Could Sound Make You Levitate?

Imagine: a series of objects floating in midair without magnets, strings or visible supports. With acoustic levitation sound waves alone can suspend droplets, beads and even small solids to seemingly defy gravity! In this episode of Field Notes, Hannah shows Michael this astonishing device, revealing how precisely tuned sound can manipulate matter. Behind the mesmerising floating objects lies a combination of physics, mathematics, and engineering that turns vibrations into invisible hands. How do sound waves create stable points in space? What can acoustic levitation teach us about controlling particles, studying delicate chemical reactions, or even exploring new materials? And why does watching something float so effortlessly feel like glimpsing...a little magic? Welcome to The Rest Is Science: Field Notes. Every Thursday, Hannah and Michael rummage through their personal troves of scientific treasure and source discoveries that explain our understanding the universe, oddities that scramble our brains, objects that hint at forces we’ll never see...and a few things that are essentially just plain cool. Expect deep dives into the science behind each pick, the spark that grabbed their attentions, and the sheer delight they get from sharing it all with you. They’ll also be tackling your questions, so email The Rest Is Science at [email protected]. You can watch the Pitch Feed experiment live, here. ------------------- 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 ThorntonVideo & Social: Bex TyrrellAssistant Producer: Imee MarriottProducer: Becki HillsSenior Producer: Lauren Armstrong-CarterHead Of Digital: Samuel OakleyExec 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?

  Would you like to levitate, Michael?

• 2:23Michael Stevens?

  I would love to, every day.

• 2:25Hannah Fry?

  Wouldn't it be good? Wouldn't it be good? Well, today on Field Notes, I uh, I'm gonna give you that chance. There's a couple of caveats, small ones, don't worry about them, we'll come to them in a bit, but I have got a uh, a little acoustic levitator with me.

• 2:39Michael Stevens?

  Oh, really?

• 2:40Hannah Fry?

  Have you ever played with one of these?

• 2:41Michael Stevens?

  I, I have, but one that was so small, it could only levitate like a tiny little bead of styrofoam, polystyrene, for those of you across the Atlantic, and it was so undramatic.

• 2:54Hannah Fry?

  That's exactly what I've got.

• 2:57Michael Stevens?

  Oh, no. Does it also make this noise that's like

• 3:02Michael Stevens?

  and you're like, oh, please. Okay.

• 3:05Hannah Fry?

  Yeah, I've got that and some calculations.

• 3:07Michael Stevens?

  Let me say, let me say, I've never played with one, but I can't, I don't believe it's possible, especially something as cool to levitate as styrofoam.

• 3:17Hannah Fry?

  Oh, [bleep].

• 3:20Michael Stevens?

  So that's what you brought me. You brought me a sonic levitator.

• 3:24Hannah Fry?

  And some calculations about how many of these things you'd need to levitate you.

• 3:28Michael Stevens?

  Okay, so what a wonderful intro. Aren't you excited to show this to me now?

• 3:32Hannah Fry?

  I've never backed myself more, Michael. This is uh, I mean, I should have managed your expectations a bit better, shouldn't I, really? I should have said-

• 3:39Michael Stevens?

  Yeah, I think, I think so. But I will say that, that I've experienced it, but I think that you talking about it and explaining it will show me why it is so cool.

• 3:52Hannah Fry?

  We'll see, shall we? Okay. A friend of mine at Cambridge University has been toying around with this little acoustic levitator. Incidentally, actually, you know, math departments are completely full of people who care a lot about acoustics. Did you know this?

• 4:09Michael Stevens?

  Yes, I bet.

• 4:11Hannah Fry?

  Like jet engines, for example, uh, when they were first created, they were so noisy that for starters, it was like completely unworkable for commercial flight. But secondly, the vibrations were so dramatic that they would break the components inside of the engine. And who did they turn to to make them all quiet? The mathematicians, my friend.

• 4:32Michael Stevens?

  Right.

• 4:33Hannah Fry?

  There is a guy who, a mathematician who works in the same department as me, who is now working on a car seat. That essentially works as noise cancellation for the road around you. Doesn't that sound nice?

• 4:48Michael Stevens?

  Oh, wow. Is it safe? I feel like I need to hear some of these noises.

• 4:53Hannah Fry?

  Do you? I think maybe if you're a passenger, maybe it's not for the driver.

• 4:57Michael Stevens?

