By building a digital model of the Antikythera Mechanism, scientists may have finally exposed a key function of the ancient device, revealing a design that required some seriously advanced thinking.
Pulled from a shipwreck off the coast of Crete in 1901, the 2,000-year-old Antikythera Mechanism has baffled scientists for decades. New research published in Scientific Reports presents a hypothetical model of the astronomical instrument, which Tony Freeth, the lead author and a mechanical engineer at University of College London, says is the first to conform to “all the physical evidence and matches the descriptions in the scientific inscriptions engraved on the Mechanism itself,” he said in a statement.
The hand-powered device is the oldest known analog astronomical computer, an early example of complex mechanical engineering. Dating back to ancient Greece, the device modeled astronomical phenomena and events, such as lunar and solar eclipses and the positions of the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn.
Only a third of the Antikythera Mechanism was recovered, and nothing like it exists for comparison. The incomplete relic, with its 30 bronze gears and 82 individual fragments, has forced scientists to speculate as to what it looked like, what it was used for, and how it worked.
In 2016, scientists presented the results of a decades-long investigation into the relic. Using an X-ray scanner, scientists were able to document 3,500 characters of explanatory text—a kind of instruction manual—embedded onto the device. Analysis of this text suggests the Antikythera Mechanism is not a true computer, in that it’s not programmable. Rather, it was a machine designed to convey our place in the universe and forecast celestial events like lunar and solar eclipses.
Fragment A, the largest part of the device, consists of bearings, pillars, and a block, while Fragment D contains a disk, the purpose of which is unknown, a 63-toothed gear, and a plate. The purpose of the new study was to gain a better understanding of the gearing system at the front of the mechanism, which is largely missing.
The inscriptions made mention of a cosmic mechanical display, in which the planets and Moon, represented by marker beads, moved around on rings. As the authors write in their study, “no previous reconstruction has come close” to creating a model that actually adheres to this apparent specification. To that end, the team took a stab at recreating this missing—and presumed—component 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,” wrote the authors, which included mechanical engineer Adam Wojcik, also from UCL.
Indeed, the ancient Babylonians chronicled the motions of the planets, while the ancient Greek philosopher Parmenides developed a mathematical model to explain these movements.
Inscriptions on the device made mention of celestial cycles assigned to Venus, at 462 years, and Saturn, at 442 years. The scientists associated these numbers with synodic cycles, which describe the length of time it takes for a celestial object to return to its original position relative to our perspective on Earth. These cycles were important to the ancient Greeks on account of their geocentric view of the universe. Looking up into the night sky, the planets sometimes appear to briefly pause and swing back and forth as they—and we on Earth—orbit the Sun (i.e., retrograde motion), in what is an optical illusion. (A fantastic example of this can be seen here, in which the Moon appears to go backward.) As a fun fact, the word “planet” comes from the Greek word for “wanderer.”
The Greeks, believing that the planets revolved around Earth, were puzzled by these retrograde motions, and they devised some rather convoluted theories and mathematical explanations to make it all work, many of them flat-out wrong.
Looking at the Antikythera Mechanism itself, the researchers realized that components in Fragments A and D matched the mechanical motions of Venus, “which exactly models its 462-year planetary period relation, with the 63-tooth gear playing a crucial role,” said David Higgon, a PhD student and co-author of the paper, in the UCL statement. The scientists then determined the cycles of the remaining planets, which they did using the ancient Greek formulas, and then incorporated these cycles into “highly compact mechanisms, conforming to the physical evidence,” according to the paper.
What this all means is that the Greeks, with their geocentric view of the cosmos, made it unnecessarily difficult for themselves when designing the Antikythera Mechanism. Instead of showing the planets—represented by beads moving along concentric circles—moving in a single direction around the Sun, they had to show the planets shimmying back-and-forth during their cycles as they moved around Earth. Incredibly, this had to be done for each of the five planets, with the relative position of each having to be accurate at any given time. At least, assuming this is how the machine actually worked.
Equipped with their calculations, the scientists then designed and digitally recreated this monstrously complicated thing. The scientists “created innovative mechanisms for all of the planets that would calculate the new advanced astronomical cycles and minimize the number of gears in the whole system, so that they would fit into the tight spaces available,” said Freeth. Indeed, the gear arrangements couldn’t be arbitrarily large, as the hypothesized components needed to fit inside the device, including spaces no larger than 25 millimeters deep.
A 30-minute film about this research, showing how this model came together, can be seen on Vimeo.
The simulated machine appears to work, but simulated is the key word. The authors are correct in saying a major step still needs to completed.
“Now we must prove its feasibility by making it with ancient techniques,” said Wojcik. “A particular challenge will be the system of nested tubes that carried the astronomical outputs.”
Nice. Sounds like the team is about to embark on some experimental archaeology, in which an actual physical model of the Antikythera Mechanism will be built. Boggles the mind to think we might struggle to recreate this “creation of genius” some 2,000 years later, in what is a remarkable example of lost technology.