Daniel and Kelly’s Extraordinary Universe - Can quantum gravity save physics?

Episode Date: February 20, 2020

Daniel and Jorge discuss loop quantum gravity with a special appearance from Bianca Dittrich, a PhD in gravitational physics and an expert in loop quantum gravity and spin foam. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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On the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone.

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So make sure you listen to Good Game with Sarah Spain 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, do you think physics isn't a rut? A rut, like, we've been solving deep problems and delivering amazing technology for too long. You're getting tired of it? Yeah, I mean, it's getting a little repetitive, all these discoveries. No, I mean, like, is it on the right track, you know? Do you think it will it get to the final deep questions about the universe?

I don't know. Sometimes I wonder if we need, like, a revolution in physics. Ooh, does physics need to be disrupted? Somebody out there should start Uber for physics. I'm more of a lift person, to be honest. I think they have a better outlook in the world. But yes, that's what I mean. You know, I want to be able to call a physicist anytime with my phone.

Well, you already have that. That's this podcast. Nice. I'll give you four stars, Daniel here. Hi, I'm Jorge. I'm a cartoonist and the creator of Ph.D. Comics. Hi, I'm Daniel Weitzen. I'm a particle physicist, and I'm here to answer any question of physics on your app any time. Welcome to our podcast. Daniel and Jorge invent new physics apps for people who need physics on demand. Daniel and Jorge make up terrible business ideas and pretend they're awesome.

No, it's Daniel and Jorge Explain the Universe, a production of our heart. Radio. In which we talk about all the things amazing and beautiful, but crazy and bonkers about our universe. Because the more we learn, the more it makes sense, the more it seems surprising and amazing. You know, we joke about it, but I think it would be kind of a useful app, did you think? Like, anytime anyone has a question about anything, you could just request a physicist on your phone and the nearest or the most available physicist would answer and then answer your question. Do you think that would be used a lot? Like, what kind of questions would people ask? How do we reconcile the different theories about quantum physics, I'm sure.

No, I think it's more prosaic. It's like, can I build a force field to keep my teenager in his bedroom all night long? Also, how does my toaster work? Why doesn't my toaster work? That'd probably be the number one question again. Can you come fix my toaster? No, we're not engineers. You need a different Uber for that.

Yeah, but think about all those grad students and postdocs and physics who are looking for a little extra money. you know, they would, I'm sure they would sign up to answer people's questions. Yeah, you know, there actually is a physics consulting service where if you think you have the great next theory of physics, but you're not being taken seriously by the mainstream establishment, there is a service where expert physicists will read your theory and give you, like, top level criticism of it, why it's probably not the winner of the next year's Nobel Prize. Yeah, it's called Daniel at Daniel and Jorge.com. It's true. There are people who send me their theories to questions at danielanhorpe.com and I try to take a look at them. But there is a service which will spend, you know, half an hour or an hour actually digging into your theory. Yeah. Wow. But they charge a lot, don't they? Don't they charge you like $50 an hour or something? You think that's a lot? You think like, you know, deep expertise of the universe should come at like $750 an hour? Sure. I mean, you know, I want to know how my toaster works, but not for $50. $50. I can just buy a new toaster oven for $50. Well, then I guess you don't really want to know how it works. You just want to buy a new one.

I want to buy a transparent toaster so I can see how it works. Well, that's the difference between the scientist and the engineer. The engineer just wants to make it work and the scientist wants to know why it doesn't work. Yeah, we just want to eat toast. That's the basic difference. But sometimes scientists also want a theory that just works. And in physics, we're making progress towards sort of like answering those. deep questions of the universe, but we're not quite there yet. Yeah, you guys have been pretty successful.

You have a standard model of the universe and some pretty good theories. You know, you have the standard model, not the non-standard model. We should have called this something else, right? Standard model is just so boring. It's like the beige model of the universe. We should have called it the amazing model. Yeah, but you have pretty much everything answered, right, kind of, except for some basic things about the universe.

Yeah, we've made a lot of progress, which is incredible. we've explained electromagnetism, we've explained the weak force, we made a lot of progress in understanding the strong nuclear force, and then in a totally different camp with totally different people using completely different mathematics and ways of thinking, we've made some in rows into understanding gravity. Yeah, but there are some, you have all these great theories, but there's something not quite right, right? Like, it works, it's pretty successful for a lot of things, but there's something kind of

fundamentally almost wrong with all of your theories, wouldn't you say? Yeah, the problem is we have no theory that describes sort of all of it. We have people who started from the quantum mechanical side of things, understanding that, building an incredible mind-bending theory of the universe. That seems to be like an accurate description of the way things actually are. And then we have people working from the other side, starting from gravity and saying, like, let's understand gravity is a bending of space, man. And they're actually making progress also.

