“The Structure of Scientific
Revolutions” 1962
An overall model of a particular problem on
which a number of theories are based.
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“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.”
1. Kuhn’s History of Science
Descriptive Project:
Immature Science
Revolution
Normal Science
Crisis
Anomalies
old paradigm
unexplained observations
puzzle solving
competing new
paradigms
one dominant paradigm
Mopping up operation
unsolved puzzles ignored
unexplained observations and
alternative interpretation ignored
until enough accumulates to overturn
current paradigm
unexplained observations
1. Kuhn’s History of Science
Immature Science:
No prevailing school of thought
Various disparate theories
Competition
1.
2.
3.
4.
5.
6.
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.
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GREAT PARADIGM SHIFTS IN SCIENCE
1. Geocentrism → Heliocentrism
2. Two sets of laws of nature (earth and heavens) → One
set of universal laws of nature
3. Young earth/catastrophism → Old
earth/uniformitarianism
4. Alchemy → Atomic theory
5. Fixity of species → Evolution of species
6. Immature science (no paradigm) → Germ Theory
7. Atomic theory → Subatomic particles
8. Classical mechanics → Quantum mechanics
9. Classical Mechanics → Relativity
10. Static Earth → Continental Drift Theory
11. Uniformitarianism → Catastrophism (a mixed
paradigm)
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.”
Two Separate Sets of Laws in the Universe: The Earth and the Heavens
→
Universal Laws of Nature
1.
2.
3.
4.
Planetary Motion: elliptical motion (Kepler)
Newton
A mathematician, not a scientist, per se.
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.
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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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.”
“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
Principles of Geology
Elements of Geology
“The present is the key to the past.”
1.
2.
3.
4.
5.
6.
Sedimentary layers and fossil evidence
James Hutton
Hutton was a farmer and definitely not trained as a scientist. He
was an observer but not an experimenter
The earth is old… very old. (no vestige of a beginning…)
Hutton fell short here. His book was not well written or widely
read, so we must mention Lyell as the one whose stubbornness and
courage won the day for uniformitarianism.
In the 19th century evidence of areas such as Scandanavia actually
rising out of the Baltic Sea was revealed, along with evidence for
ice ages and so forth.
Old Earth/Uniformitarianism → Still Old Earth/Catastrophism
(actually a mixed paradigm)
1. a. The Cambrian Explosion. (530 MYA). All five animal phyla
appeared in 10 ± 10 million years. Sudden appearance of
extremely complex live forms with no obvious precursor.
b. Mass Extinction events.
• 240 MYA 90-95% 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.
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. 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.
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.
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
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.
When blue light is shone on the emitter plate,
a current flows in the circuit
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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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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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Light consists of particles,
now known as photons
A photon hitting the emitter
plate will eject an electron
if 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!
Electrons behave like waves!
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Determines the probability of an electron
arriving at a
certain spot on the screen
After many electrons,
resembles the interference pattern of light
Electron interference pattern after (a) 8 electrons, (b) 270 electrons, (c) 2000
electrons, and (d) 6000 electrons
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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
Classical Mechanics → Relativity
According to Classical Mechanics:
Things which are absolute
Things which are relative
(independent of motion)
(depend on motion)
mass, time, length
According to Relativity:
Speed of light
speed of object, 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.