# Alex Peek blog

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Wednesday, August 15, 2018

## Johannes Kepler and the mathematical universe

Photo source: Wikimedia Commons

Johannes Kepler (1571-1630) was a German astronomer and mathematician best known for discovering that planets orbit the sun in an ellipse. Mathematician Eric Temple Bell said,

"Kepler's laws were the climax of thousands of years of an empirical geometry of the heavens... Only Kepler's Pythagorean faith in a discoverable mathematical harmony in nature sustained him." (The Development of Mathematics, 1940)

Historian Herbert Butterfield said,

"Kepler in the first thirty years of the seventeenth century 'reduced to order the chaos of data' left by Tycho Brahe, and added to them just the thing that was needed - mathematical genius." (The Origins of Modern Science, 1949)

The rest of this post is some quotes from Kepler.

### Astronomy

"With reasoning derived from physical principles, agreeing with experience, there is no figure left for the orbit of the planet but a perfect ellipse." (Astronmia Nova, 1609)

"I certainly know that I owe it [the Copernican theory] this duty, that as I have attested it as true in my deepest soul..." (Quoted in Joannis Kepleri Astronomi Opera Omnia by Christian Frisch)

"Gravity is a mutual affection between cognate bodies towards union or conjunction..." (Astronmia Nova, 1609)

"There is a force in the Earth which causes the moon to move." (Essay Dedicated to Archduke Ferdinand)

### Philosophy of mathematics

"Since geometry is co-eternal with the divine mind before the birth of things, god himself served as his own model in creating the world..." (Hamonices Mundi, 1618)

"Geometry is one and eternal shining in the mind of God. That share in it accorded to humans is one of the reasons that humanity is the image of God." (Hamonices Mundi, 1618)

"...nothing can be known completely except quantities or by quantities. An so it happens that the conclusions of mathematics are certain and indubitable." (Quoted in Joannis Kepleri Astronomi Opera Omnia by Christian Frisch)