The problem is these two theories, don't agree with each other. They don't play well. They don't have completely different views of how the universe actually is. They're sort of incompatible. It's kind of like if you're building a bridge across the Atlantic and you know, you build one side starts building a bridge and the other side starts building a bridge from their side and you find out that you're nowhere near each other in the middle. Yeah, exactly. Or you're using technologies which just cannot fit together. And that's the problem, right? You're hoping that there is one truth that you can start in different places, in your investigation and sort of work together

to find the central truth. But sometimes we wonder if these models just depend on your perspective. There's different ways to look at the universe and some are successful and some are limited. And so we don't know, like, which is the right way to look at the universe if either of them are even right

or if we need something totally new. Right, if either of them, right? Because it almost sounds like maybe both of them are not looking at the world, at the universe in quite the right way, you know, if you can't make them work together. Yeah, and there's a lot of examples in history where physics has been like very confidently almost wrapped everything up except for a couple of little details, which turn out when you pull on them unravel everything and reveal like a completely different view of the universe. That was quantum mechanics, you know?

In the late 1800s, people felt like we've almost got this thing wrapped up except for like, you know, the photoelectric effect and the black body radiation, which revealed, of course, that the universe is quantized on a fundamental scale, which blew everybody's mind. Kind of makes you wonder if maybe physics needs to be shaken up a little bit, you know, kind of reset or, you know, disrupted or, you know, start from a totally new perspective. Yeah, I think it's possible. Physics today has all those elements of needing a new idea, of needing a new perspective, of discovering, of stumbling over something which shows us that we've just been asking the wrong questions or starting our solutions from the wrong point of view. And that's not embarrassing.

You know, that's the way we explore the world. We start from our current understanding. We see how long it works. And when it breaks, we think, can we just add another little widget to it? Or do we have to toss everything out and build it from a different kind of bit? In today's episode, we'll be talking about one such idea that might help bridge this connector gap between quantum mechanics and gravity. And it's a pretty new theory, wouldn't you say? It's sort of come out in the last maybe, what, 10 years, 20 years?

I think it has its history. in the 80s, but it's been picking up steam in the last 10 or 15 years. And it's sort of emerging as a dark horse. It was like first was sort of laughed off as a fringe theory and, you know, not nearly as popular as other theories of everything in quantum gravity. And so I think it's recently gaining some sort of respectability. It's like millennials, you know, born in the 80s, but kind of easily discounted. But now they're taking over the world. Are millennials getting respectable?

When did that happen? When we died? I'm working on my theory of quantum respectability, and currently I have zero. There you go. So today we'll be talking about that theory, and the theory is loop quantum gravity. What is it? Why is it in a loop? And will it solve all the problems in physics?

And here I have to make a shout out to one of our listeners, Jim Melko. Jim has been sending me questions for about as long as we've been doing this podcast, and he has been consistently asking for a podcast episode about loop quantum gravity. So thanks for your patience, Jim. Here's your episode. Awesome. Has he sent you any ideas worthy of a noble price yet? Jim has sent a lot of ideas and they're always fun to read.

So if you have ideas about the universe or just questions or there's something you really want to understand more deeply and you think we might be able to break it down, please send your questions, your suggestions, your fundamental new theories of the universe to questions at Daniel and Jorge. com. Yeah, thanks to Jim for listening and to everyone out there listening. And so as usual, we were wondering how many people out there know or have heard of loop quantum gravity. It's sort of a, it's sort of a, it has two sort of technical familiar words, but then a pretty common word, which is loop. I was very curious in these interviews to see if anybody had heard of this thing and had any ideas. So I went in with a completely open mind. So before you hear these answers, think to yourself, do you know what? loop quantum gravity is, could you describe it?

What would you answer? Here's what people had to say. I mean, I would assume it has something to do with gravity. No. Nothing at all. Nothing at all? Nothing at all. So I heard of quantum mechanics.

I read a brief history of time. Okay. But I don't know what loop quantum gravity could be. What came to mind first was entanglement, but I don't think that necessarily has anything to do with that. So it's just, as opposed to just making up something that I think it might be, I don't know. I have not.

No, no idea what that means. I am not. No, I have it. I do not. Nothing? I don't know. Okay. All right, not a lot of penetration in the public market.

No, these folks have to work on their PR for sure. Yeah, string theory has them beat, for sure. Maybe they need to get it mentioned in the next Big Bang Theory episode. Oh, maybe we should create a set to them called Loop Quantum Gravity. I want to see you pitching. that to some executives. Like, hey, it worked for the big bank theory. We just need another

physics theory named, titled sitcom that makes fun of nerds. Yeah, well, I'm in as long as we have characters that both are smart and can talk to human beings. Oh, really? Yeah. Is that off the table?

Do you know any? Do you know any? Oh, that hurts, man. That hurts. So not a lot of people seem to have heard of I mean, I imagine they, most of them have heard of quantum mechanics or heard the word quantum, if anything from the Marvel movies. And they surely have heard of gravity, but loop quantum gravity is pretty, pretty unknown. Yeah, it's a little bit esoteric. But it's fascinating and it has really interesting ideas.

