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    2000 Year Old Computer Rebooted

    A British museum curator has built a working replica of a 2,000-year-old Greek machine that has been called the world's first computer.

    A dictionary-size assemblage of 37 interlocking dials crafted with the precision and complexity of a 19th-century Swiss clock, the Antikythera mechanism was used for modeling and predicting the movements of the heavenly bodies as well as the dates and locations of upcoming Olympic games.

    The original 81 shards of the Antikythera were recovered from under the sea (near the Greek island of Antikythera) in 1902, rusted and clumped together in a nearly indecipherable mass. Scientists dated it to 150 B.C. Such craftsmanship wouldn't be seen for another 1,000 years — but its purpose was a mystery for decades.

    Many scientists have worked since the 1950s to piece together the story, with the help of some very sophisticated imaging technology in recent years, including X-ray and gamma-ray imaging and 3-D computer modeling.

    Now, though, it has been rebuilt. As is almost always the way with these things, it was an amateur who cracked it. Michael Wright, a former curator at the Science Museum in London, has built a replica of the Antikythera, which works perfectly.

    In the video from New Scientist below, Wright shows how the machine works.

    In short, Antikythera's user interface is deceptively simple, operated by a simple knob on the side. This conceals the intricacy within, amounting to a complex mathematical model, tracking the movements of planetary bodies and incorporating a series of submechanisms to account for the eccentricities of their rotation.

    A dial on the faceplace featured the Greek zodiac and an Egyptian calendar; pointers showed the location of the moon and the five planets known at the time. On the machine's back, an upper dial shows a 19-year calendar (matching the solunar cycle) and the timing of upcoming Olympic games. A lower dial shows a 76-year cycle (when the Olympic and solunar cycles coincide) and indicates the months in which lunar and solar eclipses can be expected.

    According to New Scientist, this is the first working model of the Antikythera computer to include all of the device's known features. And, like the original machine, it has been built of recycled metal plates. That's right: The Antikythera mechanism is not only the world's oldest computer, it's also the world's first green computer.



    About the death of Archimedes

    MARCELLUS and his men blockaded Syracuse, in Sicily, for two years. The Roman general expected to conquer the Greek city state easily, but the ingenious siege towers and catapults designed by Archimedes helped to keep his troops at bay.

    Then, in 212 BC, the Syracusans neglected their defences during a festival to the goddess Artemis, and the Romans finally breached the city walls. Marcellus wanted Archimedes alive, but it wasn't to be. According to ancient historians, Archimedes was killed in the chaos; by one account a soldier ran him through with a sword as he was in the middle of a mathematical proof.

    One of Archimedes's creations was saved, though. The general took back to Rome a mechanical bronze sphere that showed the motions of the sun, moon and planets as seen from Earth.

    The most intriguing thing about the latest finding, however, is that Syracuse was Archimedes's home city. He lived a century before the Antikythera mechanism was made, so he could not have created this particular device. But the link to Syracuse, plus Cicero's description of Archimedes's model, hint that he could have been the original inventor of this type of gadget, with the Antikythera mechanism part of a technological tradition that he started.

    We know from ancient texts that Archimedes pioneered the use of gearwheels to achieve different force ratios - to lift weights, for example. And one of the few biographical details we know about him is that his father was an astronomer. So it wouldn't be completely unexpected if he had the idea of using his gearwheels to model the motions of the heavens. Tantalisingly, one of his lost treatises was entitled "On sphere-making".

    The theory of epicycles was very new when Archimedes lived, if it existed at all, and astronomers had no way to model the elliptical orbits of the moon and sun. So his original design might have been relatively simple, perhaps a schematic model showing the sun, moon and planets rotating around the Earth at various but constant speeds. Later, other craftsmen could have built on this, coming up with more sophisticated gearwork to incorporate the latest astronomical knowledge - including that of Hipparchus - as it became available, with the designs being shipped across the Greek world. Hipparchus is chiefly known for his insistence on what now seems obvious to us: that astronomical theories should accurately match observations. Perhaps he or his work influenced a switch from a schematic spherical model to a mathematical calculator that displayed the precise timing of celestial events on flat dials.


