Two Scientific Theories Both the theories of Ptolemy and Copernicus actually fit the available evidence- what are you going to do? Hey, who cares who is.

Two Scientific TheoriesBoth the theories of Ptolemy and

Copernicus actually fit the available evidence- what are you going to do?

Hey, who cares who is right, at leastwe are incolor!

Image source: Wikipedia. Image source: Wikipedia.

What is a scientific theory?

Scientific hypotheses – a tentative explanation that accounts for a set of facts and can be tested by further investigation.

Scientific theory – Systematic sets of concepts that provide explanations for observing patterns in nature. Theories provide frameworks for relating data & guiding future research. Theories change as new data become available.

What makes a good scientific theory?

A good scientific theory:

1) Has logical consistency - parts of it don’t contradict other parts

2) Agrees with the data3) Suggests verifiable causes that explain and predict 4) Advanced comparisons (simplicity, tradeoff of

generality and specificity, distinction between non-fatal difficulties and fatal difficulties)

Occam's RazorNamed after the English philosopher, William of

Occam (1300s).

Two or more models accurately explain the observations? No Problem!!!

Best model is the simplest one fewest assumptions/modification needed to fit the observations.

1285-1349(died in the BlackDeath)

a.k.a the Principle of ParsimonyI’m the original

KISS guy - “Keep It Simple, Stupid”

Image source: University of St Andrews, Scotland.

Ptolemy vs. CopernicusSo, what theory is most acceptable?

Occam says Copernicus

Won’t really know until Galileo

We have a winner!

Image source: University of St Andrews, Scotland.

CopernicusThere were scientific objections problems with a

Heliocentric solar system:

1) A moving Earth violated common sense:

-Why didn't objects fly off the spinning Earth?

-Why don’t flying objects get left behind?

2) If the Earth is moving, why don’t stars also move (parallax effect)? Answer: They are really, really, really far away (but this wasn’t known)

Ptolemy vs. CopernicusSo, what happened?There was always that nagging voice from

the right-hand side of the powerpoint.

So, astronomers basically accepted the Copernicus idea the basis for calculation (at which it worked), but did not accept it as a reality of movement.

Sure is alot simplerand pretty accurate.

Galileo Galilei (1564 – 1642)

I’m not feeling verycomfortable in thishighly starched shirt.

The resolution was provided by Galileo, using new technology.

Image from Wikimedia Commons

Ye olde telescope(a refractor, for those in the know)

Image source: Wikipedia, courtesy of Michael Dunn.

Image source: Stephanie Smith, Space Telescope Science Institute.

New technology allowed two new observations

1) The moons of Jupiter

2) The phases of Venus

The Ptolemaic system and the Copernican system madedifferent predictions abound the shadows on Venus.

Geocentrism Heliocentrism

Back to HeliocentrismNew technology (telescope) allowed Galileo to make

observations that are consistent with Heliocentrism and not with an Geocentrism.

Result is the Heliocentrism is adopted by scientific community.

Vindicated!(but happilyvery dead)

Image source: Wikipedia.

And, thus begins the first chapter of

science vs. religion I belong to the medievaltradition of authority matteringthe most. The text (Bible and,to a lesser degree, Aristotle).

I am developing a new tradition of trusting observation and reason.* (following from the ancient Greeks and the Renaissance) Image from Wikimedia Commons

Image from Wikipedia.

A solution was found

Galileo wrote a book, Dialogue Concerning the Two Chief World Systems, was published in 1632, with formal authorization from

the Inquisition and papal permission.

And, the Pope’s own views (Aristotelian Geocentric view)

on the matter had to be included in Galileo's book.

Mo Curly Larry Dumber Dumbest Dumb

The Three Stooges

Salviati, Simplicio, and Sagredo:That’s what I’ll call them. Heh, heh.

Meet the Three Characters in Dialogue Concerning the Two Chief World Systems

Image from Wikimedia Commons

Image from Wikimedia Commons

The problem with literary license: It isnot what you say, but how you say it

Salviati: I greatly doubt that Aristotle ever tested by experiment whether it be true that two stones, one weighing ten times as much as the other, if allowed to fall, at the same instant, from a height of, say, 100 cubits, would so differ in speed that when the heavier had reached the ground, the other would not have fallen more than 10 cubits.

Simplicio: His language would seem to indicate that he had tried the experiment, because he says: We see the heavier; now the word see shows he had made the experiment.(My note: Simplicio is defending by an appealto authority, not a refutation of evidence).

Sagredo: But I, Simplicio, who have made the test, can assure you that a cannon ball weighing one or two hundred pounds, or even more, will not reach the ground by as much as a span ahead of a musket ball weighing only half a pound, provided both are dropped from a height of 200 cubits.

Image from Wikimedia Commons

The problem was that Pope Urban VIII

sounded a lot like Simplicio

This did not make the pope happy.

Image from Wikipedia.

Galileo had made a big mistake.

Do not anger the authorities.

Galileo maintained that hewas surprised by the criticism.

Just because the church hasn’t likedthe idea for 200 years….besides, why can’t a guy have a little fun.

Image from Wikimedia Commons

Image from Wikipedia.

The Problem = The Inquisition

The Inquisition was a permanent institution in the Catholic Church charged with the eradication of heresies.

