that's it.
Speaker 1: Like electrons can only interact with force particles. They can't
Speaker 1: interact with other matter particles, not directly. Like if you
Speaker 1: look at the equations of the standard model, we have
Speaker 1: all of these fields and we say very specifically which
Speaker 1: fields can talk to the other fields, and the electron
Speaker 1: can only talk to the photon field, the W field,
Speaker 1: the Z field, and actually also the Higgs field. Wait
Speaker 1: are you saying that like an electron can actually be
Speaker 1: on top of another electron, is in there some sort
Speaker 1: of like universe rule that says no to electrons can
Speaker 1: be in the same place. This certainly is that rule,
Speaker 1: and so quantum mechanics prevents that from happening. But that
Speaker 1: would never happen anyway, because electrons, though they can't talk
Speaker 1: to each other directly, they can talk to each other
Speaker 1: via the photon. And so the way we build up
Speaker 1: our description of the universe is we have these little
Speaker 1: basic building blocks, like what are the simplest things that
Speaker 1: can happen, and then from that you can build up
Speaker 1: more complex things. You can say, well, an electron can
Speaker 1: only talk to a photon, but that means a photon
Speaker 1: conduct an electron. So then you put together this two
Speaker 1: step process when electron talks to a photon, which passes
Speaker 1: the information to another electron, sort of like when the
Speaker 1: parents are arguing and the interact via the kids. You know,
Speaker 1: tell your mother that dinner will be ready at six pm.
Speaker 1: I don't know what you're talking about, Daniel, what sort
Speaker 1: of house are you running there? I mean, I've just
Speaker 1: seen that in the movies. I've never had an argument. Right, Well,
Speaker 1: we'll tell our agent that I don't agree with them,
Speaker 1: all right, Remember that this is like our description of
Speaker 1: the universe. We try to boil it down to the
Speaker 1: simplest set of interactions, and then we can use those
Speaker 1: to try to describe all the complex phenomena that we
Speaker 1: see out there, some of which can be described with
Speaker 1: just the basic pieces, and some of which requires us
Speaker 1: to put two or three of these pieces together to
Speaker 1: describe everything that happens. But it's kind of weird to
Speaker 1: think that if there wasn't a photon field, then you
Speaker 1: could have electrons kind of running into each other, kind
Speaker 1: of right occupying the same field in the same spot.
Speaker 1: It's pretty hard to think about a universe without a
Speaker 1: photon field because it would break a lot of our laws.
Speaker 1: Remember we have this episode about gauge invariants actually need
Speaker 1: photons around for electrons to behave properly to like conserve
Speaker 1: electric charge and all that stuff. Member forces aren't everything
Speaker 1: in physics. They're also just rules of quantum mechanics. Electrons
Speaker 1: can't be in the same state as another electron, and
Speaker 1: that's not like due to a force, it's just something
Speaker 1: electrons don't do. Alright, So then all electrons have to
Speaker 1: go through the photon field to talk to each other. Um,
Speaker 1: what about things like courts, So quirks can do the
Speaker 1: same thing. Quarks interact with all the same particles that
Speaker 1: electrons do, plus gluons. So if two quirks are approaching
Speaker 1: each other, they have a lot of different ways to
Speaker 1: talk to each other. They can exchange ws, they can
Speaker 1: exchange zs, they can exchange photons, or they can exchange
Speaker 1: those crazy particles, the gluons, and so again. Corks don't
Speaker 1: talk to each other directly. Right. Matter particles never interact
Speaker 1: directly with matter particles. What they do is they interact
Speaker 1: via the fields they create, which is equivalent to saying
Speaker 1: that they interact via these force particles. Right again, just
Speaker 1: to be totally clear, you can imagine like the electromagnetic
Speaker 1: field that a cork generates because cork has electric charge
Speaker 1: like two thirds or minus one third, and another cork
Speaker 1: is flying through that field and fields of force. That's
Speaker 1: what the field is. Right. Another equivalent way of thinking
Speaker 1: about it is thinking of that field is a bunch
Speaker 1: of virtual particles being created by the first cork. There
Speaker 1: are two equivalent ways of thinking about particles interacting either
Speaker 1: via fields or via virtual particles. But I guess maybe
Speaker 1: like a philosophical question is, could you have a universe
Speaker 1: without a photon field or a gluon field and still
Speaker 1: like makes sense mathematically, like is it just coincidence that
Speaker 1: somehow course can talk to each other via the glue
Speaker 1: on field or is it not even possible for courts
Speaker 1: exist without gluons. I mean philosophically, you can put together
Speaker 1: all different kinds of universes. You can put together universes
Speaker 1: with just quirks in them, or just electrons and them.
Speaker 1: Of course you wouldn't get any interesting complex structure. Like
Speaker 1: everything that we know and love about the universe comes
Speaker 1: from the fact that these particles do interact and make
Speaker 1: protons and neutrons and atoms and chemistry and ice cream
Speaker 1: and all that good stuff. So you wouldn't get anything interesting.
Speaker 1: And if you have these fields and they couldn't talk
Speaker 1: to each other, you couldn't form really any kind of
Speaker 1: complex structure. Also without these forces. Remember, these forces exist
Speaker 1: to preserve symmetries that we observe in nature between these particles.
