The Rest Is Science – "This Glass Was Made By Lightning"

Hosts: Professor Hannah Fry & Michael Stevens (Vsauce)
Date: January 29, 2026

Episode Overview

In this lively edition of "The Rest Is Science," Hannah Fry and Michael Stevens take listeners on a journey through mind-bending scientific curiosities, from the true nature of mirrors to the explosive potential of miniature black holes and the creation of glass by lightning strikes. The episode lives up to its premise—challenging things "we think we know"—with playful thought experiments, deft explanations, and a tour of curious artifacts, like fossilized lightning. Listeners are encouraged to question familiar phenomena, shifting their perception of the ordinary—and perhaps to fear hamsters just a little.

Key Discussion Points & Insights

1. Why Do Mirrors Flip Us Horizontally, But Not Vertically?

(Begins ~03:08)

• Listener question: Why do mirrors flip us left-to-right but not top-to-bottom?

• Michael:

  • It’s a misconception: “Of course the answer is it's not flipping you horizontally. It's flipping you inside out. Everything that you present to a mirror gets reflected right back.” (03:39)
  • Flipping occurs because of our orientation relative to the mirror, not because the mirror "chooses" to reverse horizontally.
  • When you turn an object towards the mirror, you’re the one reversing it.
  • Analogy: The mirror gives back exactly what hits—it does not apply its own transformation; we perceive the reversal by virtue of how we envision flipping to match our reflection.

• Hannah:

  • Using tracing paper, the image matches the mirror view if you look through it, reinforcing that the mirror isn’t flipping horizontal/vertical but front-to-back.

• Michael:

  • Describes “inside out”: “My back and my front have been pushed through each other… and now I’m looking at myself squished inside out.” (05:38)

Memorable Quote:

"It's like the mirror is grabbing you by the nose and like popping you inside out."
— Hannah Fry, 06:13

2. How Dense Would a Hamster Have to Be to Become a Black Hole?

(Begins ~07:06)

• Hannah:

  • Ran the math for a "chubby Syrian hamster" (~150g).
  • To become a black hole (using the Schwarzschild radius), the hamster needs to be compressed to 2.2 × 10⁻²⁸ meters—over 10 trillion times smaller than a proton!
  • The required density: 3.3 × 10⁸¹ kg/m³ vs. a neutron star’s density (~10¹⁷ kg/m³).
  • Comparison: The mass of a hamster into that tiny volume is as bizarre as "a grain of sand compared to the entire Earth" (08:30).

• Michael (playful):

  • “Does it hurt the hamster?” (09:00)
  • Imagines a “miniaturizer machine” scenario: the hamster is unharmed and only realizes its newfound gravitational pull.

• Implication:

  • The hamster-black hole would be so unstable it would evaporate via Hawking radiation in 10⁻²⁶ seconds, instantly converting mass to energy.
  • Energy released: ~3.2 megatons of TNT — about 200 times Hiroshima's atomic bomb.

Memorable Quote:

"If you turned your hamster into a black hole, you would create a nuclear bomb."
— Michael Stevens, 11:31

• Takeaway:
  • The smallest creatures can make a difference… violently.

3. If the Earth Was the Size of a Pool Ball, Would It Be Smoother Than Any Manmade Object?

(Begins ~12:26)

• Hannah:

  • Introduces the myth about Earth's (relative) smoothness.

• Michael:

  • Debunks the myth: Earth scaled to a pool ball would feel as rough as 320-grit sandpaper, not perfectly smooth.
  • The pool ball’s regulation pertains to sphericity, not surface texture.
  • Real pool balls, under a microscope, exhibit scratches much smaller than Earth's largest features, debunking claims.

Memorable Quote:

"This whole Earth is smoother than a pool ball nonsense. Come on, let's grow up. Earth is bumpy. Its bumpiness deserves some credit."
— Michael Stevens, 18:45

• Physical sense:
  • Human touch can detect objects as small as 13 nanometers; a giant with a finger the size of Earth could distinguish cars from houses on Earth's surface.

