Thrills, chills, and plenty of spills- one of the entrants in the Tsukuba Challenge 2010 being cheered on by enthusiastic supporters

They`ve been getting ready for the big race for weeks, months, maybe even years. Training, training, and then more training- working to improve speed stamina and coordination: knowing that every SECOND will count in the pursuit of victory.

And it  all comes down to Thurday and Friday of this week, at an event for which they will be converging on Tsukuba from all over Japan. For victory. For the prize. For the glory!

No. I am not talking about the famous and very popular Tsukuba Marathon, which will be held later this month ( on the 28th), and in which thousands will run. I`m referring to the 4th annual Tsukuba Challenge, also known as the Real World Robot Challenge- in which about 70 robots- on-wheels of various design will try to negotiate a course around Tsukuba`s Central Park. This year the course will run a gruelling 1.1 kilometers, from Tsukuba`s Expo Center, around the pond at Tsukuba`s Central Park, then over the pedestrian bridge to Nova Hall! There will be various designated stopping points along the way.

If you think this sounds difficult, IT IS. In fact, last year only 5 out of 72 teams could complete the course, which was much shorter than what they will have to navigate this year.   

A practice run over the pedestrian bridge between Tsukuba Center and the Expo Center

If you`ve been around Tsukuba Center over the past few months, more specifically on the pedestrian road between Nova Hall and the Expo Center, you have almost surely seen the curious sight of some of the teams practicing the course with their robots. It is a strange sight indeed to see groups of two or three green-capped, name-tag wearing OTAKU (computer nerd) types clustered around the odd looking, diminutive, wheeled vehicles ( often made using wheel chairs, of all things!), making their way along the path at what could only be called a SNAILS PACE.

The Tsukuba University team ironing out some technical problems during a practice run

Starting tomorrow( Thursday November 18) at 10 AM at the Tsukuba Expo center will be a trial run  which will be held over a 240 meter coure. Those who successfully complete it, will be able to take part in the FINALS on the following day, also starting at 10AM.

Passing by the Tsukuba Library on a practice run

Since Tsukuba is Japan`s SCIENCE CITY, and is now perhaps the capital of cutting edge robot technology, this event seems to me just perfect. Much more appropriate for the city than the Tsukuba Matsuri ( in which the main theme is a group of floats which are taken from a very famous festival in Aomori prefecture-after they have finished using them there), or even the Tsukuba Marathon, since there are many marathons held all over Japan ( a dime a dozen!).

So come on out tomorrow and the next day for a unique, TRULY TSUKUBAN event.  Join the nerds cheering the robots on! At the rate they go it will take quite a long time. They will need plenty of encouragement to make it to the finish line!

In fact, however, the finishing time will be 4PM tomorrow and 1:30PM, the next day.

See you there!

One of the many robots entered in the race which make use of a wheel-chair

The starting point- at the Expo Center

For a hundred years we have got used to the idea of space-time as a unifying construct of spatial and temporal dimensions. We have also got quite used to the idea of animated picture-shows, which give the illusion of three-dimensional motion using a succession of two-dimensional images. Put space-time and film together, and we get science-fiction movies. But the fabric of space-time can be studied much more prosaically by considering a few simple objects in a limited number of dimensions.

Take some ordinary handy three-dimensional object - a Pepper, say - and consider it passing through a two-dimensional plane. To do this, imagine cutting the Pepper up into thin slices, and converting the slices into a slideshow. As you run the slideshow, a first pepper-slice appears, and then a succession of slices wriggle around - all slightly different shapes and sizes - and finally disappear.

We can easily recognise the whole Pepper as the sum of all pepper-slices together, simultaneously. In other words, our familiar still-life Pepper, as it passes through a plane, does not change shape as such; it is just an irregular shaped object moving in space.

But now imagine the perspective of the inhabitants of a fictional 'Flatland' - a planar domain inhabited entirely by flat shapes such as squares, circles and assorted sliced grocery products.

The two-dimensional citizen of Flatland would recognise the passage of the Pepper through their plane only as a procession of changing pepper-slice shapes in time. The idea that the pepper-slices could collectively be regarded as a single fixed-shape object in a higher dimension would be completely alien (or at least, counter-intuitive) to the Flatlander.

To perceive the Pepper not as an array of separate 2D slices at different times, but as a whole 3D object at the same time, the Flatlander would have to imagine a sort of time-ordered stacked-up archive of all the stills from the pepper-slice movie - a sort of incorporeal frozen movie-object (conceptually parked partly in a hypothetical third spatial dimension).

