Download Galileo and the Church

Astronomy 111 – Lecture 10
Galileo Galilei
And
Sir Isaac Newton
Galileo Galilei
• Main Themes for today :
– Important Discoveries with the telescope:
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Moons of Jupiter
Phases of Venus
Craters & Mountains on the Moon
Sunspots
– Confrontation with the Church
The First Modern Astronomer
• Galileo Galilei (1564-1642)
– Italian Contemporary of Kepler
– First modern scientist (in many ways)
• Gifted mathematician
• Brilliant observer and experimenter
• Preferred experimentation and measurement to philosophical rhetoric.
– Staunch anti-Aristotelian
– Often at odds with the scholarly establishment
The Aided Eye
• The telescope was invented in 1608 by Dutch spectacle makers.
– Tradition says by Hans Lipperhey (?)
• Word spread fast:
– In April 1609, one could obtain them in eyeglass shops in Paris.
– First one reached Italy in August of 1609
• Galileo learned about the telescope in 1609, but did not get a chance to see one.
• Based on a description, and acquainted with lens making, he made his own.
– Solved many technical problems, and came up with a design that produced good-quality
images with a magnifying power of 20x.
“a most beautiful & delightful sight”
• Galileo soon turned his telescope on the night sky.
– In 1610, he published his telescopic observations in the Sidereus Nucius (The
Starry Messenger).
– Later observations published in letters, and in a longer work, The Assayer, in
1623.
“a most beautiful & delightful sight”
• Among these observations were:
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Craters and Mountains on the Moon
Sunspots & Solar Rotation
Moons of Jupiter
Phases of Venus
• Galileo made other important observations
– Milky Way is made of myriads of faint stars
– odd shape of Saturn.
Fact 1 : About the Moon
• Galileo found craters and mountains on the Moon:
– Moon was not a smooth, perfect sphere as taught by the Aristotle and Ptolemy.
– Surface was “... rough and uneven, and just like the surface of the Earth itself...”
– Galileo was able to measure the heights of lunar mountains using their shadows.
• Conclusion : The Moon was another world like the Earth.
Fact 2 : About the Sun
• Galileo observed sunspots:
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Bright surface of the Sun had dark spots that changed and moved across its surface.
Discerned solar rotation over time.
Sun was not a perfect body, and was in fact rotating.
Contemporaries also reported them (they appear in Chinese records as early as 28 BC, but nobody in the west
had access to this knowledge).
– Conclusion: The Sun imperfect, contrary to Aristotelian and Ptolemaic teachings. Further, if a
huge object like the Sun were rotating, why not the Earth?
Fact 3 : About Jupiter
• Galileo discovered 4 moons orbiting Jupiter
– Jupiter appeared as a disk.
– 4 points of light that followed it and moved in orbits around it.
– Deduced that they were moons (We now call them the Galilean Satellites of Jupiter)
• Conclusion: The Earth is not the only center of motion in the Universe.
– There was a solar system in miniature around Jupiter for all to see!
Fact 4 : About Venus
• Venus goes through phases like the Moon
– Sequence of phases and changes in diameter proved conclusively that Venus orbits the Sun.
– Ptolemaic theory predicts the opposite of what is observed with the telescope.
• The Sun was also a center of Motion.
• Profoundly damaging to the Ptolemaic system.
– Didn’t prove the Copernican system (it was also consistent with the Tychonic system).
Galileo’s Impact
• The impact was immediate and forceful:
– Skeptics claimed that the telescope was lying (and Galileo, too) and entrenched.
– Kepler was delighted, and soon got his own telescope, as did many others.
– Many scholars began to take the Copernican system seriously.
• The discoveries brought Galileo immediate fame throughout Europe.
– With telescopes everyone could literally "see for themselves". More than all the profound
philosophical speculations or obscure mathematical arguments, this was behind the
tremendous impact of Galileo's observations.
– These phenomena were observed facts of nature, and had to be confronted.
This Road leads to trouble…
• Galileo knew he could hold his own on the ground of scholarly confrontation.
– He was now by far the most famous scientist in Europe, and immensely influential.
• This position led him to miscalculate his own influence, and to badly misjudge the
influence of his enemies.
Galileo and the Church
• 1616:
– The Church officially declares that the heliocentric theory is “philosophically false and at
least an erroneous belief.”
– De Revolutionibus is officially banned.
– Galileo was called to an audience with Cardinal Robert Bellarmine, who cautioned him
verbally to stop teaching and defending the Copernican model in public.
An important ‘Dialogue’
• 1624:
– Galileo writes “A Dialogue on the Two Chief World Systems”, ably defending the Copernican
system.
– Seeks permission from Pope Urban VIII to publish it, but is rebuffed.
• 1632:
– Galileo’s dialogue is published in Florence, written in Italian (Tuscan), not Latin.
– It was an instant success & widely acclaimed.
The Trial of Galileo
• 1633:
– Enemies of Galileo convinced Pope Urban VIII that a character in the Dialogue (Simplicio) who
ineptly defends Ptolemy is a thinly veiled caricature of the Pope himself.
