Many people fall into one of two camps; those who believe in UFOs, aliens abductions etc (this group is worryingly numerous), and those who think anything to do with aliens is best left to the cranks. Both are wrong.

Think of it. So many trillion stars; can we be sure that none of them harbour life? Clearly, no. Can we be sure that any of them do? Apart from the Sun, no. What can we do to find out? Theorise? No. Search? Yes. We have telescopes, and they may very well have technology - possibly at an incredible level of advancement.

Let's assume that they do exist. In the unlikely event that their technology had stagnated at our level, we could detect them now, if they were close enough. Let's assume that the technology of at least some alien civilizations involves electromagnetic waves (light, radio, heat etc.). Perhaps aliens do not use EM technologies; but it is at least possible that they do, since light, heat and radio waves are extremely important phenomena in our universe. Even if, like us, the aliens were not signalling deliberately, the various electromagnetic waves (only some of which would be readily detectable at interstellar distances) produced by their technology would be leaking into space.

Here I am, advocating practice rather than theory; but this page is mostly theory. In it, I examine the likelihood of life arising elsewhere. A rather quixotic endeavour, you may think; and you would be right. However, I think it worthwhile for people to realize that SETI deals with real issues, albeit ones which theory can only illuminate to a slight extent. What's more, I like examining the development of life on Earth - it is truly remarkable that supernova remnants can spontaneously organise themselves in such a way as to be capable of thought.

DO THEY EXIST?

The short answer is that I don't know. Many people think they know, but I don't think anyone really does.

Back in the 1960s, Frank Drake and Carl Sagan undertook the first-ever SETI (Search for ExtraTerrestrial Intelligence) project, named 'OZMA'. In 1974, a message was transmitted to a galaxy around 25,000 light years away.

Somewhere around this time, Drake came up with the 'Drake Equation', which is the best way of calculating whether aliens exist. However, it is not adequate (through no fault of Drake), as there are too many unknown factors - it yields wildly different results according to who is using it.

I will now take a closer look at the equation (don't be put off, this won't be complicated), but stress that of course, I cannot enlighten you as to whether aliens exist or not. Drake makes the crucial point that the 'existence of extraterrestrials is not an issue that can be determined on the basis of theory, no matter how compelling the arguments. SETI is by definition an experimental science'. As a theorist by nature, all I can do is to make guesses, point to some areas which need further investigation, and, I hope, demonstrate that SETI is a serious and enormously important issue which deserves a considerable investment of time and resources. If you would rather deal in more concrete matters, I would advise you to look at other pages on this site.

'Every tactical problem in the search endeavor rests on some age-old philosophical conundrum: Where did we come from? Are we unique? What does it mean to be a human being?'

- Frank Drake

The Drake Equation: N = n* f^p n^e f^l fⁱ f^c L
(this is only one version of the equation)

Is this unattainable mathematical gibberish? No. Here's what it means: 'N' is the number of aliens (of the types we might be able to communicate with) that exist. All the other letters stand for the things one needs to find out in order to determine 'N':

n* is usually taken to stand for the number of stars in the Milky Way galaxy. Note that the search area is already being narrowed down - many have thought this reasonable as a starting point, because the nearest galaxy, Andromeda, is 2 million light years away - approximately 19,000,000,000,000,000,000, or 19 quintillion kilometres, rather a large distance. However, we must be careful not to draw conclusions about what priorities aliens assign to interstellar communication, and therefore what power their signals might have. In any case, there are scenarios in which even those alien civilizations which don't devote any effort to interstellar broadcasts might be detectable intergalactically. For example, aliens might surround their star with a sphere of matter, the better to harness its energy. Such a structure, the 'Dyson sphere' dreamt up by Freeman Dyson, would be readily detectable over immense distances.

f^p is the number of stars whose environs can support life. It is perfectly reasonable to question whether we can only expect life to exist around stars which are reasonably similar to our Sun. But unless you are very much more intelligent than me (and probably even if you are), you will find it difficult to make a useful analysis of the possibility of aliens arising under very different circumstances from the ones which gave rise to Earth's biosphere. As an abstract exercise, speculations about incredibly weird aliens are certainly interesting; but I'm going to stick to what I have a chance of getting to grips with.

n^e is the number of planets in each solar system that are suitable for life;

f^l is the number of these planets on which life actually develops;

fⁱ is the number of planets with life on which intelligence develops;

f^c is the number of planets with intelligence on which a technological civilization develops;

^L is the number of planets with a technological civilization which has survived until today (or more precisely, until sending a signal which we could receive today; or - well, I won't go into it).

