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Lau ChongFuk 200809 First Term Lecture 7 Scientific Methodology and Its Objectivity The Birth of Modern Science The Birth of Modern Science
► Francis Bacon (15161626): English philosopher ► Induction as the Scientific Method Novum Organum (New Organ) Supposed to replace the method in Aristotle's Organon Starting with Sensible Experience Experimentation and Observation Generalization ► From Observations to Particular Laws ► Galileo Galilei (15641642) ► From Particular Laws to Universal Laws Logical Positivism ( ‰ M ‰ Łp “ Logical Positivism ( H“
► The Vienna Circle (1920s) ► AnalyticSynthetic Distinction (‰ H M ‰“ Ł ** p “ )
) The Ideal of Rigorous and Unified Science Analytic Proposition: ►Depends solely on the meaning of its terms ►E.g.: “All CU students are students.” ►Logic and Pure Mathematics Synthetic Proposition:
►Natural Sciences ►Depends also on the empirical world ►E.g.: “All CU students are clever.” Logical Positivism (Zp“ y ‰ Łł “ Logical Positivism (‰
► With or without Cognitive Meaning (�Ł �‰ p )
) )? The Criterion of Verifiability (�Ł p ‰ ► Reductionism/Foundationalism ( p � Cognitively meaningful statements are either analytic or those synthetic statements that are verifiable in principle, e.g., statements in Logic, Mathematics and Sciences. All other statements lack cognitive meaning, e.g., some statements in Metaphysics, Religion, Aesthetics. All scientific knowledge is based on logical inference from simple “atomic” or “protocol sentences” that describe observable facts. �/�p �Ł ‰ ) Popper’s Falsificationism Popper’s Falsificationism
► Karl Popper (190294), Austrian British Philosopher ► Falsificationism ( p Science consists of universal state ments like “all metals expand when heated.” Universal statements can never be fully verified. Experimental observations can support a scientific hypothesis, but never prove it. But, a scientific theory can be disproved or falsified by experimental findings. Falsifiability (�Ł �p ) is a criterion for science. ‰ Ł ‰) DuhemQuine’s Holism DuhemQuine’s Holism
► Pierre Duhem (18611916), French Physicist and Philosopher of Science ► W. V. O. Quine (19082000), American Philosopher ► Holism (‰ �� p �Ł ) When an observation is inconsistent with a theory, it is possible that the theory or some other assumptions are wrong. Therefore, it is neither possible to verify nor to falsify a scientific theory. “Our statements about the external world face the tribunal of sense experience not individually but only as a corporate body.” Kuhn’s Paradigm Shift Kuhn’s Paradigm Shift
► Thomas Kuhn (192296), American Historian and Philosopher of Science ► Paradigm Shift (�Ł ) p ‰ A scientific revolution occurs when an accepted paradigm cannot explain anomalies that are encountered so that a new paradigm is necessary. Examples of paradigm shifts in science include the transition from the geocentric to the Copernican heliocentric cosmology and the Newtonian physics to the Einsteinian Relativistic physics. According to Kuhn, different paradigms are incommensurable ( p Ł ‰ / p � �p ). / Scientific Methodology Scientific Methodology
► 1. 2. 3. 4.
► “Official Version” of Scientific Method: But the reality looks different: Observation: Gathering Data Induction: Formulating a General Hypothesis Deduction: Making Specific Prediction from Hypothesis Verification: Testing the Hypothesis by Experiments Observations are theoryladen. No pure observation! Conjectures and speculations are common. Mathematical models play a decisive role. Many other contingent factors contribute to the discovery of a scientific theory. Criteria of Adequacy Criteria of Adequacy
► 1. 2. 3. 4. 5. Criteria for a Good Scientific Theory
Testability Fruitfulness, or Predictability Scope, or Comprehensiveness Simplicity, or Economy Conservatism, or Consistency with Existing Theories T. Schick, Jr./L. Vaughn, How to Think about Weird Things: Critical Thinking for a New Age, 4th ed., New York: McGrawHill, 2005, chap. 7. Testability (I) Testability
► A renowned fortuneteller tells you the following things (after receiving $45,000)! You had a big trouble last year. Bigger trouble awaits you. But I can save you from it if you pay another $45,000 for a sacrificial rite. ► A scientific theory or hypothesis must be definite and precise in order to be testable. ► This is a minimal (or necessary) condition! Ł► p
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► “A hypothesis is scientific only if it is testable, that is, only if it predicts something more than what is predicted by the background theory alone.” ► An apple falls from the tree. Why?
► A scientific theory or hypothesis Testable Theory: Gravitation Untestable Theory: God did it! must be informative. Fruitfulness, or Predictability Fruitfulness, or Predictability
► “Other things being equal, the best hypothesis is the one that is the most fruitful, that is, makes the most successful novel predictions.” ► Example: Bended Light Newton’s Mechanics vs. Einstein’s Relativity Theory Scope, or Comprehensiveness Scope, or Comprehensiveness
► “Other things being equal, the best hypothesis is the one that has the greatest scope, that is, that explains and predicts successfully the most diverse phenomena.” ► Example: Kinetic Energy Newton’s Mechanics: Einstein’s Relativity Theory: 1
12 K E = mv 2 2 −2 v 1 3 m0v 4 5 m0v 6 K E = mc0 1 − 2 −1 = m0v 2 + + + ... 2 4 2 c 8c 16 c 1 K E ≈ m0v 2 for v ≪ c 2 Simplicity, or Economy Simplicity, or Economy
► “Other things being equal, the best hypothesis is the simplest one.” Which curve, H1 or H2, fits the data better? Why?
x x x x H
2 The line doesn’t fit the data, does it? x The Copernican Revolution The Copernican Revolution
► Ptolemy’s Geocentric theory ( Ł*“ ¤ F ) ‰ p ► Copernicus’s heliocentric theory (Ł“ ¤ F ) ‰ p * Copernicus’s theory is simpler! Conservatism, or Consistency with Conservatism, or Consistency with Existing Theories
► “Other things being equal, the best hypothesis is the one that is the most conservative, that is, the one that fits best with established beliefs.” ► Example: Uranus’ ( p �Ł � ) orbit and the Discovery of Neptune ( p �Ł ) � Rejecting Newton’s mechanics Or introducing a new planet? Remarks Remarks
► The Criteria are important, but they do not constitute the necessary conditions for a good scientific theory. ► There can be conflicts between the criteria A good theory doesn’t need to satisfy all the criteria. Simplicity vs. conservatism in the case of Copernican vs. Ptolemaic theory. Fruitfulness vs. conservatism in the case of classical vs. quantum mechanics. ► Choosing between theories is not a purely logical, calculative process. ...
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- Spring '08
- scientific theory, good scientific theory