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Cosmological claims

In 1584, Bruno published two important philosophical dialogues (La Cena de le Ceneri and De l'infinito universo et mondi) in which he argued against the planetary spheres (Christoph Rothmann did the same in 1586 as did Tycho Brahe in 1587) and affirmed the Copernican principle.

In particular, to support the Copernican view and oppose the objection according to which the motion of the Earth would be perceived by means of the motion of winds, clouds etc., in La Cena de le Ceneri Bruno anticipates some of the arguments of Galilei on the relativity principle. Note that he also uses the example now known as Galileo's ship.

Theophilus – air through which the clouds and winds move are parts of the Earth, to mean under the name of Earth the whole machinery and the entire animated part, which consists of dissimilar parts; so that the rivers, the rocks, the seas, the whole vaporous and turbulent air, which is enclosed within the highest mountains, should belong to the Earth as its members, just as the air in the lungs and in other cavities of animals by which they breathe, widen their arteries, and other similar effects necessary for life are performed. The clouds, too, move through accidents in the body of the Earth and are in its bowels as are the waters. With the Earth move all things that are on the Earth. If, therefore, from a point outside the Earth something were thrown upon the Earth, it would lose, because of the latter's motion, its straightness as would be seen on the ship moving along a river, if someone on point C of the riverbank were to throw a stone along a straight line, and would see the stone miss its target by the amount of the velocity of the ship's motion. But if someone were placed high on the mast of that ship, move as it may however fast, he would not miss his target at all, so that the stone or some other heavy thing thrown downward would not come along a straight line from the point E which is at the top of the mast, or cage, to the point D which is at the bottom of the mast, or at some point in the bowels and body of the ship. Thus, if from the point D to the point E someone who is inside the ship would throw a stone straight up, it would return to the bottom along the same line however far the ship moved, provided it was not subject to any pitch and roll."

Bruno's infinite universe was filled with a substance—a "pure air", aether, or spiritus —that offered no resistance to the heavenly bodies which, in Bruno's view, rather than being fixed, moved under their own impetus (momentum). Most dramatically, he completely abandoned the idea of a hierarchical universe.

The universe is then one, infinite, immobile... It is not capable of comprehension and therefore is endless and limitless, and to that extent infinite and indeterminable, and consequently immobile.

Bruno's cosmology distinguishes between "suns" which produce their own light and heat, and have other bodies moving around them; and "earths" which move around suns and receive light and heat from them. Bruno suggested that some, if not all, of the objects classically known as fixed stars are in fact suns. According to astrophysicist Steven Soter, he was the first person to grasp that "stars are other suns with their own planets."

Bruno wrote that other worlds "have no less virtue nor a nature different from that of our Earth" and, like Earth, "contain animals and inhabitants".

During the late 16th century, and throughout the 17th century, Bruno's ideas were held up for ridicule, debate, or inspiration. Margaret Cavendish, for example, wrote an entire series of poems against "atoms" and "infinite worlds" in Poems and Fancies in 1664. Bruno's true, if partial, vindication would have to wait for the implications and impact of Newtonian cosmology.

Bruno's overall contribution to the birth of modern science is still controversial. Some scholars follow Frances Yates in stressing the importance of Bruno's ideas about the universe being infinite and lacking geocentric structure as a crucial crossing point between the old and the new. Others see in Bruno's idea of multiple worlds instantiating the infinite possibilities of a pristine, indivisible One, a forerunner of Everett 's many-worlds interpretation of quantum mechanics.

While many academics note Bruno's theological position as pantheism, several have described it as pandeism, and some also as panentheism. Physicist and philosopher Max Bernhard Weinstein in his Welt- und Lebensanschauungen, Hervorgegangen aus Religion, Philosophie und Naturerkenntnis ("World and Life Views, Emerging From Religion, Philosophy and Nature"), wrote that the theological model of pandeism was strongly expressed in the teachings of Bruno, especially with respect to the vision of a deity for which "the concept of God is not separated from that of the universe." However, Otto Kern takes exception to what he considers Weinstein's overbroad assertions that Bruno, as well as other historical philosophers such as John Scotus Eriugena, Nicholas of Cusa, Mendelssohn, and Lessing, were pandeists or leaned towards pandeism. Discover editor Corey S. Powell also described Bruno's cosmology as pandeistic, writing that it was "a tool for advancing an animist or Pandeist theology", and this assessment of Bruno as a pandeist was agreed with by science writer Michael Newton Keas, and The Daily Beast writer David Sessions.