Pluralità dei mondi, vita, cosmo. Il sogno di Giordano Bruno

In La Cena delle Ceneri Giordano Bruno wrote that “the moon is no more a heaven for us than we are a heaven for the moon”, anticipating, in some ways, what would later be called the principle of mediocrity or the Copernican principle: we are not privileged observers and the Earth is by no means a special place in the cosmos. For a long time this insight, supported by the belief that life is a widespread phenomenon in the Universe, drove speculation and thus the search for intelligent life forms on other celestial bodies. However, the first images of the Martian soil already gave a bleak picture, and the same happened a few years later with Venus, only in appearance similar to Earth, in fact a burning hell surrounded by an atmosphere of carbon dioxide. The belief that we are not in a privileged position, on a special planet, has given way to new interpretative hypotheses, on the basis of which life, a fortiori intelligent life, would be a rarer phenomenon than we might have expected. Recent advances in the field of astrobiology have made it possible to detect more than 5,000 exoplanets in our galaxy, and this undoubtedly opens up new exploration pathways for the search of extra-terrestrial life as well. Many questions arise: will we be able to recognise extraterrestrial life forms once we have them in front of us, or will they be so different as to be unrecognisable? Should such a discovery occur, will we have any direct duties towards alien ecosystems and exobiospheres? Who will decide what principles should guide future interactions and what criteria should be adopted? If, on the other hand, such contact never occurs, would our cosmic importance be magnified? Would our duties toward our common home be strengthened? And again: do we have a duty to protect our planet exclusively, or should the possibility of abandoning it to colonise new celestial bodies not be excluded?