Daniel and Jorge Explain the UniverseDaniel and Jorge explain how space can get twisted up around spinning objects.
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Hey Daniel, do people ever send you their personal theories of the universe?
Oh? Yeah, I get plenty of those.
Yeah, what do you think they're hoping for?
A lot of them want to prove Einstein was wrong?
Really game high? I guess after all these years aren't we convinced Einstein was right.
Actually, I'm pretty convinced Einstein was wrong.
Wait, what you think you know better than Einstein.
I don't have a better theory of the universe, but I'm pretty sure his theory general relativity is not a correct description of nature.
Well, you should come up with your own theory then, yeah, and then I could send it to myself and then you can answer it on the podcast Done Nobel Prize for the two of Us chu Ching. Hi am Moreham, a cartoonist and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist, and I would love if somebody out there proved Einstein wrong.
Yeah, maybe even the ghost of Einstein.
Einstein's grandchildren, son of Einstein, or daughter of Einstein. Einstein had a pretty scandalous family situation, so I wouldn't be surprised if some of his kids or grandkids or great grandkids were a little grumpy at him.
Well, they definitely inherd. It a nice brand name. So I mean, can you imagine going for a job and putting Eisin on your resume and people are like, yeah, he's probably not or she's not, probably not smart enough, not likely to happen, right.
It's a lot of pressure. What if you want to be a basketball player and your name is Einstein and they're like, get off the core of Einstein.
Go back to your talk board there.
Yeah, exactly what did they call it? When an actor can only get one kind of rule type cast? Right? Like Einstein and all of his generations are all going to be forced to be doing fundamental physics, right.
I haven't seen a lot of stand up comedians, right, or artists named Einstein.
Well, they probably change their names, right, they have stage names, you know, the comedian formerly known as Einstein.
I guess that would help them. But anyways, welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we make everybody out there in Einstein by explaining to you everything that we do know about our crazy, beautiful, hot, and wet and weird universe and everything that we don't yet understand from the tiniest little bits of space and how they fit together to make this incredible, emergent, bonkers, beautiful world to the vast nature of the cosmos. How far does it go on? What's outpassed? There will we ever see it, we wrap up all those questions and explain them to you.
Yeah, because it is a vast universe full of intricate secrets and lots of wonders for us to discover hiding and playing sight sometimes right even around our own neighborhood.
It is exactly. I look at the universe like the biggest murder mystery or the grandest detective novel ever written. It's like a big puzzle figuring out how does it work. We're gathering clues and trying to narrow it down and figure out, like what really makes the universe tick?
What does it have to be a murder mystery?
Daniel?
I feel like you just went kind of dark there, like like somebody had to die to make the universe.
Well, you know, the universe is going to kill you, joorhe.
I'm sure it's not the universe itself, but maybe my eating habits.
Well, I just think it adds some drama. You know, it's always more fun to work on a mystery if there's a body involved, I suppose. I don't know. That's why there's that whole genre of murder mysteries, right, It's not like you know who got gently tapped on the head in the library with the candlestick. You know, it's like who got killed? So, yeah, this is a big mystery. We want to understand what is the fundamental nature of the universe, what are the rules by which it runs? How can we figure that out? And frankly, I'm amazed that we really made any progress at all.
Yeah. I guess if the mystery was just word that I put my reading glasses, that wouldn't attract a lot of viewers there, or physicists, to be honest, yeah, exactly.
Or true crime novelists named Einstein.
All right, Well, we like to talk about all the great mysteries out there on the universe, and also we like to talk about what scientists are doing to uncover those secrets and figure out what's really going on, because there are a lot of interesting projects and interesting science experiments going on right now as we speak, trying to peer further into the universe and closer to the very nature of matter.
That's right, because even though folks like Einstein gave us a beautiful glimpse into how the universe might work, we are still figuring out whether his vision is correct or not, whether it describes the way the universe actually works, or if it's just like a very effective approximation which from some point of view seems to be successful in predicting what happens in weird situations.
Yeah, and so you're convinced that Einstein is wrong, you said earlier, like you're pretty sure he's wrong, or you think he's wrong.
I think he's got to be wrong. I mean, there's no way general relativity is correct. Why not, Well, it flies in the face of the nature of the universe as we know it. We know that the universe is quantum mechanical. We know that nothing is smooth and continuous. But general relativity assumes that the universe is smooth, it's continuous, that you can like slice up space and time into infinitely small pieces, that you can know everything about the configuration of particles, for example. It just ignores the fundamental nature of the universe that's been revealed to us over the last one hundred years. And that's why it breaks down. For example, we have singularities at the hearts of black holes and at the beginning of the universe. Those singularities reflect a failure of the theory. So it just can't be right and yet it works.
