Daniel and Jorge Explain the UniverseListener Questions 32: Particles, particles, particles!
Daniel and Jorge answer questions from listeners like you, all about the particles around us.
See omnystudio.com/listener for privacy information.
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Hey hoor you ready for this?
Well, I don't know I had kind of a big lunch.
Oh, let me guess what you had for lunch.
Oh, well, that's not hard. I always have cereal. But which kind of cereal though? Mmm?
Something made out of protons, neutrons, and electrons maybe.
Ooh, clothes. I had a new cereal called neutrin oaths. Now I'm just kidding as just regular atom based cereal. How did you know?
Well, you know, you gave me a massive hint telling me it was a heavy lunch.
Mmm, right right, And only things with protons, neutrons, and electrons have mass.
That's right. Maybe you should try something lighter, like a photon based meal.
Hmm. That sounds like a brilliant and delicious idea good for my diet. Hi am Jorge I, a cartoonist and the co author of Frequently Asked Questions about the Universe.
Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I'm pretty glad that I can't eat photons.
Well, how do you know? Have you tried? Have you tasted them? Have you shown a flashlight down your throat? I think they do that as the doctors all the time, So I think you have eaten photons.
Yeah. Well, but if I lay down in the sun for a nap, for example, I still sometimes wake up hungry.
M Maybe you shouldn't put on sunblock the no photon diet, But I mean, do you nap with your mouth open? Though? Have you tried that?
I've not tried napping with my mouth open. But I was imagining that maybe humans would evolve to photosynthesize, so we could just like absorb photons as we walk around or lay in the sun.
Oh wow, it's pretty cool. Yeah, we could all be green with envy and photosynsthis.
It'd be pretty hard to go on a diet, though, I guess you'd have to like walk around with an umbrella.
You could sell a diet sunblock, I guess yeah, or parasol would be like a new fashion accessory for the super thin.
Stay thin and pale.
But welcome to our podcast. Daniel and Jorge explain the Universe, a production of iHeartRadio.
In which we don't eat photons, but we do gobble up all of the information provided to us by the particles in the universe. We are made of particles. Everything around us is made of particles, and in their incredible dance They convey to us everything that is happening out there. They tell us about the fundamental nature of the universe at the smallest scales, and they come together to describe the sweeping motions of enormous galaxies in the dance of galactic clusters as they get pulled apart by dark energy. Everything around us is made of particles, and all of our understanding of it is stored in particles in our brain.
Yeah, because it is a tasty and brilliant universe, full of amazing things to discover, full of information beaming down to us from the light of stars and planets and nebulas out there in the cosmos, ready for us to digest and absorb all those amazing knowledge nutrients from the universe.
And the most amazing thing about the particles that make up your brain is that they are curious about all the other particles. These particles want to understand those particles, and that bubbles up in the form of questions, Questions that we ask about the nature of the universe around us. Questions we ask ourselves, questions we ask our friends, Questions we whisper to ourselves quietly at night when we stare up at the Stars and Questions we send two podcast hosts.
Yeah, the world is full of questions. Everyone has questions. It's kind of an inherent part of being human, and in this podcast we like to answer some of those questions. Most of the time, at least we like to ask them. We don't always answer them.
I guess we answer them as best as we can. Some of these things are tough. Explaining concepts in an understandable way which are often just described mathematically can be a real challenge, but we knew our best to boil it down to the essential ideas.
I guess saying I don't know is also an answer, So technically we do every question. Yeah we have no idea is a valid answer to not just a good book.
Absolutely, And sometimes when I'm posed with an especially difficult conceptual question like can you make me understand why X, Y, and Z happens? I'll walk the hallways here, you see, and I'll ask the theorists, why do you think this happens? Why do you think that happens? You have an intuitive understanding of this, And often I'll get very different ideas and sometimes conflicting accounts for why things happen, which just tells you that even the experts don't always deeply understand the why right.
Right because the X and the Z are easier or what.
Because sometimes the ABC's are easier than the.
X, Y, Z.
Well, they do come first, I guess. But it's not just the scientists and the physicists of the world that asks questions. Everybody asks questions. Everyone looks up at the stars, at the sky and the things around them, and they wonder what's going on? How does it all work?
They do, and especially our listeners are curious folks. We hope that you are listening to the podcast because you wonder about the nature of the universe, and because you want to understand it. You want to do more than just here an explanation. You want those pieces to fit together in your mind in a way that you can manipulate it, that you can rotate it and probe it from different angles and make sure that it sort of hangs together. And when it doesn't, we encourage you to write to us so we could help you fill in those gaps.
So today on the podcast, we'll be tackling listener questions number thirty two. Oh my goodness, we've done thirty two of these listener question episodes.
Oh we have. We get lots and lots of listener questions. Many of them come to our email address to questions at Danielandhorhe dot com and we answer all of them. So if you have a question, please don't be shy. But sometimes we get a question which I think will be really fun to talk about or is quite tricky. It requires me to do a little bit of background research, and for those we ask people to send in some audios so we can talk about it on the podcast Interesting.
And So if this is our thirty second listener Questions episode and we do about three questions an episode, that means we're close to like one hundred questions. Oh yeah, I mean one of you. Anyone sending their question in now could be the one hundred listener question we answer on the podcast.
Wow, are we going to give away a prize?
Yes, a possible answer.
I think we should at least shower them in digital confetti or.
Something, send them a gift or an emoji some competti.
Yeah instead of a gift, you just got a gift.
There you go, leave out the tea. They get a gift or a gift. We do love answering questions from listeners, and today we have some pretty interesting questions in that they're all about particles and kind of about mass. It seems. Were you feeling in a kind of particle mood or do you think these questions just all came in at the same time.
No, these questions are not sorted by when they arrive. I try to group them together. So the concepts are a little bit related. So we do a batch about black holes, and a batch about particles, and a batch about how physics might kill you, so we can dive a little bit deeper into the topic.
All right, Well, today we have three particularly particle questions, some of them about virtual particles, about particles that may or may not exist, and also about what kind of particle light is. And so our first question comes from Carter, who wants to know about all the other particles in existence.
Hi, this is Carter, and my question for you is why do particles other than the electron, the electron, nutrino, and the up and down quarks exist if we only need those four particles to build up the world around us.