  Okay, okay.

• 4:58Hannah Fry?

  Anyway, there's just a lot of people who are working on acoustics and one of them has got this little acoustic levitator. So here is the acoustic levitator. It's in a little 3D printed box. My friend is Matthew Nethercoats, by the way, who let me steal this in order to impress you, Michael, which was, which was

• 5:20Hannah Fry?

  I'll try a lot harder next time, I'll put it that way.

• 5:22Michael Stevens?

  Um, okay. No, no, no, no. This looks cool. This looks cooler than the one that I've seen. It's like, it's like a hand sized.

• 5:29Hannah Fry?

  Like a hand sized, there you go.

• 5:30Michael Stevens?

  And it looks like some kind of Star Trek teleporter.

• 5:34Hannah Fry?

  It does, yeah. So you've got two bits, one, one at the top, one at the bottom, and inside um, there's a dome effectively that is filled with lots and lots of tiny little speakers that are all pointing towards this kind of central space. Sort of, hmm, how can you describe it? Uh, I never watched Star Trek. Um, but isn't there um, some device in there where you teleport people? You can sort of imagine stepping in here and being teleported. I think that's the best way to describe it.

• 6:01Michael Stevens?

  Yeah, right. But those are speakers pointed up and down, focused on some point in the very middle in between them.

• 6:10Hannah Fry?

  The idea here then is that uh, sound is a wave, right? Sound is like you have this membrane on a speaker that vibrates backwards and forwards. And as it does so, it pushes and then pulls the air that surrounds it, creating this wave. Um, now if you have all of these speakers that are tuned to exactly the right frequency and pointing in exactly the right way, then what should happen is that in some places, the, the vibrations will sort of add up together and in some places, those vibrations will cancel each other out. So that you should get some little effectively jail cells in here of air, where the air is perfectly still, while all the air around it is like vibrating like crazy.

• 6:51Michael Stevens?

  So is it running now? Is it producing the the the the sound?

• 6:54Hannah Fry?

  It is, which I can't hear. I assume you can't hear, but

• 6:58Michael Stevens?

  I can't hear it either.

• 6:59Hannah Fry?

  A hundred meters down the road, there are several dogs that are now crying because it is so high pitched.

• 7:03Michael Stevens?

  Very high pitched. Okay, so the idea is that sound waves are compressed, there there there are waves of of of air that's been compressed and rarefied. And if you get what like two two compressed waves side to side, you can like hold something in the air.

• 7:20Hannah Fry?

  Exactly.

• 7:21Michael Stevens?

  Now, could you change the frequency of the sound with this device? And change where these levitation points are?

• 7:28Hannah Fry?

  Not this one, unfortunately. I think I need to to write to Matthew Nethercoat and tell him he needs to make a more impressive device.

• 7:35Michael Stevens?

  I'm not down on this. I think it's really cool. I think it looks really neat.

• 7:40Hannah Fry?

  I know what you're thinking. That sounds fun, but I want to go. I need to levitate me. Or at least an ant, you know, that would be.

• 7:48Michael Stevens?

  Well, yeah, no, I've I've seen them levitate living frogs.

• 7:53Hannah Fry?

  Hmm.

• 7:53Michael Stevens?

  In laboratories with very powerful versions of this. And I'm wondering what the applications are beyond the amusement.

• 8:00Hannah Fry?

  Well, okay, let's stick on the fun for a second here because um because let's say the average human weighs about, I don't know, what do you reckon, seventy five kilograms, something like that? That's what I've done with my calculations. Um, this particular levator has seventy two little transducers right around here. Uh, so if you wanted to raw power lift a human, you are going to need two hundred and sixteen million of them, which is

• 8:23Michael Stevens?

  Oh.

• 8:24Hannah Fry?

  I would say quite a lot.

• 8:26Michael Stevens?

  That's a lot, but let's say you did it.

• 8:28Hannah Fry?

  Let's say you did it.

• 8:29Michael Stevens?

  Be able to hear the sound or would it still be ultrasonic?

• 8:31Hannah Fry?

  Well, here's the thing. Um, you need them to be like super, super loud, right? Um, in order to uh in order to actually have the sort of strength between them to to be able to lift this human. Uh, you can get them up to about one hundred and twenty decibels, but remember you've got two hundred and sixteen million of them. Um, now the slight problem is that any sound above one hundred and seventy decibels can cause organ and joint damage, just because it vibrates you so violently uh that you you start to implode. Um. Anything above two hundred and forty decibels, that would be lethal.

