Are Magnets The Most Familiar Mystery On Earth?

Deep beneath our feet, churning molten metals create an invisible shield that holds our atmosphere in place and protects all life from the Sun. Some animals can sense it directly. Take the quantum effects in a robin’s eye, whales who cross oceans using no landmarks at all, or the bacteria that line themselves up to this unseen force. Join Professor Hannah Fry and Michael Stevens as they explore magnetism and ponder how a compass knows where to point? Where did the original source our magnetic field come from? What that field might feel like? And why magnets just be the most familiar mystery on Earth. ------------------- For more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit ⁠⁠https://cancerresearchuk.org/restisscience ⁠⁠ Cancer Research UK is a registered charity in England and Wales (1089464), Scotland (SC041666), the Isle of Man (1103) and Jersey (247). A company limited by guarantee. Registered company in England and Wales (4325234) and the Isle of Man (5713F). Registered address: 2 Redman Place, London, E20 1JQ. ------------------- Find The Rest Is Science all over the internet by ⁠⁠clicking here.⁠⁠ ------------------- Video Producer: Adam Thornton Video & Social: Bex Tyrrell Assistant Producer: Imee Marriott Producer: Becki Hills Senior Producer: Lauren Armstrong-Carter Head Of Digital: Samuel Oakley Exec Producer: Neil Fearn Learn more about your ad choices. Visit podcastchoices.com/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Hannah Fry?

  This episode is brought to you by Cancer Research UK.

• 0:02Michael Stevens?

  Dinosaurs walked the Earth 180 million years ago. But you know, cancer was part of their story, too. Scientists have found tumors in ancient fossils.

• 0:13Hannah Fry?

  Well, that is a part of the reason why cancer is a big, big part of our story, right? It's the other side of evolution. It's the most complex disease that we face. There are more than 200 types of cancer in total, each with distinct characteristics, challenges and mysteries.

• 0:28Michael Stevens?

  And that complexity demands scale. Cancer Research UK is the world's largest charitable funder of cancer research, with more than 4,000 scientists, doctors and nurses working across more than 20 countries in the search for answers. And then sharing their discoveries beyond borders.

• 0:45Hannah Fry?

  And the impact of this collaboration is clear, because over the last 50 years, the charity's pioneering work has helped to double cancer survival in the UK. That is more people who are living longer, better lives.

• 0:57Michael Stevens?

  Fossils can show us the past, but research is shaping the future. And for more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit cancerresearchuk.org/restisscience.

• 1:14Speaker 02

  Observe the North American dad. 50s, great polo collection. He enters his vehicle information on Carvana. An offer appears in minutes. Remarkable. He squints, reads it again, smiles and says, "Dang, that's a good offer." The highest form of approval. No haggling, no hassle. No one called him "boss." He's still on the couch. Astonishing. Sell your car today on carvana.com. Pickup fees may apply.

• 1:45Speaker 03

  This episode is brought to you by Indeed. You're ready to level up your business, but the pressure to find the right person to make that happen is intense. Indeed sponsored jobs can help carry the load. It boosts your job post to help it reach quality talent fast. Cut through the chaos with Indeed sponsored jobs. Get a $75 sponsored job credit at indeed.com/podcast. Terms and conditions apply. Hiring now? Then this is a job for Indeed sponsored jobs.

• 2:21Hannah Fry?

  Welcome to The Rest Is Science. I am Hannah Fry. I'm a mathematician. If you cut me open, I would bleed equations. But I have been making science programs for about a decade or so.

• 2:32Michael Stevens?

  And I'm Michael Stevens. I am a barbecue pit master in my personal life. But you may know me from my YouTube channel, Vsauce, where I make science content, math content, psychology content, whatever I'm interested in. And today I'm interested in magnets. Why do we live on a magnet? Can animals feel magnetism? And I'm going to talk about how I believe that humans can feel magnetism emotionally. But first of all, Hannah, how do magnets work?

• 3:03Hannah Fry?

  I mean, I can give you a sciencey sounding answer about electrons and about spin and about spin cancelling each other out and the properties of particular atoms. But if you really want to know how they work, I mean, at some level, it's going to involve acceptance, Michael.

• 3:21Michael Stevens?

  It does. At some level, we have to just say magnets work because we find ourselves in a universe where they do. It is a fundamental ingredient in our universe, just like gravity. The thing is, people don't question gravity in the same way because we experience it so often. It's normal that things fall.

• 3:40Hannah Fry?

  It's a little bit like saying, well, how did your aunt end up in the hospital? You say, oh, well, because she fell over on some ice. And it's like, okay, but why?

• 3:49Michael Stevens?

  Yeah. Feynman draws this great comparison to asking how magnets work and why they work to, well, what level of explanation do you want? She's in the hospital because she slipped on the ice. Why did she slip on the ice? Well, because ice is slippery. Yeah, but why is ice slippery? Well, because water expands when it freezes. And so a pressure that compresses it causes it to melt a little bit. So you're actually standing on a liquid layer on ice. Well, why does water expand when it freezes? Well, the molecular properties of water are quite unique.

• 4:21Hannah Fry?

  Hydrogen bonds.

• 4:22Michael Stevens?

  And this goes on and on. But why did she slip? Well, because she's old. Well, why does that? That affected, well, because your balance and your muscle control changes. And psychologically, maybe she was distracted. And suddenly you realize there is no end. Same with magnetism, same with gravity, same with everything. Okay, the Insane Clown Posse asked, just a few months ago, Donald Trump, the President of the United States, said, no one knows what a magnet is. And they got ridiculed for statements like that.

• 4:48Hannah Fry?

  I don't know who Insane Clown Posse are.

• 4:50Michael Stevens?

  Are you not a juggernaut?

• 4:52Hannah Fry?

  Do I look like a juggernaut?

