Astronomy 350L (Fall 2006)
The History and Philosophy of Astronomy (Lecture 4: Antiquity II)
Instructor: Volker Bromm TA: Jarrett Johnson The University of Texas at Austin
Astronomy and Cosmology in Antiquity: Two Threads of Thought • Mai Mainst nstream ream (ort (orthodo hodoxy) xy)
Antiqu Ant iquity ity I (Se (Sep. p. 7)
- Plat Plato, o, Eudoxus, Eudoxus, Aristot Aristotle, le, Hipparch Hipparchus, us, Ptolemy Ptolemy - Tw Two-s o-sphe pherere-uni unive verse rse - Ear Earth th-ce -cente ntered red (ge (geoce ocentr ntric) ic) - Plan Planetary etary motio motion: n: in circles, circles, deferen deferent-epi t-epicycl cycle e
• Dis Dissen sentt (he (hetero terodoxy doxy))
Antiqu Ant iquity ity II (Se (Sep. p. 12)
- Pyth Pythagor agoras, as, Democritu Democritus, s, Epicurus, Epicurus, Stoics, Aristarc Aristarchus hus - Dem Democrit ocritus us (atomism) (atomism) and Aristarchu Aristarchus s (Sun-cente (Sun-centered) red) - clo close se to to moder modern n world world view view - but forgo forgotten tten (supp (suppresse ressed) d) for 1,400 1,400 years years
Great Thinkers of Antiquity
Democritus
Zeno (Stoa) Aristarchus Pythagoras
Pythagoras: Pythago ras: A Universe governed by Numbers
• Py Pyth thag agora oras s (c. (c. 580580-500 500 BC) BC) • fo foun under der of sc scho hool/ ol/se sect ct (Pythagoreans) • ma math thema emati tica call struc structu ture re of reality / universe • my myst stic icis ism m of num numbe bers rs
Pythagoras: Pythago ras: A Universe governed by Numbers
Divine Tetractys: 1 + 2 + 3 + 4 = 10 - sy symbo mboliz lizes es the the uni unive verse rse!!
Pythagoras: Pythago ras: Music of the Spheres
(Andrea Palladio, 1508-1580)
- Mus Musica icall harmony: harmony: Whole Whole number number ratios ratios (1:2, (1:2, 2:3…)! 2:3…)! - Sam Same e rati ratios os in the heav heavens ens Music Mus ic of the Sph Spheres eres!! - In Inau audi dibl ble e to to us! us!
The Pythagorean Model of the Universe (5th cent. BC)
• Ear Earth: th: nonnon-cent central, ral, and in moti motion on • re reje ject cted ed be begi ginni nning ng of 4th cent. BC
Ancient Two-sphere-universe: - Next Q: What is rotating? Earth or Sphere of Fixed Stars???
Hypothesis: The Earth? - act actual ually ly pro propos posed ed by Her Heracl acleid eides es of Pon Pontu tus s (4th cent. BC) - that obvio obviously usly can can explain explain observati observations ons (and we now now know that it is true)
But: Why was this (correct) hypothesis rejected and rediscovered only ~2,000 years later?
The Th e Ep Epic icur urean ean Un Unive iverse rse
• Epicuru rus s (c (c.. 34 340 - 270 BC) BC) • Ph Phililoso osophy phy of Happ Happine iness ss
• At Atom omis istt natura naturall philos philosoph ophy y - fu furt rthe herr devel develop op Dem Democr ocrit itus’ us’ id ideas eas - an infin infinit ite e univer universe se
The Epi Epicur curean ean Univer Universe: se: Atomis Atomistt Origin Origins s • Al Alll matt matter er made made up fro from m atom atoms s • Ato Atoms ms are indi indivis visibl ible/un e/undest destruc ructab table le • Ato Atoms ms of of diffe different rent sha shapes pes/siz /sizes es • Ato Atoms ms mov move e throu through gh empty empty spa space ce (c. 460-370 BC) Q: Is space finite or infinite???
The Epi Epicur curean ean Univ Universe erse:: Infini Infinite te Space Space A: Space has to be infinite!
