New research into ripples in the fabric of spacetime suggests that a nearly 2,000-year-old cosmic calculator followed the lunar calendar instead of the solar calendar.
The hand-cranked “Antikythera Mechanism” was recovered in pieces from a sunken shipwreck in the Aegean Sea in 1901, sparking more than a century of research into how it was made—and why. The box-shaped mechanical computer used gears and dials to track ancient astronomical events like solar eclipses and the movements of planets.
Now researchers are using groundbreaking work on gravitational waves, ripples in spacetime caused by events such as black hole mergers or stellar collisions, to unravel the mechanics of the ancient Greek gears of Antikythera. (The device is named after the Greek island near where it was found.)
“It has given me a new appreciation for the Antikythera Mechanism and the work and care that Greek craftsmen put into its making – the precision of the positioning of the holes would have required very precise measuring techniques, and an incredibly steady hand to punch them,” study co-author Joseph Bayley, a research fellow at the University of Glasgow’s department of physics and astronomy, said in a statement.
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The new study builds on previous research from 2021 that used X-rays to show “new details of regularly spaced holes” under one of the mechanism’s broken rings, the statement said. This section, known as a “calendar ring,” is labeled with ancient Egyptian month names engraved in Ancient Greek, according to the British Horological Institute.
Computerized X-ray images “also revealed inscriptions describing the movements of the sun, moon and all five ancient planets and how these were depicted in front as an ancient Greek cosmos,” according to the older 2021 study published in Nature.
That 2021 study also noted the interdisciplinary nature of the Antikythera Mechanism: “Solving this complex 3D puzzle reveals a creation of genius – combining cycles from Babylonian astronomy, mathematics from Plato’s Academy and ancient Greek astronomical theories. “
The new study, in the Horological Journal, suggests that researchers can predict how many holes were in the calendar ring using statistical models derived in part from gravitational wave research. The research found that the calendar ring likely contained 354 holes, which follows a lunar year of 354 days (or 12 cycles of waxing and waning moons). Unlike the 365-day solar year that most people use today, the ancient Egyptian calendar followed a lunar year, as does the Islamic calendar still used around the world.
The team also drew inspiration from YouTuber and machinist Chris Budiselic’s channel Clickspring. Budiselic built a replica of the Antikythera Mechanism while conducting independent research. Budiselic’s team suggested that the ring could contain somewhere between 347 and 367 holes.
One form of analysis, led by Glasgow astrophysics professor Graham Woan, came from Bayesian statistics. This “uses probability to quantify uncertainty based on incomplete data,” the statement said.
The other part, from gravitational-wave research led by Bayley, was adapted from statistics used with data from the Laser Interferometer Gravitational-Wave Observatory (LIGO), which tracks ripples in space-time. (Woan is also a LIGO investigator.)
Both statistical studies independently suggested that the ring has 354 or 355 holes. Previous studies had suggested that the lunar calendar was more important to the makers of the Antikythera Mechanism, but the new study “significantly increases the likelihood that this was the case,” Bayley said in the statement.
“It’s a nice symmetry,” Woan added, “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.”