The Internet Isn't in the Sky. It's Under the Sea

When you send a message across the world, it almost never goes through space. It travels as flashes of light through glass, along cables on the ocean floor. Here's what those cables are, how light carries your data, and what can break them. Timestamps - 0:00 Not through space 0:22 1. What they are 1:02 2. Data made of light 1:39 3. What breaks them 2:19 The cloud is under the sea What's covered: • Hundreds of undersea cables, over 1.5 million km of them, carry almost all the data travelling between continents • Inside a cable: glass fibres about as thin as a hair, wrapped in steel, copper and plastic, about as wide as a garden hose • Why cables near the shore get extra armour and are buried, and how cable ships lay them • 1858: the first transatlantic telegraph cable, Queen Victoria's 98-word message, and why it failed within weeks • How light carries data: flashes, bouncing inside the glass, repeaters every 50–100 km, and many colours per fibre • Why a signal crosses the Atlantic in about three hundredths of a second • What breaks cables: about 200 faults a year, mostly fishing gear and anchors (not sharks), and the 2022 Tonga eruption that cut a country off for five weeks Sources: • TeleGeography, "Submarine Cable FAQs" (2026), with FCC and International Cable Protection Committee data • Engineering and Technology History Wiki (IEEE), "Transatlantic Cable" • History.com, "The First Transatlantic Telegraph Cable Was a Bold, Short-Lived Success" • J. K. Perin (2018), Spectrally and Power Efficient Optical Communication Systems, PhD thesis, Stanford University (arXiv:1806.01945) • AFP via CBS News (22 Feb 2022) and AP via VOA (16 Feb 2022) on the Tonga cable The cable routes on the map are illustrative, and the crossing time is calculated (about 5,600 km ÷ 200,000 km/s). Subscribe to RSNBL for more.