• 9:05Michael Stevens?

  Wow.

• 9:05Hannah Fry?

  And so at two hundred and sixteen million, I think that the reality is we could levitate you. Uh. It's just, it would be so loud your head might explode. Small caveat, small caveat.

• 9:15Michael Stevens?

  It's worth it. It's worth it.

• 9:17Hannah Fry?

  You wanted drama. My God, I can give you drama. So, okay, this is like a cute little fun toy that you can play with. But there is actually a reason behind this stuff. So in the nineteen sixties, nineteen seventies, NASA, they they developed these kind of levitators. Um. Partly because they wanted to see what it would be like to have a effectively a microgravity environment.

• 9:39Michael Stevens?

  Oh, yeah.

• 9:40Hannah Fry?

  You can imagine if you were like suspending instead of tiny little um balls here, you were suspending cells or like other sort of organic matter. Um. It's effectively the same as like being suspended in zero gravity. You're not going to feel the force of the earth because it's counteracted by the this little cage of air that is um that is wrapped around it. You can also put liquids in this, which is kind of interesting, but there are some quite interesting medical applications of this stuff. If people have kidney stones in their body, what you can do is with acoustic beams is nudge small fragments of kidney stones. You sort of break them up with ultrasound and then you nudge them into positions in the body where they could sort of be naturally cleared.

• 10:22Michael Stevens?

  Huh.

• 10:23Hannah Fry?

  There's also, this is the one that I really like, you can have a targeted drug delivery with this. So you can create a um a sort of micro bubble, load it up with a drug, you can inject it. But then, if you want to move it to very specific areas of the body uh and then burst the bubble using ultrasound to release the medication. And this is particularly useful if you have something like uh chemotherapy, for instance, so some sort of like drug that has like a really bad toxicity and you want to reduce the side effects that it can interact with other parts of your tissue on the way to the bit that it actually wants to um to interact with.

• 11:02Hannah Fry?

  There's also like this idea that you can use these kind of acoustic levitators. I mean, essentially what you have here is like a beam of sound that moves stuff.

• 11:10Michael Stevens?

  Yeah, and it can move anything made of matter, whereas trying to move things around in a body with like magnets or something would require what you're moving to respond to the magnet. And they're ultrasonic, so they don't bother us.

• 11:24Hannah Fry?

  Yeah, just the neighborhood dogs.

• 11:26Michael Stevens?

  Yeah.

• 11:27Hannah Fry?

  The other thing, so, so, I mean, in general, moving things around the body, you can also use this for pill-sized cameras. So you swallow a little camera, then you want to move it around the digestive system. For instance, you can use these kind of acoustic beams to, to move it all around the body.

• 11:40Michael Stevens?

  Right, a little micro cinematographer could make a movie in my body controlling with sound waves. And sound waves could be a lot harder to jam than like radio waves.

• 11:52Hannah Fry?

  In what way? Go on.

• 11:54Michael Stevens?

  Well, I mean, like, if you want to control something remotely using radio waves, there's going to be some limitations on when you can use those and through what mediums, but perhaps sound can fill in the gaps.

• 12:08Hannah Fry?

  Because if you think about it, if you, if you happen to be swallowed by a human and we're sitting inside of their stomach and someone was shouting from outside, you would expect to hear it. Like, the sound vibration would still get inside. In fact, actually, you know, you know, that whole thing about babies when they're in their mother's stomachs, there's certain frequencies which they hear that end up being really soothing.

• 12:27Michael Stevens?

  Yeah. And there's things that they see as well. Like, skin is not completely opaque. The growing, developing baby in the womb isn't in darkness, especially if the mom's topless in bright sunlight. It's like, kind of like red in the womb.

• 12:42Hannah Fry?

  Oh, wow.

• 12:43Michael Stevens?

  To the human eye. Yeah. Yeah. And they've done studies where they've projected, like, using lasers, different shapes onto the womb that the baby could see.

• 12:53Hannah Fry?

  Yeah.

• 12:54Michael Stevens?

  Uh, this is, of course, a baby that's developed enough to have a retina, and the, the babies react to shapes. In fact, they're seen to react to and look at and stare longer at shapes that are similar to a human face. Like, it's instinctive.

