Daniel and Jorge Explain the UniverseDaniel and Katie bushwack their way between theories of gravity and electromagnetism, looking for the elusive connection.
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Year this Friday and Saturday, starting at ten thirty pm Eastern seven thirty Pacific. Hey, Daniel, have you guys figured out how to make quantum mechanics and gravity work together?
Yet?
Ooh hit me hard with a nasty question, run off the bat. Huh, Well, unfortunately we haven't figured it out yet.
Well what have you guys been working on and how long have you been working on it? For decades?
More than one hundred years?
Actually, Well, and I thought I was a little bit behind on my deadlines, So you know how long you think it's going to take? Another weekend, another thousand years. Can I get it in by Monday?
You know, the only progress we've really made is coming up with some long, confusing names for it.
Like Mississippi or quantum gravity.
No, that would be much too clear.
Okay, like gravito, quantum field, hydrodynamically.
I think you should be a physicist, Katie. You have the knack for it.
I know how to throw a ball and look at it go up and come down, so I'm already halfway there.
Hi.
I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I desperately want to know the underlying rules of the universe.
I am Katie Golden. I am not a particle physicist. I host a podcast about animals. But that doesn't mean that I couldn't maybe try to smash quantum mechanics and gravity together if you give me a government grant.
I think everybody who's not a particle physicist should introduce themselves that way. Hi, I'm Sally. I'm not a particle physicist.
I think that makes the most sense.
In that case, I should start off by listing all the things that I'm not. Every time I introduce myself to somebody, I'm not an Olympic gymnast, I'm not a Wall Street trader dot dot.
Com, i am not a hot dog eating champion.
Yet we can all aspire to stuff. Well. Welcome to the podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio in which we aspire to be particle physicists. We all want to understand the way the universe works. We all want to figure it out, to zoom down to the tiniest little bits of the universe, the basic building blocks and the rules that intertangle them, and zoom out from that picture to understand how it all comes together to make our amazing hour bonkers are wonderful, our delicious universe.
Yeah, like a nice stew of concepts all mingled up in the stars. So yeah, I mean it is interesting because I think we've talked a little bit on the times that I've been on the show about quantum mechanics. We've talked about gravity, We've talked about sort of this distinction between the physics involved in the really tiny and the really huge, and how it's a bit of a puzzle to fit those together.
Yeah, the basic strategy of physics has always been to zoom down to the littlest bits of the universe to try to understand them, and then hope that we can carefully, one step at a time, zoom out and figure out how those things come together to make our world. You know, how electrons and protons come together to make atoms, and atoms come together to make molecules, and molecules come together to make proteins, and proteins come together to make steak and ice cream and all the delicious things that you eat. That's sort of like reductionist approach. We zoom down and then one at a time step back up to understand our world. Has long been the approach we wanted to take to understand the universe, and that's worked for lots of stuff, like the way we understand ice cream and blueberries and steak and goats and all that stuff. But you're right, Katie, there's one big thing that it hasn't been able to explain, maybe the biggest, most important thing that shapes our universe, and that's gravity. How everything seems to attract itself, or how things flow through space time. We still don't understand how that bubbles up from the tiniest little bits of.
The universe because gravity is sort of, I guess, like a big force that we observe. So like you know, you feel gravity on a planet. Maybe you and I I have our own gravitational pull, but it's much weaker than a planet, so we're not going to notice it. But is gravity something you can really measure much when you get really small, like say you're looking at particles, Like does a particle have its own gravity? Or can you even measure gravity of say like a neutron or a proton or an electron.
Yeah, that's exactly the puzzle. On a theoretical sense, we don't know how to stitch these two things together, and we'll talk about that more during this podcast. But even more frustrating, in experimental sense, we can't even see what the universe does. Basically, the job of physics is to explain what is the universe doing, what's happening out there, and why does it make sense? And the first step there is to see what's happening in the universe. And so the first thing you want to do if you want to explain the gravity of little particles, the quantum mechanical understanding of gravity is to see gravity operating on little particles. That's basically what you're asking. And the challenge there is that gravity is so dang weak compared to the other forces of electromagnetism, even the weak force and definitely the strong force, Gravity is like a bajillion zillion quintillion times weaker, which is why, for example, like a simple fridge magnet can overpower the gravity of the Earth and hold your recipe against your fridge or your pictures of your kids and their cousins. It's not hard to overcome the gravity of an entire planet with a tiny little bit of electromagnetism. And so when you're looking at a tiny particle, a proton or a neutron, its gravity is basically zero. It's so hard to measure. The smallest thing we've ever measured the gravity of is something like on the order of a gram, you know, which means it has like ten to twenty particles in it. So no, we are nowhere close to being able to see gravity operate on particles so that we can then try to explain how it all works.
