The same advanced techniques used to detect gravitational waves in the cosmos have shed new light on the operation of the oldest known analog computer. Astronomers at the University of Glasgow applied statistical modelling methods, developed to analyse gravitational waves, to establish the likely number of holes in one of the broken rings of the Antikythera mechanism.
The results provide new evidence that one of the components of the Antikythera Mechanism was probably used to trace the Greek lunar year. They also reveal the remarkable technological craftsmanship achieved by the ancient Greeks.
The mechanism was discovered in 1901 by divers exploring a shipwreck near the Aegean island of Antikythera. Although the shoebox-sized artifact was fragmented and eroded, it contained a complex array of gears with intricate tools.
Decades of research have established that The mechanism dates back to the 2nd century BC. and functioned as a manually operated mechanical computer. Its outer dials, connected to internal gears, enabled it to predict eclipses and calculate astronomical positions of the planets with unparalleled precision for its time.
In 2020, new X-ray images of one of the mechanism’s rings, known as the calendar ring, revealed details of regularly spaced holes beneath the ring. However, because the ring was broken and incomplete, It was unclear how many holes it originally had. Initial analysis by Antikythera researcher Chris Budiselic and his colleagues suggested the ring dated to sometime between 347 and 367.
In a new article published in the Horological Journal, 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, corresponding to the lunar calendar, instead of 365 holes, which would have followed the Egyptian calendar. The analysis also shows that 354 holes is hundreds of times more likely than a ring of 360 holes, an amount suggested in previous research.
Professor Woan used a technique called Bayesian analysis, which uses probability to quantify uncertainty based on incomplete data, to calculate the probable number of holes in the mechanism using the positions of the surviving holes and the placement of the remaining six ring fragments. Their results showed strong evidence that the mechanism’s calendar ring contained 354 or 355 holes.
At the same time, Dr Joseph Bayley, a colleague of Professor Woan at the University’s Gravitational Research Institute, adapted techniques used by his research group to analyse signals from the LIGO gravitational wave detectors. These detectors measure tiny ripples in space-time caused by massive astronomical events such as the collision of black holes.
The methods used by Woan and Bayley provided a complete probabilistic set of results, which again suggested that the ring probably contained 354 or 355 holes in a circle of radius 77.1 mm, with an uncertainty of about 1/3 mm. They also revealed that the holes were placed with extraordinary precisionwith an average radial variation of only 0.028 mm between each hole.
Bayley, a co-author of the paper and a research associate at the School of Physics and Astronomy, said in a statement: “Previous studies have suggested that The calendar ring followed the lunar calendarbut the dual techniques applied in this work greatly increase that probability.”
Professor Woan added: “It is a clear symmetry that we have adapted the techniques we use to study the universe today to understand more about a mechanism that helped people track the heavens nearly two millennia ago.”