If you multiply n*, f^p, n^e, f^l, f^i, f^c, & L together, you get N. That part is easy. But actually finding out the values of the various factors is difficult - in some cases, presently impossible. In addition, each factor can be divided into numerous 'subfactors', all of which need solving. For example, in order to know whether simple life is likely to evolve into intelligent forms, one needs to know whether a backbone is essential, and if so, how likely it is to evolve.

One of the main problems with the equation is that there is only a precedent of 1 - the Earth - from which to draw; any speculations based on the possible discovery of ancient Martian life are just that - speculation. As every scientist knows, one example is nowhere near enough, especially for a calculation with so many components. What follows, therefore, will fall somewhere between

• a description of how evolution unfolded on Earth, and
• speculations about the likelihood of parallel evolutions unfolding elsewhere.

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Having said all that, I will now embark on the (perhaps useless) task of examining (not calculating) some of the factors in the Drake Equation.

For what it's worth, my intuition is that the conditions needed for life to develop are rather specific. This is mainly based on a feeling that one of the major steps in the development of life - namely, the emergence of a self-replicating organism - cannot be achieved without conditions being 'just so'; the right chemicals present, the right temperature, perhaps even the right types of clay. (Since writing this, a book called 'Rare Earth' came out - in early 2000 - which puts the case very well).

n* NUMBER OF STARS IN THE MILKY WAY GALAXY:
This is the easiest one. There are about 300 billion stars in our galaxy (there are 10₂₁, or 10 sextillion, stars in the observable universe).

f^p NUMBER OF STARS WHOSE ENVIRONS CAN SUPPORT LIFE:

Population 1/Population 2 stars.
Population II stars are not thought capable of supporting life. Situated in and around the galactic centre, many of them are excessively small. Stars in the fringes of our galaxy - out along the spiral arms - are more variable in size because the gas they are formed from is more irregularly distributed than in the galactic core*. In addition, violent chain explosions and black holes may be too common in the densely-packed core.

Only 20% of stars are population I; of these, 50% are 'second generation'. A second-generation star is one which includes heavy elements. Many heavy elements are only produced in the unbelievable violence of a supernova. It is estimated that there have been around 500 million supernova explosions in population one stars in the Milky Way Galaxy; these are the ones which interest me, because they are in what would seem to be the life-friendly areas of the galaxy. The cosmologists tell us that 'first generation stars' and their environs have no heavy elements; further, it was not until well into the Universe's history that enough stars had exploded, and enough of the heavy elements been generated, for life to develop. Just how long, neither I nor anybody else knows, although as usual, some people have taken up firm positions without knowing enough.

* It is of some interest that the distinction between population I/population II stars is characteristic of spiral galaxies (such as our own); it may be that other types of galaxy have more population II stars, and therefore less chance of life (comments/enlightenment?)

Star sizes are categorized as follows, in descending order: W O B A F K G M R N S. The standard mnemonic for this, "Wow! Oh, Be A Fine Girl, Kiss Me Right Now, Sweetheart", betrays its date of formulation. Each category is subdivided into nine; our own sun is a G2 class star. Decades ago, the eminent astronomer Otto Struve analyzed the speed at which the various types of star were spinning (by gauging the degree to which their spectral lines were spread out by the rotation), and made the highly significant finding that whilst all the massive stars (W, O, B, A and F types) were spinning at enormous speeds, all G, K and M-class stars were spinning far more slowly.

So?

