When Dimitrios Kondos and his team of sponge divers discovered the Antikythera wreck in 1900, they weren’t trying to write history or upset archaeologists’ understanding of high tech at the end of the 1st century. BC. They were mostly killing time.
The crew made a few dives off the Greek island of Antikythera while waiting for favorable winds to continue their journey to North Africa. While diving, they spotted a wreck. A recovery mission in 1901 produced a large hoard of statues, sculptures and coins, putting the site on the proverbial map. All of these things happened long before anyone realized that the expedition had also returned with irrefutable evidence of the world’s first analog computer: the Antikythera Mechanism.
The Antikythera Mechanism today consists of some 82 fragments, but only about a third of the original device is thought to have survived. Researchers have known the device was a calendar for decades, but understanding that an object represents a calendar and understanding exactly how it was constructed are two different things. This is especially true when said object represents a level of manufacturing sophistication that European civilizations would not reach again for 1000 to 1400 years.
Functionally, the Antikythera Mechanism is a type of orrery, a mechanical model of the solar system that shows the procession of various planets and moons over time. The device once contained an intricate system of gears that modeled both the five known planets of antiquity as well as the epicycles these planets were believed to follow. Ancient astronomers believed that the planets moved in circular orbits, but the geocentric, perfectly spherical models of planetary motion popular at the time could not explain the retrograde planetary motion we sometimes observe from Earth (the motion apparent retrograde occurs when a planet appears to be moving backwards in the sky).
Over the past few decades, a number of projects have attempted to uncover new details about the Antikythera Mechanism and how it works. In 2005, researchers used X-ray computed tomography to decode new, previously unseen details on the back of the machine. Dr. Tony Freeth worked on this project nearly 20 years ago, and he led the most recent attempt to figure out exactly how the Antikythera Mechanism was originally constructed.
Scientists who have attempted this task over the decades are not without some idea of what the device looked like. We know the dimensions of the box in which the mechanism was originally kept, which usefully constrains its size and physical dimensions. There are fragments of an “instruction manual” on the inside front and back covers of the box. However, as Freeth et al write:
Our challenge was to create a new model to match all the surviving evidence. The characteristics of the main driving wheel indicate that it calculated planetary movements with a complex epicyclic system (gears mounted on other gears), but its design remained a mystery. The tomography revealed a multitude of unexpected clues in the inscriptions, describing an ancient Greek Cosmos9 at the front, but attempts to solve the gear system failed to match all the data. The proof defines a framework for an epicyclic system at the front, but the spaces available for the gears are extremely limited. There were also unexplained components in Fragment D, revealed by the X-ray scanner, and technical difficulties in calculating the phases of the Moon. Then came the discovery in tomography of surprisingly complex periods for the planets Venus and Saturn, making the task much more difficult.
According to the authors, they have created the first model that plausibly demonstrates all known functions of the Antikythera Mechanism. It’s the kind of claim that might seem impossible to verify given how little of a device we still have, but the authors argue the opposite, saying, “What struck us so hard in creating the current model, that’s how few those options are: the constraints created by the remaining evidence are tight and very difficult to meet.
What follows in the article is a dozen pages explaining how Freeth and his team assembled their working model of the complete Antikythera Mechanism. If the idea of calculating the most probable design of a complex system of gears under near impossible conditions interests you, you seriously dig this paper.
According to the authors, the assembled machine could have looked like this:
Freeth and his colleagues do not claim to have reconstructed the literal and exact mechanism of Antikythera, but they believe that theirs is the first reconstruction that fully describes what the machine was capable of while simultaneously offering a consistent and practical model of how it was built. .
Unknown unknowns, finally known
The existence of the Antikythera Mechanism is a humble reminder of how little history is actually preserved in historical records. Early 20th century scientists were stunned by the device’s existence, in part because it doesn’t look like a unique piece or the only such example. First-gen prototypes tend to have lots of metaphorical threads hanging from the back and the occasional application of tape. The initially modest group of rock divers fished out of the ocean was once a highly finished product.
Archaeologists believe there was more than one Antikythera Mechanism built along similar lines. The Roman statesman Cicero wrote a description of a device that may have been a planetary, claiming that Archimedes designed two of them and they were brought to Rome by General Marcus Claudius Marcellus in 212 BC. While none of these devices are believed to be the literal Antikythera Mechanism, it could be that the ancient Greeks were building similar devices 200 years before the one we were lucky enough to dredge out of the Mediterranean was built.
If the model that Freeth et al put forward is correct, it means that scientists in the 20th and 21st centuries have finally unveiled the specific functions provided by the Antikythera Mechanism. In doing so, they gave us a clearer idea of the traditions of knowledge upon which it was based. One of the most interesting facts about the Antikythera Mechanism is that the gear that tracked the progress of the Moon correctly modeled the fact that it moves at different speeds at different points in its orbit. The ancient Greeks didn’t understand complex orbital dynamics, but they found a way to accurately model behavior they couldn’t (correctly) explain.
Having an accurate model of both what the Antikythera Mechanism did and how it did it is a scientific breakthrough, as long as the new model stands up to long-term scrutiny.
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