Astrophysicists from the University of Glasgow used gravitational wave detection techniques to finally determine which calendar the Antikythera mechanism tracked — and it all started with a YouTube video
In 1901, Greek sponge divers hauled a corroded bronze object from the seafloor near the island of Antikythera. Decades of study revealed it to be a sophisticated mechanical calculator — shoebox-sized, packed with dozens of interlocking bronze gears, and designed to model astronomical cycles. Today it is recognised as the world’s oldest known analog computer, predating ENIAC by nearly two millennia.
One of its greatest mysteries centred on the so-called calendar ring — a damaged component whose regularly spaced holes were first imaged clearly by X-ray in 2020. Only six fragments of the ring survived, leaving researchers unsure whether it originally held 354, 360, or 365 holes — each number corresponding to a different ancient calendar system.
The breakthrough began with a YouTube channel. Chris Budiselic, who runs Clickspring, had been documenting his attempt to build a working replica of the mechanism and published precise measurements of the surviving holes online. Astrophysicist Graham Woan at the University of Glasgow came across the data — and saw a statistical puzzle he could solve using tools from his own field.
“It struck me as an interesting problem, and one that I thought I might be able to solve in a different way during the Christmas holidays, so I set about using some statistical techniques to answer the question.” — Professor Graham Woan, University of Glasgow
Woan and his colleague Joseph Bayley applied Bayesian analysis alongside signal-processing methods borrowed from LIGO — the gravitational wave observatory that detects ripples in spacetime from colliding black holes. The verdict was clear: the ring is vastly more likely to have had 354 holes, corresponding to the lunar calendar, than 365 holes, which would have followed the Egyptian calendar — and 354 holes is hundreds of times more probable than the previously proposed 360-hole count.
Equally striking was the craftsmanship the analysis revealed. The holes were precisely positioned with extraordinary accuracy, with an average radial variation of just 0.028 mm between each hole — a level of precision that would have required specialised measuring tools and an exceptionally steady hand, suggesting ancient Greek technology was far more advanced than previously assumed.
The study, published in the July 2024 issue of The Horological Journal, was summed up by Woan himself:
“It’s a neat symmetry that we’ve adapted techniques we use to study the universe today to understand more about a mechanism that helped people keep track of the heavens nearly two millennia ago.”