The world's first cuckoo clock

28. November 2010 13:43

Antikythera mechanism fragment A c. Jo Marchant

Here's a mystery regarding the Antikythera mechanism. If you've seen photos of the largest surviving piece of this ancient calculator (such as the one on the left), you'll be familiar with its largest gearwheel. It's clearly recognisable because it has four pieces cut out of it, giving it wide spokes in the shape of a cross. Antikythera scholars call this wheel b1.

The four spokes on b1 have some small holes in them, suggesting that some other structure was once attached to - and therefore carried around on - this wheel. But what? And for that matter, why does this wheel even have spokes? All of the other surviving gearwheels in the mechanism are solid discs.

Back in the 1990s, the mechanic and curator Michael Wright came up with the idea that b1 carried other gearwheels - a type of gearing known as epicyclic - and that this was used to model the motions of the planets. The Greeks thought that each planet moved in little circles, called epicycles, as it traced a larger orbit around the Earth. Wright built a model to show how these gears would have worked (see video).

As for the spokes, Wright reckons that the maker of the device cut out the spaces in this large wheel simply to save on valuable bronze.

Although no trace of Wright's epicyclic gearwheels survives, it's a brilliant and plausible suggestion - the inscriptions on the mechanism suggest that it did model the planets somehow - and other Antikythera experts have assumed that he was probably correct.

But now there's a rival theory. I wrote last week about a study suggesting that the Antikythera mechanism didn't model the epicycles of the planets after all - that it was actually modelling earlier astronomical theories.

 So if this cross-shaped gearwheel wasn't carrying around epicyclic gearwheels, what was it carrying?

Jim Evans, an expert in the history of astronomy at the University of Puget Sound in Tacoma, Washington, and the lead author of the latest study, suggests that four little statues or figurines could have been mounted on the spokes of b1, perhaps representing the four seasons, or winds associated with those seasons.

Automated figures in the Prague astronomical clockAs b1 turned in the course of a year, one after the other of these figures would have appeared in a small window on the front face of the device. For example, the Greeks associated Boreas, god of the north wind, with winter; Zephyros, god of the west wind, with spring; and the Etesian winds with later in the summer.

As well as explaining what b1 was carrying, Evans says this theory also explains why it had spokes.

"The figurines would have ridden around on b1, and would usually have been flat against the wheel," he told me. "When one of them reached the window, a mechanism attached to the plate below b1 would have pushed an arm up through one of those large gaps in b1, to cause the figure to come forward and appear out of the window." He adds that he and his colleagues have been working on some mechanical designs for exactly how this might have worked.

I love the idea of little deities popping up through a window in the front of the Antikythera mechanism, like the world's first cuckoo clock! But how likely is this?

When I asked Alexander Jones, a historian of astronomy at the Institute for the Study of the Ancient World who has studied the Antikythera mechanism, he described the idea as "a little bit desperate". And Evans himself admits that the whole thing is "highly conjectural".

That said, Evans points out that displays involving moving figures were very popular in Medieval astronomical clocks (for example see detail from the Prague astronomical clock, above), which may be directly descended from devices like the Antikythera mechanism. And we know that the ancient Greeks did use automated figures too. For example, Hero of Alexandria, working in the first century AD, was famous for his steam-powered devices, that among other things drove miniature people, animals and birds.

Tower of the WindsThe idea also reminds me of the Tower of the Winds (which I've blogged about before). It's an octagonal tower in the ancient Greek marketplace in Athens and it dates from the first or second century BC - just the same time as the Antikythera mechanism. It originally had a weather vane on top, and you can still see carvings of the gods associated with the eight winds at the top of its outer walls (see pic, left). Inside was an impressive water clock.

No physical trace of this clock remains save for the holes in the floor where it once stood, but Derek Price - a historian of science who also spent decades working on the Antikythera mechanism - reconstructed its workings in the 1960s. From the positions of the floor markings he concluded that this water clock was of a known type that included a revolving astronomical display, and he suggested that it probably had moving figures that struck the hours.

So although there is no direct evidence for the existence of pop-up figures in the Antikythera mechanism, the idea is at least possible, consistent with the surviving remains of the device, and in the spirit of the type of thing that Greeks were doing at the time. Evans also says he hopes that his suggestion will serve as a reminder to keep an open mind about the mechanism's features: "An ancient mechanic may have seen more possible uses for those holes on the spokes of b1, as well as the spaces between the spokes, than we might."


Did gearwheels inspire epicycles?

24. November 2010 21:35

Representation of the Moon's orbit, with epicycles. Andreas Cellarius (1708)

The Antikythera mechanism is by far the most sophisticated piece of technology that survives from the ancient world. This corroded mass of battered bronze gearwheels languished at the bottom of the sea for more than 2000 years, before being salvaged by sponge divers in 1901.