Cosmic-edge riddle: • no ed edge ge,, no no cen cente ter! r! • co conta ntain ins s in infi fini nitel tely y many atoms (Why?) • in infi fini nity ty of wor world lds s and and teeming with life! • Fi Firs rstt pos posed ed by Ar Arch chyt ytas as (5th cent. BC)
The Th e Ep Epic icur urean ean Un Unive iverse rse • pop popula ularize rized d and pres preserve erved d by Lucre Lucretiu tius: s: `De Re Reru rum m Na Natu tura ra ’ (On the nature of things) - Con Conse serva rvati tion on of of mat matte ter: r: Ex nihilo nihil fit (Nothing comes from Nothing)
Lucr Lu cret etiu ius s (9 (966-55 55 BC) BC)
- red redis iscov covere ered d in 141 1417: 7: highly influential in early Renaissance
The Th e St Stoi oic c Uni Unive vers rse e
• Fou oun nde der: r: Zeno of of Ci Citium (c (c.. 33 330 – 260 BC BC) • Gre Great at influe influence nce for 500 500 years (Roman (Roman arist aristocra ocrats) ts)
Stoic Philosophy: Famous Adherents
(Emperor Marcus Aureliliu us)
(Seneca, Nero’s teacher)
The Sto Stoic ic Univer Universe: se: Basic Basic Pr Princ incipl iples es • Eve Everyt rything hing in Cosmo Cosmos s is perv pervaded aded by logos - heaven, - heaven, Earth, people, universe as a whole • Logos Logos manifested manifested as pneuma • St Starr arry y cos cosmo mos s is is fin finit ite e • Emb Embedde edded d in infinit infinite e void (space (space witho without ut matter matter)) • Ete Eternal rnal cycl cycle e of confla conflagrat gration ion and and recurren recurrence ce
The Th e St Stoi oic c Uni Unive vers rse e
Fixed stars Finite cosmos Earth
Infinite void ???
Three Thr ee Worl World d Systems Systems:: Plenum Plenum vs vs Vac Vacuum uum Aristotelian
Stoic
Epicurean
• space:
-finite
-infinite
-infinite
• m a tte r :
-finite
-finite
-infinite
Aris Ar ista tarc rchu hus s of Sam amos os (3rd cent. BC)
• Prop Proposed osed heli heliocen ocentri tric c uni univers verse e •
(`Copernicus of Antiquity’)
Origi Ori gina nall book book lost lost,, the theor ory y only only sur surviv vived ed bec becau ause se Arch Archim imede edes s ment mention ions s it! it!
“But Arista Aristarchus rchus broug brought ht out a book…His book…His hypothe hypotheses ses are that the fixed stars and the Sun remain unmoved, that the Earth revolves about the Sun in a circle, the Sun lying in the middle of the orbit, and that the sphere of the fixed stars… Is so great…” (Archimedes, The Sand-Reckoner )
• Grea Greatt distanc distance e to fixed fixed stars stars explai explains ns why we don’t don’t see stellar parallax!
Reminder: How do we know that Earth moves?
• Not observ observed ed (too (too small) small) until until 1838 1838 (Bessel (Bessel)! )!
The Great Library in Alexandria
Aristarchus: Size of the Solar System
• Siz Size e and and dist distance ance of the Moo Moon: n:
Dmoon~1/4 x DEarth
240,000 miles
Aristarchus: Size of the Solar System
• Dis Distan tance ce to the the Sun (`Ast (`Astron ronomic omical al Unit’) Unit’)::
DEarth-Sun~19 x DEarth-Moon (Today: DEarth-Sun~400 x DEarth-Moon
7 million km 150 million km)
But: Dominance and Persistence of Mainstream Model
• Pto Ptolem lemaic aic-Ari -Aristo stoteli telian an universe universe completel completely y dominated astronomical thought for 14 centuries (till Renaissance/Copernicus) • Why was was this this (wrong (wrong)) system system so so long-liv long-lived? ed? - intr intricat icate e connection connection to Aristo Aristotelia telian n philosophy philosophy - it was ver very y success successful ful in expla explaining ining data data - durin during g Middle Middle Ages Ages adopted adopted by Catho Catholic lic Church Church as dogma (see trial of Galileo)
• Corr Correct ect ideas ideas of of Arista Aristarchu rchus s and atomi atomists sts had to be painfully recovered in Renaissance!