Awesome question, Thank you, Carter. It's amazing to me that you have a question like that.
Absolutely Carter is twelve years old, and he's already at the forefront of particle physics, asking questions we don't know the answers to. Yeah.
I think when I was twelve, I was mostly just wondering what I was going to have for lunch that day.
I think when I was twelve, I was watching the movie Stand by Me over and over every single day for a summer.
Oh, I mean the one where they find a dead body.
Yeah. I don't know why I watched that every single day for a summer, but I remember there was a summer where I watched that in the morning and then I wrote computer programs in the afternoon. Unlike that was my summer.
Wow, sounds like you got a lot of sunlight, or at least a light from your monitor exactly.
The Carter apparently is thinking about the nature of the universe and how it comes together and why there are weird particles out there.
Yeah, because, as he said, we only sort of need a certain number of particles to make the things around us. Like everything we can see and touch and stand on and look up at this skuy at is pretty much made out of only three particles, right, I mean he mentioned the fourth but most of the things that are made out of three particles.
Yeah, he's right that the things that we are made out of technically are just three particles. But as we'll talk about, the other particles do play a role in determining the nature of our universe. It would be quite different if those particles didn't exist.
All right, Well, maybe let's review things a little bit. So why is it that everything that we're made out of is only made out of three particles?
So everything that we are made out of is made of atoms. Right, If you zoom in really really far, you see that your hand and the table next to you, and the lama that maybe you wrote to work on this morning are all made out of molecules, which are built out of atoms from the periodic table, everything around us, right, All the kinds of matter that you're familiar with are made out of atoms. This excludes, of course, dark matter, which is some other weird kind of stuff that's part of the universe but we don't understand at all. So all this sort of familiar kind of matter, the kind of stuff you can see and taste and eat, is made out of atoms. And those atoms are made out of electrons, and then in the nucleus there are protons and neutrons. Inside the protons and neutrons are quarks. Protons and neutrons are made out of two different kinds of quarks. Two ups and a down make a proton, two downs and an up make a neutron. So out of upquarks, down quarks, and electrons you can build basically any atom, and from that you can build any chemical and from that you can build anything. And the thing that's incredible to me is that it's not just that all the stuff around us is made out of these three particles. It's also made out of these three particles in the same relative abundances, Like a kilogram of lava and a kilogram of kitten have the same number of each kinds of these particles inside of them. It's just the arrangements that are different between them.
Interesting. Yeah, it's amazing that you can reduce the almost seemingly infinite variety of stuff in the universe into three things. And like you said, it's amazing, it's just all about the arrangement. Although I think you said it's all kind of the same proportion, Is that really true? Like a cloud of hydrogen doesn't have the same number or proportion of particles as like lava does.
It it almost does. Hydrogen, of course, mostly has just protons, and though there are forms of hydrogen that also have a neutron, and most atoms have an equal balance between protons and neutrons. So most of the stuff out there in the universe has the same number of protons and neutrons in it, and that means the same number of upquorks and down quarks inside. You're right that most of the universe is hydrogen, which means that most of it are protons, which means that there are more upquarks out there than down quarks. The stuff that we made out of, the stuff that we interact with, is mostly not hydrogen. I mean, I don't know if you're having hydrogen for lunch, for example, but if you're having things made out of more complicated atoms, then mostly it's an equal number of protons and neutrons, which means an equal number of upquarks and down quarks.
I do have a lot of gas right now, but I don't think it's hydrogen. But that's interesting. I hadn't thought about it before that there are maybe more up quarks in the universe than down quarks.
Yes, there definitely are, because the universe is mostly hydrogen out there, like it started out as mostly hydrogen, and it's still mostly hydrogen. Even those stars have been working furiously to make heavier elements in their cores, and it's been billions and billions of years. They really only made a little bit of a dent. So most of the matter out there in the universe, the visible matter of our kind, is hydrogen, just as a caveat Remember that there's five times as much dark matter as any kind of atomic matter out there in the universe. So anytime we're talking about this, we're only talking about the fraction of atomic matter in the universe. And that's all made out of atoms by definition.
Right, because we are talking about matter particles, right, there are other particles besides matter particles.
That's right, And so the upcork, the down cork, and the electron these are particles we call fermions. There spin one half particles. But as you say, there are other particles out there in the universe, and there's a different kind of particle. They are particles we call force particles. These are bosons. For example, what holds the proton together. It has three quarks inside of it. They're tied together by gluons. So gluons are inside the proton, and they're just as much part of the proton as the quarks are. They're just sort of like less long lived. There's a huge swarm of gluons inside the proton, and in fact, most of the mass of the proton is not the quarks, it's the gluons. So it's like you have these three very light quarks held together by incredibly massive ocean of gluons, but each individual gluon doesn't last very long.
Right, Right, It's kind of like when my kids make a craft. It's like it's mostly hot glue, a mess of hot glue, with some you know, popsicles things holding it the glue together.
Yeah, So most of the energy inside the proton, which is what contributes to its mass, is due to the gluons. So you know, can you say that the proton is made partially of gluons, Yes, you can, but you can't like point to a gluon and say this is the gluon inside the proton because they're constantly just getting passed back and forth between the quarks, whereas the quarks you can say, here's an up quark. I see where it is. It's this same upcork. It's been part of the proton for a long time. It's a stable state, right right.
So we're all made out of up and down quarks and electrons, and you're saying that we also sort of need the particles that glue things together and then keep them together. But I wonder if Carr's question was more about the other matter particles that have mass but that don't form the things that we're made out of, you know, things like the top core and the extra quarks and the other neutrinos and the extra electrons.
Right, yes, So just to complete the story of the forced particles, there's not just the gluons. Of course, there are photons inside of us. There are Higgs bosons that give mass to the particles. There are weak bosons like the WN, the Z. All these things are playing part of this dance of how those matter particles are fitting together. But you're right, there are other matter particles, and I think these are probably the ones that he was referring to, because it's not just the electron. The electron has a heavy cousin called the muon and has an even heavier cousin called the tau. And that's true of all of these fermions. The upcork has two heavy cousins, the charm and the top. The down cork has two heavy cousins, the strange and the bottom. And you know, a fundamental question, which is, I think, basically is what Carter was asking, is why do these exist? Why are they there? Why isn't there just a single generation? Or why if we have other particles, are they not totally different? Why are they so similar basically tweaked copies of this first generation. The short answer to that is the title of our great book, which is, we have no idea sort of why it is that way. We can't say the universe has to be this way. What we can say is that if the universe wasn't this way, it would look very different. That is, we would notice if you like deleted them from nature. Right.