The device was originally a mechanical computer (some people prefer to say calculator), which used Greek astronomers' state-of-the-art theories to model the movements of the Sun, Moon and planets in the sky.

Well that's what scholars thought, anyway. But a new paper on the mechanism, published earlier this year in the Journal of the History of Astronomy, suggests that they might have got things back to front. Jim Evans, an expert in the history of astronomy based at the University of Puget Sound in Tacoma, Washington, and his colleagues Alan Thorndike and Christian Carman have made the most accurate measurements yet of the Antikythera mechanism's zodiac dial, used to display the positions of celestial bodies in the sky.

Evans described his work at an event held in March at the Getty Villa in Los Angeles, at which he and I discussed the Antikythera mechanism (see video). His analysis has various technical implications for the way that the device displayed information - to be honest when I first heard him speak I thought it was the kind of thing that only true Antikythera geeks would get excited by. But when I went through the paper in more detail I saw this knock-out sentence, right at the end:

"Finally, if the maker of the Antikythera mechanism used gears to model Babylonian astronomical cycles, and if, as is likely, the mechanism reflects a craft tradition going back to the time of Archimedes, this raises the fascinating, but unprovable, possibility that epicycles and deferents entered Greek astronomy, not because of natural philosophical considerations, but because some geometer applied a geometrical image of gearing to a cosmic problem."

Representation of the apparent motion of the Sun and planets as seen from Earth. Encyclopaedia Britannica (1777) The theory of epicycles - the idea that celestial bodies moved in small circles as they traced larger orbits around the Earth - is arguably the most famous aspect of Greek astronomy. Although often scoffed at, it was actually very good at explaining the apparent movements of the Sun, Moon and planets through the sky, and it pretty much defined our view of the cosmos (see top three pics for various examples) until Kepler came up with the idea of elliptical orbits in the early 17th century AD.

What Evans and his colleagues are suggesting is that geared devices like the Antikythera mechanism didn't model this theory after all. They inspired it.

That's huge. It would give mechanical models a starring role in the history of astronomy, in other words in the way that we have come to understand the universe around us. If Evans is right then without models like the Antikythera mechanism, there would have been no epicycles, and for 2000 years we would not have seen the cosmos in the way that we did. Our modern understanding of how the solar system works would presumably still be the same, but the history of how we reached this point would be dramatically different.

I've written a feature about this latest work in this week's edition of Nature. But here's a summary of what led Evans and his colleagues to suggest this idea.

First, a bit of background about epicycles. The Greeks generally thought that the celestial bodies in the solar system - the Sun, Moon and five known planets - were orbiting Earth. They saw these celestial bodies as divine, and believed that their orbits must therefore consist of perfect circles.

Epicyclic model for the motion of Mercury, by 14th-century astronomer Ibn al-ShatirBut this isn't what you see when you look at the sky. The Sun and Moon (because the orbits of the Earth and Moon are actually ellipses, not circles) appear to speed up and slow down. And the planets (because they're orbiting the Sun, not the Earth) have a rather inconvenient habit of changing direction.

To explain this, the Greeks came up with the idea that celestial orbits were made up of different circles superimposed on one another. For example they reckoned that each planet traced a small circle - an epicycle - at the same time as moving around its larger orbit - the deferent. Similar theories of the Sun and Moon's motion involved superimposing one circle onto another with a slightly different centre.

When researchers who had X-rayed the surviving pieces of the Antikythera device published a reconstruction of its workings in 2006, they noted a crucial piece of gearing that was used to drive the Moon pointer. A "pin-and-slot" mechanism allowed one gearwheel to drive another around a slightly different centre, giving an undulating variation in speed. This pin-and-slot mechanism was itself mounted on a bigger 9-year turntable, effectively modelling how the orientation of the Moon's ellipse rotates around Earth.

This seemed to be a lovely demonstration of an epicyclic lunar theory used by the Greeks, translated into wheels of bronze. This type of gearing, in which gear wheels ride round on other wheels, is still described as epicyclic.

Epicyclic gearing from Michael Wright's reconstruction of the Antikythera mechanism. c. M. WrightAlthough the relevant gearing for the Sun and planets does not survive, researchers assumed that if the mechanism was using epicyclic gearing to model the motion of the Moon, it was probably doing the same thing for these other bodies too. The photo on the left shows the epicyclic gearing that models the motions of the planets in a reconstruction made by Michael Wright (see how it works in this video).

