Daniel and Jorge Explain the UniverseDaniel 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.
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Hey, Daniel, do you think physics is in 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 you 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 am Jorge. I'm a cartoonist and the creator of PhD comics. Hi.
I'm Daniel Whitson. I'm a particle physicist and I'm here to answer any question of physics on your app anytime.
Welcome to our podcast. Daniel and Jorge invent new physics apps for people who need physics on demand.
Daniel and Jorge makeup arrable business ideas and pretend they're awesome.
No, it's Daniel and Jorge Explain the Universe, a production of iHeart 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, did we joke about it? But I think it would be kind of a useful app. Don't 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 physicists 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 we must know.
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. Can you come fix my toaster? No, we're not engineers. A different uber for that.
Yeah, but think about all those grad students and post talks 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 danielanhorge dot com.
It's true. There are people who send me their theories to questions at Danielinhorge dot 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 fifty dollars an hour or something.
You think that's a lot. You think, like, you know, deep deep expertise of the uni verse should come in like seven to fifty an hour.
Sure, I mean, you know, I want to know how my toaster works, but not for fifty dollars. We want to buy any toaster omen for fifty dollars.
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 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 not the non standard model.
We should have called it 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, 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've made a lot of progress and 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 inroads 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.
What didn'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 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 site, 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 old 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 eighteen hundreds, 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 minds.
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 it's come out in the last maybe what ten years, twenty years.
I think it has its history in the eighties, but it's been picking up steam in the last ten or fifteen 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 eighties but kind of easily discounted. But now they're taking over the world.
Are millennials getting respectable? When did that happen?
When we die?
Then I'm working on my theory of quantum respectability and currently I have zero.
There you go. So today we'll be talking about 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 Milcho. 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. As he said you, any idea is 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. Two questions at Daniel and Jorge dot 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 lup 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 this thing and had any ideas. So I went in with a completely open mind. So before you hear these answers, thanks to yourself. Do you know what luke quantum gravity is? Could you describe it well?
Would you answer? Here's what people had to say. I mean, I would assume it has something to do with gravity, nothing at all.
Nothing at all, nothing at all. So I heard of quantum mechanics. I've read like Brief History of Time. Okay, I don't know what luke quantum gravity could be.
What came to mind at 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 I am, No, I haven't, I do nothing.
I don't know, all right, not a lot of penetration in the public market.
No, these folks have to work on their pr for sure. Ye, 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 septem called loop quantum gravity.
I want to see you pitching that.
Like, Hey, it work for the Big Bang 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, do you know any oh that hurts? Man?
That hurts so not?
Well, not a lot of people seem to have heard of it. 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 none of which you will have to understand together 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 di originally from Germany. Also studied in Germany and then oscillated between Canada and Europe a number of times and aed upt in Canada. It's a Calameter Institute faculty researcher.
All right, cool, So Bianca explain 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? Oh, there's a question nobody's ever asked a physics I need to ask that.
Get a crunchy outside, but the inside will still be cold.
Black hole temperature. Yes, 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 Janka explained to you. Daniel was so first of all, I guess, what is this big problem in physics that 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, they 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 many, so different theories about the universe. You know, wouldn't they all sort of meet at the 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 a 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 its 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 short 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 electroweakforce. 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 step reminders, 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, 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 is a complete reconception 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 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 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 in exillion ways and it works. It describes very tiny deviations in 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, black holes. Yeah. And the thing to understand the things that's going to be make it in conflict with quantum mechanics is that it's a classical theory, meaning that it assumes that you can describe everything perfectly, that everything has a position and a direction and a location, right, and that the space is 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 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 weird 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 did makes 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 that 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, 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, where 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 no on sensical results. I mean, I have to add this bit to it, 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. This is 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.
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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 abstracts 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 you know, 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's Bianca talking about that question.
It's one of the really big outstanding questions and physics, and my view really means quantum gravity should include a new notion of space time. We have to replace it, however, with something completely new. We expected that the change cry dramatically is a foundation so 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. There are ripples in this electromagnetic 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 could 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't 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.
Well, couldn't you just make the bending also kind of uncertain? I'm just trying to figure out why why you can't marry the two, you know, why can't 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 Luke, quant gravity is. You just basically invented the idea for the gravity right.
Right now, Thank you very much.
That's right. And you know this other idea is 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 like it 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. Is 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 at 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 why don't It's like, you know, the mess in my closet, let's just ignore it.
It's the engineering in you, man, that's the engineering the scientist in me is desperate to know. I have to know it 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 that you may never come out, like.
You have all these rejected toaster microwave protypes in.
