Speaker 1: Hey, Daniel, is particle physics actually useful for anything?
Speaker 2: I mean it's good for like understanding the universe for sure.
Speaker 1: Yeah, But what can I use particles for? Can I
Speaker 1: use a charm quark charm my way into a better life?
Speaker 2: I think you're plenty charming already without any charm quarks.
Speaker 2: But we might be able to, like use muons to
Speaker 2: help us get to the moon.
Speaker 1: What just because they start with an M, because there
Speaker 1: are one letter off from moon and muon?
Speaker 2: I'm just reaching here. Man.
Speaker 1: Do you use a muans to feed cows?
Speaker 3: You know?
Speaker 1: Or grow more corn?
Speaker 3: More?
Speaker 2: Meuse less corn? I mean, nothing is certain in science,
Speaker 2: but that's probably a no.
Speaker 1: Why not? Don't cows eat muans? Don't they eat muuons?
Speaker 2: I think muons actually cause cows to mutate and make
Speaker 2: new kinds of cows.
Speaker 1: Oh well, maybe we'll get a taste of cout of it,
Speaker 1: In which case particles would be useful.
Speaker 2: Better steaks through physics, that's.
Speaker 1: Right, better particle burgers. Hi am jorg Im, cartoonist and
Speaker 1: the author of Oliver's Great Big Universe.
Speaker 4: Hi.
Speaker 2: I'm Daniel. I'm a particle physicist and a professor at
Speaker 2: UC Irvine, and I like believing that physics raises the steaks.
Speaker 1: The steaks like the cow steaks. Yeah, we've got to
Speaker 1: raise some steaks or the burgers maybe.
Speaker 2: I mean you're always talking about setting the steaks and stories.
Speaker 1: Right, Yeah, that's always important, but usually makes the emotional steaks,
Speaker 1: not the raw or well done kind.
Speaker 2: Well, I like to get my stakes at the restaurant
Speaker 2: called mcguffins.
Speaker 1: So do you like them rare or well done?
Speaker 2: I rarely eat steaks. Actually, it's the truth.
Speaker 1: He eats steaks rarely or rarely eat steaks.
Speaker 2: Yeah, I almost never eat steaks. My son is a
Speaker 2: big fan of protein, but he prefers chicken and turkey.
Speaker 2: He's the poultry man.
Speaker 1: Oh I see, he likes it lean.
Speaker 2: He likes it with wings.
Speaker 1: Nice's nice to stay lean and flighty as well. But anyways,
Speaker 1: welcome to our podcast Daniel and Jorge Explain the Universe,
Speaker 1: a production of our Heart Radio in.
Speaker 2: Which we help your brain to take flight and trim
Speaker 2: all the fat from your understanding of the universe. We
Speaker 2: think it's possible to zoom out there with our minds
Speaker 2: and understand everything that happens in the universe from the
Speaker 2: tiniest little particles to the biggest, most massive black holes,
Speaker 2: and our goal is to break it all down and
Speaker 2: explain it to you.
Speaker 1: That's right. We try to prevent your brain from having
Speaker 1: a cow thinking about the amazing and vast universe we
Speaker 1: live in, with all the complete physics and mechanics that
Speaker 1: are happening. We try to boil it all down to
Speaker 1: make it digestible and lean. We trim all the fat
Speaker 1: out of science communication while trying to keep it still
Speaker 1: plenty juice. And it's all one hundred percent organic, right,
Speaker 1: These no chemicals in this podcast.
Speaker 2: I mean, I guess everything's a chemical.
Speaker 1: So yeah, I mean I did use growth horribones to
Speaker 1: inflate my intelligence a little bit.
Speaker 2: But one of the reasons we're talking about such practical
Speaker 2: matters is because one of the criticisms of particle physics
Speaker 2: is that it can be kind of abstract, Like, are
Speaker 2: the questions of particle physics really useful to you on
Speaker 2: an everyday basis or is it more of a philosophical
Speaker 2: search for understanding of the nature of the universe.
Speaker 1: Yeah, you got to kind of wonder what is smashing
Speaker 1: all those particles together, spending billions of dollars. What it
Speaker 1: is that all useful for? How is that helping humanity
Speaker 1: move forward and maybe eat better as well?
Speaker 2: And of course there are lots of indirect benefits, just
Speaker 2: understan in the nature of the universe is its own
Speaker 2: prize and is priceless. But every dollar we invest in
Speaker 2: basic research comes back to us in terms of technological
Speaker 2: advancements and economic output and education and employment. So it's
Speaker 2: definitely a worthy way to spend money, I say, with
Speaker 2: absolutely no conflict of interest whatsoever.
Speaker 1: I was gonna say it definitely means employment for certain
Speaker 1: people like physicists.
Speaker 2: Perhaps it certainly does, but it benefits everybody because investment
Speaker 2: in basic research always leads to revolutions and our understanding
Speaker 2: and in technology and all sorts of stuff.
Speaker 1: Yeah. I guess without physics there wouldn't be this podcast,
Speaker 1: which sort of employs us right.
Speaker 2: And improves the lives of everybody on Earth.
Speaker 1: I guess if physics wasn't around, we'd have to talk
Speaker 1: about something else or explain the universe using other things.
Speaker 2: Absolutely, but sometimes particle physics can be more directly useful.
Speaker 2: Things we learned about weird particles exotic matter can actually
Speaker 2: be put to use to help us solve everyday earthly mysteries.
Speaker 1: It might actually also help us have X ray vision
Speaker 1: in a way. So today on the podcast, we'll be
Speaker 1: taxing the question can we use muons to see inside
Speaker 1: of things? What kinds of things are we talking about?
Speaker 1: Daniel m all kinds of boxes?
Speaker 2: Yes, absolutely, escape rooms, people's pockets, safes and banks.
Speaker 1: Yeah, oh boy? What's inside the burgers at McDonald's.
Speaker 2: Perhaps nobody wants to know that for real, that's not
Speaker 2: why you go to McDonald's.
Speaker 1: I don't think we'll get grand funding for that question.
Speaker 2: Now that's a situation where knowledge can ruin something.
Speaker 1: Yeah, yeah, but it is an interesting question whether we
Speaker 1: can use meons to see inside of things? You mean,
Speaker 1: is this sort of like using muons as X rays?
Speaker 2: Kind of Yeah, it's a similar idea. Can we use
Speaker 2: penetrating radiation to reveal something that is hidden from us?
Speaker 2: Can we look inside something without opening it up?
Speaker 1: Can we just use X ray? I thought that was
Speaker 1: already invented.
Speaker 2: We can use X rays, but X rays also have
Speaker 2: their limits, and some muons might open up the possibility
Speaker 2: to see inside things that are otherwise still close to us.
Speaker 2: Even with X rays hmm.
Speaker 1: Interesting. All right, we'll dig into it, but first, as usual,
Speaker 1: we were wondering how many people out there had thought
Speaker 1: about using muons to see inside of things and how
Speaker 1: we might be able to do that.
Speaker 2: Thanks very much to everybody who plays the game for
Speaker 2: this section of the podcast. We love hearing your voice,
Speaker 2: and if you would like to participate, it's very easy.
Speaker 2: It all happens over email. Just write to me too
Speaker 2: questions at Danielandjorge dot com.
Speaker 1: So think about it for a second. Do you think
Speaker 1: we can use muons to see inside of things? Here's
Speaker 1: what people had to say.
Speaker 4: No idea, absolutely, But I know that there's some talk
Speaker 4: of making a Muon's collider or something like that. I
Speaker 4: read about that in some news reports. So I'm gonna say, yeah, ah,
Speaker 4: why not. You know, if you can accelerate them enough
Speaker 4: and they don't dissipate energy like electrons, there should be
Speaker 4: a way to create collisions.
Speaker 3: I'm going to say, yes, I listened to your whole
Speaker 3: podcast about muons, but I've completely forgotten what they are.
