Daniel and Kelly’s Extraordinary Universe - What's the problem with the Standard Model?

Episode Date: February 16, 2023

Daniel and Jorge talk about the holes in the current theory of the Universe.See omnystudio.com/listener for privacy information.

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listen to Good Game with Sarah Spain, an IHeart women's sports production in partnership with Deep Blue Sports and Entertainment on the IHeart Radio, app, Apple Podcasts, or wherever you get your podcasts. Brought to you by Novartis, founding partner of IHeart Women's Sports Network. Hey, Daniel, are you guys done with physics yet? Done with physics.

I mean, we're just getting started. Yeah, but didn't you build that large Hadron Collider? Didn't that answer all of your questions? Nah, there's always more stuff to figure out, man. Wait, you mean people pay $10 billion for that? and now you need more money? That was just like the down payment on the project. What?

Was that in the fine print? We missed that somehow? Research is exploration, man. There are never any guarantees about what we're going to find. But I thought the Higgs boson completed the standard model. I mean, it's called the standard model. Aren't you done? It's the standard model.

Now we want to upgrade it to like the super standard model. Sounds like you need to go work for Apple. Sounds like we should work for FTX. Sounds like we paid you $10 billion for the wrong model. Can we have $100 billion, please? Hi, I'm Jorge. I'm a cartoonist and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I will never be done asking questions about the nature of reality.

But what if you get the final answer? Wouldn't you be done? Well, the lesson from that book is that you're never done. That even if you do get the final answer, the next question is, well, why this answer and not something else? Why do we live in a universe where the answer is 42 and not 47? What does it mean anyway? The questions multiply. Maybe the ultimate answer is because.

That's a non-answer. It's an answer. It's not a very satisfying answer. And in the end, we're looking for explanations, not nonsense. Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio. In which we try to satisfy your curiosity about the nature of the universe. Why is the world made up of tiny little particles frothing together to build up our reality? How far down do you have to go before you can really understand the universe at its most basic level?

And is there even a most basic level or is there an infinite tower of questions all the way from galaxies down to black holes, down to particles, down to strings and then down to whatever strings are made of. Yeah, it's an incredible universe full of gigantic phenomenon like black holes and galaxies and clusters of galaxies, but also with a lot going on at the microscopic level with atoms and particles and tiny little quantum blips. And somehow it all seems to be ruled by the same rules, the same rule supplies from the tiniest levels to the most cosmic of all levels. It really is incredible how many layers of zoom we have for the universe.

universe. Like we can think about the universe on the scale of super clusters of galaxies, objects that are hundreds of millions of light years across, and they follow gravity. We can make predictions about how they swirl around each other. And then you can sort of adjust your zoom knob and think about planets and stars. And you can adjust your zoom knob again and think about rocks and liquids. And you can do it again and think about atoms. You can do it again. You can think about protons. You can do it again and think about quarks. And we just don't know how many layers of zoom are there. And we don't actually even know the answer to the question of whether they all follow the same rules. You know, our reductionist approach assumes that there is

a basic nature to the universe with a certain set of laws from which everything else emerges, but that's sort of a philosophical assumption. We're not even sure that's true. Do you refine yourself, Daniel, reading a scientific paper that you printed out on paper and then you're trying to zoom in with your fingers? Does that work? I do sometimes click on blue links on printed out papers and I'm frustrated that they don't just like print out the right paper for me. That would be awesome. You could click on a link on a paper and your printer would just print the next paper. But it is pretty amazing that we know so much about the universe from the tiniest levels to the largest of all stages, the entire universe. And I guess the hypothesis, like you said,

is that there's one set of rules that somehow rules at all. That's certainly one philosophical approach. We call that reductionism, the idea that the tiny dominates the huge. And it sort of makes sense to us intuitively the things emerge from the smallest bits. But if you dig down into it, there's not really a whole lot of justification for it. I mean, why should the small dominate the large? Why can't rules emerge at the larger levels as well and dominate the small? Wait, who said the tiny dominate the large? I would say that the particles here on Earth are pretty much subject to whatever the sun wants to do.

I think the sort of standard philosophical approach to physics is to imagine that there are basic rules at the smallest scale. and those rules somehow weave themselves together to make our reality. And so in order to understand the basic nature of the universe, we should dig deep into the smallest particles to try to find the smallest of the smallest of the small. And along the way, we have made a lot of progress, a lot of encouraging results. We've understood the nature of the periodic table based on how protons and neutrons and electrons fit together to make all of those different atoms. We've even understood how protons and neutrons are built out of smaller pieces.

So there are a lot of hints that suggest that we should keep. digging down into the nature of reality to understand how the bigger things emerge. It's kind of interesting how physics has covered both ends of the spectrum, but not the stuff in between. Like you start out small with the particles and atoms, but then at something you're like, ah, that's chemistry. And after that, biology. And after that, you know, political science.

We don't care about that. But then once you get to like the size of the planet or the solar system, and you're like, oh, okay, now I'm back. Now I'm interested in this again as a physicist. will take over from here until the end of the universe. Yeah, that's right. And it's really fascinating, sort of from a sociological point of view, because for a long time, those communities,

the astrophysics community and the particle physics community, were totally separate. The people who worked on galaxies didn't really spend a whole lot of time talking to the people who built colliders and smashed particles together. Though they were in the same department, they didn't really overlap very much. But more recently, those communities have come together because there is a common mystery.