There, that's right, all these 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 suggest, you know, infinite amount of energy in a radiated 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 the 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 Orges 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 force area 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 is it 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 as like a Newtonian gravity as a force and quantizing that gravitational field directly. Instead take Orges idea, which is just takes 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, like 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 ten to the minus thirty five where things break down, then there isn't a problem.
Let's just ignore the closet and assume that a closet is Quanti said, 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.
Sounds like you're trying to make gravity quantized. You're not trying to make quantum things the bendy like space.
Well, if space is bendy and quantized, then yeah, quantum things move through quantized bend 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 solve 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 nineteen fifteen a little bit.
That's right. We're going to party like it's nineteen nineteen.
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. No, 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 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, 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, they're also probably quantizing time.
Well, it's like you're 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 minimumount 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 is like chain mail. If you're into D and D, you know, it's like a bunch of links that are all connected to each other. And space comes out of that, right spaces, 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.
To 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 and.
A single podcast in a single let's do it.
You have enough come for this to be a physicist.
So for the what do you call the hat the hat trick, A.
Hat trick, You're going to go for three Nobel prizes.
That's when you go, yeah, fifteen minutes left.
That's when you invent the perfect toaster. Microwave combination that definitely is worth a Nobel Prize. Well, nobody knows what these 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 it 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 it?
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 sort of trap, like you can't think about these as loops in space. They're not like circles on some axis, right, because then you have 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 these 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 at 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. M okay, And so you went with them loops. I was like, they went with loops.
I think it's not a terrible idea. You know, they could have called it the bubble quantum gravity but or full it. But you know, we talked about this another time in the podcast. You can think of these things as little bubbles and 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, spacefoam 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 if 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 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, let's take a quick break.
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Okay, Donnie, 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. The 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 a 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 Looke 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 a The other idea is the opponent of Luke 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, has a lot more people working on it, people are sort of more excited about it, whereas Looke quantum gravity is like, you know, the younger sibling in terms of theories of quantum gravity.
The underdog, exactly 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 gonna have a completely different picture of the world, but it's going to give the same predictions sort of at my scale. You should still describe how a ball flies over my neighbor's wall and how 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 measure 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 machetes 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 thirty 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, 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.
Are not necessarily wrong, but it would again change the way we think about the 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 velocities relative. There is no absolute frame, and so this would 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 fa 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 to form 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 glad for def going for the hat trick here, brilliant physics. Wait wait till you see why what I pull out at the last five minutes.
And the other is to accept it and to say, hm, 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 that is 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 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? I 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 in the beginning of the episode, the place this would really be important, the place you would notice it 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.
Dan, that's right, we're opening the closet and all.
Who knows what's in there and who knows what's been growing?
And so I asked Bianca that the professor, because she thinks about this stuff, right, she thinks about what happens inside black holes when gravity gets really strong, 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 will 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 the normal.
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 blue gravities 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? It's crazy stuff? Yes, is your answer.
You're gonna go with the s And that's my third Nobel Prize claim.
Or is that the conclusion to your pitch or your loop Quantum gravity sitcom episode?
There you go at the end of season twenty, 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 lupy going on, and this would be a these small effects. So what you need to do is like have a race between photons of different frequencies high frequency versus low frequency, and the race 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.
I need to know where they're coming from, right.
Yeah, So we have these sources which are variable, like quasars 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 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 torture acronym for I don't even know what is it really, it's called integral YAP. And what they found they didn't see anything right, They didn't see any difference in the arrival times.
Didn't any loops.
I didn't see any loops. And they were able to say that if there are loops, they're smaller than ten to the minus forty eight meters.
What they can do that, that's one client 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 thirteen orders of magnitudes smaller than what we think the size of the loops are. So like that seems pretty definitive.
Yeah, but what did the loop quantum gravity folks say.
Well, you know, there's only one branch of loop quantum gravity. The people who say that maybe that's 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, these things, and all sorts of complicated interactions between light and space, and so it just sort of rules out one branch of 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 it's one head of two physicists emerge.
But they're fascinating, you know, and each one is a wonderful exploration. Is 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 gotta know, right, Yeah, I mean I think that's how microways were bent. It actually by accident, by looking at something else. And where would we be? Where would burtas be these days.
That's right.
And you know, there have been actually fascinating advances in microwave and 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 drives 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 and fancy. And actually drop by my house and delivered one of these prototypes, which has been a lot of fun.
That's amazing that you let one of you our listeners into your house.
Hey, he was offering a brand new appliance, so I thought. And while he was there, I asked him about Luke 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 Luke. Quantum gravity is and who knows, and maybe it is the 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 did this podcast cost me in terms of your physics time?
One loop one? That's ten to the minus thirty five dollars.
Ten to the minus thirty five dollars.
One plank dollar.
Yeah, a pika 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.
Before 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 Danielandhorge dot 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.
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