Speaker 3: So I am going to take a kiss and say, yes,
Speaker 3: you can use mulons to see inside something.
Speaker 5: I would imagine using muons to look inside things would
Speaker 5: be what the same principle is using an electron microscope.
Speaker 5: I suspect muons are smaller than electrons, so for them
Speaker 5: to bounce off something and give an image to be
Speaker 5: bouncing off very small sub atomic particles.
Speaker 2: I don't know what a mion is.
Speaker 1: So I don't know, all right. I imagine a lot of
Speaker 1: people are like that person who said they don't know
Speaker 1: what a muon is. They don't know, but it sounds
Speaker 1: like a reasonable question. A lot of people will seem
Speaker 1: pretty optimistic about this.
Speaker 2: Yeah, if a muone is some new kind of particle,
Speaker 2: maybe it's got some new kind of powers or abilities
Speaker 2: or properties that lets you do new kinds of stuff.
Speaker 2: That's the optimism.
Speaker 1: All right, Well, let's put a steak through this question,
Speaker 1: and they started the basics, Daniel, What is exactly a muon?
Speaker 1: A lot of people seem to have heard us talk
Speaker 1: about it, but maybe forgotten. What it is.
Speaker 2: A muon can best be understood is like a heavier version,
Speaker 2: a more massive version of the electron. It's very very
Speaker 2: similar to the electron, has a lot of the same properties,
Speaker 2: same kinds of relationships as the electron, but it's more massive.
Speaker 1: I see, So it's a particle, And I guess maybe
Speaker 1: we should mention that the universe has particles, or at
Speaker 1: least the potential to create particles or further to exist particles,
Speaker 1: and a muon is one of these particles.
Speaker 2: Yeah, there are lots of particles that make up me
Speaker 2: and you and all the normal matter that's out there.
Speaker 2: If you drill inside of us, you find molecules and atoms,
Speaker 2: and those atoms are made of protons and neutrons and electrons.
Speaker 2: The protons and neutrons are made out of quarks. So
Speaker 2: at the most fundamental level, everything that you and I
Speaker 2: are made out of, and everything that you and I eat,
Speaker 2: including steaks and cows, are made up of upquarks and
Speaker 2: down quarks and electrons. So those are the three basic
Speaker 2: building blocks of normal matter. But there are other kinds
Speaker 2: of particles out there that the universe can make. They're
Speaker 2: sort of on the menu, but they're not stable and
Speaker 2: they're not involved in building normal, everyday atomic matter. So
Speaker 2: there's sort of various categories of particles out there. Ones
Speaker 2: it can be made and exist all over the universe,
Speaker 2: and ones it can be made but only exist briefly.
Speaker 1: Or at least in the current universe that we have, right,
Speaker 1: I think we talked about maybe before, Like maybe in
Speaker 1: the early universe, the particles like nuons were common and
Speaker 1: they would hang out.
Speaker 2: Yeah, the frequency of which you find these particles definitely
Speaker 2: depends on the temperature of the universe because the unstable
Speaker 2: particles muons, charm corks, top quarks are a lot more
Speaker 2: massive than the other particles that take more energy. These days,
Speaker 2: it's rarer to create that kind of energy because the
Speaker 2: universe is more spread out and colder. Back in the
Speaker 2: early days of the universe, it wasn't as hard to
Speaker 2: get enough energy together to make a muon or a
Speaker 2: top quark. They always have a short lifetime, though they
Speaker 2: still don't last very long, but they're made much more
Speaker 2: often in the early universe. These days, it takes more
Speaker 2: specialized conditions like humans smashing particles together or cosmic rays
Speaker 2: hitting the atmosphere to create the conditions to make these
Speaker 2: weird particles. They still don't last for very long.
Speaker 1: So like the meon you said only lives for a
Speaker 1: few microseconds, right.
Speaker 2: Yeah, the muon lives for two point two microseconds before
Speaker 2: it decays into an electron and a couple of neutrinos,
Speaker 2: and we call the muon like a cousin of the
Speaker 2: electron because it has a lot of the similar properties.
Speaker 2: It's negatively charged like the electron is. It's paired with
Speaker 2: the neutrino the way an electron is. So in our
Speaker 2: sort of table of particles, we put the quarks in
Speaker 2: one category and these other particles we call leptons in
Speaker 2: another category because the muon, and like the electron, also
Speaker 2: doesn't feel the strong nuclear force that the quarks do.
Speaker 1: I see. So it's basically an electron, but somehow it
Speaker 1: just has a more mass to it. Like the label
Speaker 1: that says this is this is how much an electronic way,
Speaker 1: it just happens to be more for the muon, But
Speaker 1: other than that, it's almost exactly the same, Like it
Speaker 1: has the same electrical charge and all the other quantum values.
Speaker 2: Right, Yeah, it's about two hundred times more massive than
Speaker 2: the electron. And nobody knows why that is, Like why
Speaker 2: does the electron have this mass and the muon have
Speaker 2: that mass? These are just numbers that we've discovered in
Speaker 2: the universe without any explanation. You might think that the
Speaker 2: Higgs gives an explanation for why some particles have more
Speaker 2: mass than some have less. And it's true that the
Speaker 2: muon has more mass than the electron because the Higgs
Speaker 2: interacts with it more, giving it more mass, but that
Speaker 2: doesn't explain why there's a difference. It just kicks the
Speaker 2: can down the road. Instead of asking why does the
Speaker 2: muon have more mass than the electron, we now ask
Speaker 2: why does the muon interact with the Higgs more than
Speaker 2: the electron does. The Higgs explains what mass is, but
Speaker 2: not why some particles have more or less of it.
Speaker 2: It's still just two numbers without an explanation. Now there's
Speaker 2: two are interaction strength instead of mass. And there's a
Speaker 2: third version of the electron called the tao, which is
Speaker 2: even more massive. And this is the general pattern of
Speaker 2: the particles. Each of the particles we talked about, the electron,
Speaker 2: the upcork, the down cork has two copies of it
Speaker 2: which are more massive. So this is some deep symmetry,
Speaker 2: some structure to the universe that we've observed. We've organized,
Speaker 2: we've seen the pattern, we've laid it out of the table,
Speaker 2: but we've not understood it. And the mew one was
Speaker 2: like one of the first clues we had that there
Speaker 2: was more out there to the universe than just the
Speaker 2: particles that made up our matter.
Speaker 1: But I guess, you know, what does it mean that
Speaker 1: it only lists for two point two microseconds? Like does
Speaker 1: that even count as existing? You know, like why I
Speaker 1: didn't call it a thing if it's only around for
Speaker 1: two point two microseconds? You know, like can it move
Speaker 1: around that much? Or or is this one of these
Speaker 1: like relativistic things where to us it lists or two
Speaker 1: point two microseconds, but maybe it's going really fast it
Speaker 1: lives for a really really long time.
Speaker 2: I think yes to all of that, although you know,
Speaker 2: the timescale is always relative, like we only live for
Speaker 2: one hundred years on the time scale the universe, that's
Speaker 2: basically nothing. Do we even count as existing? I would
Speaker 2: say yes, right, because time scales are relative relative to
Speaker 2: some other particles, like the top quark lives for ten
Speaker 2: to the money twenty three seconds, But we still think
Speaker 2: that it's a thing. Like the neutron lasts for I
Speaker 2: think eleven minutes before it decays, So these timescales are
Speaker 2: all relative. What we actually mean by two point two
Speaker 2: microseconds is in the muon's rest frame, like if you
Speaker 2: had a muon in front of you at rest, and
Speaker 2: you started a clock when it was created, and you
Speaker 2: waited until a decayed, that would be two point two microseconds.
Speaker 2: But you're right, relativity plays a big role. Muons are
Speaker 2: often moving really really fast, especially when they're created in
Speaker 2: the atmosphere, So if they're moving near the speed of light,
Speaker 2: then a clock that's moving with them is slowed down.