You've seen an ice skater spin. Remember how she speeds up when she draws her arms in? The same applies to any rotating object, including stars. Struve's results therefore show that the mass of G, K and M stars is not all contained within the star itself; there seems to be additional mass reducing the star's spin, in the same way as the ice skater's arms reduce hers. Does this mean that most of these stars (or at least the ones that don't have another star as a close companion) have planets? Perhaps. But one should bear in mind that the unseen mass need not take the form of planets - it could, for example, consist of millions of drifting asteroids or comets, as in our own Asteroid Belt, Kuiper Belt and Oort Cloud. Here, however, we are able to draw encouraging analogies with our own Solar System. Just think of the proliferation of moons of various sizes revolving around our local planets; there are great size variations. Again, though, there is a counterargument - haven't I just described how smaller suns have satellites, while bigger suns don't? By analogy, the distribution of matter around planets may not be the same as that which obtains around suns like our own (this is Philip Morrison's idea, not mine). Matter behaves very differently on different scales - something that nanotechnologists are finding out to their cost.

Astronomical observations are not yet very precise when it comes to finding planets - especially small planets which are relatively distant from the parent star - so at present, indirect evidence (such as Struve's "ice skater hypothesis") can be extremely useful. Hubble Space Telescope images of the Orion nebula "show many proplyds e.g. disc-shaped dust clouds swirling around young stars. The presence of these planetary nurseries, themselves located within stellar nurseries, certainly suggests rampant planet formation throughout the universe"¹. In fact,

"more than half of them are surrounded by flat disks of dust and gas. In many cases the parts close to the star seem to be empty of dust and gas, as if planets had already formed there, gobbling up the interplanetary matter. It is not definitive evidence, but it strongly suggests that stars like our own frequently, if not invariably, are accompanied by planets. Such discoveries expand the likely number of planets in the Milky Way galaxy at least into the billions." [Carl Sagan, 'Billions and Billions']

¹ Michael Meyer: 'Ex astra: Life from the Stars Organic chemistry amidst the stars'

New information on planets outside our Solar System is coming out all the time; you could try The Astrobiology Web or Universe Today for updates.

n^e NUMBER OF PLANETS IN EACH SOLAR SYSTEM THAT ARE SUITABLE FOR LIFE:

It is frequently argued that because microorganisms (the example often used is the anaerobic archaebacteria who live in extreme conditions in hot springs) live under such-and-such conditions, it is therefore possible that they could originate under such conditions on other planets. Since some archaebacteria live at high temperatures, it is argued, life can originate in these circumstances - and, perhaps, in similarly harsh ones elsewhere.

This argument needs to be skewered. Humans can survive in space; but we couldn't originate there. It is far more likely for an organism to adapt to survive harsh conditions than for it to actually originate from scratch under such conditions. The first organism will always evolve under relatively easy conditions (whatever those are); later, it can make gradual jumps* to progressively more difficult environments. I am not making any claims about whether life could originate in hot springs or not; I am just remarking that the criteria for 'origin-friendliness' and for habitability are different.

* "Punctuated Equilibrium" only consists of sudden evolutionary jumps if you're thinking on a geological (i.e. incredibly long) time-scale. It's an instructive and probably valid theory, and applies for example to the aftermath of the disaster that wiped out the dinosaurs; at that time, mammals diversified very quickly, filling the newly-emptied ecological niches. Gould and Eldredge, the originators of the theory, do not claim that punctuated equilibrium is a challenge to Darwinism; unfortunately, though, some people have taken the theory to be a refutation of Darwin's great theory.

f^l NUMBER OF THESE PLANETS ON WHICH LIFE ACTUALLY DEVELOPS:

It has been claimed that the percentage of essential elements of life - carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS) - does not vary greatly between different lifeforms. I would be interested in finding out the degree to which this holds; if it is relatively universal, it would indicate - at least to my intuition - that natural selection would tend to favour this kind of molecular arrangement in any carbon-based lifeform - whether terrestrial or alien. I say this because if not all of them were necessary for all terrestrial species, there is a very good chance that natural selection would remove one or more for the sake of economy. If the molecular recipe for life is so precise - resistant even to moulding by natural selection - then perhaps it is the only one that works.

