Philosophical Issues of Computer Science Historical and philosophical analysis of science Instructor: Viola Schiaffonati March, 17 th 2016
Science: what about the history? 2 Scientific Revolution (1550-1700) as a paradigmatic case Astronomic revolution From astronomy to physics Scientific method
Ancient Greek astronomy 3 Two-sphere universe (mainstream from IV BC) Earth-centered (geocentric) Planetary motion: in circles
Aristotle s universe 4 Earth is in center Planets, including Sun, move around earth, affixed to crystal spheres (55) Universe is finite, has edge Two distinct regions of the cosmos: The Heavens (supralunar) perfect, no change, circular motions Terrestrial (sublunar) change, non-circular motions
The philosophy behind it 5 A coherent framework of all of nature Astronomical concepts tied up with terrestrial physics (theory of motion) Theory of gravity depends on Earth being in center of the universe Finite universe, bounded by spherical edge There cannot exist a vacuum (plenum theory) Cosmos is eternal, guaranteed by spherical motion
The problem of planets motion 6 Retrograde motion of planets, opposite direction to daily motion (E-W) of celestial sphere Deferent/epicycle solution (III-II cent. BC) Circles within circles Designed to precisely explain planetary motions (to save phenomena), but also to be in accordance with the accepted philosophy
The Ptolemaic system (II cent. AD) 7 Aristotelian but dominated by mathematical precision Circles within circles (deferent/epicycle) Designed to precisely explain planetary motions Proliferating complexity but it never quite worked It remained patchwork and more and more complicated (Copernicus monster)
Why so successful? 8 Ptolemaic-Aristotelian universe completely dominated astronomical thought for 14 centuries (till Renaissance/Copernicus) Why was this (wrong) system so long-lived? Intricate connection to Aristotelian philosophy Very successful in explaining data During Middle Ages adopted by Catholic Church as dogma (see trial of Galileo) Correct ideas of Aristarchus and atomists had to be painfully recovered in Renaissance!
Copernicus De Revolutionibus Orbium Coelestium 9 On the Revolution of the Heavenly Spheres (1543): a work outlining an alternative picture of the universe First detailed theory in which the earth moves around the sun instead of vice versa (heliostaticism) De Revolutionibus: not a revolutionary book, but a revolution-making one!
Copernican system 10 Earth has two motions Revolving on its axis once a day Orbiting the sun once a year Heavenly motions still circular Most orbits as complex compounds of circles (not single circles) Ptolemy s and Copernicus systems about equally complicated Some phenomena (planets motion) better explained by Copernicus theory (at least in qualitative terms) Slow, but inexorable ascendancy of Copernican system Provides starting point for New Astronomy (Kepler ) Some advantages in (Neoplatonic) elegance
Intellectual climate 11 Humanism: anti-aristotelian strain (rediscovery of Platon) Neoplatonism Search for underlying (mathematical) structure of reality Mathematical harmony Reformation: restoration of lost (pure) original state of the Church Voyages of discoveries: new spirit of discovery Invention of the press: rapid dissemination of knowledge
Kepler s Astronomia Nova (1609) 12 Copernicanism combined with obsession in finding mathematical harmony in the structure of the heavens Elliptical orbits (three laws of motion planets) Massive simplification and better predictive accuracy Mathematical tools to prove the superiority of the Copernican system
Galilei s Sidereus Nuncius (1609-10) 13 Use of the telescope to observe the heavens (not invented but improved by him) Observation of a multitude of phenomena contradicting Aristotle s view of the world (supralunar and sublunar distinction) Need to have a new science to solve definitively some astronomic problems (e.g. planets motion) From Aristotle s theory of natural motions (centrality of the notion of purpose) to modern science!
Galilei s Dialogo sopra i due massimi sistemi 14 Combination of mathematics and experiment to begin the formulation of a new science of motion New science making sense of the idea of a moving earth and explaining familiar facts about dropped and thrown objects Combination of empiricism and mathematical methods Sensate esperienze and certe dimostrazioni Galileo forced to recant his Copernican beliefs by Inquisition spending his last years under arrest
Newton s Principia (1687) 15 Unified mathematical treatment of motion both on earth and on heavens Newton showed why Kepler s elliptical orbits were the inevitable outcome of the force of gravity operating between heavenly bodies Combination of Copernicanism and a form of mechanicism (world made up of tiny corpuscles of matter interacting only by local physical contact) Newton s physics as the combination of the mechanical worldview and of a post-mechanical view Some forces (gravity most importantly) are posited and not interpretable in mechanical terms
Three answers 16 How does science work? Three answers, or pieces of an answer Rivals, alternative starting points, or paths into the problem Empiricism Mathematics and science Social structure and science
Empiricism 17 Empiricism: the only source of real knowledge about the world is experience Empiricism and science: the only source of real knowledge about the world is experience, but science is especially successful because is organized, systematic, and especially responsive to experience Problem: direct empirical tests are no guarantee of success (see history of science) Role of experience more fundamental than that of reasoning in making sense of what we observe
Mathematics and science 18 What makes science different from other kinds of investigation, and especially successful, is its attempt to understand the natural world using mathematical tools Peculiarity of science as an attempt to quantify phenomena and detect mathematical patterns in the flow of events Alternative view to empiricism or view that can be combined with it (see Galileo Galilei: sensate esperienze and certe dimostrazioni) Are we really sure that all of science makes use of mathematics to understand the world (Darwin s On the Origin of the Species)?
Social structure and science 19 What makes science different from other kinds of investigation, and especially successful, is its unique social structure Elaborate networks of cooperation and trust Balance of cooperation and competition A great deal of what went on in the Scientific Revolution had to do with working out new ways of policing, controlling, and coordinating the actions of groups of people in the activity of research
Some important consequences 20 End of the separation between theory and practice Episteme and techne (from Greek conception) Virtuous relationship between the invention of new (microscope) or better (telescope) instruments and the progression of sciences (optics) Technical knowledge is precise (as theoretical knowledge) and guided by precise theoretical principles and laws Increasing importance of applicative and engineering sciences within society Engineering scientists
References 21 Godfrey-Smith, Peter (2003), Theory and Reality. An Introduction to the Philosophy of Science, Chicago University Press Kuhn, Thomas (1957), The Copernican Revolution: Planetary Astronomy in the Development of Western Thought, Harvard University Press Westfall, Richard (1971), The Construction of Modern Science: Mechanisms and Mechanics, John Wiley & Sons Inc.