i. When intuition fails.

When we ask ourselves if we have neighbours in the cosmos, and if it is possible to make contact with them, the first questions we have to answer are what is it and what is ``outer space'' like.

Let's suppose we are in city of Mar del Plata: We know South Africa is across the sea, but we would never think of shouting from the beach and expect someone to answer from the other side, or try to get there swimming. One of the greatest swimming achievements, the crossing of the English Channel, took Matthew Webb almost 22 hours of swimming in 1875. Assuming a swimmer could maintain the same pace all the time, without drinking nor sleeping, crossing the South Atlantic would take about six months (obviously shortly after leaving, he would drink plenty of water -but salty- and plunge into the eternal sleep).

Our notions about the width of the ocean depend on the fact that we have studied it (or not) in school. Throughout history, different cultures have elaborated mistaken ideas on the size of the Earth, which in general barely contained the region they inhabited and knew. In the same way, the primitive models of the universe were very poor. The sky was a mere vault or roof leaving ``outside'' enough room for hell, paradise and other property used by the Gods.

The first accurate notion about the Earth dimension obviously comes from having measured it. The oldest determination from which there is notice was carried out by Eratostenes in the third century BC. In those times, Aristarco explained the rotation of Earth over its axis and its movement around the Sun, made inexact measurements (but not absurd) of the distances to the Moon and Earth and suggested that the Earth orbit occupied a tiny region of space compared to the distance to the stars.

Anyway the model the Church accepted as ``true'' was Ptolomeo's, in which the universe in reduced to a round Earth surrounded by spherical, concentric shells in which the Moon, the Earth, the Sun and the planets move. The stars are situated in the last sphere.

Thanks to the fact that the ancient Greek works had been translated to Arabic because of caliph Harun al Raschid's initiative, the knowledge was not totally lost. About 1450 printing (unknown by Europeans in those days) is reinvented by Guttenberg. When the Turks conquer Byzantium, the original works of the Greek become widespread in Europe, as the scholastics had translated them from Arabic to Latin.

Copernicus takes some of Aristarco's ideas and proposes a system in which ``the centre of the spheres is near the Sun'' and only the Moon orbits around the Earth. Men like Galileo and Kepler abandon the Christian dogmatism and give birth to modern science: Mere philosophy is left out and knowledge is sought through the observation of nature. Since then, astronomers start measuring the real size of the sky: In 1672, Cassini and Richter determine the distance to Mars accurately. The distance to a near star (61 Cygni) is first determined by Bessel only in 1838, but the delay in this calculations is due to the need of high precision measurements and not to the lack of knowledge of anything of importance. Herschell discovers the ``spiral nebulae'' in the eighteenth century. Even if from the beginning it is suspected that these nebulae are in fact galaxies similar to ours, the confirmation of this idea, as well as the discovery of our location inside the Milky Way are matters of recent history.

Today we can say that astronomers know the distances to planets, stars and galaxies with acceptable precision. But we should also recognise that the notions about these matters of those who are not astronomers are often as wrong as they were in medieval times.

Just to try to have an idea of astronomical distances, let's figure we are travelling in an express train. At a constant speed of 70 km per hour we could travel around the world ( if there was such railroad) in about 24 days. Travelling to the Moon would take only some eight months, but reaching Venus, our nearest neighbour planet, would take more than 160 years. A trip to the nearest star would take about 66 million years, much longer than mankind has existed on the Earth.

Obviously we have to think of a faster means of transport. At the speed of a plane, getting to the closest star would take about 5 million years, so it is no good either. Moreover, if we could travel at 400000 km per hour (velocity ten times faster than what a rocket needs to escape the Earth attraction) we would leave the Moon behind in less than an hour and could reach Mars in just ten days. It would take us only two years to reach Pluto's orbit 6800 million km away from the Sun, but from then to the nearest star we would still have 12000 years of travel. The universe is much bigger than we care to realise and it is made basically of empty space.

Anyway, velocity is important only when we are in a hurry. Astronomers study physical phenomena that take place in other galaxies and the chemical composition of the stars without having to travel to them although their light has travelled thousands or millions of years to reach us. In the same way they could study the aliens if they appeared.

ii. When imagination is scarce.

In all times, the man has populated the skies with a multitude of beings. Even when the universe was just a mere recipient containing the Earth, and the Sun existed only to illuminate and heat people, it was supposed that all that shed had been created by a god, with the help of countless angels, demons seraphs, etc. Of course this multitude of beings is not a sole property of Christianity, it appears all over the wide spectre of religious beliefs.