I will make two caveats to this, however:

• The existence of a wholly different kind of life - based on a very different conjunction of molecules or units - could not be ruled out.

• It might (conceivably) be that by the time the ancestor of all terrestrial life emerged, it was already so advanced that its fundamental functions depended profoundly on the CHNOPS elements, with the result that removing any one of them would bring the whole edifice crashing down. In other words, the trunk of our tree of life could only grow once; thereafter, all that grew was branches (albeit magnificently varied ones).

A particularly interesting suggestion for how life emerged has been given by A.G.Cairns-Smith.

Dr. Gunther Wachtershauser of Munich, Germany (who appears to be taken seriously by academics, although he's a patent lawyer by trade) is currently pursuing a similar idea; he is having a reasonable amount of success in generating complex organic molecules on a surface (such as iron and nickel ores, which are good 'molecular activators').¹

In any case, I am not sufficiently familiar with the details of prebiotic Earth and early life to reach a conclusion as to how it began. For that matter, I don't know if anyone is.

For a philosophical/evolutionary discussion of the costs and benefits of intelligence, see my article 'The Human's Trunk'.

Important influences on evolution.

These are very numerous, and I am doubtless unaware of many of them. For what it's worth, here are a few:

Crises seem to galvanise evolution.

The crust (outer layer) of the Earth is made up of tectonic plates, very roughly 20 in number. Some of these plates are comparatively light, and therefore protrude from the seas, which rest on the heavier (oceanic) plates. The currents of hot rock within the Earth move these plates around at speeds of perhaps 10 centimetres a year. These currents of molten rock are thousands of kilometres thick; their pace is agonisingly slow, but they are enormously powerful. It takes a lot to halt one of the plates which ride atop them.

245 million years ago (we speak of these timespans so easily! I find it remarkable and admirable that our species has been able to measure these vast ages with such precision), it is contended, many of these plates came together to form the 'supercontinent' named Pangaea. As you might expect, the currents under the plates did not suddenly stop when the plates above them met; their vast momentum crushed the plates together. Under this unbearable strain, the plates heaved and buckled and shuddered. In places, huge mountains were formed; in many places at or near plate boundaries, the plate simply could not endure the stresses, and broke - millions of tons of boiling magma and dust shot forth, blackening the land and obscuring the sun. A great chill descended over the Earth (this is all very biblical isn't it?). 95% of all species died; 52% of all families of species were exterminated.

Tectonic plates have been hugely important for the evolution of Earthly intelligence. As well as opening a plethora of niches by annihilating species, their activities have continually brought together and separated vast tracts of land, thereby joining and splitting whole ecologies, preventing evolution from becoming too comfortable with its solutions. They have also produced huge climatic changes; for example, the coming-together of North and South America precipitated climate changes around the world - among them the important deforestation in Africa, which impelled some of humanity's ancestors to take to the savannah. Tectonic plates created lots of land; nutrients washed off the land into shallow seas, creating a promising environment for the evolution of complex life.

One effect of such changes is to favour innovation; for large animals, it is quicker to learn than simply to inherit behavioural instincts. Brains which can learn need to consume more energy in order to carry out the requisite calculations; but when environmental niches change, the animal which learns is often better-equipped to seize the new opportunities, and offset its greater energy consumption. Where an environment is stable, it will still be sufficiently complex to provide room for intelligence; but when new challenges come along, the smart big animals and the quickly-reproducing microorganisms will often be best positioned to adapt (one culturally, and the other biologically) before they can be wiped out.

It has been argued that large continents are important in encouraging competitiveness in land species; they tend to provide a large diversity of mutually-accessible environments, and therefore competition between large numbers of species and behavioural strategies. When such species come across the less competitively-honed inhabitants of smaller continents (such as Australia) and islands, they are likely to emerge on top.

Because the sea is a less varied environment than the land, one could argue that it is, other things being equal, less likely to promote diversification among its inhabitants. As Isaac Asimov observed, it may also be important that light travels better through air than through water; because of its comparatively short wavelength (high frequency), light can carry more information than, for example, sound, which has much longer wavelengths. Because the underwater environment is darker, aquatic creatures are less able to make use of the informational richness of light.

