Quantum Birds

0:28Wait, you're listening. October, I traveled to a mountain in Pennsylvania. It's dusk. It's a place called Hawk Mountain Sanctuary. And I was there to join a group of volunteer researchers to wait in the cold and the dark. Hoping to catch some owls. Catch some owls? Yes, but not just any owls. These were northern saw-wet owls. Do you know what a saw-wet owl is? No. What is the deal with these birds? So I'm going to be dryly scientific here. and describe northern solwood owls as cosmically cute birds. Okay. Because they are. So Scott Wadensal here, he's a natural history author. He was actually the guy that invited me up to come see these owls.

1:12They're the smallest owl in the east. They're about the size of a soda can. And do you ever just take one and put it in your pocket? We're not allowed. They're like kittens. They're kittens, but they're owls. They have these huge eyes. They weigh a little bit more than a robin. And to catch them... Oh, this net is so thin. Hopefully they won't see it. You have to string these wispy black nets up in the woods. Just fire it up. Watch your ears. You set up speakers, and you blast this sound. What is that? Uh, that is a recording of a mating call of a male sawwood owl. Sounds like a truck backing up.

1:48It's the sexy sound of love if you're a female sawwood owl. You're romantic. Anyway, so you get all that stuff set up. You walk away from the nets. You hunker down and you just hang out, like play cards and stuff. Yep. And why are they trying to catch these owls? Well, they're migrating owls. So if they can tag them. We can find out how long these birds live, where they travel. Do they come back to the same place every year? Do they have the same mate every year? Do they go to the same place in the winter? It's like they get this window into the bird's life, which is great and cool. But actually, the reason I was there that night, was because I had recently become really obsessed with a very particular part of a bird's body.

2:29What part? What's the part? I will tell you in a minute. But anyway, so we got the net set up. And then after sitting around for a whole hour... Are you going up? We're going up. We'll go see what's... Oh my gosh. We went to check the nets.

2:47And in the first hour... Looks like no owls in the nets. There were no owls. So don't be discouraged. Not at all. We didn't catch anything in the first net check last night, and then we had a very busy night. And in the second hour... Okay, second time looking at the nets. There were... No owls again. No. Does WNYC have a reputation for being a jinx? Oh, no. Do you think that's what... No. And at some point in the night, we had been joined by this group of kids, this young birders club, and they were so excited to see owls and they were being amazing sports. But, you know, it was past their bedtime.

3:26It was getting colder and colder. Stars are coming out. Like the wind was picking up and these nets were just so empty. Ah, man. And I started to have this thought like, man, we are just sitting in the woods listening to a garbage truck backing up and owls are not coming. It's about nine o 'clock at night. But then on the third hour... I'm taking the nets again the third time.

4:02I think there might be one.

4:07There's one. Owls. There's an owl. Wow. There's two of them. In the glow of my headlamp, I could see these two tiny bundles of brownish-white feathers caught out of the air like fish in a net. Oh, I can see a yellow eye. Wow. Got him? The volunteers detangled them from the nets. Come on, open up your little channel. And brought them down to the kids. He's looking at me. And they watched as they were weighed and measured. And we put a little leg band with a nine-digit unique serial number on their leg. And then Scott did this very surprising thing. I'm going to lift the facial disc away here. Like, you know, they have these disc faces.

4:56Yeah. Scott gently lifted forwards one side of the owl's face. And you can actually see that ear opening. And it reveals this crazy inner head world of the owl. Why did you get there? It was like this surprisingly deep ear hole. It had this sort of like inner cave thing, all these nooks and crannies. And it was all covered with like a very thin layer of pinkish skin. But the wildest part was that... That gray thing you see is actually the back of the eyeball. You can see the back of the huge bulging eyeball in its head. Like you see it. It's a little trap door to the back of the eyeball. Yeah, pretty much.

5:40Oh my God. I couldn't believe it. Why would their face open like a door? I don't know, but it was amazing and it was so weird. And, and like, I was so excited that we got to see this owl's eyeball. Like so much of it. That was the coolest thing I've ever seen. Because, like, that's kind of the whole reason I was there, to take a good look at the eye of a bird. Hmm. Okay. How come? Because I had recently learned that it's possible that one of the biggest biological mysteries of all time, this fleshy, feathery animal mystery, could be answered finally by tapping into the most abstract, far-out-there hidden realm of the universe.

6:30A place where the laws of space and time are completely upended. And that all of that is somehow happening somewhere inside. She's glaring. The eye of a migrating bird. Okay, I have no idea what you're talking about. Okay. But I would like to. Great. I was hoping you would. So before we go totally sci-fi, I'm just going to do a quick little orientation of things. Okay. So as you know, many birds migrate. Right. Twice a year, this enormous avian river is passing overhead, you know, just stitching the continents, stitching the hemispheres together as they have been doing for millions of years. And the big biological mystery that humans have puzzled over for millennia and something we've actually talked about at Ready Lab before a couple of times is basically just how do they do it?