Speaker 1: So there are symmetries among the corks and symmetries among
Speaker 1: the electron and the other particles that are preserved by
Speaker 1: these forces. Check on our episode Engage Symmetry to explain
Speaker 1: a little bit more what I mean. You have to
Speaker 1: have these forces if the universe has these symmetries, though
Speaker 1: we don't know why the universe has these symmetries. So
Speaker 1: you could in theory create other universes without these symmetries
Speaker 1: and without the forces, but they would be pretty boring. Yeah,
Speaker 1: there would be there would be any sequels probably, well,
Speaker 1: I guess it's sort of It's sort of an interesting
Speaker 1: philosophical thing to think about. Like, you know, there are
Speaker 1: matter particles, and those matter because that's what they make
Speaker 1: stuff out of. But the force particles, you know, they
Speaker 1: seem to only be there so that the matter particles
Speaker 1: can talk to each other, and so like are they
Speaker 1: there just to make the other ones interact? Or are
Speaker 1: they they because they have to be there, or are
Speaker 1: they're there by coincidence? It is an interesting philosophical question.
Speaker 1: You know, we observe these things in the universe. That
Speaker 1: doesn't answer the question of why they are there. What
Speaker 1: we can do is think about, like what other possible
Speaker 1: universes could you put together, and then think about why
Speaker 1: we have this one, and we do see these amazing
Speaker 1: mathematical symmetries that tell us that the force particles really
Speaker 1: do complement the matter particles in this way, that they
Speaker 1: preserve these internal mathematical symmetries. But you know, you can
Speaker 1: also have other kinds of universe, So we can imagine
Speaker 1: other kinds of universes that do follow their own self
Speaker 1: consistent laws, you know, like universes with just photons in them,
Speaker 1: universes with just luons in them. Right, you can imagine
Speaker 1: those universes. They could exist. You can write down the
Speaker 1: equations for them on paper, you can think about them
Speaker 1: in your mind. You can do computer simulations. That doesn't
Speaker 1: tell you why we have quirks. So much of what
Speaker 1: we do in particle physics is just observation. We see
Speaker 1: this out here in the universe. We try to describe
Speaker 1: it mathematically. We don't know why this universe and not
Speaker 1: another universe. We just don't know. Just describing what you see,
Speaker 1: we are we describing what we see. We're trying to
Speaker 1: boil it down to as few rules as possible to
Speaker 1: describe all the complexity, and then we're trying to look
Speaker 1: at those rules and say, hey, does this make sense?
Speaker 1: Could have been different? Why is it this way not
Speaker 1: another way? Mostly we're still pretty clueless about the answers
Speaker 1: to those questions. So many things about the particles that
Speaker 1: just don't make any sense and don't seem to have
Speaker 1: any reason at all. You know, why are there three
Speaker 1: kinds of electrons? We have no idea, all sorts of
Speaker 1: interesting questions, all right, Well that what seems to be
Speaker 1: observed is that matter particles don't interact with each other.
Speaker 1: They do it through force particles. And so the question
Speaker 1: is what the force particles interact with? Can they interact
Speaker 1: with themselves like the photon? Can the photon interact with itself?
Speaker 1: So again not directly, right, A photon only interact with
Speaker 1: particles that have electric charge. So the photon can interact
Speaker 1: with the electron, or the muon or any of the quarks.
Speaker 1: It can also interact with the w boson, which is
Speaker 1: not a matter particle. The rule for the photon is
Speaker 1: that it only interacts directly with particles that have electric charge.
Speaker 1: Particles like the z and the neutrino it cannot see,
Speaker 1: it cannot interact with them. And interestingly, the photon itself
Speaker 1: doesn't have electric charge. It's neutral, so the photon cannot
Speaker 1: directly bump into another photon. Well, okay, so you're saying
Speaker 1: that a photon can't interact with it itself. Can any particle,
Speaker 1: Can any force particle interact with itself? Or can any
Speaker 1: particle in general interact with itself? Actually, yes, some of
Speaker 1: them can. Like a gluon interacts only with particles that
Speaker 1: have strong charge color, right, like the quarks, for example,
Speaker 1: and not the electrons. But the gluons themselves have color,
Speaker 1: so gluons can interact with themselves. Two gluons who find
Speaker 1: each other in the universe can bounce directly off each
Speaker 1: other without using some other intermediate particle. Wait, they can,
Speaker 1: like they can bounce off, but they don't use an
Speaker 1: intermediary to bounce off. They can just bounce off. Gluons
Speaker 1: can talk directly to each other. And that's one of
Speaker 1: the reasons why the strong force is so strong and
Speaker 1: so weird and so much of a pain in the
Speaker 1: butt to do any calculations with, because gluons just can't
Speaker 1: stop talking to each other. You know, quirks are constantly
Speaker 1: generating gluons, and those gluons talk to each other and
Speaker 1: the other quirks, and it's a huge tangled mess. Photons
Speaker 1: are much easier because once you make them, they don't
Speaker 1: talk to each other. They can fly along inside each
Speaker 1: other and hardly interfere with each other. So gluons are
Speaker 1: very chatty and that's kind of a pain. Are you
Speaker 1: saying they're very sticky and that's the problem. They are
Speaker 1: indeed very sticky. Absolutely, Are you sure there's no like
Speaker 1: hidden particle that they're using to intert react with it themselves,
Speaker 1: Like isn't that weird that? Like electrons can interact with electrons,
Speaker 1: but gluons can interact with glue ups. It is weird,
Speaker 1: And the mathematics you need to describe gluons becomes very
Speaker 1: different from the mathematics you need to describe photons. And
Speaker 1: W's disease. And that's another thing that makes a strong
Speaker 1: force so weird and so powerful. It's very different kind
Speaker 1: of particle. Another example is the Higgs boson. The Higgs
Speaker 1: boson can also interact directly with itself, like Higgs boson
Speaker 1: flying through space can bounce into another Higgs boson, or
Speaker 1: it can radiate the Higgs boson. It can like pop
Speaker 1: off one of itself. WHOA. But then, so what's the
Speaker 1: difference between the higgs boson and like the electron or
Speaker 1: the photon that ignores itself. Well, the rule is the
Speaker 1: photon can only interact with particles that have electric charge,
Speaker 1: because that's the photon's job is to preserve electric charge
Speaker 1: in the universe. Higgs boson interacts with anything that feels
Speaker 1: the weak force, and that includes the higgs boson itself.