However, these observations do not directly answer the question of whether large continents (or large bodies of water) give rise to intelligence (as opposed to competitiveness). I imagine that they help; ingenuity is basically a way of achieving competitiveness. For more on this, see my article 'Whether the development of human-level intelligence was inevitable' in the 'evolution and uses of intelligence' page.

If a planet is too big, it will be more difficult for large animals - and therefore large brains - to evolve. Why?

If you look at a large animal (say an elephant) and then at an insect (say a fly) you will notice some major differences in the proportion of the various body parts. In the smaller animal, the limbs will be proportionally thinner, and the structural support (i.e. bones in the elephant's case) more flimsy. So what? Well, there is a reason that the biggest animals live in the sea (the blue whale is the largest animal ever to have lived - bigger than any dinosaur). Think about what happens when you put on weight. The surface of your skin (I am simplifying) exists in two dimensions - you could spread it out over a flat surface if you were feeling particularly masochistic - and expands in two dimensions (let's say up/down and left/right). Should the fancy tickle you, however, you would find it very difficult to spread your insides out evenly over a flat surface. As you get fatter, your guts expand in three dimensions (up/down, left/right, and in/out). So as an animal gets bigger - as the surface of its skin covers more area - its insides expand much more quickly than its body surface. For this reason, gravity imposes a size limit on animals (or at least those living on reasonable-sized planets). Animals which near this limit - like elephants or rhinos - tend to have very thick bones to support the disproportionate weight. I do not know whether there are other reasons why very large planets cannot support intelligent life (for example, perhaps their atmosphere is too dense or too cold, or the requisite elements - carbon, oxygen, hydrogen and the rest - cannot come together in the correct way); if there are none, then we might expect the intelligent species to be located in the seas - only there could they grow large enough.

f^c NUMBER OF PLANETS WITH INTELLIGENCE ON WHICH A TECHNOLOGICAL CIVILIZATION DEVELOPS:

• VIRUS: The idea that aliens would have viruses is actually not very daring. On Earth, there are some organisms that have machinery (i.e. DNA, proteins etc.) for replicating themselves, and there are freeloaders - viruses - who don't bother to make self-replication machinery. Instead, they hijack someone else's. Such Darwinian processes are the only ones which we can imagine creating intelligent life. (The 'God hypothesis' does not qualify, because there is no explanation as to how God arose.). If natural selection of lifeforms operates on other planets, then it is (I think) inevitable that viruses will exist; some organisms are bound to exploit such delectable short cuts to reproduction. So: could a virus wipe out technologically savvy alien beings? I cannot give a definitive answer, but my feeling is that it couldn't. Precisely because there would probably be viruses on populated alien worlds, it is unlikely that aliens would be genetically* homogenous (I go into more detail on this elsewhere on the site). If they were technological, they might exist in greater numbers than at previous times in their evolution, when they would have been more subject to the vagaries of nature. Many civilizations would understand the uses of sterile environments, and could resort to that if the worst came to the worst. And it is likely that for resource reasons, many of them would live off their planet, in groups which could stay apart if necessary.

• WEAPONS OF MASS DESTRUCTION: I think that a central component of intelligence is the ability to innovate in the face of difficulty. If nuclear winter came, we would not huddle together in a cave and hope for the sun to break through; at least some of us would generate our own heat - if not via electricity, then using wood. If there were no wood, then stores of petrol. If all fossil fuels had been used up, then some humans would most likely find another solution. 'Tis the nature of this beast. If aliens exist, and if some of them have developed a technological civilization, it is because they can innovate. The only thing I can think of which might kill them off is if they literally blow their planet to pieces without having some representatives dwelling in safety elsewhere. It is probably feasible to make the requisite weapons; in principle, the power of the hydrogen bomb is almost unlimited - and of course, who knows what catastrophic devices advanced civilizations might construct? But can you envisage a likely scenario where most alien civilizations are so stupid as to blast themselves into oblivion? I can't. But neither can I logically disprove the suggestion.