And those ideas could have really deep implications. It's the kind of theory, which if it's correct, really changes the way we think about the entire universe and the fundamental nature. of our relationship with it. So it's super fun to think about. And it's also really complicated and very technical and there's a humongous amount of complicated math involved, none of which you will have to understand to get the basic ideas today. Which is why Daniel, you went out there and found an expert to talk to about this topic, right? That's right, because I'm a particle physicist and my expertise doesn't extend to theories of quantum gravity. So I went and I talked to Bianca Ditrich. She's a professor at the Perimeter Institute in Canada, and she's an active researcher

on the forefront of quantum gravity. So here is Bianca. So my name is Bianca Dietrich. I'm originally from Germany, also studied in Germany, and then oscillated between Canada and Europe a number of times, and ended up in Canada at the Perimeter Institute as a faculty researcher. All right, cool. So Bianca I explained to you what loop quantum gravity is? Yeah, I had a long conversation with Bianca about why we need loop quantum gravity, how it solves the problems in physics,

where the current criticisms of it are, how we could test it, and of course, then I had to ask her at the end about black holes. Of course, because every good conversation ends in a black hole. Literally, right? Maybe at the end of the universe, all that

every conversation everyone will ever have. All that information will end up. Maybe in a black hole. Well, what happens if you take a black hole and you put it in a toaster oven? There's a question nobody's ever asked if it exists. I need to ask the app. Where's the app? We get a crunchy outside, but the inside will still be cold.

Black hole temperature. Yeah, so what if I put a black hole in a microwave then? Do I heat up the inside of the black hole? That's a question I've never thought of. That's really a fun question. All right. Well, step us through what Bianca explained to you, Daniel. So first of all, I guess, what is this big problem?

in physics that needs to be fixing. The big problem is that, as we said earlier, we have two different basic ideas about sort of how the universe works at the smallest scale. And they start from very different places. And as you said, when they come together across the Atlantic, they just don't meet.

And those two ideas are quantum mechanics and general relativity, Einstein's theory of gravity. It's weird to me that there would be two so different theories about the universe, you know? Wouldn't they all sort of meet at the, you know, plus and minus mathematical level? Well, you'd hope so.

And this is sort of the way physics starts. You know, if you're caveman, cave woman physicist, you begin building your model of the universe by sort of looking at all this stuff around you, cataloging what it can do, and then saying, can I understand all of this stuff in the simplest possible terms? And so you're like, all right,

there's the thing where things fall down. There's a thing where lightning comes from the sky. You know, there's a thing where there's wind. And then you have a very long list of stuff. and you try to boil it down and say, oh, you know, this lightning thing is the same as this other thing where I get zapped and things falling down is actually the same thing as stars moving through the sky. There's all these moments when we sort of shrunk the list of ideas we need to explain the universe. And so you hope that as this list gets shorter and shorter, they fit together nicely.

And that's happened a lot of time so far. Electricity is the same thing as magnetism. And it's all part of this other thing called the electro-week force. That has happened. But sometimes you get, you know, you get two puzzle pieces and they just don't fit together. All right. So maybe a reminder, Daniel, what each of these theories are? Like, what's the easy way to describe what general relativity is?

And what's the easy way to describe what quantum mechanics is? So general relativity is a way to try to understand what is gravity. And remember that Newton said gravity is things pulling on each other, things that have mass pull on each other. So... It's like a force. Yeah. Newton thought... That was the old thinking.

That was the old thinking. Newton thought gravity is a force. And it seems kind of like a force. It acts like a force like electricity and magnetism. And he was able to write down an equation that described how the earth moved around the sun and how the moon moved around the earth. And it works pretty well. Now, Einstein came along and he gave us general relativity, which was a complete reconstruction of how gravity works. He said, no, no, gravity is not a force. Gravity is a change in the shape of space and time itself. Like you have a blob of mass or blob of any kind of energy density, it changes the shape of space, and that's what makes things move

in curves. Rather than moving in what feels like a straight line to us, things move through bent space. It's not like a mysterious invisible force that pulls things together. It's more like when things exist, they distort, they bend the space around them, and that's why they come together. Yeah, and it's a beautiful idea, and it's been tested a gazillion ways, and it works. It describes very tiny deviations in, you know, Mercury's orbit. It describes how light bends around the moon during an eclipse. Big stuff. Big stuff, yeah, really thoroughly, extensively tested.

It predicted gravitational waves, which we've actually seen. Black holes, too, right? In black holes, yeah. And the thing to understand, the thing that's going to make it in conflict with quantum mechanics is that it's a classical theory, meaning that it assumes that, like, you can describe everything perfectly, that everything, has a position and a direction and a location, right? And that the space it's operating in is smooth. Like you can subdivide space as many times as you want. Between me and you, there's

an infinite possible locations for like a ball that we're throwing back and forth. That's Einstein's vision of space. Right. It assumes that everything is kind of smooth and continuous and there are no bumps in the universe at the microscopic level. That's right. You can zoom in forever, according to to Einstein and general relativity, and things still stay smooth. And everything has a fixed location, right? The ball is somewhere, and space and time makes some sense. There's no uncertainty or weirdness. That's right.

The world can be known. Everything can be determined, according to general relativity. But then you have quantum mechanics. That's right. And then on the other hand, building from the other side of the ocean, you know, the toaster side of the ocean instead of the microwave side of the ocean, completely mixing metaphors there, is quantum mechanics. And quantum mechanics, of course, developed in the early part of this century to explain some things that didn't make sense.