Speaker 2: And so the reason muons can actually survive from the
Speaker 2: top of the atmosphere where they're made to hit us
Speaker 2: on the ground is because their time is slowed. So
Speaker 2: from our perspective, they can last for much much longer
Speaker 2: than two point two microseconds, long enough to make it
Speaker 2: to the surface of the Earth.
Speaker 1: And what is it mean that it decays or does
Speaker 1: it disintegrade? Does it like the energy just diffuses or
Speaker 1: transforms it through something else? What does that actually mean?
Speaker 2: Yeah, sometimes we think about decay as like something breaks
Speaker 2: up and you get the component bits. It's like cracking
Speaker 2: something open, breaking it into its basic legos, like an
Speaker 2: atom broken up into its protons and neutrons. That's not
Speaker 2: what's happening here, because when a muon decays, it turns
Speaker 2: into an electron and two neutrinos. But it's not like
Speaker 2: the electron and those neutrinos were inside the muon. It's
Speaker 2: not like the muon is made of the electron and
Speaker 2: the two neutrinos. Instead, think of that energy as passing
Speaker 2: from the muon field to the electron field and the
Speaker 2: neutrino fields. Remember that all these particles are really just
Speaker 2: ripples in universe spanning fields that feel all of space.
Speaker 2: Every part of space has a muon field, an electron field,
Speaker 2: and the three different neutrino fields. So it's happening here
Speaker 2: is that those fields are coming into contact, they're interacting,
Speaker 2: and the muon field oscillations in that field are not stable.
Speaker 2: They like to decay down into the electron field and
Speaker 2: the neutrino fields. So that's what's happening here.
Speaker 1: But maybe a question is like why is it so unstable,
Speaker 1: Like what makes the muon field which makes muons prone
Speaker 1: to be to basically dissipating or disappearing, and not, for example,
Speaker 1: the electron field, which seems super duper stable.
Speaker 2: The electron would like to decay, but there's nothing for
Speaker 2: it to decay into because it's the lowest mass particle
Speaker 2: in this chain, it's the lightest charged particle, and so
Speaker 2: the muon can decay to an electron, which is a
Speaker 2: lower mass particle, and so it does because in doing so,
Speaker 2: it spreads out the energy. The universe doesn't like to
Speaker 2: have a lot of energy concentrated in one place, likes
Speaker 2: to spread it out. It's like entropy at a most
Speaker 2: basic level. And so a high mass particle will tend
Speaker 2: to decay into lower mass particles if it can, because
Speaker 2: that provides more arrangements of that energy. Instead of having
Speaker 2: all of it just in mass, now you have it
Speaker 2: in a lower mass particle, plus lots of different possible
Speaker 2: momentum states. So the quantum mechanical probabilities are just much
Speaker 2: more for lower mass particles, and so they're more likely
Speaker 2: to happen.
Speaker 1: But I guess, maybe why doesn't Why can't the electron
Speaker 1: break into something smaller? Is it just like we just
Speaker 1: haven't seen it do that, or maybe it's impossible.
Speaker 2: Well, we haven't seen an electron decay. We think electrons
Speaker 2: are stable. Though it's possible that electrons live for like
Speaker 2: a trillion years, we just never seen one decay because
Speaker 2: they just last for a long, long time, right, it's
Speaker 2: the same with the proton. We think the proton is stable,
Speaker 2: but we don't know. We've never seen one decay, so
Speaker 2: we think it might be stable or very very very
Speaker 2: long lived. But for the electron to decay, there would
Speaker 2: have to be something for it to decay into that
Speaker 2: also has electric charge. Because electric charge is conserved, it
Speaker 2: can't just go away. We don't know if any lower
Speaker 2: mass charged particle than the electron, So it's sort of
Speaker 2: like the bottom rung of the ladder, which is why
Speaker 2: energy sort of gets stuck there.
Speaker 1: I see, okay, so well, then the muon decays because
Speaker 1: it can decay to other particles. Does it get triggered
Speaker 1: by something, or if you just leave a meuon there,
Speaker 1: it'll be like okay, I'm done, and then it breaks apart.
Speaker 2: If you just leave a muon in the vacuum, it
Speaker 2: will decay. Mwan flying through space will decay on their own.
Speaker 2: They can also interact with stuff because they have charge.
Speaker 2: They can interact with electrons, and they can interact with
Speaker 2: protons and all sorts of stuff. So if you slam
Speaker 2: them into a block of lead, for example, they will
Speaker 2: interact and that can also trigger the decay, but muons
Speaker 2: on their own will also just decay.
Speaker 1: Can they appear out of nowhere? Like, what does it
Speaker 1: take to make a muon? Or how are they made
Speaker 1: if they're a thing in the universe. Is it just
Speaker 1: whenever you have enough energy concentrated into one spot or
Speaker 1: what's the origin story of a muon?
Speaker 2: So the origin stories that you get enough energy into
Speaker 2: sort of a higher mass field to feel that can
Speaker 2: decay into muons. Energy likes to flow down the lower
Speaker 2: mass fields like rungs down the ladder, So you got
Speaker 2: to get enough energy into a higher mass field and
Speaker 2: then it can decay into muons. So the typical way
Speaker 2: that muons are made naturally in our environment is they
Speaker 2: have a cosmic ray, which is like a proton slimming
Speaker 2: into some particle in the atmosphere, which creates a lot
Speaker 2: of energy density in one space, and then you create
Speaker 2: some very massive, unstable particle, and a lot of particles
Speaker 2: decay into muons, So you might create like a pion
Speaker 2: or a chaon. These are more massive particles that like
Speaker 2: to decay into muons, and then those decay in the atmosphere,
Speaker 2: giving you a muon which flies down to the surface.
Speaker 2: Of the Earth.
Speaker 1: But don't you need where does the charge come from?
Speaker 2: Protons are charged, right, so the charge comes from the
Speaker 2: cosmic ray, and also there's loss of charge in the
Speaker 2: upper atmosphere. Even a neutron slamming into a particle in
Speaker 2: the upper atmosphere, and like disintegrating an oxygen molecule can
Speaker 2: create showers of charged particles.
Speaker 1: M where does the negative charge come from? Isn't a
Speaker 1: photon neutral?
Speaker 2: Well, first of all, we have two flavors of muons.
Speaker 2: We have negative muons, which are the normal ones, and
Speaker 2: then anti muons, which are positively charged. In particle physics
Speaker 2: we don't really care so much about it, and both
Speaker 2: of them are created in the upper atmospherees, So we
Speaker 2: have anti muons and muons created in the upper atmosphere.
Speaker 2: But your question is a good one. If you start
Speaker 2: from a positively charged proton, how you end up making
Speaker 2: like a negatively charged muon. The answer is that there's
Speaker 2: just a lot more stuff in in this interaction then
Speaker 2: we're describing, Because a proton is a big complicated bag
Speaker 2: of quarks and it slams into something else in the atmosphere,
Speaker 2: which is a big complicated bag of other protons and neutrons,
Speaker 2: so there's plenty of charges around to create something which
Speaker 2: decays into a negatively charged particle and balance it out
Speaker 2: with all the rest of the stuff. So a proton
Speaker 2: can turn into a huge shower of negative and positive
Speaker 2: particles with a total charge of plus one. So you
Speaker 2: can have lots of muons and anti muons created in
Speaker 2: these showers.
Speaker 1: All right, Well, whether you're pro or anti muon maybe
Speaker 1: is the question of the episodes. Can we use a
Speaker 1: muon to see inside of things and maybe put these
Speaker 1: giant particles to use that's the question. Let's dig into that,
Speaker 1: But first let's take a quick break. All right, we're
Speaker 1: talking about the electrons, cousin, more massive cousin, the muon,
Speaker 1: and whether it can be used to see inside of
Speaker 1: things like steaks and cows perhaps.