• MASS SUICIDE: Again, possible in (bad) theory, but probably unlikely.

• TOTAL ENVIRONMENTAL COLLAPSE: Here, I am tempted to mock the 'Mother Nature will strike back' school of thought (which I have been privileged to come across at first hand). Suffice it to observe that Mother Nature, Gaia (in the sense in which the word is used popularly), and the rest of them don't exist; there are just individual lifeforms and their interactions. Life is too diverse and creative, and intelligence too innovative, for environmental damage of the present type to eliminate food supplies to intelligent beings. We can bet against total environmental collapse unless the atmosphere is completely blown away by weapons of mass destruction. A meteorite or comet would probably not do it, because there would most likely only be a short period before a new civilization (such as our own) realized the threat and installed appropriate safeguards.

• OTHER: I can't think of everything. Perhaps there is some Armageddon which strikes all technological civilizations. This is the Drake Equation, remember - we can't use theory to tell us whether aliens exist; we just don't know enough.

HOW SMART WOULD THEY BE?

The amount of information known to man is expanding rapidly. Although it is arguable that this increase is mainly quantitative, there is no doubt that the accuracy and productiveness of science and technology is also increasing very quickly. The template for this knowledge production is of course the human brain (in conjunction with computers and other tools). Most of our technologies have arisen in the last 10,000 years or so; a disproportionate amount of these in the last couple of hundred. Whilst it is questionable whether we are heading towards some 'omega point' where the manipulation of information gains power with almost infinite speed, the curve of progress is incredibly steep when one considers the length of time it took to produce the human brain.

Imagine a 'graph of cultural progress', and visualise yourself sitting inside the curve (representing knowledge, technological skill, all that) which runs from the bottom left upwards, and towards the right. Assume for a moment - a big assumption - that the curve will continue on its steep upward climb. Imagine that you are able to move up and down, but not backwards and forwards. The date is about 10,000 BC. The curve moves backwards, the lower end disappearing into the past. It presses against you (remember that you can't move backwards with it), forcing you upwards. After 20 years, you switch bodies; reborn as an infant, the process continues; the curve moves backwards, forcing you upwards; the baseline of the graph becomes more and more distant. Stop after 600 reincarnations. Look around you. How far away is the baseline? Around you is Earth in the late twentieth century. Die and be reborn, over and over, and again and again, around 250 million more times (once a second for eight years). At the end of all this, how far away is the baseline? What is around you?

In the last 10,000 years - since cultural takeoff - around 400-500 human generations have passed. If reasonable numbers of ETIs exist, we can probably expect that the earliest alien cultural takeoff occurred at least 250 million human generations ago, if not far more. The reasons for this are as follows (I would appreciate any corrections from people knowledgeable about astrophysics):

The (our?) Universe is estimated to have come into existence 13 billion years ago, give or take three billion. It took hundreds of millions of years for matter to cool down enough to form atoms, of which stars were a byproduct. None of the universe's early stars could have had life as we know it in their environs; our kind of life depends on heavy elements such as carbon, oxygen, nitrogen, phosphorus and sulfur. The heavy elements needed to be formed and blown into space by novae and supernovae, slowly to congeal into new, '2^nd generation' stars with planets. However, second-generation stars would not have formed all that long after the first stars; the very biggest stars have life cycles of 'only' 10 million years or so, after which they blast much of their vast innards - including heavy elements - into space. Let us assume, therefore, that 10 billion years ago was the earliest time at which life could begin to evolve. Let us further assume that nowhere did life evolve more quickly than happened on Earth, but that extraterrestrial life was able to evolve intelligence of our level. 5 billion years ago, therefore, the first alien of human-level intelligence developed. Shortly thereafter, cultural takeoff occurred; the aliens sat inside the curve in the progress graph, and were pressed higher and higher; perhaps until now, 250 million human generations later. To make a very fanciful extrapolation, they would have at least many billion times as much to teach us as we could teach Stone Age man. Fanciful - but perhaps worth considering; we shouldn't always let our predictions be bounded by our imaginations.

