the scientific method. scientific method

The Scientific Method

Scientific Method

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Scientific Method

Scientific Method: Description Orderly and cautious means of

building supportable, evidence-based understanding of the natural worldobservationshypothesesdeductionstheory

• explanations for natural phenomena• experiments test predictions reproducibly

Scientific Method: History

Egyptian period (15th century BC) Edwin Smith and Ebers Papyra, medical

manuscripts (+demons ) Ancient Greece (5th century BC)

Plato: teaching of arithmetic, astronomy and geometry in schools

Aristotle: empiricism• all human knowledge comes at first from senses

and experience: slice of apple• denies that humans have innate ideas


Roger Bacon (13th Century) repeating cycle of observation, hypothesis,

experimentation and the need for independent verification

Francis Bacon (17th Century) "The understanding must not therefore be

supplied with wings, but rather hung with weights, to keep it from leaping and flying. … when it is done, we may entertain better hopes of the sciences."

“..by successive steps not interrupted or broken, we rise from particulars to lesser axioms; and then to middle axioms, one above the other; and last of all to the most general ”


René Descartes (17th Century)1. "never to accept anything for true which I did not

clearly know to be such; …. avoid precipitancy and prejudice, and to comprise nothing more in my judgment than what was presented to my mind...

2. divide each of the difficulties under examination into as many parts as possible, and as might be necessary for its adequate solution.

3. conduct my thoughts by commencing with objects the simplest and easiest to know, I might ascend by little and little to the knowledge of the more complex

4. assured that nothing was omitted in every case to make enumerations so complete, and reviews so general"


Isaac Newton1. admit no more causes of natural things than such as are both

true and sufficient to explain their appearances simple 2. to the same natural effects we must, as far as possible, assign

the same causes concept of theory, applies to the general 3. The qualities of bodies … are to be esteemed the universal

qualities of all bodies whatsoever. 4. look upon propositions collected by general induction from

phenomena as accurately or very nearly true, notwithstanding any contrary hypotheses that may be imagined, till such time as other phenomena occur, by which they may either be made more accurate, or liable to exceptions.

"To explain all nature is too difficult a task for any one man or even for any one age. 'Tis much better to do a little with certainty, and leave the rest for others that come after you, than to explain all things."

Scientific Method: Elements

Characterization Hypothesis Prediction Experiment


Characterization Subject/problem/unknown Careful thought Definitions Observations Measurement Counting Lab Instrument Statistics


Characterization phase can require extended and extensive study, even centuries. thousands of years of measurements, from the

Chaldean, Indian, Persian, Greek, Arabic and European astronomers, to record the precession of the planet Earth

Newton condensed these measurements into consequences of his laws of motion.

perihelion of the planet Mercury's orbit exhibits a precession which is not fully explained by Newton's laws of motion.

observed difference for Mercury's precession, between Newtonian theory and relativistic theory was one of the first pieces of evidence for Einstein's theory of General Relativity.


Characterization (example) Gregor Mendel, mathematical basis of genetics the mechanism of the gene unclear Bragg's laboratory at Cambridge University

made X-ray diffraction pictures of various molecules, starting with crystals of salt

Using clues which were painstakingly assembled over the course of decades, beginning with its chemical composition, it was determined that it should be possible to characterize the physical structure of DNA, and the X-ray images would be the vehicle


Hypothesis development “Assumption” in the Greek A hypothesis is a suggested description of the subject A provisional idea whose merit is to be evaluated Requires work to be refuted or accepted Should be falsifiable Testable Confirmation does not imply that hypothesis is proven, remains

provisional the form of a mathematical model

X is greater than Y or Z decreases exponentially with W formulated as existential statement

The globe is round… DNA example: the race to determine the structure of DNA

• Francis Crick and James Watson hypothesized that this molecule had a helical structure: two intertwined spirals.

• Linus Pauling was hypothesizing a triple helix…


Valid statements: Chocolate may cause pimples. Salt in soil may affect plant growth. Plant growth may be affected by the color of the

light. Bacterial growth may be affected by temperature. Ultra violet light may cause skin cancer. Temperature may cause leaves to change color.