• 4:54Michael Stevens?

  Well, no, but I thought for the show, you like wash off the makeup. Is this not Fago?

• 4:59Hannah Fry?

  I really am that boring, Michael.

• 5:01Michael Stevens?

  My goodness. All right, look, so years ago, in a song called Miracles, they rapped about magnets.

• 5:08Hannah Fry?

  Yeah.

• 5:08Michael Stevens?

  How do they work? And a lot of people ridiculed them for that statement.

• 5:14Hannah Fry?

  Because this is the thing, right? You can, you can answer it at different levels. You can start off and you can say, you take a particular type of metal, something like iron, and you interact it with an existing magnetic field. There is a force of attraction or repulsion that appears. And then you could go a bit deeper. And you could say, there are field lines that appear around a magnetized object, which you can see with iron filings. And you go a bit deeper still, and you could say, down at the, the, the level of electrons, it's to do with the spin cancelling out or not in some materials. You kind of keep going and keep going and keep going. But ultimately, even once you're taking quantum effects into account, there, there is always a level at which you just have to sort of say, because it is?

• 5:56Michael Stevens?

  Yes, there's a level where you have to say, look, ultimately, it is an intrinsic property of our universe. In the same way that there is gravity. Why? Well, I don't know. If there wasn't, maybe we wouldn't have evolved to ask. But that's a just so story. Even the, the magnetic field lines you see when you sprinkle iron filings on a magnet, even those aren't showing you the field as it was before you sprinkled it. The iron affects that field. So you're seeing the iron's effect on the magnet. But what did it look like before? It just was. And so, well, I think, I think that, yeah, if you want an answer, when people start making fun of those who are curious about magnets, you're right. It's ultimately the existence of charge,

• 6:42Michael Stevens?

  like the electromagnetic force as a thing in our universe, is a property stuff has. And we know that when charges move, they create a magnetic field. They just do. Okay. But here's the thing. Electrons are charged, and they move, in a sense, around a nucleus. But they don't spin. And yet, we say they have spin.

• 7:07Michael Stevens?

  Okay, we're getting really into the weeds here, because there is, there is no quick answer. But if we, if we accept that electrons have a charge, and that they move in certain ways, some of which don't involve movement at all, spin, I'm looking at you. They create a magnetic field. And those magnetic fields tend to be not lined up in most things. But in certain materials, they can line up and have a macroscopic manifestation. And that's what a magnet exhibits.

• 7:36Hannah Fry?

  In iron, in nickel. I mean, very few things that actually have magnetic properties.

• 7:41Michael Stevens?

  That's right.

• 7:41Hannah Fry?

  And we just so happen to be living on a planet full of the stuff.

• 7:45Michael Stevens?

  But how did the Earth get magnetized? I remember being a kid, doing the magnet thing in like, 4th grade, and you would take a, a paperclip and swipe it over a magnet over and over again. And now, the paperclip is a magnet. Did someone do that to Earth?

• 8:00Hannah Fry?

  Well, the Earth is sort of doing it to itself, inside. And within, within the Earth's, you know, if you're going to go down into the center of the Earth, you have this, this solid iron core, and then you have this, this sort of magma, right? This sort of swirling metallic substance. And because the Earth is spinning, but also because it's very, very hot in the core and cooler at the outside, you have these currents. So this, this magnetized metallic liquid is continually moving around. That's one of the things that supports and continues the, the fact that the Earth has this magnet within it.

• 8:35Michael Stevens?

  So what we don't know is where it started. We know Or at least there's the theory, the geodinamo theory that says that moving conductive liquids can maintain and even grow a magnetic field. Do they produce one by themselves? I don't think so. But if there's another magnetic field around, like say from the early sun, the sun may have been much more magnetic when it was young. And the earth could have been in that stronger magnetic field. It's sloshing around this molten iron. And that magnetic field gets kind of ripped and stretched. And it can persist because of this rolling motion. And it still persists persists today.

• 9:18Hannah Fry?

  Because I think this is it, right? Okay, we started off by joking about how no one knows how magnets work. But why is the earth itself a magnet? I mean, this is a very strange thing, if you think about it, that north and south, magnetic north, magnetic south, which by the way, ever so slightly different from from geographical north and south, that they are there and can be sensed by aligning magnets floating them on water. Like, why is that? Where did the earth's magnetic field come from?

• 9:47Michael Stevens?

  Yeah, we don't totally know. It's not like the earth has a giant horseshoe shaped wily coyote magnet inside of it. What the earth does have inside of it, though, is a lot of metal. It's got a solid metallic core because pressure is so high. A little further out, it's got molten metal, mainly iron. There's some nickel, there's some sulfur, there's other stuff there, but most of it's iron. And iron has a property where its atoms can get lined up. But the iron in the in the in the outer core is too hot to be a magnet. Okay, like a magnet couldn't even survive down there, and yet it's magnetic. So there's this whole theory called geodinamo theory, which says somehow a spinning planet that's cooling, that has molten ferromagnetic metals in it.

• 10:32Michael Stevens?

  Will have swirls of this fluid because of its own rotation. And a moving electrically conductive fluid can grab on to a magnetic field and hold it so that it persists and can even grow. And so at some point in Earth's history, it grabbed on to a magnetic field, maybe from our young sun, which may have been more magnetic in the past, and it's just been holding on to that. I mean, it's not like there's a battery down there that's sending current through wires. It's just that deep inside the planet, there's molten metal that's moving and somehow that motion amplifies or holds on to magnetic fields, like a dynamo that keeps this magnetic field alive.

• 11:14Michael Stevens?

  So the solar wind can stretch it and shape it, but the source is within. We're carrying it with us. And that means the entire Earth is just this big magnet covered in life.

• 11:25Hannah Fry?

