X-rays unlock secrets of the world's oldest computer
A team of scientists at the University College London has shed new light on the Antikythera Mechanism – the world's first computer and one of the ancient world's greatest technological mysteries. Using new imaging data, the multidisciplinary UCL Antikythera Research Team found that the 2,000-year-old device was not only a calculator, but an accurate model of the Cosmos as it was known to the ancient Greeks.
In 1901, Greek sponge divers found a sunken ship dating back to the 1st century BCE off the coast of the island of Antikythera in the Aegean Sea between Crete and the Peloponnese. Aboard was a treasure of artworks that may have been meant for a triumph parade for Julius Caesar in Rome.
Among the various statues, pots, and jewels were fragments of a lump of corroded bronze. A year after being recovered, it was realized that there were gear teeth sticking out of one of the fragments. Examination soon revealed that what became known as the Antikythera Mechanism was like nothing that had been previously found or even suspected from the ancient world.
To put it simply, it was an analog computer powered by turning a wheel to perform a wide range of astronomical calculations using differential gearing – something the Greeks were supposed to know nothing about. Worse, there wasn't anything remotely like this device known from the time of the ancient Greeks. In fact, such complex gearing wouldn't be seen again until the development of astronomical clocks in Europe in the 14th century.
This was like opening up a Viking tomb and finding the remnants of an ancient airplane inside, so it's a small wonder that the Mechanism sparked over a century of controversy. The device was far too damaged to be dismantled and only 30 percent of it has survived two millennia under the sea, but researchers measured it closely and probed its inner mechanism using X-rays, gamma rays, and 3D X-ray tomography.
What they found was that, when intact, the gear mechanism sat inside a bronze box with a wheel on one side to turn it (the crank wouldn't be invented for another 1,300 years), and display dials on the front and back. In addition, there were Greek inscriptions that were a sort of instruction manual for operating it and interpreting the results.
The back panel calculated Moon phases, the Moon's orbit, eclipses, and various calendar functions. Enough of the gearing in the back survived to reconstruct the gear train, but most of the front panel and almost all of the gearing for it were gone. However, the inscriptions showed that this panel could predict the movements of the Sun and the five known planets, Mercury, Venus, Mars, Jupiter, and Saturn.
By looking at 3D X-ray images of the fragments, the UCL team found a number of bearings, pillars, a block, and a 63-toothed gear and plate. In addition, X-rays of what was left of the front panel showed the numbers 462 and 442, which are the cycles of the paths that Venus and Saturn, respectively, follow as they travel across the sky.
What is remarkable is that if the Mechanism could calculate planetary cycles, it's dealing with some fairly complex sums because the planets don't follow neat arcs in the sky. They speed up, slow down, and even reverse course and loop backward for a bit before going forward again. By taking the clues presented by the surviving bits of the Mechanism, the team was able to correlate them with an ancient Greek mathematical method described by the philosopher Parmenides. This not only confirmed the cycles for Venus and Saturn, but allowed the team to reconstruct the cycles for the other planets as well.
In particular, the team was able to match up the 462-year planetary period relation of Venus with the 63-toothed gear, and then reconstruct the possible mechanism for the front panel for it, the Sun, and the other planets. What's more, the way the Antikythera Mechanism operates shows that it is an accurate model of the Cosmos as it was understood by the ancient Greeks.
Even the inaccuracies of the Mechanism were telling because these weren't due to the engineering, but the astronomical theory behind it. The Greeks believed that the planets revolved around the Earth rather than the Sun, which makes it extremely difficult to accurately predict their movements.
So far, the team has progressed to building a reconstruction of the Antikythera Mechanism using modern techniques. The next step is to build a version as the Greeks would have done.
"This is a key theoretical advance on how the Cosmos was constructed in the Mechanism," says Dr. Adam Wojcik of UCL Mechanical Engineering. "Now we must prove its feasibility by making it with ancient techniques. A particular challenge will be the system of nested tubes that carried the astronomical outputs."
Source: University College London