The Nature of Science
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Truth
Proof
Belief Evidence
Debate Consensus
Human activities are the major cause of global warming.
1. I agree
2. I think that humans have a small role in
global warming
3. I disagree that human activities that any role
in global warming
4. 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.
B.
C.
D.
E.
A small but vocal minority of scientists believe that
the theory of evolution is true
Scientific opinion is about evenly split as to whether
evolution really explains the diversity of life on Earth.
Scientific opinion runs about 90% in favor of the
theory of evolution and about 10% opposed.
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.
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
Baloney detection kit
1.
2.
3.
4.
5.
6.
7.
8.
9.
How reliable is the source of the claim?
Does the source make similar claims?
Have the claims been verified by somebody else?
Does this fit with the way the world works?
Has anyone tried to disprove the claim?
Where does the preponderance of evidence point?
Is the claimant playing by the rules of science?
Is the claimant providing positive evidence?
Does the new theory account for as many phenomena
as the old theory?
10. Are personal beliefs driving the claim?
Science is NOT
a democracy!
Although the media seem to think it is…
Peer Review:
2-3 other scientists, not involved in the study, read
your paper and determine whether it has any
obvious errors.
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…
Scientific
consensus
“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
Human activities are the major cause of global warming.
1. I agree
2. I think that humans have a small role in
global warming
3. I disagree that human activities that any role
in global warming
4. 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.
B.
C.
D.
E.
A small but vocal minority of scientists believe that
the theory of evolution is true
Scientific opinion is about evenly split as to whether
evolution really explains the diversity of life on Earth.
Scientific opinion runs about 90% in favor of the
theory of evolution and about 10% opposed.
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.
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.
2.
3.
Studies show that there is a slight risk of
developing autism due to vaccines but the benefit
outweighs the risk
Studies have shown that there is no cause-andeffect relationship between vaccines and autism
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