What is a symmetron?

00:00:08
Speaker 1: Hey, Jorge, are you a collector?

00:00:10
Speaker 2: What do you mean like a debt collector?

00:00:13
Speaker 1: I mean, like, do you have a room in your house full of original Transformers still in the packages?

00:00:19
Speaker 2: I wish, but no. Those might be worth a lot of money now, but no, I actually took them out and played with them, although I wish you had those also.

00:00:27
Speaker 1: So is that the source of your encyclopedic knowledge of Pokemon and Transformers?

00:00:31
Speaker 2: What do you mean?

00:00:32
Speaker 1: Well, you know, every time I describe some new hypothetical particle, you tell me that's actually the name of a Transformer.

00:00:39
Speaker 2: I don't think that's because I'm an expert. I think that's just because all physics names sound like Transformers.

00:00:44
Speaker 1: Or maybe because we actually stole them from Transformers.

00:00:47
Speaker 2: What do you have to give credit then, to Hasbro in your papers?

00:00:51
Speaker 1: Yeah, we give them a share of the zero dollars we make off of each particle.

00:00:55
Speaker 2: What do you mean you don't work for free?

00:00:57
Speaker 1: Do you the particles?

00:00:59
Speaker 3: Do?

00:00:59
Speaker 2: Did you tax dollars?

00:01:16
Speaker 4: Hi?

00:01:16
Speaker 2: I'm Hori mccartoonist and the author of All Our's Great Big Universe.

00:01:20
Speaker 1: Hi I'm Daniel. I'm a particle physicist and a professor at UC Irvine. And I hope you never have to name a particle. Wait, why not, doesn't it mean you discovered it. Oh I'd love to discover a particle. But then I'm given that huge responsibility of choosing a name. And frankly, after all our conversations, I'm terrified.

00:01:38
Speaker 2: You're terrified of cartoonis criticizing your name choices.

00:01:44
Speaker 1: I'm terrified of legacy history.

00:01:46
Speaker 5: Man.

00:01:46
Speaker 1: People who have given particles silly names. History doesn't look kindly on them. Oh.

00:01:50
Speaker 2: I see, so that's your excuse for not having discovered a particle.

00:01:53
Speaker 1: That's one of my many excuses.

00:01:55
Speaker 2: Yes, that sounds a little convenient.

00:01:58
Speaker 1: Know the truth is, I would love to discover particle. And in that case, you know, I just crowdsourced the name hmmm, to your kids, maybe to the internet. So it ended up with like particle face.

00:02:09
Speaker 2: Is it a website? Like? Is there a website for coming up with particle names?

00:02:13
Speaker 1: Not yet, but what a great idea.

00:02:15
Speaker 2: You can find anything on the Internet. I wonder what happened if you ask Chad Gpt to come up with a name for a new particle.

00:02:21
Speaker 1: Let's do it. Naming a new particle is a significant responsibility. It suggests we avoid personal or self referential names. We should consider its properties, we should go after historical figure, we should consult with the scientific community. See, this is serious stuff.

00:02:36
Speaker 2: I feel like maybe that chat GPT's trained on your neuroses. It seems to know your anxieties. Maybe maybe it's been learning all this time that you've been talking to it.

00:02:45
Speaker 1: No, I think chat GPT and I are both trained on the neurosis of the internet.

00:02:50
Speaker 2: Hmmm, well, now you have chat GPT, so you have no excuse for not discovering a new particle.

00:02:55
Speaker 1: All right, I'll get to work.

00:02:56
Speaker 2: But anyways, welcome to our podcast. Daniel and Jorge explain the universe production of iHeartRadio.

00:03:01
Speaker 1: In which we are absolutely desperate to understand the nature of the universe, to uncover new particles and forces, to reveal the fundamental nature of space and time, and to put it all together, to explain our experience in this crazy cosmos.

00:03:18
Speaker 2: WHOA, WHOA desperate. I don't know if we could go that far. It make us sound kind of thirsty.

00:03:24
Speaker 1: I am thirsty for knowledge. Absolutely, Yes, you're thirsty to get it on with the particles of the universe. I mean, I've said it before. I would invite aliens to Earth, even if I knew they were going to zap Us from orbit, if they would only tell us the truth of the universe.

00:03:38
Speaker 2: Boy, you would make that choice for the entire human race.

00:03:41
Speaker 1: I'm thirsty, man, I got a thirst, and it's got to be quenched.

00:03:45
Speaker 2: It sounds like a good excuse to put you in a rocket ship and shoot you out of here. You're clearly not on our side.

00:03:51
Speaker 1: I'm on the side of knowledge, man.

00:03:55
Speaker 2: You're on the side of dinner apparently. But yeah, it is an interesting universe and we are are really at a loss for understanding how it all works, what it's all made out of, and what are the rules that govern what can happen and what cannot happen in the universe.

00:04:08
Speaker 1: Though you might feel like the universe is pretty well understood scientifically speaking, and historically, we're just beginning our journey of understanding it. In one hundred years or in five hundred years, people will look back on this era of science and say, Wow, they were very clueless about how the universe worked.

00:04:26
Speaker 2: Do you think that's a very optimistic view of humanity.

00:04:28
Speaker 1: That will be around in five hundred years To look back.

00:04:30
Speaker 2: You mean, yeah, that we're not going to go into the post apocalyptic healthscape of humanity, and we'll look back at this time as maybe the peak of humanity.

00:04:41
Speaker 1: In our caves in a few hundred years, scratching out podcasts for our few listeners. We will look back to the golden age of science when Daniel didn't discover anything.

00:04:50
Speaker 2: We're going to look back and be like, what's a podcast?

00:04:54
Speaker 1: Was that a particle?

00:04:55
Speaker 2: Who had time for that?

00:04:57
Speaker 1: You're right, I'm implicitly being optimistic, assuming that scientific knowledge will continue to accumulate and the pace will continue to accelerate the way it has over the last decade, fifty years, even one hundred years. I'm hopeful. But that requires us to survive and maintain society and to make science a priority.

00:05:15
Speaker 2: Yeah, and not to sell us out to the hungry aliens.