  Because the fact that the Earth is spinning is key here, right? And the fact that the Earth is cooling down is also key because you have this temperature difference between that really, really hot center, the central core, and then it's much cooler the outside as you get towards the Earth's crust. That temperature difference, it's sort of like, imagine a pot of water. As it's boiling, you have this circulation current that happened from the very hot bottom to the much cooler top, which moves the water around in the same way that it's moving all the liquid inside the Earth around. But then also the spin on the Earth is helping as well. You have this Coriolis effect. So you get all of these little eddies, these little currents, these little swirls inside

• 12:03Hannah Fry?

  of the Earth, and that is what is perpetuating this magnetism that somehow or other initially arrived on Earth that the Earth has grabbed on to and kept going for all of these billions of years.

• 12:18Michael Stevens?

  You know what's exciting is that just recently, we managed to create a geodynamo in a lab.

• 12:24Hannah Fry?

  Oh, yeah.

• 12:24Michael Stevens?

  So researchers took a two Cubic meter vessel of molten sodium, which is really electrically conductive. And they spun it up like in a giant blender so that parts of it were moving at like 15 meters a second. And sure enough, it like took the existing magnetic fields in the room, one of which was from Earth, and held on to it and magnified it. And even after they stopped spinning it, it maintained that magnetic field. That's probably what Earth does.

• 12:57Hannah Fry?

  But this is what's so strange because it's like, okay, well, where did that original magnetic field come from? Because it's not there anymore. I mean, you used to get a little bit of magnetism from the sun, especially when you have solar flares and so on, but but it's, I mean, not enough to have that there must have been some seed somewhere at some point that originally this this kind of intergalactic bar magnet.

• 13:19Michael Stevens?

  Yeah.

• 13:19Hannah Fry?

  Like that sort of floated past our planet that gave it the original magnetism.

• 13:25Michael Stevens?

  I know, like some aliens came by on their bar magnet ship four and a half billion years ago. And they were like, oh, crap, we just made a mess of that planet. They tried to clean it up and they were like, it's not going away. We'll just get out of here and don't tell anyone. But thank goodness, our planet is a magnet because that magnetic field interacts with charged particles that fly at us from the sun and protect us. They they redirect those particles so that our atmosphere isn't just obliterated by them.

• 13:54Hannah Fry?

  This is where you get the northern lights, right?

• 13:56Michael Stevens?

  Exactly.

• 13:57Hannah Fry?

  But it's where the Earth's magnetic field is concentrated, sort of exiting, exiting from the north and south. And then that is where you see these northern lights is interacting with the with the sun's magnetic.

• 14:08Michael Stevens?

  Yeah, the charged particles get funneled into the atmosphere there. They create these beautiful lights, but that also protects our atmosphere as a whole from just being peeled away by this powerful radiation. Mars, not a magnet.

• 14:21Michael Stevens?

  And guess what? Tell me about its atmosphere.

• 14:22Hannah Fry?

  Mm hmm.

• 14:23Michael Stevens?

  Does it protect the Martian surface from ultraviolet light?

• 14:25Hannah Fry?

  Absolutely not.

• 14:26Michael Stevens?

  Think again.

• 14:27Hannah Fry?

  Mm hmm. Serious sunburn on the surface of Mars.

• 14:29Michael Stevens?

  Serious sunburn.

• 14:30Hannah Fry?

  They call it the red planet for a reason.

• 14:32Michael Stevens?

  That's right.

• 14:33Hannah Fry?

  Well, one other interesting thing about the fact that it is this geodynamite, right? The fact that it's the swirl of the inside of the Earth that is that is creating this magnet or that is allowing this magnet to exist means that it's nowhere near as stable as you think. And the really nice thing is you can see in rock, especially when you have volcanoes, for example, as lava ends up solidifying, if there's iron inside of that lava, the iron will line up with the Earth's magnetic field, then cool and then get frozen in place, which means that you can go back really, really ancient lava flows and you can see the direction that the Earth's magnetic field was pointing in. And it's not always that north is north and south is south.

• 15:18Hannah Fry?

  This thing has flipped. It's flipped many, many, many, many, many times over the history of the Earth.

• 15:23Michael Stevens?

  Do you think it's bad when it flips?

• 15:25Hannah Fry?

  It'd be pretty confusing, wouldn't it? If you were out on a sailboat.

• 15:29Michael Stevens?

  That would be a hilarious, like, public announcement. Hey, everyone, compasses still work, but like opposite the way they say they do.

• 15:37Hannah Fry?

  Exactly.

• 15:37Michael Stevens?

  Like, the end that's painted red is now gonna point south for maybe only 12 years, maybe for another few million. We think Earth's magnetic poles flip, on average, about every 450,000 years.

• 15:51Hannah Fry?

  But we're in a long stretch of stability now, right?

• 15:54Michael Stevens?

  Yeah, it's been about 800,000 years since they flipped. So some people say we're due for a flip and it's gonna be catastrophic, but.

• 16:02Hannah Fry?

  It probably takes about 1,000 years for the flip to actually happen.

• 16:05Michael Stevens?

  Oh, it's not, it's not like an instant.

• 16:06Hannah Fry?

  It's not like you wake up one day and north is south and south is north.

• 16:09Michael Stevens?

  Oh, bummer.

• 16:10Hannah Fry?

  That's, that's not how it works.

• 16:12Michael Stevens?

  I think that sometimes these reversals might be.

• 16:16Michael Stevens?

  Just another consequence of something else terrible that happened? Because we can't find that extinction events and pole reversals might line up. It could be that an impact creates a lot of volcanoes and change in Earth's interior that can lead to a switch. But really, the animals all died, not because of the magnetic switch, but because of the ash in the air, because of the impact. Also, Earth's magnetic north pole is actually Earth's south magnetic pole.