Speaker 2: And also may be solving mysteries of archaeology.
Speaker 1: Ooh, you mean like ancient buried cows.
Speaker 2: Yes, maybe ancient buried cows? Literally?
Speaker 1: Did early man eat steak or not? Or were they
Speaker 1: v in?
Speaker 2: Can you age a steak for thousands of years and
Speaker 2: still have it be tasty?
Speaker 1: Did Paleoman actually follow the paleodiet? We might use meons
Speaker 1: for that all right, So we talked about what the
Speaker 1: meon is. It's the more massive cousin of the electron,
Speaker 1: and that it rarely lasts more than two point two
Speaker 1: microseconds in nature in the universe. So if it's so
Speaker 1: elusive and unstable, how did we discover this heavy particle.
Speaker 2: Well, it turns out that muons are everywhere because cosmic
Speaker 2: rays are constantly slamming into the upper atmosphere, creating showers
Speaker 2: of particles, a lot of which turned into muons. So
Speaker 2: there are ten thousand muons per square meter per minute
Speaker 2: at the surface of the Earth.
Speaker 1: By cosmic rays, you mean like just other particles going
Speaker 1: really really fast somehow hitting the Earth exactly.
Speaker 2: Sometimes people think that space is a vacuum. It's emptiness,
Speaker 2: there's nothing out there, but the Sun is pumping out
Speaker 2: protons and electrons and all sorts of stuff, and the
Speaker 2: galaxy has lots of sources of high energy particles. So
Speaker 2: we're really flying through a wind of particles, meaning that
Speaker 2: you can think of them as like tiny little meteors
Speaker 2: hitting the upper atmosphere one proton at a time, or
Speaker 2: maybe an iron and nucleus at a time in creating
Speaker 2: a little shower of energy, just the same way that
Speaker 2: a meteor hitting the atmosphere will interact with the atmosphere
Speaker 2: and get friction and break up and slow down. A
Speaker 2: tiny particle like a proton, with enough energy will create
Speaker 2: a shower of particles which eventually reaches the surface of
Speaker 2: the Earth, and a lot of those are muons. There
Speaker 2: are also photons and electrons and other stuff in there,
Speaker 2: but muons are the most penetrating. They tend to pass
Speaker 2: through matter without interacting, so a lot of them make
Speaker 2: it to the surface of.
Speaker 1: The Earth's sort of a good thing, right, we didn't
Speaker 1: have the atmosphere and we were getting hit directly by
Speaker 1: cosmic grays, we might not be around today, right. These
Speaker 1: costomic grays are very harmful, so it's a good thing
Speaker 1: they're being kind of broken up into muons.
Speaker 2: Yeah. The atmosphere is like a big blanket that protects
Speaker 2: you from the radiation of outer space. When astronauts go
Speaker 2: up into space, they have to take special precautions to
Speaker 2: avoid being slammed into by all of this radiation. When
Speaker 2: there's like a solar storm, the astronauts have like a
Speaker 2: panic room that can go into with extra shielding to
Speaker 2: protect themselves from all that radiation. But the higher up
Speaker 2: you go in the atmosphere, the more radiation you're exposed
Speaker 2: to because more these particles survive. So every time you
Speaker 2: take a flight, for example, you're exposing yourself to more radiation.
Speaker 2: This is one reason why like flight attendants and pilots
Speaker 2: are limited to how many days a month they can work.
Speaker 1: All right, So then the atmosphere breaks up the cosmic
Speaker 1: grays and you said, turns them mostly into muons or
Speaker 1: rarely into meons. How often are muons created by these
Speaker 1: cosmic rays.
Speaker 2: It's sort of like a chain. The proton creates a
Speaker 2: bunch of particles, which then decaynees is something, which then
Speaker 2: decaynes something, and the muon is like an end product.
Speaker 2: Then it tends to last the longest. So saw like
Speaker 2: the muon dominates the production of particles. You also make electrons,
Speaker 2: and you make neutrinos, and you make photons. The neutrinos
Speaker 2: and the muons are the ones that make it through
Speaker 2: the rest of the atmosphere. They tend to interact a
Speaker 2: little bit less than electrons and photons, so you see
Speaker 2: them on the surface of the Earth more often.
Speaker 1: Oh, I see you're also making a lot of electrons
Speaker 1: and other particles. But maybe like the electrons get stopped
Speaker 1: by all the remaining air in the atmosphere.
Speaker 2: Exactly. Electrons like to interact with stuff. The electrons passing
Speaker 2: through air will interact with those molecules much more often
Speaker 2: than muons do. Muons are more penetrating.
Speaker 1: And why is that? Are they just more antisocial?
Speaker 2: It actually has a really fascinating explanation that has to
Speaker 2: do with special relativity, and this is the power that
Speaker 2: muons have to let us see through things. Muons are
Speaker 2: more penetrating because they have more mass, so they're two
Speaker 2: hundred times more massive than the electron. Otherwise, from a
Speaker 2: particle physics perspective, they're very similar. They feel the weak force,
Speaker 2: they feel electromagnetism, they don't feel the strong force. But
Speaker 2: if you shoot a beam of muons into like a
Speaker 2: block of lead, you'll get a lot more out on
Speaker 2: the other side than if you did with electrons. And
Speaker 2: the reason is their mass.
Speaker 1: Is it like to have more inertia? Is that kind
Speaker 1: of what you're getting at? Just like you know, if
Speaker 1: I shoot a small pebble into a pool or something,
Speaker 1: or if you throw shoot a bulling ball through it,
Speaker 1: like the bowling ball will get through the pool further.
Speaker 1: Or is it some other kind of mechanism.
Speaker 2: It's another mechanism. It's actually because they are interacting less
Speaker 2: because they see less of the material. It's a special
Speaker 2: relativity effect. If you have an electron and a muon
Speaker 2: at the same energy, the muon is actually going slower
Speaker 2: because it's more massive, like more of the energy is
Speaker 2: taken up creating a mass of the muon. So if
Speaker 2: you give them the same energy, the muon is moving
Speaker 2: slower as a lower velocity than the electron at the
Speaker 2: same energy because it has more mass.
Speaker 1: So then you're sort of constraining things to be all
Speaker 1: the same energy.
Speaker 2: Yeah, exactly, because it's the typical energy that these particles
Speaker 2: are produced at in these showers. So if you have
Speaker 2: an electron and muon of the same energy, the muon
Speaker 2: is going slower and that affects how it interacts because
Speaker 2: it sees less of the material. To an electron moving
Speaker 2: nearly the speed of light, everything in front of it
Speaker 2: is squeezed by special relativity. Remember we talked about how
Speaker 2: things moving near the speed of light look shorter. That's
Speaker 2: also true from their perspective. An electron whizzing through the
Speaker 2: atmosphere sees the distance to the surface of the Earth
Speaker 2: as closer than we see it because it's moving fast
Speaker 2: relative to the surface of the Earth, so things are squeezed.
Speaker 2: As a result, it can interact with more the atmosphere.
Speaker 2: Or another way to think about it is like the
Speaker 2: atmosphere is denser because all that gas is like the
Speaker 2: Lorentz contracted in front of it into something a little
Speaker 2: more dense. So it can interact with more of the
Speaker 2: atmosphere because it's moving at a higher speed and has
Speaker 2: more of this special relativity enhancement.
Speaker 1: Wait, that doesn't make a whole lot of sense to me.
Speaker 1: Like you're saying, like the rest of the atmosphere to
Speaker 1: an electron, because it's moving fast, the atmosphere looks thinner
Speaker 1: and more dense, and so it's harder to get through it.
Speaker 1: But it's still the same length to us. Isn't it
Speaker 1: like it's squeezed, but it's still the same It's going
Speaker 1: through the same amount of stuff as the slower nuon.