00:05:18
Speaker 1: Hmm though that would fast forward us into the future of knowledge and dinner. But what if the aliens don't have all the answers? Well, what if they have the answers and we just can't grock them? Oof? So frustrating. I just sold the human race for nothing.

00:05:32
Speaker 2: Yeah, you might want to look at the menu first, figure it out. Before they sell us all out.

00:05:40
Speaker 1: But we can't rely on those aliens or even those future humans. We got to figure it out. We are working hard today to try to understand the nature of the universe on the largest scales, how big is it, how much bigger is it getting? And how quickly is it getting bigger.

00:05:53
Speaker 2: That's right. We're on our own trying to figure out the mysteries of the universe, and it all starts with asking questions and coming up with maybe sometimes crazy ideas to try to explain how it all works.

00:06:03
Speaker 1: We're pretty sure that most of our ideas about how the universe works and the largest scale, the size of it, the shape of it, the rate of its expansion, why it's expanding, why that expansion is accelerating, We're pretty sure those ideas are wrong. And what we looked back on is just sort of like initial explorations. But that's crucial. Science is not a straight line. It's a zigzag wandering through a dark forest hoping to find the clearing and.

00:06:27
Speaker 2: So sometimes you have to get creative about it and even come up with things that sound like transformers or pokemons, or maybe come up with transformers that would be pretty cool. They could help us find the answers to the universe.

00:06:39
Speaker 1: You think they'll be mad when they discovered to've been stealing their names for particles for a few decades.

00:06:44
Speaker 2: Or maybe they'd be honored to be named after certain particles.

00:06:47
Speaker 1: Now you're the one being optimistic.

00:06:48
Speaker 2: Yeah, I am an optimist prime And so today on the podcast, we'll be tackling the question what is a symtron.

00:07:03
Speaker 1: And what does it transform into?

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Speaker 2: What does it not transform into?

00:07:08
Speaker 1: Maybe it transforms us into aliens that do understand the universe.

00:07:13
Speaker 2: What is a symmetron? I don't think I've heard that word before, but it sounds a little bit like symmetry and tron, so something electronic.

00:07:21
Speaker 1: You're not far from the truth. Yeah, boom podcast over.

00:07:24
Speaker 2: Do you know why the word tron or ending a word with tron somehow implies electricity or technology or particles. Do you know the origin of that? I'm asking if you know, because I don't know.

00:07:34
Speaker 1: I think the word ion comes from some Greek word, but I'm not an expert in the etymology of particles.

00:07:41
Speaker 2: Oh, you're saying like, maybe that's where the word electron comes from.

00:07:46
Speaker 1: Yeah, although you know the electron originally was named something else. The discoverer of it, JJ. Thompson called it a corpuscule, and then later it was renamed electron. But my guess is that all these ons come from ion, which is a Greek word.

00:08:00
Speaker 2: Well, I guess that was a good thing, because otherwise we'd be associating technology. But the word puscal with the ending puscol, and everything would be named pusicle. The bad guy in Transformers would be called megapuscal. But I'm guessing this is maybe one of those creative ideas that a scientists have come up with to try to explain some deep mystery of the universe.

00:08:21
Speaker 1: It is indeed well as usually.

00:08:23
Speaker 2: We were wondering how many people out there had heard of a symmetron or could guess what it is or what it transforms into. So Daniel went out there into the internet again to ask people what is a symmetron.

00:08:37
Speaker 1: Because this podcast is all about audience participation, you guys can write us questions and we'll answer. You can hear your voice on the podcast speculating about the topic of the day. If you'd like to join this group, please write to me two questions at Danielandhorge dot com.

00:08:51
Speaker 2: So think about it for a second. Is it a pokemon or is it a robot? Here's what people had to say.

00:08:57
Speaker 6: Well, it's either a transformer or a quantum particle or both. Symmetron, it obviously has something to do with symmetry. Other than that, I can't really hazard a guess.

00:09:10
Speaker 5: Guessing based on the on at the end of it that like a photon or a beryon, that it's some kind of particle that conveys a type of symmetry.

00:09:20
Speaker 3: Well, symmetron makes me think of cyclotron, and a cycloton I think is the old term for a well another term for a particle collider and symmetron symmetrical would be sort of means that it's the same in some way. Maybe is it a strait as opposed to a ring format particle collider?

00:09:43
Speaker 4: Well, I've never heard of a symotron. It sounds like a particle that exhibits some special symmetry, But lots of particles exhibit symmetry, which makes me think it's probably some theoretical symmetry we haven't seen yet that defines what this particle is.

00:09:55
Speaker 3: A symmetron, is a device that you can set on top of your piano to the pace it goes.

00:10:02
Speaker 2: No, I guess it's a.

00:10:03
Speaker 1: Particle and it communicates symmetry between other particles. I have no idea.

00:10:11
Speaker 7: Is that a particle wave it's identical to another particle? Cancels it out?

00:10:21
Speaker 5: Maybe?

00:10:22
Speaker 2: Or all right? Some creative answers here.

00:10:26
Speaker 1: Well, I mean you put this name on anything. You could name it your cat, right, The answer to the podcast could be like, Symmetron is my cat?

00:10:33
Speaker 2: Oh, there you go. You could name your cat Symmetron. Yes, but isn't that a big responsibility also to name your cat?

00:10:40
Speaker 1: Hmmm? That's true, although I don't think history will judge you as much because it's probably just between you and the cat, mostly unless the cat becomes famous.

00:10:49
Speaker 2: Yeah. Well, also, you don't mind your cat unhappy with you? I hear that's a bad thing. It would be a catastrophe in IIan.

00:10:55
Speaker 1: It's the cats who are in charge.

00:10:56
Speaker 2: But yeah, it's an interesting idea, and so let's dig into this, Uh, Daniel, what is a symotron?

