Paradigm theoty by Thomas Kuhn

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

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

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

4. KuhnKuhn (1)(1)
1. Kuhn’s History of Science1. Kuhn’s History of Science
Descriptive Project:Descriptive Project:
Immature Science
Normal
Science
Anomalies
Crisis
Revolutio
n

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

6. KuhnKuhn (1)(1)
1. Kuhn’s History of Science1. Kuhn’s History of Science
Immature Science:Immature Science:
No prevailing school of thoughtNo prevailing school of thought
Various disparate theoriesVarious disparate theories
CompetitionCompetition

7. REQUIREMENTSREQUIREMENTS FORFOR A CHANGE IN PARADIGMA CHANGE IN PARADIGM
1.1. A significant body of evidence arisesA significant body of evidence arises
which the old paradigm cannot explain.which the old paradigm cannot explain.
2.2. A young scientist on the fringe ofA young scientist on the fringe of
science.science.
3.3. A theoretician (usually).A theoretician (usually).
4.4. A shot in the dark.A shot in the dark.
5.5. Courage, stubbornness, patience,Courage, stubbornness, patience,
communication skills, etc.communication skills, etc.
6.6. A dramatic predicted consequence thatA dramatic predicted consequence that
the old paradigm could not have madethe old paradigm could not have made
which proves true.which proves true.

8. • GREAT PARADIGM SHIFTS IN SCIENCEGREAT PARADIGM SHIFTS IN SCIENCE
• 1. Geocentrism1. Geocentrism →→ Heliocentrism Copernicus (Galileo, Keppler)Heliocentrism Copernicus (Galileo, Keppler)
• 2. Two separate sets of laws of nature on earth and in the2. Two separate sets of laws of nature on earth and in the
““heavens”heavens” →→ One set of universal laws of nature NewtonOne set of universal laws of nature Newton
• 3. Young earth/catastrophism3. Young earth/catastrophism →→ Old earth/uniformitarianismOld earth/uniformitarianism
Hutton and LyellHutton and Lyell
• 4. Fixity of species4. Fixity of species →→ Evolution of species DarwinEvolution of species Darwin
• 5. Undividable atoms5. Undividable atoms →→ Subatomic particles (J J Thompson andSubatomic particles (J J Thompson and
others)others)
• 6. Classical mechanics (waves vs particles)6. Classical mechanics (waves vs particles) →→ Quantum mechanicsQuantum mechanics
(wave/particle duality)Einstein, Planck, Heisenberg, DeBroglie(wave/particle duality)Einstein, Planck, Heisenberg, DeBroglie
• 7. Fixed mass, time and length7. Fixed mass, time and length →→ Relativity EinsteinRelativity Einstein
• 8. Uniformitarianism8. Uniformitarianism →→ Catastrophism (actually a mixedCatastrophism (actually a mixed
paradigm)paradigm)
• 9. Static Earth → Continental Drift Theory9. Static Earth → Continental Drift Theory
• 10. ???? → Germ Theory Pasteur, Lister, Sammelweis, Snow,10. ???? → Germ Theory Pasteur, Lister, Sammelweis, Snow,
HolmesHolmes

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/CatastrophismYoung Earth/Catastrophism→→Old Earth/UniformitarianismOld Earth/Uniformitarianism
Young Earth/CatastrophismYoung Earth/Catastrophism
1. The earth is only a few thousand years old. It was created1. The earth is only a few thousand years old. It was created
pretty much as it is.pretty much as it is.
2. The physical features we can see on the earth are the result2. The physical features we can see on the earth are the result
of the initial creation, plus catastrophic events (such as the flood).of the initial creation, plus catastrophic events (such as the flood).
Old Earth/UniformitarianismOld Earth/Uniformitarianism
1. The earth is very old: many millions of years at least.1. The earth is very old: many millions of years at least.
2. The physical features on the earth are the result of very2. The physical features on the earth are the result of very
slow and gradual processes which can be observed today andslow and gradual processes which can be observed today and
which have occurred at essentially the same rate since creation..which have occurred at essentially the same rate since creation..

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

14. WILLIAM SMITHWILLIAM SMITH
““Each stratum contains fossils peculiar toEach stratum contains fossils peculiar to
itself”itself”
Cenozoic (new life) 65 mya to presentCenozoic (new life) 65 mya to present
Mesozoic (middle life) 250 mya to 65Mesozoic (middle life) 250 mya to 65
myamya
Paleozoic (old life) 530 mya to 250 myaPaleozoic (old life) 530 mya to 250 mya

16. Charles LyellCharles Lyell
Principles of GeologyPrinciples of Geology
Elements of GeologyElements of Geology
““The present is the key to the past.”The present is the key to the past.”