Speaker 1: The Higgs boson has this weird ability to talk to itself,
Speaker 1: and again this is not something where we understand why
Speaker 1: it is this way. But if it wasn't this way,
Speaker 1: the higgs boson couldn't do its job. We talked to
Speaker 1: the podcast about the higgs boson and its relationship to
Speaker 1: Mexican hats. How it has this weird vacuum energy that
Speaker 1: gives it the power to apply mass two particles, and
Speaker 1: that comes partially from its interaction with itself. That's what
Speaker 1: makes the higgs boson weird, and just the right way
Speaker 1: then it can give mass to these particles. So it's
Speaker 1: again not something we totally understand. So I guess you're saying,
Speaker 1: as far as we know, the photon can't interact with itself,
Speaker 1: at least directly, and so that kind of answers the
Speaker 1: question of the episode, right, like, can't interact with itself directly? Yeah, directly,
Speaker 1: Although you know, how we organize these things in our
Speaker 1: minds doesn't necessarily determine what happens out there in the universe.
Speaker 1: We have this strategy of let's make the simplest possible
Speaker 1: basic ideas and then build everything out of it, like
Speaker 1: the way you might describe the universe in terms of
Speaker 1: legos and say I only need these lego pieces to
Speaker 1: describe anything I can build out of legos. That doesn't
Speaker 1: necessarily limit what you can make out of legos, and
Speaker 1: it would be like artificial to say, what can I
Speaker 1: make out of only these pieces nobody really cares right
Speaker 1: with out there in the universe is all sorts of
Speaker 1: crazy combinations of those pieces. So while it's true that
Speaker 1: in our model to photons can't bump against each other
Speaker 1: directly or definitely ways for photons to interact indirectly, and
Speaker 1: we see that in the universe, but I guess, just
Speaker 1: to be clear, like if I take a flashlight and
Speaker 1: I crossed the beam with another flashlights beam, like nothing
Speaker 1: happens zero. Well, two photons don't touch each other directly,
Speaker 1: but they do have ways passing information against each other,
Speaker 1: so effectively photons can interact. Again, not directly. They have
Speaker 1: to like use an intermediary like other electrons or other particles.
Speaker 1: But in the same way that my electrons can't interact
Speaker 1: with your electrons directly, they do it via photons. My
Speaker 1: photons can't interact with your photons directly. We have to
Speaker 1: do it via electrons. But does that mean that I
Speaker 1: can just pile photons on top of each other? Can
Speaker 1: photons just be like in the two photons, Can they
Speaker 1: be in the same place at the same time? Photons
Speaker 1: actually can because they don't follow the same rules as electrons.
Speaker 1: They have different spin. They're integer spin, which means they
Speaker 1: are bosons, and quantum mechanics says that matter particles for
Speaker 1: meons cannot be in the same state at the same time.
Speaker 1: But no rules like that ex us for bosons. So
Speaker 1: you can pile as many bosons as you want on
Speaker 1: top of each other. And that's why, for example, we've
Speaker 1: been able to do things like make Bose Einstein condensates,
Speaker 1: which is a bunch of bosons on top of each other,
Speaker 1: have the same wave function macroscopically act like a quantum object.
Speaker 1: You can do the same thing with photons. Can have
Speaker 1: as many photons as you want in the same state.
Speaker 1: That's why I like lasers work. For example, m M yeah,
Speaker 1: I hear. You can stick a bunch of bozons two
Speaker 1: in a small cart. They do that in some particle collider.
Speaker 1: The circuses particle collider does feel like a circus subtimes.
Speaker 1: It is a ring, right, it's a ring. It's a
Speaker 1: three ring circus out there in Tineva. We do our
Speaker 1: best to keep the energy high. So you're saying that
Speaker 1: photons cannot interact with themselves directly. What does that mean?
