The Nature of Science

Truth ProofBelief EvidenceDebate Consensus

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Human activities are the major cause of global warming.

1. I agree2. I think that humans have a small role in

global warming3. I disagree that human activities that any role

in global warming4. I am not well-informed enough to have an

opinion either way

Which of the following is true of Darwin’s Theory of Evolution by Natural Selection?

A. A small but vocal minority of scientists believe that the theory of evolution is true

B. Scientific opinion is about evenly split as to whether evolution really explains the diversity of life on Earth.

C. Scientific opinion runs about 90% in favor of the theory of evolution and about 10% opposed.

D. While widely accepted by most scientists, there would still be “reasonable doubt” about whether evolution is true -- Judicial proof is much harder to achieve than scientific proof.

E. None of the above: evolution is the only plausible explanation for the diversity of life on earth.

The scientific method:

The scientific method

• Based on proposing and testing hypotheses

• hypothesis = educated guess

“I believe…”

Based on what?

Evidence.

Baloney detection kit

1. How reliable is the source of the claim?2. Does the source make similar claims?3. Have the claims been verified by somebody else?4. Does this fit with the way the world works?5. Has anyone tried to disprove the claim?6. Where does the preponderance of evidence point?7. Is the claimant playing by the rules of science?8. Is the claimant providing positive evidence?9. Does the new theory account for as many phenomena

as the old theory?10.Are personal beliefs driving the claim?

Baloney detection kit

Science is NOT a democracy!

Although the media seem to think it is…

2-3 other scientists, not involved in the study, read your paper and determine whether it has any obvious errors.

Peer Review:

After publication in the scientific literature:

• The rest of the scientific community now has the opportunity to try to reproduce your results.

• Open debate in the scientific community• All scientists get a chance to review it!

If the idea survives open debate in the scientific literature…

Scientificconsensus

“Consensus” does not mean that 100% of scientists will agree with the idea, only that the vast majority do.

Example:

“human activities are the major cause of global warming”

400 scientists disagree. HOWEVER…

Only about 10 of them have expertise in climate science and closely-related fields. The other 3000 climate scientists agree with the statement.

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* National Oceanic and Atmospheric Administration * Environmental Protection Agency * NASA's Goddard Institute of Space Studies * American Geophysical Union * American Institute of Physics * National Center for Atmospheric Research * American Meteorological Society * The Royal Society of the UK * Canadian Meteorological and Oceanographic Society * American Association for the Advancement of Science# Academia Brasiliera de Ciencias (Brazil)# Royal Society of Canada# Chinese Academy of Sciences# Academie des Sciences (France)# Deutsche Akademie der Naturforscher Leopoldina (Germany)# Indian National Science Academy# Accademia dei Lincei (Italy)# Science Council of Japan# Russian Academy of Sciences# Royal Society (United Kingdom)# National Academy of Sciences (USA) * Australian Academy of Sciences * Royal Flemish Academy of Belgium for Sciences and the Arts * Caribbean Academy of Sciences * Indonesian Academy of Sciences * Royal Irish Academy * Academy of Sciences Malaysia * Academy Council of the Royal Society of New Zealand * Royal Swedish Academy of Sciences

Human activities are the major cause of global warming.

1. I agree2. I think that humans have a small role in

global warming3. I disagree that human activities that any role

in global warming4. I am not well-informed enough to have an

opinion either way

Hallmarks of Science: #1

Modern science seeks explanations for observed phenomena that rely solely on natural causes.

(A scientific model cannot include divine intervention or other supernatural explanations)

Hallmarks of Science: #2

Start with the simplest possible model: make predictions, tests and refinements.

(Simplicity = “Occam’s razor”)

Hallmarks of Science: #3

A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations.

“No other explanation” does NOT prove anything!

What is a scientific theory?

“Theory” has a different meaning in science than in everyday life.

In science, a Theory is NOT just a good idea! A Scientific Theory:

—Explains a wide variety of observations with a few simple principles, AND

—Must be supported by a large, compelling body of evidence.

—Must NOT have failed any crucial test of its validity.

Which of the following is true of Darwin’s Theory of Evolution by Natural Selection?

A. A small but vocal minority of scientists believe that the theory of evolution is true

B. Scientific opinion is about evenly split as to whether evolution really explains the diversity of life on Earth.

C. Scientific opinion runs about 90% in favor of the theory of evolution and about 10% opposed.

D. While widely accepted by most scientists, there would still be “reasonable doubt” about whether evolution is true -- Judicial proof is much harder to achieve than scientific proof.

E. None of the above: evolution is the only plausible explanation for the diversity of life on earth.

Science is about probabilities, not certainties

The hypothesis: Smoking causes lung cancer

Reality: Smoking dramatically increases one’s chances of developing lung cancer

Anecdotes vs. Studies

Anecdotal evidence: “My grandmother smoked a pack a day for 60 years, she lived to be 75.”

Scientific study: Monitor the health of 1000 smokers and non-smokers for 20 years. Compare rates of lung cancer, longevity, etc.

Power of suggestion

Have you heard claims that vaccines can sometimes cause autism in children?

Which of the following is true:

1. Studies show that there is a slight risk of developing autism due to vaccines but the benefit outweighs the risk

2. Studies have shown that there is no cause-and-effect relationship between vaccines and autism

3. Studies into the proposed links between autism and vaccines have not yet been conducted

Conclusion Science vs. non-science

Science seeks explanations that rely solely on natural causes progresses through development and testing of models of

nature models must make testable predictions

A scientific theory A model that explains a wide variety of observations in terms

of a few general principles Has survived repeated and varied testing Subject to modification as new data and observations are

acquired