The Rest Is Science: Could Sound Make You Levitate?

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

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.

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])

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.”

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? |

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)

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.

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.