• 16:46Hannah Fry?

  Oh, really? Is it upside down?

• 16:48Michael Stevens?

  Yeah.

• 16:48Hannah Fry?

  Oh!

• 16:49Michael Stevens?

  It's upside down. Because we made up a rule of how to name the poles of a magnet. And we use the right-hand rule.

• 16:57Hannah Fry?

  Sure.

• 16:57Michael Stevens?

  If electrical current flows this way, from my palm to my fingertips, using my right hand, my thumb points in the north direction.

• 17:03Hannah Fry?

  That's up.

• 17:04Michael Stevens?

  Yeah, so we make magnets, because we had to arbitrarily decide which one's north, which one's south.

• 17:08Hannah Fry?

  And this is the field that you can see if you put in ion filings, effectively. Which way around is it wrapping from the?

• 17:12Michael Stevens?

  That's right. And so, yeah, you turn some current on through a coil, goes this way, that way's north. Oh, shoot. When you make a compass using this mechanism, the north points to the north. But they should repel, since they're the same? Which means that actually, as a magnet, Earth's north pole is its south pole.

• 17:33Hannah Fry?

  Tell you what I don't understand, and I've actually, until, literally, this conversation, I have never thought to be curious about it. When it flips, right? On the occasions when it flips, it does, it is that north and south swap. It's not like suddenly north is at the equator. And presumably, that must be because of the spin. That must be because of the coriolis.

• 17:51Michael Stevens?

  Well, it can. There's a thing called an excursion, where the north pole doesn't just, like, flip, but it, like, goes to the equator and back.

• 17:59Hannah Fry?

  It wobbles.

• 18:00Michael Stevens?

  It can, yeah, it can wobble quickly.

• 18:02Hannah Fry?

  But it's stable along that axis, right? Of like, the north-south axis.

• 18:06Michael Stevens?

  It's most stable that way, yes.

• 18:07Hannah Fry?

  Because of the Earth's spin.

• 18:08Michael Stevens?

  Because of the Earth's spin.

• 18:09Hannah Fry?

  But why doesn't it exactly align with the geographic north? Because geographic north-south is, is if you put a skewer through the Earth on the axis that it spins around, that would be the geographic north-south, and then the magnetic north-south is ever so slightly off.

• 18:25Michael Stevens?

  Yeah.

• 18:25Hannah Fry?

  Why? I don't know.

• 18:27Michael Stevens?

  I don't know either. They're different by about 11 degrees. And the magnetic pole keeps moving. It's moving from Canada to Siberia right now. It's actually quite close to the geographic north pole, the actual pole that the Earth spins around.

• 18:44Michael Stevens?

  But it used to be much further south, down into Canada. It moves at about 40 kilometers a year, about 25 miles a year at tops, from what we've observed. I've always wanted to go there and watch a compass needle stop pointing in some direction, like on the surface, but just point down. Like, that right there, that's it.

• 19:07Hannah Fry?

  Yeah, here you go. Okay, because you basically have this kind of boiling blob of liquid metal that is wobbling around all over the place. And it just wobbles roughly in the same place as this kind of skewer through the Earth and the way that it spins.

• 19:23Michael Stevens?

  I don't know what causes it to drift around and not keep lining up with our rotation axis. But there are a lot of factors that affect Earth's magnetic field. Even the tides and the motion of the ocean changes it because salt water is electrically conductive. And so, it's a mess. If you want to be really precise by using a compass, you're going to notice that, like, it's just not... It's all over the place.

• 19:51Hannah Fry?

  Also, the Earth's spin is not absolutely consistent.

• 19:53Michael Stevens?

  No, it isn't. It isn't. But why 11 degrees?

• 19:58Hannah Fry?

  But then I think maybe we're just thinking about it as though, at this moment in time, it's 11 degrees. But we shouldn't think of it as static in time. It's something that's just...

• 20:06Michael Stevens?

  That's right.

• 20:06Hannah Fry?

  If you sped it up and watched it over the last, you know, four billion years, it's kind of all over the shop.

• 20:11Michael Stevens?

  Yes, and it and reversals seem very random. They don't seem to correlate with any, like, known other process.

• 20:19Hannah Fry?

  Okay, I'll tell you what else would be different. If it did flip, not only would sailors end up going in the wrong direction, but there is one paper that came out about 10 years ago that talked about dogs pooping. Have you heard about this?

• 20:34Michael Stevens?

  I have. Is it true?

• 20:36Hannah Fry?

  I don't know.

• 20:37Michael Stevens?

  First of all, tell our listeners what you're talking about.

• 20:39Hannah Fry?

  All right, so this is a paper, it was called Dogs Are Sensitive to Small Variations of the Earth's Magnetic Field, published in 2013, peer reviewed, right?

• 20:47Michael Stevens?

  Sure, yeah.

• 20:48Hannah Fry?

  Frontiers in Zoology was the journal. And I mean, credible researchers, over a two-year period, they followed 70 dogs from 37 different breeds, they recorded the directions of the dog's spines during their defecations and their urinations, and they demonstrated statistically that they appeared to align with the Earth's magnetic field direction.

• 21:12Michael Stevens?

  When they pooped.

• 21:12Hannah Fry?

  Yeah. One thing I will say is that there have been replication studies on this, people have tried to repeat the experiment and have not found a statistical correlation.

• 21:22Michael Stevens?

  I'm not surprised. I believe a dog could maybe sense Earth's magnetic field.

• 21:27Hannah Fry?

  Yeah.

• 21:27Michael Stevens?

  However, why they would want to poop facing north, I don't know. I can't think of a helpful evolutionary reason.

• 21:34Hannah Fry?

  No, I agree with you. I agree with you. But that's interesting, though, that you wouldn't be surprised if they could sense it.

• 21:41Michael Stevens?