What are the objections to the scenario I have constructed? There are several.

The science writer John Horgan believes that there is a 'ceiling' beyond which science - and perhaps technology - cannot develop. What's more, he believes - as outlined in his book 'The End of Science' - that we are already approaching that ceiling. He argues that in science today; the major discoveries - evolution; the electromagnetic spectrum and the fundamental relatedness of major physical forces; geometry; dimensionality; and so on - seem already to have been made; all that remains is the 'structural innovation' - the technology.

I would question Horgan's ideas in three ways. Firstly - as he acknowledges - people have often been mistaken in thinking that they are at the 'pinnacle', the end of history. Secondly, it may be that there are plenty of discoveries which are simply beyond the reach of the human mind. Why the italics? Well, as I argue on my Artificial Intelligence page, human intelligence is likely - given time - to be hugely surpassed by machine intelligence. Accordingly, a vast 'new' arena of scientific discovery may be opened up. Thirdly, as Gerard K. O'Neill notes, people do not often appreciate the time lag between fundamental scientific discovery and the dependent technological innovation (of course, some technological development precedes fundamental scientific research; if we didn't have telescopes, we couldn't formulate realistic theories about how the Universe was formed). For example, James Clerk Maxwell's 19^th-century discovery of the electromagnetic spectrum has had absolutely huge repercussions (i.e. electricity and dependent activities), many of which will be unfolding for untold years to come. Another example is the discovery of the double helix by Crick and Watson in the early '50s; the truly enormous potential of bio-engineering is only beginning to unfold. So even if Horgan is right in saying that we have made all the major scientific discoveries (and it seems a preposterous assumption to me, whatever about whether he's right), technological development (and its concomitants) has a very long way to go.

Another objection is that it is immoral to spend money on SETI. After all, aren't there more pressing problems on Earth? Shouldn't we attempt to cure cancer and end poverty before spending billions searching for aliens who may not exist and who would in any case be too far away to actually meet? Here's a summary of these objections:

 1. SETI is not guaranteed to succeed.
 2. There are also no guarantees that humanity will benefit from contact with ETI.
 3. And it is more than likely that we wouldn't physically meet up with them.

The first two of these statements could be applied to a vast range of human activities, many of which are publicly-funded. Are music classes guaranteed to provide a love of classical music? P.E. classes a love of exercise? Do children always benefit from contact with museums? Why should people like Stephen Hawking be funded for working out how the Universe began and will end - will those activities put food on our tables and keep us healthy? For that matter, why should money be spent on cancer when more lives could be saved more cheaply by providing aid in famine-stricken areas of Africa? Now, some of the above objections to SETI may actually be fair; but if you agree that public funds (and wisely-apportioned private funds) should not be spent on museums, music classes, P.E., Stephen Hawking, or cancer research, then you are a true social revolutionary.

As for the argument that we wouldn't physically meet up with ETIs, that could perfectly well be applied to books or the internet. Those activities don't involve direct contact with intelligent beings. Should we therefore do away with them?

From the point of view of adventurousness and curiosity, contact with ETIs would probably be the most important scientific discovery in Earth's history. SETI could have some economic or social benefits, but there is really no guarantee of that. Perhaps we are selfish; perhaps it is a disgrace that we are spending money on intellectual and sensual fun while people are starving and being tortured in distant lands. But even if we do think this, it is my opinion that there are many activities that should be given the chop before SETI is.

IS SETI DANGEROUS? WHAT WOULD SUCCESS DO TO US?

Should we avoid carrying out a SETI - or deliberately sending messages - because the aliens might come and gobble us up, or use us as slaves? First of all, I think that the conquest of Earth by a more advanced extraterrestrial culture is unlikely. SETI need not involve actually signalling to the ETI; we can perfectly well receive messages without sending any - or more precisely, without intentionally sending any. Unintentionally, of course, all sorts of messages have been streaming out from Earth, at 300,000km/sec, since the invention of radio and television. Now, if they do find out where we are, would they want to conquer Earth? Perhaps; but there are several factors counting against this.

