Details of the Antikythera mechanism, a 2nd century BC computer, have been revealed.
The same advanced techniques used to detect gravitational waves in space have shed new light on operation of the oldest known analog computer. Astronomers from the University of Glasgow used statistical modeling techniques developed for analyzing gravitational waves to establish the likely number of holes in one of the ruptured rings of the Antikythera Mechanism.
The results provide new evidence that one component of the Antikythera mechanism was likely used to trace the Greek lunar year. They also demonstrate the remarkable technological prowess achieved by the ancient Greeks.
The mechanism was discovered in 1901 by divers who were exploring a shipwreck off the island of Antikythera in the Aegean Sea. Although the shoebox-sized artifact was fragmented and destroyed, it contained an intricate series of gears with sophisticated tools.
Decades of research have established that the mechanism dates back to the 2nd century BC. and functioned as a hand-operated mechanical computer. Its external dials, connected to internal gears, made it possible to predict eclipses and calculate the astronomical positions of the planets with an accuracy unprecedented for its time.
In 2020, new X-rays of one of the mechanism’s rings, known as the calendar ring, revealed details of evenly spaced holes underneath the ring. However, since the ring was broken and defective, It was unclear how many holes it originally had. An initial analysis by Antikythera researcher Chris Budiselik and colleagues found that the ring corresponded to a year between 347 and 367.
In a new article published in the journal watch magazine, The Glasgow researchers describe how they used two statistical analysis techniques to reveal new details about the calendar ring. They argue that it is much more likely that there were 354 holes in the ring, corresponding to the lunar calendar, instead of the 365 holes of the Egyptian calendar. The analysis also shows that 354 holes are hundreds of times more likely than a ring of 360 holes, the number suggested by previous studies.
Professor Vaughan 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 remaining six ring fragments. Their results convincingly proved that the calendar ring of the movement contains 354 or 355 holes.
At the same time, Dr Joseph Bailey, Professor Vaughan’s colleague at the university’s Institute for Gravitational Research, adapted the methods used by his research group to analyze signals from the LIGO gravitational wave detectors. These detectors measure small ripples in spacetime caused by large-scale astronomical events such as the collision of black holes.
The methods used by Vaughan and Bailey provided a complete probabilistic set of results that again suggested that the ring probably contained 354 or 355 holes in a circle of radius 77.1 mm, with an error of about 1/3 mm. They also found that the holes were placed with extraordinary precisionwith an average radial deviation of only 0.028 mm between each hole.
Bailey, a co-author of the paper and a research fellow in the School of Physics and Astronomy, said in a statement: “Previous studies have shown that the calendar ring corresponded to the lunar calendarbut the dual methods employed in this work greatly increase this probability.
Professor Vaughan added: “There is a clear symmetry: we have adapted the methods we use today to study the universe to better understand the mechanism that helped humans track the skies almost two millennia ago.”