So darn well, well you don't think it works. But maybe there is a singularity. I don't know, isn't that possible.
Well, we talked about this in our fun episode about singularities. But singularity is like a mathematical oddity. It's like an infinity. It's a failure. It's like when the theory is going, I don't know, you know, it's not a real prediction, Like you can't actually have infinite density. It's nonsensical.
It's like, it's like having an infinite universe, which I hear you support as a theory.
That's true, And it certainly could be that weird mathematical features of the universe that we dismiss as artifacts could actually be real. Right, it wouldn't be the first time that had happened. But it seems to me like a failure. And also it seems to me impossible to reconcile general relativity's view of the universe as smooth and continuous with this quantum mechanical nature of the universe. We see that it's discrete, we see that there are smallest bits, We see that there is limited information. So we're desperate to know the true story of the universe how it actually works. But to do that, we need to see Einstein's theory fail. We need to find a place where it's wrong.
Yeah, and that's really hard because so far as you said, Einstein's theory is pretty good. It's past every test with flying colors.
It's got an A plus plus plus plus plus plus, Like, nobody's ever seen general relativity get anything wrong. No matter what configuration of matter or weird effects you study, or crazy intense things going on in the distance universe like black holes colliding, general relativity gets it spot on.
Yeah. And so there's a big question of whether or not Einstein's theories are ultimately correct or not. And there is one experiment right now, right above you, most likely trying to figure that out.
That's right. We physicists are inventing more and more crazy scenarios to try to test the details of these predictions of general relativity, hoping to get it wrong, hoping to find a scenario where Einstein's theory fails and forces us to come up with another theory, or like gives us a clue as to how to formulate that next theory.
So today on the podcast, we'll be talking about what is frame dragging? Now, I have to say, Daniel, it feels like a disappointing title. After all that build up. I felt like we should have, you know, probing the mysteries of the nature of space and time. But know you were going with what is frame dragging?
Well, that's because frame dragging is one of the mysteries of space and time. It's one of these bizarre effects predicted by in our relativity that people go out to see, like is this actually real or is it just a mathematical artifact or was Einstein wrong?
Or it could just be that you're taking a picture frame and dragging it across the floor. It could go either way.
Yeah, it doesn't really conjure up the gravity of the situation if you ask me.
But coincidentally, it does have to do with gravity, right, and Einstein's theory about how it all works.
Yeah, and reference frames like this idea of where you put your axes, your X, Y and z and how you measure your position and your velocity is absolutely fundamentally central to the whole concept of relativity. And so you know that gives you clues to what it might be about. And I think this is a super fun topic and I especially hope that it's being enjoyed by one particular listener out there. Heis from the Netherlands. He wrote to us last week and he said that he really liked our podcast, but that it had led to more than one occasion in which he burned dinner.
Oh no, well out of frustration or of just not paying attention.
Apparently, he listens to our guests while he's cooking, and when things get really complicated or interesting, he ignores what's on the stove and these things go up in flames. Wow.
I feel like we're destroying this person's family life here, if not his actual at home.
Yeah. He also said that his kids know not to ask him anything or for anything when he's listening to the podcast, because he'll just ignore them.
He or she should invite their kids to listen with him her which kid doesn't want to know about frame dragging.
Yeah, so pay attention to the podcast, learn the secrets of the universe, but also don't burn your dinner.
Sorry, flip the chicken right now, good before it gets overcooked.
Yeah, let's pause so that he's can finish the dinner.
All right, Well, this is an interesting question, and so as usual we were wondering how many people out there had even heard of this question and what it might mean or even have an answer. So, as usual, Daniel went out there and ask people on the internet what is frame dragging?
So thanks to everybody who was willing to play along. And if you have listened to the podcast and chuck along with these answers but never contributed your own, please write to me to questions at Danielanjorge dot com and volunteer. I promise it's fun.
Here's what be glad to say.
I'm going to guess that it has something to do with photography, maybe photographing of planets in a three dimensional space where we can only view them in a two dimensional aspect. We take enough pictures of the two dimensional aspects to drag them together to create a three dimensional picture.
Frame dragging is when it's moving day and none of your friends show up to help. Frame dragging. From Phazic's point of view, I don't know.
