When Dimitrios Kondos and his crew of sponge divers found the Antikythera shipwreck in 1900, they weren’t trying to make history or disrupt the understanding of high-tech archaeologists at the end of the 1st century BC. Mostly they were killing time. .
The crew made some dives off the Greek island of Antikythera in anticipation of favorable winds to continue the voyage to North Africa. While diving, they spotted a shipwreck. A recovery mission in 1901 produced a rich supply of statues, sculptures and coins, placing the site on the proverbial map. All of these things happened well before anyone realized that the expedition had returned even with incontrovertible evidence of the world’s first analog computer: the Antikythera mechanism.
The Antikythera mechanism today consists of approximately 82 fragments, but only about a third of the original device is believed to have survived. Researchers know that the device has been a calendar for decades, but understanding that an object represents a calendar and understanding exactly how it was built are two different things. This is especially true when said object represents a level of manufacturing sophistication that European civilizations would no longer reach for another 1000 – 1400 years.
Functionally, the Antikythera mechanism is a type of planetarium, a mechanical model of the solar system that shows the procession of various planets and moons over time. The device once contained a complex system of gears that modeled both the five planets known in antiquity and the epicycles they were believed to follow. Astronomers in ancient times believed that planets moved in circular orbits, but the geocentric and perfectly spherical patterns of planetary motion popular at the time could not explain the retrograde planetary motion we occasionally observe from Earth (apparent retrograde motion occurs when a planet appears to be moving backward in the sky).
Over the past few decades, numerous projects have attempted to guess new details about the Antikythera mechanism and how it works. In 2005, researchers used X-ray computed tomography to decode new details previously invisible on the back of the machine. dr. Tony Freeth worked on that project nearly 20 years ago and spearheaded the most recent attempt to guess exactly how the Antikythera Mechanism was originally built.
Scientists who have attempted this task over the decades are not without some idea of what the device was like. We know the dimensions of the box in which the mechanism was originally kept, which usefully binds its dimensions and physical dimensions. There are snippets of an “instruction manual” on the inside front and back covers of the box. As Freeth et al write, however:
Our challenge was to create a new model that matched all the surviving evidence. Features on the main drive wheel indicate that it calculated planetary movements with a complex planetary system (gears mounted on other gears), but its design remained a mystery. Tomography revealed a wealth of unexpected clues in the inscriptions, which describe an ancient Greek Cosmos9 in the front, but attempts to fix the gear system failed to match all the data. The evidence sets a framework for a planetary system at the front, but the spaces available for the gears are extremely limited. There were also unexplained components in fragment D, revealed by X-ray CT, 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 created the first model that plausibly demonstrates all known functions of the Antikythera mechanism. This is the kind of claim that might seem impossible to verify given how little of the device we still have, but the authors argue otherwise, saying, “What really struck us in making the current model is how few these options are. : the constraints created by the surviving tests are rigorous and very difficult to satisfy “.
What follows in the article are more than a dozen pages explaining how Freeth and his team assembled their model for how the whole Antikythera mechanism must have worked. If you like the idea of calculating the most probable design for a complex gear system in near-impossible conditions, you will seriously dig this paper.
According to the authors, the assembled machine could look like this:
Freeth and his colleagues do not claim to have reconstructed the exact Antikythera mechanism, but they believe theirs is the first reconstruction that fully describes what the machine was capable of while offering a practical and cohesive model of how it was built.
Unknown strangers, finally known
The existence of the Antikythera mechanism is a humbling reminder of how little history is actually preserved in historical record. Scientists of the early 20th century were amazed at the device’s existence in part because it it does not do it looks like a one-of-a-kind or one of a kind example. First generation prototypes tend to have a lot of metaphorical threads hanging from the back and feature the occasional free application of tape. The initially unassuming lump of divers caught in 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 planetarium, claiming that Archimedes had designed two and that they were brought to Rome by General Marcus Claudius Marcellus in 212 BC Although none of these devices are thought to be the mechanism literal of Antikythera, 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 is thought to have been built.
If the model advanced by Freeth and others is accurate, it means that 20th and 21st century scientists have finally unmasked the specific functions provided by the Antikythera mechanism. In doing so, they gave us a better idea of what traditions of knowledge he drew upon. One of the most interesting facts about the Antikythera mechanism is that the gear that tracked the Moon’s progression correctly modeled the fact that it travels at different speeds at different points in its orbit. The ancient Greeks did not understand complex orbital dynamics, but they found a way to accurately model behavior they could not (correctly) explain.
Having an accurate model of 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.