For example, the mystery of, of dark matter. We discovered it through astronomical observations that reveal that there's stuff out there that is not made of our kinds of particles. And now we have particle physicists searching for that dark matter. So now we have a new kind of physicist astroparticle physicists that work both on the biggest things and the tiniest things in the universe. But you're right, skipping everything in between. Yeah, I feel like you guys skip over anything that's messy and complicated. I wonder if that says something about your personalities. I do think that I got into physics to avoid all the complications of chemistry and biology. That's certainly true. We like

approximating things as simple objects, dots, spheres, circles whenever we can. Planets, right? Planets are also just circles to you. So, suns, right? Basic kindergarten shapes, as long as you stick with that, then you're a physicist. I think kindergarten is probably too advanced. I mean, I wouldn't want a triangle-shaped planet or anything. Wouldn't that be interesting, though? I'd be like, oh, that sounds like chemistry to me. I'll focus on the spears. It sounds like geometry. Forget about it. Exactly. We do have a pretty interesting view of the universe now and an interesting model that describes how things work at the tiniest levels and that we are hoping extends to the largest of levels. But we do have a model about the universe and we've been building it over centuries, right? Yeah, physics builds our concepts of the universe sort of on these levels, right?

We have like the atomic level where we think about the elements and then we zoom in and we think about the nucleus and then we zoom in and we think about the quarks. And at the level of the quarks and the electrons, you're right, we have a very nice picture of all those particles, how they interact, what they do. And that model also explains all the experiments that we can do, smashing particles together at very high energies and all sorts of other very detailed exhaustive experiments. The picture we have of those particles we've been putting together for about 100 years, it sort of all clicks together very nicely now. Yeah, it's a pretty good theory that describes what we can see and it works pretty well. However, we sort of know it's not the final theory or the ultimate theory of the universe. That's right. Physics is never done asking questions.

And even if we have a beautiful concept which clicks together and explains experiments, this is this will always come up with ways to keep the project going. Conveniently, you'll figure out a way to keep your job and going. You think being driven by curiosity, staying up late at night, wondering about the nature of the universe is convenient? It's almost like an obsession. And so to the end of the program, we'll be asking the question. What's the problem with the standard model?

I think I know the answer, Daniel. Is it me? Am I the problem? Well, that's one problem, yes. But maybe your main problem is that you call it the wrong thing. I mean, you call it the standard model. Not everyone thinks it's the standard one, but now you're saying it's not standard. Yeah, you'll be amazed to discover that we can't even actually agree about what is the standard.

model. Some people think the standard model is one thing. Other people think it's something else. So it turns out the standard model is not actually standard. Sounds like you guys have no standards when it comes to naming things. Especially models. It doesn't surprise me that we didn't impress you on this one. But really maybe the question we are asking here today is what are the problems with the standard model, right? Because there's not just one problem with it. There are many. There are many problems. There are unanswered questions. There are cracks in it. There are missing pieces. There are things we know the standard model cannot describe. All of these things are vital hints and clues laying the path for the next generation of physicists who we hope will reveal a deeper understanding

into the nature of reality. So maybe a better name would have been the model-ish or the sort of model? The non-standard sort of model. Well, as you usually were wondering how many people had thought about this question, have wondered what are the missing pieces of the standard model? What's wrong with it. So thank you very much to everybody who answers these questions for this segment of the podcast. We thoroughly enjoy hearing your thoughts and we would love for everybody else to have a chance to participate. If you would like to put your voice on the podcast answering these questions, please write to me to questions at danielanhorpe.com. I will set you up. So think about it for a second. What do you think are the problems with the standard model? Here's what people

have to say. I feel like we're confident about how gravity works like on the Microsoft. or macroscopic level, and then we're confident about quantum mechanics, but we don't know how to relate the two, and that's the problem. As I understand it, the standard model describes a proton and the nucleus and electrons, and the problem with it is that it describes them as little actual points in space, as opposed to excitations of various quantum fields. Therefore, I remember you saying actually in the podcast that it's actually an incorrect interpretation to imagine these little things as particles or little discrete points in space.

Maybe the problem is that it doesn't have anything for the dark matter and dark energy, but my problem is that standard model has many things to remember, and it's too difficult for me. I think the main problem with the standard model is that there's no room for gravity, and I think especially with the Higgs, it kind of almost finalized it. So now we're kind of stuck. Well, I think that the problem with the standard model might be that it is incomplete. It may not have the particles to describe, for example, quantum gravity, so it can't be reconciled with general relativity.

Well, I think the problem with the standard model is that, A, people are unsure about the missing pieces in the pattern, missing holes in the periodic table type deal of the standard model and people are curious if there is some sort of emergent or if it's some sort of an emergent phenomena of smaller particles even smaller than those that we observe in the standard model. All right. A lot of awesome ideas here. There seem to be a lot wrong with the standard model.

I think this might be the first time we can say that every single answer is correct, 100%. Wow, that's amazing. So we're done. Turns out the listeners are answering the questions for themselves. We have trained everybody so well that we have worked ourselves out of a podcast. That's right. We have reached the singularity. Thank you, everybody. It's been great. Well, it sounds like maybe you need some different standards for the standard model.

You know, like they have the gold standard, the platinum standard, green standard, the tin can standard. Well, you know, I do think it's a strange name for a theory, the standard model. It's like calling something modern physics. You know, what we teach as modern physics these days is physics as we knew it about 100 years ago. So when they started calling it modern physics, they sort of painted themselves into a corner. And that happens every time you give something a name like that. It's like calling the draft of your paper, final, final, ready to submit. You know that's not the one you're going to submit.