So here's the new bit. Evans has now shown that the Antikythera mechanism may not have worked this way after all. He used X-ray images to accurately measure the divisions on the device's main dial. This dial has two concentric scales, one showing the 360 degrees of the zodiac, and one showing the 365 days of the year, so that pointers moving around it can show both the date, and the position of celestial bodies in the sky.

Just less than a quarter of this dial survives. The 360 zodiac divisions should of course be very slightly wider than the 365 day divisions. But Evans found that although evenly spaced, the zodiac divisions in this surviving portion are actually closer together. To make a full circle, other parts of the zodiac scale must compensate by being extra widely spaced.

This was done on purpose, Evans believes, to model the uneven progress of the Sun through the sky. Instead of the Sun pointer moving at varying speed around an equally divided dial, it moved at constant rate around an unequally divided dial.

Evans' analysis suggests that half of the zodiac dial had extra-narrow divisions - a "fast zone" - and half had extra-wide divisions - a "slow zone". This scheme would have modelled the Sun's motion reasonably accurately and is identical to an arithmetic theory that Babylonian astronomers used for the Sun, known as System A. The Greeks borrowed other Babylonian astronomical theories, so it's not a huge stretch to think that they used this one too.

If Evans is right (and others in the field are taking his suggestion seriously) then the Antikythera mechanism did not use epicyclic gearing to model the movement of the Sun after all. It used conventional geartrains to model much older astronomical theories.

This may therefore be the case for the planets too. Evans thinks that they were shown on five individual dials, perhaps showing the timings of events in their cycles rather than their position in the sky - again, no epicycles required.

As discussed above, the Antikythera mechanism did use epicyclic gearing to model the varying motion of the Moon. But Evans points out that the amplitude of variation encoded in the pin-and-slot mechanism is closer to that used in older arithmetic theories than in the epicyclic theory used by the Greeks.

He believes that rather than modelling epicycles directly, a mechanic looking for a way to represent an older, arithmetic theory of the Moon's motion may have hit upon the idea of using gearwheels mounted on other wheels to produce the cyclic variation that he was after. In other words the inventor of epicycles was not an astronomer, but a mechanic.

Once astronomers realised that epicyclic gearing could closely model what was going on in the sky, they could have borrowed the idea of superimposed circles, and incorporated it into their own theories of how the cosmos was actually arranged. The clockwork universe was born.

Not much is known about when and how the idea of epicycles first arose, but the credit is traditionally given to an astronomer called Apollonius of Perga who lived in the third century BC. Geared astronomical devices seem to have arisen at around the same time - although the Antikythera mechanism itself dates from the second or first century BC, the Roman author Cicero wrote that Archimedes made one in the third century BC. So the timing is about right for such machines to have inspired the idea of epicycles.

Over the following centuries, there could have been an ongoing interaction between mechanics and astronomers as the theory was developed and refined. "Maybe we need to rethink the connection between mechanics and astronomy," says Evans. "People think of it as purely one way, but maybe there was more of an interplay."  

If this had happened, wouldn't somebody have written about it somewhere? Not necessarily, says Evans. He points out that the history of astronomy has generally been written by philosophers, who would have downplayed the role of mechanics.

Greek astronomy, he says, combined "a low road of nitty gritty arithmetical calculations", with "a philosophically-oriented high road" that was based on aesthetically pleasing geometric theories. "The people who wrote the history were philosophers of the high road. If there were the influence of something mechanical, it's not surprising that it wouldn't be there in the history. The historians emphasised the clean, the pure, the philosophical."

As Evans admits, it is impossible to prove where the idea of epicycles came from. But his analysis is fascinating food for thought. And a reminder, if we needed one, not to take anything about the Antikythera mechanism for granted.


How the Maya fought the floods

6. November 2010 07:46

Satellite photo of wetland area in Guatemala c. Reuters/NASA

"Usually in archaeology there's an elite focus on the majestic cities that we can wonder at. But the burning question is aways how did they feed these populations."

That's Stephen Houston, an expert on Maya civilization at Brown Unviersity in Providence, Rhode Island. He's commenting on a story on Nature's website today about how the ancient Maya used an elaborate system of canals to reclaim vast swamps and turn them into farms.

The Maya lived in the Yucatan Peninsula in central America, from before 1000 BC, with the civilisation reaching its height from about 400 BC to 900 AD. They're famous for their impressive stone pyramids, such as at Chichen Itza in Mexico, or Tikal in Guatemala, and for their achievements in maths and astronomy. But they lived on rough, rocky terrain, mixed with huge areas of wetland (see satellite photo) created by rising sea levels. So, as Houston says, how did they manage to grow enough food for their huge populations?