Well, it's kind of interesting that you would ask, or that anyone would ask that question, right. I mean, we know these sort of heavy cousin versions of the electron and the quarks exist because they can be made in a particle collider. For example, Right, that's how we know they exit tant exist even though you don't see them around very much.
Yeah, So by exist we mean they're part of the laws of the universe, not necessarily that there are any in existence at any moment.
Right, And so they can exist. And so the question I guess is like, why is it that they can exist if we don't see them around us very much? Right? Because everything we know that think that things are made out of around us are just the basic electron and up and down quarks. Why can these other heavier particles exists?
Yeah, and there's lots of really fascinating angles there. One is like, if there are these heavier particles, why do we only see the lighter ones. Why are the lighter ones the only ones that seem to be around And the answer to that is that nature doesn't like heavy stuff. It tends to spread out the energy, so the heavy ones are short lived. They tend to decay into the lighter ones. So if you made a bunch of all the different kind of particles, including the heavy ones and the light ones, the heavy ones would very quickly just turn into the lighter ones. Like the top quark doesn't last for very long. It lasts for like ten of the minus twenty three seconds before it turns into a bottom cork, and then the bottom cork decays into a strange cork, which decays then into a down cork for example. And so these things just don't last very long. That's why they're not around. But the deeper question, which I think you're asking, is like why can they exist at all? Why are they on the menu? And why three generations? And why not two? And why not four?
Right?
I think that's the deeper question you're asking.
Yeah, well, I think they're both deep questions, right, like why can they exist? Yes, first of all, and also why is it that right now we only see one kind? I mean, those are two big questions, right.
Well, the answer to why can they exist is really just a flat out we don't know. We don't know if the universe has to be this way. To answer the question why can they exist? You have to think like what kind of answer would be satisfactory? And one kind of answer would be to say this is the only way the universe could exist, like it mathematically would be inconsistent, or it just wouldn't make sense, or it doesn't hang together or there's no other way for it to be than to have three generations. We don't think that's true right now, Like we could imagine a universe without those things. It would still have laws of physics which function well, and it would make sense. It would just be quite different, like it would look very different from our universe. But that doesn't mean that it couldn't exist. And maybe out there, somewhere in the multiverse it does. There are universes with one generation or seven generations or seven thousand generations. The short answer is this is just a number three, and we don't know why three and why not one.
It's not something in the equations of math of the universe that maybe tell you why they have to exist, like it just to make things click or something.
Not right now, and right now, it's just descriptive, you know, we don't understand it, sort of the way like we used to not understand why there were so many atoms, like why isn't there just hydrogen? Why are these other weird atoms also out there? These other elements. Now we do understand it. We understand that those things emerge from how smaller pieces come together and create these other opportunities. So it's possible that these other generations are like that, that they're all made out of some smaller bits. That electrons and quarks are not the smallest things in the universe. There are even smaller things squiggles or squaggles or whatever. And the way that squiggles and squaggles come together make all these various options. We don't know that that's true right now. We're just in the descriptive phase. We see these particles, we catalogue them, we describe their interactions. We don't know whether they emerge from something deeper, which determines this structure we see.
Right And the other question is why do we own we see the lighter particles now, because I think we've talked about this before, that like maybe in the early universe there were the conditions for the heavier particles to exist. There were like back then it was common to have those larger, heavier particles, but just right now you don't see them.
Yeah. The short answer is that the universe is cold and old. So back when the universe was young and hot, then there was enough energy density to create these particles. All the time, they still decayed. That these particles are very short lived. The heavy ones they turned into the lighter particles. That's just the natural way of the universe. Energy density spreads out right, second law of thermodynamics. But back then there was enough energy to constantly just be creating them out of the vacuum. So the universe was a hot soup of all of these particles, and there was so much energy that didn't really matter which ones had mass and which ones didn't, because there was much more energy around than any of the mass of these particles. So they were all very very fast moving particles. But as the universe cooled down, it basically wasn't capable of making these particles on its own anymore, and all the heavy ones decayed into the light ones, and then it's just capable of keeping the lighter ones around making those And now the universe is very cold and very old, and so the only way you can make these heavy particles now is to artificially recreate those conditions by, for example, slamming two protons together to create a dot of very high energy density. And that's exactly how we discover that these particles still can exist in our universe, even though they don't very often naturally.
Right, And so that's kind of the answer for why we don't see them around anymore, right, is that they die, right, and they've all died out basically, right, Like maybe the early universe had a bunch of them, but they're like, you know, I'm done, I'm out.
Yeah. Well, it's just not hot enough to make those anymore. And you know, there are conditions naturally that will create them, like when protons hit the upper atmosphere at very very high energy cosmic radse from space, they also create these particles. So it's not just a large hadron collider capable of making these conditions. It does occur naturally. But when they do, they decay away very very quickly, so you don't find like a pile of top quarks line around. You can dig into the Earth to find them. And it's fascinating that some of these things are stable and some of them are not. Right, Like, we don't have the conditions to make iron, for example, here on Earth, but iron is stable. Once you've made it in the heart of a star, you can take it out of that and bury it in a planet and they'll sit there for billions of years. Top quarks are not like that. They're not stable, so you make them in the early universe. You can't then just find hunks of top quark lying around all right.
Well, then I guess maybe to extend Carter's question, then, like if the universe couldn't make these heavier particles besides the electron up and down quarks, if it was maybe impossible, or if they didn't exist with the universe, Notice, would it be any different than it is right now?
Yeah, you might wonder like, would the only difference be for particle physicists creating these collisions into the large hadron collide or would anybody else? Notice would the universe be any different?
Well, apparently we don't sort of need them to have the world around us right now because they don't exist right now, right, You don't see a lot of them around, So why do we need them? I guess it's pro Carter's question.