So it is possible to conceive of different entities across the dimensions of space-time, though it can sometimes be hard work - even for familiar objects in familiar dimensions.

It is especially challenging where an object in one dimension appears as more than one object in another. For example, imagine a chunk of tree, say a trunk with a single branch off it, passing through the plane of Flatland. First to make an appearance is the roughly circular cross-section of the trunk. As the tree cross-section passes through, it enlarges and sprouts a branch, so that by the time the whole chunk has passed through the plane, there are two roundish cross-sections - that of the trunk and that of the branch. As far as Flatlanders are concerned, where once there was a single object; there are now two separate objects. But from our three-dimensional perspective, there is only the one single three-dimensional object in space: the chunk of trunk-plus-branch.

A similar thing happens when three-dimensional objects connect or diverge over time. For example, when a chicken lays an egg, what was one three-dimensional object becomes two. The post-chicken egg and the post-egg chicken are clearly separate, in our three-dimensional mindset; but they are nevertheless connected through time. In fact, just as our tree trunk and branch - although appearing as separate slices in Flatland - form a single solid object in space, the chicken and its egg can be seen as part of the same diverging object in space-time. In other words, we have a sort of frozen continuum of chickens and eggs stacked up back through time - a four-dimensional object.

Indeed, a family tree is exactly like this: a four-dimensional structure of parents and offspring, a series of separate three-dimensional family members, with different individuals appearing at different positions in time.

Indeed, the whole 'tree of life' - the entire earthly family tree of people, hominids, dinosaurs, eggs, chickens, peppers, sticky rice and unclassifiable creepy-crawly things forms part of a single planetary 'creature', a quivering tentacled four-dimensional entity reaching through space-time.

An alien observer might think of life on Earth as a single grotesque mass of mutant organic tissue, coupling with itself here, spewing out offspring there, consuming and expelling parts of itself, all the while racked by fractured identities, a short-term ancestral memory and a penchant for self-harm. Such a monstrous 4-D Earthling might be just the stuff of the alien's own science-fiction movie.

If we had never invented transparent materials like glass, we might not believe that such magical invisible materials - that are both solid and see-through - could really exist.

Yet glass is a technological reality, made from rather mundane earthly kinds of ingredients like sand and limestone. These are, of course, entirely opaque, made up of atomic elements such as silicon, sodium, calcium and carbon. And these atoms are all made of even smaller particles like protons and electrons, each of which is so small as to be invisible in the first place.

Of course, when we look at an atom close up, we realise that there is very little there to see anyway: it is mostly empty space. The size of the atomic nucleus relative to the diameter of the whole atom is similar to the size of a tennis ball compared to, say, the diameter of a medium-sized town. And a town consisting of a tennis ball surrounded by empty space would be a town you could see right through.

Indeed, this emptiness pervades all matter around us that is built from atoms. Almost all of the volume of our towns, tennis balls, cats and cream cakes is just empty space: completely void, save for a few microscopic specks of matter dusted here and there. In a sense, it is a wonder that we, and everything around us, are not all completely see-through.

(If everything actually were see-through, of course, we wouldn't be able to see anything at all. We couldn't even see the insides of our own eyelids, from the backs of our retinas).

The difference between substances that are transparent and those that are opaque is to do with their structure at the molecular level. In other words, the different appearance of glass and sand or coal and diamond is due to their different molecular structures, even if these are made up of the same kinds of atoms, which in turn are made up of a kit of the same sub-atomic particles like neutrons or quarks. So transparency and opacity are effectively properties of the built structures, rather than properties of the individual parts in the building kit.

The historic discovery that the stars and planets are made out of the same kinds of elements found on Earth was a significant breakthrough in our understanding of the universe. On the one hand, this made the universe more familiar, and its component parts more, well, universal. On the other hand, it also opened up the possibility of outlandish life-forms inhabiting other planets, which were now understood to be other 'worlds' rather than just heavenly nightlights. As a result, we tend to be more imaginative with our alien biology than our alien chemistry.

If we were visited by an unidentified flying object made out of some strange invisible-looking material, we would most easily believe that it was the technological product of an alien life-form, rather than imagine that objects from outer space were made from some special extra-terrestrial substance - invisibilium, let's say - that was alien to chemistry.