When renaissance arrived, superstitions started to give way to scientific thought and the man began to know the world he lived in. However, the idea of a universe densely populated was accepted from the beginning as something natural, which is no surprise in a times where they could believe frogs were made of mud.

Astronomers have discovered that the laws of nature are universal. The same physical laws that are valid on the Earth are also verified on the Moon, the other planets, the stars and the most remote galaxies. The process of life started on the Earth when a molecule capable of making copies of itself was formed. Even if up to now we have not found life in any other place of the universe, it does not seem impossible that the same process can occur in another place if conditions are favourable. The long evolution process has generated through time, a countless number of species of the most diverse sizes and shapes. In spite of the obvious differences between a man and a carrot, both are extremely related organisms, as they share a common ancestor (though of course, it is a very distant one). That is why the discovery of extraterrestrial life (even if it was the simplest bacteria) would be of transcendental importance for biology: all the forms of life studied to the present have the same origin (including the man and the carrot).

At this point the reader will easily perceive the difference between the aliens of fiction and those about whose existence we can speculate in a more or less coherent way. The first flying saucers and Martians first appeared on the cinema, and shortly after, began to be spotted on the skies. Its no surprise that movie aliens have human characteristics, as it would be difficult to write a plot about cockroach shaped aliens that communicate among themselves through smell, and lacked ``intelligence''. But what it is indeed alarming, is the lack of imagination of fantastic realism advocates.: although there is a wide variety of aliens (of different colours and shapes, some with little antennas, different number of fingers, etc.) almost all have humanoid characteristics. While on Earth there is a huge diversity of animals and vegetables, some of the strangest and most unusual forms (in spite of all sharing a common predecessor) it is incredible that the aliens, that should be different from everything we know because of their different origin, not only they look alike among them, they also resemble so much one of the terrestrial animals, by chance the Homo Sapiens!

The existence of aliens that look like us is easy to justify from a religious point of view. If we believe that God created man at his image and resemblance and accept that could also have created the alien to his image , then the similarity between the man and the alien is not a prove of the lack of imagination of the former, but a manifestation of divine power. But then if the extraterrestrial beings are divine manifestations, it appears to be more adequate to keep on calling them angels, goblins, demons and seraphs.

iii. On galactic empires.

Giordano Bruno sustained that the universe was infinite and reasoned that, as in our region there is a Sun surrounded by planets, the same would happen in other regions (naturally Christians burnt him alive for being heretic). In other words, Giordano Bruno's basic idea was that we did not occupy any honorific place in the universe, that the Earth was just another planet among many and that the Sun was just one more among countless suns. Astronomers have discovered that nature laws are universal: The same laws verified on Earth are valid on the Moon, the planets, the stars and the most faraway galaxies. As we are here, why should not all the confines of the universe be inhabited...?

It is tricky to say ``all the confines of the universe''. If we reduce the Earth with all its countries, oceans, deserts and gigantic mountains to the size of an orange, then the Moon would be a small nut orbiting some four metres away. The sun would be a big globe the size of a five-storey building and it would be one and a half kilometres from the orange. Planet Pluto and its satellite Caronte would be two grapes 70 km away. Apart from `` the sun'', in all this space we would only find the eight biggest planets with its satellites and other minor bodies like asteroids, comets, etc. The biggest of planets, Jupiter, would be a huge one and a half metre ball, orbiting at 8 km from ``Sun''. A real waste of space.

Although some planets seem to have adequate conditions for life, until now we have not found anything alive in what we have visited. In our scale model, to find the next ``sun'' (another building-size ball) We would have to travel more than 400000 km (more than the real distance to the Moon!) and would probably find that there is no appropriate orange there! It is clear than that it is a great mistake to assume that ``in every place of the universe happens the same as in ours''. In almost every place there is absolutely nothing, except for empty space.

The other deceit is to say ``as we are here''... The universe has some 15000 million years of existence and the Earth about 4700 millons. The first recognisable humans appeared about a million years ago. Thanks to the great radio telescopes we can try to communicate with hypothetical cosmic radio listeners since a little more than thirty years ago. If we compare the universe with a one hundred year-old man, we have learned to speak just six seconds before we turned one hundred. Beyond the distance problems, after one hundred years of silence, we expect to communicate with another old man who also had to learn to speak (and listen) in the same six seconds we did...! The whole history of mankind is an ephemeral instant compared with the age of the universe, so we should not be so pretentious as to demand that just in our times, an alien who wants to chat shows up.