I have no idea frame dragging nothing, all right, Not a lot of people seem to have a good idea here, like the one who said it's moving day and none of your friends want to help you move drag your art frames around.
Yeah, that's a great one. Should have ordered more pizza man, sorry.
Or yeah, you know, hired perhaps so. Yeah, it's a pretty interesting question because it doesn't sound physics z. But I'm guessing it has something to do with maybe like frames of reference or coordinate systems or something like that.
Exactly, it has to do with a really bizarre prediction of general relativity. Remember that general relativity is Einstein's theory of gravity and replaced Newton's theory. Newton says two objects with mass will pull on each other, that gravity is a force, but Einstein tells us that gravity shouldn't be seen as a force. It's actually just due to the fact that space and time curve around massive objects. And if you can't see those curves, like we can't detect them directly, then things will move in a surprising way, and they move as if they were under some force. And that's what gravity is. It's the effect of the curvature of space time itself. Most of the time, those two things totally agree. Like you could treat gravity as a force like Newton did, or you could treat gravity as the bending of space time like Einstein does. It doesn't really change the way the Earth moves around the Sun, for example. But there are some cases where they disagree, and that lets us probe Einstein's theory as different from Newton's theory.
Really, I thought it was sort of like mathematically burned in that it was the same thing. But no, there are exceptions.
No, they are fundamentally different ways of seeing the universe, and they give different predictions in some cases. In almost every case they don't, which is why Newton's theory worked so well. Right, Newton got a lot of stuff right, because for the most part his theory is correct, and like, that's a lesson getting a bunch of experiments right, And like nailing predictions for hundreds of years in a row doesn't mean that your theory is fundamentally true. It doesn't mean that it's an actual description of nature. It just means the experimentalists having come up with a way to break your idea. Yet.
Yeah, And I imagine for Einstein it was a little bit like it is now for us with him in that you know, at the time, Newton was like the eyesight of this day and for him to be like, I think Newton's wrong, people were like, what you think you're smarter than Newton.
Or for sure. And remember that Einstein is further in time from Newton than we are from Einstein. So I think Newton was probably like an even grander, you know, person in the history of science due to the passage of time, like his ideas had stood longer, and whereas Einstein, like, you know, you can see movies of the guy, you know, he's like a real person.
Well, they are the effects of internet relativity, which you know makes time seem to go faster, all right, So there are instances where Einstein's theory of special relativity is different than Newton's, and so we can test whether or not the theories are correct exactly.
And it really comes down to things spinning. Like for Newton, it doesn't really matter if the Earth is spinning, its gravitational pull on the Moon is the same. Like for Newton, the only thing that gravity depends on are the masses of the two objects and their relative distance. If you know Newton's equation gmm over R squared, there's no factor in there that can be influenced by the fact that the Earth is spinning. It's irrelevant because like the configuration of the mass doesn't actually change. Right, If you have a perfect sphere and you spin, it doesn't change the distance between any of the objects. But for Einstein's theory it does matter.
Right, But as long as the I guess the center of mass of the Earth is kind of on the spin axis, right.
Yeah, If you have a perfect sphere and it's spinning around its center, then its gravity is totally unaffected by its spin, according to Newton, because the only thing that Newton cares about is the relative distance between two little bits of mass, and so if that's not changing, then the gravity shouldn't change at all, right.
And specifically like between the center of masses of the two things. Right, that's the only thing that counts for Newton.
Yeah, for Newton, that's all that counts. You can treat the Earth, for example, as if it was a point particle with the same mass, and you put that point particle at the center of mass, and all the other effects of some things being closer and some things being further away cancel out, which is a pretty cool, nice simplification. It makes a lot of physics much easier to do.
But Einstein's special relativity is not the same.
Einstein's theory of general relativity says that spin does matter, that the way an object spins affects the way that it bends space and time, and that will change the gravitational effect on objects moving around a spinning Earth versus a non spinning earth, and we can do experiments to see if that's correct.
Wait, what you mean the spinning somehow changes the way it's bending space around it. Yes, even for a perfect sphere.
Even for a perfect sphere, what it does is it drags the space around it a little bit. It pulls the space itself, and that's why they call it frame dragging. It's sort of like if you had a ball and you dipped it in honey, and then you spun the ball a little bit. You would get the honey dragged along with the ball, right, There'd be a little bit of friction, they would pull it along with it. Einstein says that if you have a really big massive object, then you spin it, then you drags space itself along with the object. So they should have called it like space dragging or something, but they call it frame dragging.