Some experiments we saw, which just could not be described using a classical understanding of electromagnetism. It was really what was light that gave us the first clues. We did a whole podcast episode about the photoelectric effect and how we know the photon is a thing. And they did these experiments that just didn't make sense unless you thought of light as being made of tiny little packets of energy. Rather than a smooth, continuous beam, you had to think about it as these tiny packets. Right. When you zoom in, things don't behave nice and smooth and continuous. They're sort of lumpy and clumpy.

Yeah. And there were also just some problems with the theory. Like there's a kind of radiation in the universe called black body radiation, which is just how things glow. Like everything in the universe has a temperature, and it glows with that temperature. And quantum mechanics predicted that. Well, classical theory, electromagnetism predicted a certain spectrum. Like, if you're this temperature, you should glow with this color.

If you're that temperature, you should glow with that other color. The problem was that it predicted that for certain temperatures, you should glow at a crazy, nonsensical color. Like, you should get an infinite amount of radiation. The original theory, the one before quantum mechanics, said that things at certain temperatures should have an infinite amount of light at very, very low wavelengths, right? It really, really sort of, it's called ultraviolet light, and that they should have like a ridiculous amount, an infinite amount of ultraviolet light, which is nonsensical.

So you can do an experiment basically that proves that general relativity doesn't work for all cases? Well, you can do an experiment that proves that the old theory of electricity and magnetism doesn't work. And we knew that didn't work. We're like, okay, this theory is making a prediction that just doesn't make sense. But if you add quantum mechanics to it, quantum mechanics says, oh, that's just because light is not continuous. If you make light into chunks, then if you predict that you don't see this crazy behavior. And that's in fact what we saw in nature. And so we needed to sort of change the theory. The theory gave nonsensical results. I mean, to add this bit to it, this bit that says, okay, well, there's a minimum size to a photon. And that solved that problem.

It said, okay, now you can make realistic predictions. And so, but the thing to understand is that, like, quantum mechanics changes also the way we think about the universe, right? It says things are uncertain. Things are fluctuating. There's this, like, crazy randomness, the heart of the universe. All right, so those are the two big titans in physics theories, right? General relativity and quantum mechanics that try to explain the universe. And the problem is that they don't play well together. So let's get into a little bit of why they don't play well together

and whether this idea of loop quantum gravity can help solve that. But first, let's take a quick break. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay.

Terrorism. Law and Order Criminal Justice System is back. In Season 2, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Oh, wait a minute, Sam.

Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate.

Well, according to this person, this is her boyfriend's former professional. and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not?

To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Joy Harden Bradford. And in session 421 of Therapy for Black Girls, I sit down with Dr. Othia and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal. Because I think hair is a complex language system, right, in terms of it can tell how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyper fixation and observation of our hair, right?

That this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled. We talk about the important role hairstylist play in our hair. our communities, the pressure to always look put together, and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, don't miss session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to Therapy for Black Girls on the iHeartRadio app, Apple Podcasts, or wherever you get your podcast.

All right, Daniel. So general relativity and quantum mechanics don't play well together. Is it fair to say? Is it kind of like, I'm trying to think of an analogy, is it kind of like microeconomics and macroeconomics? Like, you know, macroeconomics is good for, you know, big economies and countries and microeconomics is good for like how people make decisions. But like somehow they don't always, it's weird to think about where they meet in the middle. Perhaps. But in those two cases, one should be an extreme case of the other. Here, it's really you have a fundamental different view of how the universe works. You know, it's more like totally different kinds of art, you know, like figurative art versus symbolic art. Like, what's a better way to like describe the human experience? You know, is it through abstract splashes of color or is it by, you know, depicting the things we see in interesting juxtapositions or something? I don't know. Right, right. It's like a totally lens or totally set of glasses. Yes, it's a completely different way of thinking about the world. And people have been trying for a long time to bring them together to say, all right, are these things in conflict or can we make a consistent sort of quantum theory of gravity that brings it all together? Right. And so here is Bianca talking about that question. It's one of the really big outstanding questions in physics.

And then in my view, it really means quantum gravity should include a new notion of space time. We have to replace it, however, with something completely new. We expect that it will change quite dramatically the foundations of physics and get very interesting insights into the nature of space and time. All right. So it seems like we need something totally new here. And so, Daniel, can you explain to me kind of what the problem is? Like, why can't they play well together the ones that we have? Well, people have been trying to bring these two things together since basically they've existed.

You know, people have been working on making gravity into a quantum theory for a very, very long time. But, you know, quantum theories traditionally thinking about forces very differently than gravity does. They think about forces as like ripples in a quantum field. You know, you have like the electromagnetic field and you think about how do photons communicate the electromagnetic field. They are ripples in this electromagnetic field. field and you quantize those ripples. That's how quantum mechanics thinks about forces. But in general relativity, a force is really more like a bending out space. That's right. And mostly you can do this. You can say like, all right, well, can I make a quantum

theory of gravity? Can I build a theory where I exchange where gravity is a field and it has ripples and those ripples are quantized, just like I can for electromagnetism? And mostly you can. Actually, you can. It's mostly it works. But it fails in some moments. Couldn't you just have quantum fields in a general relativity, you know, world? You know, like couldn't you have quantum particles that bend space as well? Like, why can a quantum particle also bend space like a planet? Well, but then gravity is coming from something that's classical, that's smooth and continuous. And general relativity is just not a quantum theory, right?

