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The Rest Is Science
The Rest Is Science

Why Sharks Attack The Internet

November 05, 2026 • 49m

Summary

⏱️ 10 min read

Overview

Hannah Fry and Michael Stevens explore the fascinating world of undersea internet cables, revealing how the internet's main arteries are surprisingly thin fiber optic cables lying on the ocean floor. Hannah brings a physical sample to show Michael, explaining how these cables work, their vulnerabilities, and the incredible technology that allows them to transmit data at nearly half a quadrillion bits per second. The episode also covers the etymology of planet names, the mathematical beauty of knot theory, and the hosts' personal superstitions despite being science-minded people.

Introduction and Deep Sea Internet Cables

Hannah introduces a deep sea internet cable she borrowed from someone she met at a pub, sparking an enthusiastic discussion about submarine cables. The physical sample reveals the surprising thinness of these crucial internet arteries - only about 21 millimeters in diameter at their thickest point. Despite their small size, these cables carry far more internet traffic than satellite networks like Starlink, with the entire Starlink fleet carrying only as much data as a single cable.

  • Hannah met someone at a pub who lent her a deep sea internet cable sample to show on the podcast
  • The cable cross-section looks like the Tower of Babel with staggered cylindrical layers
  • Most people imagine these cables as sewage-pipe sized, but they're actually the diameter of a garden hose
  • The armored reinforcement layers only exist near shorelines to protect from anchors and trawlers
  • The entire Starlink fleet carries only as much internet as one of these cables
" The entire Starlink fleet only carries as much internet as one of these cables. "

Cable Structure and Ocean Floor Reality

The discussion reveals that for most of the ocean, only a remarkably thin cable - just 21 millimeters in diameter - lies on the seafloor. The white protective coating seen in the sample represents what actually spans thousands of kilometers across ocean floors. Inside this thin exterior are even finer fiber optic strands, thinner than hairs, which carry all the data through pulses of light.

  • The actual cable on the ocean floor is only 21 millimeters thick - the width of the white layer in the sample
  • The fiber optic strands inside that carry data are as thin as hairs
  • Some cables are over 10,000 kilometers long
  • It would be too expensive to armor-plate the entire length, so most of it is just the thin cable

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