17. Old Earth/ UniformitarianismOld Earth/ Uniformitarianism
1.1. Sedimentary layers and fossil evidenceSedimentary layers and fossil evidence
2.2. James HuttonJames Hutton
3.3. Hutton was a farmer and definitely not trained as a scientist. HeHutton was a farmer and definitely not trained as a scientist. He
was an observer but not an experimenterwas an observer but not an experimenter
4.4. The earth is old… very old. (no vestige of a beginning…)The earth is old… very old. (no vestige of a beginning…)
5.5. Hutton fell short here. His book was not well written or widely read,Hutton fell short here. His book was not well written or widely read,
so we must mention Lyell as the one whose stubbornness andso we must mention Lyell as the one whose stubbornness and
courage won the day for uniformitarianism.courage won the day for uniformitarianism.
6.6. In the 19In the 19thth
century evidence of areas such as Scandanavia actuallycentury evidence of areas such as Scandanavia actually
rising out of the Baltic Sea was revealed, along with evidence forrising out of the Baltic Sea was revealed, along with evidence for
ice ages and so forth.ice ages and so forth.

18. 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.

22. 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?

24. • ATOMIC THEORYATOMIC THEORY
• 1. The Law of Constant Composition (LaVoisier).1. The Law of Constant Composition (LaVoisier).
• 2. John Dalton.2. John Dalton.
• 3. A good theoretician… a questionable3. A good theoretician… a questionable
experimentalist.experimentalist.
• 4. Atoms exist (even though I cannot see them)4. Atoms exist (even though I cannot see them)
• 5. Not a huge issue.5. Not a huge issue.
• 6. Table of atomic masses, gold cannot be made from6. Table of atomic masses, gold cannot be made from
another element, idea of a balanced chemicalanother element, idea of a balanced chemical
equation…equation…
• Bottom line, this is the fundamental theory of chemistry.Bottom line, this is the fundamental theory of chemistry.
• Atomic Theory:Atomic Theory:
• 1. Elements are made up of identical atoms.1. Elements are made up of identical atoms.
• 2. The atoms of the elements are immutable (i.e. once2. The atoms of the elements are immutable (i.e. once
a copper atom…)a copper atom…)
• 3. Compounds form when atoms combine in an integer3. Compounds form when atoms combine in an integer
ratio.ratio.

25. 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

26. 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

27. 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.

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

29. Experimental ObservationsExperimental Observations
• Only light with a frequency greater than aOnly light with a frequency greater than a
certain threshold will produce a currentcertain threshold will produce a current
• Current begins almost instantaneously, evenCurrent begins almost instantaneously, even
for lightfor light
of very low intensityof very low intensity
• Current is proportional to the intensity of theCurrent is proportional to the intensity of the
incident lightincident light

30. Problems with Wave Theory ofProblems with Wave Theory of
LightLight
• The wave theory of light is unable to explainThe wave theory of light is unable to explain
these observationsthese observations
• For waves, energy depends on amplitude andFor waves, energy depends on amplitude and
not frequencynot frequency
• This implies that a current should beThis implies that a current should be
produced when say, high-intensity red light isproduced when say, high-intensity red light is
usedused

31. Einstein’s ExplanationEinstein’s Explanation
(1905)(1905)
• Light consists of particles,Light consists of particles,
now known asnow known as photonsphotons
• A photon hitting the emitterA photon hitting the emitter
plate will eject an electronplate will eject an electron
if it has enough energyif it has enough energy
• Each photon has energy:Each photon has energy:
Albert Einstein won a Nobel Prize for
his work on the photoelectric effect
and not his theory of relativity!

32. Double-Slit ExperimentDouble-Slit Experiment
to illustrate wave nature of lightto illustrate wave nature of light

33. Double-Slit ExperimentDouble-Slit Experiment
with electron gunwith electron gun
Electrons behave like waves!

34. Interference Pattern ofInterference Pattern of
ElectronsElectrons
• Determines the probability of an electron arrivingDetermines the probability of an electron arriving
at aat a
certain spot on the screencertain spot on the screen
• After many electrons,After many electrons,
resembles the inter-resembles the inter-
ference pattern of lightference pattern of light
Electron interference pattern after (a) 8 electrons, (b) 270 electrons, (c) 2000
electrons, and (d) 6000 electrons

35. SummarySummary
• Waves and particles exhibit very different behaviourWaves and particles exhibit very different behaviour
• Yet, light sometimes behaves like particlesYet, light sometimes behaves like particles
– spectrum of blackbody radiationspectrum of blackbody radiation
– photoelectric effectphotoelectric effect
• And electrons sometimes behave like wavesAnd electrons sometimes behave like waves
– interference pattern of electronsinterference pattern of electrons
• In quantum theory, the distinction between wavesIn quantum theory, the distinction between waves
and particles is blurredand particles is blurred

36. 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.