Speaker 5: No.
Speaker 2: Yeah, but it sees more of the material at once.
Speaker 2: It's like it has more atoms to interact with so
Speaker 2: this is a quantum mechanical process, and it has like
Speaker 2: a probability to interact with an atom. An electron flies
Speaker 2: by an atom, there's a chance it's going to interact
Speaker 2: and a chance that it's not. The more atoms it
Speaker 2: flies by, the more likely it's going to interact and
Speaker 2: lose some of its energy. So if you squeeze more
Speaker 2: atoms into the same space, then it's got a higher
Speaker 2: chance of interacting. And what special relativity does is because
Speaker 2: the electron is moving faster, it Lorentz contracts the stuff
Speaker 2: in front of it basically squeezes in more atoms at once.
Speaker 1: I see, you sort of have to change the way
Speaker 1: you're thinking about how these particles interact. Like you're saying,
Speaker 1: like you know, an electron when it hits a wall,
Speaker 1: it's not actually touching the wall. It just gets close
Speaker 1: enough to it that there's some sort of quantum mechanical
Speaker 1: transmission between the two that makes them technically interact.
Speaker 2: Right, Yeah, exactly. And that's why, for example, neutrinos can
Speaker 2: pass through a light year of lead. They're passing through
Speaker 2: the same material and they're not like dodging around those particles.
Speaker 2: It's not a mechanical physical interaction of things touching. It's
Speaker 2: a quantum mechanical interaction of forces. The neutrino just doesn't
Speaker 2: interact with those particles at all, like phases right through
Speaker 2: that stuff, because it doesn't feel electromagnetism. It only has
Speaker 2: a smaller chance to interact with every single particle. So
Speaker 2: that's why neutrinos pass through almost everything, and that's why
Speaker 2: there's a difference between the penetrating power of muons and electrons. Muons,
Speaker 2: being more massive at the same energy, are effectively moving slower,
Speaker 2: so they have less of this special relativity boost where
Speaker 2: they can interact with otherwise further away atoms that now
Speaker 2: look closer to them, and so they can feel their fields.
Speaker 1: So as thee electron is a showering down coming down
Speaker 1: the atmosphere, you're saying it sees the bottom of the
Speaker 1: atmosphere as closer, which might make it more likely to
Speaker 1: But I guess the weird thing is that, you know,
Speaker 1: if it does interact with the bottom of the atmosphere,
Speaker 1: what didn't it mean it made it through the atmosphere,
Speaker 1: And so it's really, isn't it sort of the same
Speaker 1: thing probability?
Speaker 2: It's a cool way to look at it. But it
Speaker 2: can interact with the bottom of the atmosphere while still
Speaker 2: not being that far through the atmosphere because to it,
Speaker 2: the bottom of the atmosphere is not that far away,
Speaker 2: so it can still feel those fields right right, it
Speaker 2: feels it closer.
Speaker 1: But if it interacts with the bottom of the atmosphere,
Speaker 1: isn't it the same as making it through the atmosphere,
Speaker 1: Like it's kipped everything above and it made it to
Speaker 1: the bottom of the atmosphere. That means it made it
Speaker 1: through the atmosphere.
Speaker 2: It doesn't have to make it to the bottom of
Speaker 2: the atmosphere in order to interact with things at the
Speaker 2: bottom of the atmosphere. Remember, all of these things are
Speaker 2: action at a distance. You're feeling the fields of things.
Speaker 2: Two electrons don't have to touch each other in order
Speaker 2: to interact. They just have to feel their.
Speaker 1: Field or I guess maybe, But I mean it's like,
Speaker 1: what's the difference between an electron that makes it through
Speaker 1: the atmosphere and interacts with the bottom of the atmosphere
Speaker 1: and an electron that sees the bottom of the atmosphere
Speaker 1: is closer and interacts with it. Aren't they both the
Speaker 1: same result, and that don't both mean that they made
Speaker 1: it through the atmosphere.
Speaker 2: So higher speed electron is more likely to interact because
Speaker 2: it sees more of the atmosphere, and it's going to
Speaker 2: interact at a higher altitude than a lower velocity electron,
Speaker 2: which doesn't see as much of the atmosphere because a
Speaker 2: special relativity boost. And so even if you're interacting with
Speaker 2: things that are lower down, your actual location is still
Speaker 2: higher up.
Speaker 1: Oh, I see you're talking about it might decay before
Speaker 1: it reaches the bottom of the atmosphere. It's not necessarily
Speaker 1: interacting with the bottom of the atmosphere. Like if it
Speaker 1: touches the bottom of the atmosphere, it means it made
Speaker 1: it through the atmosphere, doesn't it.
Speaker 2: Well, electrons don't decay, right, All they can do is interact.
Speaker 2: But again, you can interact with something at the bottom
Speaker 2: of the atmosphere without being there, right the same way
Speaker 2: like the Earth is interacting with the Sun without touching
Speaker 2: the Sun, because if you can feel its gravity at
Speaker 2: a distance.
Speaker 1: All right, well, let's assume that then that that's the case.
Speaker 1: And so you're saying neuons can make it through more
Speaker 1: of the atmosphere or anything in particular, just because they're moving,
Speaker 1: they tend to be moving slower, although if you had
Speaker 1: a fast moving meuon, that wouldn't be.
Speaker 2: The case exactly, And we actually see those at the
Speaker 2: Large Hadron Collider. We can make muons with enough energy
Speaker 2: that they're moving at very relativistic speeds and they interact
Speaker 2: with matter like electrons do, so we can see like
Speaker 2: muon created showers when we happen to make a really
Speaker 2: really high velocity muon. It's just a feature of muons
Speaker 2: and electrons at the energies that they tend to be
Speaker 2: produced at in our cosmic rays here on Earth because
Speaker 2: of the ratio of their masses.
Speaker 1: I guess, couldn't you just use a slower moving electron.
Speaker 1: Wouldn't that be the equivalent of a slow moving muon?
Speaker 1: Then then the electron could penetrate things more.
Speaker 2: Yeah, it's a good question. You can slow down electrons,
Speaker 2: but then there are other effects that are going to
Speaker 2: come into play that are going to make it interact more.
Speaker 2: So there isn't a window there for electrons to do
Speaker 2: the same trick that muons can do.
Speaker 1: I think what you're really saying is like you're trying
Speaker 1: to use muons, not as a general concept, but neuons
Speaker 1: that are particularly created in the cosmic rays when they interact,
Speaker 1: when they slam into the atmosphere. You're trying to put
Speaker 1: forward the idea of using these meons that are showering
Speaker 1: as as maybe like an X ray machine.
Speaker 2: Yeah, exactly. Muons have this window of energy in which
Speaker 2: they can penetrate really really deeply. If they move more slowly,
Speaker 2: then they run into the same atomic physics that electrons have.
Speaker 2: They can get captured. They move faster, then they get
Speaker 2: the realtivistic effects, and they interact just like electrons. But
Speaker 2: muons have this special window, this energy range in which
Speaker 2: they can pass through a lot of matter, much more
Speaker 2: than X rays can. X rays can pass through some
Speaker 2: kinds of matter, which is why you can use them
Speaker 2: to see your bones and inside your body, but muons
Speaker 2: can pass through a lot more matter than X rays can.
Speaker 2: X rays, for example, cannot pass through huge blocks of granite.
Speaker 1: But you sort of skip through something, which is you said, electrons,
Speaker 1: even if you slow them down, are not as good
Speaker 1: as muons for X rays applications.
Speaker 2: And why is that, Well, they'll get captured by atoms
Speaker 2: like electrons moving slowly will just get captured, but not
Speaker 2: a muon. A muon moving really slowly also will get captured. Yeah,
Speaker 2: muon has a window. It's got a minimum energies do
Speaker 2: this and a maximum energy in order to do this
Speaker 2: penetrating trick.