There's going to be a ready to submit Virgin 7 before you actually turn that paper in. So then what do you teach you at the graduate level? postmodern physics deconstructivist physics impressionist physics yeah no we've avoided giving an updated name

like super modern physics or actually modern physics we just teach whatever it is we know now well I guess there's a classical physics so you gotta figure out how to distinguish it from that right yeah well we usually think about

classical physics and quantum physics and quantum physics obviously more recent than classical physics what do you call this podcast physics light diet physics no this is the juice man we are squeezing physics to extract all of the core ideas and

understanding this is like a shot of physics this is like the frozen concentrate can of physics this is like that protein powder man this will beef you up in your physics knowledge

the beef of your brain might not be great for your kidneys but it'll make your mind strong All right. Well, let's dig into this. Daniel, I guess, first of all, what is the standard model? And is it really standard? So the standard model is our description of nature at the deepest level that we have seen so far. You know, we have six quarks. We have six leptons. We have forces that tie them all together. The standard model is what we call our theory of how all of that works. And it really has emerged from a piece of work that started like about 150 years ago with Maxwell as he tied together, electricity and magnetism into a unified concept of electromagnetism.

That was really like the first step towards having any sort of holistic understanding of various phenomena in physics and like one big idea. Right. But then this sort of this was after Newton, right? Like Newton had an idea of how forces and masses and things interacted and work. This is more about like, let's break it down and think about all the different kinds of forces that are out there. Yeah.

Newton was thinking about how masses move and the effects of gravity, but there are lots of other phenomena out there that can't be explained by gravity, right? Like electricity and magnets and all sorts of other stuff. And Maxwell brought a bunch of things together and put them sort of under one umbrella. He developed sort of the standard model of electromagnetism. And that's sort of like the founding kernel of today's standard model. He explained how forces operate in terms of fields and how a bunch of different forces really were part of one bigger picture. Right. And he was looking specifically at electrical things. like you said, and magnetic things, but not gravity,

but it's still kind of using Newton's equations to think about like, hey, if I put this magnet in this field, how is it going to move and why does it move like that? It's Newtonian in the sense of F equals MA. He was calculating the electric force, for example, on an electron, and you can use F equals MA to deduce how the electron accelerates. So it's part of mechanics in that sense. But really, he was digging deeper or he was wondering just like,

what is the source of these forces? Why are there forces in the universe and can we explain all of them in terms of a single idea rather than having like a long list of different ones? And is that where the name the standard model came in? The standard model as a name didn't really appear until much, much later, like a hundred years later. So we have electromagnetism from Maxwell and then that was turned into a quantum theory when we develop quantum mechanics. And it's sort of fine men and a bunch of other folks that turned electromagnetism into a quantum field theory, which is the more model. version of it. That was about the 1950s-ish, and he and some other folks won the Nobel Prize for that. So then we had a quantum version of electromagnetism, but we also had these other forces.

We had like the weak force. And Steve Weinberg, who won a Nobel Prize, figured out how to bring the weak force together with electromagnetism. And that's the first time people really called as sort of the standard model. And he wrote a paper called a theory of leptons, which is what brought the weak force together with electromagnetism. And around then is when people started calling it the standard model. I see. I guess what you mean by the standard model is like, hey, we have all these different ways that particles and things can be pushed and all these different forces that they seem

to experience. Can we put all of these forces into like one umbrella or one, you know, equation or theory? And if we can, then that's kind of standard because it covers everything. Yeah. Although, of course, the standard model doesn't cover everything yet, right? Even the standard model we have today does not describe everything as we'll dig in to in a minute. So we should think of it as like sort of our current best work in progress description of all the particles that we can't explain so far. But it's sort of like, you know,

we're all building a barn together. Let's all work on the same project at least and try to put the whole thing together into one edifice. But it's sort of like how far we've gotten. It's like working draft underscore seven. Now when you say that you're putting all these different forces under one theory, what does that mean? Does that mean that all these forces are somehow related to each other, they somehow interact with each other, or are they separate? It's just about putting them under the same grouping. Yeah, that's a really great question. I think there's two ideas there. One is putting the forces in the same mathematical language. Like, can we describe these things in terms of the same basic concepts? And the basic concept we have for the standard

model are these fields that fill space and carry information and momentum around. And that's the basis for why electromagnetism can push on things and why the weak force can push and pull on things and also why the strong nuclear force can. So we have a mathematical sort of formula for how that happens. And the standard model is cool because it puts all these things sort of in the same mathematical language. For those you who know some physics and math, it means we can describe everything as a quantum field theory just by specifying its Lagrangian, just by saying, here's where the fields are, here's how they wiggle, and also here's how they talk to each other. That's sort of like the language we've developed for the standard model.

But there's another level to it, which is deeper, which is that sometimes we can see symmetries there. We can say, oh, look, this piece of the math over here and that piece of the math over there, if you bring them together, they actually click together into something simpler. So that's what we've done, for example, with electromagnetism and the weak force. We've combined them into one mathematical structure we call the electro weak force. So there's sort of two levels to that. One is just writing it in the same language, and the other is noticing patterns and simplifying things, by bringing them together.

Because I guess it could have been that that wasn't the case, right? It could have been that, you know, you study electromagnetism. It's like, oh, it works in this way and there's this math to describe it. Then when you looked at how particles pull on each other through a different force, like the strong force or the weak force, you know, you study that. And then it turns out that you need a totally different kind of math for that. And the two maths are not compatible. That could have been the case.

That could have been the case, exactly. And in fact, that is the case for gravity. We have no way currently to bring gravity into this mathematical framework. That's one of the problems we'll talk about later. And so it hasn't succeeded in every single case, but it has succeeded for these fundamental forces, the strong force, the weak force, and electromagnetism. All right. So then that's the standard model.

It's something that describes all the known forces except gravity and all of the particles except a whole bunch of parts. You make it sound like such an amazing achievement. But really, this is the accumulation of a huge amount of knowledge and effort and ideas by so many smart people over decades. You know, it really does represent an incredible insight into the nature of the universe. But of course, there's a lot of work left to be done. Yeah, just like 95% of the story is left. But let's call it the standard model anyways.

