“When I was studying under the distinguished Michael Maestlin at Tubingen six year ago, seeing the many inconveniences of the commonly accepted theory of the universe, I became delighted with Copernicus, whom Maestlin often mentioned in his lectures, that I often defended his opinions in the students’ debates about physics. I have by degrees – partly out of hearing Maestlin, partly by myself – collected all the advantages that Copernicus has over Ptolemy.”

A segment (Ѻ) of the reaction path of Kepler.

“Many years ago, I accepted Copernicus’ theory, and from that point of view I discovered the reasons for numerous natural phenomena which unquestionably cannot be explained by the conventional cosmology. I have written down many arguments as well as refutations of objections. These, however, I have not dared to publish up to now. For I am thoroughly frightened by what happened to our master, Copernicus. Although he won immortal fame among some persons, nevertheless among countless – for so large is the number of fools – he became a target of ridicule and derision. I would of course have the courage to make my thoughts public, if there were more people like you. But since there aren’t, I shall avoid this kind of activity.”

“The search for cause and effect, the striving to reduce everything to law and order, the explanation of the universe in terms of machine—all this Pavlov carried over from Kelvin, Maxwell and Helmholtz. But in physics, causality, machines, law and order have disappeared. Schrodinger even regards them as infantile concepts—as infantile as Kepler’s hypothesis that angels push the planets around the sun.”

— Anon (1936), New York Times editorial [1]

“Our sixteenth-century Fernel viewed the body as a tenement for faculties. One faculty was that which actuated the various bodily movements. Then came Descartes with is robot [see: Cartesian automata], a mechanism actuating itself. Such too had been Descartes’ thought with respect to the motions of the macrocosm. For Kepler still, a century later than Fernel, though each planet was ridden by an angel. Then later with the ‘reign of law’ that guidance became a ‘force’, e.g. gravitational. Today that ‘force’ has in turn disappeared. There remains a curvature of space. The human mind looking at nature has had to dehumanize its point of view—it has, using Samuel Alexander’s word, to ‘deanthropize' itself. It has to dispense with ‘causation’, which is regarded as an anthropism, but is yet a final cause. It is more faithful to William of Occam.”

— Charles Sherrington (1938), Man on His Nature [2]

“What makes planets go around the sun? At the time of Kepler some people were saying that there were angles behind them beating their wings and pushing the planets around in orbit. As you will see, the answer is not very far from the truth. The only direction is that the angles sit in a different direction and their wings push inwards.”

— Richard Feynman (1965), The Character of a Physical Law [3]

Left: the sun conceptualized, in Egyptian theology, as disc, or sun god Ra (3100 BC), being carried through the sky by a bird; later described as the phoenix by Herodotus. Right: a medieval (500-1600 AD) conception of “angles”, the Christian reconceptualization of the bird-conceptualized deities of the Egyptian Ogdoad/Ennead creation myth pantheon pushing planets or what seems to be angels moving the planets by crank arm mechanism. [5]

“When Kepler began to wonder why the planets move as they do, for a while he entertained the then-popular notion that planets were pushed by angels. After all, planetary motion had been found to be quite lawful and regular, yet there was no obvious agent to give them a push, as Aristotelian physics required. But Kepler did not leave it there, he wanted to know more about ‘how’ the process worked, and after considering and discarding many hypotheses over many years (some of them fantastical and mystical), he finally stripped away the supernatural notions and worked out his three purely mathematical laws of planetary motion.”

— Donald Simanek (2006), “Why Not Angels?” [5]

“Give me a fruitful error any time, full of seeds, bursting with its own corrections. You can keep your sterile truths for yourself.”

— Vilfredo Pareto (c.1810), comment on Kepler [6]

“Einstein is a genius in higher physics and ranks with Copernicus, Newton and Kepler.”

— William du Bois (1932) (Ѻ)

“The chief aim of all investigations of the external world should be to discover the rational order which has been imposed on it by god, and which he revealed to us in the language of mathematics.”

— Johannes Kepler (c.1620) (Ѻ)

“If a person be too dull-witted to comprehend his knowledge or to enfeebled by his wounded piety to believe Copernicus, I encourage him to dismiss the school of astronomers and, if he wishes, even those among the condemned philosophers he favors, and pursue his own interest and cease his earthly wanderings.”

— Johannes Kepler (1635), Perioche ex Introductione in Martem; cited by Otto Guericke (1672) in New Magdeburg Experiments on the Vacuum of Space (pg. 24)

“And I cherish more than anything else the ‘analogies’, my most trustworthy masters. They know all the secrets of nature, and they ought to be least neglected in geometry.”

— Johannes Kepler (c.1620) (Ѻ)