Speaker 1: Does that mean they can interact indirectly? Yes, they can
Speaker 1: interact indirectly. That the process is a little bit different
Speaker 1: than electrons interacting. Like when electrons come by, one of
Speaker 1: them can just radiate a photon which is absorbed by
Speaker 1: the other electron and go on. It's b this, right,
Speaker 1: doesn't cost anything but energy to radiate a photon. Now
Speaker 1: imagine the case with photons. Two photons are approaching each other,
Speaker 1: can one of them just radiate an electron which is
Speaker 1: then absorbed by the other one. Can't actually do that
Speaker 1: because that would violate conservation of electric charge. Photon can't
Speaker 1: just create an electron out of nothing. In order to
Speaker 1: interact without other electron has to do something slightly different.
Speaker 1: It has to die yet. Wait, the light has to die. Yeah,
Speaker 1: the light has to die in order for it to
Speaker 1: interact with the other photon. It has to convert into
Speaker 1: an electron and a positron. So the photon doesn't just
Speaker 1: like emit an electron which is then absorbed by the
Speaker 1: other photon. It converts into a new pair of particles,
Speaker 1: an electron and oppositron, and then those guys can interact
Speaker 1: with the second photon, can they or does the other
Speaker 1: photon also have to turn into a pair of electron
Speaker 1: and an anti electron, you know that electron oppositron pair.
Speaker 1: They can interact directly with a photon because photons can
Speaker 1: interact with charged particles, and so if you have a
Speaker 1: photon coming in, it could convert into this pair, one
Speaker 1: of which or both of which can interact then with
Speaker 1: that photon, and so you can deflect that other photon
Speaker 1: with the first photon. But the first photon doesn't just
Speaker 1: like emit something go on its way, it has to
Speaker 1: kill itself as to transform into an E plus e
Speaker 1: minus pair. Okay, so let me see if I'm understanding
Speaker 1: the picture. You have two photons heading towards each other, right,
Speaker 1: Darth Vader is swinging his lightsaber. Luke Skywalker is you know,
Speaker 1: moving to Perry and one of the photons turns into
Speaker 1: an electron anti electron pair, and then those somehow deflect
Speaker 1: the other photon that's still alive. Is that what you're saying,
Speaker 1: like it can actually bump it. That's exactly what happens,
Speaker 1: because the electron impositron can interact with the photon. What
Speaker 1: they can absorb the photon, or they can deflect the photon.
Speaker 1: All sorts of things can happen there. Now, this dependent
Speaker 1: on the first photon doing that split splitting off into
Speaker 1: a pair of electron anti electron particles. Or is this
Speaker 1: like a quantum mechanical thing where like a photon is
Speaker 1: always kind of splitting into a pair of these particles
Speaker 1: all the time, but with a certain you know, probability. Yes, exactly.
Speaker 1: A photon isn't just a little packet of energy in
Speaker 1: the photon fields flying through space. It's constantly creating e
Speaker 1: plus e minus pairs and then going back to being
Speaker 1: a photon, and sometimes it creates e plus and minus pairs,
Speaker 1: and those things really their own photons, which create more
Speaker 1: e plus dem mondus pairs, which then collapse back. So
Speaker 1: it's just like buzzing swarm of particles all the time.
Speaker 1: So what happens when two photons come near each other
Speaker 1: is that sometimes they pass right through each other and
Speaker 1: ignore each other. Sometimes one of the photons will interact
Speaker 1: with one of these e plus e midus pairs that
Speaker 1: briefly exists. So it's sort of probabilistic what happens when
Speaker 1: two photons come near each other. But the way that
Speaker 1: they can interact is through the creation of this matter
Speaker 1: antimatter pair. Momentarily, wait, what like sometimes that photon will
Speaker 1: bump into another photon and sometimes not, or does it
Speaker 1: always happen, but just a little bit like is it
Speaker 1: quantum in that way? Or just want to photon feel
Speaker 1: a little bit of force or does it only sometimes
Speaker 1: feel a force? Well, there's an infinite number of possibilities,
Speaker 1: because it's an infinite number of ways that a photon
Speaker 1: can split into these pairs, which can then split into
Speaker 1: the pairs. And so technically what happens when a photon
Speaker 1: passes to another photon, It has an infinite number of possibilities,
Speaker 1: and so then if you measure that photon, then you're
Speaker 1: gonna get one of those possibilities, and in principle, one
Speaker 1: of those possibilities is zero deflection, though in practice actually
Speaker 1: measuring zero deflection is probably impossible because you're measuring things
Speaker 1: with physical systems, and so you're never going to get
Speaker 1: the photon at exactly the angle that it came in at.
Speaker 1: Mm hmm. I see you're saying, there's always some sort
Speaker 1: of interaction, but it's quantum mechanical, so there's sort of
Speaker 1: a probability range of things that can happen, like if
Speaker 1: I shoot a photon and another photon, it is going
Speaker 1: to bump into each other through these split of the
Speaker 1: particle antiparticle pair um. But what actually happens is sort
Speaker 1: of probabilistic, like it can be the did a little
Speaker 1: bit or a lot, or maybe not at all exactly,
Speaker 1: and sometimes crazy things happen, like sometimes the two photons
Speaker 1: come together, they both create the E plus E minus pair.