We could even imagine the aliens themselves could be invisible - or at least, evolved to be more or less transparent, like extra-terrestrial jellyfish or fibre-optic stick insects.

In fact, successfully adapted invisible aliens could even travel in their invisible spaceships to settle new planets. We could imagine just a few precautions they would need to keep as invisible as possible, if they came to live on Earth.

For a start, an otherwise invisible alien would have to watch out that it would not cast a refractive shadow, if its body were to bend or scatter the light in an unearthly manner. Then, it should avoid smoky bars, in case its breathing created telltale smoke signals in the atmosphere. And, it should avoid attracting too many flies, bouncing off its invisible body.

An invisible immigrant should take particular care when eating out. Imagine that our alien has found itself a nice piece of fruit, packed with tasty seasonal insects, or some leftover human meal, say a pizza with extra toppings of maggots and fungus. The danger is that once ingested, the terrestrial food will remain visible as it passes through the transparent alimentary tract, so that the alien becomes horribly visible from the inside out: a walking squelching sack of bile and compost-fodder. To remain decently invisible, the alien would be well advised to bring its own invisible food chain, from home.

And if successfully transparent - magically solid but see-through just like glass - then invisible aliens need not be confined to science fiction.

Of the five classically recognised senses, the sense of smell sometimes seems like the one we value the least. Smell can seem little more than a foretaste of real taste, or touch. And smellscapes themselves sometimes seem limited compared with other sensory worlds. Unlike intricate visual imagery or complex orchestral compositions, it seems that there is less scope for creating rich aromatic assemblies or symphonies of smell.

Yet, while smell may not seem as direct and instant as seeing or hearing, it can still have its uses. Like the knight's move in chess, it may not always be the fastest or strongest agent, but can get around corners where others can't reach. You may be able to smell what you can't see or hear, and people and things can leave telltale smells once they have long gone from sight or earshot.

Humans can apparently distinguish about ten thousand smells. We may not be consciously aware we have such an olfactory catalogue at our disposal, although just thinking about food can get us imagining. We can distinguish a tuna from a salmon by their smell. One could say that each species, at least, has a smell. And foods like noodles or dumplings that never lived the life of individual species also have their characteristic smells. We can combine species to get more smells: lemon and lime, salt and vinegar or duck and plum sauce have their own distinct aromas. Herbs and spices help multiply the number of smells, to create an explosion of aromatic possibility.

Because the sensation of smell is based on the detection of chemical molecules, we would expect similar kinds of smell to permeate other parts of the universe: planets smelling of iron or methane, at least, if not moons smelling of custard dust. And yet, we must expect lots of new smells to be out there, just as when going abroad you find different concoctions of food smells, even coming from the same natural ingredients. And if a terrestrial chicken can smell different from a terrestrial duck, and a courgette from a cucumber, we must expect alien main courses and accompaniments, however closely they might resemble their Earthling equivalents, to smell a bit different too.

Indeed, the more exotic and complex the alien environment, the more smells we might expect to encounter. We can imagine that sophisticated alien civilisations might create their own synthetic aromas - like different kinds of under-tentacle deodorant, interior chrysallis-freshener, or pollinate-me perfume.

In fact, for all we know, smell might play a much more important role in the lives of certain alien civilisations. Perhaps some alien races can not only detect but mentally catalogue any chemical elements, being able to distinguish the smell of ununnilium from unununium as easily as we can distinguish sulphur from chlorine, or alcohol from H2O.

And perhaps - like Earthling dogs - some alien races may use smell much more, not only to perceive their world, but as a deliberate means of communication. Perhaps a race of alien canines use an array of aromas to transmit messages to each other, and eventually develop a system of telecommunications based on smell, so that a smell carefully emitted in one location can be picked up remotely at another location. Just as humans use cellphones for voice communication, we could imagine our extra-terrestrial tail-waggers sending excited scent messages to each other on their smellphones. And just like voicemail, smellmail would allow subscribers to access any messages deposited while they were out.

Any kind of smell-message, after all, is just a package of smelly molecules - crafty particles too small to sense by sight or touch. So a long-distance smellmessage could in principle have the effect of transmitting a small package of significant particles over great distances. Just as our radio and TV transmissions escape from the Earth to beam out across the galaxy - where they might some day be picked up by some alien civilisation with the right kind of receiver - it is possible to imagine some alien smellmessage transmitted a long way over space and time and eventually picked up on some receptive planet. The message itself might be something quite trivial - some shaggy dog gossip, or a domestic dispute over a buried bone. But, more important than the message might be the medium itself: some kind of chemical package, like a spore, that could end up seeding life on another planet.