00:11:02
Speaker 1: So, a symotron is a hypothetical new particle that of course also comes with a field that has really unusual properties, and physicists invent a new field and particles sometimes not just for fun. We don't just like line in the grass and be like, h what if there's this kind of particle. We do it to explain something we've seen in the universe. The whole process of physics is like go out there, see stuff that's happens, and then try to build a model that explains it. And when the model fails, we add new who's it's and what's it's to try to get it to describe the universe. So the symmetron is a new thing people are trying to add into our model of physics to explain some stuff that we otherwise can't explain.

00:11:43
Speaker 2: Although sometimes in the history of physics it has been the case that you just kind of like tool around in the lab and you discover stuff.

00:11:50
Speaker 1: Right. Oh, there was a golden era the particle Zoo, when every time you turned on the accelerator you saw a new particle and you could give it.

00:11:56
Speaker 2: A name every time.

00:11:58
Speaker 1: It was incredible, and they cranked up the energy boom new particles made. It was amazing. I missed those days, hmmm. They were decades before I was born, but I still miss them.

00:12:08
Speaker 2: But I think we're talking about a theoretical particle here, not one that we have discovered or seen or explored experimentally, just one that we have dreamed of to try to explain something that is happening that we can't explain.

00:12:22
Speaker 1: Yeah, and the same spirit that, like the Higgs boson, was conceived of theoretically. Peter Higgs saw this pattern in nature and he thought, hmm, this would be so much prettier. It would make much more sense if we added a new particle and feel to the story. And it all worked out mathematically and beautifully, and then we went out and looked for it. So you can add things theoretically, but if they don't actually describe what's happening in the universe, it's not very useful. So in this case, people are again adding a new theoretical particle to try to explain some stuff that otherwise doesn't make sense.

00:12:52
Speaker 2: Okay, So then what is the mystery that the symotron hopes to resolve?

00:12:56
Speaker 1: So the simitron is here to do battle with a really big question in physics, which is why is the universe expanding faster and faster every year? Like we know the universe is really big. We can look out there and see stuff that's really far away. We've known for like one hundred years that the universe is expanding. You look out in every direction and you see galaxies moving away from us. But a couple of decades ago we got precise enough measurements about how that expansion is changing over time that we learned something kind of shocking that the expansion is not slowing down like Einstein thought, but that it's actually speeding up. There's something out there accelerating the expansion of space.

00:13:36
Speaker 2: Meaning it's getting bigger, faster and faster each time.

00:13:39
Speaker 1: Yeah, space between galaxy clusters is getting bigger, and every year it's getting bigger at a higher rate. So we new space is being created faster.

00:13:48
Speaker 2: And faster, and they're not just running away from alias that want to eat them.

00:13:54
Speaker 1: They may be accomplishing that, but it's sort of the secondary thing. And in physics we give this a name dark energy, But just because we give it a name doesn't mean we understand what's going on or we can explain what's happening. So far, this is just observational. We've seen this in our telescopes and in our measurements and we've tried to grapple with it. We've like, what could explain this, What possible mechanism could we have that could generate this kind of crazy accelerating expansion.

00:14:21
Speaker 2: Because I guess the idea that it's accelerating is weird, right, Like, if it was expanding at a constant rate, then you might assume that, well, maybe you had some initial velocity from the beginning of the universe and so it's just coasting and getting bigger. But the idea that it's accelerating means there's something going on, right, something must be powering this acceleration.

00:14:42
Speaker 1: Yeah, exactly. It was really shocking in the context of Einstein's general relativity because in his model, if you have a universe with mass in it, that causes negative acceleration of the expansion basically pulls everything together. It curves the universe, and it pulls everything together. Basically just gravity should pull the whole universe together. But when Hubble and others discovered that the universe is expanding, then people thought, all right, so we have an expanding universe as you say, initial velocity, but still should be negative acceleration because all the gravity should be pulling everything together, and we didn't know if there's gonna be enough gravity to pull everything back together to like squeeze it down into a big crunch, or if there's gonna be so much velocity that it coast forever, slowing down but never actually come back. Then we discovered that neither of those are the case, and what actually happening is something else is giving us positive acceleration, is increasing the rate of expansion every year.

00:15:34
Speaker 2: Now, back then, do we know that it was space itself that was expanding or did we maybe think that all the galaxies were just moving through space and getting further apart from each other.

00:15:43
Speaker 1: How far back then are you talking Einstein and Hubble? Are you talking discovery dark energy twenty years ago?

00:15:50
Speaker 2: I mean before an hour ago before. I'm becoming familiar with this topic.

00:15:57
Speaker 1: Well, ever since we've had general relativity, we've understood that to describe the expanding universe is to describe the expansion of space itself, because general relativity tells us that the universe has a shape and it has curvature, and so you can't have like a single reference frame for the whole universe. Instead, you should think about it as like a reference frame for each galaxy, and then those reference frames are moving relative to each other in space is expanding between them, So you can't really answer the question like what is the velocity of that galaxy and measured in our frame? You really just have to say, they have a frame, we have a frame, and the space between them is expanding.

00:16:35
Speaker 2: But back then, did we know that, Like when we first noticed that the galaxies were moving away from us, did we know that it was space it's expanding, or did we maybe at first thought, oh, they're just moving away from us through space.

00:16:47
Speaker 1: Well, all this requires is general relativity, which we've had well before we knew the universe was expanding. So the answer is yes, we've described in terms of expanding space since the beginning. This might sound a little confusing to listeners because we often talk about the receipt eschen velocity of galaxies, and when you hear about the expansion of the universe, we talk about these velocities, and for stuff that's really really far away, you could even say that recession velocity is faster than the speed of light. That's just sort of a sloppy shorthand that's saying, well, look, we know it's space expanding but that's hard to think about. So let's just pretend we could measure the velocities of those galaxies. If we could do that, what would that velocity be? But those velocities aren't meaningful. We can't actually measure those things because we don't have a single frame that puts both galaxies in it. So the technical way to think about it accurately is to think about separate frames with space expanding between them.

00:17:35
Speaker 2: You're saying, like, these velocities are really just the expansion of space getting bigger.