• 13:09Hannah Fry?

  Wow.

• 13:10Michael Stevens?

  I'm being serious. Like, um, this, this pattern right here, they don't seem to care very much about. Okay, that's three dots in a triangle shape.

• 13:19Hannah Fry?

  Mm hmm.

• 13:20Michael Stevens?

  But they will, for like twice as long, follow and look at an upside down triangle of dots, which is like an, like two, two eyes and a mouth.

• 13:28Hannah Fry?

  I mean, it's essentially like your, your, I, I'm, I always think in terms of a British plug, whenever I see this experiment, it's sort of like, hold a British plug in the correct orientation, baby don't care, turn it upside down, baby cares.

• 13:41Michael Stevens?

  Really? Of course.

• 13:43Hannah Fry?

  I've only seen it for, for babies that have been born.

• 13:46Michael Stevens?

  Yeah, well, apparently it would work on a prenatal baby. What can they hear? Could they hear this? Like, is this, is this frequency that this machine's running at? Is it something that like teenagers can hear, but not old people?

• 14:00Hannah Fry?

  Like the mosquito noise or the?

• 14:02Michael Stevens?

  Yeah.

• 14:02Hannah Fry?

  Did you have that in the States where they had a, um, they had a device that was designed to stop teenagers from hanging out in public areas?

• 14:09Michael Stevens?

  Yeah, and I experienced one at this show I did, where I was like, why is there that buzzing noise out here? And all the guys working there were like, oh, you can hear it. I don't know if I could hear it still, this was years ago, but I was really proud that I could still hear this noise. It's supposed to scare away, or not scare away, it's supposed to annoy juvenile delinquents.

• 14:28Hannah Fry?

  Well, this thing is about 20,000 hertz, so it's quite possible that young children could hear this. I have a young child in my house, shall I go and ask them?

• 14:35Michael Stevens?

  Well, yeah, let's do an experiment.

• 14:38Hannah Fry?

  Shall I for real?

• 14:39Michael Stevens?

  Uh, yeah, and see if they can guess when it's on or off, to see if they're getting it.

• 14:46Michael Stevens?

  Okay, here's our test subject.

• 14:47Hannah Fry?

  Here's our test subject, okay. You want you to have a listen and see, you tell me when you can hear it. Can you hear that? Yes. Can you hear that?

• 14:56Michael Stevens?

  No.

• 14:57Hannah Fry?

  Oh. Can you hear that? Yeah. Can you? I can't hear that. I can't hear any of these.

• 15:03Michael Stevens?

  Wow, super kid.

• 15:04Hannah Fry?

  Super kids, 19,000 hertz he went up to. I stopped at about 12,000.

• 15:10Michael Stevens?

  But this acoustic levitator that you've got, it's using 20,000 hertz.

• 15:13Hannah Fry?

  It's 22, 22,000.

• 15:15Michael Stevens?

  22, wow. Okay, so it's shaking the air 22,000 times a second, creating waves of compressed air separated by rarefied air. And these, these waves like collide from the top and bottom. And what's going on? The compressed waves can sync up and create an even more compressed wave. And if a rarefied area and a compressed one meet, they just make normal air.

• 15:41Hannah Fry?

  Exactly.

• 15:42Michael Stevens?

  And this somehow creates like a cage of air pressure that can hold very lightweight objects.

• 15:47Hannah Fry?

  Exactly. Try and put something in that's much larger and it'll just flop around all over the place and eventually fall. But if you get something that's the right size and not too heavy so that it doesn't sort of overwhelm the, the force that's being exerted by the, the surrounding air pressure, then yeah, you can have it successfully levitate. I mean, I always thought levitation was a bit of a science fiction myth, but it turns out it actually isn't.

• 16:11Michael Stevens?

  Well, yeah, I mean, I got stuck on defining levitation because this isn't levitation. It's, it's using force of air pressure to resist gravity.

• 16:19Hannah Fry?

  How dare you? It's not touching the ground, Michael. You're, you're being way too strict with your definition.

• 16:24Michael Stevens?

  Okay, so then what about, do airplanes levitate? They, they're not touching the ground.

• 16:28Hannah Fry?

  Shush, shush, shush, shush now. Let's go to a break.

• 16:31Michael Stevens?

  Okay, let's go to a break.

• 16:40Speaker 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.