Speaker 1: To those that annihilate and like destroy each other and
Speaker 1: you end up with just an E plus E minus
Speaker 1: pair which comes out. So it's like two photons come
Speaker 1: together and then an electron and positron come out, So
Speaker 1: it's like light gets converted into matter. Wait what so
Speaker 1: if I collide to photons, I'm going to get some
Speaker 1: bits of matter out of it. Sometimes. Yeah, don't those
Speaker 1: two things annihilate each other also instantaneously? Well, you know,
Speaker 1: this possibility for lots of different things to happen. But
Speaker 1: if they've come in opposing each other and then the
Speaker 1: electron and positron fly out the other direction, that they're
Speaker 1: not likely to then annihilate each other. But yeah, that's
Speaker 1: also a possibility. WHOA. So, like, if I point my
Speaker 1: flashlight at another flashlight, stuff is happening, Like stuff can happen.
Speaker 1: The light is going to bump into the other light.
Speaker 1: And also I could be creating matter out of my flashlights. Yeah,
Speaker 1: you are creating matter and antimatter if you cross the stream,
Speaker 1: So be careful out there, folks. Yeah, it sounds kind
Speaker 1: of dangerous. Little did I know? I could have ended
Speaker 1: the universe as a kid crossing some flash lights together.
Speaker 1: The other thing to understand is that you know, we
Speaker 1: build up this picture of how particles interact using these
Speaker 1: basic like tinker toys. You know, this one can talk
Speaker 1: to this one, and then you can change those things
Speaker 1: together to make more complex interaction. The more pieces of
Speaker 1: the chain you need to use, the less likely it
Speaker 1: is for things to happen, because it's like two quantum
Speaker 1: mechanical things have to happen, both of which are not
Speaker 1: that likely. So particles interacting directly is more likely than
Speaker 1: particles interacting indirectly. If you have to have multiple steps
Speaker 1: in your chain, it's less and less likely. So light
Speaker 1: by light scattering, for example, is less likely than light
Speaker 1: scattering off of electrons because that's more direct. All right,
Speaker 1: So it sounds like the answer is actually a little
Speaker 1: bit complicated, like everything in particle physics, and so let's
Speaker 1: get into how we have actually observed this in experiments
Speaker 1: and seeing light bump into other kinds of lights. Get
Speaker 1: into that, but first let's take another quick break. All right,
Speaker 1: we're talking about the question of whether photons can bump
Speaker 1: into each other. Like if I point a flashlight and
Speaker 1: across its being with another flash line, what's gonna happen?
Speaker 1: Is it just gonna keep going, or is it gonna
Speaker 1: bump into each other? And it sound like that, like
Speaker 1: the answer is they're gonna bump into each other, like
Speaker 1: not directly, like the photons can interact with the other photons,
Speaker 1: but they kind of do through these other quantum mechanical possibilities. Exactly.
Speaker 1: Everything in your body is a constant swarm of particles
Speaker 1: turning into other particles, and so if you want to
Speaker 1: interact with something else, you've got sort of lots of
Speaker 1: options being presented simultaneously. So the fact that photons don't
Speaker 1: interact directly with other photons is not really limitation, because
Speaker 1: they can talk to each other via electrons or via
Speaker 1: other charged particles. Yeah, I'm not feeling quite myself today.
Speaker 1: Is it because of my qualty mechanical nature or maybe
Speaker 1: just the fact that didn't sleep enough last night? Well
Speaker 1: I thought you said everybody always gets the same jorhe Yeah,
Speaker 1: and sometimes that whorrie sleepy and sometimes less sleepy, but
Speaker 1: it's still the same whor Hey, maybe we need to
Speaker 1: put you in the particle beam and charge you up
Speaker 1: a little bit. Yeah, it's my answer everything. That's what
Speaker 1: I need a sun time bed. I feel like you're
Speaker 1: telling me that if I take a flashlight and I
Speaker 1: crossed its beam with another flashlight, they're going to interact
Speaker 1: with each other. Like the light beam is going to
Speaker 1: hit the other light beam and mater can come out
Speaker 1: or light's gonna get scattered. But that's kind of not
Speaker 1: my experience, you know. I feel like if you point
Speaker 1: to flash at each other, like the beams just go
Speaker 1: through each other. Yeah, mostly that's not your experience because
Speaker 1: it's pretty rare because it has to have two steps
Speaker 1: to happen. It's less likely than particles interacting directly. It's
Speaker 1: also very strongly a function of the energy. The higher
Speaker 1: energy the photons, the more likely this is to happen.
Speaker 1: So photons in the visible spectrum don't actually have that
Speaker 1: much energy, and so it's harder for them to create
Speaker 1: eat these E plus e minus pairs because electrons have mass,
Speaker 1: and so it's costs more of their energy to make
Speaker 1: the E plus e minus pairs, so it's less likely
Speaker 1: for them to happen. So if you want to see
Speaker 1: this happen, you need really high energy photons. That's where
Speaker 1: it's more likely for photons to bounce off each other. Oh,
Speaker 1: I see, so you're saying, when I crossed my flashlight beams,
Speaker 1: they are mostly going through each other, mostly ignoring each other.
Speaker 1: But they are maybe in a very low scale, like
Speaker 1: very improbable. There are little photons here and there that
Speaker 1: are scattering with each other or creating matter and antimatter,
Speaker 1: almost certainly, because they are a huge number with a photon.