All right, well, let's dig into the problems that we have with this standard model. What are the missing pieces? What are the things it can't describe? and what are the things it may never describe. But first, let's take a quick break. The U.S. Open is here, and on my podcast, Good Game with Sarah Spain, I'm breaking down the players

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You don't sound very impressed. I am impressed, yeah. Describing, you know, 4% of the universe or less is a pretty good achievement. Yeah, what grade would you give somebody if they got a 4% on their test? You're the professor. Well, what would you give one of your students if they got 4% on a physics test? Yeah, well, you know, I'd have to say, what's the curve? Think about all the other alien species out there that have been working on physics for the same amount of time. How far have they gotten?

And really, you've got a greatest on that curve. I see. You're all about lowering your standards. Is that what you're saying? I'm all about calibrating, man. I'm all about calibrating. In this case, lowering your standards. Maybe.

Maybe it could be that alien species out there basically figured it all out in about 20 minutes. And we've been struggling with it for hundreds or thousands of years, depending on how you count. And we've hardly made any progress. Or maybe there are aliens out there that have been working on these problems for millions of years and having gotten as far as we have. We just don't know. So then what grade would you give us? A for effort? I'd have to go with incomplete.

But that's going to look bad on my transcript, Daniel. Yeah, I don't think anybody should hire us until we have a sense for whether we're good at this or not. Hire the human race. All right, well, let's talk about the problems with the standard model, which I guess is the shining achievement of physics, right? It describes most of the forces that we know about, the strong force, the electoral weak force.

And it describes most of the particles that we know about, including all of the ones that we're made out of. Yeah, and before we reveal all the chinks in its armor, let's just spend a moment to appreciate it because it means something kind of cool about the human experience. It means that basically everything you interact with, every event in your life, everything that happens to you is mostly explainable. Like there isn't really any magic left in your experience of the universe. Every experience you have, we can mostly explain in terms of the fundamental physics that we do so far understand. You know, lightning and stomach aches and all sorts of things, we think we mostly understand the basic physics of that. Even if we can't always make it practical, we can't predict the path of hurricanes.

We don't think that there are mysteries in physics that actually affect your everyday life. And that's a new experience for humanity, right? Most humans over the years have lived in a world that was fundamentally not understood by them. Yeah, it is pretty amazing how much we can describe now. Although we were sort of there already kind of like 100 years ago, right? Like stomachase, we could have predicted 100 years ago. You don't need quantum physics for that. Yeah, I'm not sure if doctors even now understand the stomachase.

Maybe I shouldn't give them too much credit. But, you know, there were lots of interesting puzzles about the way the world worked and the particles that were out there that we hadn't figured out yet until we brought them together into this picture of the standard model. But now we mostly understand the world that is around us. Though as we dig deeper, of course, there are lots of holes. and questions that come up. All right.

Well, let's dig into some of these holes and missing pieces of the standard model. And let's start with the big one, the heaviest one, the most massive one, gravity. Gravity really is the most missing piece of the standard model. Like all the forces that we do experience

in our everyday life, the strong force, the weak force, electromagnetism, gravity is the one that we cannot describe yet using the standard model, which is, in the end, a quantum mechanical description of the nature of the universe.

But gravity, we have a classical theory. We have general relativity, which ignores quantum mechanics and describes space as a bendy place where particles can move smoothly. Yeah, I know we've talked a lot on the podcast about the problems with marrying quantum mechanics and gravity, but maybe it gives a sense of why that's so hard. Like, I can calculate the gravity between the sun and the earth. Why can I calculate the gravity or gravitational force

between, you know, an electron and a proton? Well, if you knew exactly where the electron and the proton were, then you could calculate them. You would know the distance, you'd know the masses, all that stuff. But you can't, right? It's possible to know the location of a particle. But electrons are quantum objects, right? So they don't always have a specific location. They have like a probability of being here and a probability of being there.

And one question about gravity is like, well, how does that work? Is the gravity of the electron also probabilistic? Like, does space bend a little bit where the electron might be and a little bit somewhere else where the electron? might be, or does gravity collapse the electron's wave function, requiring it to be in one place so that it sort of knows how to bend space, the right amount, and exactly where? I guess maybe the question is, like, we can calculate the force between an electron and a proton, right? And as I understand it, it involves, like, exchanging a photon. But you can't calculate that force and what happens to those two particles. Why can I do the same

with gravity? Like, if I have an electron and a proton, why can I just calculate how much force they put on each other? So if you're thinking about the electromagnetic force between a proton and an electron, you're right. You can calculate that force and you can think about it in terms of photons. And that's a quantum mechanical theory that allows the electron to have a probability being here and a probability being there. That's all cool because electromagnetism is a quantum theory. It allows all of that.

It treats its objects as quantum objects. But gravity so far is not. Gravity is a classical theory. And in order to know how much space bends, you have to know where something is and you have to know its trajectory through space and time. and that's not possible for quantum objects. So people have tried what you suggested, like, well, let's build a quantum theory of gravity

and think about exchanging little particles for those forces. They call them gravitons. And so people certainly have worked on that. They have tried to add gravity to the standard model to make it a quantum theory. The problem is those calculations don't work. Like, we don't know how to do it yet.

Gravity is a different kind of force than electromagnetism is it requires a slightly different sort of mathematical construction to describe it. And those constructions sort of fail. When we try to do those calculations, we get crazy numbers. We get infinities and negative infinities. It just sort of hasn't worked out yet. The crucial way that gravity is different is that it couples to itself.

