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PHY 156 – Spring 2009I.3 – Nature of Science

Science is the great antidote to the poison of … superstition.

Adam Smith, The Wealth of Nations, 1776

Goals: • Define “science”: What are its essential properties?

• Know how to apply science to get answers:

How does the process work?

• Know the language of science

Why is it so confusing?

• Distinguish science from non-science

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Doing Science• Hollow Earth Society: claims the Earth is a

hollow ball and we are living inside it

• Evidence:– Survey of Great Lakes around turn of 20th

century showed Earth’s surface as concave– The soles of your shoes curve up not down –

you’re walking on the INSIDE surface!

• How would you convince them?

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Which is more important in science: getting the correct answers, or the

process of finding and testing answers?

A. The answers themselves

B. The process of finding and testing answers

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Science

• A way of knowing – a process

• Not just a collection of facts

• “Science is facts; just as houses are made of stones, so is science made of facts; but a pile of stones is not a house, and a collection of facts is not necessarily science”

Henri Poincaré

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Is the sky blue on a clear day?

How do you know?

Did someone tell you?

Did you see it for yourself?

What if I told you it wasn’t?

Do you BELIEVE the sky is blue or do you ACCEPT it as reality?

J. Heafner: www.sticksandshadows.com

Questioning your assumptions

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Observed Fact (A) or Inference (B)?

• Observed Fact: in principle, anyone can verify it for himself/herself

(can be directly & repeatedly observed)• Inference: uses observed facts + assumptions /

logic / math

• The Moon’s angular size is 0.5º– (The Moon spans an angle of 0.5º on the sky)

• The universe is nearly 14 billion years old

• The Earth is 93 million miles from the Sun

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• Goes beyond patterns

• Figuring out the “rulebook” for nature

Hallmark of Science: #1• Science seeks explanations for observed

phenomena that rely solely on natural causes

Explaining the Observations

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Science isn’t everything…Even when we have a well-tested “rulebook”….

knowing the rules doesn’t tell us where they come from!

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Figuring out the Rules

Where Creativity Comes In: Coming up with the explanation

“We especially need imagination in science. It is not all mathematics, nor all logic, but is somewhat beauty and poetry. “

Maria Mitchell (1818 – 1889)Astronomer and first woman elected to

American Academy of Arts & Sciences

How Science Keeps us Honest:• “What distinguishes Science from other forms of learning is its

emphasis on predicting and testing (experimentally) as a way of sorting out ideas which sound good, but are false, from ones which present a more accurate model of how the world actually works.”

– Doug Duncan

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Science• “Science is a way of trying not to fool yourself”

– Richard Feynman

• Science:– Latin scientia means knowledge– Today, knowledge that makes predictions that can be

tested through rigorous observation and experiment

Hallmark of Science: #2• Scientific model must make testable predictions

about natural phenomena.– If predictions don’t agree with observations, the

model must be revised or abandoned

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Hallmarks 2) Testing against observations

• Verifiable observations:– What counts as an observation that can

be used to test predictions?– It’s acceptable if, in principle, (given

appropriate training / equipment), you could conduct the test yourself

• Eyewitness accounts?

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Scientific Claims / Hypotheses• Must be a natural explanation

• Must be backed up with evidence:• Must explain observed phenomena• Its predictions must agree with observations

• Must be capable of being proven wrong• Must be testable!

Non-science: Any claim that does not meet these criteria (Hallmarks) is not scientific, regardless

of whether it is ultimately true or false!

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Concept Check

Is this a scientific claim?

Lightning is caused by the god Zeus throwing bolts at the Earth; doing so whenever he is angry

A) YesB) No

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Sanity Check! (Credit to Paul Hewitt)

Which of the following statements is a scientific claim?

(A) Human beings will never set foot on the Moon.

(B) Some of the laws that govern Nature cannot be detected by scientists.

(C) It is possible that in some other galaxy the laws of physics are fundamentally different than the laws we are acquainted with in this galaxy.

J. Heafner: www.sticksandshadows.com

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Science or not?

• Non-science:– That which is assumed to be unexplainable

• All scientists search for explanations that are assumed to exist.

• Science can’t be used to get an answer that doesn’t exist. Science has limitations!