You said it and not I. It should have called it a better name, for sure. But what do you mean, like a drag space. How can you drag space?
Long?
Like, how can you pull on space?
Yeah? How can you pull on space?
Right?
Well, what is eu in space? We don't know. But space can do a bunch of weird things, right. It can bend, and it can ripple, and it can twist. So what we talk about when we say space is curved, really what we mean there is not that it's like curved like a big sheet relatives to some other direction. But we're changing the relative distances between points in space, so that, for example, the shortest path from A to B is no longer what you would imagine to be a straight line, but a different path because the distances between the points along the way have been shrunk. So in the same way, you can talk about dragging space with you as this weird effect an additional sort of curvature of space, Like when an object is spinning, it curves space differently around it than if it isn't spinning.
Does that due to the fact that, you know, maybe the particles or the masses at the surface of the sphere have some kind of velocity and so there's some sort of you know, sort of lag in its effect to the things around it, or how would you explain what's causing that dragging of space?
You're right that Newton assumes that gravity is instantaneous. Like in Newton's world, if an object disappears, then it's gravity disappears instantaneously, even for objects really far away. But in Einstein's world, gravity takes time for information to propagate. So if the sun disappears, we don't notice that for eight minutes. In this situation, I don't think that's the explanation for frame dragging, because frame dragging exists even in a object that's been spinning for like a long long time, and then it's no change, no update, you know, like information needs to propagate, so it can be like a steady state situation. It's not like a transient effect. A better way to think about it is as the gravitational version of electromagnetic induction, if you're familiar with that concept.
All right, well, let's get a little bit deeper into this frame dragging and most importantly, how could we measure it and potentially prove Einstein wrong. But first, let's take a quick break.
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All Right, we're talking about proving Einstein wrong, and there's a bunch of people out there trying to do this. Right, there's an official government funded experiment trying to prove his theories wrong.
Yeah, there's lots of ways that we've been testing Einstein's theories. One, of course, was just like looking for black holes. That was a prediction of Einstein's theory, which turned out, of course, to be correct. Another is gravitational waves. People were looking to see if space itself would ripple when two black holes orbit around each other and then finally gobble each other up. And you know, we saw those. That's pretty awesome. And so all of these things are tests of Einstein's relativity. But there's a series of folks developing like hyper sensitive tests to look for like these like small little deviations because we can't like organize our own black hole experiment where we're like shoot one black hole at another, so we have to do the experiments here on Earth. And because gravity is so weak, the effects are really really small. Effects that are like really dramatic when black holes are involved, are really not very dramatic when ping pong balls are involved.
What about black pingo balls?
Oh my god, we didn't try that.
Hold on a second, yeah, yeah, noble price please. All right, So one of these effects that you're trying to test is called frame dragging, which is how a spinning object kind of drags space around at the edges. But there's another effect that has to do with gyroscopes, right.
Yeah, All these effects can be well measured by gyroscopes because what they do, in effect is makes something spin. Like the Earth has its gravity, it's pulling on you, but if it's spinning, its gravity will also give you a little bit of a twist. And so we measure these things by using gyroscopes. And you're right, there are two different effects that can happen to a gyroscope. Here, one is this frame dragging effect, and the other is this really awesome effect, this geodetic effect. It's called that lets you measure the curvature of space directly. You can exactly measure whether or not space is curved by putting a gyroscope in orbit around a planet.
Now, a gyroscope, again, is just like a spinning mass, right exactly.
You take something and you spin it, and you try to make it really precise so it doesn't wobble, and because of a conservation of angular momentum, if nothing touches it, it should keep spinning. Right, So, if there are no external forces on a spinning object, it should keep spinning the way like if you push something in outer space, it should keep going forever unless something stops it. Because of angular momentum. If you spin something like the Earth, and the Earth is a gyroscope, it should keep spinning. And so you can measure if there's any force on a gyroscope by seeing if the angle of its spin changes or if its spin rate.
Changes, and also like if it starts tilting too right.
Mm hmm exactly, they call that precession. So if you put some force on a gyroscope, you could slow it down or you could change the angle of its spin if it tilts a little bit.
And so that's what these experiments are. There's one in particular called the gravity pro B experiment.
