Graham Bradley - PowerPoint Presentation

Slide1

Graham Bradley

Geog1006

Ideas in Geography:

‘The Scientific Method’

(Part 1)Slide2

Lecture 1What is science?

Geography and scienceScientific explanationScientific reasoningFrancis Bacon and induction

David Hume’s problemKarl Popper and falsification The hypothetico-deductive methodExample: climate changeSlide3

What do you think science is?

Sceptical (up to a point)Based on observation, data, experimentationConclusions are tentativeTheories (models) can be tested / falsified

Assumes a chain of cause and effectExplains by generalisingOften quantitative and mathematicalSlide4

But what do scientists think science is?

“Ask a scientist what he conceives the scientific method to be, and he will adopt an expression that is at once solemn and shifty-eyed: solemn because he feels he ought to declare an opinion; shifty-eyed because he is wondering how to conceal the fact that he has no opinion to declare”

Sir Peter MedawarUCL Professor of Zoology 1951-1962Nobel Prize in Medicine 1960Slide5

What are the goals of science?

DescriptionIdentification and classification of entities, events & patterns

PredictionUse observed regularities to infer unobserved phenomenon

Explanation

Explicate the causal relations between described and predicted phenomenon

Stewardship/Control

(

applied science/engineering

)

Apply knowledge to bring about desired outcomeSlide6

What is scientific explanation?

Cause and effect – to explain a phenomenon is to say what caused itE.g. What is the cause

of lake acidification?Covering laws – show that phenomenon to be explained is ‘covered’ by some general law of natureE.g. Darcy’s Law (groundwater flow) Q = KiA

General law & particular facts

→ explanation

Every reliable prediction is a potential explanationSlide7

Deduction

Inference, by reasoning, from general to particular: from theory to data

Premises: i) every mammal has a heart; ii) every horse is a mammal. Conclusion: Every horse has a heart.Premises: i) all ‘U’ shaped valleys were formed by glaciers; ii) Wasdale is ‘U’ shaped valley.Conclusion: Wasdale was formed by a glacier

Valid if the truth of premises guarantees truth of conclusions & false otherwise.

Conclusion is either true or false

Induction and deductionSlide8

Induction

Process of inferring general principles from observation of particular cases: from data to theory

Premise: every horse that has ever been observed has a heartConclusion: Every horse has a heart.Premises: i) Death by cholera spatially clustered; ii) spatial clusters around water pumps.Conclusion: water pumps are the source of cholera.

Conclusion goes beyond information present, even implicitly, in premises

Conclusions have a degree of strength (weak -> near certain).

Induction and deductionSlide9

Induction and deductionSlide10

The origins of science:Aristotle (384-322 B.C.E.)

Plato – emphasis on a priori knowledgeAristotle – greater emphasis on a posteriori

knowledge Empirical inquiry of “the form within things”Elements: earth; air; fire; water; aetherTeleology – nature reflects inherent purpose and directionAristotelian view remained dominant until 16th

CSlide11

Attorney General, Lord Chancellor of England and philosopher who inspired the formation of the Royal Society

Rejected many a priori assumptions of Aristotelian view and advocated the Baconian

method of inductive inquiry: Identify phenomenon and rank list of things in which it occursUse inductive

reasoning to

verify

the cause of phenomenon

Francis Bacon (1561-1626)

Can induction identify causes?Slide12

Rev. Thos. Bayes (1702-1761

)Formalise scientific process via probabilityBayes’ Theorem: solves the inverse (inductive) problem i.e. gives probability of a hypothesis being true given some data and

any prior knowledgeTHIS is how science is really done! BUT is (sort of) subjective as requires stating priors explicitly P(H|I)Ignored for 200 years: replaced by “statistics” – estimate reliability of a given set of data (compared to infinite other possible sets) in the light of a given (null) hypothesis (model). But we don’t HAVE infinite other data sets in practive

Posterior

Likelihood

PriorSlide13

Eg Laplace & the mass of Saturn

Laplace (1749-1827) estimated M

Saturn from orbital data i.e. H is the posterior prob(M|{data},I) where I was background knowledge of orbital mechanics etc.Shaded area shows degree of belief that m1 ≤ M

Saturn

< m

2

(right to within < 0.7%)

How do we interpret this pdf in terms of frequencies?

Some ensemble of universes all constant other than M

Saturn

? Distribution of M

Saturn

in repeated experiments?

