Scientific Ways of Knowing

Raphael’s School of Athens Image from Wikimedia Commons

The scientific method

• State the problem

• Gather information about the problem

• Form a hypothesis

• Perform an experiment to test the hypothesis

• Record and analyze your data

• State a conclusion

Don’t scientists just always use the scientific method?

NO!

The problem is that it is pretty clear that there is not a single method that scientists use.

State the problemGather information about the problemForm a hypothesisPerform an experiment to test the hypothesisRecord and analyze your dataState a conclusionCommunicate your conclusions

Scientific Ways of KnowingInduction (or inductive logic) – Proceeding from

examples to general rules or principles

Induction leads to empirical approaches of understanding

Deduction (or deductive logic) – Using rules to understand examples

Deduction leads to theoretical approaches to understanding

Premise 1: Every horse is a mammal.

Premise 2: Every mammal has a heart.

Conclusion: Every horse has a heart.

Deductive Logic

Premise: Every horse that has ever been observed has a heart.

Conclusion: Every horse has a heart.

Inductive logic

Deduction

Given Model/Concept Expected Data

Induction

Inferred Model/Concept <- Actual Data

Deduction & Induction

Scientific Ways of Knowing

Raphael’s School of Athens Image from Wikimedia Commons

Scientific Ways of Knowing

Science’s intellectual underpinnings are philosophy.

Plato – Pointing upward, indicating that knowledge comes from pure thought, emphasizing theoretical models and a deductive approach.

Aristotle – Pointing down, indicating that knowledge comes from the world, emphasizing empirical data and an inductive approach

Image source: Wikipedia.

Francis Bacon (1561-1626)

In the 1500s, he introduced inductive logic in its modern form.

I started college at 12.

Widely attributed as the founder of British empiricism and the originator of the essay.

Image source: Wikimedia Commons.

Bacon did not do science himself. Rather, he put forward the idea of induction in his philosophical workNovum Organum.

He suggests that the success of science “all depends on keeping the eye steadily fixed on the facts of nature and so receiving their images simply as they are.”

Image source: Wikimedia Commons.

Scientific Ways of KnowingInduction -> Approach is observing (Empiricists)

1. Natural Observation – observation of natural system without manipulation

2. Experimentation – observation of natural system with manipulation

Deduction -> Approach is modeling (Theoreticians)1. Theoretical modeling –quantitative models designed to

make predictions of geometry or behavior of natural systems

Empirical Approach

Empirical approaches require that data is collected from the natural world.

Consequently, scientists are very careful about observations (something that everyone will agree on) versus inferences/interpretation (something based both on observations and an individual’s perspective).

Image removed due to copyright: Gary Larson “The Far Side” cartoon: Cavemen inside animal trap: “Shhhh, Zog!... Here come one now!! (copyright 1982) by FarWorks Inc.

Make five observations about this cartoon.

Image removed due to copyright: Gary Larson “The Far Side” cartoon: Cavemen inside animal trap: “Shhhh, Zog!... Here come one now!! (copyright 1982) by FarWorks Inc.

Make five inferences based on your observations of this cartoon.

Image removed due to copyright: Gary Larson “The Far Side” cartoon: Cavemen inside animal trap: “Shhhh, Zog!... Here come one now!! (copyright 1982) by FarWorks Inc.

Observation – Provide five observations

Inferences/Interpretations – Provide five inferences that correspond to the observations

How do we know the Earth is round?

All evidence is not equally good!

Scientific Ways of KnowingInduction -> Approach is observing (Empiricists)

1. Natural Observation – observation of natural system without manipulation

2. Experimentation – observation of natural system wit manipulation

Deduction -> Approach is modeling (Theoreticians)1. Theoretical modeling –quantitative models designed to

make predictions of geometry or behavior of natural systems

You can see a lot just by observing.

Yogi BerraImage source: Wikipedia.

Evidence = Relevant observations & interpretations

Of all discoveries and opinions, none may have exerted a greater effect on the human spirit than

the doctrine of Copernicus. The world had scarcely become known as round and complete in itself when it was asked to waive the tremendous privilege of being the center of the universe. Never, perhaps, was a greater demand made on mankind - for by this admission so many things vanished in mist and smoke! What became of our Eden, our world of innocence, piety and poetry; the testimony of the senses; the conviction of a

poetic - religious faith? No wonder his contemporaries did not wish to let all this go and offered every possible resistance to a

doctrine which in its converts authorized and demanded a freedom of view and greatness of

thought so far unknown, indeed not even dreamed of.