– Galileo is summoned by the Roman Inquisition and a document is produced alleging that
Bellarmine in 1616 specifically forbade him to discuss the Copernican system in any way
– Modern scholarship has shown that this document is a forgery.
The Charges against Galileo
• Galileo faced two charges:
– Disobedience of Bellarmine’s 1616 order.
– Misleading censors who published his book.
• Publicly humiliated and threatened with torture, Galileo had no choice
but to admit guilt, and “abjure, curse and detest the aforesaid errors and
heresies...”
Galileo under House Arrest
• Galileo was placed under house arrest at his villa in Arcetri near Florence
until his death in 1642.
– Despite this, in 1636 he finished “The Two New Sciences” describing his earlier
experiments in mechanics.
– Published in Protestant Leyden in 1638.
• Laid the foundations of classical physics.
And still, it moves !
• Galileo spent his final 4 years in blindness, and died under house arrest,
on January 8, 1642.
• On Christmas Day of that same year, Isaac Newton was born in
Woolsthorpe(England).
• In 1992, 350 years later, Pope John Paul II officially declared Galileo
innocent.
Isaac Newton’s ‘Principia’
• Isaac Newton (1642-1727)
– Born in Woolsthorpe in rural England on Christmas Day of 1642 (Old Style, England had not yet adopted the
Gregorian Calendar).
– Mother was a widow who remarried after he was born.
– Raised by his maternal grandmother.
– Grew up a solitary boy quite unfit as a farmer.
– Quiet, irascible, and solitary as an adult (he never married). He was always fearful that others would steal from
him.
– Graduated from Cambridge 1665
How the Plague comes into play
• During Plague years 1665-1666, Cambridge closed and he went home to
Woolsthorpe.
• Spent two years in Woolsthorpe, during which he
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Invented the integral and differential calculus.
Developed the binomial theorem.
Started fundamental work on optics.
Formulated his laws of motion & gravitation.
• He published none of it until years later.
Being a Professor
• In 1669 (at age 26!) he became the Lucasian Professor of Mathematics at Trinity
College, Cambridge.
• Settled into the life of a Cambridge don:
– Continued fundamental work on optics (invented reflecting telescope).
– Carried out a variety of experiments.
– Was always unprepared for classes and hated to teach.
Newton’s ‘Principia’
• In 1684, Newton was prevailed upon by Edmond Halley to publish his work on
motion and gravitation.
– Newton took 3 years to reproduce his work
– Halley paid the publication expenses out of his own pocket, after wheedling, cajoling, and
flattering Newton into finishing it in 1687
• The result : Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural
Philosophy)
An important Book !
• The Principia is one of the most important books in history:
– Laid the foundations of modern physics.
– Completely swept away the last vestiges of the Aristotelian view of the world.
– Replaced older, empirical descriptions with quantifiable, causal explanations of the nature of
the physical world.
• Unified all motions into three simple laws.
The First Law of Motion
• Every body will stay in a state of rest or uniform motion in a straight
line unless that state is changed by forces impressed upon it.
• Often called the law of inertia.
– Property of matter that it resists having its state of motion changed.
Talking about motion
• Some key terms explained :
– All motion is composed of two parts:
• Speed (how fast is it going)
• Direction (where is it going)
– The combination is called the VELOCITY:
• Velocity = how fast, and in what direction.
– Change in motion is acceleration
• Measures how fast the velocity changes.
• Change can be in speed, or direction, or both!
The Second Law of Motion
• The size of an acceleration is directly proportional to the force
applied, and inversely proportional to the mass of the body.
• Further, the acceleration will take place in the same direction as
the applied force.
The mathematical expression
• Expressed Mathematically:
• a = F/m
– Acceleration is proportional to force, and inversely proportional to
mass.
• F = ma
– Force is mass times acceleration.
What, the heck, does that mean ?
• Second law has two parts:
– Quantifies a "force" in terms of its effects on a massive body.
• Forces produce accelerations.
• The more mass a body has, the less it will be accelerated by a given force.
– Forces and accelerations have a direction:
• Accelerations are in the same direction as the applied forces.
What is the relevance for our planetary motion
problem ?
• Planets are continually changing the speed and direction of their motion as they
orbit the Sun.
– Move along ellipses with the Sun at one focus.
– Move fastest when at perihelion, slowest when at aphelion.
– They are thus accelerating in response to a force.
• What force?
• Newton : The Force of Gravity !
The Third Law of Motion
• For every force applied to a body, there is an equal and oppositely
directed force exerted in response.
• Or, as it is more commonly stated:
– To every action there is an equal & opposite reaction.
Forces always come in pairs !
• The third law brings together the first and second laws, which deal with single
bodies.
• Unifies them in the case of the interaction between two (or more) bodies via forces.
– If I set an apple on a table, it pushes down on the table with a force equal to its mass times the
acceleration due to gravity.
– To hold it stationary, the table must be exerting an equal and opposite upward force.
A tremendous improvement
• Newton’s laws of motion provide a complete, quantitative explanation of
the motions of objects.
– They are simple, easily stated in either words or mathematics.
– Universal Physical Laws that apply to all moving objects, on the Earth or in the
heavens.
– They unify phenomena. Everything explained with the same set of self-consistent
rules.