  Yeah.

• 21:42Hannah Fry?

  Because, I mean, you and me sitting here, how's your sensation on the magnetic field of the Earth?

• 21:46Michael Stevens?

  I can't feel it.

• 21:47Hannah Fry?

  No.

• 21:48Michael Stevens?

  I'm not aware of it. It's happening, it's going through my body, I am in it, and yet I don't feel it.

• 21:54Hannah Fry?

  It seems as though other creatures can, and that is what we're going to be talking about once we come back after this break. If you happen to be listening to this podcast while out on a dog walk, just whip out a compass and take notes of which direction. Maybe we should turn this into a citizen science experiment.

• 22:07Michael Stevens?

  I love that, an experiment. Take photos of your dog pooping, send them directly to Hannah, right? Yeah. We need close-ups, guys. It's for science.

• 22:16Hannah Fry?

  My email address is [email protected].

• 22:29Speaker 03

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• 23:35Michael Stevens?

  Welcome back. Good to see you. Hannah, we were talking about dogs. We were talking about defecation.

• 23:41Hannah Fry?

  Uh huh.

• 23:41Michael Stevens?

  Let's change the subject.

• 23:42Hannah Fry?

  Okay.

• 23:43Michael Stevens?

  But not totally. I want to keep talking about animals because there's evidence that many animals, many living things on Earth can actually sense and like feel Earth's magnetic field.

• 23:53Hannah Fry?

  Of course there is. I mean, if you take migratory birds, for instance, how on Earth? This has been a question, a longstanding question over hundreds and hundreds of years. How do robins, for example, know where they're going? How do they move around to different climates, fly south for the winter? And there was always this question of how on Earth do they know where they're going? And it looks like, and looks like actually is the operative word here. It looks like they are seeing the magnetic field of the Earth.

• 24:23Michael Stevens?

  It looks like they're seeing it.

• 24:25Hannah Fry?

  Looks like they are seeing it.

• 24:26Michael Stevens?

  Tell me more.

• 24:27Hannah Fry?

  Okay, so back in the 1960s, they had some experiments where they put robins in, in special cages, which had sort of like a type of paper on the outside. So if the bird wanted to fly, its wings would just hit the paper, leave ink on the paper, and you could tell which direction they were aiming for.

• 24:45Michael Stevens?

  Right.

• 24:45Hannah Fry?

  Okay. Now, these particular cages were also sort of cone shaped, so the bird was sort of sitting in the middle, and as it would fly up, you could tell. And then what they started doing was they started messing with the magnetic field around this particular cage. Measure with the intensity of it, measure with the direction of it, measure with the inclination of it, which direction the the field lines are going in. And they demonstrated that the birds would change the direction they wanted to fly in based on what was going on with the magnetic field.

• 25:13Michael Stevens?

  Ah.

• 25:14Hannah Fry?

  So this is like back in the 1960s and people are like, okay, cool, right? That's so robins are using the magnetic field of the earth or magnets somehow.

• 25:21Michael Stevens?

  They have some form of magnetoseption.

• 25:25Hannah Fry?

  Exactly.

• 25:26Michael Stevens?

  Sense not just light and sound and touch, but magnetism.

• 25:29Hannah Fry?

  I mean, honestly, magnetoseption makes it sound like it deserves its own superhero series, right?

• 25:35Michael Stevens?

  Because we use it to describe superheroes because you it's just unbelievable that you could sense this thing that we did not evolve to sense.

• 25:43Hannah Fry?

  Totally, but here is where it gets even wilder because it looks like the sensing is all going on inside the eye of the robin. So there's a very particular protein that appears in a robin's eye. It's called a cryptochrome. And when blue light hits this protein, it forms this pair of electrons whose spin becomes quantum entangled. Okay, so essentially what happens to one happens to the other. I mean, that's the most ridiculously oversimplified explanation of quantum ever, but just go with me for a second.

• 26:13Michael Stevens?

  Yeah, I'm going.

• 26:14Hannah Fry?

  Okay, so here's the thing, the earth's magnetic field, which is incredibly weak when you're talking at this this scale, but it's enough to really subtly change the probability that that pair of electrons will either recombine or separate out. So I mean, effectively, what's happening is it has this protein, which is so sensitive to magnetic fields, that where the magnetic field is present or stronger or or which direction it's going in, it changes the chemistry in the retina, essentially. And that pattern, that chemical pattern, is interpreted by the robin's brain.

• 26:54Hannah Fry?

  So what we think it's actually seeing is this sort of faint ghostly pattern that aligns with magnetic north. So it's it's not like it's not like a metal detector, it's not got like a compass inside it. We think that it sees the magnetic field of the earth as a kind of directional glow within its field of vision.

• 27:17Michael Stevens?

  Wow.

• 27:18Hannah Fry?

  Isn't that amazing?

• 27:20Michael Stevens?

  So it's probably a visual phenomenon.

• 27:24Hannah Fry?

  Probably a visual phenomenon.

• 27:25Michael Stevens?

  Either things are glowing a bit more north or south.

• 27:29Hannah Fry?

  It's not like its head sort of like to a magnet.

• 27:31Michael Stevens?

  It's not like the eye is being like pulled a little bit all the time.

• 27:35Hannah Fry?

  Don't think so.

• 27:35Michael Stevens?

  And they're going, oh, once it gets cold, I need to start following that pull. But maybe it's when it gets cold, I need to follow the glow. And I want to say brightness or color because it could be a third thing.

• 27:46Hannah Fry?

  Absolutely.

• 27:47Michael Stevens?

  That's also visual that we've never seen. Wow.

• 27:49Hannah Fry?

