Gravitational wave researchers shed new light on the mystery of the Antikythera mechanism

Techniques developed to analyze ripples in space-time detected by one of the most sensitive scientific instruments of the 21st century have helped shed new light on the function of the oldest known analog computer.

Astronomers at the University of Glasgow used statistical modeling techniques developed to analyze gravitational waves to determine the likely number of holes in one of the broken rings of the Antikythera Mechanism, an ancient artifact featured in the movie “Indiana Jones and the Dial of Destiny.”

While the film version allowed the intrepid archaeologist to travel through time, the Glasgow team’s results provide fresh evidence that one of the components of the Antikythera mechanism was most likely used to track the Greek lunar year. They also offer a new perspective on the remarkable craftsmanship of the ancient Greeks.

The mechanism was discovered in 1901 by divers while exploring a sunken wreck near the Aegean island of Antikythera. Although the shoebox-sized mechanism shattered into fragments and eroded, it quickly became apparent that it contained a complex array of gears that had been unusually intricately machined.

Decades of subsequent research and analysis proved that the mechanism dates back to the second century BC and functioned as a kind of hand-operated mechanical computer. External dials attached to internal gears allowed users to predict eclipses and calculate the astronomical positions of the planets on a given date with an accuracy unmatched by any other known contemporary device.

In 2020, new X-ray images of one of the mechanism’s rings, known as the calendar ring, revealed new details of the regularly spaced holes that lie beneath the ring. Because the ring was broken and incomplete, it was unclear how many holes there were originally. Initial analysis by Antikythera researcher Chris Budiselica and colleagues suggested it was probably somewhere between 347 and 367.

Now in a new article published in Horological magazineGlasgow researchers describe how they used two statistical analysis techniques to reveal new details about the calendar ring.

They show that it is much more likely that the ring had 354 holes, which corresponds to the lunar calendar, than 365 holes, which would follow the Egyptian calendar. The analysis also shows that 354 holes is a hundred times more likely than a ring with 360 holes, which previous research suggested as a possible number.

Professor Graham Woan of the University of Glasgow’s School of Physics & Astronomy is one of the authors of the paper. He said: “Late last year, a colleague pointed me to data obtained by YouTuber Chris Budiselic, who was trying to create a replica calendar ring and was researching ways to determine how many holes it contained.

“It struck me as an interesting problem, and I thought I could solve it in a different way over the Christmas holidays, so I started using some statistical techniques to answer the question.”

Professor Woan used a technique called Bayesian analysis, which uses probability to quantify uncertainty based on incomplete data, to calculate the likely number of holes in the mechanism using the positions of the surviving holes and the locations of the six ring fragments that survived. His results showed strong evidence that the mechanism’s calendar ring contained either 354 or 355 holes.

At the same time, one of Professor Woan’s colleagues from the university’s Institute for Gravity Research, Dr. Joseph Bayley. He adapted the techniques used by their research group to analyze the signals picked up by LIGO’s gravitational wave detectors, which measure tiny ripples in space-time caused by massive astronomical events such as colliding black holes as they pass through Earth, to probe the calendar ring.

The Markov Chain Monte Carlo and nested sampling methods used by Woan and Bayley provided a comprehensive probabilistic set of results, again suggesting that the ring most likely contained 354 or 355 holes in a circle of 77.1 mm radius, with an uncertainty of about 1/3 mm . . It also reveals that the holes were precisely located with extraordinary precision, with an average radial deviation of only 0.028 mm between each hole.

Bayley, a co-author of the paper, is a research fellow in the School of Physics & Astronomy. He said: “Previous studies suggested that the calendar ring probably followed the lunar calendar, but the dual techniques we used in this work greatly increase the likelihood that this was the case.

“It gave me a new appreciation for the Antikythera mechanism and the work and care that Greek craftsmen put into making it – the precision of the placement of the holes would have required highly precise measuring techniques and an incredibly steady hand to punch them.

Professor Woan added: “It is a neat symmetry that we have adapted to the techniques we use to study the universe today to better understand the mechanism that helped people observe the heavens almost two millennia ago.

“We hope that our findings about the Antikythera Mechanism, while less supernaturally impressive than those made by Indiana Jones, will help deepen our understanding of how this remarkable device was made and used by the Greeks.”