Yeah, these are really fun experiments. Basically, somebody said, what if we take a gyroscope and we put it out in space and we orbit the Earth. Now, Newton says that if the gyroscope is perfect and the Earth is the spear, et cetera, et cetera, that gyroscope, once you started spinning, will spin forever the same way, and orbiting the Earth Earth will have no effect on it. Right because orbiting the Earth just pulls on it and it has gravity. It makes it orbit, but it shouldn't change the direction of the gyroscope. That's what Newton says. That the gyroscope will forever point the same direction, but the geodetic effect and the frame dragging effect, both of them will twist this gyroscope a little bit. So they came up with this experiment, gravity probe B, which is basically nothing but like a really super duper precise gyroscope in space in orbit.
Around the Earth on a like a satellite, right.
Yeah, it's its own space craft. It's its own satellite just dedicated to actually these four spinning balls moving around the Earth.
So it's a pro because it's an experiment and it's probing gravity, and it's B because it's the second one. Right. Gravity Probe A was another experiment.
Yeah, that's right. Gravity Probe A was a different space based experiment to probe gravity, but it was probing a different feature of gravity, and it used like a totally separate setup. It had like a hydrogen maser on it, and it was measuring the equivalent principle whether gravity is really the same as the acceleration. You know, the whole idea of Einstein's general relativity is that gravity, this force we feel, is just the curvature of space. And so they were out there to measure whether you could tell the difference between like the curvature of space and other accelerations, and of course they found that you couldn't.
Yeah, so the Gravity Probe A confirm Einstein's theory, so it didn't prove him wrong. And now we have launched this Probe B to further test that, and that was launched a while ago, right, almost fifteen years ago.
Yeah, I was launched in two thousand and four, and they sent it up there and they studied these gyroscopes for a couple of years before they got the results. But this is a really really hard experiment. Like, not only is it really complicated, because like even understanding the general relativity of whether testing is complicated, but building a gyroscope that's sensitive enough to see these effects, which are really really tiny effects is just like a huge technical challenge.
Because I guess these effects of gravity are not that strong around us like here and on Earth, because the Earth is not that massive, you know, astronomically speaking, like if you were in a black hole. Around a black hole would be easier to measure these things.
Yeah, if you had stronger gravity experiments, these things would be obvious. And also if these things were obvious in our environment, we would have noticed them, right. Newton would have had to incorporate them into his theories just to get like the orbits of the planets right and stuff. And so these are very very small effects, which is why you need very very sensitive experiments because remember gravity is actually a very very weak force, like it dominates the universe in the end, controlling its structure. But it's a very weak force compared to everything else. You know, you can overcome gravity with a simple kitchen magnet. Every bolt of lightning has a lot more energy than the gravitational field of the Earth, and so it's hard to see a very small effect gravitationally because you have to isolate it from everything else.
I guess maybe it wouldn't have been easier to send these pros like to orbit Jupiter or something, just something heavier.
It's so easy to orbit Jupitery or the Sun, Right, why don't just send it into the Sun.
Why don't they put me in charge here?
No, you're right. It's definitely would have been an advantage to have a more massive object, But it's also just harder to control and communicate with a satellite that's much further away, and it's just it takes years to get there, and you need propellant and you can't repair it and all this kind of stuff. So it's just easier to work in near earth orbit.
All right, So let's just maybe describe for folks how this experiment works. I mean, we know it's got a little tiny gyroscope inside of it, but how does that work? What does the gyroscope look.
Like, so the gyroscope has to be super super accurate. What you really would love to do is just have a spinning ball in space and nothing around it, just like totally isolated. Have a ball spinning in space and measure as it goes around the Earth whether it's direction of spin is changing. But of course you can't just put a ball in space. You have to measure it somehow, and you have to protect it. So they built this whole spacecraft round this spinning ball, and they want this ball to be spinning, but they don't want the spacecraft to touch it. So what they do is they have this ping pong ball sized sphere of quartz, and it has to be really super spherical because if it's lopsided in any way at all, then it will like develop a wobble and then you won't be able to measure these really small effects. So they spent like a decade perfecting how to make the roundest object in the history of humanity.
What they spent ten years just polishing this little ball.
Yeah, they'd mine this perfect quartz in Brazil and then they have this factory in Germany which can like polish them and melt them and get them in exactly the right configuration. And this thing is I'm not joking, the most spherical object ever manufactured. Like it has its own entry in the Guinness Book of World Records.
Wow.
Well, so, first of all, it's a perfect crystal like it's one perfect lattice of quartz atoms, and then it's been polished and shape to be this the roundest thing ever.
The roundest thing ever. It's three ten millions of an inch from perfect sphericity. Like the difference between you know, the radius at one point and the radius anywhere else is this infinitesimal amount. It's amazingly smooth.