Yeah, so we actually do need them. They do play a role, Like there's not enough energy to make them actually exist, but virtual versions of themselves can exist. They can like participate in interactions even if they can't ever exist on their own, And that's important because they do end up playing a role. For example, the Higgs boson itself has a bunch of mass, and that mass comes from interacting with not just the particles that do exist, but all the particles that can possibly exist. So if those other particles, the top cork and the bottom cork, weren't on the menu, the Higgs boson would have a very different mass and it would behave differently, right, So that would change how everything operated.
Well, not just the Higgs, but basically every other particle would weigh the same or have a different mass.
Yeah, it would change how the Higgs field is balanced. And so that would change the mass of all of the particles. And so it's a very sort of delicate Rube Goldberg machine, you know, it all sort of hangs together in this very complex way. It also would affect how the universe had evolved from the very early stages. You know, we think that in the very beginning of the universe, matter and anti matter were made in the same proportions. Now, of course, it's almost all matter. We don't understand very well why that is, but the hints we have suggest that it has to do with these other weird particles like strange quarks and bottom quarks, that they don't have symmetries, that there's a difference between particles made of strange quarks and anti strange quarks, for example, that the universe prefers for those to decay into matter rather than antimatter. It's not something we've totally solved, but we think these other generations play a big role in that. So they weren't around, then there might just be a perfect balance between matter and antimatter, which would have all just annihilated into photons and the universe would just be light. That would be no matter left over.
Woh, sounds like either way we just all weigh a little less.
We'd all be brighter too.
Yeah, well, all right, well I think that answers Carter's question. Why do particles other than electron nutrina up and done quarks? Is this we don't know, but definitely the universe would be a lot different, And if they didn't exist, we probably wouldn't be around to ask this question.
That's right. But maybe one day we'll peer inside the electron and the quark and we will understand why they exist and why their cousins exist. So future generations of podcast listeners might be asking questions about why those little squiggles and squaggles.
Again, it could be carter It could become a particle physicist.
Do it, Cartery.
His parents are going, no, what have you done?
I bet they prefer particle physicists to a cartoonist.
I mean, some cartoonists are pretty rich. I don't know any of them, but here some of them are pretty rich.
Yeah. We'll have Mac groning on the podcast.
All right, well, awesome question, Thank you, Carter. So let's get to some of our other questions about particles from listeners. But first let's take a quick break.
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All right, we're answering listener questions and today's theme is particles and masks and little tiny things in the universe.
We're drilling down to the core questions about the universe, like how do you pronounce Matt Groening's name anyway? Groaning graining, I've never understood.
And so our next question comes from Ricky from New Zealand.
Hey guys, my name is Rocky. I'm from New Zealand. I've been listening to the podcast for a few months. They're really enjoying it. So I thank Thames for I have a question about light. I was wondering how it would have affected the growth of the universe and how it would affect our out of everyday life now if light had any form of mass to it.
Thinking, great question, Thank you, Ricky. I think his question is how would the universe be different if light had mass? And I guess specifically, like how would it have developed differently and how would it be different for us today if it had mass.
Yeah, so this is a super fun question and it led me down a little rabbit hole of reading thinking about why is it anyway that the photon has no mass? And do we actually know that the photon has no mass?
What? Okay, First of all, most people think the photon or light has no mass.
That's right, And in our current theory it has no mass, like the standard model of particle physics assigns it to be exactly zero mass. But that's the theoretical description, right. You can also go out in the universe and you can ask, well, can we measure the mass of light? Can we do experiments to tell us whether light has any mass? And you know, experiments are always a little bit fuzzy statistical fluctuations or a limit to your sensitivity, and so a really fine question to ask is like, well, how do we know that light has no mass?
Interesting, nobody's try to weigh it, I guess, But isn't it impossible for light to have mass, Like then it can go as fast as the speed of light? Right, then you would have to change the name of the speed of light.
Yeah, that's right. If light had mass, then it wouldn't act the way we describe it. You know, all the properties we talk about for light, that it moves at the maximum speed of the universe, that it can't have a restrame, all of these things require it to not have mass. That doesn't mean that it doesn't have mass, right, That's just like our description of the universe has light with zero mass in it. You can also ask the question like, does our description of the universe require light to have zero mass? Could you have a universe where light does have mass. Is it necessary, as we were talking about earlier, for light to have no mass, or why does our universe give mass no light?
But I thought in our theories that if something had mass and if it was going at the speed of light, it would need infinite energy.
That's right. So if light has mass, then it wouldn't be moving at the maximum speed of the universe, what we're currently calling the speed of light. But you can devise theories of the universe where light does have mass and then doesn't move at that maximum speed.
Oh, we could have a universe where there was a maximum speed, but light wouldn't move at that speed exactly Like you can just give mass to light and the universe would still work.
Yeah. In fact, we don't even really know why our universe doesn't give any mass to light. You know, the mass of the other particles like the W and the Z. These come from the Higgs boson, But the W and the Z are really very very similar to the photon, and in the very early universe they all had no mass, and then the Higgs field settled into its weird value and it gave mass to the W and to the Z and zero to the photon. You might ask, like, why zero. Well, the answer is, we don't know. It's sort of unexplos It could have given some mass to the photon, but it didn't, and if it had, then our universe would be a little bit different. We don't know why the Higgs boson gives the photon zero mass. It doesn't have to. It's like a parameter, and we seem to be at or very near zero for the photon's mass. But it could have been different.
Is it that the Higgs field just ignores the photon like it just doesn't interact with it, or it does interact, It just assigns a value of zero mass to it.
It definitely interacts with it. You know, the photon is part of the electroweak theory, where you can bind an electromagnetism where the photon operates in the weak force, where you have the ws and the zas. So in the early universe, the photon, the two w's, and the zs, they're like a gang of four. They're all very related. They're part of this larger group, and the Higgs comes along and it picks three of them mount and says, you guys all get mass and photon you get none.
And you're saying that we don't actually know if light has zero mass, like nobody has ever measured it, or I guess we've never measured that something can go faster than light. Would that tell us that light has mass? Like if we ever measure something going faster than light, maybe that means that the maximum of the universe is higher than the speed of light, and light maybe has some mass.