  Isn't that great? And here's the other thing about it. I mean, well, okay, there's many, many great things about this. For starters, that idea of kind of quantum chemistry wizardry, like normally it doesn't really work when you interact it with sort of squishy bits of flesh, you know? Like biology and quantum is it's very, very difficult to get these effects to work. And this is something that's happening at, you know, bird's eye temperature, you know, within a biological being, which is really extraordinary.

• 28:20Michael Stevens?

  A being that literally has a bird brain.

• 28:22Hannah Fry?

  Literally, literally has a bird brain. It brings a whole new meaning to bird's eye view too, doesn't it?

• 28:28Michael Stevens?

  It does.

• 28:29Hannah Fry?

  Suddenly bird's eye, this bird, particular bird's eye has got a quite interesting view. We also now know because of the experiments that they've done, that it's not the intensity of the magnetic field that it is, that it's sort of seeing or being drawn to. But the thing that that that makes it know where it is, north or south, is almost certainly the inclination of the magnetic field. Let me explain that ever so.

• 28:55Michael Stevens?

  Yeah.

• 28:55Hannah Fry?

  So if you imagine the earth as though it's like a barge magnet with iron filings around it, that those iron filings would go in this sort of a direction. So they kind of come out, they spurt out from the top where the the north pole is. From from from now on, I'm going to use inverted commas.

• 29:11Michael Stevens?

  Sure, fine.

• 29:13Hannah Fry?

  They spurt out from the north and then they go around the earth and then re-enter.

• 29:17Michael Stevens?

  In like a hoop, like ears on the earth.

• 29:19Hannah Fry?

  Exactly. And so if you think about it at the equator, those lines are effectively going parallel to the line of of of the earth itself. Whereas when you're up at the pole, they're coming straight out. They're going sort of, they're coming perpendicularly out of the ground.

• 29:35Michael Stevens?

  Yeah.

• 29:35Hannah Fry?

  And so you will be able to tell how far north or south you are by looking at the angle that those field lines make with the ground that you see beneath you. So what we think that they are doing is that is what is they are sensing the inclination

• 29:51Michael Stevens?

  Right.

• 29:52Hannah Fry?

  of those field lines. And the reason why we know this is because, uh, once again, you can put this, put the robin very safely and, you know, ethically in this particular cone shaped cage with the, with the paper on the outside. And you can rotate the inclination angle using something called a Helmholtz coil, essentially a big electromagnetic device. Let's say the bird wants to be in South London. Okay. Uh, this particular time of year, that's, that's where it wants to be. If you change the angle of, uh, inclination of, of, of the magnetic field so that suddenly it believes that it is in Scotland, for

• 30:32Hannah Fry?

  instance, uh, then the bird, the robin will demonstrate something called, uh, Zugrue, which is German for migration anxiety.

• 30:40Michael Stevens?

  Nice.

• 30:41Hannah Fry?

  Which is like, okay, get me, get me the hell out of here. I do not want to be here. So you can trick the bird into believing that it is at the wrong spot on the earth, which is something that it is seeing with its eyes.

• 30:54Michael Stevens?

  Sees with its eyes.

• 30:55Hannah Fry?

  Isn't that amazing?

• 30:57Michael Stevens?

  We've got to teach birds to paint.

• 31:00Michael Stevens?

  And get them to go, oh yeah, you know, here's what an apple looks like. But then they draw all of these like lines on it. And we're like, what's that? And they're like, well, that's the magnetic inclination. You do not see that?

• 31:10Hannah Fry?

  Come on, you dumbass.

• 31:11Michael Stevens?

  Yeah, right? How do we do that? Okay.

• 31:14Hannah Fry?

  Isn't that good?

• 31:15Michael Stevens?

  That's really cool.

• 31:16Hannah Fry?

  It's not just robins that have this, by the way. There's, there's a, a number of different creatures that have this same protein. But there are other animals that do these long migration patterns that appear to be using magnetic field of the earth to navigate, but that aren't necessarily doing it in exactly the same way. So whales, for example, um, if you look at, uh, blue whales and humpback whales, their paths along the ocean, they follow these magnetic contour lines, essentially lines of constant magnetic strength, of the field strength. It's almost like they're sort of reading this invisible map on the seafloor.

• 31:53Michael Stevens?

  Right.

• 31:54Hannah Fry?

  Choose the shortest path, they don't, you know, kind of.

• 31:56Michael Stevens?

  They're not just going perpendicular to the motion of the sun.

• 31:59Hannah Fry?

  No, no.

• 32:00Michael Stevens?

  It's correlating with the magnetic field line.

• 32:02Hannah Fry?

  Exactly, exactly. And so the theory is about whales is that there's sort of this, this, um, this hierarchy of things that they're following. So number one is the magnetic field of the earth. Then they're also using things like the ocean soundscape, things like the smell or water chemistry. But the coastline, the seabed depth, that kind of thing. But then something that can muck it all up is the sun and the stars. And if the sun has a bit of a hissy fit, by which I mean chucks out some unexpected magnetic nonsense, it can mess whales up.

• 32:39Michael Stevens?

  So like when there's a lot of sunspots, because sunspots are aberrations in the earth's surface, where areas become cooler because of like a bunch of magnetic flux right there that's stopping convection from happening. And by the way, sunspots are not dark. They look in a photograph like a big black spot, but they're really still extremely bright. They're just so much less bright than everything that's hot around them. They look dark.

• 33:02Hannah Fry?

  Right, exactly. Or solar flares, anything like that, anything that's really sort of.

• 33:06Michael Stevens?

  Magnetically noisy.

• 33:07Hannah Fry?