– If they hypothesis isn’t at risk, it isn’t science!– If the evidence doesn’t support it, it isn’t

science!

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• Is Earth round?• Does Earth really spin?• Does Sun orbit Earth?• Is Earth’s rotational axis tilted?• Is Earth at the center of the Universe?• Do other planets orbit Earth?• Is there a supreme deity?• Does casual use of <5mW handheld

green laser pointers ruin astrophotos?

The Language of Science:Consider these questions...

J. Heafner: www.sticksandshadows.com

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If you answered “yes” or “no” without• considering the scientific validity of the

question,• considering HOW you know the answer,• or considering WHY you accept the answer,

then you’re operating under a “belief system” rather than under valid science.

Language Continued

J. Heafner: www.sticksandshadows.com

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Science and belief systems can peacefully coexist…

…AS LONG AS we understand that they have different, and not interchangeable, purposes.

SCIENCE ISN’T ABOUT BELIEFS

It’s about:• Observed Facts• Inferences (observations + logic)• What natural explanation best fits the evidence?• Continued testing of models

SHOW ME THE EVIDENCE BABY!J. Heafner: www.sticksandshadows.com

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Belief:To you: has nothing to do with evidence• To scientists: “We believe” often equivalent to “evidence

tells us” – Should say: “Evidence tells us that electrons behave this way.”

rather than “We believe electrons work this way.”

Faith:• To you: unquestioning belief without evidence• Scientists sometimes say: “We have faith in our results”

when they mean “We have confidence in our results”

Scientific results • NOT based on faith. • Based on evidence.

Who is to blame for muddled terminology? • Scientists! We’re terrible communicators!

Consistent Terminology

J. Heafner: www.sticksandshadows.com

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What we should say…

• Scientists have determined that…• Scientists have confidence in …• Scientists have concluded that …• Analysis of data suggests…• This evidence leads to the logical conclusion…• Observations of ___ support the idea of __• The weight of the physical evidence supports …• The best observational / experimental evidence indicates ….

So why don’t we?

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Clicker QuestionOnly one of the statements below uses the term

theory in its correct, scientific sense. Which one?   

A) I have a new theory about the cause of earthquakes, and I plan to start testing it soon. 

B) Evolution is only a theory, so there's no reason to think it really happened. 

C) Einstein’s theory of relativity has been proven true

D) I wrote a theory that is 152 pages long. E) Big Bang Theory has been tested and verified

through repeated and varied observations

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• To you: “theory” connotes “uncertainty”

• To me: “scientific theory of…” is equivalent to “body of knowledge known as…” (e.g. relativity), and means it is well-tested and accepted!– Example: Big Bang Theory

Theory of Relativity

Consistent Terminology

J. Heafner: www.sticksandshadows.com

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Jargon Alert!

You’ll know when I use an astronomical term you don’t understand – but as you’ve seen, we may use common words differently!

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Process: Idealized Scientific Method

Organized approach to explaining observed facts with a TESTABLE model of nature

Hypothesis = tentative explanation

Question = curiousity

Results: should be same no matter who conducts the test

Modification &Self-correction!

Creativity!

Astronomy relies on Observation more than Experiment

Inferences based on results verification or falsification

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Hallmarks of Science (from text)

3) Science progresses through the creation and testing of models of nature that explain observations as simply as possible

Occam’s Razor:

All else being equal, scientists prefer the simplest explanation

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Clicker QuestionWhich of the following is not part of a good scientific

theory?  

A) A scientific theory must explain a wide variety of phenomena observed in the natural world.  

B) A scientific theory cannot be accepted until it has been proven true beyond all doubt. 

C) A scientific theory must make testable predictions that, if found to be incorrect, could lead to its own modification or demise.  

D) A scientific theory should be based on natural processes and should not invoke the supernatural or divine.

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Never “proof”• Can never “prove” a

model or theory

• Confidence grows as repeatedly verified, supported by evidence

• Scientific theory– Well-tested– Generally accepted– Not proven

absolutely• New observations might

not match predictions theory must be modified

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Convincing Others

For a model to become an accepted theory, everyone must agree!

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Back to Hollow Earth

• Hollow Earth Society: claims the Earth is a hollow ball and we are living inside it

• Is this a scientific claim?

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