Exactly. We have definitely tried to measure the mass of light, and every experiment is consistent with light having no mass. So you know, this is sort of a theoretical exercise. The best description of the universe that we see around us is one where light has no mass. Don't be confused about that. We're not saying the light might have mass or we think it does have mass. We're just saying there's not necessarily any a priori reason for it to not have mass. But it's the best description of what we see out there. So we can do a bunch of experiments to try to measure the mass of light. And if light had a lot of mass, it would be obvious, right, it would look very different, things would travel faster than it. Right. The most sensitive experiment. The best way to see if light has even a tiny little bit of mass is to look at the Sun's magnetic field and how the solar wind moves through it. Because remember, photons are part of the electromagnetic Fiel field, and so if light had even a little bit of mass, it would change how electromagnetic fields propagate through the universe. It would be a little bit weaker if light had a little bit of mass. So the Sun's magnetic field is like the biggest electromagnetic effect in our neighborhood, and so it's the most sensitive test. So by looking at the Sun's magnetic field, we can tell that light, if it has any mass, it's an incredibly small value.
I see. I think you're saying that according to the theories, light could have mass, but according to our measurements, we think light has no mass.
Exactly. There's a parameter in the theory that could give mass to light. We set that parameter to zero because that's the value that's most consistent with all of the experiments, all of our descriptions of the universe as we see today are consistent with light having zero mass.
All right, Well, now let's get to Ricky's question. How would the universe be different if light had mass?
So the universe would look pretty different, But it depends on how much mass light had. You know, if light had a lot of mass, then everything would be very, very different, because it would make the electromagnetic force quite different. You know, the electromagnetic force is very powerful. It's much more powerful than the weak force. But that's because the photon has no mass and the weak bosons do have mass.
Wait, how does having mass make the force weaker?
Well, you know there's a connection between these forces and the particles, right, So the electromagnetic force comes from the photon. The photon is a thing that does the job of the electromagnetic force, and so if the photon was massive, it couldn't do his job as well. It would move more slowly, it would cost more energy to make it. This kind of stuff just like the way the weak force does. Because the particles that transmit the weak force, the W and the Z particles, they're also.
Heavy, right, like when you get two magnets together, or like what keeps your atoms together in your body is the electromagnetic force, and so it's the photon is sort of like the transmitter of that force, right mm hm. And so I guess if that transmitter had mass, it would just be sluggish, right, or it would sort of appear it more easily.
Yeah, it would be like shorter range. You know, it wouldn't have as far an impact like the weak force right now is basically like the electromagnetic force, but with heavy photons, right, So what would happen if the photon had mass? Electromagnetism would be a lot more like the weak force. It would be much weaker, it would have shorter range.
It's like instead of email communications between people right now, we would be back to like stone tablets, kina, right, like the way that things communicate had a lot of mass to them. You know that society wouldn't function as quickly.
Right, Yeah, it would be very different. And also light wouldn't be as long lived. Right. If light had mass, it could decay into other particles. Right now, we're very privileged because a photon created billions of years ago and super far away can travel through the universe basically forever until it hits something like maybe it hits the James Webspased telescope and we get to see a really old distant galaxy. That's because that photon is stable. It's because the photon is massless. If the photon had mass, then along the way he could like turn into other stuff. It could decay into lighter particles depending on how much mass it had, and so the universe wouldn't be as visible.
Mm Like if I send you a stone tablet email, it might break along the way, or most likely will break along the way, right.
Yeah, almost certainly. Yeah, ZS and w's created by distant galaxies don't get here. They turn into other stuff and fizzle out, and so we don't see them. We see photons from those galaxies because they're massless, because they're stable, so they can fly forever.
All right, I'll cancel my news startup idea stone mail.
It's probably very secure though, right, do you encrypt it is in cuneiform?
No? I think it probably doesn't rock, all right. So then if the light has mass, then the electromagnetic force would be a lot weaker, shorter range. How would that affect the universe, Well.
First of all, you could do really fun experiments in that case, because you could like catch up to photons, you could be in their our ference frame. You could have photons that are at rest. You could like have a pile of photons. You know, we don't know what a photon looks like right now. A photon you only see it if it hits your eye. A photon passing by you. You can't see right, You can't ever catch up to a photon. But if photons had mass, then they could be at rest and so you could like hang out with a photon. So that would be pretty different. You know, eurnars like us who are curious about what particles are like d quite different.
Well, although can we do we know what an electron looks like? What does an electron look like?
What does an electron look like? You know, whatever it does to a photon that bounces off of it. So yeah, you have to probe these things with something.
So what would you probe light with more light?
You could probe it with electrons. You could use a scanning electron microscope to look at photons at rest.
M interesting, all right, So we could maybe get a closer look at light if it was moving slower because it had mass. How else would things be different?
What Ricky was also asking about how it would affect the evolution of the universe. You know, we know that very early on in the universe there was this plasma of all sorts of crazy goop. There were photons, there were particles, there was dark matter, and all it was sort of oscillating back and forth and slashing in and out amid all of these acoustic ripples. And the rate of those ripples and how things were slashing back and forth depend on the fraction of dark matter and normal matter and photons, and so that would all be different if photons had mass, because it would affect the gravity of that situation, and so it would affect how those things are slashing. And that slashing is very important because it ends up controlling where the dark matter pooled together, which turns out to influence how galaxies form. So the whole structure of the universe could be very different if you tweak those initial ingredients even a little bit.
Well, how would the starture be different, Like would we be more dark matter ish or would the mass? Would we have black holes earlier? You know what would be different about how it looks.
So part of this slashing has to do with dark matter pulling things in and then photons pushing things back out. That's why we get these like ripples, these oscillations, and so photons aren't as powerful if they have mass. If they contribute to pulling things in rather than pushing things out, then things would oscillate differently. And those oscillations are were caused sort of the pattern of galaxies that we see today, And so we'd have galaxies at like different distances from each other right now, because those oscillations are were caused galaxies to form like here and not there, and so the overall large scale structure of the galaxies would definitely be different. You might also get different size pools of dark matter which would make different size galaxies. But I'd have to like run a bunch of really complicated simulations to know for sure.
I see, like maybe the universe would be good clustered together more, or maybe it might be sparser or something like that.
It's all a very very delicate recipe, you know, sort of like a Sioux fle You change the ingredients a very small amount and it can come out quite differently.
Yeah, that's why I don't like baking or cooking just stressful.
Well, I'm glad you weren't in charge of baking the universe.
Yeah, you don't want to be in charge of baking anything much less everything everything. But I guess, you know, being selfish, how would it affect me of light head mass?