That seems kind of hard because like science is mostly about say either direct observation or so setting up an experiment. So if you can't even see it happening or figure out how to observe it in particles. How can you ever figure out how it works on such a small scale.
Yeah, great question. Well one is you don't give up.
Oh I was just gonna go for just give up, never.
Give up, Never give it. People are doing these incredible experiments. It's really an amazing accomplishment to figure out how to test gravity on the smaller and smaller things. And there's this history getting all the way back to like Cavendish torsion experiments of lead balls a weigh a few pounds, down to smaller objects and smaller objects, and very recently down to stuff like smaller than a raisin, you know, a few grains of sand of material. And I really want to underscore that there's a special scientific skill there. It's not like mathematics or genius insight into philosophy. It's experimental bravura.
You know.
It's what Ray might call engineering. It's like figuring out how to make your experimental system so quiet and so clean and so pristine that you can force the universe to reveal one of its secrets. It's a really special skill in science. And so those folks are working hard and drilling down, but yeah, they're like twenty orders of magnitude away from figuring it out, so it's going to be a while. The other thing is, you could, you know, try to visit a black hole. Inside a black hole, we think that gravity and quant mechanics are both relevant because obviously there's strong gravity, but also things are squished really really small at the singularity inside the black hole. Of course, that's inside the black hole beyond the event horizon. So we still haven't figured out how to probe that.
Yeah, we've talked about this. It is not in the budget to go to a black hole just yet.
No, so instead you might want to make your own black hole and then study the patterns of its hawking radiation to try to get some clues as to what might be inside of it. But nobody succeeded in making a black hole yet, and if they did, it might destroy the Earth, and so there are some questions there. So while the experimental side is super tooper frustrating, we can try to make some progress on the theoretical side thinking deeply about the universe, eating special mushrooms and having insights about connections and mathematical symmetries between these two ideas, to look for links, to look for connections, to look for ways to fit them together in our minds that might give us some new clues as to how to bridge these two fundamental pillars of modern physics.
Now, do you get university funding for mushroom tripping in the sake of theoretical physics?
If you can convince the funding agency that it's essential for your research to make progress, then ya, I'll bet you. And so today on the podcast, we'll be exploring one of those potential directions to bring gravity and quantum mechanics together to try to fit these two genius insights about the way the universe works into one mega insight. And today in the podcast, we're asking the question, what is gravito electro magnetism? Boy? Is that a mouthful? I feel like this must have been named by some German person. Yeah, every time they come up with a name for something, they just like stick a bunch of words together into one super long word.
Instead of coming up with a new word, it's used the words you already have, but stick them all together.
Imagine if you came up with new ice cream flavors that way. Cookies and cream all one word.
Wait, it isn't already?
No, No, I think that's exactly how they figured it out.
Like, I think it's interesting that I don't think I've ever seen a question before of the audience where people are just like I can't even comprehend the name of this.
That's right, And so this was maybe a little bit unfair to drop this on the listeners, But what the heck? I think it's fun to ask the guys questions about things you never heard about. So thanks very much to everybody who volunteers for this audience participation segment of the podcast and is caught awareby by very technical physics questions without an opportunity to prepare. We really appreciate you being gained for this. If you would like to play for future episodes of the podcast, please write to me two questions at Danielanjorge dot com. So before you hear these answers, think about it for a minute. What do you think gravito electromagnetism could be? Here's what some listeners had to say.
Is it the electrocharge put off by strong gravity?
Maybe?
I don't know how you combine gravity and electromagnetism, but it sounds like some kind of combo of the two. So maybe it's the way in which electromagnetic fields are affected by gravity.
Or vice versa.
I'm going to guess that gravito electromagnetism is the impact that gravity has on the electromagne that A four.
I wonder what insane clown Posse has to say about gravito electromagnetism, and if they know how it works? Does that call back too old? Now? Am I old?
I'm not going to comment on it. I will say that I am approaching fifty and so I've embraced being fifty by calling myself fifty before I even got there. And my kids think it's weird that I round myself up to fifty, but I love it.
I do that too, I round up, so I'm not so shocked when it happens.
Exactly That's what I was thinking. And then my daughter asked me. She said, well, does that mean when you turn fifty one, you're gonna round yourself up to one hundred?
Why not?
Yeah? I thought, you know, for the sake of consistency, I guess I have to.
I mean, you know, then you could be the oldest person on Earth, even before you start getting a pension.
That's true. I'm just hoping to get some of those compliments like wow, Daniel, you look good for it. All right, But back to the time of quantum mechanics and gravity, we see people are struggling to understand what this word means. But there is a sense there that it's about some relationship between gravity and electromagnetism. Maybe gravity is caused by electromagnetism, or maybe you get electric charges from gravity. There's some fun ideas in there.
