Secrets of ancient Greek 'computer' solved by Glasgow astronomers

The mechanism dates to the second century BCE and was discovered in 1901 by divers exploring a sunken shipwreck near the Aegean island of Antikythera.

Thought to have been the size of a shoebox when it was complete, the device was broken into fragments, including a complex series of gears and cogs which were unusually intricately-tooled.

The machine has fascinated researchers for more than a century — and featured as a time-travel device in the Indiana Jones film The Dial of Destiny.

After decades of research it was proposed that device – often described as the oldest known analogue computer - was a form of solar calendar, capable of predicting the positions of the moon, planets and eclipses decades in advance.

No construct of comparable intricacy would be created until the 14th century, though the mechanism’s precise function continues to be debated.

The mechanism is badly degraded (Image: NQ)

Researchers in Glasgow now say they have solved a piece of the puzzle, thanks to techniques used to analyse the ripples in spacetime detected by one of the 21st century’s most sensitive pieces of scientific equipment.

Astronomers from the University of Glasgow used statistical modelling techniques originally developed to probe gravitational waves released by colliding black holes, and applied them to one of the rings on the mechanism.

In 2020, new X-ray images of one of the devices segments, known as the calendar ring, revealed fresh details of regularly spaced holes underneath. But as the ring was broken, it wasn’t clear how just how many holes were there originally.

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Initial analysis by Antikythera researcher Chris Budiselic and colleagues suggested it was likely somewhere between 347 and 367.

Working during the Christmas holidays, the Glasgow researchers used two statistical analysis techniques to reveal new details about the calendar ring, and came to the conclusion the artefact was “vastly” more likely to have had 354 holes.

This corresponds to the lunar calendar, meaning the device could also track the path of the moon as well as other heavenly bodies.

The astronomers’ findings are published in a paper in the Horological Journal.

The researchers are more used to probing the mysteries of the cosmos (Image: Glasgow University)

Professor Graham Woan, of the University of Glasgow’s School of Physics & Astronomy, one of the authors of the paper said: “Towards the end of last year, a colleague pointed to me to data acquired by YouTuber Chris Budiselic, who was looking to make a replica of the calendar ring and was investigating ways to determine just how many holes it contained.

“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 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 placement of the ring’s surviving six fragments.

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 at the University’s Institute for Gravitational Research, Dr Joseph Bayley, also heard about the problem. He adapted techniques used by their research group to analyse the signals picked up by the LIGO gravitational wave detectors, which measure the tiny ripples in spacetime to scrutinise the calendar ring. 

The methods Woan and Bayley used provided a comprehensive probabilistic set of results, again suggested that the ring most likely contained 354 or 355 holes in a circle of radius 77.1mm, with an uncertainty of about 1/3 mm.

It also reveals that the holes were precisely positioned with extraordinary accuracy, with an average radial variation of just 0.028mm between each hole. 

The device featured in the latest Indiana Jones film (Image: PA)

Bayley, a co-author of the paper, is a research associate at the School of Physics & Astronomy. He said: “Previous studies had suggested that the calendar ring was likely to have tracked the lunar calendar, but the dual techniques we’ve applied in this piece of work greatly increase the likelihood that this was the case. 

“It’s given me a new appreciation for the Antikythera mechanism and the work and care that Greek craftspeople put into making it – the precision of the holes’ positioning would have required highly accurate measurement techniques and an incredibly steady hand to punch them. 

Professor Woan added: “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. 

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

  The paper, titled ‘An Improved Calendar Ring Hole-Count for the Antikythera Mechanism: A Fresh Analysis’, is published in Horological Journal.