Could Sound Make You Levitate?

Summary

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The Rest Is Science: Could Sound Make You Levitate?

Host: Professor Hannah Fry
Co-host: Michael Stevens (Vsauce)
Air Date: January 8, 2026

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Episode Overview

In this episode, Hannah Fry and Michael Stevens dive deep into the curious phenomenon of acoustic levitation—the science of using sound to lift objects. The discussion blends playful skepticism with rigorous explanations, experimental demos, and practical insights, ultimately revealing that what feels like science fiction is, at least for small objects, real science. Along the way, Michael and Hannah explore the mathematical, physical, and medical ramifications of sound-based manipulation, highlight the limits of current technology, and indulge in enthusiastically nerdy tangents about human perception, scientific creativity, and classic experiments.

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Key Discussion Points & Insights

1. Field Notes: Acoustic Levitator Demo

[01:21–07:00]

• Hannah introduces Michael to a tabletop acoustic levitator (crediting Matthew Nethercote at Cambridge University), igniting both skepticism and excitement.
• Device Description:
  • A “hand-sized” 3D-printed dome containing 72 tiny speakers, all focusing on a central point.
  • Speakers are positioned “like a Star Trek teleporter” ([04:31]).
• Basic Science:
  • Sound as a Wave: Speakers vibrate membranes, pushing air to create pressure waves. Precisely tuned, overlapping sound waves can create “nodes” (areas of stillness) where light objects can float ([05:10–05:51]).
• Demo Sound:
  • Hannah turns on the device. Neither host can hear its ultrasonic whine, but “100 metres down the road there are several dogs that are now crying” ([05:59], Hannah Fry).

2. How Does Acoustic Levitation Actually Work?

[05:10–06:21]; [13:15–14:47]

• Waves Collide: When two sound waves of the right frequency and phase meet, they create standing waves; objects can be trapped in nodes by air pressure differentials.
• Frequency: The discussed device uses 22,000 Hz—above human hearing for most adults ([14:13–14:15]).
• Levitation Cage: These “cages of air pressure” only successfully trap very small, very light objects—like beads of Styrofoam (polystyrene).

3. Could You Levitate a Human?

[07:00–08:15]

• Calculations: To levitate an average human (~75 kg) would require 216 million transducers at 120 dB each ([07:00]).
• Lethal Sound Levels: Attempting this would create a sound “so loud, your head might explode.”
  • Quote, Hannah Fry:

    “Any sound above 170 decibels can cause organ and joint damage... Anything above 240 decibels, that would be lethal. And so at 216 million, I think that the reality is we could levitate you. It’s just—it would be so loud, your head might explode. Small caveat. Small caveat.” ([07:32–08:15])

• Michael’s Response:

  “It’s worth it. You wanted drama.” ([08:15], Michael Stevens)

4. Real-World and Medical Applications

[08:15–10:40]

• Historical Experimentation: NASA used acoustic levitators in the ‘60s and ‘70s for simulating microgravity.

• Medical Tech:

  • Kidney Stones: Using acoustic beams to nudge and break up kidney stones for easier passage ([09:00]).
  • Targeted Drug Delivery: Encapsulating drugs in “microbubbles” moved and burst at target sites via ultrasound, with the goal of minimizing toxicity elsewhere in the body.
  • Pill Cameras: Ultrasonic steering for cameras that can “film inside the body.”

• Michael: “A little micro cinematographer could make a movie in my body, controlling with sound waves.” ([10:40])

• Comparison to Magnets: Michael notes.

  “Trying to move things around in a body with, like, magnets, ... would require what you’re moving to respond to the magnet. And they’re ultrasonic, so they don’t bother us.” ([10:11–10:24])

5. Sound Perception and Human Hearing

[11:08–14:13]

• Sound Transmission in the Body: Discussion of how sound travels into the human body, including prenatal auditory perception.
  • Michael references experiments where fetuses react to face-like shapes projected by lasers through the womb ([11:53–12:41]).
• The Mosquito Device: Brief stories about high-frequency devices meant to deter teenagers ([13:00–13:28]).
• Live Kid Experiment:
  • Hannah tests her device on her child, demonstrating the generational cutoff for ultrasonic hearing.
    • “Super kid. 19,000 hertz you went up to. I stopped at about 12,000.” ([14:04–14:10], Michael Stevens)

6. Levitation vs. Support: Philosophical Musings

[15:11–15:28]

• Michael questions whether this qualifies as “levitation”—isn’t it just air pressure holding things up? Are planes also levitating?
• Hannah retorts:

  “How dare you. It’s not touching the ground. Michael, you’re being way too strict with your definition.” ([15:19–15:24])

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Notable Quotes & Memorable Moments

• On the limitations of acoustic levitation:
  Hannah Fry, [07:32–08:15]

  “Any sound above 170 decibels can cause organ and joint damage... at 216 million, I think that the reality is we could levitate you. It’s just—it would be so loud, your head might explode. Small caveat. Small caveat.”