Timothy Beach and his wife Sheryl Luzzadder-Beach, both physical geographers, have been studying the remains of irrigation canals in northern Belize for the past twenty years, and reported on some of their latest work at the Geological Society of America meeting in Denver, Colorado, this week. The canals have been studied before, but the pair are using tools such as satellite imaging and isotope analysis combined with more than 60 excavations to try to work out how widespread the canals were, and exactly how they were employed.

The researchers reckon that this canal system in Belize covered an area 100 kilometres across, and was used to divert water and create new farmland. The water table in this area varied throughout the year - sometimes it was two metres below the surface, sometimes the land was completely flooded. The Maya responded by digging canals and throwing the soil onto adjacent land, creating raised fields on which they grew crops such as avocado, grass and maize.

Some of the efforts seemed piecemeal, but Beach says that others were "preplanned, large-scale efforts" involving ditches up to 900 metres long. And if the Maya were doing this in northern Belize, it seems likely that they were using the same methods elsewhere too - today around 40% of the Yucatan peninsula is swamp.

Ingenious. But sadly there was a downside - one of the theories for what caused the downfall of the Maya civilisation is that by converting the wetlands to avoid floods, they induced a catastrophic drought.


Portal to a hidden world

2. November 2010 16:15

Simulated decay pattern of a Higgs boson

Every so often an idea comes along that is so mind-blowing it transforms your perception of reality. Yet, once you've been exposed to this new worldview, it becomes hard to see how things could be otherwise.

Here's one of them.

Most people who follow the progress of physics have heard of "dark matter". It is made up of particles that we can't see or feel. Cosmologists only know it is there because they can detect the gravitational pull it exerts on distant galaxies, but they reckon it makes up around a quarter of the mass of the universe.

But what if there are other types of matter that don't interact with any of the particles and forces that we know, not even gravity? What if these particles interact with their own forces, and form more than a few featureless clumps? What if there is a whole "dark universe" with stars and planets and even life forms, that we are oblivious to?

The idea is discussed in a book called Massive: The missing particle that sparked the greatest hunt in science, by journalist Ian Sample. It's out in the US today (and was published in the UK in June).US and UK editions of Massive

The book is about the hunt for the Higgs boson - a particle whose existence was first suggested in the 1960s to explain why fundamental particles have mass. Massive tells the story of this elusive entity from the first scribbles in the notebook of a young father called Peter Higgs, to the multi-billion-dollar atom smashers (most recently the Large Hadron Collider at CERN, near Geneva) built in the hope of creating it.

I really enjoyed Massive because it weaves the physics into a compelling human story; it's a science book that reads like a novel*. But for anyone who has been wondering why scientists care so much about the Higgs, the final chapter is also the best discussion I've read of what it will mean if they do finally manage to make the Higgs boson, and what finding it might tell us about the nature of the universe.

For me the most fascinating possibility Sample describes is that the Higgs could reveal the existence of dark, hidden worlds. He points out that until now, particle physics has been completely anthropocentric, focusing on the particles that make up our bodies, or that we can detect.

But, he says, some physicists are starting to question whether this is all there is: "Why should the particles of matter we have found and the four forces of nature we are aware of be the only ones there are? There is no reason why the human body should be equipped to sense everything in the universe, and the existence of dark matter proves it is not. The extraordinary possibility is that there could be a host of particles and forces that are going about their business in a world that is entirely beyond our perception." 

If so, there's no reason to think that this hidden world should be any less complex than the one we know, or even that it, too, shouldn't harbour life. If the physicists are right, "what we call reality - that is, everything we know - is part of a much greater and more complex reality that we are completely oblivious to."

I'd never really thought about this before, but now that Sample has made the point, it makes sense. It even starts to seem pretty unlikely that the stuff that we happen to be able to detect and measure should be everything there is, or even a significant fraction of everything there is. I guess it's just one more logical step in realising that we're not the centre of the universe after all.

Where does the Higgs come in? According to Sample, physicists think that the Higgs boson, and the field with which it is associated, will be tenuously linked to other Higgs fields that give mass to particles in the hidden world, forming a "bridge that provides a way to peer into the hidden world and look at the kinds of particles from which it is made".

If hidden worlds exist, then any Higgs boson made in the LHC could decay into invisible hidden-world particles, which might then break down into "real" particles that we can see. To the LHC's detectors, this would look like a sudden burst of particle tracks coming from nowhere. Scientists could then work backward to build up an idea of the kinds of hidden-world particles the Higgs boson must have decayed into.

Until then we'll just have to imagine what ghostly goings on could be passing through our bodies right now...

* As I know the author rather well I am probably biased in favour of this book. But I honestly think I would have loved it anyway.