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Thomas Kuhn 1922-1994

Thomas Kuhn 1922-1994. “The Structure of Scientific Revolutions” 1962. PARADIGM. An overall model of a particular problem on which a number of theories are based. Max Planck.

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Thomas Kuhn 1922-1994

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  1. Thomas Kuhn 1922-1994 “The Structure of Scientific Revolutions” 1962

  2. PARADIGM An overall model of a particular problem on which a number of theories are based.

  3. Max Planck • “A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.”

  4. Kuhn (1) 1. Kuhn’s History of Science Descriptive Project: Immature Science Revolution Normal Science Crisis Anomalies

  5. Paradigm Diagram old paradigm unexplained observations competing new paradigms incommensurate puzzle solving one dominant paradigm Mopping up operation unsolved puzzles ignored unexplained observations unexplained observations and alternative interpretation ignored until enough accumulates to overturn current paradigm

  6. Kuhn (1) 1. Kuhn’s History of Science Immature Science: No prevailing school of thought Various disparate theories Competition

  7. REQUIREMENTS FOR A CHANGE IN PARADIGM • A significant body of evidence arises which the old paradigm cannot explain. • A young scientist on the fringe of science. • A theoretician (usually). • A shot in the dark. • Courage, stubbornness, patience, communication skills, etc. • A dramatic predicted consequence that the old paradigm could not have made which proves true.

  8. GREAT PARADIGM SHIFTS IN SCIENCE • 1. Geocentrism  Heliocentrism Copernicus (Galileo, Keppler) • 2. Two separate sets of laws of nature on earth and in the “heavens”  One set of universal laws of nature Newton • 3. Young earth/catastrophism  Old earth/uniformitarianism Hutton and Lyell • 4. Fixity of species  Evolution of species Darwin • 5. Undividable atoms  Subatomic particles (J J Thompson and others) • 6. Classical mechanics (waves vs particles)  Quantum mechanics (wave/particle duality)Einstein, Planck, Heisenberg, DeBroglie • 7. Fixed mass, time and length  Relativity Einstein • 8. Uniformitarianism  Catastrophism (actually a mixed paradigm) • 9. Static Earth → Continental Drift Theory • 10. ???? → Germ Theory Pasteur, Lister, Sammelweis, Snow, Holmes

  9. Example: Geocentrism → Heliocentrism 1. a. Lunar eclipses b. Changing brightnesses of planets c. Retrograde motion of planets (Ptolemy: cycles and epicycles) 2. Copernicus! 3. Trained as a mathematician, not as a scientist. 4. The earth moves. 5. Wrote: On the Revolution of Celestial Orbs. Published on his deathbed, with an apologetic preface. 6. Sun and other planets spin on axis. Planetary phases. Other moons? All observed by Galileo, who published “The Starry Messenger” And “Dialogue of the Two Chief World Systems.”

  10. Two Separate Sets of Laws in the Universe: The Earth and the Heavens → Universal Laws of Nature 1. Planetary Motion: elliptical motion (Kepler) 2. Newton 3. A mathematician, not a scientist, per se. 4. The reason the apple falls to the earth is the reason the moon goes around the earth. 5. Wrote “Principia.” 6. Space Travel Comets should come back.

  11. Young Earth/CatastrophismOld Earth/Uniformitarianism Young Earth/Catastrophism 1. The earth is only a few thousand years old. It was created pretty much as it is. 2. The physical features we can see on the earth are the result of the initial creation, plus catastrophic events (such as the flood). Old Earth/Uniformitarianism 1. The earth is very old: many millions of years at least. 2. The physical features on the earth are the result of very slow and gradual processes which can be observed today and which have occurred at essentially the same rate since creation..

  12. James Hutton • How old is the earth? “No vestige of a beginning, no concept of an end” • “The plant which is best adapted to the climate, and the soil, will continue to prosper in the place. But, the most prosperous plant must be that which will furnish, with its maturated seed, a vigorous race of fertile plants; and these will be the more and more accommodated, in the varying power of vegetation, to the soil and circumstances in which they grow.”

  13. WILLIAM SMITH “Each stratum contains fossils peculiar to itself” Cenozoic (new life) 65 mya to present Mesozoic (middle life) 250 mya to 65 mya Paleozoic (old life) 530 mya to 250 mya

  14. Charles Lyell Principles of Geology Elements of Geology “The present is the key to the past.”

  15. Old Earth/Uniformitarianism → Still Old Earth/Catastrophism (actually a mixed paradigm) 1. a. The Cambrian Explosion. (530 MYA). All five known body plans appeared in 10 ± 10 million years. Sudden appearance of extremely complex live forms with no obvious precursor. b. Mass Extinction events. • 240 MYA 90% of all known species disappeared. • 65 MYA 80% of all known species disappeared. (at same time as Chixlub asteroid and Iridium layers) 2. Alvarez (first major paper on Chixlub) 3. ? 4. A gigantic asteroid hit the earth in the distant past, killing off the dinosaurs etc. 5. The fight still goes on. 6. More catastrophic events will poke their heads up eventually if we look.