00:17:40
Speaker 1: Yeah, exactly, And you know that because you can't measure that acceleration. Like, if you wanted to think about it in terms of acceleration, then all those galaxies should be accelerating away from us. You should be able to measure that acceleration. You like, have an accelerometer in that galaxy. You should be able to measure it. But you can't because there is no real acceleration there. It's just the expansion of space. If you put a ball in the back of a pickup truck, doesn't slant one side because space is expanding in some direction, right, it stays flat. Because we don't measure any local acceleration. Because we're not accelerating in our frame, even though the expansion of space between us and other galaxies is accelerating. And all of this happily lives within general relativity, but it requires an explanation the same way like you need mass to bend space, you need something to provide this negative pressure to expand space. And the big question about dark energy is what is that? What is doing this thing? What is providing the energy to accelerate the expansion of space.

00:18:35
Speaker 2: Okay, I think you're saying that space it's growing. It's not just growing, it's growing faster and faster so that the galaxies look like they're accelerating away from us. But really it's just the expansion of space that's like going a double time. And so the question now is what's powering all that creation of new space? And so that's kind of what dark energy is a placeholder for.

00:18:57
Speaker 1: Yeah, dark energy says something's doing it, we don't know what. And the cool thing is you don't have to throw away general relativity. General relativity has a knob in it. This is called Einstein's cosmological constant. You could just crank this knob up and say, what if there's energy in empty space. If all of empty space is filled with potential energy, then general relativity says, exactly this would happen. The question is is that what's happening is the universe filled with this potential energy? Where does it come from? What field would that be? So you can incorporate it into general relativity if you have like a field that has a lot of potential energy. But we don't and we can't explain that. So there's like a mechanism within gr to do this, but we don't know how to turn that mechanism on.

00:19:37
Speaker 2: Meaning like you have your equations and you put a number in if there's a term in the equations that explains or that would account for this acceleration of space growing. And so now the question is like what is that number? What's causing that number? Is it a field? Is there a particle associated with it? Are there pokemons hidden inside of there?

00:19:57
Speaker 1: Yeah, that's exactly right. General relativity says, if you have a field with high potential energy, then that translates into a number in these equations, and that creates accelerating expansion. But what is that field with potential energy? We look around to all the fields we know, like the Higgs field, which actually does have significant potential energy. And we try to calculate what number we should put into the equations, and we get some number, But the number we should put in from our calculations is different from the number we need to explain the acceleration by a huge amount, by ten to the one hundred. So if there's potential energy out there in the universe, it's not from a field we know about.

00:20:33
Speaker 2: Well, all right, well let's get into those discrepancies and let's go deeper into this mystery that might be solved by this simitron. So let's stick into that. But first let's take a quick break. All right, we're talking about the symitron, which is so far are an imaginary or imaginative particle that scientists have thought it to try to explain why the universe is getting bigger, faster and faster. And Danielie, we're saying that we have equations for the universe. There's a number there that maybe explains or that would give you a universe that's expanding faster and faster. But now the question is what is that number. Is it a field like our other fields, or is it just a fudge factor? Or is it just the finger of God.

00:21:29
Speaker 1: Yeah, we actually know what the number is, right, We know exactly what number you need in the equations to get the accelerating expansion that we see. The question is where does that number come from? And there's a bunch of possible explanations. One is like, look, every universe just sort of has a number, and ours is generated with this one. Let's just sort of like give it up, shrug it off anthropic explanation and say there is no answer. It just is what it is. Move on. Nothing to see.

00:21:54
Speaker 2: Here, meaning it doesn't correspond to anything physical. It's just that the equations of our universe don't balance out to zero. They balance out to some random number.

00:22:03
Speaker 1: Yeah, Einstein's cosmological constant can come from a field of potential energy. But you can also just put a number in and say, oh, these are the equations of our universe. They have this number in them. Why that number? Well, you know, every universe gets a random number, and there's an infant number of universes and this is the one that we're in. It's not a great explanation, but it's an explanation.

00:22:21
Speaker 2: I mean, like, why does the universe have to balance out to zero. You could ask that question too, right, why does the balance out to three point four or seven.

00:22:29
Speaker 1: Or forty two? Right, that's the best number anyway.

00:22:32
Speaker 2: Right, Yes, that's the answer.

00:22:34
Speaker 1: That's the answer exactly. And now we finally found the question. But those of us who are curious about the universe aren't satisfied with just being told I don't know it is what it is. Move on. We want to know if there is an explanation. And so many times in the history of science we found things that looked weird and we dug deeper and we have found explanations, reasons why it had to be this and not something else. And so some people have explored this idea of like, let's create new fields that have potential energy that maybe could explain why we have this number and not some other number that we need to put into Einstein's.

00:23:07
Speaker 2: Equation, meaning like we need this number to make the equations balance out or to match what we see out there in reality. And so let's pretend that this number actually represents or maybe comes from some kind of physical field of the universe.

00:23:20
Speaker 1: Yeah, exactly, because then we get to kick the can down the street and say, oh, the expansion is due to this potential energy from this field, and then we can ask what's this field all about? Why does it have to exist? How does it fit in with the other fields? And we get to, you know, keep asking questions. Yeah, stay employed, stay curious, stay curious, don't be so cynical.

00:23:38
Speaker 2: All right, Well, so then the idea is end that this constant, this number in the equations represents a field, and is this this symmetron field.

00:23:46
Speaker 1: Then no, so the cimitron field is a slightly weirder version of this. The simplest idea is to just use a constant, but there is no field out there that we know about that provides this constant. So instead people are trying another idea. Instead of having a constant, to add a different term.

00:24:01
Speaker 2: It wasn't the Higgs field a constant too.

00:24:03
Speaker 1: They put in a number which isn't constant. The Higgs field is a constant. It's just not enough, right. The Higgs field provides a tiny little bit, but doesn't provide enough to explain the accelerating expansion. So people thought, oh, well, let's try adding a different kind of term. Instead of just adding a number, let's add something which has a derivative, right, which doesn't disappear when you ask about the changes.

00:24:23
Speaker 2: Meaning something that's changing with respect to time for example, Yeah, like a variable, like a variable instead of a constant.