It does sound like a little scammy. It sounds like something where someone's trying to sell something to me, because it's just so many technical sounding words all smashed together. It's like, yeah, I kind of want to know what it is. The only thing I can think of, like these listeners is just that it's like kind of trying to smoosh the concepts of gravity and electromagnetism together, but I kind of want to know more specifically what that is and how that works.
Yeah, and so delay the groundwork. I think we need to spell out a little bit of detail about like why this problem is hard. Why is it difficult to bring gravity and electromagnetism or gravity, and quantum mechanical theories of forces together in general, and so we should probably start with those quantum mechanical theories. And you know, we talked about electromagnetism because it's one of the fundamental forces that we know about in the universe. And all of these fundamental forces are quantum mechanical, meaning that we have a theory of quantum mechanics that describes particles and how they move through space or how they exist and how they have probabilities to exist. And those quantum mechanical theories, those Shroninger equations and the lagrongins and the Hamiltonians, all those mathematical structures are quantum mechanical and they describe the forces. So we have electromagnetism, we have the weak force, and we have the strong force. All these things can be described using a quantum mechanical theory. It means we know how to calculate what happens when one particle pushes or pulls on another particle using one of these forces. Like when two electrons are coming near each other, they repel each other and they use these forces to do so. They use electromagnetism, and think about that quantum mechanically, either as one electron has a big electromagnetic field and that's pushing on the other electron, or if you prefer the particle picture, you can imagine that the two electrons are exchanging photons. They're tossing photons back and forth, and that's how they're pushing on each other. But either way we have a nice quantum mechanical picture from the ground up, from the littlest bits of these three fundamental forces, electromagnetism, the weak force, and the strong force.
So is gravity even weaker than the weak force?
Gravity is like ten to the thirty times weaker than the weak force. It's almost unimaginably weak. It's so much weaker than the other forces that it's a big puzzle in physics. Like in physics, we look for patterns and clues. We expect things that are similar in nature to all operate in under similar principles and have similar numbers. So if you want to lump gravity in as one of the forces, then you've got to answer the question, why is it so much weaker than the other forces? Not by a factor of ten, not by a factor of one hundred, not by a million, but ten with thirty zeros behind it. That's a big deal.
And so like the difference between electromagnetism, the weak force, and strong force like is not nearly as big as the difference between all those three and gravity.
Yeah, exactly. The strong force is like ten times more powerful than electromagnetism, which is like one hundred times more powerful than the weak force, which is like a gajillion billion of jillion times more valuation.
To hang on, that doesn't even sound like a number, Okay, but I get it. So gravity is so incredibly weak it doesn't even seem like it's in the same category as these other things. It's like comparing it like a blue whale to an ant.
Yeah, that's exactly right. Now. Fundamentally, that's not a problem. Like it's possible that you could have for forces in the universe and one of them is just much weaker. There are ways that you can do that. It's not an insert amountable issue. It's strange and it would make you ask like why is that and to look for explanations, but mathematically it doesn't prevent us from describing it. That's not the challenge with gravity. If you sit down and try to describe gravity using some kinds of maths similar to the way we describe electromagnetism and the weak force and strong force, to come up with like a quantum theory of gravity that describes it as a force. Then you start to build in gravitational fields, and you can think about the quantized ripples in those fields as particles. In this case, it would be the graviton. So when two planets come near each other and pull on each other, the quantum picture of gravity would have them exchanging gravitons the way two electrons are like exchange photons. So you can start to go down that road mathematically and things seem okay. You just like dial the force way way down to make it super duper weak, But then you run into a lot of mathematical problems actually making that theory work.
How do you check your math in a situation like this, like, what are the kinds of mathematical problems that you run into and how do you know that they're problems?
Yeah? Great question. The way that you know that your theory is working or not working is that you try to use it and you see if it gives reasonable results. Like, if you ask, I want to push these two particles together, I want to calculate the probability of various outcomes. I want to know the particles are going to bounce off each other, or if they're going to scatter off at this angle or at that angle. So you try to calculate things, you try to make predictions in physics. For your predictions to be reasonable, there's some limits. There's some restrictions, like your predictions can't have probabilities greater than one. If you ask, like is my electron going to go left or right? And your theory says you have one hundred and seventy five percent chance of its going left, And you're like, well, that's that seems wrong.
That can't wait right, So when my gym teacher told me to give it my one hundred and ten percent, like, that's not right, that's physically impossible. That's right, one hundred and ten percent of my.
All your gym teacher is violating the fundamental.
Rules of physicals call them up right now.