But data consist of orbital periods, and these multiple expts. didn’t happen

Posterior

Likelihood

Prior

Best estimate of M

Degree of certainty of M

The posterior pdf expresses ALL our best understanding of the problemSlide14

Karl Popper (1902 - 1994)

Can deduction identify causes?Impossible to

verify a universal statement which would require infinite observationsPossible to falsify a universal statement with a single counter-observation

Falsifiction is deductive: if the single case is false then it logically follows that the universal case is also false

Popper stated some theories thought to be scientific at the time are unfalsifiable and therefore not science

e.g. Freud’s psychoanalysis; Marxist theory

Reference: Popper, K., 1959.

“

The Logic of Scientific Discovery

”Slide15

Example: Climate Change

What has caused global warming?Slide16

How much of the observed change is

due to natural variability and how much to anthropogenic influences?Slide17

Natural Variability and Climate Change

Internal mechanismsOcean/atmosphere interaction e.g. ENSO

Thermohaline circulation

External mechanisms

Ash from volcanic eruptions

Variability in solar irradianceSlide18

Effect of Volcanic AshSlide19

Variations in Solar IrradianceSlide20

Anthropogenic carbon dioxideSlide21

Competing Hypotheses

H1 The observed record is consistent

with natural climate variability onlyH2

The observed record is consistent

with natural and anthropogenic forcing

Use proxy record of global temperature and

General Circulation Models to test the hypothesesSlide22

First Hypothesis:

The observed temperature record is consistent with natural climate forcing only

FalsifiedSlide23

Second Hypothesis:

The observed temperature record is consistent with natural and anthropogenic climate forcing

CorroboratedSlide24

Problems of Falsification

Most scientists are not trying to falsify theories:e.g. When asked ‘What if relativity had been falsified?’ Einstein replied:

‘I would have been sorry for the dear Lord as my theory is correct.’Tenacity – It may be good to hold on to a falsified theoryPopper: ‘He who gives up a theory too easily in the face of apparent refutations will never discover the possibilities inherent in his theory’

e.g. Uranus didn’t conform to Newton’s laws - the discovery of Neptune

Corroboration

– Degree of testing a theory has undergone

Popper argued a highly corroborated theory has a greater level of

‘

truthlikeness

’

, but the logical conditions for comparison cannot be met

Popper was unable to provide a logical method of consistently choosing between unfalsified theoriesSlide25

Realism: physical world is real;

Presuppositions: world is orderly and comprehensible;

Evidence: science demands evidence;Logic: science uses standard, settled logic to connect evidence and assumptions with conclusions

;

Limits: many matters cannot usefully be examined by science;

Universality: science is public and inclusive;

Worldview: science must contribute to a meaningful worldview.

Gauch

(2006): “Seven pillars of Science”Slide26

Summary

Scientific methods address empirical claimsDemarcation criteria: empirical, laws, testable etcScientific explanations: cause & effect, covering lawsScientific reasoning: inductive or deductiveThe problem of induction

Karl Popper and falsificationThe hypothetico-deductive methodFinal thought: How do scientists choose between

unfalsified theories?Slide27

Reading:

Okasha, S., 2002. “Philosophy of science, a very short introduction” Recommended introduction for the general reader. Also available as audio book.

Chalmers, A. F., 1999. “What is this thing called science?” 3rd editionRecommended text for anyone with an interest in the philosophy of science.Inkpen

, R., 2005. “Science, philosophy and physical geography”

Introduction to philosophy of science for physical geography undergraduates

.

Gauch

, H. (2003) The Scientific Method in Practice

Gauch

, H. (2006) Science, Worldviews and Education, Sci. and

Edu

., DOI 10.1007/s11191-006-9059-1.

see

bothon

Moodle

Montello, D. R. and Sutton, P. C., 2006. “An introduction to scientific research methods in geography”

Beginners guide to empirical aspects of human and physical geography research, with well balanced introduction on the philosophy of science and its place in geography.

Orme

, A. R., 2002.

“

Shifting paradigms in geomorphology

”

Geomorphology, Vol. 47, Issues 2-4, pages 325-342

A paper of particular interest to physical geographers.Slide28

What’s in a theory?

Natural Science – Social Science – Humanities

Sets of assumptions, ideas, arguments and conclusions

An analytic structure designed to provide a general explanation of observations

A set of interpretive principles that facilitate a specific rational or moral analyses