Observatoire de Paris
<-   Conclusion  

Of course, all we have said above concerns life and intelligence in OUR galaxy. Since we can observe billions (!) of galaxies in the sky (see for instance the recent images of the Hubble Space Telescope or the ESO telescopes in Chile, which reveal between 2000 and 3000 galaxies in small sky parts of 10'×10', i.e. 40 billion galaxies in the entire sky), this increases the probability for the existence of extraterrestrial life (and extragalactic). However, this factor 1010 is maybe not sufficient to obtain Nciv > 1 if Pvie and Pint are very small. In this case we would be alone in the universe.

If we are alone in our galaxy, but not in the universe, this would only make sense if physics evolves to such an extent that we could overtake the current limits given by relativity (nothing can propagate faster than light).

In both cases (alone in the universe or in the Galaxy), we can wonder about the sense of our existence, and about our "responsibility".

The science-fiction (and scientific) writer I. Asimov gave a nice interpretation of his view about the evolution of humanity in the Galaxy (Foundation Cycle).


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  • INTELLIGENCES EXTRATERRESTRES, Jean Heidmann, Opus Sciences, Odile Jacob, 1996.
  • LA BIOASTRONOMIE, François Raulin, Florence Raulin-Cerceau & Jean Schneider, Que Sais-Je ?, Presses universitaires de France, 1997.
  • ARE WE ALONE ?, Paul Davies, Penguin Science, 1995.
  • EXTRATERRESTRIALS, édité par Edward Regis Jr., Cambridge University Press, 1985.