• 17:10Hannah Fry?

  This episode is brought to you by Cancer Research UK.

• 17:12Michael Stevens?

  Every second, your cells release millions of microscopic signals, fragments of DNA, tiny molecules, little molecular whispers.

• 17:21Hannah Fry?

  And scientists are trying to work out how to read them. It's called a liquid biopsy. And this is a test that looks for these tiny little traces of cancer through the body's fluids, often long before symptoms of cancer itself actually end up appearing.

• 17:35Michael Stevens?

  So today, we're asking, can you really detect cancer from clues floating around in blood, urine, spit and tears?

• 17:42Hannah Fry?

  Short answer, yes. Longer answer, how?

• 17:45Michael Stevens?

  How?

• 17:46Hannah Fry?

  Okay. I mean, this is it, right? Because, okay, cancer doesn't just appear out of nowhere. It leaves these molecular fingerprints in your body, this long before symptoms end up showing. These little fragments of DNA, these proteins, other little molecules that end up floating around your body, in your bloodstream, for example, as your cells are dividing, as they're growing and as they're dying. Like a sort of internal messaging system and whether you can tap into it.

• 18:11Michael Stevens?

  And the challenge is sensitivity, because you've got a lot of cells that are not cancer.

• 18:16Hannah Fry?

  Yeah. I mean, there's a whole load of stuff floating around your body.

• 18:19Michael Stevens?

  Well, Cancer Research UK researchers are building tools sensitive enough to detect these markers.

• 18:25Hannah Fry?

  Yeah, these faint little signals and detect them even earlier. And this is different, this is separate from traditional biopsies, right? Which kind of go in, it means surgery, it means needles, it means you take tissue samples from a suspected tumor or the surrounding tissue around the tumor. And that is amazing, but it really only gives you a snapshot of one tiny area of the body at that one moment in time.

• 18:48Michael Stevens?

  But a liquid biopsy is less intrusive and it's liquid that has come in contact and can contain traces from all over the body.

• 18:56Hannah Fry?

  Yeah, yeah, like one breath, which is collecting up the molecules that have travelled around your entire body. You know, or urine or blood tests.

• 19:05Michael Stevens?

  It's a quiet revolution, right? It is testing the blood and other bodily fluids instead of the tumor without surgery.

• 19:12Hannah Fry?

  And the key thing is that because those fragments, because they can come from different parts of the tumor, it means that just a small sample... You can put these clues together and you can get a really full picture of what's going on inside.

• 19:24Michael Stevens?

  One thing I think is really cool is that platelets, which like we've all heard about, they're the things that help you heal when you get cut. They block off the blood flow so the healing can begin. Platelets really help with this search because they also suck up these molecular traces in the blood.

• 19:39Hannah Fry?

  Yeah, these things act like little hoovers, right? They're picking up tiny bits of tumor DNA, all those that circulate around the body and concentrating them. And, I mean, they can help us unlock overlooked cancer clues.

• 19:51Michael Stevens?

  Exactly, and the MRD Edge technology is more like an amplifier that can make the really quiet traces loud enough for researchers to find.

• 20:00Hannah Fry?

  The whole thing about this, liquid biopsies, this isn't just a theory, this is something that's already been trialed in hospitals to monitor how well cancer treatments are already working.

• 20:10Michael Stevens?

  Yeah, the aim is precision, knowing exactly when a treatment works, when to switch course, and when cancer might return, so doctors can always be one step ahead.

• 20:18Hannah Fry?

  And Cancer Research UK, they come into this by connecting the lab work, doing the data science, the clinical trials that make all of this stuff possible.

• 20:25Michael Stevens?

  So it's discovery that's happening, that's in motion, it's innovation beginning to make its way towards everyday care.

• 20:31Hannah Fry?

  Of course, the goal here is that you can spot cancer early and then tailor every single decision around the individual person based on what's going on in their body at that moment in time.

• 20:41Michael Stevens?

  That's right, doctors can detect and be aware of the smallest changes so that they can adjust treatment in real time.

• 20:48Hannah Fry?

  Yeah, rather than having long stretches between biopsies, for example. And, and this shifts medicine from being just reaction to prediction as well. Instead of waiting for symptoms to arrive, you can get one step ahead.

• 21:00Michael Stevens?

  And the same science that spots cancers earlier could become part of routine checkups.

• 21:05Hannah Fry?