Like a photon doesn't feel other photons because photons only feel things that have electric charges. And photons don't have electric charges. But gravity feels everything because gravity feels everything with energy. And so it's sort of a much crazier system to try to describe using this quantum mechanical apparatus. And so far, it just hasn't worked. You mean like maybe the idea of a graviton itself feels gravity? Like a graviton has energy and therefore it also affects the particles through its gravity. Exactly.

Whereas a photon doesn't feel the electromagnetic force. And so it's just simpler to do those calculations. That doesn't mean it's impossible to have a quantum theory of gravity. It just means it's going to need sort of new mathematical tools that we just sort of haven't invented yet. The tools that we have used so far haven't worked. Can you just invent a graviton that doesn't feel it's great? own gravity? You can do that and that's sort of actually the first step in an approximate theory of gravity, you know, like a perturbative theory where we say let's try to describe part of gravity

and assume that the graviton has negligible effect on the gravitational shape. Why can it have zero effect? Well, that would be inconsistent with what we think about general relativity and how gravity works. General relativity says that space bends in response to energy density. And so if gravitons carry that energy, then they should also bend space. Well, maybe just don't apply general relativity at the quantum level. Yeah, so people are building new theories of gravity. The tricky thing is that we have a lot of measurements of gravity already. So if you develop a new theory of gravity, it has to also describe everything we've observed

so far about how planets orbit each other and about black holes and all these things that happen at the big scale. You know, the scale of planets and stars and galaxies, general relativity is past all of these tests with flying colors. So if you develop a new theory, it has to reproduce all of the. those calculations as well. And so far, you haven't been able to do that. So far, we haven't been able to do that.

All of our mathematical attempts has sort of blown up in our hands. Sounds like a heavy situation there. But let's get to some of the other things missing in the standard model because some of them are pretty big. For example, 95% of the universe is not covered by the standard model. Yeah, the standard model is really good at describing the kind of stuff that we are made out of atoms and molecules and quarks and leptons and all these kinds of things. But in the last few decades, we've discovered that that's not what most of the universe is made out of.

We know that if you take a random chunk of space, like a cubic light year, and you ask how much energy is in there, it turns out that the energy devoted to quarks and leptons and all the kind of things that we do understand and are described by the standard model is only about 5% of the energy in that cube. And then another like 25% is due to dark matter. So weird new kind of matter that we know is out. there. We can see its gravity and all sorts of other effects. We just don't know what it is and what kind of particle it's made out of, except that we're sure it's not made of our kinds of particles. Or at least we know, or we think it's not made out of the particles that are

currently tallied up by the standard model. It's possible that it is made of a particle, a different kind of particle, or something that then you could add to the standard model. That's right. That would be the new standard model standard model underscore final or update version two or whatever but none of the particles that are currently in the standard model the quarks the electrons the muons the towels the neutrinos none of those can explain what dark matter is and that's a whole really fascinating topic people can dig into with a bunch of podcast episodes about why isn't dark matter neutrinos or how do we know dark matter is not some weird clump of quarks floating out there or primordial black holes or something like that but we're pretty sure that dark matter is not

made out of anything that's currently described in the standard model, which means it's something new, something weird. And you're right. If we figured out what that was, we would have to add it to the standard model. Right. But it could also be the case that maybe dark matter is made out as something that is not described by the mathematics of the standard model, right? Just like gravity. Could be something not even compatible with the standard model. Absolutely. And it's a sort of extraordinary bit of extrapolation to even assume that it might be, right? Because we've looked at a tiny fraction of the stuff in the universe and we developed mathematics that works to describe mostly that and then we imagine that oh maybe the rest of it also you know even though we know the rest of it is

different and important and fundamental ways from the bit we have studied so it's sort of a leap to say maybe we can use the same tools to describe the rest of the universe maybe right but also maybe not it might be that dark matter is not made of particles at all there are theories of matter that don't have a sort of scale that as you zoom in always look the same same, right? These things are called unparticles. There's all sorts of other crazy bonkers ideas that are not particle-based dark matter. If you ask me, that's what I would love for us to discover. Because instead of just like adding a new piece to the standard model and building on quantum field theory, it would point to us a new way that the universe operates, a completely different sort of foundational

construct that can describe reality. That would be pretty exciting. But also the standard model doesn't describe dark energy, which is like 67% of the universe, right? Two-thirds of the universe is also unexplainable by the standard model. Yeah. And when we say two-thirds, again, we're thinking about a sort of fictional chunk of the universe and accounting for the fraction of the energy, right? We don't know how big the universe is. So when we say two-thirds of the universe, some people might be confused about it.

What are you talking about if the universe is infinite? Two-thirds is also infinite. So that's what we think about in terms of energy density. Like take a chunk of the universe and ask how much energy is in that chunk and how is it apportioned? Well, two-thirds of the energy of any chunk. of the universe, we think is devoted to this thing called dark energy, as you say. And dark energy is just our description of the fact that the universe is expanding and that expansion is accelerating.

That every year space is getting bigger and it's getting bigger faster every year. And that requires some energy. And as space gets bigger, it makes new space and that new space has dark energy in it. And so dark energy is a sort of runaway effect. It keeps creating more of itself, which creates more of itself to create more of itself. And so actually the dark energy fraction of the universe is growing. It's now the dominant fraction. And unless something changes, we think it's going to forever dominate our destiny.

