Astrophysicists improve understanding of Antikythera mechanism

Techniques used to detect gravitational waves in the universe have shed new light on how the oldest known analog computer worked.

Astronomers at the University of Glasgow 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.

The findings provide new evidence that a component of the Antikythera Mechanism may have been used to track the Greek lunar year. They also provide a new perspective on the remarkable technological prowess of the ancient Greeks.

The mechanism was discovered in 1901 by divers exploring a sunken wreck near the island of Antikythera in the Aegean Sea. Although the shoebox-sized mechanism was broken into pieces and corroded, it soon became apparent that it contained an unusually complex set of gears.

Decades of research and analysis have shown that the mechanism dates back to the 2nd century B.C. It functioned as a kind of handheld mechanical computer. External discs connected to 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 modern device.

In 2020, new X-ray images of one of the mechanism’s rings, known as the calendar ring, revealed new details about the regularly spaced holes at the bottom of the ring. However, because the ring was broken and incomplete, it was unclear how many holes it originally had. A preliminary analysis by Antikythera researcher Chris Podislik and colleagues suggests it was probably made between 347 and 367.

New technologies

Now, in a new study published in the Horological Journal , Glasgow researchers describe how they used two statistical analysis techniques to uncover new details about the calendar ring. They show that the ring is more likely to have 354 holes, which corresponds to the lunar calendar, than 365 holes, which corresponds to the Egyptian calendar. The analysis also shows that 354 holes is hundreds of times more likely than a ring with 360 holes, which previous research has suggested as a possible measure.

Professor Wan used a technique called Bayesian analysis, which uses probability to measure uncertainty based on incomplete data, to estimate the likely number of holes in the mechanism using the locations of the remaining holes and the positions of the six remaining segments of the ring. Their results showed strong evidence that the movement’s calibration ring contains either 354 or 355 holes.

Meanwhile, one of Professor Wan’s colleagues at the university’s Institute for Gravitational Research, Dr Joseph Bailey, has adapted the techniques his research team uses to analyse signals picked up by the LIGO gravitational wave detectors, which measure tiny ripples in space-time caused by massive astronomical events such as black hole collisions, as they pass Earth to examine the calendar ring.

The methods used by Wan and Bailey provided a full range of probabilistic results, which again suggested that the ring may contain 354 or 355 holes in a radius of 77.1 mm, with an uncertainty of about 1/3 mm. It also reveals that the holes were placed with extreme precision, with an average radial variation of only 0.028 mm between each hole.

“Previous studies have suggested that the calendar ring is likely to follow the lunar calendar, but the dual techniques we applied in this work greatly increase the likelihood of this happening,” said Bailey, a co-author of the paper and a research associate in the School of Physics and Astronomy.

“It is a clear parallel that we have adapted the techniques we use to study the universe today to understand more about the mechanism that helped people view the sky nearly two thousand years ago,” Professor Wan added.