p160 kuhn classroom lecture 2

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• Crisis (questioning the paradigm)• Factors for choosing between paradigms• Subjectivity of paradigm shift



PARADIGMPARADIGM

PARADIGMPARADIGM• Ideas about what kind of stuff• Ideas about what kinds of behaviors• Ideas about what kind of stuff• Ideas about what kinds of behaviors


PARADIGMPARADIGM

• Methodology• Interesting questions (puzzles)• What counts as a good explanation

• Methodology• Interesting questions (puzzles)• What counts as a good explanation

• Ideas about what kind of stuff• Ideas about what kinds of behaviors• Ideas about what kind of stuff• Ideas about what kinds of behaviors


If paradigm is right, these puzzles have solutions … but we

can’t find them!

If paradigm is right, these puzzles have solutions … but we

can’t find them!PHIL 160PHIL 160PHIL 160PHIL 160

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• Proliferation of different adjustments to the paradigm• Erosion of agreement about fundamentals• Suspicion that paradigm is fatally flawed

• Proliferation of different adjustments to the paradigm• Erosion of agreement about fundamentals• Suspicion that paradigm is fatally flawed


shared assumptio

ns

shared assumptio

ns different assumptio

ns

different assumptio

ns

How to keep doing science?How to keep

doing science?


How well does each paradigm do with:

How well does each paradigm do with:

• Resistant puzzles?• Solved puzzles?• New puzzles?

• Resistant puzzles?• Solved puzzles?• New puzzles?


• Fit with paradigms in nearby fields?

• Fit with paradigms in nearby fields?

How well does each paradigm:How well does each paradigm:



• Fit with your aesthetic sense (or with the way

the world “feels” to you)?

• Fit with your aesthetic sense (or with the way

the world “feels” to you)?

• Fit with your observations of the

phenomena?

• Fit with your observations of the

phenomena?



• Competing paradigms of planetary motion

(Ptolemaic vs. Copernican)

• Competing paradigms of planetary motion

(Ptolemaic vs. Copernican)


Another historical example:Another historical example:


1. Sun’s yearly movement against the background of the zodiac constellations (one full circuit/year).

(Includes positions of sunrises and sunsets, positions of noontime sun on solstices and equinoces.)

Utterly commonsense assumption: the Earth isn’t moving.


whole celestial sphere rotates once per day.whole celestial sphere rotates once per day.


whole celestial sphere rotates once per day.whole celestial sphere rotates once per day.

Sun travels along ecliptic approx 1o per day (full circuit once per year)

Sun travels along ecliptic approx 1o per day (full circuit once per year)


2. Planets’ movement against the background of fixed stars.

(Different rates for different planets.)

Very convenient fact: Each of the planets travels roughly along the belt of zodiac constellations (the ecliptic).

Can use 2-dimensional model (the plane the ecliptic cuts through the celestial sphere)


Earth at center. (“Geocentric” system)

Sun and planets orbiting Earth on circular orbits of various sizes.


3. Mars, Jupiter, and Saturn have a “retrograde” (backwards) motion at various points in their movement against the background of the zodiac constellations.


4. Mercury and Venus always stay within a certain maximum angular distance of the Sun.

These behaviors of “inner planets” (Mercury and Venus) and “outer planets” (Mars, Jupiter, and Saturn) require modifications to plain circular orbits around Earth.


Planets travel on little circles (epicycles) …





… which go around Earth on deferent (big) circles)







Retrograde motion observed when planet is on inside of its epicycle.Retrograde motion observed when planet is on inside of its epicycle.


SUN

CMARS

EARTH


Inner planets stay within a certain maximum angular distance of the Sun.

Important feature of Ptolemy’s model:Center of a planet’s epicycle stays lined up with the Sun on its orbit of the Earth.


SUN

EARTHVENUS

C


Explains retrograde motion of outer planets.

Explains maximum angular distance of inner planets from Sun.

But:Some portions of planets’ orbits are faster, others are slower.

Planetary orbits are not perfectly circular.


Shift Earth slightly from center of orbit. Shift Earth slightly from center of orbit.

Eccentric modelEccentric model


Equant modelEquant modelShift planet’s center of motion from center of orbitShift planet’s center of motion from center of orbit

P sweeps out equal angles in equal times.(Slower on top of circle, faster on bottom)P sweeps out equal angles in equal times.(Slower on top of circle, faster on bottom)


EARTH

MARS

C


What was a clean system is now pretty complicated.

Hard to use to make predictions, calculations.

(No longer strictly geocentric.)

Unsolved puzzles:No explanation for sizes of epicycles and deferent circles.

No explanation for why epicycles of inner planets orbitEarth at same rate as Sun and stay lined up with Sun.


Put Sun at center of the system

Earth and planets on circular orbits around the sun.

Drop the epicycles!


SUN

C

EARTH

MARS


SUN

EARTH

VENUS


Copernicus explicitly argued that his system was geometrically equivalent to Ptolemy’s.

(Predict the same planetary motions from a less complicated model.)


SUN

CMARS

EARTH


SUN

C

EARTH

MARS


SUN

EARTHVENUS

C


SUN

EARTH

VENUS


How do the Ptolemaic and Copernican paradigms fit with paradigms in nearby fields?

Aristotelian Physics (grounded in 4-element theory of matter):

“Everything goes to its natural place.”

Heavy elements (like water and earth) go toward center of universe, light elements away from center.


Christian theology:

Earth at center of creation;

Earth as unique (not just another planet).


Fit with observations: TIE

Fit with observations: TIE

(Make identical predictions)

(Make identical predictions)


Solving/dissolving unsolved puzzles:

COPERNICUS

Solving/dissolving unsolved puzzles:

COPERNICUS(Don’t have to explain

alignment of epicycles if there are no epicycles)

(Don’t have to explain alignment of epicycles if there

are no epicycles)


Fit with other theories:• Physics: PTOLEMY• Theology: PTOLEMY

Fit with other theories:• Physics: PTOLEMY• Theology: PTOLEMY(No astronomer is an island)(No astronomer is an island)


Aesthetics (simplicity):

COPERNICUS

Aesthetics (simplicity):

COPERNICUS(All those epicycles

make things confusing)(All those epicycles

make things confusing)


Split decision: who wins?

Split decision: who wins?

(Which factors are most important for the

choice?)

(Which factors are most important for the

choice?)


Relative importance of:

Relative importance of:•Unsolved puzzles?

•Solved puzzles?•Fit with data?•Puzzle-solving power?

•Unsolved puzzles?•Solved puzzles?•Fit with data?•Puzzle-solving power?

Answers depend on which paradigm you’re

in!

Answers depend on which paradigm you’re

in!


What we observe is

paradigm dependent!What we observe is

paradigm dependent!

(So, how is a paradigm shift progress?)

(So, how is a paradigm shift progress?)

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p160 kuhn classroom lecture 2

Education

copernican phil

resistant puzzles phil

normal science crisis

kinds of behaviors phil

paradigm ideas

paradigm factors

paradigm comparison

planets travel