Although our existence on the Earth is recent, life has existed almost since the planet was formed. (although during most of this time, there were just bacteria and primitive algae). This means that even if the existence of ``intelligent civilisations'' is unlikely, the proliferation of primitive ways of life must be relatively common. Will we ever be able to leave the solar system and travel to the stars...?

With the present means we could make a sounding that reached the closest star in just 15000 years, and the centre of the galaxy in some one hundred millons years. A civilisation that dominated interstellar travelling, could occupy the whole galaxy in a few million years, without the need to travel at science fiction velocities. From the mankind point of view, these periods of time are too long: 15000 years ago, troglodytes were painting cavern walls and one hundred million years ago, the planet was populated by dinosaurs. But there are fossils of fairly complex bacteria that date from 3500 million years ago, compared to which one hundred million years less or more are not much of a thing. Going back to the comparison with the one hundred year old man, the needed time to occupy the whole galaxy would be, in comparison, less than an month. In other words, if there was an extraterrestrial civilisation that dominated interstellar travelling, they would have already occupied the galaxy. It seems unlikely that two oldies, after sitting down for one hundred years, decide to go for a ride exactly in the same month.

In the above paragraphs, I have considered the possibility of communication with extraterrestrial intelligence or that a civilisation expands over the galaxy. Is not it possible that the aliens make ``exploring travels'' and then return to their world...? In this case time is the critical factor: some million years are nothing compared to the age of the universe but they are a significant amount of time compared to the times through which species evolve.

When living cells reproduce, from time to time some``copy errors'' take place. The competition between these copy errors, that tend to destroy the genetic information of the species, and the natural selection that permit that only the variations adapted to the environment proliferate, cause the evolution and diversification of species. It is possible to reduce the copy errors by having more than one copy of the genetic information. In fact in terrestrial biology the genetic information is quite redundant. But if they were even more redundant (and the copy errors less likely) evolution would be impossible. There must be copy errors in order to permit the existence of an intelligent species. A living species that would spread over the galaxy would be diversified in many different species, in the same way ant species that live in South America are different from their African counterparts. This is why the ``exploring travels'' are not possible, as when returning home, the explorers would find that ``their'' world is inhabited by other species.

iv. Why do tall tale tellers proliferate?

As we have seen in the introduction, belief in extraterrestrial beings has deeply religious fundamentals.

Consequently, it is natural that these ideas proliferate when there is freedom of belief. The idea of someone controlling what one must believe ( or do not believe) is terrifying, but in order to permit that real freedom of thought exists, it should be guaranteed an education good enough to enable us to think critically.

Many of the beliefs (involving UFO's or not) end up in massive suicides (to get on the hypothetical flying saucer that came hidden behind comet Hale-Bopp) or to hide criminal activities. And UFO issues are unquestionably harmless if compared for example, with the deaths provoked by alternative medicines.

Obviously in a market economy, such a wide clientele of believers cannot be left unnoticed. Any writing on flying saucers, Bermuda Triangle or astrology sells much more than a science text written for the public in general. This is no surprise, as one who writes science popularization articles has to face some problems: He has to solve the difficulty of making a complicated matter understandable for an as heterogeneous a public as possible, he must make his work interesting and entertaining, and he will probably find it hard to make his works known, as those who have the power do not like people who ``brighten the fools''. To write a book on flying saucers no previous training is necessary and the only requirement is that the story is fantastic enough to catch the reader's imagination. And there is no risk of making anyone angry.

There is a chink for the search of ``real'' aliens. There is the exploring missions, like the vehicles that touched down on Mars and analysed ground samples in search of any living thing. Even if nothing has been found so far, these investigations have the advantage of not requiring the existence of an advanced alien civilisation which has tried to communicate with us in the exact moment so that their message arrives just when we can receive it. They are oriented at detecting any form of life, even the most primitive one. The disadvantage is that we can only investigate the worlds we have within our reach, that is to say (up to now) the solar system. From the economic point of view this missions represent a considerable investment, but they reflect in the development of new technologies and new job openings, as it is necessary to design and build new spatial artefacts. The other approach to searching for real aliens are projects like SETI (search for extraterrestrial intelligence) that try to capture radio emissions from hypothetical technologically advanced civilisations. The problem these programs have is that they use the same sources as the other astronomers. To use a telescope, a scientist must present a plan indicating the subjects he plans to investigate and a summary of the previous results. Only the best projects get a green light. It is clear that when funds for alien intelligence search projects are destined, those responsible are not asked ``how many extraterrestrial civilisations you discovered last year''. This is why the search for extraterrestrial intelligence evolves in a narrow edge between real science and tall tales.

Translation by Gerardo A. Ostrov - gerarost@yahoo.com