Speaker 1: So then you were saying, how were these muons discovered?
Speaker 2: So these muons were discovered in cosmic rays. People were
Speaker 2: studying electrons and somebody had even discovered the anti electron,
Speaker 2: and they're studying these particles by watching them move in
Speaker 2: magnetic fields and seeing how they curve, and they saw
Speaker 2: something which looked kind of like an electron and had
Speaker 2: a charge like an electron. They curved in a magnetic
Speaker 2: field the same direction as an electron, but they didn't
Speaker 2: curve as much, and it penetrated much more deeply, like
Speaker 2: you could put slabs of lead in front of your
Speaker 2: detector and you would still see it. So nineteen thirty
Speaker 2: six physicistic Caltech first discovered.
Speaker 1: These things and they bend less in a magnetic field
Speaker 1: because of their mass, right, basically their innership or is
Speaker 1: it also some weird quantum interaction.
Speaker 2: No, it's no, it's a very classical thing. It's just
Speaker 2: because of their mass. Yeah, mmmmm, I see.
Speaker 1: All right, Well let's get into how you might use
Speaker 1: muons to penetrate things, see inside of things, maybe discover
Speaker 1: ancient artifacts inside of pyramids. So let's dig into that.
Speaker 1: But first let's take another quick break. Or we're talking
Speaker 1: about neons and how you can use them to see
Speaker 1: inside of things, and we talked about how meons sort
Speaker 1: of have an extra penetrating effects more than its cousin,
Speaker 1: the electron, because it's heavier. And so the idea is
Speaker 1: then to use this like an X ray basically, like
Speaker 1: shoot it at something and if it gets through, then
Speaker 1: that tells you what's inside of the thing.
Speaker 2: Yeah, you can sort of use it as a way
Speaker 2: to measure the density of something. If you have an
Speaker 2: object and you don't know if inside of it is
Speaker 2: nothing like a vacuum or a huge block of super
Speaker 2: dense uranium, you can try to shoot it with a
Speaker 2: bunch of muons and count how any come out. By
Speaker 2: figuring out how many make it through, you can tell
Speaker 2: what the density of something is. This only works if
Speaker 2: you have something which has a chance to make it through, Right,
Speaker 2: If you just shoot photons at a block then none
Speaker 2: of them are going to make it through. They're all
Speaker 2: going to get absorbed. Doesn't tell you anything about what's inside.
Speaker 2: But if you have a particle which has a chance
Speaker 2: to make it through for some densities, then you can
Speaker 2: measure the rate at which does make it through and
Speaker 2: figure out what the density of that stuff was, right.
Speaker 1: Right, I guess it's sort of like X rays. Like
Speaker 1: X rays, if I just shine of flashlight onto my body,
Speaker 1: it's going to bounce off the skin, or at least
Speaker 1: most of the photons, because the light is at a
Speaker 1: certain wavelength. But if I change the wavelength to that
Speaker 1: of an X ray, it will go through my body.
Speaker 2: Sort of, yeah, exactly, some of the X rays will
Speaker 2: make it through. And if you have an X ray
Speaker 2: detector on the other side, you can pick that up
Speaker 2: and by looking at the pattern of where the X
Speaker 2: rays made it through and didn't make it through, you
Speaker 2: can tell what the density of stuff is. And that's
Speaker 2: how you can tell the difference between like bone or
Speaker 2: metal and soft tissues, which have different densities and therefore
Speaker 2: different absorption for the X rays. So it's exactly the
Speaker 2: same principle for muons, except that muons will make it
Speaker 2: through things that X rays will not survive, which allows
Speaker 2: you to effectively X ray or muon ray other kinds
Speaker 2: of things that you couldn't otherwise see inside.
Speaker 1: So in the case of an X ray and actually
Speaker 1: can go through my body because it's a different wavelength,
Speaker 1: which what makes it go through my body more than
Speaker 1: say the life from a flashlight.
Speaker 2: So X rays have more energy their higher frequency, right,
Speaker 2: And the interaction with a photon with the materials in
Speaker 2: your body depends on the energy. But a whole episode
Speaker 2: about transparency. Why photons can go through some things and
Speaker 2: can't go through other things, and it's all about whether
Speaker 2: they will interact. Photons can interact with matter depending on
Speaker 2: their energy. They can get absorbed if there are atoms
Speaker 2: out there that can eat them.
Speaker 1: Because atoms only like to eat photons that are a
Speaker 1: particular frequency, right, Yeah, exactly, Like they don't just like
Speaker 1: any photon. They have to be a special frequency because
Speaker 1: of quantum mechanics.
Speaker 2: Yeah, they have various energy levels. They have these ladders
Speaker 2: of energies, so they can absorb photons of like just
Speaker 2: the right energy, and that affects what photons can pass
Speaker 2: through your body or through glass. Or through metal or
Speaker 2: any kind of stuff.
Speaker 1: So that's why X rays can go through things more
Speaker 1: than regular light. And we talked about how muons can
Speaker 1: do that too. Why is that because they don't they
Speaker 1: have a specific energy range that makes them go through
Speaker 1: but not interact with the atoms, say inside my body.
Speaker 2: Yeah, exactly. At certain energy range, they won't be captured
Speaker 2: by atoms, and they're not quite going fast enough to
Speaker 2: have a special relativistic boost where they interact with lots
Speaker 2: more atoms than otherwise, and so they can make it
Speaker 2: through a lot of this material. And so you can
Speaker 2: see muons even if you're like deep underground, you put
Speaker 2: a muon detector like meters and meters underground, those muons
Speaker 2: will pass right through that solid rock and hit your
Speaker 2: muon detector.
Speaker 1: Now, is the idea that you're shooting these muons like
Speaker 1: you're creating them and shooting them with like an X
Speaker 1: ray gun or a mewray gun and then catching them
Speaker 1: on the other side, or is the idea that you're
Speaker 1: using the ones that are showering down on us from
Speaker 1: the atmosphere.
Speaker 2: In principle, you could do both. Right, If you have
Speaker 2: a muon beam, then you could put stuff in the
Speaker 2: muon beam in order to do these kind of tests.
Speaker 2: There is a muon beam. It's cern and we've put
Speaker 2: cell phones in it and stuff like that. It's a
Speaker 2: lot of fun. But it's hard to build a muon beam.
Speaker 2: It's hard to point a muon beam. It's hard to
Speaker 2: bring stuff to a muon beam.
Speaker 1: Why why is that?
Speaker 2: Why is it hard to bring stuff to the muon beam?
Speaker 5: Now?
Speaker 1: Like, why is it hard to make a muon shoot
Speaker 1: a gun?
Speaker 2: Yeah? Great question. Muons are created from the decays of
Speaker 2: other particles. So the way you make a muon beam
Speaker 2: is actually you smash protons into like a block of
Speaker 2: material like graphite, which creates a shower of other stuff.
Speaker 2: It's basically stimulating what's happening in the upper atmosphere. Then
Speaker 2: a lot of those things decay into muons. So you
Speaker 2: need a proton accelerator of sufficient energy, and there just
Speaker 2: aren't that many of those. They're not that portable. You
Speaker 2: need like a linear accelerator. You need magnets to filter
Speaker 2: some of this stuff out.
Speaker 1: How big would it have to be? Like can you
Speaker 1: make it a handheld version or do you need like
Speaker 1: a building size anything to shoot muons.
Speaker 2: Yeah, that's a great question. What's the smallest muon gun
Speaker 2: in the world. Definitely the size of a large physics laboratory.
Speaker 2: Not something you can pick up and carry, though you
Speaker 2: might be able to put it in the back of
Speaker 2: a flatbed truck. But mostly it's unnecessary because the world
Speaker 2: is filled with muons from cosmic rays. Like there's a
Speaker 2: constant stream of these things just naturally produced in the atmosphere,
Speaker 2: and you can just use those.