Like, it assumes that you know everything about the location and the time and the position. But couldn't you just make the bending also a kind of uncertain? I'm just trying to figure out why you can't marry the two. Why can these particles and these fields exist in a world that is as Einstein envisioned it with the bending and the gravity? That's exactly what loop quantum gravity is. Jorge, you just basically invented the idea for loop quantum gravity right to her on the fly. I'll take my double prize right now. Thank you very much.

That's right. And, you know, this other idea, this like let's take the gravitational field and think about it as a quantum field that mostly works. The important thing to understand is that it only fails when gravity gets really, really strong, right? Things like inside a black hole. And what happens is that it makes nonsense predictions. Just like we saw for the black body radiation, it predicts like infinite amount of energy will be released. But we know that's not true. We know it doesn't happen. And so the theories work except in extreme circumstances. And that's what makes it really hard. It's like it's easy to fix a theory when you can see it breaking, that these theories, general relativity and

quantum mechanics, they only disagree about, like, what happens to the inside of a black hole? And we can't see that. Why don't we just ignore black hole? If we just ignore black holes in the universe, wouldn't that make our lives a lot? Wouldn't that make physics a little bit easier, you know, because it's all, it seems like, it seems like everything breaks in a black hole. And so it's like, you know, the mess in my closet. Let's just ignore it. That's the engineering in you, man. That's the engineer. The scientist in me is desperate to know.

I have to know what's going on inside a black hole. Yes. Have you created a black hole in your closet? Because if so, I'm coming over and I want to check it out. I think we're close to the singularity, to be honest, in there. You don't want to go in there. You may never come out. You have all these rejected toaster

microwave prototypes in there. That's right. All these are rejected app ideas as well. And so these two things aren't working together. Well, people have tried, but They just give nonsense predictions. Like the calculations you get suggests, you know, infinite amount of energy irradiated inside a black hole when gravity gets really strong.

And we can't easily test that because we don't have a black hole. And I don't have a galaxy-sized particle collider. I would need to create this sort of energy density in order to break quantum gravity. And so what we need is we need to see inside a black hole or we need a new idea. And so we need Jorge's vision of quantum gravity. I have an idea. How about something called loop quantum gravity? That's such a great name, too.

All right, so we have these two four theories, and, you know, one of them has a Thunderbolt cable connector, and the other side is a mini USB cable connector, and so they don't fit. And so that's what this idea of loop quantum gravity is. It's like maybe it's like an adapter that makes it to work, or is it a totally new cabling system? Yeah, it says instead of trying to think of gravity is like, a Newtonian gravity as a force and quantizing that gravitational field directly, instead take Jorge's idea, which is just take space itself and quantize that and say, well, maybe general relativity is basically right, except that instead of working on a smooth, continuous space, we work on a space

that is quantized. There are pixels of space. Instead of space being infinite and smooth, there are like little chunks of space. It would explain how quantum particles move, or it would explain how gravity can be quantized? It would allow us to build a theory of quantum gravity that doesn't make nonsense predictions because it basically makes the places where those predictions get nonsense impossible.

Like the predictions of quantum gravity break down at really high energies and really small distances. So the idea is basically, well, what if really small distances aren't allowed? Like, there's just nothing smaller than 10 to the minus 35 where things break down. Then there isn't a problem. Let's just ignore the closet and assume that a closet is quantized and it's just one thing. I see.

Yeah, it's not ignoring the closet. It's saying the closet doesn't exist. You were so worried about the closet. It turns out it's impossible. There is no closet. It sounds like you're trying to make gravity quantized. You're not trying to make quantum things, bendy, like space. Well, if space is bendy and quantized, then yeah, quantum things move through quantized, bent, bendy space.

Oh, so this would allow you to bend space in a quantized way? Yeah, it would allow you to bend space in a quantized way. And it's kind of a beautiful idea because it's very similar to the origin of quantum mechanics itself, right? We solved the problem of black body radiation of this thermal emission giving crazy numbers by saying, oh, maybe we can just quantize photons, and that mathematically solves that problem. Here, we're solving the problem of infinite emissions inside black holes and really high energies

and small distances by saying, oh, maybe we quantize space, and so those small distances are impossible. So there's a beautiful sort of analogy there to previous structures of solutions that suggest, like, tentatively like, ooh, maybe this is the right track. Because it feels like 1915 a little bit.

That's right. We're going to party like it's 1919. Yeah. People are growing mustaches and wearing top hats and you're like, I like it. I like it. Except for the fact that like no women are allowed to do physics back then. Oh, no. That's the bad part. All right. So the idea is that maybe space and time itself, like space and time, like there are no, there's no infinite as at least small second. That's right. And that's a question people have been sending me over email many times.

If you quantize space, do you also quantize time? And, you know, space time is a fabric in this theory, and they're deeply connected. And so if you're quantizing space, then yes, you're also probably quantizing time. It's like there's actually a ticking clock to the universe maybe. Yeah, there's a minimum time that makes sense. You know, you can't infinitely divide a second into arbitrarily tiny slices. There's a minimum amount of time below which makes no sense. Okay.