Wow, I'm imagining some you know, old German person with a little polishing cloth going r rub for ten years. Is that how they did it?
Yeah, that's basically it. That's basically it. And they have to make four of these things because they wanted independent measurements. So they have four of these things. And like to give you a sense of how smooth this is, if you took one of these things and you blew it up to be the size of the Earth, then the difference between like the highest mountain and the deepest trench would only be eight feet.
So it's like it's smooth at the atomic level.
Yeah, there's forty layers of atoms. Difference between the highest peak on this thing and the deepest like scratch on it, forty atoms. So that German lady over there polishing it, you know, she's doing it atom by atom.
So then you take these small quartz balls and then you spin them up. Then that's your gyroscope. Do you put four of them and you spin them up before you launch them, or do you spin them up once you get the space.
You spin them up down here on Earth, right, because you've got to test them. But then you also spin them up and get them started up there in space. But you can't just like touch them. You can't, like if you touch this thing, then you'll ruin it, right, And so they spin them up first, they levitate them electrostatically by you know, having this like electric field, and then they spin them up by shooting a stream of helium at them. They get them going four thousand revolutions per minute.
Wow, Like it's got little jets of helium, you know, hitting it kind of on the sides.
Yeah, exactly. It provides a little torque by shooting this stream of helium at it and then it evacuates the chamber so there's no helium left. So you have this whole spacecraft and it's sort of surrounding this levitating ball of spinning quartz, but it's not touching it.
Oh, I see, it's just floating in space. But it doesn't drift to the size or anything.
Have these electrostatics to try to keep it from drifting to the side, because the spacecraft can drift a little bit, right, or something hits the spacecraft, then it might bump into the ball. So they have these little like electrostatic controls to try to like push it along with the spacecraft. It's sort of like that game operation. You know, you got to like not touch the sides ever, or you got a big buzz.
Yeah, And I guess if Newton was right and Estein was wrong, then this little quartz ball would keep spinning for a really long time, Like you know, it would just be spinning in space, no friction, no air resistance, so it just spin for a really long time. Right.
Yeah, if we've done it perfectly, it would spin forever. Right. They've not done it exactly perfectly, but they estimate that once they spin this thing up, it shouldn't slow down due to friction or impurities for fifteen thousand years, which is a pretty awesome feet of engineering.
And then you said they put up four of these, there's like four different spacecraft or like one spacecraft with four little quartz balls.
It's one spacecraft with four little quartz balls in them. And that way they get like not totally independent measurements, because four totally separate spacecrafts would cost a lot more. This way, if one of the balls goes wonky or has an impurity in it, they have like three backups. But they ended up all four of them working and giving them measurements. And then they combine the information from all the balls in that one spacecraft to give them a measurement of these procession effects.
Okay, so I guess then the question is, once you get these little balls spinning, do they spin like that for fifteen thousand years or do they start wobbling and wiggling due to general relativity? So let's get into how they measured that wobble and what does it all mean, Daniel, But first let's take another quick break.
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All right, we're talking about frame dragging and the gravity pro b experiment and how it's trying to prove Einstein wrong. All right, I said, so far, we've put these four perfect quartz balls up into space, we spun them up, and now we're trying to see if somehow the dragging of space by spinning Earth will somehow make these balls wubble exactly.
So there's two effects we're looking for here, one is the geodetic effect, which measures the curvature of space itself, because a gyroscope going around the Earth direction it's spinning will actually twist a little bit because the space in its vicinity is a tiny bit curved, and that applies basically a little force different from the actual just force of gravity pulling it towards the center of the Earth and gives it a little twist. Right, the force of gravity just pulls towards the center of the Earth. This geodetic effect gives it a little spin. And the frame dragging is a separate effect that's pulling space along with it, and it gives it a different kind of spin. So we're looking for two different sort of spin changes in these gyroscopes. One tells us about the geodetic effect and the other one orthogonal to it, tells us about frame dragging.
And so we're trying to measure really small wobbles in these spinning balls. And so how do we measure these things?
Yeah, that's a real challenge, right, You got these spinning balls, you don't ever want to touch them. So how do you tell how a perfect sphere is spinning? If you can't even touch it right. So what they do is they coat the spheres with super conducting niobium. It's this weird element and if you get niobium really really cold, and when it spins, then the charges niobium generate a magnetic field, and so you can measure the direction of the magnetic field, which tells you exactly how this sphere is spinning without touching the sphere itself.