00:24:29
Speaker 1: Exactly, a variable instead of a constant. Now, for a long time, this has not been a very popular idea because that does more than just explain the expansion of the universe and its acceleration. It also creates new forces. It says, oh well, if you have something which it varies, it basically changes how gravity works in a way that creates a new force on things, so like a fifth force. So this has not been a very theoretically popular way to go because it creates a fifth force, and you know we don't see any fifth forces.

00:24:56
Speaker 2: But I guess the question is, if a constant explains the expansion of the universe, why do you need a viable Why don't you stay with a constant.

00:25:03
Speaker 1: Because we don't have an explanation for that constant.

00:25:05
Speaker 2: So then the idea is just make it more complicated.

00:25:08
Speaker 1: The idea is to make it more complicated. Say, maybe a constant is the wrong way to go. We couldn't make a work with a constant. We have no way to explain that constant. So instead, let's choose a different term that's not constant, that's variable. It's like, let's look under a different kind of rock because we ran out of the original kind of rock.

00:25:23
Speaker 2: I guess maybe explain to our listeners what does it mean to explain it? Like how does the constant fail to explain the expansion?

00:25:29
Speaker 1: The constant on its own wouldn't fail to explain it, Like we know what constant you would need to put in there to explain the accelerating expansion. We just don't know how to justify that content, like where did it come from? There's no field we know about that can explain that constant.

00:25:42
Speaker 2: But then if you put it viable, couldn't you also ask the same question like why is it there?

00:25:47
Speaker 1: Absolutely, if you put it in a variable, you also need to justify it. It's just another idea, and then you need to explain like where does that come from? The answer is, oh, comes from a new field that we haven't seen yet. Well, let's talk about what that field is and how we might see it and what it would look like.

00:26:01
Speaker 2: Oh, I see, No, actually don't see it. Sounds like maybe you're just making it more complicated, just to make it more complicated, to see if maybe the universe is actually more complicated. But it sounds like it's not, though, because it sounds like a constant, you know, matches what we see experimentally.

00:26:19
Speaker 1: You know, when you're in the early days of scientific ignorance, you try lots of things. You try the simplest thing first usually, and that's like just put in a constant that hasn't really worked because we don't have any way to explain those constants. So now we're trying the second simplest thing, like, well, let's put in something which changes a little bit, which has features and wiggles and is a little bit more complicated, and let's just see what that predicts. And if that's the universe we live in. Yeah, maybe we do live in a more complicated universe. Maybe there isn't a constant in this equation. Maybe there is something that changes. I see.

00:26:48
Speaker 2: You're just kind of exploring what these things can be. Like, maybe what you're measuring is more complicated than what you're actually see.

00:26:56
Speaker 1: Yeah, exactly. It's like if you notice cookies disappearing from your kit, encounter simplest explanation that your kids eat it. But you know, maybe there's some new animal out there you never discovered before that only eats kitchen cookies, and so you should consider the hypothesis and it might take you new places, like let's go look outside to find evidence for this new crazy cookie eating animal because maybe it does exist in your universe in the same way. Here, like the simplest explanation hasn't really panned out, So some people are like, well, let's look for a slightly more complicated cookie eating universe.

00:27:25
Speaker 2: But did you ask your kids if they took the cookie first.

00:27:30
Speaker 1: In this hypothetical scenario, I have somehow alibied them out of the cookie eating.

00:27:35
Speaker 2: Yes, I see, Well, why not even go further? It was aliens that ate the cookies?

00:27:41
Speaker 1: Yeah, exactly. You could go further and there are people doing that, right. There's no limit on what you can do in theoretical physics. It's just a question of like, is it a good idea, is it compelling, does it lead to something we can test? Is it an interesting thing to explore? And it's just up to the individual, Like I'm sure there's some theoretical physicist out there going like, oh, yeah, I have an even more complicated theory that you're really cool.

00:28:01
Speaker 2: I guess what I'm really asking is you're saying that you can't really explain a constant for that equation. So are you saying that maybe adding a variable will lead you to an explanation of that variable.

00:28:11
Speaker 1: Yeah, exactly. Let's put in a variable and see if we can explain it. Let's explore the consequences of that variable. What does it mean for other things in the universe. What predictions does it make? Can we go out and test those? If you predict that there's some new cookie eating lizard in your backyard, then you have something to go look for, you know, scratches on your window or something. So in the same way, we're like, let's add a slightly more complicated theory of the universe to explain this accelerating expansion and also see what else it predicts that maybe we could find.

00:28:40
Speaker 2: All right, So, then the cimotron field is a special new kind of field which has a variable and not a constant in the equations of the universe. Tell me about this field.

00:28:48
Speaker 1: So mostly these fields are really not mainstream theoretical physics for one important reason, which is that the variable nature of them produces this extra force, and people are like, well, we've never seen extra force, so that's out. So if you're going to build this kind of theory and you really want to make it work, you have to come up with an explanation for why we haven't seen it yet.

00:29:08
Speaker 2: Wait, why does it predict the force?

00:29:10
Speaker 1: Because when you put that number into Einstein's equation to figure out how things move, you end up having to take a derivative of it. If it's a constant, that goes away. If it's not a constant, if it's a variable, then it's derivative doesn't go away. Its rate of change with time is non zero, and that changes how things move, and effectively, that's like a force.

00:29:28
Speaker 2: It sticks around it like influences the acceleration of other things in the equation, and so therefore that's what you call a force.

00:29:35
Speaker 1: Yeah, Basically, it's like it changes how gravity works, as if there was another force out there, right, But.

00:29:40
Speaker 2: We haven't seen a force like that, And so now the question is like, how do you contort your theory so that it explains why we haven't seen its force?

