On the 1st of August 2000 the Search for Extra-Terrestrial Intelligence (SETI) Institute in the U.S.A. issued an important press release. A new radio telescope would be built in California to detect faint radio signals that may originate from other intelligent life in our Galaxy. Numerous small telescopes covering about 1 hectare will comprise the new alien eavesdropper. Paul Allen (co-founder of Microsoft) is the major benefactor, contributing US$11.5 million to the Allen Telescope Array ( ATA, as it will be known), which should be complete in 2005.

As an astrophysicist that spends too much time wondering about future avenues of research funding I was strangely delighted and sceptical at the same time upon reading this news. Yes, I believe that such a project is worthy of support.

Worthy in the sense that many scientific endeavours are not done because they are easy, but because we, as humans, have an insatiable thirst for knowledge and exploration. Sceptical because I tend to believe that the chance of success, that is, the ATA detecting an alien transmission, are remote. Let me explain.

Increasingly since Percival Lowell in the late 1800s described "canals" on Mars (presumably built by intelligent Martians) we have been bombarded with many suggestions that we are not alone in the cosmos. From "War of the Worlds" to innumerable UFO sightings and more recently films such as Close Encounters of the Third Kind, E.T. and Contact, the projected "hope" is that we are not isolated in our Galaxy, or indeed the Universe. Yet, that may indeed be the case, and that such hopes are just human wishes for cosmic companionship.

A simple yet powerful argument for the non- existence of other intelligent life (at least in our Galaxy) was put forward by Enrico Fermi (1901-1954). The Nobel Prize winning physicist pondered "If they exist, why aren't they here?"

The Fermi Paradox, as it has come to be known, can be simply understood. Humans, as an example of intelligent life, have very quickly invented and utilised technologies that enable us to send radio communications over vast distances. It is not beyond belief that within a few centuries humans will also have the capability to (robotically) explore our Galaxy. It is commonly agreed that this exploration of the whole Galaxy could be completed in as little as 5 million years.

Fermi's Paradox kicks in when we look at how much time has preceeded us. Our Galaxy is around 13-15 billion (where 1 billion is 1,000 million) years old, and the age of our Earth, is about 4.5 billion years. Hence there are many sets of five million years in those preceeding years. If we are typical of intelligent life, and such life wants to or needs to explore their surrounds, then there has been ample time for them to evolve and fully explore our Galaxy, and hence arrive at Earth. There is no evidence of this. So, Fermi would say no E.T.s exist.

So why am I also happy to hear about the announcement of construction of the ATA? That's easy. Astronomy seems to frequently reveal things about our Universe that are not expected or even predicted. Eighty years ago we thought that our Galaxy was the universe. We now believe that the universe has at least 150 billion galaxies. Fifty years ago the Steady State Theory, in which matter was continuously created, was the preferred cosmological description. These days the Big Bang model of a hot, condensed, creation start to our universe is now widely supported by observations.

The fact that we have not been visited by aliens or their robots, (apologies to T.V. viewers of "Roswell" programme and alien abduction supporters), may in fact tell us more about the survival probability of intelligent life forms, and their desire to explore rather than their frequency in our Galaxy. In that sense, the Fermi Paradox may be too simplistic.

The uncertainty in predicting the frequency of other intelligent life forms in our Galaxy however may strengthen the case for looking, or rather in this case, listening. Frank Drake, a radio astronomer who initiated the first SETI programme some 40 years ago developed an equation that attempts to predict the number (N) of intelligent life forms or "observable civilisations" in our Galaxy. The Drake equation as it is now known has seven multiplicative factors, the first being the star formation rate in our Galaxy (R), the last factor, the average lifetime of a communicating civilization (L).

The Drake Equation

In between these two factors the Drake equation comprises the fraction of stars having solar systems, the average number of "Earthlike" planets (suitable for life) in a typical solar system, the fraction of those planets on which life forms, the fraction of life-bearing planets where an intelligent species evolves, and the fraction of intelligent species that become capable of interstellar radio communication. As you can see each factor is related to its predecessor thus highlighting the special "cosmic" requirements or fine tuning of physics, biology, geology and chemistry needed for our existence.

Since the estimates for each of the seven factors can vary widely, it is quite easy for E.T. proponents (including Drake) to formulate a large number of observable civilisations. Conversely, for the sceptics it is equally easy to calculate a very small, statistically insignificant number. The fact is, we just don't know with accuracy many of the seven factors.

Recent planet searches, though presently biased against detecting Earth-like and lower mass planets, would suggest that our habitable solar system is rather unique. How typical is our industrial and technological progress? What is the longevity of our new technology world? Of course the one thing that a comprehensive SETI search (coupled with new astronomy research) can do is refine and improve the Drake equation!

One wonders what we may hear from an alien transmission? Our first human radio transmissions are most certainly not what we would want as cosmic greetings! As well, whilst we are soon to enter a new phase of listening with the ATA, if we are serious about cosmic communication shouldn't we be investing the same amount of money (and thought) in a radio message to the cosmos? Take note IBM, Intel, Sun Microsystems and dot.coms for whilst Microsoft helps us to listen for E.T. your companies could be funding the ultimate cosmic advertisement.

Glen Mackie is Lecturer and Assistant Coordinator Swinburne Astronomy Online (SAO) in the Centre for Astrophysics and Supercomputing, Swinburne University of Technology.

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Last updated December 13, 2000