Oh interesting, it's like you cod it with sort of like a magnet type of thing, and then since it's spinning, it generates a magnetic field that you can measure if it wobbles or not.
But it's a very very slight magnetic field because it's a very thin layer of niobium, and you want to put a very thin perfect layer on it so you don't ruin, you know, the polishing job that your germ and buba has done. And so they have to use these really cool magnetometers called squids that are these fun quantum magnetomic devices that we should do a whole other podcast about. But they're very very sensitive to very small magnetic fields. These are magnetic fields or like one ten billionth of the earth magnetic field, so you can't just like put up any compass up there, you've got to have a really sensitive magnetometer.
Oh wow, but doesn't man like probing this magnetic field also affect the spinning ball, Like, isn't there like a danger of like accidentally pushing it when you're when you're trying to poke it.
Absolutely, And that's why you don't want to have like another magnet up there. So you have this squid device which is very very sensitive and minimally feeds back to the spinning sphere. Which you're right. You can't measure anything in this universe without affecting it, and that includes magnets. Right, use a magnetic probe to probe magnets, it's going to have a little bit of a feedback effect. But here they think that that feedback effect is negligible compared to the magnetic field it's being generated.
All right, So then these magnetometers are super sensitive. If the little ball's wobble by even a one tenth of a milli arc second, which is like like a billions of a couple of billions of a degree, right, then they would notice.
Yeah, that's right. And so it's just super incredible that they even built this thing. And you know, it took decades and decades. People have been thinking about this for a long time, but they're all these engineering problems, like how do you get a gyroscope this smooth, how do you measure it, how do you keep it from bumping into the spacecraft? How do you develop a magnetometer or this sensitive? So all of these different problems were like total roadblocks for a long time, and then one by one they were able to overcome them and actually put this thing together and actually build it and send it into space and make it work. So it's a real tourative force of engineering and physics together.
So it went up into two thousand and four, and they got results in two thousand and seven, so we know what happened.
We do know what happened, And because Einstein is still taught in school, then you'll know the answer already, which is that they confirmed Einstein's prediction. So Einstein's theory can be used to predict exactly the curvature of space as you go around the Earth, and the geodetic effect is twist on the gyroscope. It can also be used to predict how much space is being dragged along by the Earth and this gives a smaller effect in a different direction. And so they saw both of these and both effects are totally consistent with what Einstein predicted.
No way, So like we send these things up there, and they did exactly what Einstein predicted, Like you can see how these things wobble due to the bending of space, exactly.
You can see these things get twisted by space itself. It's hard to think about how gravity can make something twist, right, Like we're familiar with gravity making something move in a circle, but actually, like also given a twist, it's because it's twisting space as well, right Like when space gets dragged along by the Earth, it makes these weird, sort of sheer effects in the fabric of space itself, and those come out to be like a little twist. I think it's also maybe helpful to try to visualize what's going on with the geodetic effect. You're probably familiar with, Like how you can measure the curvature of space if you take like a triangle and you add up all the angles, and on flat space, if you add up all the angles, then they all add up to one hundred eighty degrees. But on a curved surface, you might get different angles. Well, there's another even cooler way to think about how space is curved, and that's by thinking about a circle. You take a circle that's on a flat space and you compare its radius to its circumference. Then the relationship is tupi. Right. That's famous, of course, But if space is curved, then that no longer holds because, for example, the radius can get longer if space is curved. So imagine, for example, a circle around the Earth, and if the Earth wasn't there, you could measure the radius of that circle. You know where the center of the circle would be sitting nominally at the center of the Earth, and that would be the radius of the Earth, and the circumsance of the circle would be the circumference of the Earth. But because space is bent, then the path actually gets a little bit longer, right, because like imagine, for example, you have like a circle with a bubble in it. If you move along the bubble, then you're going to measure larger radius than if you're just moving exactly towards the center.
Right. It's like trying to measure the equator from the north pole. You'd have to sort of go around the curvature of the Earth.
Yeah, and so what we're doing here is we're sort of measuring, you know, pie in some sense, we're measuring whether moving around the Earth sort of lines up with the radius of the Earth. So that's one thing that the geodetic effect is measuring, is the local curvature. And if there was no curvature in that space, then moving around the Earth a gyroscope wouldn't process at all. But because there is that little bit of curvature, then things don't quite line up. You know, the radius and the circumference don't have the right relationship. So you get this very small effect that's the geodetic effect.