Speaker 1: So even if the probabilities are tiny, one or two
Speaker 1: photons are probably doing something crazy in those beams. You
Speaker 1: won't notice it because it's such a tiny fraction and
Speaker 1: it's impossible, and they're drowned out by the other photons.
Speaker 1: But almost certainly, some of those photons are dancing together.
Speaker 1: That's pretty cool. I means I can make matter and antimatter,
Speaker 1: like in my house. I just take two flashlights and
Speaker 1: cross the beams. Yeah, and you're making positrons momentarily. And
Speaker 1: you're saying, like, the higher the energy, So if I
Speaker 1: X ray flashlights than that would they would interact more? Yeah,
Speaker 1: X rays would interact more. And this is something we
Speaker 1: have actually done. We have studied this. We have created
Speaker 1: matter just from colliding light that in order to do it,
Speaker 1: we need higher energy beams of light than even X
Speaker 1: rays can provide. Yeah, these are like real experiments you've
Speaker 1: done in colliders, So tell us about this. So, first
Speaker 1: of all, how do you make two light beams into matter?
Speaker 1: So your first thought might be like, let's take two
Speaker 1: lasers and shoot the match each other and see what happens, right,
Speaker 1: or across them at least, Yeah, or two lightsabers, light sabers,
Speaker 1: that would be even cooler. Yeah, that's the closest thing
Speaker 1: we can do to lightsabers. Right. The issue is that
Speaker 1: while lasers are really good at making coherent sources of
Speaker 1: monochromatic light, you know, photons all with the same phase
Speaker 1: and all with the same wavelength, they're not actually great
Speaker 1: at making very high energy photons, like you can have
Speaker 1: an intense beam. We got lots of photons per second
Speaker 1: from lasers, but you can't make photons with a lot
Speaker 1: of energy per photon. Because his limitations on the cavity
Speaker 1: and how you can actually make lazing happen, which requires
Speaker 1: reflections and residences. Even X ray lasers are hard to do.
Speaker 1: We need things like well above X rays, well above
Speaker 1: gamma rays, like super high energy photons. So the way
Speaker 1: we do that is not by creating light sources at all,
Speaker 1: but by going to our colliders and using the photons
Speaker 1: radiated from the other particles that were smashing together. So
Speaker 1: and to make high energy light you use colliders. But
Speaker 1: isn't it doesn't get scattered all over the place, Like
Speaker 1: isn't it hard to like harness that or aim those
Speaker 1: photons at another source of photons. It is tricky, and
Speaker 1: we don't actually create photons and our colliders. You know,
Speaker 1: if the l C, for example, we're colliding protons, right,
Speaker 1: but protons have electric charge, which means that they're constantly
Speaker 1: radiating photons, especially when they're flying really fast and bending.
Speaker 1: So protons and the l A C for example, is
Speaker 1: surrounded by a swarm of photons which have really high energy.
Speaker 1: And to get even higher energy, which you need is
Speaker 1: not a proton which just has one electric charge. You
Speaker 1: need something with even more electric charge because it will
Speaker 1: generate higher energy and higher number of photons. So for that,
Speaker 1: we don't collide protons. We collide gold or lead nuclei.
Speaker 1: Like you take gold, you strip off all of the electrons.
Speaker 1: So now you have something with like a very very
Speaker 1: strong positive charge and you put that in the collider
Speaker 1: instead of protons, and you swing those around and they
Speaker 1: generate huge numbers of photons which can then smash into
Speaker 1: each other, meaning they glow like the the ring glows.
Speaker 1: But then how do you, like, how do you focus
Speaker 1: these so that they, you know, collide with another set
Speaker 1: of photons. Yes, you can't focus them at all. We
Speaker 1: do this anyway because we're interested in collisions of heavy
Speaker 1: nuclei for other things like park gluon plasma, and we're
Speaker 1: gonna do an episode about that soon. So we already
Speaker 1: have this program to put gold in the collider accelerated
Speaker 1: and smash it into other gold particles, because that's really
Speaker 1: cool and fun to do. But sometimes the gold particles
Speaker 1: miss each other. So say, for example, you have the
Speaker 1: gold particles swinging around the collider and they don't actually
Speaker 1: smash into each other. They miss. They call this an
Speaker 1: ultra peripheral interaction. As they pass by each other because
Speaker 1: both of them are surrounded by these glowing swarms of photons.
Speaker 1: Then those photons smash into each other. So like two
Speaker 1: gold atoms that do a near miss, then their photon
Speaker 1: swarms will bang into each other. And that's how you
Speaker 1: study photon photon collisions at very high energy mm you
Speaker 1: actually like miss the gold particles and you're hoping that
Speaker 1: they're they're glow their relative respective glow then collides. Yeah, exactly.
Speaker 1: It's like you have two celebrities moving through a party
Speaker 1: and their entourages smash into each other get into a fight. Yeah,
Speaker 1: what always seems to happen, right, exactly. That makes the
Speaker 1: most exciting videos the next day anyway, And so remember
Speaker 1: we can't like aim these gold particles very precisely. It's
Speaker 1: just that sometimes we miss and then we don't get
Speaker 1: a gold gold collision. But hey, we can look at
Speaker 1: that and see if we saw a photon photon collision instead.