• On applications in medicine:
  Hannah Fry, [09:00–09:22]

  “With acoustic beams... you sort of break [kidney stones] up with ultrasound, and then you nudge them into positions in the body where they could... be naturally cleared.”

• On pill-sized cameras:
  Michael Stevens, [10:40]

  “A little micro cinematographer could make a movie in my body, controlling with sound waves.”

• On strict definitions:
  Michael Stevens, [15:11–15:19]

  “I got stuck on defining levitation, because this isn’t levitation. It’s using force of air pressure to resist gravity.”
  Hannah’s retort: “How dare you. It’s not touching the ground. Michael, you’re being way too strict with your definition.”

• On the generational threshold for ultrasonic hearing:
  Michael Stevens, [14:04]

  “Super kid. 19,000 hertz you went up to. I stopped at about 12,000.”

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Important Timestamps

| Segment | Time | Details | |------------------------------------|----------|---------------------------------------------------------------------| | Acoustic levitator showcase | 01:21–07:00 | Demo, structure, basic physics | | Scaling up: human levitation math | 07:00–08:15 | Power requirements, safety issues, maximum decibels | | Medical applications discussion | 08:15–10:40 | NASA origins, drug delivery, kidney stones, pill cameras | | Sound in the body and perception | 11:08–14:13 | Human/fetal hearing, “Mosquito” deterrents, in-home kid test | | Philosophical levitation debate | 15:11–15:28 | What counts as levitation? |

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Listener Questions & Final Segment Highlights

1. Can a Human Out-Swim a Shark?

[20:40–25:27]

• Depends on the shark—for slow species like the Greenland shark, yes. For a mako, no chance.
• The conversation broadens into how swimsuit technology and finger positioning affect human swim speed, ultimately blending humor and advanced fluid dynamics.

2. Invent a Useless-but-Scientific Machine

[25:36–30:19]

• Michael: A titration-based color-changing clock.
• Hannah: Long-duration hourglass concepts, leading to a tangent about the pitch drop viscosity experiment (running since 1927).
• Fun Fact: “There’s an hourglass in Japan that goes for an entire year... It’s one of my dreams to go and visit it.” ([27:14], Michael Stevens)

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Summary Takeaways

• Acoustic levitation is a real effect that exploits the physical principles of standing sound waves and air pressure nodes.
• Limitations: Current acoustic levitators only work for tiny, lightweight objects. Scaling up to human-sized objects is theoretically possible, but practically lethal due to sound pressure.
• Medical and industrial uses are already here, with ongoing work in manipulating kidney stones, targeted drug delivery, and navigating in-body cameras—all via sound.
• Philosophical lines blur between levitation, support, and the definitions of physical force.
• Perception of sound, especially ultrasonic frequencies, varies by age—a point humorously demonstrated live with Hannah’s child.
• Curiosity and scientific playfulness define the episode, making advanced concepts feel accessible and fun.

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Listening to The Rest Is Science will leave you marveling at the strange corners of everyday reality—and believing, just for a moment, that with enough speakers and some imagination, even levitation might not be just a fantasy.

Transcript

[A]

This episode is brought to you by Cancer Research UK.

[B]

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

[A]

Well, that is 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.

[B]

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.

[A]

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. More people who are living longer, better lives.

[B]

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 restiscience.

[A]

Would you like to levitate, Michael?

[B]

I would love to, every day.

[A]

Wouldn't it be good?

[B]

Wouldn't it be good?

[A]

Well, today on Field Notes, 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 little acoustic levitator with me.

[B]

Oh, really?

[A]

Have you ever played with one of these?

[B]

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.

[A]

That's exactly what I've got.

[B]

Oh, no. Does it also make this noise that's like. And you're like. Oh, please.

[A]

Okay, yeah, I've got that in some calculations.

[B]

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.

[A]

Oh, I guess I.

[B]

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

[A]

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

[B]

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

[A]

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

[B]

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

[A]

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, maths departments are completely full of people who care a lot about acoustics. Did you know this?

[B]

Yes, I bet.

[A]

Like jet engines, for example. 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. Right 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?

[B]

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

[A]

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

[B]

Okay, okay.

[A]

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 Nethercote, by the way, who let me steal this in order to. In order to impress you, Michael. Which was. Which was. I'll try a lot harder next time. Let me put it that way. Okay, I'm going to.

[B]

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 size.

