e have been on the search for extraterrestrial intelligence (SETI) for a couple of centuries. While there are several possibilities of finding and communicating with extraterrestrial intelligence (ETI), and while we might be able to call each other, we probably won’t actually be able to do lunch. In fact, our phone calls will tend to be one-sided, and last for a very long time.

The modern SETI program began in 1959. Dr. Frank Drake started searching, using the National Radio Astronomy Observatory facility in West Virginia. The first signal he discovered was not from ET but from a terrestrial source. The many human-based radio sources have proven to be a serious problem to observers who are using spectra other than that of visible light. Possibly as a result of this, Drake turned to theory and came up with a well-accepted equation, which, as knowledge of the universe increases, will give us ever-closer estimates of the odds of finding ETI.

In one sense we have been searching for and trying to communicate with ETI from the dawn of history. Our ancestors viewed their environment as being controlled by gods who usually lived in the sky. To communicate with these beings so as to appease and influence them, our forefathers would carry out various rituals. Then, near the start of the scientific revolution, other attempts were made.

Pascal proposed laying out a right large triangle in Siberia with squares on each side that would be visible to the residents of Mars. This picture of the Pythagorean theorem would show that we understood mathematics. Other attempts included the Guzman award in France in 1900, to be given to the first person to communicate with another planet – excluding Mars, for it was claimed that communication would be too easy. Then, in 1959, scientists began a more systematic and rational approach.

This approach requires three essential principles agreed upon by nearly all scientists and philosophers.

The uniformity of nature – natural laws are the same throughout the universe.

The Copernican Principle – the Earth does not have a special place in space or time.

The principle of plenitude – anything that can happen, will happen.

There are also assumptions we make that help us consider the problem of SETI but which, if found to be incorrect, do not affect our basic set of principles. First, we assume the inevitability of life and technology; namely, that life is an inevitable outcome of the chemistry of the universe and that technology is an inevitable outcome of life.

The second assumption is that of temporal mediocrity. This is an extension of the Copernican Principle and means that we are not alive during a special period in the life of the universe; therefore we do not exist because of something special about the universe at this time.

Lastly, we assume that the fundamental laws of the universe as we currently know them will not be superceded by an ETI superscientific technology. We will have to do most of our exploring by data exchange with other civilizations. Interestingly enough, this might lead to a ‘Galactic Internet.’
The first question we need to try and answer is “What is life?” Rocks, minerals and crystals are not alive; mammals, insects, fish are alive. What differentiates the two is the fact that only living things metabolize and reproduce. Metabolism is the process of taking in substances that can be used to generate energy. Reproduction, well, we all know about that. Naturally the universe isn’t that simple. Things like viruses and prions are not well defined in these terms.

Still, there seem to be a number of conditions necessary for life to develop and exist. If we find these conditions elsewhere, we can assume life might also be found. Since, at its most basic level, life is a chemical process, a neutral environment in which chemical reactions can occur is essential. Water offers such an environment. Since the most basic chemicals of life seem to be carbon, hydrogen, nitrogen and oxygen, these elements must be present. There also needs to be energy in some form to drive the necessary chemical processes. Heat in any form will do.

Finally, we need a relatively stable environment or the larger molecules will break down before reaching the level of complexity that might be considered lifelike. On the other hand, too stable an environment means the evolutionary process is thwarted.

As for the definition of intelligence, over the ages humans have changed the definition so as to limit it to humans. Once, intelligence meant toolmakers and users until we observed that various apes make and used tools. Language was a criterion until strong evidence was found that various non-human organisms have languages. For lack of a final agreed-upon definition, we’ll define it here as the ability to change one’s environment as needed; i.e., to be intelligent is to solve problems. As a derivative of this we will add the ability to understand and use the electromagnetic (EM) spectrum. Here on Earth that sure limits intelligence to us humans, finally!

So where do we look for life? We consider three distinct regions. First, the Solar System or those places that we could visit with today’s technology. Next are stars in our local cluster that we could consider visiting but which would take a major investment in resources to reach. Finally, everything else in the Universe; these, of course, we cannot consider visiting with our current understanding of natural law.

Of most interest in our Solar System is Mars. We know that in the distant past Mars supported an environment similar to that found on Earth. Europa, a satellite of Jupiter, seems to have liquid water underneath its surface. Thus, we find the neutral liquid medium.

Until recently we have been able only to look for electromagnetic signals from nearby stars. Our observational capabilities are now reaching the point where it may become possible to see evidence of pollution or other environmental properties on the planets around other stars.
Beyond the local cluster we are limited to only EM communication.

Since the type of ETI we are looking for needs a planetary surface, we must first determine if there are any extrasolar planets. The most successful method depends upon observing the effect of large planets on their star. As the star and a planet as big as Jupiter orbits the center of mass for that star-planetary system the star wobbles. This wobble is detectible on Earth, even if the planet that causes this motion is invisible to us. Although this method will detect only large planets there are probably smaller ones also. Using this observational technique, as of April 2001 we have discovered 67 extrasolar planets.