And so what does that mean? I guess space is not really like space. space is more like a clump of little spaces? Well, the reason it's called loop quantum gravity is that the way to think about it is that space is a bunch of these little loops and they're sort of woven together. And so think about space as like chain mail if you're into D&D. You know, it's like a bunch of links that are all connected to each other and space comes out of that, right?

There are these, the fundamental thing in the universe are these little loops and the loops are woven together and the way that things move through space and the way that gravity happens is how these little loops interact with each other and pull on each other and are built together. So what are these little loops? They're like little bits of the universe? That's the next Nobel Prize, man.

You want to win two Nobel Prizes in a single podcast? In a single pot? Let's do it. You have enough hubris to be a physicist. Go for the, what do you call the hat? A hat trick? A hat trick? Are you going to go for three Nobel Prizes? We got 15 minutes left, Daniel.

Let's do it. That's when you invent the perfect toaster microwave combination. That definitely is worth a Nobel Prize. Well, nobody knows what these little loops are. And, you know, that's sort of the next question. Like, if you can start from these little loops and build a theory that describes everything and predicts the universe and is consistent with everything we know, then the next question is you're like, well, why these little loops?

What do they mean? How do we get those little loops? Right. Where do they come from? Do they emerge from something deeper? you know, physicists are great at making answers that create more questions. But I guess why call them loops? Are they actually like little rings that are tied together? What is that? Why not call them, I don't know, bubbles or pixels or, you know what I mean?

Like what is it about the idea of a loop that gives it the name, loop quantum gravity? Well, I guess bubbles would work also, but I think it's just a visualization idea, you know, that these things are linked together in a sort of a mesh. And, you know, there are also loops, like we're doing calculations around in a circle. But you have to avoid a sort of trap. Like, you can't think about these as loops in space. They're not like circles on some axis, right? Because what is that axis? We're talking about the very nature of space itself.

It's not like these loops are somewhere. And like this loop is at this point and that loop is at that point. The loops are the points. Like space is this thing. We're talking about like the nature of. space itself, which is really hard to sort of wrap your mind around. Oh, I see. You were just looking, you guys were just looking for, like, a word that implies that space is made up of little things that are kind of interconnected or overlapping,

right? Or, like, hooked together. Mm-hmm. Okay, and so you went with loops. I wasn't there. Rainbow Looms. They went with loops. I think it's not a terrible idea. You know, they could have called it bubble quantum gravity, but, you know, or float. Maybe people will have heard of it. But, you know, we talked about this another time in the podcast. You can think of these things as little bubbles, and then you get to talk about things like space foam and quantum foam because these loops aren't fixed, right?

They can, like, fluctuate in and out of existence. I see. So these are all related ideas, loop quantum gravity, space foam, quantum foam. They're all sort of coming at this idea of a bubbly space. Yeah. And thinking about space not as continuous and smooth, but have made up of little quantized bits. Like, let's quantize space itself because general relativity is an attempt to understand gravity

in terms of the nature of space. And so if we're going to get a quantum theory of gravity, the idea is let's just quantize space itself. All right. So that's quantum loop or loop quantum gravity. And so we'll get into what are some of the open questions and why people think it may or may not be the ultimate answer to how the universe works. But first of it, take a quick break. December 29th, 1975, LaGuardia Airport.

The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. We're being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and Order Criminal Justice System is back.

In Season 2, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Podcasts or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon.

This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating.

He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Joy Harden Bradford. And in session 421 of therapy for black girls, I sit down with Dr. Athea and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal.

Because I think hair is a complex language system, right? In terms of it can tell how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyperfixation and observation of our hair, right? That this is sometimes the first thing someone sees when we make a post or, or real. It's how our hair is styled. We talk about the important role hairstylists play in our community, the pressure to always look put together,

and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, don't miss Session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to therapy for black girls on the iHeartRadio app, Apple Podcasts, or wherever you get your podcast. Okay, Daniel, what does it all mean? What does loop quantum gravity mean if it's true or if it's not true?

And why do we think it might not be true? All right, well, here's the big letdown, right? So, so far it seems like... You're going to break the loop. I'm going to break the loop, yeah. It seems like a beautiful idea. It seems really promising. It seems like dot, dot, dot the next obvious step in physics, right?

problem is there's a lot of problems with it and there's a lot of open questions and that doesn't mean it's not going to work it just means it's far from clear that it is going to work oh i see there's room for skepticism yeah and even among physicists there's a lot of skepticism about loop quantum gravity it's a bit of a fringe theory there are a lot more people working for example on string theory which is a completely different attempt to unify gravity and quantum mechanics and all of the other forces all at once. String theory is like a theory of everything, whereas loop quantum gravity is like,

let's just focus on making gravity a quantum theory. If you can do that, then that's another way to unify these two big theories. Yeah, so string theory is sort of the other idea. It's the opponent of loop quantum gravity. Let's build a tunnel under the Atlantic instead of trying to make these two bridges work. And string theory is a much bigger community.

