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Fragments of the Antikythera mechanism

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The 2000-year-old Antikythera mechanism, often described as the world’s first computer, was a sophisticated bronze device that modelled the cosmos. Researchers have assumed it featured pointers moving around a dial like the hands on a clock, but a new study suggests that the celestial bodies were shown using a series of bejewelled, rotating rings.

The machine dates to the first century BC and was discovered in a shipwreck near the Greek island of Antikythera in 1901. Scientists have spent more than a century decoding its battered remains, which include inscriptions, measuring scales and more than 30 bronze gearwheels.

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Modern reconstructions based on detailed X-ray images of the surviving pieces show it was a box around 30 centimetres high, operated by turning a handle on the side. On the back were two spiral dials, showing a calendar – including the timing of the Olympics – and dates of predicted lunar and solar eclipses.

Much of the front part of the mechanism is missing, but researchers agree that a large circular dial displayed the motions of celestial bodies through the sky. Complex trains of gearwheels calculated the back-and-forth motion of the planets, as well as the variable speed of the sun and moon.

Inscriptions deciphered in 2016 revealed that Venus and Saturn were represented by mathematical cycles not previously known from ancient Greek astronomy. For example, the Greeks are known to have described the back-and-forth motions of Venus using an 8-year cycle or a more accurate 1151-year cycle, but the inscriptions on the Antikythera mechanism describe a 462-year cycle.

Tony Freeth at University College London and his colleagues suggest that the Greeks could have deduced this from the known cycles using a step-by-step arithmetic method originally described by the philosopher Parmenides in the 5th century BC. The team used the same method to derive similar cycles for the other planets, for which the inscriptions are missing, and constructed a new gearing scheme that they claim fits all the available physical evidence, including a previously unexplained 63-tooth gearwheel, as well as the surviving inscriptions.

They conclude that the celestial bodies weren’t represented using pointers, but instead by concentric rotating rings. The inscriptions hint that coloured, semi-precious stones may have shown the position of each planet on its ring.

Freeth says he is confident that the new scheme “is essentially right”, and describes it as “a beautiful system”. He thinks the mechanism could have been used to calculate the outcomes of astronomical theories, instead of working out the maths by hand. “It was a prediction machine,” he says. “You just turn the handle and it shows you.”

Mike Edmunds at Cardiff University in the UK, who has worked on the Antikythera mechanism, says the proposal is “ingenious” but cautions that with so few surviving clues, it is impossible to know for sure whether any theoretical reconstruction mirrors the original.

He also notes that the newly proposed design involves many extra gearwheels, and wonders whether such a complex mechanism could have turned smoothly and operated for long periods without breaking.

Freeth says the team’s next challenge is to make a physical model using 2000-year-old techniques, to prove it really would.

Journal reference: Scientific Reports, DOI: 10.1038/s41598-021-84310-w

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