  Yeah, much less invasive, much more predictive. I mean, you can imagine a future where you go and have a blood test and it is as routine as, I don't know, getting your car in for a service, only this blood test is monitoring everything that's going on in your body and could potentially save your life.

• 21:20Michael Stevens?

  So Cancer Research UK's researchers are bringing the future closer, they're turning detection into protection.

• 21:26Hannah Fry?

  And what is remarkable is just how quickly this field is moving. You are getting discovery beginning to shift from the lab into hospitals. And when we learn to read the body's signals, we can get ahead of cancer. We can have the best shot at beating it.

• 21:39Michael Stevens?

  For more information about Cancer Research UK, their research, breakthroughs, and how you can help them, visit cancerresearchuk.org/RestIsScience.

• 21:57Michael Stevens?

  All right, we're back and we're going to answer some questions from you. I want to start with this great question from Neil, who asked, will a person ever swim faster than a shark?

• 22:10Hannah Fry?

  No, next question.

• 22:13Michael Stevens?

  Whoa, whoa, whoa, whoa, whoa, wait a second. This is one of those questions that suffers from the problem of being a bit too broad. Like, what do you mean by a shark?

• 22:19Hannah Fry?

  Yeah.

• 22:20Michael Stevens?

  Like, there are sharks that swim really slowly. The Greenland shark only swims at about one mile per hour.

• 22:28Hannah Fry?

  Wow.

• 22:29Michael Stevens?

  That's about point three, four meters per second.

• 22:32Hannah Fry?

  That's extremely slow. Isn't that the one that's also like 400 years old?

• 22:36Michael Stevens?

  Yeah, yeah. And so I could outswim one of them, but I can't outlive them. Maybe it's a balancing scale. And the fastest human speed is like almost two and a half meters per second.

• 22:48Hannah Fry?

  Which, how does that convert to miles an hour?

• 22:51Michael Stevens?

  About five and a half miles per hour.

• 22:52Hannah Fry?

  Okay, that's pretty good. You could definitely outrun a Greenland. Is that with or without fins?

• 22:57Michael Stevens?

  That's without fins. That's just using the flesh your mother gave you.

• 23:02Hannah Fry?

  What I will say is I can definitely not swim that fast.

• 23:06Hannah Fry?

  Yeah, that's a sort of Michael Phelps territory.

• 23:09Michael Stevens?

  No, it definitely is like a very unique speed to be traveling at.

• 23:13Hannah Fry?

  I also want to know how motivated the shark is. So I sort of feel like even fast sharks, whatever the fastest shark might be. What do you reckon the fastest shark is? Like a, I mean, not a hammerhead, they're aerodynamically useless.

• 23:26Michael Stevens?

  I mean, Google says the fastest shark is the shortfin Mako, which can travel at 31 to 46 miles per hour in the water.

• 23:34Hannah Fry?

  Well, well, this is a whole jumble of units we've got going on here, isn't it?

• 23:39Michael Stevens?

  That's a whole jumble. How many fathoms per day?

• 23:43Hannah Fry?

  Knots per month.

• 23:47Michael Stevens?

  Look, the point, what I love about the question, though, is that it's framed by asking, will a person ever swim faster than a shark? As though human swim speed is something that is changing and it's getting better and better. And in some ways it is, this also belies that kind of like, that modern sensibility that like, things are just going to get better and stronger and records keep getting broken. And in some ways it is true, like, we do learn more about nutrition and swimming techniques and also swimming technologies like fins and swimsuits. I think there were some swimsuits that were allowed in Beijing at the Olympics that are no longer allowed, but because they were allowed for that one Olympics event, a bunch of records were set.

• 24:29Hannah Fry?

  Yeah.

• 24:29Michael Stevens?

  And so we're at the point where the limits of human bodies are now being augmented and we're going beyond it.

• 24:36Hannah Fry?

  Hmm, because I think that's the thing, actually, particularly about swimming, is that you have to wear a swimsuit, right? You can't do nudie swimming, that would just not be okay. And so you have to have some kind of, you know, designed object on your body.

• 24:50Michael Stevens?

  What do you mean you can't swim naked?

• 24:52Hannah Fry?

  I mean, you can if you want to, but maybe not in competition in the Olympics.

• 24:56Michael Stevens?

  Right, right.

• 24:57Hannah Fry?