If we say "Trees will change color when it gets cold." we are making a prediction

If we write, "Ultraviolet light causes skin cancer." could be a conclusion


Formalized Hypotheses A tentative relationship is stated One is "independent" and the other is "dependent."

independent variable: controlled by the scientist dependent variable: the one that you observe

and/or measure the results example: If skin cancer is related to ultraviolet light ,

then people with a high exposure to UV light will have a higher frequency of skin cancer.

If leaf color change is related to temperature , then exposing plants to low temperatures will result in changes in leaf color.


As an example, someone who enters a new country and observes only white sheep, might form the hypothesis that all sheep in that country are white.Falsifiable (by observing a single

black sheep)


Example of what is not a hypothesis: Our hypothesis is that (or we propose

that) by using a fiber optic probe we can detect cancerous lesions in the mucosa of the stomach. application

Circular argument Limited knowledge, non-innovative

Hypothesis Example

Hypothesis:

“Queen Isabella, I believe that the world is not flat, but round.”

Specific Aims (used to test the hypothesis)

“I will sail west to reach the East.”


Prediction from the hypothesis useful hypothesis will enable predictions predict the outcome of an experiment or the

observation of a phenomenon in nature essential that the outcome be currently unknown.

• the outcome known it's called a consequence If the predictions are not accessible by observation or

experience, the hypothesis is not yet useful for the method, wait for others who might come afterward, and

perhaps rekindle its line of reasoning based on a new technology or theory

Edmund Halley's prediction of the year of return of Halley's comet which returned after his death.


Prediction, DNA example: When Watson and Crick hypothesized that DNA was

a double helix, Francis Crick predicted that a X-ray diffraction image of DNA would show an X-shape


How to get about testing the hypothesis? experimentsThe specific aims state what you want

to do in the order in which you want to do it

Think of your aims as experiments designed to test your hypotheses

Ranking Criteria Most scientifically

sound Can I test this? Can I narrow down the

field of hypotheses? Time/cost to achieve

outcome How easy/hard is the

experiment Equipment,

environment, and expertise available?

Testing Method to be used – does

it test my hypothesis? How many measurements

do I need? What controls do I need? How long will this take?

• data collection• data analysis

Will the results be definitive?


Scientific Method: What to do with your data?

It does not matter if the results of your experiment are what you predicted Am I using the best tools? Do I need to revise my experimental design? Negative data is valuable Does the data lead to new experiments?


Iteration some consideration will lead the scientist to

repeat an earlier part of the process failure to develop an interesting hypothesis

re-define the subject they are considering failure of a hypothesis to produce interesting

and testable predictions reconsideration of the hypothesis or the subject

Failure of the experiment to produce interesting results reconsidering the experimental method, the hypothesis or the definition of the subject


Verificationresults must be reproduced by others

within the science communityGeorg Wilhelm Richmann killed by

ball lightning to his forehead (1753) when attempting to replicate the 1752 kite experiment of Benjamin Franklin

Scientific Method: Scope

Scientific method: can be applied to anything within the range

of our experiences something has an effect on our lives can formulate theories and try to predict

what this effect might be does not aim to give an ultimate answer.

iterative and recursive nature it will never come to an end

any answer it gives is provisional. cannot prove or verify anything in a strong

sense

Scientific Method: Community Scientific community:

ensure the integrity of the scientific method Peer review evaluation

scientific journals • Scientist editor reviewer(s)• Reviewer: fellow (usually anonymous) scientists • recommend publication, reject, publication with

suggested modifications, or, sometimes, publication in another journal.

serves to keep the scientific literature free of unscientific or crackpot work

cut down on obvious errors improve the quality of the scientific literature peer review may inhibits the circulation of unorthodox

work, and at other times may be too permissive

Scientific Method: Community

reproduction and record-keeping common practice to repeat the experiments in

order to duplicate the results• further validating the hypothesis.• debug systematic errors in experiments• check for deliberate falsifications

detailed records of their experimental procedures• provide evidence• effectiveness and integrity of the procedure • assist in reproduction• assist in the conception of new experiments• Intellectual property