Or maybe your gym teacher is a quantum gravity theorist, because that's exactly what happens when we try to make a quantum gravity theory. Gravitons are really tricky because they don't just transmit gravity. They have energy themselves, which means they also couple to gravity. They feel gravity, they emit gravity. So like when you emit a photon, photons don't feel electromagnetism, they don't bounce off of other photons, they don't emit other photons. Right, Photons don't feel electric charges because they are neutral. They don't have a charge themselves, so they will like fly right through an electric field. But a graviton has energy, and gravity is felt by everything with energy. So gravitons feel gravity, which means they emit more gravitons, and those gravitons emit more gravitons, and pretty soon you have an infinite number of gravitons, and you start to get nonsense answers out of your theory.
When you say a graviton, right, I'm thinking of a particle sort of like a photon. But photons we've actually measured, right, We've actually been able to sort of get physical evidence of their existence, Like, do we have like physical evidence of the existence of gravitons as like an existing thing other than just knowing that gravity exists?
We do not have any evidence of gravitons. We have a very successful theory of gravity. It's Einstein's theory of general relativity that describes how space and time bend around masses and that affects how things move, and that's very very precise, but that describes gravity as not a force. It's like a bending in space and time. We're going to switch over and try to think about gravity as a force instead of bending in space and time. Then you need these gravitons, and nobody's ever seen them. The reason they're so hard to see is precisely because gravity is so weak. Like electromagnetism is a pretty strong force. Electrons are radiating photons all the time. It's not a rare thing to happen in the universe, but gravitons are more rare because gravity is so weak, and they're much harder to see because gravity is so weak, so the impact of like one graviton would be very very hard to detect. So we don't know that gravitons are real, but they are a necessary part of a theory of quantum gravity that tries to make gravity look like a force and fit it into this quantum mechanical framework so far, and nobody's even been able to make the math works to have like a consistent theory that we could even go out and test in experiments.
So we can't make the math work. We can't even find any evidence that gravitons exist. Things are looking pretty good, pretty good so far. Maybe we should take a quick break. I will look around see if I've got any gravitons just kind of lying around, you never know, And then when we get back, maybe we can take another crack at this and see if there's any anything that actually where the math. You carry the ones and it all works out.
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All right, So bad news. Daniel couldn't find any gravitons on a single one. I'm also out of milk, so things aren't looking so good here. Do you have any good news for me? In our effort to smoosh together quantum mechanics and general relativity.
I didn't figure it out in the last couple of minutes, but you know, a lot of clever people have been thinking about this and trying to find some connections between gravity and electromagnetism, or between electromagnetism gravity sort of going both directions, like trying to make gravity look more like electromagnetism and the theoretical side, or giving up on that and trying to make electromagnetism look more like gravity. So we don't have any experimental results to guide us, but we can still think deeply about the structure of these theories and try to make some theoretical progress in our minds. Magic mushrooms or no.
All right, so we're in the mindscape. What are we doing in order to solve the hurdle of the math not mathing in this idea because it sounds like we were sort of trying to think of planets as like scaled up particles and gravity as like a force between them, as if they're giant particles. And that didn't really work, Like, is there another approach that you could use, or is there a way to like fine tune that approach such that it actually does work.
Yeah, So the short answer is there isn't a great approach, but that doesn't mean we can't make progress. And I think people should understand that. In theoretical physics, it's not like you sit down one day and you just come up with the whole.
Theory movies lied to me.
You're entering like a mathematical jungle. You're not sure if there is a path through, and it takes exploration. Exploration is not just something we do in experimental physics or in experimental biology. We're like walking through a literal jungle looking for new kinds of frogs. In theoretical physics, you can also explore. You can just like try stuff and say well, I'm gonna go in this direction and see if it works out, kind of like when you're trying a proof in tenth grade geometry and you're like, well, I'm not sure this is gonna get me where I need to go, but I'm gonna play around with these angles. And so in theoretical physics, people are trying something that has a long tradition dating all the way back to like Maxwell. James Clerk. Maxwell in the eighteen hundreds was looking at theories of electricity and theories of magnetism, and he tried something cool. He said, well, let me write down the equations for electricity and write down the equations for magnetism and try to smooth them together and make them look as much like each other as possible. And when he did that, he realized, oh, my gosh, these basically have the same equations. And not only that, but you can click the equations together because sometimes electric field cause magnetic field and vice versa to make one bigger picture. So we had this great insight, which is where we got the theory of electromagnetism. So now people are trying to do something similar. They're saying, let's look at the equations for electromagnetism and the equations for gravity and see if we can find relationships. Are they like a mirror image of each other? Can we somehow find patterns there and then use that to guide us through this intellectual jungle to a theory that combines gravity and electromagnetism into one big theory.
So for someone just theoretically who does not have a grasp of what theoretical math would look like, and when you say equations, like what that is?
Like?
So are we talking about like you have five equations that you have to memorize to understand gravity? Like are there hundreds of equations? And when you're trying to like smash together equations, you know, is it sort of like a brilliant mind where you just see floating numbers kind of going together and doing things like what in terms that someone like me who math is trying to calculate a tip? How does that work?