  Maybe not two and a half meters per second, Michael, that's all I'm saying.

• 25:01Michael Stevens?

  Right.

• 25:02Hannah Fry?

  But those particular swimsuits, they had a couple of design features. So one was that, um, because what you really want to do is you want to basically have your, your butt, uh, higher in the water, like as high in the water as you can. So they had like some elements of buoyancy in them.

• 25:16Michael Stevens?

  Oh.

• 25:17Hannah Fry?

  They also, along the sort of skin of the swimsuit, um, they had like, uh, sort of microscopic design which allowed the water to slip over it much easier so that you didn't get this sort of, any resistance or drag on the surface. And then I think also they were basically like Spanx, they were basically like four sizes too small for the human that was wearing them to make them as streamlined as possible, sort of minimize their surface area.

• 25:43Michael Stevens?

  Fascinating, okay.

• 25:45Hannah Fry?

  So all of those things, uh, you know, those things are, oh, actually, one other thing about swimming, in fact, you know, this idea that humans can swim faster as time goes on, when I was a kid, swimming lessons, they would say that you have a flat palm and that your fingers are stuck together. But actually, now that I have a PhD in fluid dynamics, Michael, I know that that is not true, I know that that is, that is not the best way to swim. Because in fact, actually, if instead of having your hand flat, you have it sort of cupped. But also, if your fingers are slightly further apart, what happens is that, for starters, you're just displacing more water by having your hand curved. So basically, if you have your hand in like a natural relaxed position,

• 26:28Hannah Fry?

  what happens is you get these little eddies that appear, this turbulence that appears between your fingers. Um, that are, uh, you know, if you get it at the right distance, that are impenetrable to water going through. So you effectively increase the size of your hand by having your fingers slightly apart. Basically, you wanna like, think of your hand as these big scoops going through the water.

• 26:48Michael Stevens?

  Right. And those eddy currents are almost like webbing.

• 26:51Hannah Fry?

  Yeah.

• 26:51Michael Stevens?

  Made of water that stops water from going through. That's really cool.

• 26:57Hannah Fry?

  So maybe, maybe science will make people swim faster.

• 27:00Michael Stevens?

  I know. Watch out, Mako Shark. Thanks for the question, Neil. Uh, you wanna take Ellie's question?

• 27:06Hannah Fry?

  Yeah, go on. Uh, Ellie asks, if you had to invent a completely useless yet scientifically fascinating machine, what would do it? And what basic principle of physics or chemistry would it exploit?

• 27:16Michael Stevens?

  Okay, I've, I've had this idea for a long time. I want to build a clock that uses a titration process to tell time. So what you've got, in, in my mind, you've got like a a beaker with some kind of solution in it, and you're dripping another chemical into it at a regular interval, like one drop per second. And you do this all day, all right? And the more of the above chemical falls into the one below, the more the color changes. So, for example, maybe it's becoming more and more red throughout the day. And then on the clock, there's a, a gradient from, from clear to red, and you just like turn it until it matches the color of the beaker.

• 27:59Michael Stevens?

  And that happens to be the time that it is. So to check the time, you just go, let's look at this. How red is it? And you move the dial until the red's match and you go, oh, wow, guys, it's, it's afternoon now.

• 28:10Hannah Fry?

  I like that so much. I've actually wanted something like a, like an hourglass um, for a really long time that lasts much longer than an hour, right? I've, I wanted one. You know, there's some things that you wanna do every couple of weeks, right? Every couple of weeks, maybe you want to like water your plants, for example. Um, and what I really wanted is a physical device that you can turn over, leave it, and then know when two weeks is up. Unfortunately, if you use sand or something, they end up being so gigantic that they're completely impractical. It's like the size of a room.

• 28:39Michael Stevens?

  I know, I know. Well, there's a, there's an hourglass in Japan that goes for an entire year.

• 28:44Hannah Fry?

  Is there? How big is it?

• 28:46Michael Stevens?

  It's really big and it's supported way up on these just giant metal truss. And on New Year's Eve every year, they turn it over and it's beautiful and it's one of my dreams to go and visit it.

• 28:58Hannah Fry?

  Oh, that's incredible. But this idea of having a liquid that drops, I like this a lot because there's the, um, there's that experiment, the pitch drop experiment. You know about this, I imagine?

• 29:07Michael Stevens?

  Hmm. Yeah, the longest running experiment.