00:29:48
Speaker 1: Yes, exactly, And so the symmetron is one of a category of theories like this, there's another that's called the chameleon theory, another that's called the galileon theory, and this one is called symotron theory, and it has a particular way to avoid being ruled out by all these experiments, as a symtron field. And this symotron field behaves differently when there's a lot of stuff around, when it's like high density materials, and when it's low density materials, So in high density regions like within galaxies and in our solar system, et cetera, et cetera, there's a symmetry in this field. There's like basically two parts of it that balance out and you get no force. So it basically doesn't exist within the galaxy, which is cool because it doesn't change how the solar system works, and we've measured that very precisely. We would have noticed if something was weird. But out past the edges of the galaxy where things are very very low density, the symmetry in this field breaks, and the broken symmetry there is what creates that force. So basically the symmetron field behaves differently. When there's a lot of mass around, it goes away, and when there's no mass around. That's when it really starts to take effect that.

00:30:55
Speaker 2: It seems very convenient.

00:30:57
Speaker 1: I think contrived is the way to think about it. Yeah, contorted, made up, and that's not something to be ashamed of. Like, this is how theoretical physics works. So like here, I have an idea that conflixs with what we know about the universe. Can I avoid that somehow? Can I add some bells and whistles to my theories to avoid this experimental measurement? I literally hear theorists doing that all day long.

00:31:18
Speaker 2: Mmm, and it has that How often does that work?

00:31:22
Speaker 1: Never so far?

00:31:23
Speaker 2: I guess never so far? Well why not keep doing it?

00:31:30
Speaker 1: Then? No? No, I mean you can go back to the Higgs theory, like Higgs have to come up with some new particle and new field which explained this puzzle and didn't violate any of the other experiments people had done. And so I'm sure that ruled out all sorts of other simpler explanations that people first considered.

00:31:46
Speaker 2: All right, So then the cymmetron field is a theoretical field, and it just so happens that you can see it around us, but maybe in between galaxies. You're saying, where there's less stuff. Maybe that's when you would see it.

00:31:59
Speaker 1: Yeah, exactly between galaxies is where you need to explain how it wakes up and accelerates the expansion of the universe, because really between galaxies and galaxy clusters is where the dark energy is happening.

00:32:11
Speaker 2: Oh so you're saying, like the cymatron field is a force, and maybe it's the force that's achilarating the expansion of the universe.

00:32:18
Speaker 1: Loosely speaking, that's accurate. We can't really think of it as a force because gravity isn't a force. It doesn't generate measurable acceleration in that way, so you can't do like f equals MA for things generated by gravity, and this is something generated by general relativity, and so it is sort of like a modification of gravity. But loosely speaking, you can think of it as like an effective force. We would see it as a force the way we see gravity as a force in our.

00:32:42
Speaker 2: Measurements, meaning it's not really pushing that the galaxies to move away from us. It's just kind of like acting there to create more space between us.

00:32:51
Speaker 1: Yeah, exactly right.

00:32:52
Speaker 2: So then how could we prove that whether the cymatron field exists or not.

00:32:57
Speaker 1: Yeah, it seems difficult because it's very conveniently impossible to detect this thing within the galaxy, which is where we live, right. But there's a recent paper where people were speculating about mimicking the environment outside the galaxy by creating very low density experiments. Essentially, try to do an experiment inside a vacuum low density where you could see this force in action, where you could detect the simitron field at work.

00:33:22
Speaker 2: WHOA, Well, so let me picture this experiment. You create a chamber like a box. You suck out all the air to create a vacuum, and if this cymtron field exists, it would maybe cause the space inside the box to expand we get bigger.

00:33:40
Speaker 1: And principle, yes, your box would get bigger, But remember that dark energy is really a tiny effect over short distances, like fractionally speaking, it's very very small. It's only really measurable over very very large distances, like between galaxies, So you'd never be able to measure the box getting bigger. Though I love that idea.

00:33:57
Speaker 2: Way would the box be bigger or would the space side of it get bigger? But then it will go through the box.

00:34:04
Speaker 1: M Well, then you have a philosophical question of what's the difference? Right? If there's more space inside the box, isn't the box bigger?

00:34:11
Speaker 4: No?

00:34:11
Speaker 2: I mean like the space that the boxes in gets bigger, but the box for me is the same.

00:34:17
Speaker 1: Well, I think the space inside the box would get bigger, though the box would remain the same. But what do you mean by the space inside the box gets bigger? You mean you measure the distance from one side of the box to the other. That would definitely grow. But this isn't the experiment they're proposing. That's impossible to measure. You could never measure that tiny growth of space.

00:34:34
Speaker 2: Yeah, let's thick to only things that are possible.

00:34:36
Speaker 1: Sure, go, they've come up with a way to detect the simotron field inside that vacuum.

00:34:44
Speaker 2: Okay, how do they do that or how do they propose to do that?

00:34:46
Speaker 1: They proposed to do it basically by doing very very precise tests of gravity. If this simtron field exists, it's like a distortion of how gravity works. And so do very precise tests of gravity. Take two masses, bring them closer together and further apart, measure the forces on them very precisely, and see if you see any deviation from general relativity without the symmetron field. That's very very tricky to do because gravity is very very weak, right, It's like ten to thirty times weaker than any other force. So these experiments have to be super duper precise. But we have some techniques to.

00:35:20
Speaker 2: Do them, so you can do this experiment.

00:35:22
Speaker 1: You can do this experiment. And people have been interested in deviations from gravitational predictions over small distances for a few decades because there are other theories that predict that also, like if there are extra dimensions to space and time more than just the three we know about, then gravity would work differently. But maybe those dimensions are really really small. So a lot of these experiments were motivated by looking to see if gravity changed when things got within like a millimeter or a centimeter apart. And until twenty or thirty years ago, nobody knew the answer to that because we could only really do gravitational measurements on like planets and stuff interacting with planets. Two rocks pull on each other with gravity, but it's very difficult to measure, so people came up with these ingenious devices to measure gravity on short distance scales. They're basically souped up versions of the original torsion pendulums that we talked about once in the podcast for how people would measure the gravitational constant. In this case, you have two rotating discs, and the discs have holes drilled inside of them, and you rotate one of the discs and let the other one free. Then you measure how the free disc is pulled by the rotating disc because if gravity is strong, and then they'll try to line up those two discs to line up the places where there's more mass and line up the places where there isn't this much mass. So if you slowly rotate one of these disks and measure the rotation of the other disc, you can measure the force of gravity between these two objects that are just like kilograms of mass.

