University of Glasgow
Techniques developed to analyze ripples in space-time detected by one of the most sensitive scientific instruments of the 21st century have shed new light on the function of the oldest known analog computer.
Astronomers from the University of Glasgow have used statistical modelling techniques developed to analyse gravitational waves to determine the likely number of holes in one of the broken rings of the Antikythera Mechanism – an ancient artefact showcased in the film Indiana Jones and the Dial of Fate.
Although the film version allowed the intrepid archaeologist to travel through time, the results from the Glasgow team provide new evidence that one of the components of the Antikythera Mechanism was most likely used to track the Greek lunar year. They also provide new insights into the remarkable craftsmanship of the ancient Greeks.
Discovery of the Antikythera Mechanism
The mechanism was discovered in 1901 by divers exploring a sunken shipwreck off the Aegean island of Antikythera. Although the shoebox-sized mechanism was broken into pieces and eroded, it was soon revealed that it contained a complex series of gears, machined with unusual complexity.
Decades of subsequent research and analysis have shown that the mechanism dates back to the second century BC and functioned as a type of hand-held mechanical computer. External dials connected to the internal gears allowed users to predict eclipses and calculate the astronomical positions of planets on a given date with an accuracy unmatched by any other known contemporary device.
Inscriptions found on the Antikythera mechanism led to a number of breakthroughs in the creation of the ‘theoretically’ rebuilt Antikythera device. (Tony Freeth et al./ Nature)
Reassessment of the mechanism specifications
In 2020, new X-ray images of one of the mechanism’s rings, known as the Calendar Ring, revealed new details of regularly spaced holes that sit beneath the ring. However, because the ring was broken and incomplete, it wasn’t clear how many holes there originally were. Initial analysis by Antikythera researcher Chris Budiselic and colleagues suggested it was likely somewhere between 347 and 367.
Now, in a new article published in the Horological magazineThe Glasgow 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 would have followed the lunar calendar, than 365 holes, which would have followed the Egyptian calendar. The analysis also shows that 354 holes are hundreds of times more likely than a ring with 360 holes, which previous research had suggested as a possible count.
Professor Graham Woan, from the University of Glasgow’s School of Physics & Astronomy, is one of the paper’s authors. He said: “Towards the end of last year, a colleague pointed me to data obtained by YouTuber Chris Budiselic, who wanted to make a replica of the calendar ring and investigate ways of determining how many holes it had.
“It seemed like an interesting problem that I thought I could solve in a different way over the Christmas holidays, so I started using some statistical techniques to answer the question.”
The Antikythera Mechanism (Fragment A – front); visible is the largest gear in the mechanism, approximately 14 centimeters (5.5 in) in diameter.CC BY-SA 3.0)
Statistical probability and gravitational waves
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 remaining holes and the placement of the six surviving ring fragments. His results provided strong evidence that the mechanism’s calendar ring contained 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 analyze the signals picked up by the LIGO gravitational wave detectors, which measure the tiny ripples in spacetime caused by massive astronomical events such as the collision of black holes, as they pass through Earth go to examine the calendar ring.
The Markov Chain Monte Carlo and nested sampling methods used by Woan and Bayley produced a comprehensive probabilistic set of results, again suggesting that the ring most likely contained 354 or 355 holes in a circle of radius 77.1 mm, with an uncertainty of about 1/3 mm. It also shows that the holes are positioned with extraordinary accuracy, with an average radial variation of only 0.028 mm between each hole.
Bayley, co-author of the paper, is a research associate at the School of Physics & Astronomy. He said:
“Previous studies suggested that the calendar ring likely followed the lunar calendar, but the dual techniques we applied in this paper greatly increase the likelihood that this was the case.
It has given 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 requires very precise measuring methods and an incredibly steady hand to punch them.”
Professor Woan added:
“It’s a beautiful symmetry that we’ve adapted the techniques we use today to study the universe to understand more about a mechanism that helped people watch the heavens almost two thousand years ago.
We hope that our findings about the Antikythera Mechanism, while less supernaturally spectacular than those of Indiana Jones, will help deepen our understanding of how this remarkable device was made and used by the Greeks.
The paper, entitled ‘An Improved Calendar Ring Hole-Count for the Antikythera Mechanism: A Fresh Analysis’, was published in Horological magazine.
Top image: Antikythera mechanism on display at the National Archaeological Museum, Athens. Source: Joyofmuseums/CC BY-SA 4.0
This article first appeared under the title ‘Gravitational wave researchers shed new light on the Antikythera mechanismand has been lightly edited, with an American spelling.
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