Speaker 1: So it's like the accident the mess ups from the
Speaker 1: gold gold physics gives us interesting photon photon physics, and
Speaker 1: you can tell that it was two photons crashing into
Speaker 1: each other. It's a big mess and it's really hard
Speaker 1: to analyze, but sometimes they do. And in fact, they've
Speaker 1: seen electrons fly out, like they've seen these gold atoms
Speaker 1: miss each other and then pairs of electrons and positrons
Speaker 1: fly out, and they've analyzed it and they're convinced that
Speaker 1: this is due to the photons smashing into each other
Speaker 1: and creating matter. Wow. Cool, Yeah, because that's the only
Speaker 1: thing that could explain where these electron pair came from exactly.
Speaker 1: It also has to do with the angles, like sometimes
Speaker 1: you get electrons just flying out randomly, and so you
Speaker 1: could really convince yourself that this is due to the
Speaker 1: process that you think it is, Like you understand the
Speaker 1: quantum mechanics of it. You calculate and say, what are
Speaker 1: the probabilities for the electrons to fly at at this
Speaker 1: angle or that angle, and you measure a bunch of
Speaker 1: them and you see them at the angles you expect,
Speaker 1: and then you can convince yourself that you haven't been fooled.
Speaker 1: So this is an experiment. This is something we've just
Speaker 1: done last year in one the Star collaboration did this,
Speaker 1: not the Large Hadron Collider but at Rick and Brookhaven.
Speaker 1: Rick is r h i C. It stands for the
Speaker 1: Relativistic Heavy Ion Collider and they specialize in gold collisions
Speaker 1: and all sorts of other crazy stuff. Now, I guess
Speaker 1: the question is do they actually have to use gold
Speaker 1: or is this just how they roll? You don't have
Speaker 1: to use gold. It's just sort of awesome. It's funny though.
Speaker 1: At the led C on the European side, they tend
Speaker 1: to use lead, so it's gold in the American side
Speaker 1: and lead on the European side. And you know sometimes
Speaker 1: you smash lead together and gold comes out. You can
Speaker 1: make gold from lead at the collider, though it's not economical.
Speaker 1: That sounds very American, like, you know, the Germans are like, no,
Speaker 1: let's use lead, of course, that's more practical, and Americans
Speaker 1: are like, whatever, it's use gold, you know. You know,
Speaker 1: I think Rick is on Long Island, and you know,
Speaker 1: maybe they like their glam. You know, they like their
Speaker 1: blaying out there. What are you saying about Long Island
Speaker 1: or I think I just said it. You know, they
Speaker 1: like things shiny, and hey, who doesn't. I'm all into
Speaker 1: shiny stuff. I think you're saying that's how Rick rolls.
Speaker 1: I think we all just got Rick rolled. I'm never
Speaker 1: gonna let you down. But anyway, at the l a C.
Speaker 1: They do the same kinds of studies where instead they
Speaker 1: use lead ions and they see interesting things. They've seen
Speaker 1: light by light collisions where you get two photons coming
Speaker 1: out at weird angles. So at Rick they've seen two
Speaker 1: photons turned into two electrons. And at Atlas, the experiment
Speaker 1: I work on at the l A C. They've seen
Speaker 1: photons bounce off each other, deflect each other, and go
Speaker 1: out at weird angles. WHOA, yeah, because I guess. So
Speaker 1: you had these lead particles miss each other and you
Speaker 1: saw light coming off and weird like strange angles. Yeah,
Speaker 1: I guess right. And but they didn't actually bump with
Speaker 1: each other. They turned into an electron anti electron pair,
Speaker 1: and then those maybe bumped into each other and then
Speaker 1: created photons that sped off in weird directions exactly. And
Speaker 1: we can only explain those weird directions using that description
Speaker 1: you just gave, which is photons interacting with each other
Speaker 1: via this weird box of electrons and positron. So that's
Speaker 1: pretty cool because it's a rare process. It's hard to reproduce.
Speaker 1: It's a really good test of like do we actually
Speaker 1: understand the quantum mechanics, And it's something that was predicted,
Speaker 1: you know, decades and decades ago physicists like in the thirties,
Speaker 1: we're thinking about this, they're like, oh, is this possible?
Speaker 1: I think it might be possible. It would be really
Speaker 1: hard to do, and it's one of these like open
Speaker 1: questions that stood for decades is this really happening out
Speaker 1: there in nature? The amazing thing about the standard model
Speaker 1: is that it seems like an ugly clue sometimes, like
Speaker 1: there's so many things we don't understand, and yet it
Speaker 1: works so well. Every time we go to check it
Speaker 1: on the details, it's exactly right. It really nails it
Speaker 1: down to the decimal places, all right. So that means
Speaker 1: that you've done that experiment. You've shown to light beams
Speaker 1: at each other, and you see that light does collide
Speaker 1: with itself. Right, Although we missed an amazing opportunity. We
Speaker 1: don't have microphones in the colliders, so we can't tell
Speaker 1: what sound it made when those two photons matched into
Speaker 1: each other. Was like or like a, I'm like, what
Speaker 1: sound do lightsabers really me? I can't know you're joking about?