It seems like maybe the problem with the standard model is that it doesn't talk about space itself, right? Like it talks about particles and quantum fields and it assumes a fixed non-changing space. But there's all these other theories like gravity and dark energy in the expansion of the universe that assumes that, space itself is changing, whereas in the standard model, it's almost like a constant or an assumption. Yeah, I wouldn't say the standard model doesn't talk about space, but you're right. It

certainly makes certain very crisp assumptions about space that are in conflict with what we know to be true. Usually quantum field theory operates on what we call like a flat backdrop. We assume that space exists and that it always has existed, right, and that it always will exist. The basic way the quantum field theory thinks about space and time is not to think about them together the way relativity does, but to think about them separately. And space is something that exists. And time is just how things change in space. And so it thinks about space and time quite separately. And Trinner's equation can describe the universe all the way back infinitely in time and all the way forwards infinitely in time.

So quantum field theory is consistent with the universe always having existed and always existing into the future. Whereas when we look at space, as you say, we see that it's changing and that it's expanding. And if you think back far enough in time, it's consistent with some crazy event that we don't understand that might even be the beginning of space. So you're right there, basic questions about the standard model's treatment of space itself that we don't know how to answer. And that's really connected to this question of general relativity, because general relativity is basically a description of what space is.

But we don't know how to unify that with our understanding of quantum mechanics. Is there even room in the standard model? Or expanding space? Like, is there even a lever you can pull there or a mechanism that allows space to expand in the standard model? You can do quantum field theory on curved space or on expanding space.

But what we don't know how to do is how to have those fields themselves create that curved space, which is what you sort of need for quantum gravity. So it's possible to do quantum field theory on other funny spaces or other dimensions or expanding spaces that gets very, very complicated. Can it even then explain the Big Bang?

or not at all. So quantum field theory can't explain the Big Bang as like a singularity, right? Quantum field theory can describe what happens in space after that, but it certainly cannot accommodate a singularity. Quantum mechanics abhors a singularity, right? Because there's a fuzziness to information and to the universe. You can't zoom everything down into a tiny, dense little dot. You can't even have a singularity at the heart of a black hole,

according to quantum mechanics. So absolutely not our description of quantum field theory is not consistent with a singularity at all. And so that's why when we talk about the Big Bang, we talk all the way back to very, very early universe and we say, well, before that, we need some picture of quantum gravity. Quantum effects and gravitational effects are both important. And we just don't have that theory. And so we don't even know how to think about what happened before that time. Well, it sort of sounds like maybe quantum mechanics and the standard model will never maybe even be able to explain why space expanded so fast during the Big Bang, right? Why did the Big Bang happen at all?

Yeah, the standard model, as we know it, has no explanation for that. It may never, right, if it can handle space expanding or ever explains space expanding. Yeah, well, we imagine that there's some future theory, some quantum theory of gravity, which can't explain that. And then when you take the version of that theory and ask what happens when space is mostly flat and mostly cold, then you get the standard model. Sort of the same way that, like, Newton's theory is a limiting case of Einstein's theory, right? Einstein's theory of relativity, we think, is a more accurate description of space. But when gravity is weak and there aren't black holes nearby, it reverts to Newton's theory, right? And so we think that probably quantum gravity is a superversion of the standard model or the other way around that the standard model is like a limiting case of some deeper theory of quantum gravity.

Right. Well, those are the two big gaping holes in the standard model, gravity and also dark matter and dark energy. But the holes don't stop there. There are still other gas in the standard model covering everything from antimatter to neutrinos. And so let's dig into these mysteries, but first, let's take another quick break. The U.S. Open is here, and on my podcast, Good Game with Sarah Spain, I'm breaking down the players from rising stars to legends chasing history, the predictions, well, we see a first time winner, and the pressure. Billy Jean King says pressure is a privilege, you know. Plus, the stories and events off the court, and of course the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very fancy, wonderfully experiential sporting event.

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AXS.com All right we're talking about the I guess the not so standard model or the standardly incomplete model The current best theory of physics so far that we're pretty sure is wrong and needs to be updated ASAP. That's your standard.

That's our standard. You know it's wrong, but we'll press on. Standard really just means work in progress. Like every theory in science is always a work in progress. Oh, I see. You're using that definition of the word standard. Like the current model. It's really just the current model.

It's just the latest update. Standard Model version 16 as downloaded onto your phone last night. by Apple. We're still on beta. Is that what you're saying? Or are we now on like gamma? We're always beta testing science. All right. Well, as we heard, there are still big things missing about the standard model, which is exciting to physicists. And there are some big things missing. But there are also other things that maybe people don't think about are missing from the standard model. Even if there weren't questions about dark matter and gravity, just zooming in on the particles that we do know about, there are lots of questions that we don't have answers to.

So you can look at the standard model and you can say, like, why is it this way? not some other way. And also, does it actually explain everything we see? One of the deepest mysteries that remain in explaining the universe that we have is why it seems to be made of matter and not antimatter. In the standard model, we have all the particles we've been talking about, but there's also a shadow particle for every single one. Every quark has an anti-quark. Every electron has an anti-electron. Every tau has an anti-tow. There's this beautiful symmetry to all the particles. They have their anti-particles. And yet, when we look out into the universe, we see that I'm made of matter, you're made of matter, our solar systems made of

matter, our galaxies made of matter. We think the nearby galaxies are made of matter. It seems like the universe is basically matter. So if the theory of particles is symmetric, how do we get this asymmetry in our universe? Where does that come from? It's sort of the big question. I think what you're saying is that the standard model does have antimatter in it, right? Like antimatter itself is not a mystery. Like the, it's not a mystery. Like the, It's actually part of the standard model. Every particle in the model has its anti-matter particle. But I think maybe what you're saying is that the model predicts that there should be the same amounts of matter and antimatter, right?

Like according to the theory, there's nothing in it that says, oh, clearly matter is the best matter. Yeah. And there's no reason we call one kind of matter matter and the other kind anti-matter except that we are made of one kind, right? There really is no difference between matter and anti-matter. No, no, no. If you're not with us, you're anti-us. If you're not made of us, you're made of the anti-us. Yeah, sorry.