00:36:46
Speaker 2: Sounds a bit complicated, so maybe let's dig into the details of this experiment and how it might or might not show the existence of the symtron field and what it could mean for our theory of the universe and the future employment of all physicists. So let's dig into that. But first let's take another quick break. All right, we are inventing fields left and right, here to try to explain the expansion of the universe, which is pretty inexplicable. The universe is getting bigger and bigger, faster and faster. We're trying to come up with an idea. A physicists have come up with the idea of a cymitron field to try to explain it. But Daniel, you're saying it requires us to measure gravity at a really really tiny small scale. Which I always thought, because you've said it several times, is that it's almost impossible.

00:37:46
Speaker 1: It's difficult. It requires real experimental bravado to figure out how to remove sources of vibration and anything else that might influence your experiment. In principle, these effects are happening all the time right in front of you. They're just drowned down by other, much bigger effects, and so in order to reveal them, you need to remove those effects. It's like if somebody's whispering the secrets of the universe but really really quietly, and you can't hear it because your neighbor is pumping some crazy death metal. In order to hear you have to isolate yourself from all that noise. So in the same way, these experiments are set up really cleverly, sort of stimilate to how ligo is done, to be isolated from everything else, so that you're measuring the right thing, this tiny little effect that you're looking for, and not being drowned out by the other much bigger effects that are more common.

00:38:30
Speaker 2: M Okay. So then you're saying that to maybe discover whether the cymmetron field exists or not, We're gonna take two discs. We're gonna place them facing each other, really close together but not touching. We're gonna spin one of them. And I guess these discs are not perfectly symmetrical, right, You're saying that maybe they have like a weight on either side.

00:38:52
Speaker 1: Or something for example.

00:38:54
Speaker 2: Yeah, and so if you twist one of them, does the gravity from that twisting disc make the other disc twist as well?

00:39:00
Speaker 1: Well? And the answer to that is definitely yes. And the question is by how much?

00:39:04
Speaker 2: Wait, what do you mean? It's definitely yes, but the other disc can't be symmetrical in there.

00:39:08
Speaker 1: Neither of them are totally symmetrical. You could think of them as like, you know, rods with masses on the ends. In practice, what they actually do is discs with holes drilled out of them. But either way, it's not totally symmetrical, and so gravity will pull on them to try to align them.

00:39:23
Speaker 2: Right, and you have to kind of rule out the effects and the other effects I might be like maybe the static electricity between the two plates, or maybe the vander wall forces maybe.

00:39:33
Speaker 1: Exactly, or the tides of the moon or anything. Right, everything else is basically bigger than this. You have to remove every possible other effect, and then you want to bring them closer and closer and closer, so you can see how gravity varies with distance, because one big clue is to see if we understand how gravity gets weaker and stronger as the distances get larger or smaller, because that's a crucial prediction of both Newton's and Einstein's theories of gravity.

00:39:58
Speaker 2: Right, there's like famously, like the the force of gravity between like the Earth and the Moon is equal to the mass of the Earth, sometimes the mass of the Moon divided by the square of the distance between the two things. Right, m M exactly the square of the distance, or is it maybe more like the square point two of the distance?

00:40:15
Speaker 1: Yeah, exactly? Or maybe does it change when you get down to really small scales exactly. Any deviation from the classical prediction means something new is happening, gravity works differently, which could be the symtron field. In this paper, they predict that if you get these two discs really really close to each other, like tens of microns apart from each other, then you could be able to detect the effect of the simitron field in.

00:40:39
Speaker 2: What way, Like how does the symtron field change gravity?

00:40:42
Speaker 1: The answer to that is very unsatisfying because there's actually lots of versions of the simtron field, and so you can get lots of different kind of deviations. So basically, any deviation from this you could explain using the symotron field the.

00:40:55
Speaker 2: Way, meaning like, if you find that the actually gravity works is the distance squared point two, then you're saying, like the point two that's the symmetron.

00:41:04
Speaker 1: Yeah, exactly. The semitron feels like a category of theories with a bunch of knobs and parameters, and if you find some deviation then you can explain it in terms of the symmetron field in almost every sense.

00:41:16
Speaker 2: Couldn't we just be wrong about gravity? Why does it have to be a symmetron?

00:41:19
Speaker 1: Yeah, we could just be wrong about gravity, and that's one thing people are looking at right And the answer could be that we're wrong in some other way, that we're wrong about the assumption that space has three dimensions, or we're wrong about how gravity works over short distances, general relativity breaks down, or this is just an effort to explain it in terms of general relativity, because if you find this and you measure a certain value, then it also explains the accelerating expansion of the universe. So that would be kind of.

00:41:43
Speaker 2: But it wouldn't improve or disprove the symmetron. I feel like you're saying it could be anything.

00:41:48
Speaker 1: Yeah, lots of theories in particle physics have that problem. Like supersymmetry can predict almost anything. So you find some new particle, can you explain it using supersymmetry? Yeah, does it mean it's supersymmetry, No, but it's still some new particle. So in this case, you find some deviation from gravity, if you've ruled out like experimental effects and you know gravity's working differently, then yeah, either space is different from what you expected, or general relativity is broken, or general relativity isn't broken and space has three dimensions, and there's some new bit added to it, like the symotron field. There's always going to be a variety of explanations. But hey, we'd be happy to be in that situation of trying to understand some weird deviation of gravity. I see.

00:42:28
Speaker 2: So like, if you find a deviation, maybe a cymotron is the reason, but maybe not. And so this is just this experiment you just described. It isn't to prove the cimitron. It's just to poke holes gravity.

00:42:39
Speaker 1: It's to poke holes of gravity. This experiment is interesting in the context of symmetrons because until recently, we haven't thought that any of these kinds of theories that have like variable additions to Linstein's equations could be tested at all, because all of them basically disappeared within the galaxy. So this is a cool way to say, oh, look, this is one we can actually test. You're right, it's not conclusive, but there are other ways we could also test the symmetron field, not just in these laboratory experiments of gravity. So there might be ways that we could discover it in different contexts. So it pulls together into a coherent idea.