    Historians have often scoffed at the Greeks for wasting their technology on toys rather than doing anything useful with it. If they had the steam engine, why not use it to do work? If they had clockwork, why not build clocks? Many centuries later, such technology led to the industrial revolution in Europe, ushering in our automated modern world. Why did it not do the same for the Greeks.

    How it worked

    The Antikythera mechanism was enclosed in a wooden box and driven by a handle on the side. As the user turned the handle, they could wind backwards or forwards in time to see the positions of heavenly bodies at any chosen moment.

    On the front of the box was a large bronze dial on which revolving pointers showed the relative position in the sky of the sun, moon and probably the five known planets, along with the date. A rotating black-and-white ball displayed the phase of the moon. Around the dial were inscriptions detailing the risings and settings of the stars at different times of the year.

    On the back (see diagram) were two spiral dials, each with an extendable pointer. Once the pointer reached the end of a spiral, it could be lifted by hand and reset to the beginning - a bit like the stylus on a record player. The top dial showed a repeating 19-year calendar used to track the motions of the sun and moon. This timescale was chosen because 235 lunar months fit almost exactly into 19 solar years. The bottom dial was used to predict eclipses, and showed the 223 months of an 18-year cycle over which eclipse patterns repeat. Inscriptions marked the months in which to expect a lunar or solar eclipse, as well as its exact time and duration.

    Incredibly, all of this was achieved by intermeshing bronze gearwheels, which multiplied the speed of rotation by precise mathematical ratios depending on the number of teeth on each wheel. Turning the handle drove a "mean sun", or date pointer, which revolved around the sky once per year. Three pairs of gearwheels then multiplied that speed of rotation by 235/19, to calculate the mean motion of the moon.

    Beyond that, things got more complicated. For example, the moon's speed as seen from Earth is not constant. The moon has an elliptical orbit, so it is sometimes closer to us (when it moves faster) and sometimes further away (when it slows down). The alignment of this ellipse rotates around Earth about once every 9 years. The idea of an ellipse would have been blasphemy to the ancient Greeks - they were convinced that celestial orbits, which they saw as divine, involved only perfect circles.

    Wheels within Wheels

    Instead, in the second century BC the astronomer Hipparchus came up with a theory to account for the moon's varying speed by superimposing one circular motion onto another with a different centre. The gears inside the Antikythera mechanism precisely model this theory. One gearwheel sits on top of another, but on a slightly different axis. A pin sticks up from the bottom wheel into a slot in the wheel above. As the bottom wheel turns it drives the top wheel round, but because the two wheels have different centres, the pin slides back and forth in the slot. This causes the speed of the top wheel to vary, even though the speed of the bottom wheel is constant.

    This pin-and-slot mechanism was carried around on a much larger turntable, with one rotation equalling 9 years, to model the shifting axis of the moon's orbit. This combined motion was then superimposed onto the mean speed of the lunar pointer, so that it matched the speed of the actual moon.

    The gearing for the sun and planets is lost, but the Antikythera mechanism almost certainly modelled these too. The planets' motions appear particularly erratic to us because they orbit the sun and not Earth. The Greeks accounted for this by superimposing small epicycles onto larger circular orbits. There is evidence that the Antikythera mechanism calculated these using what is still known today as epicyclic (or "planetary") gearing - small wheels riding around on bigger wheels.

    Jo Marchant is the author of a book about the Antikythera mechanism called Decoding the Heavens: Solving the mystery of the world's first computer


    Makes you wonder about how advanced the ancient civilizations really were; also about the concept of green computers? Any thoughts? I want one!

    Thu, Dec 18, 2008  Permanent link
    Categories: ancient technology
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