  Magnetically noisy. And there was a very famous pilot whale, a mass stranding of pilot whales in the Canary Islands. This is in two thousand and two. And everyone was like, how on earth did this happen? These poor whales that have shown up, uh, you know, they, they shouldn't be here in the first place. And then a team of scientists later worked out that there had been a large solar storm that had hit the earth's magnetosphere. Again, sounds like a superhero character, frankly, but had, had hit the earth's magnetosphere exactly the same moment that the whales went off course. And again, and again, and again, when whales end up being stranded,

• 33:48Hannah Fry?

  people can usually tie it back to some kind of disruption in the earth's magnetic field by a solar event or even a, a, a further distant celestial event that's going on.

• 34:00Michael Stevens?

  Wow.

• 34:01Hannah Fry?

  One of my favorite stories about animals getting lost because the sun's having a hissy fit is, um, in nineteen ninety seven, there was this big race, because there's still like pigeon fanciers in the UK, right?

• 34:11Michael Stevens?

  Sure.

• 34:11Hannah Fry?

  People who race pigeons.

• 34:12Michael Stevens?

  Yeah. I'm sure. I'm one of them.

• 34:16Hannah Fry?

  Do you know what? I absolutely believe you.

• 34:19Michael Stevens?

  I do too.

• 34:21Hannah Fry?

  I'm sure there's some who are listening. In fact, I would love to hear from a pigeon fancier, a real one.

• 34:25Michael Stevens?

  I could talk your ear off all day about pigeon fancying, pigeon racing.

• 34:30Hannah Fry?

  Pigeons in general, actually. I'm just, I'm, I'm quite into pigeons. Anyway, 1997, there was this big race that was being held in the UK. And in that one day, 60,000 pigeons went missing. And it was because there was this intense solar activity.

• 34:46Michael Stevens?

  Oh, the poor guys.

• 34:48Hannah Fry?

  I think in the pigeon fancying community, of course, you'll know this already. It's got a particular name, this event, right?

• 34:53Michael Stevens?

  When, when the birds get all messed up by a solar event?

• 34:56Hannah Fry?

  But, yeah.

• 34:57Michael Stevens?

  Yeah, yeah, we call it going birdzirk.

• 35:02Hannah Fry?

  You've given yourself away now. You were telling the truth all along. That's not what it's called.

• 35:07Michael Stevens?

  Oh, I did. Well, that's what we call it in my bird circle.

• 35:11Hannah Fry?

  Yeah, it's called, it's called the great pigeon race disaster of 1997.

• 35:15Michael Stevens?

  Ah, yes. See, I'm part of the pigeon fanciers reform chapter and we call it the day the pigeons went birdzirk. But go on.

• 35:24Hannah Fry?

  I just love the idea, though, that we are existing in exactly the same world as these pigeons, as the robins, as the whales, and yet we have no idea.

• 35:35Michael Stevens?

  It makes me feel really sad for them, that on a, a, a day of heavy solar activity, I'm just like, ah, this is kind of a boring astronomical event for me. But the whales are all like dying.

• 35:45Hannah Fry?

  Yeah.

• 35:46Michael Stevens?

  They're freaking out, the sun's louder than usual, whatever it is that they see is different, like, reality has changed suddenly. And I'm just like, oh, yeah, I don't know, I got like stuff to do.

• 35:58Hannah Fry?

  The thing is, is I think there is some evidence that humans do feel this.

• 36:02Michael Stevens?

  Go on.

• 36:03Hannah Fry?

  We have these cells in our body, they've got tiny little iron crystals in them, it's called magnetite. And, I mean, these are like responsive to magnetic fields, you know, in the same way a compass would be. So, so in theory.

• 36:19Hannah Fry?

  We do have something in our bodies that does, that is capable of changing according to whatever the magnetic field around us. There was also, there was one experiment where they put people, they wanted to see whether anything would change about us if you put us in these really strong magnetic fields. They got a bunch of people, they put these caps on their heads, the EEG caps, little electrodes that monitor brain activity essentially. And then they changed the direction of the magnetic field inside the chamber at these strengths that are similar to that of the earth, without letting the participants know that that was what they were doing. And they did find something kind of interesting, which is that there was a drop in the alpha brainwaves.

• 37:03Hannah Fry?

  So these are, it usually means that the brain is processing something when you have.

• 37:06Michael Stevens?

  So the brain might even process it, but it just doesn't tell our awareness.

• 37:10Hannah Fry?

  Just doesn't tell us. Because, I mean, as far as we know, right, we just, we're kind of wandering around unaware of this. We don't really.

• 37:17Michael Stevens?

  It wasn't relevant to our survival like it was for birds, for whales.

• 37:22Hannah Fry?

  Sure.

• 37:23Michael Stevens?

  But we might still have like an evolutionary vestige of the ability to sense it, but we have since stopped listening.

• 37:30Hannah Fry?

  Perhaps, yeah, yeah.

• 37:32Michael Stevens?

  Here's the thing, though. We don't feel magnetism consciously, but we're very aware of it. Like, we feel it not because of an organ, but because of, well, an organ, the brain. It's curious. We notice things. And we go, why is this compass needle doing this? Why is this magnetite, this lodestone, why is it attracted to the other one? Now, animals notice this too, but they don't care. We looked and we cared and we like, put it to practical use and we studied it and we learned about the spin of electrons, we learned about charges, we learned about the fundamental forces of the universe.

• 38:12Michael Stevens?

  And so, so to what extent do we feel it, not as a sensation, but as a result of an emotion, curiosity that we have? Curiosity is an emotion, it moves us to do or not do things. And when humans see evidence of magnetism, we get curious. We investigate it, we ask questions. How do they work? And in that way, we're moved to learn and study.

• 38:39Hannah Fry?

  In the sense that maybe we can't see it with the same bird's eye view that the robin can. But actually, we can see it because we've built technology in order to trace its path, in order to follow it, in order to use it for navigation in exactly the same way as the birds do.

• 38:55Michael Stevens?