00:43:10
Speaker 2: But I guess you know, if you put these discs closer and closer together, aren't you then violating this clues that you made about the cinmatron that it has to exist in it only exists in empty space.

00:43:22
Speaker 1: Yeah, that does get tricky. It gets tricky experimentally because having discs rotating really really close together, like fifty or ten microns is hard, and it also breaks down this assumption of load density. So then you have to make these things lighter. You have to make them smaller and smaller. So then you're playing this game of balance because you bring them closer together, which makes gravity stronger, and then you're removing mass to maintain the load density threshold, which makes gravity weaker.

00:43:47
Speaker 2: All right, so stay tuned, I guess is the answer here? Are they actually doing this experiment? Have they found anything yet?

00:43:54
Speaker 1: People are doing this experiment. It's a whole successive generations of these at the University of Washington, where people still now they could test gravity. It's centimeter scales and then millimeter scales. Now they're pushing down even further, just like a whole series of graduate students, each coming up with some new clever way to make it slightly more sensitive and over decades. It's really establishing the frontier.

00:44:14
Speaker 2: And what have they found so far? That gravity does work as a distance squared or maybe not?

00:44:18
Speaker 1: Oh yeah, so far they found exactly zero deviations from Einstein's gravity. Now we'd be talking about the Nobel Prize if somebody found a deviation from general relativity. So far it perfectly confirms.

00:44:28
Speaker 2: Gr So like the twenty years of PhD thesis, all with the same title, Einstein was right Einstein yeh, still right, Einstein was right side, Einstein's still going strong.

00:44:43
Speaker 1: Yeah, no, that's true. We keep confirming Einstein. We keep hoping to see a deviation, not because we don't like the guy, but because a deviation from the theory is an opportunity to learn something. It gives theorists an opening to add new bells and whistles to the theory that might also correspond to bells and whistles in the universe.

00:45:00
Speaker 2: Hmmm, all right, well let's talk about that then, Like, if we do this cover the symtron and the symtron field, what would that mean about our understanding of the universe.

00:45:09
Speaker 1: It would mean that general relativity is still right, Einstein was right, but that there's this term we have to add to these equations that the universe has more than just mass and energy density, that there's something else going on, this weird symtron field that changes how the universe grows. It's like a new conception of gravity.

00:45:27
Speaker 2: Wait, I thought you said gravity would stay the same. It's just that we have this new thing called the symmetron field.

00:45:32
Speaker 1: Yeah, you don't have to overthrow general relativity. The symmetron field plays nicely with general relativity, but it does change how the universe expands. It would explain basically why that expansion is.

00:45:42
Speaker 2: Accelerating, because the symotron is the force that would be pushing the universe to get bigger and bigger.

00:45:48
Speaker 1: Yeah, the symtron is that field which enters in Einstein's equations, which generates this accelerating expansion of the universe.

00:45:56
Speaker 2: And that's more satisfying than the constant explanation.

00:45:59
Speaker 1: That would be more satis fine than the constant because the constant is totally unexplained. The only explanation for the constant is that's just the number. Eat it. That's all. There's really nothing there.

00:46:09
Speaker 2: As opposed to that's just the simitron. Eat it.

00:46:13
Speaker 1: Well, the simitron gives us a handle. We could ask more questions about it, like why this symmetron field, why does it have these numbers in it? Where does it come from? How early in the universe did it appear? It gives us something to ask about, you know, it's more specific.

00:46:27
Speaker 2: Like who came up with that name? Come on, TSK not me, that's for sure. You wish it.

00:46:33
Speaker 1: I wish it had been me. Yes, okay, finally I admit it.

00:46:36
Speaker 2: Yes, yes, all right, Well what else does it say about the universe and how it's expanding.

00:46:43
Speaker 1: It could actually have impacts on the way that galaxies form. We see galaxies forming and ellipses and galaxies forming in spirals in the early universe. As the symmetron field was created and then cooled, it could have broken its symmetry in different ways between different galaxies, creating these like barriers between them, and those barriers might create like effectively walls between galaxies that are invisible that could affect how galaxies form. And so there's this other prediction that if a symmetron field is there, you could explain why we tend to see fewer satellite galaxies than we expect. So there are predictions we can make inside our laboratories and also how deep within galaxies, and it could just give us another insight into how the universe works, Like what else invisible is out there is shaping our universe?

00:47:25
Speaker 2: Who because the mysteries aren't just in the expansion of the universe, it's also sort of like how the universe ended up the way it is.

00:47:32
Speaker 1: Yeah, there's lots of open questions about the universe, and you know, physicists, just like listeners, like to tie them together. Ooh, what if this mystery is explained by that mystery and I can simultaneously solve a couple of open problems. That's really a juicy idea.

00:47:45
Speaker 2: Yeah, like, what if you're missing cookies we're taken by a new particle called the Pikachuu tron.

00:47:52
Speaker 1: Done Nobel prize, boom a cookie prize and give me ten here?

00:47:58
Speaker 2: All right, Well, another interesting idea in the field of physics and particle physics that has consequences not just at the microscopic level, but maybe at the biggest level of them all the entire universe. How it came to be and what keeps it growing bigger and bigger.

00:48:11
Speaker 1: And if this whole process of theoretical physicists inventing crazy emails and whistles staff to the universe seems a little out of hand or bonkers to you. Then, don't take that as criticism. Take it as inspiration to think of your own crazy ideas about the universe. You're in good company.

00:48:26
Speaker 2: Yeah, I mean, I'm a cartoonist. I think of crazy things all the time.

00:48:31
Speaker 1: Well, you have a PhD in podcast physics, so.

00:48:34
Speaker 2: Hey, yeah, that's right. It's not a PhD. It's a pod. I have a pod in podcast physics. All right, Well, we hope you enjoyed that. Thanks for joining us. See you next time.

00:48:51
Speaker 1: For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, This, Org, Instant, and now TikTok. Thanks for listening, and remember that Daniel and Jorge explain The Universe is a production iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.