Yeah, that's a great question. And we could start off pretty simply. You know, people are probably familiar with Newton's law of gravity. That just says that the force between two objects is proportional to the two masses divided by the distance between them squared, and then you multiply that whole thing by a constant, big G Newton's constant. So Newton's equation for the force between two objects is like g mm over R squared. All right, So that's Newton's theory of gravity. Then we can look over at electromagnetism. We can say the equation for the force between two particles that have charge, Like remember our question was like, what happens when two electrons come near each other? Can we calculate that?
Well?
Kulam's law tells us that the force between two particles goes like the charge of the two particles divided by the distance squared between them, all multiplied by a constant in this case K. So you look at these two equations, you notice instantly, like HM, these have kind of similar structures. On the top of the equation is the charge of the two objects. Where gravity the charge would be the mass, and for electromagnetism the charge is obviously the electric charge. And both of them get weaker as the distance grows by the same power you get twice as far apart. Gravity and electromagnetism both get four times weaker. You go ten times further away. The force of gravity and electromagnetism both go down by a power of one hundred. So they have very similar structures there already. That's encouraging, But.
If it was just as simple as fin sort of some of these equations that seem to look kind of similar and match them together. Like, it seems like we would have already figured this out. So what is the scale of the complexity, Like, why haven't we been able to find just like a bunch of these equations that kind of look similar and seem to have the same general structure and have them work together.
Yeah. Well, one issue, of course, is that we know that Newton's theory of gravity is not the right theory. Whoops. When Newton was a very clever man and he has a very nice theory which mostly works but not.
Quite irresponsible with apples too.
Einstein's theory of gravity is not just a reimagining. It's not just saying, look, the story is wrong. It's not a force between objects, it's a bending of space and time. It also gives different predictions, like, for example, Newton says that the force just depends on the mass. It doesn't depend on whether the object is spinning or not. So according to Newton, if you're in orbit around the Earth, whether the Earth is spinning or if it stopped spinning or spinning the other way makes no difference for gravity. Einstein says, Nope, that's not true. If the Earth is spinning, that has more energy. And since gravity is linked to energy of all kinds, not just mass, that changes the gravitational force on the object in a complicated way. So Einstein's equations are much more complicated than Newton's. He doesn't just have like one simple force equation. He's got a really complicated tensor equation, or a tensor it's just like a matrix. It's like an array in computer programming, you know, a way to keep track of a bunch of numbers all at once. So he has more complicated equations. And so you can't just say, look, Newton's law and culums are similar. You got to dig deep into Einstein's rules for gravity.
So how do we know Einstein is right and Newton is wrong. It can't just be that Einstein's got cooler hair or more complex equations.
Well, Einstein and Newton make different predictions, and famously Einstein's predictions were right. Einstein predicted stuff about how light bends around the Sun during an eclipse, and he predicted stuff about how mercury orbits the Sun and the angle of the eclipse of mercury. How that twists as mercury is orbiting the Sun. All these little differences between Newton and Einstein add up and a few special cases, so we know that Einstein's theory was right. So then people took this on. They're like, okay, well can I take Einstein's equations and try to make them look like electromagnetism. Like we were able to take Newton's law and make it look like Kulum's law. Can we take Einstein's gravity and make it look like electromagnetism? And people have actually succeeded in doing this. There are these gravito electromagnetic equations when if you write them down, you get equations that look very similar to Maxwell's equations for electromagnetism. Maxwell has four equations, and I won't get into the math with you. You know, there's like a divergence and a curl for electricity and magnetism, and Indie gravito electromagnetic equations are also four equations, and they have a very similar structure to Maxwell's equations. You should look them up and write them side by side. They look very very similar. It's eerie, it's spooky. It's like the universe is saying, oh, look, you found the pattern. It's the same over here in the gravity world and in the electromagnetic world.
This does feel like a conspiracy theorist sort of aligning charts and with a corkboard and yarn and trying to make these connections. But yeah, I mean, I'm looking at this, and you know, I don't know a look of complex math, but it Yes, they look very similar. But if we've found this, right, it doesn't mean that we've figured out how they interlock. Like we found some similarities, some equations that seem to match, but the bigger picture has not yet become clear.
