— Giordano Bruno Italian philosopher, mathematician and astronomer 1548 - 1600
Context: There are countless suns and countless earths all rotating round their suns in exactly the same way as the seven planets of our system. We see only the suns because they are the largest bodies and are luminous, but their planets remain invisible to us because they are smaller and non-luminous. The countless worlds in the universe are no worse and no less inhabited than our earth. For it is utterly unreasonable to suppose that those teeming worlds which are as magnificent as our own, perhaps more so, and which enjoy the fructifying rays of a sun just as we do, should be uninhabited and should not bear similar or even more perfect inhabitants than our earth. The unnumbered worlds in the universe are all similar in form and rank and subject to the same forces and the same laws. Impart to us the knowledge of the universality of terrestrial laws throughout all worlds and of the similarity of all substances in the cosmos! Destroy the theories that the earth is the center of the universe! Crush the supernatural powers said to animate the world, along with the so-called crystalline spheres! Open the door through which we can look out into the limitless, unified firmament composed of similar elements and show us that the other worlds float in an ethereal ocean like our own! Make it plain to us that the motions of all the worlds proceed from inner forces and teach us in the light of such attitudes to go forward with surer tread in the investigation and discovery of nature! Take comfort, the time will come when all men will see as I do.
As quoted in The Discovery of Nature (1965), by Albert W. Bettex