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Galileo and the New Cosmology David Banach Department of Philosophy.

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Presentation on theme: "Galileo and the New Cosmology David Banach Department of Philosophy."— Presentation transcript:

1 Galileo and the New Cosmology David Banach Department of Philosophy

2 How sweet the moonlight sleeps upon this bank! Here will we sit and let the sounds of music Creep in our ears: soft stillness and the night Become the touches of sweet harmony. Sit, Jessica. Look how the floor of heaven Is thick inlaid with patines of bright gold: There's not the smallest orb which thou behold'st But in his motion like an angel sings, Still quiring to the young-eyed cherubins; Such harmony is in immortal souls; But whilst this muddy vesture of decay Doth grossly close it in, we cannot hear it

3 The Music of the Spheres Merchant of Venice, Act V  How sweet the moonlight sleeps upon this bank! Here will we sit and let the sounds of music Creep in our ears: soft stillness and the night Become the touches of sweet harmony. Sit, Jessica. Look how the floor of heaven Is thick inlaid with patines of bright gold: There's not the smallest orb which thou behold'st But in his motion like an angel sings, Still quiring to the young-eyed cherubins; Such harmony is in immortal souls; But whilst this muddy vesture of decay Doth grossly close it in, we cannot hear it

4 Two Golden Ages of Astronomy

5 Ptolemy ( AD)

6 Ptolemaic Heliocentric Universe

7 Terrestrial and Heavenly Spheres

8 Cross Section

9 Terrestrial Spheres

10 Terrestrial Motion  Four Elements: Earth, Air, Fire, Water  Each Element has a natural place, its own home sphere.  All objects move to reach their goal or fulfill their potential.  Straight line, rectilinear, motion.  Less perfect.

11 Crystalline spheres

12 Heavenly Spheres  Made of a fifth Element: Aether  More perfect, circular motion  Moves in imitation of God’s perfect thought motion (Thought thinking itself).  Moved by final causality or purpose, not through contact.  All things move to the unmoved mover, just as a lover moves toward their beloved.

13 Moral structure of the universe

14 Dante’s Divine Comedy (~1300)

15 Aristotle’s Universe

16 Great Chain of Being

17 A place for everything and everything in its place

18 Parallel Hierarchies in Different Realms

19 Moral structure of the universe

20 II. Saving the Appearances  Ancient and Medieval Astronomy aimed at geometrically constructing a model of the universe that reproduced, or predicted, or “saved” the appearances we observe in the heavens.  Two kinds of motions:  1. Diurnal (Daily)  2. Yearly

21 Diurnal (east to west, every 24 hours)

22 Diurnal Motion of Stars

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24 Seasonal Motions: Stars-none Planets- Wanderers, West to East, Slow

25 Ecliptic and the Zodiac Ecliptic- Path along which the sun moves in the heavens. Tilted 23 degrees. Zodiac- Ecliptic divided into 12 sections named for the constellation in each section.

26 Sun Moving through the Zodiac

27 Two Motion of Planets  Diurnal: By participation in Motion of Heavens  Seasonal: Proper Motion of the sphere of each planet slower and from west to east.

28 A little complication : Retrogression

29 Ptolemy’s Solution: Deferents and Epicycles

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31 Music of the Spheres

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33 Copernicus’s System

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36 Copernicus’s View of Retrogression

37 Mars Venus

38 Copernicus’s View of Retrogression

39 Uses of the Systems  Astrology: All Major astronomers of the day did composed Astrological Carts.

40 Uses of the Systems  Calendar: Introduction of Gregorian Calendar: Pope Gregory XIII decreed that the day after October 4, 1582 would be October 15, 1582

41 Comparison of Complexity of the two views

42 Tycho Brahe ( )

43 Tycho Brahe’s System

44 Johannes Kepler (1571 – 1630) Equal areas in equal time R^3 = T^2

45 Dialogues Concerning the Two Principal Systems of the World  (1632)http://dbanach.com/galileo  Salviati = Galileo (Copernicus)  Sagredo = Learned Layman  Simplico = Aristotelian Professor (Ptolemy)

46 Galileo on Trial (1633)

47 Arguments for Copernican Model  Immense magnitude of the starry sphere. It makes more sense to have the smaller sphere move rather than the larger.  Contrary Motions. Having the heavens moves involves attributing to the planets two contrary motions (diurnal and seasonal)  Speed of Motion. The greater the size of the sphere, the longer it takes to revolve.  Different Sizes of Stars’s orbits. The stars move in circles of different sizes depending on their nearness to the poles.  Change of orbits. These circles have changed as the stars have moved their positions in the skies over great periods of time.  Strength of Sphere holding stars. The solidity of the sphere in which the stars are embedded to keep their motions regular also strains belief.  Great motion of Heavens would sweep Earth along as well. The motion of the stars which carries all the other spheres along with it, would surely move the earth as well.

48 Different Sizes of Stars’s orbits. The stars move in circles of different sizes depending on their nearness to the poles.

49 Change of orbits. These circles have changed as the stars have moved their positions in the skies over great periods of time.

50 Contrary Motions Two Motions: Which is the Natural Motion? How can it hear two different songs?

51 Mechanical Arguments Assumptions already against Aristotle  Immense magnitude of the starry sphere. It makes more sense to have the smaller sphere move rather than the larger.  Speed of Motion. The greater the size of the sphere, the longer it takes to revolve.  Strength of Sphere holding stars. The solidity of the sphere in which the stars are embedded to keep their motions regular also strains belief.  Great motion of Heavens would sweep Earth along as well.

52 Arguments against Copernican Model  1. Not Perpetual. The Earth’s motion would be violent not natural (which is to the center of the universe), so it could not be perpetual.  2. Parallax. The Earth should have a second seasonal motion, just as do all the other planets. This should result in changes in the observed positions of the stars, which we do not see over the course of the year.  3. Wholes same as Parts. The motion of the whole should be the same as the motion of the parts, which is to the center of the universe.  4. Projectile motion. Objects dropped or shot straight up in the air travel in a straight line up and down instead if being left behind by the motion of the earth as it rotates on its axis. Cannonball, birds, and Ship’s Mast examples.  5. Saves the Appearances. The hypothesis of an immoveable earth accords with the observed appearances of the stars and planets.

53 Parallax

54 Stellar Parallax

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56 Stellar parallax  Galileo had no definitive answer to this argument. He knew that stars would have to be very distant to observe no parallax.  ~220BC Archimedes estimates size of the universe, opposes heliocentric model because of lack of observed parallax.  First detected in 1837.

57 Projectiles Does this one go further?

58 What carries us along with the Earth? Inertia

59 Why don’t we fly off? Not in the Dialogue.

60 Force from Earth’s rotation equivalent to this rotating about 2 mph

61 Coriolis force

62 Phases of Moon

63 Phases of Venus

64 PtolemyCopernicus

65 Phases of Venus Galileo’s DrawingCopernican View

66 A New Kind of Science.  The real import of the debate was the emergence of new standards of scientific inquiry and debate.  What counts as an argument, as scientific evidence?  Could you have proven then that the Earth moves?  Can you now?

67 Ptolemaic, Aristotelian, Reasoning  Authority of Ancient figures.  Beauty and elegance of the system of the world.  Eternity and naturalness of motions.  Preference for regular circular motion as best image of God.

68 New Scientific Reasoning  Use of contemporary evidence, not authority.  Occam’s Razor. Don’t suppose more entities than are necessary for explanation.  Mechanical and practical reasoning.  Recognizing relativity. Motion must be considered from the right point of view.

69 What have we lost? What have we gained?


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