  16. Fixed Species → Evolution of Species 1. Fossil evidence. (note, this was not the principle evidence used by Darwin) . 2. Charles Darwin. 3. An exception to the rule? A brilliant and careful observer/naturalist. 4. The 14 species of finches on the Galopagos Islands “evolved” by natural selection/survival of the fittest from one original species of common finch which flew from South America. 5. Wrote “Origin of Species.” 6. The fossil record, with time and study, should fill in. Innumerable transitional fossils should be found. Q: has this proven to be true?

  17. ATOMIC THEORY • 1. The Law of Constant Composition (LaVoisier). • 2. John Dalton. • 3. A good theoretician… a questionable experimentalist. • 4. Atoms exist (even though I cannot see them) • 5. Not a huge issue. • 6. Table of atomic masses, gold cannot be made from another element, idea of a balanced chemical equation… • Bottom line, this is the fundamental theory of chemistry. • Atomic Theory: • 1. Elements are made up of identical atoms. • 2. The atoms of the elements are immutable (i.e. once a copper atom…) • 3. Compounds form when atoms combine in an integer ratio.

  18. Indivisible atoms (hard sphere model) → Subatomic Particles 1. The existence of ions (Arrhenius). Bonding and valence in general (ex: why is carbon tetravalent, why H2O not H3O?) 2. JJ Thompson (discovered the electron) Ernest Rutherford (discovered the atomic nucleus) 3. Both very young, both were theoreticians (and experimentalists) Thompson: the plumb pudding model. Rutherford: the nuclear model. 4. Democritus, Boyle and Dalton were wrong. Atoms are not the smallest particle. 5. 6. Explain ionic compounds, acids, bases, eventually all molecular prop’s.

  19. Classical Mechanics → Quantum Mechanics Classical Mechanics: Everything is either a wave (sound, light,…) or a particle (planet, atom, electron…). There is not overlap. Quantum Mechanics: Everything (including electrons and light) acts both like a wave and a particle. Q. M.: Wave/Particle duality Light: E = hf Particles (electron) λ = h/mv

  20. Classical Mechanics → Quantum Mechanics 1. a. Discrete Atomic Emission Spectra. b. Photoelectric Effect. c. Black Body Radiation. 2. Einstein (and Planck, Bohr, Schroedinger, DeBroglie, etc.) 3. Definitely a young scientist on the fringe!!!! (working in a patent office) 4. Interpret the photoelectric effect to imply that light is made of particles called photons. 5. It took more than 20 years for QM to be accepted. 6. a. the electron microscope. b. diffraction and interference of electrons.

  21. Photoelectric Effect When blue light is shone on the emitter plate,a current flows in the circuit

  22. Experimental Observations • Only light with a frequency greater than a certain threshold will produce a current • Current begins almost instantaneously, even for light of very low intensity • Current is proportional to the intensity of the incident light

  23. Problems with Wave Theory of Light • The wave theory of light is unable to explain these observations • For waves, energy depends on amplitude and not frequency • This implies that a current should be produced when say, high-intensity red light is used

  24. Einstein’s Explanation (1905) • Light consists of particles, now known as photons • A photon hitting the emitter plate will eject an electronif it has enough energy • Each photon has energy:E = hf(same as Planck’s formula) Albert Einstein won a Nobel Prize for his work on the photoelectric effect and not his theory of relativity!

  25. Double-Slit Experimentto illustrate wave nature of light

  26. Double-Slit Experiment with electron gun Electrons behave like waves!

  27. Interference Pattern of Electrons • Determines the probability of an electron arriving at acertain spot on the screen • After many electrons, resembles the inter-ference pattern of light Electron interference pattern after (a) 8 electrons, (b) 270 electrons, (c) 2000electrons, and (d) 6000 electrons

  28. Summary • Waves and particles exhibit very different behaviour • Yet, light sometimes behaves like particles • spectrum of blackbody radiation • photoelectric effect • And electrons sometimes behave like waves • interference pattern of electrons • In quantum theory, the distinction between waves and particles is blurred

  29. Classical Mechanics → Relativity According to Classical Mechanics: Things which are absolute Things which are relative (independent of motion) (depend on motion) mass, time, length speed of object, speed of light According to Relativity: Speed of light mass, time, length, Speed of object. 1. The Michelson/Morely experiment 2. Albert Einstein (this time by himself) 3. A theoretician, to say the least!! 4. Accept M & M, with all its implications. 5. patient, courageous, stubborn…. 6. light bent by very massive objects. Space is “warped” by massive objects.

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