New analysis of the Antikythera mechanism challenges age-old assumption

The inspiration for the title device in last year’s blockbuster, Indiana Jones and the Dial of Fatewas a real archaeological artifact: the Antikythera Mechanism, a 2,200-year-old bronze mechanical computer. It has no mystical time travel powers, but the device has It has been the subject of rigorous scientific research for decades, and is thought to have been used to predict eclipses and calculate planetary positions.

A new paper published in The Horological Journal found evidence that the mechanism’s calendar ring was designed to track the lunar calendar based on statistical techniques from physics, specifically the study of gravitational waves. This contradicts a centuries-old assumption among scholars of the mechanism that the calendar ring had 365 holes, and therefore followed a solar calendar, but is consistent with the conclusions of a 2020 analysis.

“It’s a beautiful symmetry that we’ve adapted techniques we use today to study the cosmos to understand more about a mechanism that helped humans keep track of the heavens almost two millennia ago,” said co-author Graham Woan, an astrophysicist at the University of Glasgow. “We hope that our findings on the Antikythera Mechanism, while less supernaturally spectacular than Indiana Jones’s, will deepen our understanding of how this remarkable device was made and used by the Greeks.”

As previously reported, in 1900, a Greek sponge diver named Elias Stadiatis discovered the wreck of an ancient cargo ship off the coast of the island of Antikythera in Greece. He and other divers recovered various artifacts from the ship. A year later, an archaeologist named Valerios Stais was examining what he thought was a piece of rock salvaged from the shipwreck when he noticed that it contained a gear. It turned out to be an ancient mechanical device. The Antikythera Mechanism is now housed in the National Archaeological Museum of Athens.

In 1951, a British historian of science named Derek J. de Solla Price began investigating the theoretical workings of the device. Based on X-ray and gamma-ray photographs of the fragments, Price and physicist Charalambos Karakalos published a 70-page paper in the Transactions of the American Philosophical Society in 1959. Based on these images, they hypothesized that the mechanism was used to calculate the motions of stars and planets, making it the first known analog computer.

Michael Wright, then curator of mechanical engineering at the Science Museum in London, made headlines in 2002 with new, more detailed X-ray images of the device, taken using linear tomography. Wright’s closer analysis revealed a fixed central gear in the mechanism’s main wheel, around which other moving gears could rotate. He concluded that the device was specifically designed to model “epicyclic” motion, in keeping with the ancient Greek idea that celestial bodies moved in circular patterns called epicycles. (This was before Copernicus, so the fixed point around which they moved was assumed to be the Earth.)

In 2021, an interdisciplinary team at University College London (UCL) led by mechanical engineer Tony Freeth, an honorary professor at University College London, introduced a new computer model, revealing a dazzling rendering of the ancient Greek cosmos. The team’s efforts built on Wright’s work as part of the ongoing Antikythera Mechanism Research Project, which performed more advanced 3D X-ray imaging using tools including X-Tek Systems in the UK and Hewlett-Packard. Those images revealed much more of the original Greek transcription, confirming that it was an astronomical computer used to predict the positions of celestial objects in the sky. It’s likely that the Antikythera mechanism once had 37 gears, 30 of which survive, and that its face had graduations showing the solar cycle and the zodiac, along with hands to indicate the positions of the sun and moon.