4. Fossilized Lightning: Fulgurites

(Begins ~21:07)

• Hannah presents an object:

  • She reveals a "pinky finger"-sized, knobbly, hollow stick—unimpressive until you see the glassy inside.

• What is it?

  • Fulgurite: natural glass tube formed when lightning strikes sand, melting and vaporizing it, creating a glassy tube.
  • The outside remains rough from sand, inside smooth from melted quartz.

• Michael:

  • Intrigued by the parallel to geodes and the sound of glass.

Notable Quote:

"What I am holding in my hand is fossilized lightning."
— Hannah Fry, 22:59

• Fun facts:

  • Darwin collected them, and they’re readily available online.
  • Lightning strikes: Can be tracked live at blitzortung.org—with associated sounds for each strike.
  • Lightning occurs mostly near the equator, rarely near the poles.

• Cosmic rays:

  • May act as seeds for lightning by triggering ionization events within clouds.

5. The Science and Story of Fulgurites

(Begins ~23:57)

• How fulgurites form:

  • The intense heat (like a "mega powerful laser") from a lightning bolt melts sand into glass instantly; the core is vaporized, leaving a hollow tube.

• Why keep them?

  • Science and curiosity; they trap tiny bubbles of prehistoric air in the cooling glass, creating time capsules of atmospheric composition (e.g., Sahara Desert, 15,000 years ago).

• Demonstration:

  • Hannah snaps one: “Whoa. That was easy. Yeah, that was brittle.” (27:30)

Notable Quote:

"They are so smooth and glassy on the inside. It sort of feels otherworldly. It sort of feels like this is a freak moment that has created this."
— Hannah Fry, 26:44

6. Fulgurite’s Radioactive Cousin: Trinitite

(Begins ~28:47)

• Trinitite:

  • Glass created by nuclear detonations (Trinity test, New Mexico) turning desert sand into green, radioactive glass.
  • Not as easily (or safely) acquired as fulgurites.

• Michael’s radioactive collection:

  • Mentions owning radioactive lead and uranium minerals for science demos—strictly non-enriched forms.

• Hannah cautions:

  • “That’s closely guarded state secrets, isn’t it? Uranium enrichment?” (30:53)
  • Michael jokes about not knowing how to make usable uranium fuel, promising: “I might make some calls.” (30:53)

Notable Quotes & Moments (with Timestamps)

• Inside-out mirror explanation:

  "It's like the mirror is grabbing you by the nose and like popping you inside out." — Hannah Fry, 06:13

• Hamster black hole energy:

  "If you turned your hamster into a black hole, you would create a nuclear bomb." — Michael Stevens, 11:31

• Earth's 'smoothness':

  "This whole Earth is smoother than a pool ball nonsense. Come on, let's grow up. Earth is bumpy. Its bumpiness deserves some credit." — Michael Stevens, 18:45

• The wonder of fulgurites:

  "They are so smooth and glassy on the inside...It sort of feels like this is a freak moment that has created this." — Hannah Fry, 26:44

• Victorian air in a fulgurite:

  "Smells modern...Smells Victorian maybe." — Hannah Fry & Michael Stevens, 28:41–28:46

Important Timestamps

• Mirror paradox: 03:08–07:06
• Hamster black hole scenario: 07:06–12:03
• Earth’s pool ball myth: 12:26–18:45
• Fulgurites revealed: 21:07–29:06
• Fulgurite as air time capsules: 27:41–28:41
• Trinitite & radioactivity: 28:47–31:44

Final Words

The episode sparkles with playful analogies, deft myth-busting, and tactile demonstrations, leaving listeners with a new appreciation for the strange truths hidden in everyday things. Whether pondering the implausible fate of a hapless hamster or holding literal lightning in your hand, Fry and Stevens invite us all to keep questioning, keep touching, and stay curious.