Right?
Because I think the electromagnetic force really basically controls everything about me, right, Like, it's not just magnets and light, it's also like chemical bonds, and why even the electron sticks to the nucleus of an atom, and why atoms stick together at all, It's all because of photons, right, Yeah, and the electromagnetic force.
Yeah. Chemistry is basically just the dance of electrons and photons, right, as those charges make atoms stable, and then those atoms form together to make molecules and all sorts of chemistry of life. And so you're really changing the very basic rules of those structures.
You know.
It's like you're taking away some of the crucial lego pieces for building things, and you're replacing them with something else, something much much weaker. And so it might be that, you know, you just can't get atoms as stable. The energy levels of atoms would definitely be different, which would lead to totally different chemistry, and it might also be interesting, it might also be delicious, but it would definitely be unrecognizable from our world.
Well, I think maybe a cool question to ask is, like, what if I had a switch in front of me that had like the mass of the photon and I just said.
Hey, don't touch it, don't touch it.
Yeah, yeah, that's what I mean. Like, what if suddenly we had the world we have right now, but all of a sudden the photon had masks we all just kind of like dissolve, explode, you know, turn too much. What do you think?
I think we were probably just sort of like drift off into a gas.
You know.
I think that a lot of our bodily consistency depends on all these bonds holding themselves together, and those bonds suddenly get weaker by a significant amount, then yeah, you basically just like sublimate into a gas.
You mean, like in the Avengers Infinitied War, like we just all turned to ash.
Yes, whoa, maybe that's how Thanos did it. Yeah, maybe that's how he did it.
Yeah, that's how he did it.
Oh man, that is you knew he was a particle physicist, right, he had that evil gleam in his eye.
That's sorry. That's how it words. You snap your fingers and you can change the universe. That's that's what physics gives you the power to do.
Yeah, and so we think that our photons probably have zero mass. If they do have mass, it's something smaller than ten to the twenty sixth of the mass of the electron. Right, So it's a very very very small value. But we can't actually say for sure it's zero, and the theory would allow for it to be non zero.
Interesting, but I guess if it did have a little bit of mass, everything might be okay, because we're still here.
M Yeah, you could have like almost zero, very very close to zero, like zero point zero, and then one hundred zeros and then a one, and the universe wouldn't be very different. We wouldn't be able to tell the difference, all right.
Well, I think that answers Ricky's question. The universe would be pretty different depending on how much mass the photon would have. In this scenario, it had a lot of mass, this would be super duper different and not the same. But maybe it has a little bit of mass. It would still be okay, and we would still be here.
Ricky, Please don't build a device that gives photons in the universe mass, or if you do, don't press the button.
That's right, dude, don't put on infinity gauntlet. Leave it where it is, or at least take out the physics stone, because that's the one that causes all the trouble. All right, well, let's get to our last question about virtual particles. But first let's take another quick break.
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All right, we're taking listener questions about particles in this episode, and our last question comes from Anthony, who is a question about virtual particles.
Hello, Daniel and Jorge. Ever since I heard your episode on virtual particles recorded back in twenty twenty, I've had a question in the back of my mind. From your explanations on the subject. I've understood that virtual particles are ephemeral, they don't last long, and that their mass may fluctuate, but that still means that at any given point in time, there must be myriad virtual particles in the universe. Someone must have surely estimated their combined mass. What does it add up to? Does the mass of all the virtual particles in the universe get counted as ordinary matter? And if not, could it account for the elusive dark matter or some portion thereof? Thank you all right, awesome question from Anthony about virtual particles and possibly as an explanation of dark matter. Do you think he's cracked the big mystery? No, genter there.
Sometimes you just got to give a clear and crisp answer.
Oh man, No, I.
Don't think that dark matter is made at a virtual particle.
Well, I'm still ready for you, Anthony. We'll try to make it work here on the podcast.
You know, you got to understand how often people write to me and say, oh, by the way, I don't really understand ABC and could that be the dark matter? It's just basically like the end of almost every question we get.
Really, well, maybe one of them might be true one day.
Yeah they might. Absolutely.
Isn't that possible?
Absolutely? And I encourage people to keep thinking about it because someday somebody will figure it out.
Hey, Daniel, I don't understand pink hamsters. Could that be the cause of dark matter in the universe? No, man, you're like the Simon Cowell here of physics today. Harsh, harsh.
Hey, people want to answers.
Yeah, all right. So the question was about virtual particles and whether maybe physicists have forgotten to take into account their mass and their effect in the universe. So step us through here. What is a virtual particle?
First of all, so a virtual particle is shocker, sort of badly named. It's not really a particle in the way that we are thinking particles. You know, what is a particle? A particle is like a wiggle in a field. So the electron, for example, is a wiggle in the electron field is a field for every particle that's out there. The electron field, the Upcuark field, the Downcark field, the electromagnetic field. All these things are fields, and they can wiggle in this interesting and particular way. We have like a little packet of energy which is self sustaining and moves through the field the way you can take, for example, a rope and you can tweak it so that you have like a standing wave which moves down the rope. Right, So particles are these sort of special oscillations of these fields in a way that lets them like move through the field. So that's what a particle is.
I see, there's sort of like a wiggle that doesn't just dissipate in the in a quantum field in the universe. Do we know why some wiggles stay around and some wiggles don't.
So we have this whole episode recently about what is a particle and it gets kind of philosophical, and so some folks think that particles are just the wiggles in fields, and the ones we define to be particles are the ones that do stay around, right, that they have this capacity for the energy to slide around in this particular way. So the way the energy moves through these fields is governed by the wave equation, just like with any other kind of wave, right like in the water or on a string. There is this mathematical equation that tells you what are the possible solutions, And there are some solutions to those equations that are self sustaining. You know that where the energy just flows in this particular way so it maintains itself, it doesn't spread out, right.
I'm thinking maybe like the if you think about a field. A quantum feels like a big sheet that you have, maybe and if you have it out there in the wind and kind of holding it up, the wind will make it kind of ripple all over the place. But every once in a while you might see like a little like a bump in that sheet that tend of forms and then can move it across the sheet. That's kind of what a particle is, right mm hmm.