There's a lot more people working on it. People are sort of more excited about it. Whereas loop quantum gravity is like, you know, the younger sibling in terms of theories of quantum gravity. The underdog. You're making me like it more now. And one reason is that it sort of hasn't yet delivered on its promise. Like what you want to do is start from this concept of loops and from it should emerge Einstein's theory of relativity. You should be like, I'm going to have a completely different picture of the world,

but it's going to give the same predictions sort of at my scale. It should still describe how a ball flies over my neighbor's wall and gravitational waves and all of that stuff. You should be able to sort of start from there and build up to general relativity. You start off imagining the world, the universe is a mesh of loops, but it doesn't give you baseballs and fences. Yeah, not yet. And it's not like they can't do it. It's just like, well, they haven't quite figured it out yet. And it's hard, right?

These are difficult things and people are hacking with their machete. through the jungle of mathematics that's involved. And it's not always clear that we have the right tools. And sometimes progress has paused for like a decade or 30 years until somebody's like, hey, we've heard this new idea from mathematics. Turns out that's exactly what we need over here. That kind of thing has happened in physics a lot of times. And there are other sort of really interesting problems with loop quantum gravity,

which actually conflict with relativity. Okay, so there's maybe something fundamentally wrong here. Yeah, or not necessarily wrong, but it would, again, change the way we think about the use. universe. Like, here's the problem with quantizing space. Say there are space pixels, right? That means that in some sense, there's a minimum distance to the universe. But what is that distance? Because we know that distances depend on velocities, right? Like, as you move faster, things get shrunk. So do things that are moving see smaller space pixels than things that are

stationary? And if so, it would mean that there is some sort of absolute velocity. to the universe, right? If you can measure your space pixel, the size of your space pixels, that tells you sort of what your absolute speed is. But special relativity has always told us velocity is relative. There is no absolute frame. And so this is sort of conflict with a really, really core concept in special relativity. Couldn't it be like the speed of light, which like it always looks the same no matter

how fast you're going? Couldn't these loops always look the same no matter how fast you're going? Yeah. So there's a lot of ways to try to solve this problem. One is to say, you know, we have these weird space pixels which deform under certain circumstances. And there's some very complicated mathematics involved to do essentially what you just described. You're really hidden out of the park today with like, I'm going for the hat trick here. Brilliant physics.

Wait to see what I pull out in the last five minutes. And the other is to accept it and to say, hmm, you know what? Maybe there is. Maybe there is an absolute reference frame. Maybe special relativity is slightly wrong. But wouldn't that throw the whole light speed thing off? Well, not all of special relativity has to be wrong. The consequence would be that light would travel at a slightly different speed

as a function of its frequency. So, like, high-frequency light would travel at a slightly different speed from lower frequency light, like x-rays and UV light would move faster than radio waves. But it'd be a really small difference. It'd be really hard to tell. All right. So there's some scale.

skepticism or I guess some open questions about it because it's not quite hitting it out of the ballpark over your fence or not into your neighbor's house or not. And so I guess the question is what does it all mean? What if it happens to be true and how are we even going to know if something like this is true? Yeah. So of course the deep question I have is what does this mean for the nature of the universe and how could we see it, right? Where would it manifest itself? And as we talked about the beginning of the episode, the place this would really be important, the place you would notice a difference, the place where it matters, is inside a black hole. Of course.

Of course, right. So let's go there. Let's go into the closet, Daniel. That's right. We're opening the closet and all of your old toaster. Who knows what's in there? Who knows what's been growing? And so I asked Bianca, the professor, because she thinks about this stuff, right?

She thinks about what happens inside black holes when gravity gets really strong and space gets twisty and I asked her like what is your mental image of inside a black hole because I want to know right I mean there's a black hole in her mind at least and I want to know what does it look like inside her mind quantum gravity effects would be only important very near the singularity where the space and curvature is really getting very large and maybe I like to think that there's a new universe which opens up with each singularity which gives us much more universes than we know of. Yeah, she went there.

She went for, there are new universes inside black holes. I love it. There's a new universe in my closet. I would believe that. And inside that closet, there are other closets

with other closets inside them. Meaning that's kind of a consequence of quantum loop gravity is that when you get to these extreme singularities, these loops kind of, what, like open up or, you know, become their own little universes?

Is that the idea? I will not pretend to even understand what that means. Because there's some crazy consequences that, like, if there's a universe inside every black hole, is our universe inside a black hole? You know, like, maybe, who knows? Yes. It's crazy stuff. Yes is your answer? I'm going to go with the yes, and that's my third Nobel Prize claim.

Or is that the conclusion to your pitch for your Loop Quantum Gravity sitcom episode? Oh, there he go. At the end of season 20, it turns out, they're all in a black hole. That's right. And, you know, we might be able to figure this out in ways other than going to a black hole. We actually do have ideas for how you could test this. And they revolve around seeing whether we can tell the difference in the speed of light from high frequency and low frequency light. If the speed of light changes, which we didn't think it did, but if it changes with frequency, then that's an indication.