Speaker 1: M What do you mean, like there's we're surrounded or
Speaker 1: being penetrated by muons from all directions all the time.
Speaker 2: Not from all directions from above, right, these things are
Speaker 2: made in the upper atmosphere and are streaming down to us. Again,
Speaker 2: there's ten thousand muons per square meter per minute, so
Speaker 2: there's not a small number of muons passing through us.
Speaker 2: And so if you want to measure the density of something,
Speaker 2: you just put like a muon detector underneath it and
Speaker 2: count how many muons are making it, and then you
Speaker 2: can tell how many were absorbed by the material, and
Speaker 2: that tells you what the density of it was.
Speaker 1: Mmm. But our neons coming at us from the sides
Speaker 1: as well, Like, aren't their cosmic rays hitting us from
Speaker 1: all directions.
Speaker 2: There's definitely an angular dependence, but most of them come
Speaker 2: straight down. It's the most likely.
Speaker 1: Direction, all right. So then the idea is that if
Speaker 1: I want to see through something, I just put a
Speaker 1: meuon detector under it. And so what are these meon
Speaker 1: detectors made out of? How do you make a muon
Speaker 1: detector if muons go through things so easily.
Speaker 2: The original sort of old school ones are these films. Now,
Speaker 2: muons are hard to stop, but they're not that hard
Speaker 2: to see like. They will leave a little trail of
Speaker 2: evidence as they go. For example, you can build a
Speaker 2: cloud chamber in your garage, which is just like a
Speaker 2: transparent box filled with water vapor super saturated in the air,
Speaker 2: and as muons fly through it, they won't be stopped,
Speaker 2: they won't lose a lot of energy, but they will
Speaker 2: interact with those things and create little a stream of droplets.
Speaker 2: So you can actually build a muon detector like at
Speaker 2: home with simple materials. There's all sorts of fun instructions
Speaker 2: on YouTube that you can follow, so they'll leave like
Speaker 2: breadcrumbs for where they were. The original ones were like
Speaker 2: fit and moultion blocks. These days, we use like charged
Speaker 2: gases or scintillating plastics in order to see these muons.
Speaker 1: You see, you don't stop the muons, You just kind
Speaker 1: of see the evidence of them going through.
Speaker 2: Yeah, exactly, it's hard to stop the muon for them
Speaker 2: to interact in a significant enough way to get slowed
Speaker 2: down to deposit all of their energy. But they will
Speaker 2: leave a little trace of energy as they go by
Speaker 2: if you have the right setup. So it's not that
Speaker 2: hard to detect muons.
Speaker 1: Interesting, all right, So then what kinds of things have
Speaker 1: we seen with a meon ray? Have we seen a
Speaker 1: instead of a cow? I think Donald's hamburger.
Speaker 2: I don't know that anybody's tried that, you know, put
Speaker 2: a cloud chamber under a cow to see what is eaten.
Speaker 2: I do not know if that experiment has been done,
Speaker 2: So I don't know if we have muon ray to cow.
Speaker 1: There's an instruction on YouTube to do that.
Speaker 2: One of the first applications of this was to measure
Speaker 2: like how much rock and the density of rock over
Speaker 2: a tunnel, Like you're building a tunnel through a mountain.
Speaker 2: You can put a muon detector in the tunnel and
Speaker 2: you can use it to measure the total mass of
Speaker 2: the rock, or effectively the density of the rock that's
Speaker 2: above you, to measure your overburden because you're basically shooting
Speaker 2: through the rock with the muons, and you can tell
Speaker 2: by counting how many muons make it to your tunnel
Speaker 2: the density of the rock.
Speaker 1: So for like construction projects.
Speaker 2: That was the first application. But then in the sixties
Speaker 2: a physicist thought, ooh, let's use this to basically X
Speaker 2: ray the pyramids, because you know, a lot of people
Speaker 2: wonder like if there's something in the pyramids, or are
Speaker 2: there hidden chambers in the pyramids. Nobody wants to take
Speaker 2: the pyramids apart because they're obviously treasures of humanity, but
Speaker 2: we would like to see inside the pyramids in a
Speaker 2: non invasive way. So in the sixties, Louis Alvarez thought, oh,
Speaker 2: let's use muons to see inside the pyramids to see
Speaker 2: if there's like an opening or a gap, or like
Speaker 2: a big void somewhere that nobody's discovered.
Speaker 1: Ooh, wouldn't that require you to put the mean detector
Speaker 1: under the pyramid?
Speaker 2: Yes, exactly, so you do need some access to the pyramid,
Speaker 2: and there are some openings, but this is limiting factor.
Speaker 2: You can't just like drill under the pyramid and put
Speaker 2: a muon detectors everywhere. There are some shafts and some
Speaker 2: chambers we know about. What you can do is put
Speaker 2: the muon detector there in the bottom of the as
Speaker 2: far below the pyramid as you can, and then measure
Speaker 2: the rate of the muons and compare it to calculations
Speaker 2: you do, like how many muons should I see if
Speaker 2: there are no additional chambers, or how many muons going
Speaker 2: in this direction versus that direction, if there's a chamber
Speaker 2: here or a chamber there.
Speaker 1: Wait, if I put a detector under a pyramid, let's
Speaker 1: say it's like a tile the size of like a
Speaker 1: one by one foot square, it can only detect the
Speaker 1: muons that are coming from right above that one square
Speaker 1: foot area, or can it detect muons from all directions?
Speaker 2: If you have like a one foot tile, it'll detect
Speaker 2: any muon that passes through that tile, you know, coming
Speaker 2: from any direction. And so if you have a few
Speaker 2: of those, then you can start to get directional information.
Speaker 2: If there's like a difference in how many muons you
Speaker 2: see in one place versus another, what do you mean, Well,
Speaker 2: the way you can tell, like the difference between parts
Speaker 2: of your body is a you have an X ray
Speaker 2: detector that's not just a point, it's like a whole array,
Speaker 2: or it takes an image. You can tell how many
Speaker 2: X rays came through this part of your body versus
Speaker 2: that other part of your body. So imagine if you
Speaker 2: could put X rays all over the bottom of the pyramid,
Speaker 2: then you could like muon X ray the whole pyramid.
Speaker 2: You can't do that, but you can put a few
Speaker 2: here and a few there based on what access points
Speaker 2: you do have, and you can get like a very
Speaker 2: rough image of what's going on inside the pyramid from
Speaker 2: your various detectors.
Speaker 1: But wouldn't that just give you like a couple of
Speaker 1: pixels basically of an image.
Speaker 2: Yeah, it's very rough, but it's better than nothing. Right
Speaker 2: right now, we have basically no image, and so this
Speaker 2: is like a way to crack it open a little
Speaker 2: bit and give you some very rough idea of what
Speaker 2: might be there.
Speaker 1: Mmm. I guess alternately, you could create a mion ray
Speaker 1: gun m hmm and shoot it from the side, right.
Speaker 1: Wouldn't that be more convenient?
Speaker 2: Yeah? Absolutely, you had a big meon detector on one
Speaker 2: side and a big meuon gun on the other side,
Speaker 2: then you could really muonograph the pyramids. That would be awesome.
Speaker 1: Were you about to take a mea on the heck
Speaker 1: out of it? Are these muons dangerous? Like if I
Speaker 1: create a muone gun and I aim it at somebody,
Speaker 1: is it going to harm them? Just like X rays
Speaker 1: are sort of harmful if you take an X ray
Speaker 1: gun and shoot it at a person for too long.
Speaker 2: Absolutely, these are radiation and muons are responsible for mutations
Speaker 2: in our DNA. They're part of the natural radiation of
Speaker 2: our environment, and they do cause mutations. So yes, in
Speaker 2: principle they can cause cancer. Right, So an intense dose
Speaker 2: of muons from a beam could definitely give you cancer.