And so any situation where you have a self sustaining wave that moves across and sort of keeps its coherence, that's what you call a particle. And if it does that, then it has special properties, like you can talk about it having a certain mass because it has motion, and you can describe the motion, you know, in terms of like a force having been applied and getting acceleration. And so there's a concept of mass of this particle. There's all sorts of properties that we tend to attribute to the kind of stuff we find. Familiar things around us have mass. So these ripples in these fields have these properties, like they have a specific mass which is related to their energy, et cetera, et cetera. All the things we tend to think of as particles. So that's what a particle is. A virtual particle is something different. A virtual particle is like a different kind of wiggle in this field. It's one that's not self sustaining. It's usually caused by the presence of other particles. So, for example, an electron is a self sustaining wiggle in the electron field, but it creates wiggles in the electromagnetic field, right, because electrons have charge, and that's what it means to have charge charge is that you create wiggles in the electromagnetic field. So an electron whizzing around the universe is making ripples in the electromagnetic fields around us, which means in some sense, it's making virtual particles in that field, which we call virtual photons. So virtual particles are like non self sustaining ripples in a field, mostly caused by the presence of other particles.
Wait what okay, First of all, you're saying that an electron can cause a ripple in the photon field. That is not a photon, but it does create photons, right, Like the presence of an electron talking to maybe another electron does create ripples in the electromagnetic field, which we call photons, but you're saying it can also make ripples that are not photons.
It can make ripples that are real photons that an electron can radiate a photon which could hit your eyeball and you can see it. It's a real photon, propagates through the universe with what we think is zero mass and follows all those rules. Electrons can also create all sorts of other ripples in the electromagnetic field, you know, just sort of like sloshy, messy ripples that don't coalesce to be a self sustaining packet. And we call all those ripples virtual particles. It would have been better if we'd given them a different name, because they really are sort of a different category of thing. But some people think of them as all part of a larger spectrum of phenomenon, so they call these real particles versus virtual particles.
I see, and I guess the big difference is that virtual particles don't last or something, right, They're not sort of cohesive packages like the regular particles. They are ripples in the quantum fields. But maybe there are sort of like messy ripples, like just the little tiny random fluctuations.
Yeah, they don't last, they dissipate. They tend to spread out, and if the source of them disappears, then they disappear.
But doesn't it take energy to make them?
It does take energy, absolutely, and so the source of them is putting some energy from its field into the target field. So, for example, electrons do give up energy into virtual photons, right, Those virtual photons capture some of that energy, right, But then they turn into other stuff. Those virtual photons turned into other fields sort of just sloshes through the universe. It's not in a coherent, self sustaining packet.
Wait what so then an electron flying through the universe will eventually slow down.
Well, an electron to transmit any energy into the photon field, it has to decelerate or accelerate, right, So it's.
To change its energy, so it would slow down.
But electron just flying constant velocity doesn't slow down and doesn't create any virtual photons. Only when it accelerates does it create any real or virtual photons. That's when it changes the electromagnetic field. Flying with constant velocity doesn't change any the field.
But I guess then maybe the takeaway instead of talking about these specific is that a virtual particle is just like a random wiggle in the quantum fields. Right, Well, it's a little bit different. Then maybe I wonder if Anthony's maybe thinking of maybe a different kind of virtual particle. Like they say that when particles sort of exist, there's also like other particles popping in and out around it, right, isn't that something they also call virtual particles, Like when you calculate the mass of a particle, you have to calculate all of the possible particles that maybe popping in and out of existence around it too.
Yeah. Yeah, And so you could ignore virtual particles completely and you could say, look, it's just particles and there are fields, and instead of thinking about virtual particles, you just think about the fields, like when the electron moves through the universe, it's interacting with the photon field. And don't try to call those things particles. Just think about them as fields. And so what you were just talking about is how particles interact with the fields that are around them. Like we were saying earlier, the fact that the top quark can exist changes how Higgs bosons move through the universe because they talk to virtual top quarks. Or another way to say that is that they interact with the top quark field that is out there in the universe, even if there are no real top quarks existing in the universe. So every bit of space is filled with these quantum fields and those fields the top quark field, the field is there even if there are no top quarks in it, right, And so the electron field is there even if there are no electrons in it. So the universe is filled with these fields, which you could also call virtual particles, right. You could think of these fields as just like a swarm of very low energy virtual particles. It's sort of mathematically equivalent whether you think about them in terms of the fields or are some over lots and lots of virtual particles.
Okay, But I think that maybe the takeaway is that we have quantum fields out there, and they do wiggle, maybe and sometimes not in super permanent particle ways. They do sort of wiggle, which maybe have energy in their wiggles, And so I think maybe Anthony is asking, like, you know, there are all these fields out there that are wiggling and have energy. Doesn't that maybe add mass to the universe, because energy in a field is sort of like having mass in the universe. Isn't it like, what's the relationship between these wiggles and do they actually have mass?
It's a great question, right, And so you can think about empty space and what's going on there, and there are these fields which you can all think of like particles. Now, do virtual particles have mass? You know, particles themselves have a specific mass because of the way they move through the universe. Virtual particles don't really have a well.
Defined mass, but do they have mass?
If you want to think about them in terms of the particle framework, then they can have mass, and those masses can be any value. You know, you can have virtual photons that have a huge amount of mass, you can have virtual top quarks with a very tiny amount of mass, but those only really exist in our calculations. Virtual particles are not things you can ever see or observe. They're only like the way other particles talk to each other, which I think is why it's maybe more natural to think about them instead, and just in terms of fields, they're just really the way that two particles talk to each other. But technically, mathematically, these particles do have mass. But you can never observe these particles, you can never interact with them. You can only interact with real particles, not with virtual particles.
But I guess we were calling virtual particles wiggles in these fields, right, So the universe has fields, there are rand the non particle wiggles in them, and so maybe Anthony's wondering, like, do these random wiggles have mass, and could that mass maybe account for dark matter?
These random wiggles do have energy, right, And all the fields that are out there in the universe have energy because quantum fields can never be at zero. That's why we talk sometimes about virtual particles popping out of the vacuum, because there isn't really zero energy vacuum out there. There's energy out there, but mostly it's potential energy. These fields have non zero potential energy, and potential energy actually has the opposite effect of mass. Potential energy can create a repulsive force in the universe. It contributes, for example, potentially to the dark energy of the universe.
