“The true way to see things as they are, is to stand between the moon and the earth, to be purely a spectator of this world, and not an inhabitant.” This extract from Conversations on the Plurality of Worlds (first published in French in 1686) neatly sums up the difference between current understandings and those of the Moderns. In his book, Fontenelle presents hypotheses about the inhabitation of the celestial bodies of our solar system to an enraptured Marquise. If we doubt, for example, that the moon could be inhabited, this is because it seems to us to shine while, from the point of view of those living on Earth, the Earth does not. However, if we looked at the Earth from a distance, as a simple “spectator,” we would notice that it also reflected the sun’s light. The prerequisite for imagining other worlds, and therefore other forms of social organization, is to take ourselves out of our natural habitat. For Fontenelle, the hedonistic logic of “why not?”—Why shouldn’t there be other modes of living and enjoyment being practiced on far-off planets? Why should we be bound to this earth with its ancestral superstitions and hierarchies?—finds scientific backing in the Galilean revolution. Newly aware that it lived on one celestial body among many, humanity gained the ability to dream of other ways of existing thanks to the telescope.Today, we are far from considering living on Earth as an obstacle to our emancipation. Instead, it has become a condition of our survival. Heliocentrism has lost its utopian power now that, faced with the threats linked to climate change and the overexploitation of the planet, we need to think in a more “down to earth” way, rather than once again pinning our hopes on technology…