7:26Like, how do they find like how do they figure out where to go? Yeah, like how does a little migratory bird leave its nest, say in Alaska, and without compass or map, manage to arrive on the same branch of the same tree in a backyard in New Zealand year after year after year? Yeah, right. And we don't know how it does that? Well, we know pieces of the answer. So birds actually use a bunch of different things to orient themselves. Like they use the stars, the sun, they follow mountain ranges and rivers, they use their sense of smell, and sort of incredibly, they can also use their sense of hearing.

8:09Birds can hear extremely low-frequency sound waves that are generated by ocean surf and tectonic activity and wind blowing through high mountain passes. And there's been some speculation that a bird migrating south through the Great Plains of North America would be able to hear the Atlantic Ocean in one ear, the Pacific Ocean in its other ear, and the rumble of volcanoes in the transvolcanic belt across the middle of Mexico dead ahead of it. Wow. So they have all these tricks. But the thing is, if you take all that stuff away, birds can still do it. They can still orient themselves in space. They can still figure out where to go.

8:53So there's like something else at work here. Like magnetic fields or something? Yes. Since the late 19th century. Biologists have thought that birds probably do use the Earth's magnetic field, which, you know, is this absolutely massive force field that surrounds the planet like a huge bubble, protecting it from the sun's solar winds. Right. But the weird thing, and part of the thing that's been stumping scientists all these years, is that... An organism really shouldn't be able to sense it. Huh. Why not? Because as humongous and important as it is, it is, like, weirdly weak. It is really, really, really, really, really weak.

9:33Really? Yeah, it's like 10 to 100 times weaker than a fridge magnet. Wow. And so like the question is just how do they sense this super weak thing? And for a long time, the assumption was that they were using crystals. These tiny little deposits of magnetic crystals called magnetite in the beak of the bird. And that was a story that we talked about in our other Radiolab episodes about this mystery. And presumably this acts like a little magnet. And therefore a compass? Pulls the beak to the north or something. Yeah, that's what I thought happened. Yeah, but the problem is like magnetite doesn't seem to be connected to the bird's brain in any way.

10:11Oh. So even if those deposits are sensing the Earth's field, there's no message getting to the brain of the bird for the bird to then say, ah, that's north, I should turn this way. So it seemed like birds must be using the magnetic field to find their way around, but like nobody could figure out how they could sense it. And this is where the mystery of how birds do what they do has just been stuck for many, many years. But now we get to the new crazy, amazing, maybe we figured it all out part. Right. Emphasis on crazy, maybe. This is where we go seriously off the rails into the deep sci-fi sounding stuff.

10:50So the story of the deep sci-fi sounding stuff actually starts in the 1970s with a guy named Klaus. A young German physicist named Klaus Schulten, who was thinking about the problem of magnetoreception in birds. At the time, biologists were all about these little iron crystals in the birds' beaks. But Schulten was thinking about some very strange physics. What's called a radical pear. A radical pear. What is a radical pear? I mean, I think it's a piece of fruit that just has red Karl Marx. A radical pair. It's like animal farm, but for plants. No. So this is like an actual pair of things. And the things that are paired are electrons.

11:39And that means that we have to take a moment here to dig into how things work down at the teeny tiny scale of itty bitty stuff. All right. We're zooming in or we're diving into a... We're diving and zooming. Diving and zooming. Here we go. down into the land of the teeny tiny electrons and protons and photons and neutrons, all that stuff. And maybe you've heard some things about this tiny world and that things get very weird down there. Yeah. Right. So this is the quantum world. Right. So the tiny things down in the quantum world, it's like they break all our normal rules of space and time. for example, one thing can be in two different places at the same time.

12:27Things can move through solid barriers. Effects can happen before causes. It's really weird. Yeah, and if this were true, like in the big stuff world, it would kind of be like you catching a ball could actually cause me to throw it to you. What? Or the ball is both in your hands and my hands at the same time. Okay. Or it's, you know, both blue and green at the same time. Like whenever I hear about this kind of thing, it's always kind of incredible, but it's like also incredible. Like you can't even it doesn't even seem real. It doesn't you can't even believe it. Totally. Totally. Yeah. And I think it's like we've just never experienced anything like this.

13:06But this is what hard hitting physicists, people have studied this stuff all their lives. You know, they swear this is true. These are just the facts of life down there. Yeah. And as weird as it sounds, there is one of these little quantum facts of life that Klaus thought might somehow help birds see the magnetic field. Yeah. Shulton had the idea that it was tied to an aspect of quantum physics known as quantum entanglement, where, oh boy, and now you're going to expect me to explain something in quantum physics. Okay. Okay, so like simple version, simple version, super simple version is that sometimes two particles can become linked in a particular way such that...