So Anthony's onto something. He's just maybe picked the wrong dark constant there is that what you're saying.
Yeah, and we know the universe is accelerating, and one way to describe that acceleration is to say, maybe the universe is filled with a bunch of potential energy that's causing that. Because in general relativity, if your space is filled with a field with potential energy that can cause repulsion, might explain inflation in the early universe, it might explain dark energy. Problem is that if we look out into the universe and measure the potential energy of all the fields we think are out there, it doesn't explain the dark energy that we see. So we have accounted for the potential energy of the fields that we see, but it doesn't explain the acceleration. It's off by a factor of like ten to the one hundred.
I see a little bit off, a little bit off. But what about Anthony's question here where he asked, what is the combined mass of virtual particles in the universe?
I would say that doesn't really have a solid answer, you know, because the virtual particles don't really have a well defined mass, so it really could be anything at any moment.
Oh interesting, but in a particular spot, maybe you know, a virtual particle could have any mass. But maybe he's wondering if overall in the universe, as an average, if you take the average of all virtual particles everywhere, or at least in like a giant space the size of a galaxy. Is that also fluctuating or do you think it has some sort of like standing mass to that average, you know, ripples and wiggles in the field.
The way I think about it is that that's just the potential energy of those fields, right. Sometimes that potential energy gets momentarily converted into virtual particles. But it's really just another way of thinking about the field as having potential energy, as having capacity to interact with the stuff around it. So I don't really think of that as having like real actual masks.
But you just said that virtual particles are sort of created and popped into existence. But those virtual particles don't have masks.
Well, they don't have mass in the same way that real particles do. Like what does mass mean? It means how particles propagate through the universe, and virtual particles don't propagate through the universe the same way real ones do. Also, remember now we're talking about like the mass from particles. We don't even understand how gravity works when it comes to particles. So if you're talking about like the gravitational impact of individual quantum particles, that's a question for quantum gravity anyway, all.
Right, well, well, then, I guess how would you summarize his question? The answer to his question like, do virtual particles have mass and can they add up to something? Or I mean, I feel like your answer is very kind of theoretical, and it seems to be depending on how you look at things in the universe. What would be a more direct answer for Anthony?
I think maybe the crispus answer is no.
No, that virtual particles don't have mass.
No, that virtual particles aren't the dark matter, They're not contributing to the mass of the universe. I think the clearest way to think about it is that virtual particles are not particles the way you are thinking about tiny little bits of stuff. Instead, just think about them as fields filling the universe. There are these quantum fields out there capable of doing stuff, and they are affecting the overall flow and shape of the universe. But in the opposite way of mass, we think they're probably contributing to the expansion of the universe rather than pulling stuff together.
Mmm. I see, okay. I think maybe then what you're saying is that virtual particles maybe even have not only do they not have mass, in the same way that particles do, but maybe they have kind of negative man or they can tribute negative mass to the universe.
As maybe you can tell. I'm not a fan of the picture of virtual particles. I prefer to think about fields as ways to interact between particles rather than virtual particles. But you know, mathematically they are equivalent. But I think they raise a whole bunch of questions that you can't really answer because particles is sort of the wrong word to describe them. I see.
So we'll just tell Anthony to rephrase this question in terms of quantum fields, and maybe you'll be in a better mood to answer this one.
Quantum fields don't contribute to the dark matter, Anthony. We think they might contribute to dark energy, but we don't really understand by how much.
But it is interesting. I mean, I can see how Anthony could have reached that conclusion, right, Like you learn about somee thing and then you learn about something else and you're like, oh, wow, that makes sense to me if they're related. I wonder if they are, right, Like it's all right to wonder these things, right.
Oh, absolutely, And sometimes two big mysteries are the answers to each other, right, Like why does this happen over there? Why does that happen over there? Oh, it turns out you were thinking about these things as disconnected, but they're actually two parts of the same coin. So I absolutely encourage people to think about how part of one mystery might be the answer to another.
That's right. And also, don't insult physicists by asking if maybe they miss something. That's one lesson we've learned today.
No, I don't feel insulted at all. And I love all of the questions, and I encourage people to think broadly and write every question they have. Please send us your questions to questions at Danielanjorge dot com.
Great, well, those are our three questions about particle physics, and Daniel asked, a particle physicist must be pretty exciting to have people ask you questions about the field you're studying.
It's super fun. I love thinking about this stuff, and I love that other folks, not just particle physicists, are interested in these questions. You know, it's easy to look up at the night sky and think about astronomy and ask questions about stars and galaxies, But it's also possible to look just down at your hand and the ground below your feet and all the matter that's around us, and wonder like what makes that up? What are the rules of it? That's what got me into part of physics, and I think that's pretty accessible.
Yeah, and it's pretty amazing to think that, you know, we have this intuitive view of our or intuitive sense of the universe as being these kind of you know, giant pool table with builder balls bouncing around, But as you drill down into these small sizes, there's all kinds of weird things.
Happening, absolutely, and sometimes we understand that only in terms of the mathematical description, which amazingly works so well and predicts the results of our experiments. We don't always have a deep intuitive understanding of it. And that's because things at the smallest level really are very different from our intuition. To build an intuitive understanding usually means explaining the unknown in terms of the known. But here the unknown is so radically different than the known that it's really hard sometimes to describe it in terms of familiar concepts. So if you hear me struggling and you hear Jorge persisting and asking the same question until we get an answer that you guys can understand, that's because sometimes it's just hard to translate these ideas from mathematics to intuition.
Right right, we need to spend a summer in front of a computer coding so that we can beam the mass right into our listeners paint that picture in our brain.
I've had many moments in science where I said, I don't understand this, but I'm just going to follow the math because the math works. It will give me a prediction. It gives me the answer I need. I don't really intuitively understand.
It, Daniel. The mask is telling me that you should send me a check for one hundred thousand dollars.
And sometimes being asked to explain it intuitively, to teach it in a class or to talk about in a podcast forces me to think about it again and dive deeper for an intuitive explanation, which helps me understand it better.
Cool. Well, thank you to all the people who send us questions. We love to answer them here on the podcast, and we hope that all of you out there enjoyed us talking about these questions and maybe or maybe not answering.
Them, certainly doing our best.
We hope you enjoyed that. Thanks for joining us, See you next time.
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