Evolution from a canine conversation? Now that would be an inter-planetary smell sensation.

A tapeworm living in the human gut has no digestive system of its own. It absorbs the intestine's processed nutrients directly through its outer surface, like a ready-made all-over- body-meal. So the tapeworm is exploiting its host's digestive system instead of investing in one of its own. It siphons off the goodness from its human benefactor - who goes to so much effort (earning a living, shopping and eating) to get the food down there in the first place - and uses it for its own sustenance.

The case of the tapeworm makes us think about what it is to be a complete organism. While we may be used to the idea that humans have some other organisms (like gut bacteria) acting as internal helpers, we may tend to think that they are not really essential, but we just tolerate them because it suits us, like the crocodile allowing the bird to pick its teeth because it can't be bothered evolving - or inventing - a toothpick of its own.

We tend to feel that we are not actually dependent on the parasite, in the way that the parasite seems dependent on us. After all, our gut provides the parasite's very home - a nice place to settle down, hatch eggs and bring up the larvae. Without 'us', there can be no 'them'. In a sense we live and breathe on their behalf. The dependency is clear in cases like the tapeworm, which we might regard as an incomplete organism - one lacking a digestive system - whereas we consider ourselves whole, even though our own digestive system makes use of live-in non-humans to help it function.

This interdependency means that humans might be regarded as 'composite' creatures by any objective observers. An alien taxonomist studying life-forms on Earth might classify us not as a distinct species, but as a composite life-form comprising not-quite-whole species of tapeworms, microbes, and homo sapiens.

Conversely, we might face difficulty in recognising distinct alien species, if they too formed a tangled jungle of taxons and taxonomists, hosts and parasites. And once we are used to ourselves as hosting parasites - like aliens within us - we can also imagine having alien parasites living off us too.

Imagine a cold-blooded alien that came to live on or in our bodies because of our warmth. Such a parasite would have no central-heating system of its own, but simply live off our body heat. All its other functions, like eating, sleeping and reproduction, it could take care of by itself.

Once it had made itself at home, it might then tap into some of the other local facilities. Imagine that the parasite could plug into the visual system of its human host. Instead of the parasite as a wretched 'bug' blindly groping around the murky bowels of its host, we could imagine this parasite perched just behind our eyes - like our own 'mind's eye' perspective - taking in the view by tapping into our optic nerve, like live video streaming. It would be able to sense all the visual richness available to the human eye, even if it had only the intellect of an insect to process the information.

Or, imagine a parasite that not only connected to the optic nerve, but plugged directly into the brain. Residing somewhere in the skull, it would not need a brain (or cranium) of its own, but could feed off the thoughts and mental processes of its host. It would have access to all the sensory information processed by the brain, and all our memory archives too.

And if there were a two-way data feed, the parasite's body might even be able to send its own requests to the brain's central processing unit, perhaps while the brain was otherwise idling. Perhaps indeed our brainless alien parasite could plug in, tune in and switch on the brain, and ask it to do a few calculations, or run a few scenarios, while we slept.

Like a 'virus' in the brain, such an alien parasite would be metaphorically feeding off our brains - rather than literally feeding off our stomachs - while happily carrying out its other bodily functions for its own benefit.

But if it is spooky to think of an alien body tapping into our brain, then how about an alien that brings its own brain, but takes over our body? It could unplug our brain, and use our body to breathe Earth air, to eat Earth food, and generally see the sights. That would be not so much a parasitic alien brain-sucker, as an invasive alien body-snatcher.

Life on Earth is a lot stranger than commonly supposed. Science fiction aliens are often a lot more like humans than many of our real-life fellow Earthlings. Even alien life-forms suggested by serious scientists may be limited in conception, compared with Earth's more exotic flora and fauna. In their book Evolving the Alien, Jack Cohen and Ian Stewart comment on this gap between 'the biology known to most astronomers', and genuine Earth biology.

A simple way of getting in touch with a known sample of biological possibility is to stop thinking of Earth as a planetary 'land', but to consider it as a mostly water-based world.