13:51What affects one will instantaneously affect the other. Like you can tweak one of them and the other will react right away, even if those particles are really, really far apart. At opposite ends of the universe. Okay. Which is, you know, just another way that tiny things break the classical rules of space and time. Because, you know, in our world, the only way for one thing to affect another is by sending some kind of signal through space, which takes time. But it's like these two particles have some kind of backdoor space-time loophole. So they're just kind of insta-linked. Right. That is weird.

14:25Yeah. And this is what scientists call entanglement. Got it. And of course, this is totally fodder for sci-fi writers, like, imagining a world with teleportation. Energize. Or whatever. It's exactly. It's beaming up Scotty stuff. No doubt about it. But also, it's a real thing. I mean, it's the basis of quantum computing. Right. Part of what makes quantum computers so powerful. Anyway, so back to Klaus Schulze. He's sitting back there in the 70s thinking about a particular kind of entangled particles called radical pairs. Not the fruit. No, right. So if you picture an atom in your high school textbook.

15:06Uh-huh. Picture it. Yeah, yeah, yeah. It has a nucleus with electrons zipping around it. Right. And a lot of times those electrons come in pairs. Now, to understand that, there is one thing you need to know about electrons, which is that they have this something called spin. Now, apparently they're not actually spinning, but this is how physicists talk about it, as if they can spin in one direction or the other. And when you have these electron pairs, their spins are linked. Now, Schultz knew it was possible for a photon of light to knock one of those two paired electrons off its atom, away from its partner.

15:45And if it happens to land on a neighboring atom, even though they are now physically separate, the electrons stay paired. They are still connected. So now those two atoms become a radical pair. They're spiritually one, in a sense, because they have these electrons that are entangled in this spooky, instantaneous quantum way. Okay. So all of this was just total stock-and-trade quantum mechanics at the time. But Shulten, doing some elaborate experiments with radical pairs in the lab, had noticed something he didn't expect. When these atoms become radical pairs, they're suddenly super-duper magnetically sensitive.

16:29Okay. Okay. So now I'm seeing the bird connection here. Okay. Yes. Yes. Okay. Okay. So, and Schultzen, like he had buddies in biology land and he was well aware of this whole, how does a bird sense the magnetic field mystery? And so he thought like, hey, maybe if there are radical pairs somewhere inside the bird, maybe these could act like a magnetic compass. And so Klaus Schulten came up with this idea and submitted it for publication, you know, wrote it up in a paper, submitted it into publication to an American physics journal, and it was rejected. He had a rejection letter saying that a less bold researcher would have consigned this idea to the wastebasket.

17:12Whoa. Yeah, I mean. He did eventually publish it in a small German journal, but. Even then, it was mostly ignored. Why did it get rejected and then ignored? I think for physicists, like on the physics side, all this quantum stuff, it's very fragile. Like as soon as there are a lot of things bumping around and into each other, these quantum effects like entanglement, they disappear and like just collapse back into normal. And this is why like Google and Microsoft, whatever, have spent a buttload of money keeping their quantum computers really, really cold. Right, right, right. And inside special things because they need to keep things very, very calm in there.

17:51Otherwise, molecules are just going to bump around and ruin everything. And the inside of a bird, or really any animal, is a very busy, bumpy place to be. So, Klaus Schulten saying that entangled pairs of electrons might help a bird sense the magnetic field, that was kind of insane. This was very difficult for many physicists to accept for a long time. As for biologists... Can you turn the volume on me down? People think I'm too loud. Especially excitable biologists. You know, when I get excited about something, I may be even louder. Like Henrik Moritzsen, who works at Oldenburg University in Germany.

18:27Yeah, now they're good. They honestly just could not understand the math. Like, my God, there is no way with my mathematical knowledge at that time or now, for that matter, can read that paper. Wow. So this is extremely hard quantum mechanics. I just gave up reading the paper, honestly. Okay, so you found this paper and you're like, oh, never mind, I can't understand. I could not, you know, imagine any experiments or anything because I didn't understand it well enough. Got it. So, Shultzen's paper and his idea just sits on the shelf collecting dust. But, lucky for us, much like the quantum world, here on the radio we have the ability to warp space and time.

19:10And so we're going to take a little break. It's going to be one minute. Okay. And in that one minute, 22 years will have passed. And we will arrive at a moment where this quantum bird theory will again take flight. Okay. So, listener, stay entangled with us. We'll be right back after this.

