The Scientific Revolution Lecture 1

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The Scientific RevolutionLecture 1
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Outline

• Lecture 1
• 16th century scientific worldview
• Copernicus theory
• Galileo and the telescope
• Lecture 2
• Galileos physics for a moving earth
• Newtons synthesis

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Background to the 16th century worldview

• 12th century European recovery of ancient
  scientific texts
• St. Thomas Aquinas (1225-1274).
• Summa theologica Compatibility of Aristotles
  thought and Christian doctrine

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13th -16th century orthodox cosmology

• Christianised Aristotelian cosmology
• Heavens consist of crystalline spheres that carry
  the sun, moon, planets and stars around the earth
• Therefore a geocentric (earth-centred) cosmology

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• John of Sacrobosco (c.1195-c.1256)
• De Sphaera (On the Sphere) (1534)

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• Peter Apian (1495-1552)
• Cosmographia (1540)

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The heavens and the earth

• Fundamental distinction between the celestial
  realm (the heavens) and the terrestrial realm
  (everything below the sphere of the moon)
• Two distinct approaches to physics

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The terrestrial realm

• The terrestrial realm the realm of change and
  corruption
• Four terrestrial elements earth, water, air and
  fire
• Natural motions always rectilinear towards their
  natural places
• Violent or forced motions

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The celestial realm

• The celestial realm is perfect, unchanging and
  incorruptible
• It comprises the heavenly bodies and their
  respective celestial spheres
• Natural motions are always circular
• All heavenly bodies
• have eternal, perfectly circular orbits around
  the earth
• are composed of the fifth element, the aether
• are perfectly smooth spheres

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Astronomy

• Predominantly in the tradition of Claudius
  Ptolemy (2nd century CE) Almagest
• Apparent irregular (retrograde) motions of the
  planets to be described in terms of uniform,
  circular motions
• A number of mathematical techniques employed to
  predict the motions of the planets

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Retrograde motion of the planets
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The epicycle
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Motives for the reform of astronomy

• Complexity, inaccuracies and inconsistencies in
  Ptolemaic astronomy
• Exploration
• Calendar reform
• 15th century Renaissance

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Nicolaus Copernicus (1473-1543)

• Born in Torun, Poland
• Studied in Krakow, Bologna and Padua
• Canon at the Cathedral of Frauenburg

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Commentariolus (Little Commentary) (1512)
fundamental ideas

• The sun is at the centre of the universe and
  the earth orbits the sun (heliocentric system)
• The motions of the sun and stars are only
  apparent. They are a consequence of the earths
  motion
• The retrograde motions of the planets are a
  consequence of the earths motion relative to the
  planets
• The earth has three kinds of motion

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Copernicus explanation of retrograde motions
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The 3 motions of the earth

• Annual motion around the sun
• Daily (diurnal) motion about its axis
• Motion in declination a gyration of the
  earths axis

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On the Revolutions of the Heavenly Spheres (1543)
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To the Reader on the Hypothesis in this Work

• Andreas Osiander (1498-1552)
• Lutheran theologian
• Copernican hypothesis not literally true, merely
  a useful fiction
• Philosophical term instrumentalism

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Copernicus Preface

• Addressed to Pope Paul III
• Motivations for introducing the new theory
• Criticisms of existing, often incompatible,
  astronomical techniques and theories
• Inspiration from predecessors who considered the
  possibility of a moving earth

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On the Revolutions reception

• Copernicus died during the year of publication
• Advanced knowledge of mathematical astronomy
  required
• Some outright support
• Some supported an instrumentalist interpretation
• Catholic Church initially muted response, but in
  1616 On the Revolutions placed on the Church
  Index of banned books

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Galileo Galilei (1564-1642)

• Born and educated in Pisa, in the Duchy of
  Florence
• Mathematician, astronomer, physicist and
  philosopher
• Taught at Universities of Pisa and Padua

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Sidereus nuncius (The Starry Messenger) (1610)
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The Starry Messenger

• Galileo takes a crude spyglass (telescope) and
  turns it into a serious scientific instrument
• Observes new phenomena in the heavens supporting
  the Copernican theory)
• Surface of the moon
• Innumerable fixed stars (plus nebulae and the
  Milky Way)
• And especially the Medicean Stars (satellites
  of Jupiter)

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The surface of the moon

• The moon is not a smooth, uniform and precisely
  spherical
• Surface similar to the earth
• Implication the earth is not unique, so it is
  not specially conditioned to be at the centre of
  the universe

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Earthshine

• Secondary illumination of the dark surface of
  the moon by the earth
• The earth is capable of reflecting the suns
  light
• Implication if other planets shine by reflecting
  sunlight, then (again) the earth is not unique

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A multitude of stars

• Stars do not appear enlarged, so they must be
  very distant
• Vast numbers of new stars
• Milky Way and nebulae made of stars
• Implications naked eye observation undermined
  authority of ancients cannot be trusted

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New worlds the Medicean Stars

• Named in honour of Grand Duke Cosimo of the House
  of Medici
• Observations of stars that move with Jupiter as
  it orbits the sun
• Implications if Jupiter can orbit without losing
  its moons, then so can the earth with its single
  moon the system of Jupiter and its moon is
  analogous to universe as a whole

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Reception and over all implications

• Excitement, but some refused to accept Galileos
  observations or his interpretations
• Galileo appointed mathematician to Grand Duke of
  Tuscany, Cosimo of the House of Medici
• Before 1610, easy to interpret the Copernican
  theory in the manner of Osiander
• After 1610, support for the reality for the
  Copernican system grew
• BUT, the Copernican system at a serious
  disadvantage without a new system of physics