If you're not part of us, you're not us. There you go. If you're not particles of us. You're agestus. Yeah, that's the interesting mystery. And you imagine, for example, the very beginning of the universe, we think probably matter and antimatter were made at the same rates. Because why not?

Because the theory of particles is basically symmetric with respect to matter and antimatter. There's antimatter quantum fields for every matter quantum field. So then the mystery is, how do you go from a universe that has the same amount of matter and anti-matter to our universe, which is almost entirely matter? And that's the unanswered question. We're looking for asymmetries. We're looking for ways the standard model prefers matter to antimatter or like processes,

forces something which produces matter preferentially over antimatter. And we have not explained that yet. Well, there are some hints in the standard model, right? Like according to the standard model, there is a slight little preference for one kind of matter, isn't there? There are some processes. that do seem to prefer matter to antimatter. In the standard model.

Yes, in the standard model, there are some, right? It's not perfectly symmetric, but these are pretty small. They're not nearly big enough to explain the asymmetry that we see. It's a hint because it's a crack in the perfect symmetry. It says maybe the universe prefers matter to antimatter. But the effects that we have discovered cannot explain what we see in the universe yet. We're missing like a huge chunk of it, like most of the asymmetry is not explained. But I guess if there was.

was in effect that was so large that it preferred a matter over antimatter to the degree that we see in the universe today, wouldn't that be, you know, kind of a big, obvious hole in the theory? Or is it possible that what prefers matter over antimatter is external to the standard model, like gravity? Yeah, that's exactly the question. And we're looking for those holes in the theory. And people are doing searches for new processes that prefer matter to antimatter. And recently they have some interesting hints for discoveries at CERN. These are called these flavor anomalies where like quarks change from one flavor to another and they tend to do it to matter a little bit more often than antimatter. And people are wondering if this is like the thread we're going to pull on that reveals the universe's preference for matter or antimatter.

But nothing is certain yet. But you're also right. It could be something else, something external to the standard model. It could be that the universe wasn't created symmetrically with matter and antimatter at the beginning because of some theory of quantum gravity that prefers matter to antimatter. We just don't know. It's a huge question mark. Well, I am pro finding the answer to that. I'm not anti-that.

Now, what are some of the other things that are missing from the standard model? There are also just a lot of missing explanations for the patterns that we see. Like if you look at the patterns of the particles, you see that there is four basic particles, the up, the down, the electron, and the neutrino. But each one has two copies, right? The up has the charm in the top. The electron has the muon and the tau. And this is sort of nice consistency there where each of the four base particles,

has exactly two copies. But the question, of course, is why, right? Why should particles have any copies? You know, there's like matter and antimatter, so particles have like a single reflection. Why do these particles have these weird, heavier copies and why two of them? That's totally unexplained. It's just sort of like what we see. And to me, it's like a hint. It's suggested there's something happening underneath out of which this emerges, but we just don't understand anything about what that is. Wait, do we know for sure there are only two or three generations of particles or is that just what we found or can find with our colliders? Is it possible that there's an infinite number of generations?

We just can never get to them because they require too much energy. It's a really cool question. We're pretty sure that there are only three kinds of each of these particles and the reason actually is the Higgs boson because the Higgs boson interacts with all of these particles. So when we make the Higgs boson at the Large Hajon Collider, we sort of make it out of these particles. We throw corks and gluons together and make a sort of a frothing mass of energy and the Higgs boson pops out of that frothing mass and it does so because it interacts with all of those particles. And so the rate at which it interacts with those particles determines how often it's

made. And if there were more of these kinds of particles, if there was like a super top cork or like a heavier bottom cork, then the theory predicts the Higgs boson would be made much more often. So by measuring how often the Higgs boson is made in our collisions, we can actually measure how many generations of particles there are because the number of generations determines how often we make the Higgs boson. So we're really pretty sure there are three. What we don't know is why there are three. Wait, could there be maybe a super Higgs boson or a heavier Higgs boson

or another generation of Higgs bosons that we don't know about? There definitely could be. We did a whole podcast about other Higgs boson. and it might be there. And there might also be other kinds of quarks that just would be different. Like they don't talk to our Higgs boson or they're different in some way. So precisely the statement we can make is these kinds of corks, the corks we have found so far, we're pretty sure they're only three of them.

But there could be other kinds of weird corks that don't talk to the Higgs the same way and do other stuff that are out there. And there's no limit on how many other weird heavy particles could exist that we just haven't found yet. But I think what you're saying is if you look at the math, If you look at the math of the standard model, it doesn't prevent you from having more generations or have your cousins of the electron. It's just that experimentally you haven't seen any

or seen any evidence that more could be there. Yeah. Directly we haven't found any. And we've looked and indirectly we have some constraints because we think if they exist, they would influence how often the Higgs boson is made the large Hedron Collider. But mathematically there's no limit.

That's right. Mathematically, there's no limit. Yeah. There's no reason the standard model couldn't have four or seven generations or 90,000 generations of particles mathematically is no reason why not. But it's an interesting clue and people wonder like, what does it mean that there are three? Is the universe like three-ish?

Is this just what it is or is there a reason for it? All right. What else is unexplained? Another really fun mystery is neutrinos, right? Neutrinos are part of this basic list and we know that they exist and they're out there and that there are three kinds of them. But we really don't understand their masses. We know that they do have mass and those masses are.

very, very small. But our theory, the standard model actually doesn't allow them to have any mass. The theory requires that they have zero mass. And yet we go out there and we measure them and we see that they do have mass. And so this is actually where people disagree about what is the standard model. The sort of official, official standard model has neutrinos with no mass. And now people have like a new version of the standard model where they've incorporated neutrino mass. And some people say that's the standard model. Wait, what do you mean the standard model doesn't allow the neutrino to have mass? What does that mean? Well, the sort of old school standard model has a bunch of rules for what these particles can do.