Consider, for example, marine creatures with a manageably exotic kind of alien-ness, such as the octopus, with its three hearts, eight arms, hundreds of suckers and millions of tastebuds. This would make a good 'alien', for a start, especially if encountered as a giant life-form somewhere in outer space (rather than a snack-sized corpse on a sushi conveyor). Or consider the squid, with its jet-propulsion chassis, or 5000 species of sponge - with no mouths, nervous systems or internal organs, but skeletons of lime or silica.

Go deeper, and we get yet more exotic fauna. Consider the bioluminescent creatures living in the pitch black depths of the abyssal plain. These have evolved to emit their own light to see by - without forgetting to evolve the eyes to see with in the first place.

Even more alien are the bacteria that live around deep sea vents: they do not require light or oxygen, but live off the heat and hydrogen sulphides, by a process - chemosynthesis - that Bill Bryson has described as 'an arrangement that biologists would have dismissed as preposterous had anyone been imaginative enough to suggest it.'

The creatures living here must surely be among the most incredibly alien of our fellow Earthlings, having evolved in a rather un-Earthlike environment with temperatures of 400 degrees and pressures of 200 atmospheres. (If we were searching for life in outer space, we could be forgiven for by-passing a planet like this).

Such an alien physical environment, harbouring an alien biology, may also suggest an alien cosmology, as viewed by any sentient inhabitant.

Imagine the totally dark 'universe' of the abyssal plain, in which the darkness just goes on and on - as far as any eye could see. Even the combination of eye and telescope might not be much use for a would-be 'astronomer' of the ocean depths. Aquatic cosmology might necessarily be rather theoretical, involving much speculation on the existence of what might lie beyond the hydrosphere.

Indeed, there might not be any reason to suppose there were anything out beyond the watery firmament in the first place. An ocean bottom-dweller would have even less reason to believe their world was surrounded by air than a land-dweller should believe 'The World' to be a globe floating in space, since the ocean floor has no 'starry sky' revealed at night to hint at an outer beyond, and no equivalents of moons or wandering planets to hint at possible formats for celestial bodies. At least land-creature science can speculate, by analogy, that if a landmass is an island surrounded by water, the whole Earth might be an 'island' surrounded in a yet wider spatial void.

Imagine the scepticism directed at a sea-floor cosmologist speculating that, instead of the abyssal universe extending forever in darkness, you could journey upwards to be touched by light, and become increasingly bathed in it, until bursting out of the water into sunshine - a sudden phase transition from an 'atmosphere' of liquid to one of gas.

Traditional sea-floor cosmologists assuming the 'common sense' position of a homogeneously dark, aqueous universe - regarded with the same nothing-there nonchalance as we consider the invisible air or space around us - might be suspicious of this fantastic break from the normal scheme of things.

An even greater leap of faith might be needed to conceive of a cosmological fabric in which the very terra firma of the ocean floor could ruck up in some places, to project out of the watery firmament entirely, and directly touch the face of the (hardly less hypothetical) gaseous heavens.

And on top of that, who would believe that this surely barren, almost topologically-inconceivable solid-air interface might be the habitat of some kind of alien creatures creeping around - or flitting above - the bed of a volatile nitrogen-oxygen ocean...?

That could be enough to tax the imagination of the brightest abysmal scientist.

In science fiction stories, aliens usually fill a variety of roles recognisable to humans. First, there are the kinds of alien who are analogues of ourselves - alien 'people' to do business with, make war or peace, dine or have experimental sex with. Then there are the scary alien monsters, analogous to predatory animals (like alien equivalents of lions or dinosaurs) or small nasty pestilent things (like alien worms or microbes). Other alien creatures might turn out to be analogous to pets that keep us company, or farmyard animals that we keep in order to eat. Finally, there may be particularly incomprehensible, unrecognisable life-forms seemingly put there to puzzle or disgust us and our scientific wisdom.

If Earth itself contained only non-human animals of those types - that we recognised as predators or prey, pets or pests, or specimens from science school - then we might be limited in imagining what an 'alien society', analogous to ours, might be like. We might simply fill the void with dreary humanoids and their quotidian quasi-terrestrial civilisations.

However, Earth biology has provided us with at least one class of creature that is both a bit like our own society and yet a bit alien: the social insects, and in particular, the bees.

A bee is recognisably a life-form; a creature with some anatomical affinity with us, but not too much: having a head with some kind of eyes, but really funky insect eyes, some kind of limbs, but a different number doing different things, and so on. A bee even looks as if it might be sentient and intelligent, or at least forms part of a social entity that appears so.

