Observatoire de Paris
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The Arecibo telescope
Copyright : NAIC / NSF

Must we wait to solve Drake's equation before searching actively for the existence of extraterrestrial life ? Based on the fact that "the movement comes walking", the creators of the SETI ("Search for Extra-Terrestrial Intelligence") project think differently, and think that we must keep on searching for life, even if we are not sure that there is something to discover.

The SETI project is based on the universality of physical laws (confirmed by astronomical observations), and on the fact that if the various probabilities Pxxx in Drake's equation are about 1, then Nciv is of order T and therefore possibly very high.

This project is based on the following hypotheses :

  • life, intelligence, and technology are a general trend of evolution, and are therefore common in our galaxy (and in the universe)
  • the time span for the appearance of intelligent life on a favourable planet is much less than the age of the Galaxy ("temporal mediocrity", in contrast to the "anthropic" principle)
  • there is no Super-science (hyperspatial flight...), i.e. the speed of light is a limit for spatial flight
  • intelligent creatures would explore the Galaxy in the form of a peaceful search for information exchange by way of telecommunications
  • there exists a "galactic club", benevolent, welcoming, and ready to help new members with an emergent technology

The detection method initially chosen is radio waves. Radio waves are electronically neutral (with a straight propagation independent from the galactic electric and magnetic fields), stable with time (contrary to radioactivity), very penetrating in space (contrary to the behavior of light with dust), easy to produce and to detect (contrary to neutrinos or gravitational waves). We can therefore suppose (but it's a bet!) that radio waves are the mode of communication chosen by extraterrestrials.

We first wanted to know which radio frequency we should try to detect. Now, the use of sophisticated radio receivers, combined with a huge number of computers (with the SETI@Home program), allow us to keep watch over millions of frequencies at the same time. We search for particular signals (narrow bands for example) which could be interpreted as artificial signals. Then we have to decode them...

The usefulness of SETI has always been controversial among scientists. After about twenty years of research (without success, but it is a really hard project), the American Congress decided to stop any help for this project. Therefore, the scientists involved in SETI turned to private financing. Now, they manage to gather the annual 10 million dollars necessary to carry on their research.

The current research is on radio observations, with large networks of radio aerials (such as the Allen network of telescopes), and optical observations. Optical research assumes that one directly sends us short laser impulses, whereas with radio waves, it is not necessary that they be sent directly towards us. However, sending targeted signals requires less energy, so this could be the solution chosen by extraterrestrials.

The detection of an extraterrestrial signal would have tremendous implications for humanity. In addition to the reactions described in the movie "Contact", we could reject most of the arguments against extraterrestrial life given in the previous section, and have a better idea of the probablility values of Drake's equation  !