It turns out, that in 16th century Italy, the Copernican proposition that the Sun is the center of the universe was a heresy. It was a heresy because it was interpreted to disagree with some biblical passages.

No one expects theSpanish Inquisition!Whoops, make that theRoman Inquisition!

Image from Wikipedia.

hmmmm…..maybe I just should have sold the telescope-thing on eBay

Galileo and the InquisitionImage source: Wikipedia.

Galileo lost. In fact, he never had a chance.He was put under house arrest until his death

in 1642.But, it is there that he did arguable most

important work by writing up his previous work and developed a whole other “way of knowing” : Experimentation

Forget experimentation, I’m still thinking abouteBay.

Image source: Wikipedia.

The list of the whole narrative:

1) Aristotle proposes theory

2) Ptolemy finds data to contrary (doesn't fit with theory)

3) Ptolemy has two choices. a: propose new theory or b: modify old theory to fit new data (which he decides to do)

4) Copernicus comes up with new theory (heliocentrism) using exactly the same data as Ptolemy. The model is simpler and explains the data just as well.

5) Using Occam’s razor (the best solution is the simplest), Copernicus’ model is superior. The idea is resisted because of social concerns and pre-conceived assumptions. Yet, the model is used because of its predictive power, but not adopted as reality.

6) New technology (telescope) allows Galileo to make observation (phass of Venus, Moons of Jupiter) that are consistent with Heliocentrism and not with an Earth-centered Universe.

7) Heliocentrism is adopted by scientists and, eventually, by everyone else.

Did Copernicus know how big a deal this was?

Yes.

Knew about planetary motion by 1508. He did not, however, publish his book “De revolutionibus” until 1543, the year he died (and thus avoided problems).

My mommaraised nofool.

Image source: Wikipedia.

Natural History

The entire narrative occurs uses one “way of knowing”: Natural History.

All anyone is doing is observing the world around them.

Scientific individuals (there weren’t really scientists yet) lived with the inherent uncertainty and lack of proof of

Copernicus’ model. However, technology (or a breakthrough in another field - optics, in this case) was

applied and resolved the issue.

The points of this part of the course (Heliocentrism):

• How to reason scientifically

• How to use evidence to make scientific theories

• Scientists may disagree, even if the evidence they use is the same

• Scientific hypotheses, theories, and laws can be based on observations of natural systems

• New technology can be required to resolve controversy

But, before Galileo arrives on the scene, we still need to deal with the dynamic duo of astronomical observation: Tycho Brahe & Johannes Kepler

Image source: Wikipedia. Image source: Wikipedia.

Observatory of Uraniborg

Brahe was given an observatory by the King of Denmark & a lot of money to run it. The equipment included a large brass quadrant for making very accurate observations of planets & stars.

He made accurate measurements continuously for 20 years.

Ima

ge

sou

rce

: Wik

iped

ia.

On his deathbed, Brahe gives all his data to Kepler, who he had only known for about three weeks. Brahe recognized that Kepler was very good at math.

But I have terrible eyesight – not a great occupational choice.

Image source: Wikipedia. Image source: Wikipedia.

Kepler has several disadvantages:1)He has bad eyesight.2)He was German during the 30 Years War.3)He was a devout, but not mainstream, Lutheran often working for a Catholic king/duke.4)He had a knack for being in the wrong place at the wrong time.5)He was not independently wealthy.6)He had to work on astrology (yes, fortune telling) to keep the dukes and kings who employed him happy. (Note: Neither Kepler nor Brahe are really scientists in the modern sense).

…and, yet, he comes up with three scientific laws based on Brahe’s data.

What is a scientific LAW?

• A law is developed when many observations or measurements point to a regular, predictable pattern of behavior in nature

What is a scientific THEORY?

• A well-substantiated, explanatory description of the world that is based on a large number of independently verified observational and/or experimental tests

In Summary:

• A scientific law attempts to describe an observation in nature

• Whereas a scientific theory attempts to explain it

• A scientific hypothesis is an educated guess

Kepler’s first law: The orbit of every planet I an ellipse (not a circle) with the sun at a focus.

Kepler’s second law: A line joining a planet and the sun sweeps out equal areas during equal intervals of time. The implication is that planets move faster as they closer to the sun in their orbits.

Kepler’s third law: The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. In other words, planets more distant from the sun have longer orbital periods (years) than close planets.

Two important points: 1) These statements are laws because they describe the regular and predictable behavior in planets. Notice that there is no explanation why these relationships exist – the statements is just that they do exist.2) All of these were determined by natural observation.

A final note on scientific laws and scientific theories

A law describes and a theory explains. A law never “graduates” into a theory, or vice versa.

A theory is much more interesting than a law. Laws are generally less contested.

The Earth: Radius & Seasons

Image source: Wikipedia.

Why do we have seasons?

Observations (provided by class):

1.In Madison, the day length differs from long (June 21) to short (December 21)

1.The southern hemisphere has summer when the northern hemispere has winter, and vice versa

Why do we have seasons?

The Earth has a 23.5º tilt. What are the implications?

Image source: NOAA.

The Earth: Radius & Seasons

Image source: Wave3 Blog, courtesy of Bjarne Siewertsen/Danish Meteorological Institute