Most of all, bees seem to 'do' stuff that we recognise, including cleaning the house, going to work, fetching supplies and feeding the brood. They have a 'system' to maintain; an economy to run. They huddle and do little dances. They make stuff - honey, wax and royal jelly. They create a remarkably rational-looking architecture, as if possessing the otherworldly know-how of an alien civilisation.

In other words, beehive society is potentially a good analogue for what an alien society might be: it is sufficiently 'alien' in terms of its specific physical characteristics, and yet it is recognisably, analogously, a society.

Bees also suit this analogous role as they are neither our predators nor our prey; they are not considered pests, nor are they really pets. Sure, we have a working relationship with bees, but they don't really work with us or for us, in the way that beasts of burden or working dogs do, directly acting to our commands. (Whoever commanded a bee?) No, we just tend to build them hives and extract honey for rent, without them ever expressly doing our bidding or giving their consent.

So we do have a rapport with them, but it's not a direct one-society-to-another reciprocity. And this is exactly the kind of semi-skewed relationship we might expect if we encountered a society of extra-terrestrial aliens. In other words, first contact with an alien society might not be as familiar as bowing or shaking hands with a bunch of conveniently upright, appropriately limbed bipeds; or at the other extreme, as odd as an audience with a vat of self-aware vapours.

Rather, making contact with an alien civilisation might be like encountering a society of human-sized bees. We can imagine going up into their hive like entering the trapdoor a giant spaceship, with black-and-yellow uniformed guards with their stings at the ready, and treated to the science-fiction spectacle of flying round the interior of a shimmering skyscraper city of cells and galleries, before zooming in on the everyday realities of hive life.

We might then have a frisson of disapproval (albeit perhaps an inappropriately anthropocentric one) at their seemingly politically incorrect authoritarian regime; the impersonal production-line rearing of their young; the oppressive gender roles - either because the females do all the chores, or because the males are even more prisoners of society, fed and groomed like concubines in a harem, their only fate as sex slaves to the monarch and death.

So we might be welcomed as alien guests of honour, feted with alien dance performances and dining on alien royal jelly. Or we might be treated strictly as equals, and commandeered into their society, for better or worse. Or treated like intruders, stung, smothered in propolis and unceremoniously fed to the larvae.

In other words, we can't necessarily guess what analogues our alien counterparts will see in us.

In his book Nature: An Economic History, Geerat Vermeij applies economic concepts - such as competition for resources, functional specialisation and economies of scale - to the natural world. The book has been described as 'Economics, as if written by intelligent aliens', perhaps because the human world is treated impartially alongside the rest of the ecosystem. (In fact, due to the authoritative treatment of marine snails, the book might be especially appreciated by intelligent alien molluscan Earthologists).

In generalising across widely differing life-forms, the book, as well as reinforcing the idea that homo sapiens is 'just another animal', invites one to wonder if the phenomena described might hold true for life on other worlds. In other words, if on Earth it was possible that a combination of originally inorganic substances could somehow organise themselves into a system of living things - that eat, compete or otherwise interact with each other in the whole runaway roadshow we call life - then why should the same not happen elsewhere in the universe?

After all, Earth must originally have seemed a rather hot, toxic place for life to start. But eventually, somehow, life got a foothold, expanded to occupy sea, land and the air, and went on to conquer most of the Earth's surface, occupying almost every conceivable space and crevice on what was once a naked mineral satellite. As life developed, the planet grew itself its own ecosystem. So what we call our environment - forests, marshes and seashores - is significantly organic: not just a physical stage-set framing the action, but part of the action itself.

Life's conquest of Earth has been so successful because it has found ways of adapting to diverse circumstances. Species have morphed, mutated and experimented with themselves until they would eventually fit a diversity of niches all over the planet. Where light has been abundant, we have evolved eyes. Where the atmosphere has been right, we have evolved wings. Where enemies abound, we have evolved camouflages and poisons. In all cases, these features have evolved independently many times and in many places. If this is so on Earth, there seems no reason why it should not happen elsewhere. The universe should be teeming with eyes and wings, mimics and stings.

All this evolutionary innovation is spurred by competition. Everywhere individuals, species and businesses are trying to out-compete each other. In open competition, the strong will take over, absorb or eat the weak. Successful species unleashed into a new environment may wipe out the native species. But strength and success are always relative, and dependent on the context. Sometimes it is the big beasts that are wiped out, while the smaller creatures live on. Big companies often swallow smaller ones; but sometimes they crash spectacularly, and the little ones pick over their remains.