Cool, and so the gravity pro b confirmed this, like these are super tiny, subtle effects. But this instrument actually wasn't able to measure this bending of space. I feel like it brings it all really home, you know, it's not just something that's happening around the edges of black holes. It's like, you can measure the bending of space around the Earth, like a few miles from where you are right now.
Yeah, if you have thirty years, eight hundred million dollars, you too can measure the curvature of space.
Yea Bezos could do this a couple of times.
Yeah, you could do it before lunch, but you're right, it's a real Twitter forest. It's amazing. It's a big effect at black holes, and it's a really almost negligible effect here. Like, nobody needs to include these calculations even in their satellite navigation problems. You know, nobody needs to worry about these things now.
But they're included in the GPS calculations, right, Like the GPS in your phone takes into account the curritual space or the effects of relativity.
Still they the GPS in your phone definitely takes into account the effects of relativity, but that's mostly the time dilation, the fact that down here on Earth we're closer to the Earth's gravitational well, and so time moves a little bit slower. So relativity is all sorts of effects. These effects, the geodetic effect and the frame dragging effect don't need to be included in GPS. If they did, then we could just use GPS directly to measure them. But you need like a special, super isolated, complicated experiment just to prove that these effects even exist, so we can safely ignore them in GPS calculations. But You're definitely right. GPS uses other effects of relativity.
Right, Yeah, I guess. I mean, you know, like the basically that bending on spacetime that Einstein figured out, it is, it's in our everyday lives.
It is.
It affects our lives. It determines whether or not we get where we're going.
All right, So then Einstein was right. No surprise there, I guess. I guess we're people expecting him to be wrong. They were they hoping he was wrong? Or are they happy to confirm it.
I think that the guys who built this satellite wanted him to be right because they set out to measure it, and, you know, to prove that this effect is real. So I suspect they wanted him to be right. But I was rooting against Einstein. I definitely wanted him to be wrong. Oh man, I got nothing against the guy. I mean, I don't know him at all. But it would be super cool to measure a different effect, right, to go up there and have these super sensitive devices that can measure the curvature of space and you see something weird, something non Einsteinian, something that gives us a clue about how the future theory of gravity needs to look.
So you always I want everyone to be wrong, Daniel, that seems like a difficult perspective to have as a collaborator.
No, but together we all want to discover flaws in our theory because those are the potential learning moments. Right. When our theory predicts something that doesn't happen, or fails to predict something that does happen, that's a time when we can pull on that thread and unravel some mystery and reveal something deep about the universe. So it's cool that Einstein was right. It's awesome. It's need kudos to these folks who built this experiment. But I think would have been much more cool if they saw something weird and new that gives us a clue about how to build a theory of quantum gravity.
Right, or at least maybe like a clue as to how to put together you know, general relativity and quantum mechanics, right, because that's still the big mystery, and probably confirming this further, it just makes it harder to figure out what's going on.
Yeah, we're sort of stuck, right. I deeply believe that Einstein's theory can't be a real description of nature. But until it fails, we don't really know what to replace it with. We don't really have a better idea, and people are working all sorts of stuff string theory and loop quantum gravity, and we have podcast episodes on that you can check out. But so far none of those really work. None of those succeed in unifying quantum mechanics and gravity, and so we're still a lot of loss. And you know, we could continue to work theoretically, just like waiting to have a good idea, but I'm hoping to get a clue experimentally. I'm hoping to break one of these things to see some new weird effect that requires us, that inspires us to come up with a new theory.
Right, and you're a quantum physicist, so I'm going to assume that you're just going to by default, root for the other team to be wrong.
That's what experimentalists try to do. Right. We're not out to just confirm people's theories as correct. We're out there to discover new stuff, to see weird things in the universe that give you clues just about how things really work.
Well, in this case, they confirm Esein's theories, and it's pretty cool that you can go out there and see the bending of space, or at least measure it with really acrid balls made out of course, but you know it's something you can measure and test and probe and get data on and know that it's actually happening in this universe.
Weird stuff like that predicted by this beautiful mathematical theory is real. Like space really is getting twisted around the Earth. This is not just a calculation. This is our universe.
All right. Well, we hope you enjoyed that, and please remember to turn your chicken or turn off the stove as you listen to this podcast. We don't want to cause any accidents out there, at least not here on Earth, maybe in space.
It's all right, and pay attention to your kids.
Well, thanks for joining us, See you next time.
Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeart Radio. For more podcasts from iHeart Radio, 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. How is us dairy tackling greenhouse gases? Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's last sustainability to learn more.
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