Introduction to Humanities Lecture 12 The Early Modern World By David Kelsey

The Copernican Revolution The Copernican Revolution: –Begun by Copernicus ( ). Published De Revolutionibus just before his death in –Prior to Copernicus, the theory presented by Claudius Ptolemy (AD ) in Almagest was dominant. Ptolemy’s theory: –Geocentric theory, which identified the Earth as the center of the universe. –The Moon, Sun and stars move around the Earth in more or less fixed spheres. –Around the spheres, at the edge of the universe, lay the crystalline sphere, beyond which was the realm of God. –Medieval scientists noticed exceptions to the Ptolemaic universe: 70 spheres and movements in epicycles…

The Ptolemaic Universe Pictures of the Ptolemaic universe:

Copernicus Copernicus continued: –As early as 1514 he outlined his heliocentric theory in the Commentariolus. –Copernicus takes a mathematical approach to interpreting the movements in the heavens. –From Copernicus we get the displacement of the Earth from the center of the universe. –He observed the retrograde motion of the planets; theorized it is caused by the motion of the observers on an earth that is not itself stationary. –Following his death his theory was widely controversial…

Copernicus theory continued Copernicus’ theory continued: Note his use of the spheres still… –1. There is no one center of all the celestial circles or spheres. –2. The center of the earth is not the center of the universe… –3. The sun is the center of the universe. –4. The distance from the earth to the sun is imperceptible in comparison with the height of the firmament. –5. Whatever motion appears in the firmament arises not from any motion of the firmament, but from the earth's motion. The earth performs a complete rotation on its fixed poles in a daily motion… –6. We revolve about the sun like any other planet. The earth has, then, more than one motion. –7. The apparent retrograde and direct motion of the planets arises not from their motion but from the earth's…

Kepler Johannes Kepler – –Makes advancements on Copernicus’ views –Used data by the great observer of the heavens Tycho Brahe. Mars… –Gives a mathematical account of the heavens that is sun centered and which matches observed data. –Published Astronomia nova in 1609, in which he asserts his first 2 laws of planetary motion…

Kepler’s first law Kepler’s first law: –1. The path of the planets is an ellipse, with the sun at one of the 2 foci that define it. Ellipses have 2 foci neither of which is it’s center. The planetary orbits have the sun at one foci. Note that how stretched out an ellipse is from a perfect circle is its eccentricty. This parameter varies from 0 (a circle) to 1 (a straight line). The eccentricities of the planets varies from.007 (Venus) to.2 (Mercury)

Kepler’s 2nd law of motion Kepler’s 2nd law of motion: –2. The areas swept out by a line from the sun to the planet are always equal in equal intervals of time. –“To understand the second law let us suppose a planet takes one day to travel from point A to point B. The lines from the Sun to points A and B, together with the planet orbit, will define an (roughly triangular) area. This same area will be covered every day regardless of where in its orbit the planet is. Now as the first law states that the planet follows an ellipse, the planet is at different distances from the Sun at different parts in its orbit. So the planet has to move faster when it is closer to the Sun so that it sweeps an equal area.”

Kepler’s 3rd law of motion Kepler’s 3rd law of motion: –The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. Captures the relationship between the distance of planets from the Sun, and their orbital periods. Suppose planet A is 4 times as far from the Sun as planet B. Then planet A must traverse 4 times the distance of Planet B each orbit, and moreover it turns out that planet A travels at half the speed of planet B, in order to maintain equilibrium with the reduced gravitational centripetal force due to being 4 times further from the Sun. In total it takes 4x2=8 times as long for planet A to travel an orbit, in agreement with the law (8 2 =4 3 ).

Galileo Galilei Galileo Galilei: – –In 1609 was the first to view the heavens through a telescope –His viewings provided evidence and data that backed up the Copernican view of the universe. –A stern defender of the Heliocentric view… –Gives us a mathematical theory of motion, which applies to terrestrial and celestial objects alike …a falling body would fall with a uniform acceleration, as long as the resistance of the medium through which it was falling remained negligible… Galileo's Principle of Inertia: "A body moving on a level surface will continue in the same direction at constant speed unless disturbed.” Galileo was one of the first modern thinkers to clearly state that the laws of nature are mathematical. In The Assayer he wrote "Philosophy is written in this grand book, the universe... It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures;...."

Implications of the Copernican Revolution Implications of the Copernican Revolution: –The universe is thought of as infinitely extended in space so it has no center –So humans beings aren’t the center of the universe –The heavens aren’t eternal, immutable and divine –The universe is thought of in purely quantitative terms, as a set of objects that interact according to fixed mechanical laws. –The universe is no longer explained in terms of final causes but instead mathematical laws. –Questions begin to arise about how the following persist in a purely mechanical and quantitative world: Value Free will Minds Secondary qualities God

The Church’s response to Galileo & the Copernican Revolution The Church’s response to Galileo & the Copernican Revolution: –In 1616 Galileo was ordered by the church not to hold or defend the view that the Earth moves around the sun. –In 1632 Galileo publishes Dialogue Concerning the Two Chief World Systems –In 1633 Galileo was ordered to stand trial on suspicion of heresy. He was found guilty of holding and defending the heliocentric view. He was then forced to recant his views and spent the rest of his life under house arrest Any publication of his Dialogue or any of his past or future works was forbidden. –In 1633 the Church prohibits any teachings or holdings of the heliocentric view –The ban was lifted in 1718…