Thomas Kuhn 1922-1994

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Thomas Kuhn 1922-1994

• The Structure of Scientific Revolutions 1962

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PARADIGM

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

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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.

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Kuhn (1)

• 1. Kuhns History of Science
• Descriptive Project

Immature Science
Revolution
Normal Science
Crisis
Anomalies
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Paradigm Diagram

• old paradigm unexplained observations
  competing new

paradigms
incommensurate
one dominant paradigm
puzzle solving
Mopping up operation
unsolved puzzles ignored
unexplained observations
unexplained observations and alternative
interpretation ignored until enough accumulates
to overturn current paradigm
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Kuhn (1)

• 1. Kuhns History of Science
• Immature Science
• No prevailing school of thought
• Various disparate theories
• Competition

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REQUIREMENTS FOR A CHANGE IN PARADIGM

1. A significant body of evidence arises which the
   old paradigm cannot explain.
2. A young scientist on the fringe of science.
3. A theoretician (usually).
4. A shot in the dark.
5. Courage, stubbornness, patience, communication
   skills, etc.
6. A dramatic predicted consequence that the old
   paradigm could not have made which proves true.

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• 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

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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.
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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.
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Young Earth/Catastrophism?Old Earth/Uniformitarian
ism

• 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..

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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.

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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

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Charles Lyell

• Principles of Geology
• Elements of Geology
• The present is the key to the past.

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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.
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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?
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• 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.

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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
props.
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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)
? h/mv
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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.
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Photoelectric Effect
When blue light is shone on the emitter plate,a
current flows in the circuit
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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

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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

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Einsteins 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 Plancks formula)

Albert Einstein won a Nobel Prize for his work
on the photoelectric effect and not his theory
of relativity!
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Double-Slit Experimentto illustrate wave nature
of light
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Double-Slit Experiment with electron gun
Electrons behave like waves!
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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
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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

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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.