[A]

Like a hand size. There you go.

[B]

And it looks like some kind of Star Trek teleporter.

[A]

It does, yeah. So you've got two bits. One. One at the top, one at the bottom, and ins a dome, effectively, that is filled with lots and lots of tiny little speakers that are. Paul. Pointing towards this kind of central space, sort of. How can you describe it? I never watched Star Trek, but there. Isn't there 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.

[B]

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

[A]

The idea here, then, is that 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. 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 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.

[B]

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

[A]

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

[B]

Can'T hear it either.

[A]

100 metres down the road there are several dogs that are now crying because it is so high pitched, very high pitched.

[B]

Okay, so the idea is that sound waves compressed, they're waves of air that's being compressed and rarefied. And if you get what, like two, two compressed waves side to side, you can like hold something in the air.

[A]

Exactly.

[B]

Now can you change the frequency of the sound with this device and change where these levitation points are?

[A]

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

[B]

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

[A]

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

[B]

Well, yeah, no, I've seen them levitate living frogs in laboratories with very powerful versions of this. And I'm wondering what the applications are beyond the amusement.

[A]

Well, okay, let's stick on the fun for a second here because. Because let's say the average human weighs about, I don't know, what do you reckon, 75 kg, something like that? That's what I've done with my calculations. This particular levitator has 72 little transducers right around here. So if you wanted to raw power, lift a human, you are gonna need 216 million of them, which is, oh, I would say quite a lot.

[B]

Um, that's a lot. But let's say you did it.

[A]

Let's say you did it.

[B]

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

[A]

Well, here's the thing. You need them to be like super, super loud, right? In order to, in order to actually have the sort of strength between them to, to be able to lift this human. You can get them up to about 120 decibels. But remember, you've got 216 million of them. Now, the slight problem is that any sound above 170 decibels can cause organ and joint damage just because it vibrates so violently that you. You start to implode. Anything above 240 decibels, that would be lethal.

[B]

Wow.

[A]

And so at 216 million, I think that the reality is we could levitate you. It's just. It would be so loud, your head might explode. Small caveat. Small caveat.

[B]

It's worth it. It's worth it. You wanted drama.

[A]

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 1960s, 1970s, NASA, they, they developed these kind of levitators partly because they wanted to see what it would be like to have a, effectively a microgravity environment.

[B]

Oh, yeah.

[A]

You can imagine if you were like, suspending, instead of tiny little balls here, you were suspending cells or like, other sort of organic matter. It's effectively the same as, like, being suspended in zero gravity. You're not gonna feel the force of the earth because it's counteracted by this little cage of air that is. 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 clear.

[B]

Huh.

[A]

There's also. This is the one that I really like. You can have targeted drug delivery with this. So you can create 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 and then burst the bubble using ultrasound to release the medication. And this is particularly useful if you have something like 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 interact with. 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.

[B]

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.

[A]

Yeah, just the neighborhood dogs. Yeah, the other thing. 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 move it all around the body.

[B]

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.

[A]

In what way? Go on.

[B]

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.

[A]

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 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.

[B]

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. Oh, wow. 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.

[A]

Yeah.

[B]

This is of course a baby that's developed enough to have a retina and 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.

[A]

Wow.

[B]

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

[A]

I mean, it's essentially like you're, you're. 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.

[B]

Really?

[A]

Of course, I've only seen it for, for babies that have Been born.

[B]

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?

[A]

Like the mosquito noise or the.

[B]

Yeah.

[A]

In the States, where they had a. They had a device that was designed to stop teenagers from hanging out in public areas.

[B]

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 was supposed to annoy juvenile delinquents.

[A]

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?

[B]

Well, yeah, let's do an experiment, Saleh.

[A]

For real?

[B]

Yeah. And see if they can guess when it's on or off to see if they're getting it. Okay, here's our test subject.

[A]

Here's our test subject. Okay, you. I 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?

[B]

No.

[A]

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

[B]

Super kid.

[A]

Super kid. 19,000 hertz. You went up to. I stopped at about 12,000.

[B]

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

[A]

It's 22. 22,000.

[B]

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 waves, like, collide from the top and bottom and. 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. And this somehow creates, like, a cage of air pressure that can hold very lightweight objects.

[A]

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 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.

[B]

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

[A]

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

[B]

Okay, so then what about. Do airplanes levit. They're not touching the ground.

[A]

Shush, shush, shush, shush. Now let's go to a break.

[B]

Okay, let's go to a break.

[A]

This episode is brought to you by Cancer Research uk.

[B]

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

[A]

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

[B]

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

[A]

Short answer, yes. Longer answer, how?

[B]

How?