Yeah, that's right, And I hear you setting me up to deliver the bad news of why they're going to work. But first there's a little bit more good, okay, which I think is a fun insight into how this works. The thing about Einstein's equations for gravity, as we were saying before or is that it gives you more than just like a straightforce between two objects. Spinning objects can create like torque and drag in space time itself, which gives all sorts of weird forces, like if you are orbiting the Earth and the Earth is spinning, then there's some frame dragging effects there. Check out our whole episode about that if you want more details. But effectively, it gives like a twist on things that are orbiting the Earth. So according to Einstein's gravity, it's not just a force between two objects. There are more subtle effects there. And the really cool thing is that in the gravito electromagnetic equations, the ones where you take Einstein's gravity and try to convert them to look like electromagnetism, you can see this emerge. And in those equations you have what they call a gravito electric field, which is sort of like the straight up Newtonian version, plus this gravito magnetic field. So basically, to explain all of Einstein's gravity, you break it up into two pieces, this analogy to the electric field and this analogy to the magnetic field. And it goes even deeper than that, because it's not just notation. It's not just like, hey, let's write this down in a cute way that looks sort of similar. There really is a conceptual connection there because an electromagnetism, the way you get magnetic fields is you take electric fields and you wiggle them like currents of electrons give you magnetic fields. So it's like velocity dependent, right. Well, the cool thing about the gravity magnetic field, this other component of these equations you have to add on to be able to describe Einstein's gravity. Where the equations that look like electromagnetism is that they create velocity dependent acceleration in just the same way. For example, those spinning masses. When the Earth is spinning, that's an acceleration because any sort of rotation is an acceleration, and that gives an acceleration. On satellites, it gives a twist, it gives a pull. So when you force gravity into this structure that looks like electromagnetism, you learn some things about gravity. It's like to sit in your mind in a way that actually gives you a little bit of insight. And that's a good sign. Like when you're bushwhacking your way through the theoretical jungle trying to make connections between things. You don't want to have to force things into categories. When they sort of naturally fall into those categories and reveal something deep about the nature of that force or the nature of the phenomenon, it's a sign that you might be on the right track. So that's the good news that there really is something satisfying about making gravity look like the equations of electromagnetism. It's not just like hacking it up into bits and shoving it in boxes.
It's not just using the same colored gelpins to write the equation exactly. That sounds very promising, right, That sounds like a very like promising path. And the fact that there's this wiggle connection where wiggling or velocity movement for gravity like creates this field is very interesting. I just I feel a butt is common.
There is a big butt, a man, I knew exactly right.
I like big butts, and I cannot lie.
Now that's a reference. I hope everybody injury. Hopefully the other brothers can't deny. Well, the thing that the other brothers can deny is that this works in difficult situations. Like we said that you could take Einstein's rules and you can express them in mathematical equations that look like electromagnetism. But there was a butt there I left off. And the butt is this only works if gravity is kind of weak, like when the curvature of space time is not very strong, when you're like far from any intense mass, when you're far away from a black hole, for example, or even from the Sun. Then this works pretty well. But when the curvature of space time gets more intense, this breaks down. Like the equations are just too complicated, too intense, we have no way to fit them into these boxes to make them look like electromagnetism. In order to do that, to take the complicated tensor equations of general relativity and to make them look like electromagnetism, you have to make a bunch of assumptions, and one of those assumptions is gravity is pretty weak. So basically what's happened here is you've avoided the hard problem. You know, the hard problem of making quantum gravity work was figuring out what happens when gravitons amid other gravitons amid other gravitons. Basically when gravity gets very very strong but it can no longer be neglected. And that's exactly the situation that gravito electromagnetism doesn't know how to answer. So it's some progress in the sense of like hm, you've found some cool connections between these theories, but only in the easy parts, not in the hard parts at all. When you get to the hard part of gravity being very strong, and every graviton is emitting ten other gravitons. Then this breaks down and it doesn't help us at all. So it's like an interesting island of understanding, but it doesn't make any progress on the really hard part of the problem describing gravity as a quantum theory when gravity is very, very strong.
But could it be revealing something about gravity still, like maybe that there is a significant difference between a strong or large amount of gravity, like the gravity of the Sun versus the Earth. If there is some kind of fundamental difference between like weak levels of gravity and strong levels of gravity, that seems like that could itself be an interesting kind of finding, even if it still doesn't solve the bigger question of how to merge those concepts.
Yeah, exactly, And that was the point I was trying to make earlier, that even intermediate progress is progress. You don't have to know if this is going to fundamentally solve the question of quantum mechanical gravity for it to be cool that you figured something out, that you've made some headway, you found some island of understanding, whether it actually connects to the mainland and reveals all the deep secrets we don't know yet, But that doesn't mean it's not worth doing and not worth exploring. Right, we've made it to this stage where we've been able to accomplish this connection between electromagnetism and gravity. It might be that hunting around and digging around, poking in various directions. Lets us build from this, right that we can go from here to figure out how to describe strong gravity. Nobody knows how to do that yet, but this is like another avenue of attack. This gives us another way to think about it. At least it might be a total dead end, or it might be the wave of the future. We haven't figured that out yet. It's like on the forefront of knowledge.
I mean, let's go with not being a dead end. We'll take a quick break and try to keep up the optimism that this is actually going towards finding a fundamental answer that'll change everyone's lives. And we're probably not going to figure it out in the ad break, but you know, I'll think about it.
