Humanities 3V. The Scientific Revolution

Lecture 20

The Trial Of Galileo

Outline

• The Astronomical Revolution

• Galileo and the Church

• Letter to the Grand Duchess Christina

Copernican System

• 1543 Publication of Copernicus’ On theRevolutions of the Celestial Orbs

• Heliocentric theory: Earth revolves aroundthe sun and rotates on its axis

• Copernicus’ picture modified by JohannesKepler (1571-1630) based on observationaldata of Tycho Brahe (1546-1601)

Galileo and the Telescope (1609)

Significant TelescopicObservations

• Face of the Moon: indicates that the Moon wasaffected by geological variations (mountains,craters) just like the Earth

• Sunspots: similarly show that the Sun is not aperfect, unchanging celestial body

• Moons of Jupiter: indicate that the Earth was notthe only center of motion

• Phases of Venus: indicate that Venus must belocated between the Sun and the Earth (as theCopernican model predicted)

Galileo, Moons of Jupiter

Galileo, Letter on Sunspots (1613)

Do Galileo’s ObservationsDisprove Aristotle’s Theory?

• Not necessarily: an opponent could discount thereliability of observations made with the telescope

• In response, Galileo had to (a) show the telescopeoffered reliable results up to the limits of theobservable (e.g. distant towers); (b) argue there was noreason to think the telescope is less reliable in the caseof celestial phenomena than terrestrial phenomena

• What’s at stake: is the distinction between theterrestrial and celestial “realms” a fundamentalassumption of cosmology, or a hypothesis subject toobservational test and refutation?

Galileo’s Rise to Fame• 1609: Observations of moon, moons of Jupiter,

sunspots, stars (10x as many as with naked eye)• 1610 Publication of The Starry Messenger

(Siderius Nuncius). Appointed “chief philosopherand mathematician” to the Grand Duke ofTuscany, Cosimo de’ Medici

• 1613 Publication of Letter on Sunspots• 1615 Denounced to the Inquisition for support of

the Copernican theory, called to Rome to defendhis views

What’s at Issue?• Galileo points out that Copernicus himself was a

priest and his book received papal approval.• Some in the Church were prepared to accept

Copernicus’ theory on instrumental grounds, as theyhad Ptolemy’s theory.

• But Galileo’s observations were evidence of thetruth of Copernicanism. The Church could notaccept this.

• In 1546 the Council of Trent had decreed that theChurch alone had the authority to interpret the ‘truesense and meaning” of scripture.

Condemnation of 1616(1) The Sun is the center of the world, and iscompletely immobile by local motion

Censure: All agree that this proposition is foolishand absurd in philosophy and is formally heretical,because it explicitly contradicts sentences found inmany places in Sacred Scripture according to theproper meaning of the words and according to thecommon interpretation and understanding of theHoly Fathers and of learned theologians.

Condemnation of 1616

(2) The Earth is not the center of theworld and is not immobile, but moves asa whole and also with a diurnal motionCensure: All agree that this propositionreceives the same censure in philosophy;and in respect to theological truth, it is atleast erroneous in faith.

Passages from Scripture• “The sun rises, and sets, and returns to its place,

from which, reborn, it revolves through themeridian, and is curved toward the North”(Ecclesiastes 1:5)

• “You fixed the earth on its foundations” (Psalm104:4)

• “God made the orb immobile” (1 Chronicles 16:30)• “Heaven is up, the earth is down” (Proverbs 30:3)• “He suspended the earth above nothingness, that is,

above the center” (Job 26:7)

Consequences for Galileo• Galileo is forbidden from discussing or defending

the Copernican theory• Later, under a new pope, Galileo is assured that he

can continue to examine the theory as amathematical hypothesis

• In 1615, prior to the condemnation, Galileo hadcomposed a detailed response to the Church’sposition, his Letter to the Grand DuchessChristina, which was not published until 1636 butcirculated widely in manuscript copies

Letter to theGrand Duchess Christina

• Galileo’s main claim: the Bible cannot be used todisprove scientific claims

• Each is an authority in its own sphere: the Biblewith respect to salvation; science with respect tothe order of nature (doctrine of double truth)

• Both express God’s will: the phenomena of natureexecute God’s commands, and our senseexperience and reason allow us to understand theimmutable order of nature

“I think that in disputes about naturalphenomena one must begin not with theauthority of scriptural passages, but with senseexperience and necessary demonstrations. Forthe Holy Scripture and nature derive equallyfrom [God]…. After becoming certain of somephysical conclusions, we should use these asvery appropriate aids to the correctinterpretation of such Scriptures and to theinvestigation of the truths they must contain,for they are most true and agree withdemonstrated truths.” (pp. 116-7)

“[T]he Holy Spirit did not want to teach us whetherheaven moves or stands still…. But, if the HolySpirit deliberately avoided teaching us suchpropositions, inasmuch as they are of no relevanceto His intention (that is, to our salvation), how canone now say that to hold this rather than thatproposition on this topic is so important that one is aprinciple of faith and the other erroneous….. Here Iwould say what I heard from an ecclesiasticalperson in a very eminent position (CardinalBaronio), namely, that the intention of the HolySpirit is to teach us how one goes to heaven and nothow heaven goes.” (p. 119)

What to Do When ScriptureAppears to Contradict Science?

• The Bible is not a science textbook: its purpose is notto teach about nature. Natural events are described ina way that common people will understand.

• Thus, biblical descriptions of nature cannot be takenliterally.

• Science becomes the authority on how to interpret theBible: when it is and is not to be read literally.

• Yet this conflicts with the Church’s claim to be thesole authority on the meaning of scripture.