Radiolab Podcast Summary: "The Darkest Dark"

Radiolab, hosted by Lulu Miller and Latif Nasser, delves deep into the mysteries of darkness in the episode titled "The Darkest Dark", released on January 17, 2025. This episode explores the enigmatic world of ultra-black deep-sea fish through the investigative journey of biologist Sanka Johnson from Duke University. Combining scientific inquiry with profound philosophical insights, the episode unravels how certain creatures achieve the darkest hues on Earth and the broader implications of these findings.

1. Introduction and Setting the Scene

Molly Webster, one of the hosts, sets the stage by sharing her experience of winter darkness, creating a personal connection to the episode's theme of darkness.

[03:17] Molly Webster: "We are in the middle of deep winter. The shortest day of the year just happened... it can feel like there's just nothing out there. There's nothing beyond it, there's nothing in it. It's just kind of this black void."

This introspection leads her to encounter Sanka Johnson, whose work redefines her understanding of darkness.

2. Sanka Johnson’s Deep-Sea Expedition

Sanka Johnson narrates his experiences aboard a research vessel navigating the pitch-black depths of the ocean.

[02:17] Sanka Johnson: "When we're at sea, beyond the ship lights, it's absolutely dark... you feel like it's asking you something."

Describing life on the ship, he emphasizes the suffocating industrial environment dominated by steel and diesel fumes.

[04:48] Sanka Johnson: "You live in a very small room... a bit like an oil rig platform without the oil."

Despite the challenges, Sanka expresses a profound passion for being at sea, highlighting the unique and isolated life aboard.

3. The Mystery of Ultra-Black Fish

Sanka introduces the core mystery: capturing images of deep-sea creatures so black they elude photography.

[06:19] Sanka Johnson: "80 to 90% of the species down there can make light... but there was this group of animals that we simply could not get a good photograph because they were just so... incredibly black."

He describes how these fish resemble "the black holes of fishes," absorbing nearly all light, making them indistinguishable from their surroundings.

4. Scientific Investigation into Darkness

To understand the unprecedented blackness, Sanka and his team investigate beyond pigments to the very structures that create color.

a. Exploring Structural Coloration

They examine butterfly wings, notably the Brooks birdwing, discovering that microscopic structures, not just pigments, contribute to their color.

[18:07] Sanka Johnson: "It's like this weird little forest where photons go to die."

Using advanced microscopy, they uncover a "honeycomb array" of tiny structures that trap light, preventing its reflection and thus creating ultra-blackness.

b. Linking to Moon Regolith

Unexpectedly, the mathematics used to study the Moon's soil ("regolith") becomes instrumental in understanding the fish's dark coloration.

[25:07] Sanka Johnson: "It turns out the soil of the Moon... is not so different in terms of the shape and size and refractive indices and absorption of these black fish."

This cross-disciplinary approach allows them to simulate and confirm how light interacts with the fish's melanosomes—the microscopic structures containing melanin.

5. Discoveries and Implications

The research reveals that the fish achieve their darkness through a precise arrangement of melanosomes, optimizing light absorption beyond what pigments alone can achieve.

[25:30] Sanka Johnson: "They were about three to four times as black right in the area where the bioluminescence was."

This discovery has significant implications for technology, inspiring engineers to develop materials like Vantablack, which absorb nearly all light.

[26:43] Sanka Johnson: "Engineers try to make little tic tacs... to make really dark materials. Solar cells are a really big deal because everyone's trying to optimize the amount of electricity you can get out."

However, despite understanding the mechanism, photographing these fish remains elusive, underscoring the effectiveness of their natural camouflage.

[27:22] Sanka Johnson: "We still can't photograph an anglerfish. We can't get a good picture."

6. Philosophical Reflections on Darkness

Beyond the scientific exploration, the episode delves into the philosophical nature of darkness. Sanka challenges the notion of darkness as emptiness, portraying it instead as a presence rich with complexity.

[30:00] Sanka Johnson: "Blackness, at least in my experience, is not an emptiness, but has an incredible presence. It feels very rich, like, you know, like it's the ultimate substance."

Molly Webster synthesizes this by highlighting that darkness contains multitudes, suggesting that what feels like an emptiness is actually a profound and intricate realm.

[29:23] Molly Webster: "Whether you're talking about a fish or the looming gloom outside of your window, what feels like an emptiness... actually contains multitudes. And not just that it is a place where all the light falls inside of it. So in a way, the darkest thing is also the brightest."

7. Corrections and Clarifications

In the concluding segments, Molly addresses factual clarifications, ensuring accuracy regarding species like dragonfish and fangtooth fish, and acknowledging advancements in ultra-black materials surpassing Vantablack.

[30:31] Molly Webster: "Dragonfish, in fact, are not the fish that have fangs that slide back into their skulls. That is the fangtooth fish..."

Conclusion

"The Darkest Dark" weaves a narrative that traverses the abyssal depths of the ocean to the frontiers of material science, all while pondering the essence of darkness. Through Sanka Johnson's relentless quest to unveil the secrets of the blackest fish, Radiolab invites listeners to reconsider their perceptions of darkness—not as mere absence of light, but as a realm teeming with hidden complexities and profound presence.

Notable Quotes:

• Molly Webster [03:17]: "There's just kind of this black void."

• Sanka Johnson [06:19]: "They're like the black holes of fishes."

• Sanka Johnson [18:07]: "It's like this weird little forest where photons go to die."

• Sanka Johnson [25:30]: "They were about three to four times as black right in the area where the bioluminescence was."

• Molly Webster [29:23]: "What feels like an emptiness... actually contains multitudes."

References:

For an in-depth exploration and to read more about ultra-black materials and deep-sea biodiversity, visit Radiolab's website.