19:39I'm Lathif Nasser. This is Radiolab. We are back from break with producer Annie McEwen. And all together, we have just made a quantum leap forward in time. How many years? 20 some odd years, something like that? 22 years. Yep. OK, so Klaus Schulten, in that time, Klaus Schulten has moved on to other things. He became a very important biophysicist. And for the most part, he set magnetoreception in birds aside until... year 2000, Schulten had a very smart graduate student called Thorsten Ritz. And he, together with Schulten, they took that old paper from the 70s and... Wrote exactly the same hypothesis again, with illustrations and in a language that biologists could understand.

20:23And they also added one really important thought, which is that they think this radical pairing thing could happen inside the eye. Because, of course, that's the place where light gets into a bird. And then it took off like crazy. Because now biologists knew where to look and what to look for. And in fact, thanks in part to Morrison's work, we now know that there is a molecule. It's a pigment protein that is found in the eyes of many birds, especially migratory birds. That can do this radical pair thing when it's hit by a photon of light. And it's called cryptochrome. A molecule that absorbs light and use this light energy to move an electron.

21:03And since then, scientists all over the world have done experiment after experiment, finding more and more supporting evidence. Showing that this idea he had back in the 1970s was correct. Okay. So, can I play this out for you? Yes, please. Okay. Ready? Here we go. Here we go. I'm ready. Let's go. Okay. So, here is the idea. A bird is flying at night under a blanket of stars. And if we were to zoom into its eyeball, we'd see cryptochrome molecules made up of atoms with a bunch of paired electrons buzzing around them. And these pairs, like I said before, their spins are linked. So they're like little spinning dance partners.

21:43One up, one down. One spins up, the other spins down. Always. Okay. So there they are. They're just dancing in their little atom home together. And they're completely uninterested in the very, very weak magnetic field of the Earth. until the bird glances up at the night sky and then bam. The photon of light that was emitted 10 million years ago from a distant start hits the bird in the eyeball. And it strikes this cryptochrome molecule and it knocks an electron away from its dance partner and it goes ka-pew and it lands on another molecule in the eyeball. That is a radical pair. And remember, even though they're separated, they're still linked.

22:23Quantumly entangled. So they're still doing their little dance, But now that they've been radicalized, they're in this highly unstable state. And they've become super duper sensitive. Ten million times more sensitive to Earth's magnetic field. And it's almost like this giant presence that was lying hidden suddenly appears.

22:49And now their dance is influenced by the magnetic field of the Earth. So now, some of the time, they do their old up-down move, but they also sometimes spin in the same direction, like both up or both down or whatever. Okay, so it's more variation, different kind of dance moves. Exactly. Yeah, and the key thing here is just how much they spin opposite and how much they spin together. That changes depending on which direction the bird is flying. Okay. So, for example, it could be like if the bird is flying north, those electrons are more likely to be spinning together, both up, up. Okay. And then let's say the bird veers right and heads due east.

23:32Now those electrons are more likely to be spinning opposite each other, up, down. Hmm. Are you with me? I'm with you. I think I'm with you. Are you? Yeah. Okay. Well, just to bring it home here, this is obviously incredibly simplified. But the important thing is that there are not just one, but millions of these radical pairs inside the eye of a bird doing their various dances all at the same time as the bird flies along. And it's not like these little bits are acting like magnets, like pulling the bird one way or the other. Instead, you've got this kind of like Rube Goldberg bit of business at the end here where different spins create different kinds of chemicals.

24:11All of that leading to the optic nerve sending electrical signals to the brain. Now, this is very, very complicated. Yes. The uncomplicated part is really. The bird now has a chemical compass in its brain. And this chemical compass exists because the electron spin interacts with the Earth's magnetic field. In other words, birds are finding their way around the planet, across hemispheres, thanks to these teeny tiny particles inside their eyeballs that are getting pushed around by this giant forest field surrounding the planet. Mmm. And so you can do something with your eyes that owls can't. Bingo.

25:02Exactly. Exactly. No owl will ever look out of the corner of its eye at you because they can't move their eyes. And that's one of the reasons, I think, why humans have always thought owls are wise. Because they never give you any side eye. They only look straight at you. On the mountain in Pennsylvania, All right, we're going to let this bird go. After we caught the owls and took some measurements and saw their eyeballs, Everybody ready? Yeah. So I'm going to hold it up with my hand. We let them go. There he goes. Yay! Yay! And now most of the research on this quantum entanglement stuff has been done on songbirds, not owls per se.

25:39But the scientists I've talked to say that if all this is right, it's likely something that pretty much all migrating birds, including these owls, do. And so after learning all this, it was just this whole other thing, standing there and watching them fly off into the night. Especially in light of something that Henrik and his team discovered in 2005. If you look into the brain of a bird and you ask, which part of the brain do you use to process magnetic compass information? The answer is in the visual system. It's seeing, basically, that is activated. The bird is not only sensing the Earth's magnetic field, it's actually seeing it.

26:25Cool.