The Scientific Revolution (17th Century)

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The Scientific Revolution (17th Century)
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I. Two Major Themes
A. The universe is mathematically ordered
1. Nature in geometric terms
2. Description
B. Mechanical philosophy
1. Nature is a machine
2. Explanation
C. Different goals often in conflict

• solution

"Nature and Nature's Laws lay hid in Night God
said, Let Newton be! and all was Light."
Alexander Pope
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II, Celestial Dynamics and Terrestrial Mechanics
The Revolution
1. De Revolutionibus Orbium Coelestium (1543) 50
years later
2. The revolutionaries Kepler and Galileo
A. Johannes Kepler (1571 1630)
1. Life
2. Mysterium Cosmographicum (1596)
a. Why did God chose 6 planets?
b. Answer 5 platonic solids
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A. Johannes Kepler (1571 1630)
3. Tycho Brahe (1546 1601)
a. Life
b. Aristotles celestial spheres

• crystalline

• perfect, unchangeable

• circular motion

• quintessence the aether

c. Tychos observations

• very precise (no telescopes)

• evidence against celestial spheres

• new star (supernova) 1572

• comet 1577

• beyond orbit of Mars

• motion non-circular

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A. Johannes Kepler (1571 1630)
4. Kepler and the foundation of celestial
mechanics
a. No celestial spheres
b. Celestial obey same laws as terrestrial
c. Kepler focuses on Mars
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A. Johannes Kepler (1571 1630)
5. Astronomia Nova (1609)

• Keplers 3 laws of planetary motion

1. Law of orbits

• The orbit of every planet is an ellipse with the
  sun at one
• of the foci

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A. Johannes Kepler (1571 1630)
2. Law of areas

• A line joining a planet (or comet) and the Sun
  sweeps out equal areas in
• equal intervals of time

• movie of Keplers first two laws

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A. Johannes Kepler (1571 1630)
3. Law of periods

• The ratio of the squares of the revolutionary
  periods for
• two planets is equal to the ratio of the cubes
  of their
• semimajor axes.

Planet Periods (s) Distance (m) P2/R2
Earth 3.2 x 107 1.5 x 1011 3.0 x 1019
Mars 5.9 x 107 2.3 x 1011 3.0 x 1019
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A. Johannes Kepler (1571 1630)
6. Sun has magnetic pull on planets (no animistic
forces)
7. Results of Keplers model

• simplicity

• no circles/ epicycles/ equants

• destroys Copernican system

• it works!

• problems

• no evidence

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B. Galileo Galilei (1564 1642)
1. Life
2. The motion problem

• Aristotle every motion requires a mover

• projectiles medium moves it along

• Middle ages impetus theory

• moving body acquires impetus

• Galileos solution inertia

• body in motion moves with
• uniform velocity forever

• in a circle!

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B. Galileo Galilei (1564 1642)
2. The motion problem

• motion and the Earths rotation

• ball dropped from a height

• if Earth in motion, ball should drop to the west

• observation ball drops straight down

• Galileo all objects on Earth share its motion

3. Galileo versus Aristotle

• A cause of natural motion cause of forced
  motion

• G no natural place motion is just a state

• object is indifferent to its place

• rest and motion degrees of the same

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B. Galileo Galilei (1564 1642)

• Projectile motion

• practical advantage better war machines

• Weights

• Aristotle objects with different weights fall
  at different
• velocities

• Galileo objects with different weights fall at
  same
• velocities (under ideal conditions)

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B. Galileo Galilei (1564 1642)
4. Galileos astronomical observations

• invention of telescope Hans Lippershey (1608)

• Galileos telescopes

• 1609 Galileo looks at the heavens

• observations

• moon is not perfect earthy

• moons of Jupiter

• sunspots

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B. Galileo Galilei (1564 1642)

• phases of Venus

• Galileo claims observations prove Copernican
  system

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B. Galileo Galilei (1564 1642)
5. Galileos scientific method

• Galileos world of ideals

• Galileo stuck in the past

• the Universe created perfectly by perfect Creator

• therefore, all motion must be circular

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B. Galileo Galilei (1564 1642)
6. Galileo and the Church

• the Reformation

• Martin Luther (1483 1546)

• 95 theses (1517)

• the Counter- Reformation (1560)

• the Inquisition

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B. Galileo Galilei (1564 1642)
6. Galileo and the Church

• Galileos social skills

The Bible teaches the way to go to heaven, not
the way the heavens go.

• G the Church should reinterpret the Bible

• 1616 De Revolutionibus banned (foolish and
  absurd and
• formally heretical)

• 1616 Galileo forbidden to hold, defend, or
  teach the
• Copernican system

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B. Galileo Galilei (1564 1642)
6. Galileo and the Church

• Dialogue Concerning the Two World Systems (1629)

• Ptolemaic versus Copernican (Brahe and Kepler
  ignored)

• three men having a dialogue

• Church gives official approval

• problems

1. Biased towards Copernican system
2. Popes statements put in mouth of Simplicio

• Result Galileo summoned to Rome to face trial
  for heresy

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B. Galileo Galilei (1564 1642)
6. Galileo and the Church

• The Trial of Galileo (1633)

• in opposition to Scripture

• lack of evidence

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B. Galileo Galilei (1564 1642)
6. Galileo and the Church

• Sentence

• Galileo made to renounce Copernican system

• house arrest

• Dialogue banned

• Galileo pardoned

• 1638 Galileo writes Discourses

7. The legacy of Galileo
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