-J.W. Goethe

Ptolmey (85--165 C.E.), aka Claudius PtolemaeusLived and worked in Alexandria, Egypt

Ptolmey used natural observation to propose Geocentrism: The Earth is at the center of the

solar system, and the planets and the sun rotate around the Earth

For the record, Aristotle proposed this earlier.

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Image source: Wikipedia.

Nicolaus Copernicus (1473-1543 CE)De revolutionibus orbium coelestium libri vi “Six Books Concerning the Revolutions of the Heavenly Orbs” (1543 CE)

Copernicus used natural observation to propose Heliocentrism: The sun is at the center of the solar system, and the planets and the Earth

rotate around the Sun

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Geocentrism and Heliocentrism are both theories

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.

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

The colloquial use of “theory” is very different from a “scientific theory”: A everyday “theory” is a scientific hypothesis.

Geocentrism! Heliocentrism!

An anachronistic rock-em-sockem matchup.Who was right? Let’s look at the evidence!

What are the relevant observations that can be used as evidence for geocentrism

or heliocentrism?

1) The sun rises and sets every day

(each 24 hours)

2) The moon goes from fully illuminated to dark to fully illuminated every ~29 days.

Image removed due to copyright: 29 phases of the moon. Available through USNO.

3) Sun, Moon, and planets all move in a single plane in space,

called “the ecliptic”

Image source: NASA Clementine Project.

The sun and some planets on the ecliptic (red dashed line)

4) The Sun does not always cover the same stars in the sky. In fact,

we can divide the sky into 12 more-or-less equal parts that lie along the ecliptic. These are the

signs of the zodiacs.

It takes the sun ~365 days to make it through all the signs of the

zodiac.

Zodiac from500s (Israel)

360° panorama of the Zodiac

Image source: Wikipedia, courtesy of NASA.

Image source: Wikipedia; image credit 2005 Digital Sky LLC

5) Some planets (Mars, Jupiter, Saturn) all appear to have

retrograde motion. That means, they move general forward (east to west), but occasionally move

backward (west to east) for short periods of time.

One picture, per night, of Mars. The movement is judged by the background stars.

One last relevant observation

Image source: NASA, courtesy of Tunc Tezel.

Ptolemy’s solution: The epicycles

Planets are not attached directly to the concentric spheres themselves. Rather, planets are attached to smaller spheres (epicycles) which themselves are attached to the big, crystalline concentric spheres (deferents).

Copernicus’ solution

It is an optical illusion for planets that are further from the sun than we are.

Actually, retrograde motion is a necessary consequence of the orbits, a type of optical illusion, if you will.

http://www.astro.uiuc.edu/projects/data/Retrograde/

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Image source: NASA, courtesy of Tunc Tezel.

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 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.

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(refractor, for youastronomical weanies)

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.

The list of the whole narrative:

1) Aristotle proposes theory (Geocentrism)

2) Ptolemy finds data (retrograde motion) that 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.

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

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

7) Heliocentrism is adopted by scientists.

The scientific method

• State the problem

• Gather information about the problem

• Form a hypothesis

• Perform an experiment to test the hypothesis

• Record and analyze your data

• State a conclusion

Galileo

Copernicus

Scientific lawsOR

Scientific hypotheses, theories

Scientific law – generalizations of observational data that describe patterns or relationships. Law change as new data become available.

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 are the points of this example:

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.

Galileo Galilei (1564 – 1642)

I’m not feeling even lesscomfortable in thishighly starched shirt.

Others were less lucky (and more outspoken) than Copernicus.

Image from Wikimedia Commons

Galileo was subject to the Inquisition, because heliocentrism was a heresy.

He was put under house arrest until his death in 1642.

But, and this is big but, it is there that he did arguable most important work and developed a whole other “way of knowing” : Experimentation

More next time!

Forget experimentation,I’ll sell my telescope oneBay and make a quick buck.

Image source: Wikipedia.