Maybe there's something loopy going on. Yeah, maybe there's something loopy going on. And this would be a really small effect. So what you need to do is, like, have a race between photons at different frequencies, high frequency versus low frequency. And the rays would have to be super long because light goes super fast, of course, and this difference is really small. And so what they do is they look for light sources that are really, really far away

and then try to measure see if there's a difference in, like, the arrival time of photons. But you would not need to know where they're coming from, right? Yeah, so we have these sources which are variable, like quasar, and pulsars that are really far away, you know, they pulse. And so you can sort of line the two up and say, well, we know these two were emitted at the same moment because they're at the top of the pulse at the same time or something. And then you can say, well, do they arrive in sync or are they sort of out of sync? And so there's a satellite which looked out and measured this and looked for this.

What did they find? Well, this is the integral satellite. And that's some tortured acronym for, I don't even know what. Is it really? Wow. It's called integral, yeah. And what they found, they didn't see anything, right? they didn't see any difference in the arrival times.

Didn't see any loops. They didn't see any loops. And they were able to say that if there are loops, they're smaller than 10 to the minus 48 meters. What? They can do that? With one experiment by looking at two photons? Yeah, by looking at these photons because the photons come from really, really far away. And so these differences would be added up across the universe and they claim they should have seen them.

They saw that they were in sync. They were in sync. Yeah, and this is 13 orders of magnitude smaller than what we think the size of the loops are. So, like, that seems pretty definitive. Yeah, but what do the loop quantum gravity folks say? Well, you know, this is only one branch of loop quantum gravity, the people who say that maybe that special relativity needs to be tweaked. Other people have solutions, as you say, to make light travel the same speed no matter what

by having, you know, crazy deformations of these things and all sorts of complicated interactions between light and space. And so it just sort of rules out one branch of loop quantum gravity. You can never kill these theories, man. They're like weeds. There's another version that crops up. They're like hydra. Cut one head off, two physicists emerge.

But they're fascinating, you know, and each one is a wonderful exploration of sort of the intellectual space of like how could the universe work? What possible universes might we live in? And the amazing thing is that there is an answer, right? There is one way that the universe actually works. And what's kind of interesting, I think, is that it wouldn't affect your everyday life. Like, things would still work the same way, but who knows what's going on down at the fundamental level, right? It could be one of these crazy theoretical ideas.

Yeah, and it's important now to scientists, but it might eventually be important to engineers, you know? Knowledge that seems impractical and useless, but reveals the fundamental nature of reality could eventually be useful. And, hey, to me, that's fun anyway. I don't really care if it's useful. I just got to know. Right, yeah. I mean, I think that's how microways were invented, actually, by accident by looking at something else. And where would we be?

Where would burritos be these days? That's right. And, you know, there have been actually fascinating advances in microwave, the technology, the engineering of microwaves. And I guess, you know, if you can unlock kind of the magic and the power that's happening at that microscopic level, who knows what you could do, right? what kind of energies you can get or what kinds of warped dries or microwave ovens? Yeah, microwave toaster ovens powered by artificial intelligence. Yeah, and so I have to give a shout out to Nico. He's one of our listeners and he heard our episode about microwave ovens, actually.

And he wrote to me and told me that they have a new fancier AI powered microwave oven, which can heat stuff up at different temperatures and monitor it to make sure the heating is all smooth than fancy, and actually dropped by my house and delivered one of these prototypes, which has been a lot of fun. That's amazing that you let one of your listeners into your house. Hey, he was offering a brand new appliance. And while he was there, I asked him about loop quantum gravity, but he didn't have any ideas. Oh, man.

There's no setting on that in the microwave. Not yet. The next version of the prototype will be quantum gravity powered, I'm sure. All right. Well, it sounds like the answer is stay tuned. You know, that's what we explain what loop quantum gravity is, and who knows? And maybe it is a way that the universe works at that level, and we may find out in the near future. That's right.

And these are the kinds of mysteries that are going to help us figure out the deep nature of the universe. You know, it's when things break, that we have an opportunity to figure out how things should work. And so it's exciting to have these kind of problems. It's exciting to know sort of where to work, even if we don't know what the answer should look like. All right. Well, we hope you enjoyed that. Daniel, how much this podcast cost me in terms of your physics time? One loop.

And it's $10 to the minus $35. $10 to the minus $35. One plank dollar, yeah. A plank dollar. Oh, good. I got a couple here in my pocket. Okay. Quantum them over to me.

All right. We hope you enjoyed that. Thanks for joining us. And as usual, thank you to everybody who wrote in with your questions. See you next time. If you still have a question after listening to all these explanations, please drop us a line we'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge, that's one word,

or email us at Feedback at danielandhorpe.com. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TIE.

EWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find find out soon. This person writes, my boyfriend's been hanging out with his young professor

a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast and the Iheart Radio app, Apple Podcasts, or wherever you get your podcasts. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people an incomparable soccer icon Megan Rapino to the show and we had a blast. Take a listen.

Sue and I were like riding the lime bikes the other day and we're like we're like people ride bikes because it's fun. We got more incredible guests like Megan in store plus news of the day and more so make sure you listen to Good Game with Sarah Spain on the IHeartRadio app, Apple Podcasts or wherever you get your podcasts.

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