University of Glasgow
Techniques developed to analyze the ripples in spacetime detected by
one of the 21st century’s most sensitive pieces of scientific equipment
have helped cast new light on the function of the oldest known analogue
computer.
Astronomers from the University of Glasgow have used statistical
modelling techniques developed to analyze gravitational waves to
establish the likely number of holes in one of the broken rings of the Antikythera mechanism – an ancient artifact which was showcased in the movie Indiana Jones and the Dial of Destiny.
While the movie version enabled the intrepid archaeologist to travel
through time, the Glasgow team’s results provide fresh evidence that one
of the components of the Antikythera mechanism was most likely used to
track the Greek lunar year. They also offer new insight into the
remarkable craftsmanship of the ancient Greeks.
Discovering the Antikythera Mechanism
The mechanism was discovered in 1901 by divers exploring a sunken shipwreck
near the Aegean island of Antikythera. Although the shoebox-sized
mechanism had broken into fragments and eroded, it quickly became clear
that it contained a complex series of gears which were unusually
intricately tooled.
Decades of subsequent research and analysis have established that the
mechanism dates from the second century BC and functioned as a kind of
hand-operated mechanical computer. Exterior dials connected to the
internal gears allowed users to predict eclipses and calculate the
astronomical positions of planets on any given date with an accuracy
unparalleled 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)
Reassessing the Mechanisms Specifications
In 2020, new X-ray images of one of the mechanism’s rings, known as
the calendar ring, revealed fresh details of regularly spaced holes that
sit beneath the ring. Since the ring was broken and incomplete,
however, it wasn’t clear how just how many holes were there originally.
Initial analysis by Antikythera researcher Chris Budiselic and
colleagues suggested it was likely somewhere between 347 and 367.
Now, in a new paper published in the Horological Journal,
the Glasgow researchers describe how they used two statistical analysis
techniques to reveal new details about the calendar ring.
They show that the ring is vastly more likely to have had 354 holes,
corresponding to the lunar calendar, than 365 holes, which would have
followed the Egyptian calendar.
The analysis also shows that 354 holes is hundreds of times more
probable than a 360-hole ring, which previous research had suggested as a
possible count.
Professor Graham Woan, of the University of Glasgow’s School of
Physics & Astronomy, is one of the authors of the paper. He 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.”
The Antikythera Mechanism (Fragment A – front);
visible is the largest gear in the mechanism, approximately 14
centimeters (5.5 inches) 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 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, had
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 like the collision of black
holes, as they pass through the Earth, to scrutinize the calendar ring.
The Markov Chain Monte Carlo and nested sampling 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.
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.
Top image: Antikythera Mechanism on display at the National Archaeological Museum, Athens. Source: Joyofmuseums/CC BY-SA 4.0
This article was first published under the title, ‘Gravitational Wave Researchers Cast New Light on Antikythera Mechanism’, and has been lightly edited, with spelling Americanized.
Since
its discovery in a shipwreck near Greece in 1900, an ancient metallic
astronomical clock, called the ‘Antikythera Mechanism’ still baffles
scientists.