Speaker 1: Would light actually makes sound? No, it all happens in
Speaker 1: the vacuum, so it wouldn't make sound. But that would
Speaker 1: be awesome. Oh jeez, Daniel, that's the cardinal sin of
Speaker 1: Star Wars is the sound of explosions in space. You're
Speaker 1: trying to tell people that sounds happening at the large
Speaker 1: Fathroom collider Science disinformation right here on the podcast. But
Speaker 1: you know, there could have been surprises. It could be
Speaker 1: that we didn't see it, or that the photons came
Speaker 1: out of even weirder angles, which would mean that maybe
Speaker 1: the photons interact in different ways from the way we expect.
Speaker 1: You know, maybe there's some other particle that appears that
Speaker 1: let's photons talk to each other, like the axion particle,
Speaker 1: or something else weird and new that we don't know
Speaker 1: if it's out there. That's one of these reasons that
Speaker 1: we do these really high precision cross checks of these
Speaker 1: little details of particle physics, because it could be in
Speaker 1: one of those details we find something weird, and that
Speaker 1: unraveling that thread is exactly how we create a whole
Speaker 1: new understanding of the universe. You know, That's how we
Speaker 1: discovered quantum mechanics, understanding why the photo electric effect wasn't
Speaker 1: exactly as we expected it to. So we never know
Speaker 1: which little cross check is going to reveal the right
Speaker 1: thread to pull on, or the right light saber to
Speaker 1: turn on that makes just the right sound. I guess
Speaker 1: it's kind of interesting to think now that photons can
Speaker 1: interact with each other, although not directly, Does that mean
Speaker 1: the I have a question of whether all particles in
Speaker 1: Does that mean that all particles can interact with themselves
Speaker 1: just indirectly like it's everything is fair game in the universe. Yes,
Speaker 1: everything is fair game in the universe. Photons can interact
Speaker 1: with themselves in directly, right, they can generate E plus
Speaker 1: e minus pairs, which can then interact back with them.
Speaker 1: Good neutrinos, like neutrinos interact with regular electromagetic things through
Speaker 1: these quantum transformations. Absolutely, neutrino feels the weak force, and
Speaker 1: you can generate a W particle, right, and that W
Speaker 1: particle can interact with electrons, and that's exactly how the
Speaker 1: neutrino feels the rest of the universe, And neutrino could
Speaker 1: indirectly interact with corks in the same way or other stuff.
Speaker 1: The only thing we don't know about is dark matter.
Speaker 1: Is dark matter of particle which forces? Does it feel?
Speaker 1: Does it feel any forces at all other than gravity?
Speaker 1: Dark matter might be out there totally inert, unable to
Speaker 1: interact with anything except for gravity. As far as we know,
Speaker 1: we don't know if it's fair game or not, but
Speaker 1: it could be. It could be just be super rare.
Speaker 1: Maybe it could just be super rare. There could be
Speaker 1: some other kind of force that dark matter can used
Speaker 1: to interact with itself, Like the whole universe could be
Speaker 1: split into different sectors. This whole group of particles that
Speaker 1: can talk to each other with forces, the ones we
Speaker 1: know and love, and another separate sector that can only
Speaker 1: talk to each other and can't interact with us except
Speaker 1: through gravity. That's possible. What about menta chlorins? Can they
Speaker 1: interact with themselves only if they make sound? Right? Do
Speaker 1: they scream in space? Maybe that's me. That's the sounded
Speaker 1: light savers actually make when they crashing to each other.
Speaker 1: It's it's a billion miny chlorians screaming at the same time.
Speaker 1: Oh wow, Now that I understand the true cost of
Speaker 1: using the force, I will be more careful about it. Yeah,
Speaker 1: it's pretty tragic. Actually, Why that put the whole different
Speaker 1: spin on Star Wars, isn't it? It really does? Yeah?
Speaker 1: I wonder is any of this cannon anything? Yeah, because
Speaker 1: your physicist right right, Absolutely, this is all official now, folks. Yeah, yeah,
Speaker 1: But the question is can meta Glorian's feel not just
Speaker 1: forces but feelings. Well, we'll have to have one on
Speaker 1: the podcast as a guest and ask it yeah, or
Speaker 1: George Lucas move whichever one will come first. All right, George,
Speaker 1: give us a call. All right? Well again an interesting
Speaker 1: look into how the universe surprises you. You You know, sometimes
Speaker 1: you think that two things can interact with each other,
Speaker 1: but through quantum mechanical magic, they sort of do. And
Speaker 1: it's almost the same thing as if they were interacting
Speaker 1: with each other. Yeah, and the universe out there is
Speaker 1: a crazy, swarming, quantum mechanical and nightmare of complexity. But
Speaker 1: somehow we can pull together these beautiful, simple stories about
Speaker 1: particles interacting with each other and use those as lego
Speaker 1: bricks to describe all the amazing complex to be out there,
Speaker 1: even gold gold near misses at very high energies. It's
Speaker 1: incredible what physics has been able to do. So I
Speaker 1: think this is the part where we thank people for
Speaker 1: joining us, and this is the part where we join
Speaker 1: off our lightsabers. Thanks for joining us, See you next time.
Speaker 1: Thanks for listening, and remember that Daniel and Jorge explained
Speaker 1: the universe is a production of I Heart Radio. For
Speaker 1: more podcast for my Heart Radio, visit the I Heart
Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your
Speaker 1: favorite shows. YEA