If the dinosaurs had not been wiped out, perhaps the first Earthlings on the moon would have had scaly tails and toothy beaks. Instead, the mammals prevailed and flourished; now humans are seemingly in charge of much of the planet, with ambitions for colonising others. But if a more successful life form comes along - an intelligent mollusc, perhaps, or a disarmingly friendly computer virus - then the humans may yet be overtaken. The history of the next millennium could yet be typed by geeks with tentacles.

In fact, there seem to be some typical patterns in the conquests of life. Species that evolve in large abundant continental areas tend to have a competitive advantage over species native to smaller, more sparsely resourced areas. So when continental species are introduced to islands or other relatively isolated habitats, they often quickly take over. This biological fitness for conquest is perhaps echoed in the human world of technological supremacy. History shows that the peoples with superior technology - whatever their culture or morals - tend to prevail over those with simpler kit.

This does not make comfortable reading for Earthlings in the face of an alien invasion. For a start, the chances are that the aliens - in order to have made it here - will have the better technology. And since Earth so far has been completely isolated from any extraterrestrial competition - from any teeming galactic 'continents' of competitive civilisations - then the chances are that the aliens will be better at taking over new habitats than we are at defending them.

In this case, we should hope that the aliens are not interested in Earth as a new home, or as a biotic filling station on some inter-galactic highway. In the circumstances, our military technology may be useless. Instead, we might have to hope that our alien visitors are Earthophiles, interested in ecotourism rather than exploitation. In which case, a book about our planet written as if by - or for - intelligent aliens might be our best hope.

Encountering life beyond Earth must rank as one of the most momentous out-of-this-world discoveries imaginable. Quite apart from raising questions about the particulars of alien life-forms, such a discovery could pose - or answer - questions on the nature of life itself. This goes far beyond the familiar territory of 'what might aliens look like' to more challenging questions such as what is life in the first place, and what - if anything - separates the animate from the inanimate?

We may tend to think of life as being, at least potentially, universal. That is, in principle there is no particular reason why life should only occur on planet Earth, any more than we should believe that the sky is the limit of the laws of physics or chemistry. It is not just science fiction, but science itself, that speculates on the possibility or probability of extraterrestrial life, a probability that has surely increased with the discovery of extrasolar planets.

We can get a feel for the extent of biological possibility from considering the similarities and differences between life-forms on Earth. Extraterrestrial life, we may assume, may have some general characteristics of the kind shared by life on Earth - such as metabolism, reproduction, predation and so on - but not necessarily the particular characteristics of specific species, such as number of legs, or number of sexes. Overall, one could imagine alien life-forms that are not animals, not plants, nor fungi, bacteria or viruses, but are things at least as different from any of these as those are from each other.

The perception of what is recognised as a life-form must be partly dependent on what varieties of life exist in a particular world, and how different they are from non-living things. An alien society consisting only of animal-like creatures, on encountering Earth, might find it hard to believe that plants - strangely passive, brainless fixtures - were 'alive' in any meaningful sense, and not just part of the scenery, like rocks and waterfalls.

Similarly, we might ourselves find, on encountering some other world, a kind of biota that changed our own perception of life, by filling in some of the spectrum of possibility between life and non-life. Perhaps in some alien world, there is some kind of mineral kingdom, populated by crystalline life-forms, who are accorded living status just as surely as any virus or fungus. Their appearance as intermediate forms between what Earthlings recognise as organic or inorganic would help to bridge between previously distinct categories of animate and inanimate, just as the knowledge of monkeys helps bridge mentally between mice and men.

And imagining a most finely graduated spectrum between animate and inanimate, it might be difficult to recognise 'life' as a definitive, exclusive state after all.

On the one hand, this would accord with a philosophy that there is a degree of 'life' or 'spirit' in all things, whether rocks or clouds, forests or fruit-bats. This perspective accords, indeed, with some human belief systems, although it has not (yet) been assimilated by science.

On the other hand, if there is really no definite separation between the living and the non-living; if the transition between the animate and inanimate is so subtle or spurious that any dividing line is effectively arbitrary, or even illusory, then this removes any special status being accorded to the living - an anti-mystical position that surely accords with scientific tradition.

