The Copernican Revolution and the Newtonian Synthesis or The Who, How, Why, When and Where the Moder

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The Copernican Revolution and the Newtonian
Synthesis or The Who, How, Why, When and Where
the Modern World Got Started

• Michael Bass
• Professor Emeritus of Optics
• CREOL, The College of Optics and Photonics
• UCF

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Just because it is beautiful
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Prelude

• For nearly 1500 years there were more important
  things to do
• survive
• However the calendar was in trouble
• 1 day too long every 128 years
• Soon Christmas would come in the spring and
  Easter in the summer and
• The infallibility of the Church was at stake.

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Science begins

• For millenia people had been accumulating
  observations
• Seasons, stars, sunrise and sunset, length of
  day, how to start a fire, flake rocks into tools,
  make metals, navigate, plant, harvest, survive!
• The Greeks developed concepts of logic (Plato and
  Socrates) and said apply it to understanding
  things.
• Science began!

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Aristotles Cosmology

• for 2000 years common sense had worked
• clearly the sky moved around the earth though
  some stars seemed fixed and some wandered
• the wanderers were the planets
• Aristotle having only these observations to go on
  proposed a universe composed of 8 crystalline
  spheres rolling around the earth which was fixed.

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The Celestial Orbs
With the earth at the center, 8 spheres carried
all else.
fixed stars
5 known planets
moon
sun
The earth was a sphere since that was the perfect
shape.
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The Workings of Aristotles Model

• It explained lunar eclipses and the earths
  shadow on the moon.
• Things moved about the earth forever as God had
  ordained them to move.
• This meant that God was free to redo things
  whenever he wished.
• The calendar worked but not too well.
• Some minor troublesome matters existed but for
  the most part were ignored.

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Epicycles

• One serious problem in Aristotles model was how
  to explain the retrograde motion of the planets.
• Sometimes they reversed direction across the sky
  and this was not accounted for by the model.
• Claudius Ptolemy in the 2nd century suggested
  that each planet turned on a small sphere
  attached to the celestial orb.

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The Ptolemaic System

• By moving on its sub-sphere the planet could
  still move as Aristotle suggested and the
  retrograde motion could be seen as an epicycle in
  the otherwise perfect circular motion.

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Saving the Model

• Most people dont like radical change and
  scientists are no different
• They often try to save the model
• This was the Ptolemaic system
• Even though such things as comets and super novas
  could not be explained the model was secure in
  peoples comfort
• Besides it was common sensical
• It was also wrong!

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Copernicus

• In 1514 the Pope asked Niklas Koppernig in Poland
  (Copernicus) to look into calendar reform.
• In the old calendar the holy days were moving
  about the year most uncomfortably.
• He couldnt do this until he understood the
  motions of the sun and moon.
• After all, calendars were based on the solar year
  or the lunar cycle.

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An Aside on Time

• Motion and time are intimately connected
• If things didnt move or change with respect to
  one another there would be no need for the
  concept of time.
• In other words, we invented time to describe
  change because without change there would be no
  time.
• Thus, Copernicus had to understand the motion of
  the objects that defined the calendar.

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The Little Commentary (1514) and On the
Revolution of the Celestial Spheres (1543)

• In 1514 Copernicus questioned Aristotle
• He tried to keep the perfect curves, suggesting
  circular orbits but of the earth around the sun
  and the moon around the earth.
• His full model wasnt published until two months
  prior to his death but the obscure priest had
  challenged the foundations of the culture of
  Christendom.
• In 1582 the Gregorian (Copernican) Calender was
  adopted.
• But his circular orbits and sun centered universe
  caused his successors problems.

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The Copernican Revolution

• Humankind was no longer the center of the
  universe.
• Just being at the center was no great honor.
• Really good things rose into the heavens.
• Stars were vastly further away from the earth
  than the sun.
• The universe was much bigger than before.
• Since the earth was now amongst the heavens (it
  moved around the seemingly fixed sun) it and the
  heavens were corruptible, imperfect and
  changeable.
• Simple models were better than complicated ones.

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Brahes Data

• A Dane, Tyge (Tycho) Brahe, was convinced more
  accurate data was critical if progress were to be
  made.
• His observations of the motions of comets showed
  without doubt that they did not follow circular
  orbits.
• If so they were cutting across Aristotles
  spheres.
• He refined measurements of the motions of the
  planets and made possible what was to come next.
• He took on Johannes Keppler as an assistant in
  1600 and died in 1602.

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Keplers Deductions

• Using Brahes data Kepler made a breakthrough
• Forget circles - the orbits of the planets had to
  be ellipses with the sun at a focus.
• The line from the center of the sun to the planet
  would sweep out equal areas in equal times.
• The planets speed changed in its orbit around
  the sun.
• The square of the planets orbital period is
  proportional to the cube of the semimajor axis of
  its orbit.

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Galileos Observations

• Galileo insisted on experimental data and on
  seeking the nearest cause.
• He used telescopes and on January 7, 1610 looked
  at Jupiter.
• It had moons!
• If moons orbited Jupiter the Aristotelian system
  must be wrong and Copernicus more nearly right.

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Galileo and the Church

• Galileos universe didnt fit that which the
  Church demanded
• in the Churchs universe there was no room for
  moons around Jupiter and distant stars (and a lot
  of stuff old Galileo had not yet seen)
• Worse yet Galileo insisted the orbits were
  ellipses not circles.
• If he persisted in insisting on the truth of his
  view then the Church was wrong and the Church
  could not be wrong.
• All he had to do was say that his was just a
  model of the universe - not actually what it
  really was.

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• Under threat of the inquisition he was forced to
  recant.
• His scientific philosophy that the simplest
  explanation was best and most likely correct
  remains with us.
• With this the Church, mixing science and religion
  inappropriately, would spend the next 380 years
  living it down.
• In 1992 the Church acknowledged that it had
  wronged Galileo and that he had been correct.
• It had banned Copernicus thoughts until 1822 and
  his book was forbidden until 1835.
• In fact, today it accepts the big bang
  cosmology but that is another story.

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An Historical Change

• At about the same time of the Churchs
  difficulties with Galileo
• Isaac Newton was born in the same year in which
  Galileo Galilei died another coincidence of
  history
• the Royal Society for the Advancement of Science
  was being established in England.
• This period also marked the ascendancy of the
  economies, empires and strength of the northern
  European, Protestant countries and the start of a
  long period where the Catholic countries of
  Southern Europe lagged behind.

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Newtons Synthesis

• The genius of Newton was his use of his laws of
  motion and the inverse square law of gravity to
  demonstrate Keplers deductions.
• No longer did things move because of mysterious
  essences or urges but because of measurable
  forces which caused changes in motion.
• Newton gave order where there had been none.

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Synthesis

• In the context of our culture synthesis means the
  bringing together of facts and sorting out their
  meaning into a simple, explanatory and predictive
  model.
• That is what Newton did.
• The others took data, massaged it but didnt
  perform the synthesis of what they knew into a
  scientific principle.

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The result of Newtons Synthesis

• A direct consequence is the growth of England, a
  very small, resource poor country, into a world
  empire.
• The industrial revolution.
• The colonization of the Americas supported by
  goods manufactured in the industrial revolution.
• The world that we know today.