• The distance between our home and theirs is such that if our physicists are right and even ET civilizations cannot travel faster than (or even as fast as) light, it is possible (though by no means certain) that they would not undertake the immense journey to Earth. But maybe our physicists are wrong.

• Earth might be no more hospitable to an alien than Venus is to us - although this is not my intuition.

• The cost and duration of travel might (conceivably) make a trip to this new Eden undesirable.

• Highly advanced cultures might - whether they are humans or machines - not be dependent on an Earth-type environment, even if they were at some time in the past.

• ETIs capable of interstellar travel could surely grow their own meat (if they were organic and meat-eating).

• Machines could do all jobs better than humans.

• RENAISSANCE/DARK AGES: The Renaissance (literally, 'rebirth') began in Italy in the 14^th century. From what little I know of the transition between the eras, there are few people who would argue that we should really have stayed back in the so-called 'Dark Ages'. The intellectual diaspora which sparked the Renaissance infused medieval Europe with learning and culture, increased tolerance, the standard of living and life expectancy, and reduced superstition and subservience. However, it may have encouraged a phenomenon which plagues Western society today: what Durkheim called 'anomie' - the lostness and confusion of those whose life is not mapped out. Although the results of the Renaissance were equivocal in that respect, it seems that by most criteria, the host countries benefited from the knowledge spreading outwards from Renaissance Italy.

• MODERN WEST/THIRD WORLD: It is far more controversial whether the spread of Western capitalism, technology and media have aided the recipients. The results have been very mixed indeed, and I do not feel qualified to make a judgement about whether the overall effect has been beneficial. However, I think there are two things worth bearing in mind: firstly, that although the absolute number of people living in poverty has increased, the proportion has diminished. Secondly, that it would be foolish for anyone to reach a final verdict at this stage - we are only at an interim stage of development.

Even with these examples, the analogy is far from perfect. In both cases, trade relations have been central; with CETI, they would probably not be.

THE PRACTICALITIES OF SETI

'The combinations and frequencies of places to look have hardly been touched'

- Frank Drake.

Traditionally, SETI searches have focused on the so-called 'microwave window', a quiet radio zone. Particular emphasis is put on the hydrogen line, which is widely thought to be the most obvious frequency on which aliens could signal. In 'Is Anyone Out There', Drake makes what could be an important practical point in this regard. The 'Drake-Helou Limit' stipulates that

'no interstellar radio signal, no matter how narrow it is when transmitted, can reach Earth with a bandwidth narrower than a few hundredths of a hertz . . . we have to take both phenomena into account: the universe's quiet zone and the Drake-Helou Limit. When you do that, you arrive at an optimum frequency of about seventy gigahertz. Here is where the most detectable signal can be created using the least power . . . The seventy-gigahertz region is inaccessible to Earth-based observers, literally blocked out by the oxygen in our atmosphere . . . we might have to put an observatory in space - in low Earth orbit, or the far side of the Moon'.

This idea is debatable; but if it applies - and, less likely, if it applies to all ET civilizations - it certainly throws a spanner in the works. All our ground-based observations would be in vain.

It should be borne in mind, however, that there are myriad ideas about where and at what frequencies to look. Dan Wertheimer, a director of SETI projects at Berkeley, remarks that if you pursue all of them, "you end up pretty much doing a sky survey"¹. In today's political climate, which is not favourable to the SETI, 'piggyback searches' are very useful. These searches - for example SERENDIP - hang unobtrusively onto the coattails of unrelated astronomical searches, and analyze the data thereby collected.

For articles on the practical aspects of SETI, click here.

¹ New Scientist, 8 May 1999, pg 16.

SO, SHOULD WE LOOK?

• SETI@home, where you can actually help in the SETI, by downloading a program that analyzes data from radio telescopes. Pretty swell.
• My page on what aliens might be like.
• My assessment of whether Ward & Brownlee's book "Rare Earth" shows SETI and related activities to be a waste of time.

For more SETI links, look at my links page.