Perhaps the whole of nature is just one big mechanism after all. Perhaps biology is no less 'mechanical' than physics: the electric pulses in brains and muscles obeying orderly laws just like planets orbiting the sun, or electrons orbiting the nucleus. After all, it is the same physics and chemistry in living bodies as in inanimate matter. Our bodies are made up of elements like calcium and carbon, zinc and iron, which are the same whether in one context viewed as cosmic dust, or in another, lunch.

In other words, we are made of the same stuff as everything else: there is no separate 'vital' substance in our bodies; no special ingredient, not found in the periodic table, that separates the living from the non living matter.

So, just as science has convinced us that the Earth and the rest of the universe are made of the same stuff, and that humans and animals are of the same stock; perhaps we can regard all matter similarly, without the illusion of a privileged status for living matter.

And so, while 'life' may be universal, the perception of life as a special state may conceivably be a limited anthropocentric perspective - perhaps paradoxically a delusion of the more self-aware animate objects.

Sentient Earthlings are in the habit of distinguishing the duality of mind and body. But while we are used to our bodies being made of ordinary matter - our tears just like the salty seas, the twinkle in our eyes just recycled starlight - we are less used to thinking of our minds in terms of physics and chemistry. Is a mind indeed something made of matter (like a brain), a real but possibly mysterious presence (like a kind of force or energy); or is the mind itself just an illusion?

If the mind doesn't physically exist, if consciousness is just an illusion, then surely our view of ourselves as sentient beings would be altered. We would find ourselves in a rather mechanistic existence where we were not much more than robots - cogs and circuits, actions and reactions - with the mental machinations just part of the built-in software, that happens to work better if we believe we have minds of our own.

Nevertheless, our perception of consciousness - and the belief that we do have a mind that we can 'make up' or 'change' - is probably too useful to discard altogether. In theory, a philosopher might insist 'I don't have a mind, I am just a bundle of molecules that thinks it thinks'. But in practice it is handy to assume that philosophers do have thinking minds, just as we tend to assume for ourselves. It is rather like all those useful working assumptions - that the Earth is flat, the sea is level, or time flows constantly everywhere - that have proved handy for most practical purposes for most of the history of humanity.

With the assumption that we do have minds, we are accustomed to believing that the mind, if it has any physical presence, is located somewhere inside our bodies - most often, literally inside our heads.

When I look, things appear in front of me, as if my mind is right there behind my eyes, with a great ringside view of the action. My mind's cosy image of being snugly situated inside my head is reinforced by having nice stereo sound coming in directly from left and right via the ears.

This perception makes one feel as if one's mind is like being on the command deck of a starship, surveying and sensing outer space from a comfortable interior environment. The difference is that a starship commander is also able to see the physical contents of this interior world: herself or himself, the rocket-thrust controls and the office furniture. However, our minds cannot see the inside of our own heads. From our mind's point of view, our bodies are 'out there' - out in space with the asteroids, not inside the ship.

Now I can survey the physical landscape out there, and recognise in it things identifiable as 'you' and 'me' and 'my office furniture'; but this is not necessarily a universally occurring state of mind.

Imagine somewhere there is a just-coalesced alien consciousness, newly formed from galactic-mind-matter. It finds itself gazing out across the universe as if through an out-of-focus telescope. At first it perceives only blurry incoherent images, but cannot yet really 'see' or make sense of anything. It doesn't yet know what it is looking at; it only gradually learns to divide up the universe into 'me' and 'not-me'.

What counts as being 'me' is not so much what is physically connected to the rest of me (a circular argument) but is effectively those parts of 'what's out there' that are directly controlled by my thoughts alone. If I can waggle a toe or tentacle just by thinking, then it's mine.

(This basic distinction between what is me and not-me is, of course, one of the first crucial hypotheses we test when first entering the world.)

This still assumes a one-to-one relationship between a mind and a body. But there could be more curious kinds of alien consciousness. Imagine, for example, a planetoid life-form which has a single brain at its core, but multiple personalities... or the reverse, a single intelligence distributed through a series of physical objects. These ideas are perhaps not so alien if we consider them not as analogues of humans as individual creatures, but as analogues of human societies.

An alien mind analogous to a human society might well appear to have a collective will, certain moods and behaviours, acting as a single being. But even if some alien higher level mind existed - made up of our minds - we couldn't be sure if it was aware of us, if it was self-aware, or what it was thinking...