• 29:09Hannah Fry?

  Since nineteen twenty seven. So this is, um.

• 29:12Michael Stevens?

  Wait, so it's gonna be hitting its a hundred year anniversary in a couple of years. That'll be a special moment.

• 29:18Hannah Fry?

  Shall we work out a way to get the rest of science to go and visit for its hundred year?

• 29:22Michael Stevens?

  Yeah, we should do a special celebratory episode there as we watch it. For those who don't know, the pitch drop is an experiment looking at the viscosity of pitch, a material that is so, so not flowing that it pours out of the funnel that it's in, like, well, I mean, so slowly that it's been almost a hundred years and it's still coming out.

• 29:44Hannah Fry?

  Yeah, yeah. I think there's only been, it's, it's, it's like tar, right? It's like the kind of thing that you would use to waterproof your roof, like that kind of thing. There's about a one drop every decade or so. I think that there's an online camera. I think that there's like a live feed.

• 30:00Michael Stevens?

  Yeah, the feed. Okay, so the experiment uses pitch that is a hundred billion times more viscous than water.

• 30:09Hannah Fry?

  Wow, that's incredible. Absolutely incredible.

• 30:13Michael Stevens?

  Can I just read you? I want to read. This is, this is so fascinating.

• 30:16Hannah Fry?

  Please.

• 30:16Michael Stevens?

  In nineteen twenty seven, Professor Parnell heated a sample of pitch and poured it into a glass funnel with a sealed stem. He allowed the pitch to cool and settle for three years. And then in nineteen thirty, he cut the funnel's stem. And since then, the pitch has slowly dripped out of the funnel. It took eight years for the first drop to fall and more than forty years for another five to follow. My gosh.

• 30:41Hannah Fry?

  Parnell, though, he never got to see it, even though he was in the same building for decades. And when, when he died, I think no one had ever, you, you sort of know that it's happened, but you come back in, you're like, damn it, I missed the drop and you've got to wait another 10 years. Um, someone who took over the experiment after, um, Thomas Parnell, uh, was like completely obsessed with it. So was waiting like 40 years, set up loads of cameras, sometimes would sleep near the apparatus when he thought that a pitch was imminent.

• 31:07Michael Stevens?

  Right.

• 31:07Hannah Fry?

  Um, in 1977, apparently he left the lab for a few minutes and then the drop fell. And then in 1988, the next time, uh, it fell again, but the camera had jammed. And then in 2000, he set up a webcam and the webcam crashed right before the drop. He is half his career trying to see a single drop in the jar and, uh, yeah, died without having seen it.

• 31:31Michael Stevens?

  What a life. I feel like you could do a pitch drop experiment timer at home and you would just set a knob to the temperature for the speed that you wanted. And you could set it for a fast speed or like remind me in six months.

• 31:44Hannah Fry?

  Yeah. Let's, let's invent that. I think, I think that's something that

• 31:49Michael Stevens?

  Let's go and write it down.

• 31:49Hannah Fry?

  You could do, you could definitely do that. I'd like a two week pitch drop timer, please. On that note, I'm going to go and, um, water my plants and try and levitate some household items acoustically.

• 32:01Michael Stevens?

  Oh, sounds like a fun time.

• 32:04Hannah Fry?

  Hmm. Very good. We'll see you next time.

• 32:07Michael Stevens?

  Yeah, we'll see you next time.

• 32:31Speaker 04

  The Great Game, strategic struggle between Britain and Russia.

• 32:39Speaker 05

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

• 32:45Speaker 04

  Holding the Russians accountable is World War III.

• 32:47Hannah Fry?

  They took down a British passenger jet containing 350 people.

• 32:50Speaker 04

  Man in the Kremlin is playing, Alex. Got to ask yourself, do you want to play or not?

• 32:56Speaker 06

  You're the Prime Minister. You've done nothing.

• 33:03Speaker 02

  We would need to understand the policy context.

• 33:06Speaker 04

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

• 33:14Speaker 07

  A FRAGO that says to kill the President of Russia?

• 33:19Speaker 04

  Yes.

• 33:21Speaker 08

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

• 33:26Speaker 09

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

• 33:30Speaker 08

  An audio drama journey like no other.

• 33:32Speaker 09

  Men like Duffy, they are our most valuable weapons.

• 33:36Speaker 08

  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.