Like, you have to keep track of the number of electrons. You can't just create or destroy electrons. You have to keep track of them and conserve the number of electrons in the universe. It's like a hard and fast rule in the old school standard model. But if the electron neutrino has a little bit of mass, then it can do something tricky to sort of break this accounting. We had a whole podcast episode recently about sterile neutrinos and all this kind of stuff. And so it breaks that rule in the old school standard model. So if neutrinos have mass, then that hard and fast rule in the old school standard model doesn't really hold up anymore as a hard and fast rule.

It's like approximate now. So we have like sort of an updated version of the standard model where you give neutrinos mass and it breaks these rules a little bit. Some people consider that the standard model. Some people consider that beyond the standard model. What happens if you do allow mass in the standard model for neutrinos? You're saying other contradictions pop up? Yeah, we don't really understand how that works yet. There's a bunch of experiments to try to measure those neutrino masses and they don't agree with

each other. There's a question about, are there actually just three neutrinos or is there like a sly fourth neutrino out there, the sterile neutrino that's been messing up a few experiments that are out there? We don't understand if neutrinos get mass the same way the other particles do through the Higgs boson or if they're a really weird particle, like maybe they are their own anti-particle, a particle called a myerana particle, which would get mass in a completely different way, not from the Higgs boson. So neutrinos are sort of the next frontier, like a part of the standard model that we've only really just begun to explore and really haven't nailed down very well.

Interesting. Well, we don't have a lot of time left, but there are still some interesting things missing from the standard model. Maybe you want to step us through this pretty quick. There's so many things we couldn't even cover them all. One of my favorites is a question of whether there are particles out there that have just a north or just a south magnetic charge. Like, where there are particles out there that have a positive or negative electric charge, but so far every particle we've seen in the universe has a balanced magnetic charge. Like you see particles with north poles and south poles.

You never see particles with just a north pole or just a south pole. That would be called a magnetic monopole. And actually the theory prefers that they do exist. Like if they do exist, the theory is more symmetric. It's more balanced than if they don't exist. So it's kind of a mystery why we don't see them. in the universe. And a lot of physicists believe that they must exist somewhere out there in the universe, but we've never found one. But probably the deepest question that's open and remaining

for the standard model is what's next? We look at all these particles and we wonder like, is this the base description of reality? It can't possibly be there. So many weird patterns we don't understand. And, you know, a hundred years ago, we looked at the periodic table. We saw these weird patterns we didn't understand. Turns out all those patterns were clues that said, oh, there's something deeper going on. All these patterns are just complexity that arise from how the little bits that things are made out of fit together. So now we're looking at the periodic table of the fundamental particles and we're seeing all these patterns that we don't understand, trying to explain them and wondering if they're made out of some smaller bits that we haven't yet seen. And maybe

those bits are made of smaller bits and those bits are made of smaller bits and maybe there's like a hundred levels between us and the base layer of reality or maybe just one or two or maybe there's no bottom. Yeah, I guess it's kind of tricky because at some level, you have the standard model and you're seeing these patterns that maybe hinted something deeper. But at the same time, you also know that the standard model is not correct, right? Like, you know they has humongous gaps in it and lots of things missing. It kind of makes you wonder how much you should read into these patterns or whether even

exploring those patterns is going to be useful. Yeah, we don't know what the best way forward is. When you read the history of physics, it's written to sound kind of linear. Like we did this and then we figured that out and then we figured this other thing out. remember that at the same time, there were lots of other branches. People were exploring other crazy ideas, which made sense to them at the time when they were at the forefront of human knowledge. But we've mostly erased those other zigzags and those other branches from our history of physics to give you a description of sort of the theory we ended up at. But now we're

here at the forefront of human knowledge right now. We just don't know what is the right way forward. Should it be quantum gravity? Should it be antimatter? Should it be magnetic monopoles? Should it be cracking open the electron to see what's inside. We don't know what's going to yield some insight. So we're all just sort of like being curious and exploring and hoping to figure something out. So the basic answer is that we've given you all this money and still a wide open question. It's still a wide open question, which makes for a wonderful, mysterious universe that we get to keep talking about on the podcast. Sounds like maybe the answer to getting our great as a species in the giant physics exam of the universe is to ask for an extent.

What's your policy in giving students extensions? I'm pretty lenient, actually. Yeah, I'm pretty lenient. What have they come to you? You say, hey, instead of doing physics, I've been spending all my money, making Marvel movies, and creating Netflix. Can I get an extension? I'm like, hmm, yeah, sure. Can I get some free tickets?

I see. You're open to being bribed as a grader. No, I think people should go out there and explore their passions and discover who they are and everybody can contribute in some way to this incredible journey we call life and the exploration of the universe. Sounds like a standard answer, Danny. Well, stay tuned as we keep exploring the universe and discovering more about what we know and what we don't know about this amazing cosmos. We hope you enjoyed that. Thanks for joining us. See you next time. iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,

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The U.S. Open is here. And on my podcast, Good Game with Sarah Spain. I'm breaking down the players, the predictions, the pressure. And, of course, the honey deuses, the six. signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very wonderfully experiential sporting event. To hear this and more, listen to Good Game with Sarah Spain, an IHeart women's sports production in partnership with deep blue sports and entertainment on the IHeart radio app, Apple Podcasts, or wherever you get your podcasts. Brought to you by Novartis, founding partner

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