Speaker 2: It's not something to play around with.
Speaker 1: Does sound like a great idea to make a muon
Speaker 1: gun or a good idea for certain applications, perhaps.
Speaker 2: Yeah, exactly, And the difficult to shield. Right once you
Speaker 2: start that muon beam, it's going to pass right through
Speaker 2: your pyramid and then through your detector, and then it's
Speaker 2: just going to keep going for kilometers and kilometers. So
Speaker 2: it's not like you can have a beam dump or
Speaker 2: something to protect people from the other side.
Speaker 1: Well, I guess it would just shoot off into space,
Speaker 1: right because the Earth is curved, or with gravity pull
Speaker 1: them back down.
Speaker 2: No, you're right there, showed off into space, So maybe
Speaker 2: you just need to angle it up a little bit.
Speaker 1: Interesting, But then you might be like shooting it. Maybe
Speaker 1: an alien civilization out there they might take offense.
Speaker 2: Yeah, you could accidentally be sending them a mewanograph of
Speaker 2: our pyramids. I don't know how they would interpret that.
Speaker 1: That's right, or a picture of cows. They'd be like, oh,
Speaker 1: that look's tasty, let's go invade them.
Speaker 2: But people have actually done this for the pyramids without
Speaker 2: building me on gun. They've just used cosmic rays and
Speaker 2: measured the rate at which the constant rays make it
Speaker 2: through the pyramids to see are there new cavities.
Speaker 1: Inside the pyramids and what have they found.
Speaker 2: So the first time they looked, they looked in one pyramid,
Speaker 2: they didn't find anything unusual. But then later on, actually
Speaker 2: in twenty fifteen, they did this for the Great Pyramid
Speaker 2: and they found what they called the Big Void, and
Speaker 2: then another opening they labeled maybe a corridor. What they're
Speaker 2: seeing is a region of the pyramid that seems to
Speaker 2: have lower density than the rest of the pyramid. So
Speaker 2: this could be like a big opening, maybe a treasure
Speaker 2: chamber filled with all sorts of jewels and fascinating information
Speaker 2: about ancient Egypt. Or maybe it's just like a gap
Speaker 2: they left in the pyramid to reduce the pressure on
Speaker 2: the rest of it. You know, it could just be
Speaker 2: like a construction trick. We don't exactly know, but there's
Speaker 2: some sort of large cavity within the Great Pyramid.
Speaker 1: Interesting. I guess what you're saying is making me feel
Speaker 1: a little skeptical just because you needed like a lot
Speaker 1: of space underneath the pyramid to create these to be
Speaker 1: certain that there's something there, right, you need to basically
Speaker 1: put a lot of these neon detectors under a pyramid,
Speaker 1: Like just putting like a couple doesn't seem like you'd
Speaker 1: be able to find or resolve any kind of real details,
Speaker 1: can you.
Speaker 2: Yeah, your resolving power definitely improves as you have more detectors.
Speaker 1: Or just more space to put these detectors.
Speaker 2: But you'd be surprised what you can accomplish with a
Speaker 2: few detectors, the same way that like a radio array
Speaker 2: is just a few detectors scattered over kilometers and kilometers.
Speaker 2: By measuring the difference between signals received by one antenna
Speaker 2: and another, you can get a lot of directional information
Speaker 2: and resolving power, almost as if you had the detector
Speaker 2: the same size as a full array. Not quite, but
Speaker 2: almost as if. So you do some complex data analysis
Speaker 2: and you can recover a lot of information with just
Speaker 2: a few measurements.
Speaker 1: Right, right, But those arrays the antennas right which you
Speaker 1: can focus and point in the certain directions to kind
Speaker 1: of get the equivalent of a giant lens. This feels like,
Speaker 1: you know, laying out a bunch of photographic negatives a
Speaker 1: film out on the ground and trying to get an
Speaker 1: image from that.
Speaker 2: Yeah, it's difficult. And if you look at the reconstruction
Speaker 2: of the void, you see it's very fuzzy. They're very
Speaker 2: uncertain but exactly where it is, how big it is.
Speaker 2: They have no idea what shape it is. This is
Speaker 2: not like a crystal clear image the way an X
Speaker 2: ray is at all. This is just like a hint
Speaker 2: that there's an under density somewhere inside this pyramid.
Speaker 1: All right, Well, it seems like a pretty cool application
Speaker 1: that maybe let's us see through mountains and tonaments and
Speaker 1: potential of bovine animals.
Speaker 2: Especially if they're the size of pyramids or mountains.
Speaker 1: What else can you use these meon rays for to detect.
Speaker 2: People have used it actually to see inside mountains like Vesuvius,
Speaker 2: for example, the famous volcano. They've used muans to try
Speaker 2: to understand what's going on inside Vesuvius to maybe do
Speaker 2: a better job predicting of when it's going to blow.
Speaker 1: Need to get under Vesuvius to do this.
Speaker 2: The best case scenario is to have a bunch of
Speaker 2: mealon detectors under Vesuvius. But if you put a bunch
Speaker 2: around it, then you can get muons which shoot through
Speaker 2: sort of at an angle. Especially if you can measure
Speaker 2: the angle of the muon, so you can tell whether
Speaker 2: they came through the mountain or whether they came from
Speaker 2: the other side, then you can get some good information.
Speaker 1: Wait, you can angle these detectors.
Speaker 5: Yeah.
Speaker 2: Absolutely. The detectors are not just like a flat sheet.
Speaker 2: They can be thick and so you can see a
Speaker 2: whole track of a muon. You can tell which direction
Speaker 2: it was going, not just that a muon was there,
Speaker 2: but the direction of its motion.
Speaker 1: Hmmm. Interesting. So you can angle these then kind of
Speaker 1: like an antenna.
Speaker 2: Yeah, kind of like an antenna exactly.
Speaker 1: Okay, it seemed like maybe you're saying you can't.
Speaker 2: No, you can. The thicker they are, the better angle
Speaker 2: measurement you can make like a cloud chamber that you
Speaker 2: can build in your garage. You can see the whole
Speaker 2: track of the muon flying through. It's really pretty cool.
Speaker 1: All right, So geology and archeology, those are pretty cool
Speaker 1: uses for particle physics.
Speaker 2: Yeah, exactly. So maybe particles will not just teach us
Speaker 2: about the nature of the universe. They might teach us
Speaker 2: about what's going on inside mountains and what humans have
Speaker 2: hidden away inside pyramids.
Speaker 1: All right, Well, another great justification for Daniel's job at
Speaker 1: the university.
Speaker 2: I'm not mute anything, but I'm definitely a favor of it.
Speaker 1: I feel like half of these episodes are just a
Speaker 1: commercial for your job in particle physics.
Speaker 2: They're a commercial for particle physics and for physics in
Speaker 2: general and trying to understand the nature of the universe,
Speaker 2: and yeah, why it matters?
Speaker 1: Should we have a disclaimer here at the bottom?
Speaker 2: Every episode is indirectly Daniel's self promotion. Yes, yeah, there
Speaker 2: you go. Yeah, absolutely, I'm totally transparent about that?
Speaker 1: All right, well, engineers, please clip that and put it
Speaker 1: at the bottom of every episode. It'll be like the
Speaker 1: fine print.
Speaker 2: And every conversation I have basically with everybody.
Speaker 1: Unless you're talking about something else.
Speaker 2: Perhaps it's all particles, man, everything is made of particles.
Speaker 1: Oh interesting, even non particles. All right, well, we hope
Speaker 1: you enjoyed that. Thanks for joining us, See you next time.
Speaker 2: For more science and curiosity, come find us on social media,
Speaker 2: where we answer questions and post videos. We're on Twitter, Discorg, Insta,
Speaker 2: and now TikTok. Thanks for listening, and remember that Daniel
Speaker 2: and Jorge Explain the Universe is a production of iHeartRadio.
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