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So we are back. We have not yet solved how to weave together electromagnetism and general relativity. Or gravity, but there has been some interesting progress that has been made that is perhaps instructive and perhaps interesting. So we had that issue that these these equations when gravity is weak, they seem to kind of align, like you have the equations associated with general relativity and then Maxwell's equations that looked similar. Then when gravity got strong, like the sun or a black hole, that kind of broke down. It no longer worked in that way. So is there another sort of angle of attack that is being exploed.
Yeah, people are trying so many different things at once, and you know, this is the way we make progress. You push your way through the jungle. Maybe you make it all the way through, maybe you run into somebody else coming from the other direction, right, and you can join you in two efforts. And so that's what's happening is a bunch of people are working on trying to make gravity look like electromagnetism. So that's the gravito electromagnetic approach that we just talked about. But some people are working in the other direction. They're saying, let's not make gravity look like electromagnetism. Let's make electromagnetism look like gravity. Right, Einstein's big idea was, let's not think of gravity as a force, let's think of it as the curvature of space time. And so people are wondering, like, can we extend that idea? Can we also do that for electromagnetism. Remember that the way Einstein did this is he said, look, it feels like there's a force between you and the Earth. Newton's description of gravity as a force is compelling because when you throw a ball in the air, it falls to the Earth and it looks like it's getting hold on. Right, we have this experience of gravity as a force. But he said that it's not actually a force. That's something of an illusion. What's happening when you toss a ball is that you're releasing it into freefall. Space itself is curved in the vicinity of mass, so there's a natural path for objects to follow in curved space time. So the ball naturally falls towards the center of the Earth. So Newton's picture is there's a force pulling on the ball, and then it hits the Earth and it stops it because the Earth is balancing that force of gravity. Einstein's picture is different. Einstein says, when the ball is in the air. It's in freefall. There is no force on the ball at all. It's just following the motion of space and time, and then the Earth stops it because the Earth itself is providing a force. It's accelerating against that natural motion of space time.
Yeah, and I think you've told me this is actually measurable, right, that there is acceleration acting. When you are, say, standing on the floor.
Exactly, jump off a building instead of the ball, and you take a scale with you, and as you're falling through the air, hurtling towards the Earth, you stand on the scale. What are you going to measure nothing? You're going to measure nothing. Yeah, right, you have no weight, and that's because you're in free fall. There's no acceleration there. You're not measuring anything. If you're standing on the surface of the Earth and you stand on the scale, then you measure your weight. That's where there's a force, right. So there really is no force on you when you are in freefall. There's a force on you when you're standing on the surface of the earth. That's the Earth pushing up against that natural emotion. So the explanation is that there is no force there. There's just a curvature of space and time, and we couldn't see that curvature, and that's why it looks to us like there is a force.
Having this as the theory about gravity, like, how do you then fit the quantum forces into this framework? Right, because like that seems fundamentally different. Those are forces, they're pulling or pushing against each other. How does that fit into this kind of idea of gravity being like the shape of existence, which sounds it's hard for me to kind of think about that, right, like the shape of the universe, the shape of the fabric of the universe, and then we're just kind of falling along it. And then you have these particles. Have we observed anything in particles that could sort of fit within that framework?
So we haven't observed anything yet, but there are some theoretical ideas. The idea is to say, well, maybe electromagnetism also isn't the force. Maybe it just looks like a force and it's actually the result of a second kind of curvature. So we have like first kind of curvature is Einstein's curvature of space time that gives us the apparent force of gravity. Space can also be curved in another way, and that curvature gives us the appearance of the force of electromagnetism. And in order to have curature in another way, you need more dimensions of space and time. The idea is like Einstein space is three plus one dimensions. Start with one dimension, which is a line. You draw a second dimension which is perpendicular to that. Now you have like a plane. You can add a third dimension which is perpendicular to both of the first two, and that gives you like three D space right where each of those three lines are perpendicular to each other. And that's it. There's no more room to add another line perpendicular to all three right.
Because space, Yeah, it doesn't work.
It's sort of crazy in mind bending. And I remember as like an eight year old trying to imagine that fourth dimension but not being able to do it. But we do think of time as sort of a fourth dimension. How those three change. So Einstein space is four dimensional, but we can extend it by adding another dimension of space and having that curvature be in that additional dimension, that fifth dimension. And you might ask, well, I can't see that dimension. I can't imagine where that dimension would be. How does that even work. Yeah, and this fifth dimension is sort of similar to the way we think about time, or like time we think about as the fourth dimension. Imagine three dimensional space and then imagine that changing through time. Right, save your full three dimensional space, but now you have like another axis along which that three dimensional space is changing. So to imagine another dimension of space itself, imagine three dimensional space and then imagine a bunch of copies of it. And this new dimension is not like the original three. Instead of going on forever, it's like a little loop. It's more like in polar coordinates, how you have an angle and the angle can't go from zero to infinity, just goes from zero to three hundred and sixty degrees and then it goes back to zero again. Right, Imagine a new dimension of space that's sort of similar. It has a maximum length. It's a circle instead of an infinite line. Take three D space and sort of move it around this circle. That's how we imagine the universe with four spatial dimensions. The first three that are normal, and then this weird rolled up dimension.