[A]

Okay. I mean, this is it, right? Because, okay, cancer doesn't just appear out of nowhere. It leaves these. These molecular fingerprints in your body. These. This long before symptoms end up showing these little fragments of DNA, these proteins, other little molecules that. 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.

[B]

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

[A]

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

[B]

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

[A]

Yeah. These faint little signals, and detect them even earlier. And this is different. This is separate from traditional biopsies. Right. Which 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.

[B]

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

[A]

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

[B]

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

[A]

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.

[B]

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.

[A]

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.

[B]

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

[A]

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

[B]

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.

[A]

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.

[B]

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

[A]

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

[B]

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

[A]

Yeah. Rather than having long stretches between biopsies, for example. 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.

[B]

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

[A]

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.

[B]

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

[A]

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 signals, we can get Ahead of cancer, we can have the best shots at beating it.

[B]

For more information about Cancer Research uk, their research breakthroughs, and how you can help them, visit cancerresearchuk.org restiscience. 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?

[A]

No. Next question.

[B]

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? Yeah, like there are sharks that swim really slowly. The Greenland shark only swims at about 1 mile per hour. That's about 0.34 meters per second.

[A]

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

[B]

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.

[A]

How does that convert to miles an hour?

[B]

About five and a half miles per hour.

[A]

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

[B]

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

[A]

What I will say is I can definitely not swim that fast. Yeah, that's the sort of Michael Phelps territory.

[B]

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

[A]

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 are aerodynamically useless.

[B]

I mean, Google says the fastest shark is the short fin mako, which can travel at 31-46 mph in the water.

[A]

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

[B]

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

[A]

Knots per month?

[B]

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.

[A]

Yeah.

[B]

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

[A]

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.

[B]

What do you mean you can't swim naked?

[A]

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

[B]

Right, right.

[A]

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

[B]

Right.

[A]

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

[B]

Fascinating.

[A]

Okay, so all of those things, 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 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, what happens is you get these little eddies that appear. This turbulence that appears between your fingers that are, 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 finger slightly apart. Basically, you wanna, like, think of your hand as these big scoops going through the water.

[B]

Right? And those eddy currents are almost like webbing made of water that stops water from going through. That's really cool.

[A]

So maybe, maybe science will make people swim faster.

[B]

I know. Watch out. Mako shark. Thanks for the question. Neil, you want to take Ellie's question?

[A]

Yeah, go on. 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?

[B]

Okay, 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 my mind, you've got, like, 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 gradient from clear to red. And you just, like, turn it until it matches the color of the beaker. 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 reds match, and you go, oh, wow, guys, it's afternoon now.

[A]

I like that so much. I've actually wanted something like an hourglass bus for a really long time that lasts much longer than an hour. Right. I wanted one. You know, there's some things that you want to do every couple of weeks. Right? Every couple of weeks. Maybe you want to, like, water your plants, for example. 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.

[B]

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

[A]

Is that. How big is it?

[B]

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.

[A]

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

[B]

Yeah, the longest running experiment since 1927.

[A]

So this is.

[B]

Wait, so it's going to be hitting its 100 year anniversary in a couple years. That'll be a special moment.

[A]

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

[B]

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 not flowy that it pours out of the funnel that it's in. Well, I mean, so slowly that it's been almost a hundred years and it's still coming out.

[A]

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

[B]

Yeah, the feed. Okay. So the experiment uses pitch that is 100 billion times more viscous than water.

[A]

Wow. That's incredible. Absolutely incredible.

[B]

Can I just read you? I want to.

[A]

This is.

[B]

This is so fascinating.

[A]

Please.

[B]

In 1927, 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 1930, 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 40 years for another five to follow. My gosh.

[A]

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 gotta wait another 10 years. Someone who took over the experiment after Thomas Parnell 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.

[B]

Right.

[A]

In 1977, apparently he left the lab for a few minutes, and then the drop fell. And then in 1988, the next time, 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's half of his career trying to see a single drop in the jar and. Yeah. Died without having seen it.

[B]

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.

[A]

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

[B]

I'm gonna write it down.

[A]

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

[B]

Oh, sounds like a fun time.

[A]

Very good. We'll see you next time.

[B]

Yeah, we'll see you next time. So what's really going on between Donald Trump and Venezuela right now? I'm Gordon Carrera, national security journalist. And I'm David McCloskey, author and and former CIA analyst. And we together, the hosts of the Rest Is Classified. In our latest emergency episodes, we go deep into the inside track of what's really going on in the spy war in Venezuela. And we're looking at how, with the help of the CIA, Donald Trump has managed to oust Venezuela's leader. So get the full insider scoop by listening to the Rest is Classified. Wherever you get your podcasts.