  Exactly. Birds use it to navigate and we don't. We do, it's called a compass. But we had to use cognition, driven by curiosity, to do it. It's like curiosity is this sixth sense that encompasses all the things that we weren't built or no longer can feel, but we want to feel.

• 39:14Hannah Fry?

  That we don't have the biology for, but we do have the brain power.

• 39:17Michael Stevens?

  Right.

• 39:18Hannah Fry?

  You know, do you know about the history of the compass? I really love this. It's exactly as you're saying. So it's like, it dates back to like, second century B.C. in China.

• 39:28Michael Stevens?

  Right.

• 39:28Hannah Fry?

  And like, there's lodestones, these sort of naturally magnetized iron ore, this sort of rock that you can find lying around in certain parts of the earth. And people notice that if you put it on water, it will orient itself, float in a particular direction. And this, you know, when they first appeared, I think people weren't using them for navigation. That happened a lot later. I think they were using it for feng shui, for divination, that kind of thing. But you're right, that it's the curiosity of like, what is this weird rock? And what, why is it changing direction when I float it on water?

• 40:04Michael Stevens?

  They use it for divination?

• 40:06Hannah Fry?

  Yeah.

• 40:06Michael Stevens?

  That would be clever. I could be like, all right, look, honey, I'm going to put this rock on this floating pad in some water. And I don't know, if it points that way, you have to wash the dishes. Oh, what do you know?

• 40:18Hannah Fry?

  Yeah, actually, when they first arrived in in Europe. So I think China started using them for navigation.

• 40:25Michael Stevens?

  Okay.

• 40:25Hannah Fry?

  Uh, knowing which way is north, of course, if they already knew that there was an object that always pointed in the same direction.

• 40:32Hannah Fry?

  They started using them for navigation about the 11th century A.D.

• 40:35Michael Stevens?

  Okay.

• 40:36Hannah Fry?

  And when they started arriving in Europe, people were like, okay, there is something deeply not okay going on.

• 40:44Michael Stevens?

  Sure, yeah.

• 40:45Hannah Fry?

  This is witchcraft, this is like wizardry, there's like devil going on here. And they didn't want to use them at all. And I think that is hilarious because the actual answer of what's really going on, you know, that no, it's not witchcraft or wizardry. It's instead there's a planet scale ledger magnetic field that's generated by this, you know, rotating molten iron core of hundreds of kilometers beneath your feet. So much, much, much weirder.

• 41:09Michael Stevens?

  And yes, I mean, we associate magnets with magic. Like, how did that magician do the trick? It was smoke, it was mirrors, it was probably magnets, right? And yet we associate superheroes with magnetic abilities. Because we feel, I think, kind of divorced from it in a way we don't feel separated from gravity. I feel quite close to the weak and strong nuclear forces, but most people don't. But we just don't encounter them. We encounter gravity and magnetism. And we want to know more about why. They seem weird, they seem magic.

• 41:41Hannah Fry?

  I mean, that's it, right? It is weirder than magic. It is more extraordinary than that. And yet, over the centuries, collectively, we've dug into it. Maybe not to the point where we can, we can fully, fully, fully explain it. There comes a point where you have to just accept it. But nonetheless, we have uncovered this thing that is weirder than magic.

• 42:02Michael Stevens?

  So at the end of the day, like, we don't feel magnetism. We don't feel Earth's magnetic field, but we do feel curious about it. And I really mean feeling in the sense of an emotion that causes motion, moves us to behave in certain ways. It causes us to build compasses and navigate and study animals and put them in boxes and point magnets at them and see what they do. And so we have come to navigate using Earth's magnetic field, not because it's an instinct, but because we're curious.

• 42:35Hannah Fry?

  Well. If you're a curious person, you've come to exactly the right place because that's what me and Mike are here for.

• 42:40Michael Stevens?

  We are magnets for the curious.

• 42:42Hannah Fry?

  Hey.

• 42:43Michael Stevens?

  Tagline that.

• 42:44Hannah Fry?

  As ever, we really want to hear from you and the things that you're curious about, too. So you can email us at [email protected].

• 42:53Michael Stevens?

  Or sign up for our newsletter at therestis.com/science.

• 42:58Hannah Fry?

  See you next time.

• 42:59Michael Stevens?

  Next time. See you then. Bye.

• 43:02Hannah Fry?

  Bye.

• 43:17Speaker 05

  Here we are getting a statement from Number 10 on that flight with 350 passengers on board.

• 43:25Speaker 06

  The Great Game: Strategic Struggle Between Britain and Russia.

• 43:31Speaker 07

  We assess, Prime Minister, with high confidence it was Russian.

• 43:39Speaker 02

  Holding the Russians accountable is World War III.

• 43:41Speaker 08

  They took down a British passenger jet containing 350 people.

• 43:44Speaker 06

  Man in the Kremlin is playing, Alex. Got to ask yourself, do you want to play or not? You're the Prime Minister. You've done nothing!

• 43:58Speaker 02

  We would need to understand the policy context.

• 44:00Speaker 06

  All the relevant context will be structured as a framework today and disseminated into an operation order, or FRAGO.

• 44:09Speaker 09

  A FRAGO that says to kill the President of Russia?

• 44:13Speaker 06

  Yes.

• 44:15Speaker 10

  New from Goldhanger. Who is going to be able to pull this off?

• 44:20Speaker 11

  You're my soldier, are you? Sergeant Tom McDuff, Duffy!

• 44:24Speaker 10

  An audio drama journey like no other.

• 44:26Speaker 12

  Men like Duffy, they are our most valuable weapons.

• 44:30Speaker 10

  Devized as a technically rigorous geopolitical action thriller. We have two tight, friendly KIA. Where Britain plays its strongest hand. He's the best. Against its strongest foe. Don't do it, Duffy! Bear Hunt. Available now wherever you get your podcasts.