Is it like when your Windows computer crashes and you're dragging like your cursor or a window around and then there's a bunch of little copies of that. They all get stacked up and messed up. Is that what we're talking about here.
Exactly, Or like when you win solitaire and the cards all stack on top of each other. It's difficult to imagine because we're used to three D space and we think in three dimensions, and so squeezing that fourth dimension into your brain is really a challenge. But mathematically it allows something very cool that allows you to have another kind of curvature. A curvature in this new dimension might be able to explain what we see as the force of electromagnetism. So in this case, not just the curvature, but the whole dimension would be basically invisible to us. This is an ancient idea in physics. It goes all the way back to nineteen nineteen. The guy Theodor Cluza came up with this just after Einstein came up with this idea of relativity, and then a few years later a guy named Oscar Klein turned it into a quantum theory in nineteen twenty six and try to calculate the size of this new fifth dimension and figured out how to be like twenty times the plank length, which means it's like super duper tiny. It's like ten to the minus thirty five meters long. So this seemed really exciting.
I have so many questions just about that, like what do you mean calculating the size of a dimension? Right?
Like, remember that this new dimension is not infinite, like right, we think that you can go as far as you want in X or and y, r and z, but this new dimension is a loop, which means it has a length. Now there's a maximum distance in this dimension. It's unlike the other ones in a really weird way. And that means that you can calculate like, well, how big could it be? What is the radius of curvature? What is the length around this dimension? So it's very different in a really counterintuitive way. And then Einstein got to work on it. He was like, all right, this is exciting.
Oh good. I trust him more than I trust me to think about it.
He thought, maybe this is exciting, Maybe I can make this work. Maybe I can explain all of electromagnetism using curvature in this fifth dimension. And yeah, he died before he found and people have been working on it for a long time and nobody's been able to crack it. There are some versions of this theory which sort of work, but they all predict that we would have seen a bunch of new particles. They predict that electrons would like vibrate in this other dimension, and they would vibrate in different ways, so you would see like different versions of the electron the way like a string can vibrate, but it can vibrate like one mode or two modes, or three modes or four modes. Electrons could vibrate in this other dimension in various ways, and you would see like heavier and heavier versions of the electron, where the heavy ones are like vibrating in this new dimension with more energy, which gives them effectively more mass. But we haven't seen any heavy electrons, or any heavy muons, or any heavy versions of these other particles at all. People thought for a while, oh, maybe the muon is a heavy version of the electron, and that's actually like, you know, something vibrating in this new dimension. But that doesn't quite work out because the electron and the muon feel the weak force a little bit differently. So the bottom line is it's an exciting direction theoretically to try to make electromagnetism work in this clusive cline theory, but it's made predictions that haven't been born out in the data, and so it's not so promising.
Well, we need to make a time machine, go back in time and then ask Einstein, first of all, how to make a time machine so that in the future we can go back in time and talk to them and then present them with all of this information. Or maybe uh, there will be a new kind of Einstein, or collectively, instead of one super genius, just a bunch of very smart people working together figuring this out exactly.
But it's promising. It's exciting that people are trying to push their way through the theoretical jungle. You know, until we figure out how to make a black hole here on Earth, or we've come up with some clever quantum gravity experiment that lets us see particles feeling gravity and understand whether they're like bending space time probabilistically, or whether gravity collapses their wave functions, or what's going on, we can only make progress theoretically. That means trying to find mathematical relationships between these theories, either making electromagnetism look more like gravity or make gravity look more like electromagnetism. So far, both paths have been sort of stuck in the jungle. But maybe one day people will find a connection between them and will all be illuminated.
That is beautiful, But you do also keep breezing past this plan to make a black hole on Earth. That sounds dangerous to me.
It is very dangerous, but also potentially we could learn a lot about the universe, so you know, may be worth the risk.
Yeah, ultimate knowledge right before oblivion. Sign me up.
Sounds good. We'll stay tuned for more hints about potential ultimate knowledge about the universe, just before you get sucked into oblivion. Thanks so very much Katie for joining me on this journey of theoretical understanding, and thanks to everybody for tuning in. Tune in next time for more science and curiosity. Come find us on social media where we answer questions and post videos. We're on Twitter, Discord, Instant, and now TikTok. 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. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from maneure into renewable energy that can power farms, towns, and electric cars. Visit you asdairy dot COM's last sustainability to learn more.
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