Scientific method

The scientific method is the way scientists investigate the world and
produce knowledge about it. Many people use the term to refer to an
idealized, systematic approach that is supposed to characterize all
scientific investigation, and which is regarded as a paradigm for
investigtion in general. It is distinguished from other routes to knowledge
by its use of controlled experiments and its requirement that results be
reproducible. However, most historians, philosophers and sociologists regard
the actual operations of science as more complicated and less orderly than
the idealized method implies.

The question of how science operates is not only academic. In the judicial
system and in policy debates, for example, a study's deviation from accepted
scientific practice is grounds to reject it as "junk science." Whether they
are diagnosing a patient, investigating a murder or researching a social
trend, non-scientists cite "the scientific method" as an ideal. Methodical
or not, science still represents standard of proficiency and reliability.

"The Scientific Method"

The idealized scientific method, often referred to simply as the scientific
method, is typically described as follows.

   * Observe: Observe or read about a phenomenon.
   * Hypothesize: Wonder about your observations, and invent a hypothesis, a
     'guess', which could explain the phenomenon or set of facts that you
     have observed.
   * Test
        o Predict: Use the logical consequences of your hypothesis to
          predict observations of new phenomena or results of new
          measurements.
        o Experiment: Perform experiments to test these predictions, to find
          just which prediction occurred.
   * Conclude: Accept or refute hypothesis
        o Evaluate: Search for other possible explanations of the result
          until you can show that your guess was indeed the explanation,
          with confidence.
        o Formulate new hypothesis

Few people believe that there is any one method that all scientists follow
like an algorithm. However, many people believe that the idealized
scientific method captures the essence of how science operates. The elements
of this method are described in more detail below.

Observation

The scientific method begins with observation. Observation demands careful
measurements.

Scientists use operational definitions of their measurements; measurements
are defined in terms of physical actions that can be performed by anyone,
rather than being defined in terms of abstract ideas or common
understanding.

For example, the term "day" is useful in ordinary life and we don't have to
define it precisely to make use of it. But in studying the motion of the
Earth, you have to define the words you use very precisely; for example,
science makes two distinct operational definitions of a day: a solar day is
the time between observing the sun at a particular position in the sky and
observing it in the same position the next time; a sidereal day is the time
between observing a specific star in the night sky at a specific position,
and that same observation made the next time.

The slight differences between different operational definitions are often
important, as they are needed to make experiments precise enough to reveal
underlying physical phenomena that may be too subtle to detect otherwise.
Distinctions in operation definitions can also be important conceptual
differences: for example, mass and weight are regarded as quite different
concepts in science.

Hypothesis

To explain the observation, scientists use whatever they can (their own
creativity (currently not well understood), ideas from other fields, or even
systematic guessing, or any other methods available) to come up with
possible explanations for the phenomenon under study. The most important
aspect of an explanation (ie, an hypothesis) is that it must be falsifiable,
that is, capable of being demonstrated wrong.

The scientist should also be -- but need not be and often is not --
impartial, considering all known evidence, and not merely evidence which
supports the hypothesis under development. This makes it more likely that
the hypotheses formed will be relevant and useful and not subject to
external bias and distortion.

In the extremely rare cases where no better grounds for discriminating
between rival hypotheses can be found, the bias scientists almost always
follow is the principle of Occam's Razor; one chooses the simplest
explanation for all the available evidence.

Prediction

A hypotheses must make specific predictions; these predictions can be tested
with concrete measurements to support or refute the hypothesis. For
instance, Albert Einstein's General Relativity makes many specific
predictions about the structure of space-time, such as the prediction that
light bends in a strong gravitational field, and the amount of bending
depends in a precise way on the strength of the gravitational field.
Observations made of a 1919 solar eclipse supported the hypothesis (ie,
General Relativity) as against all other possible hypotheses which did not
make such a prediction. (Later experiments confirmed this even further.)

Deductive reasoning is generally used to develop predictions used to test a
hypothesis.

Verification

Probably the most important aspect of scientific reasoning is verification:
The results of one's experiments must be verified.

This is both useful as a practical matter (e.g., in chemical engineering or
planetary exploration), but have sometimes demonstrated previously unknown
variations from currently accepted theory (e.g., the CPT experiments of Yang
and Lee in the 1950s which forced fundamental changes in much of particle
physics). Ideally, the experiments performed should be fully described so
that anyone can reproduce them, and many scientists should independently
verify every hypothesis. Results which can be obtained from experiments
performed by multiple scientists are termed reproducible and are given much
greater weight in evaluating hypotheses than non reproducible results.

Scientists must design their experiments carefully. For example, if the
measurements are difficult to make, or subject to observer bias, one must be
careful to avoid distorting the results by the experimenter's wishes. When
experimenting on complex systems, one must be careful to isolate the effect
being tested from other possible causes of the intended effect (this results
in a controlled experiment). In testing a drug, for example, it is important
to carefully test that the supposed effect of the drug is produced only by
the drug itself, and not by the placebo effect or by random chance. Doctors
do this with what is called a double-blind study: two groups of patients are
compared, one of which receives the drug and one of which receives a
placebo. No patient in either group knows whether or not they are getting
the real drug; even the doctors or other personnel who interact with the
patients don't know which patient is getting the drug under test and which
is getting a fake drug (often sugar pills), so their knowledge can't
influence the patients either.

"Verification" may be a misleading word, in that we don't really "confirm"
or "verify" a hypothesis so much as we fail to refute it. Karl Popper, the
philosopher of science, stressed that what is needed is falsifiability (of
predictions) and not verification or confirmation. He insisted that in a
case where a new theory has accurately (or apparently accurately) predicted
some new event, the truth of the theory has not been confirmed. Instead it
has shown itself perhaps closer to the truth (in some respect than the old
theory). He reminded all of us that Newtonian theory was considered
virtually sacrosanct for hundreds of years before being shown to be in some
respects inaccurate by Einsteins work. The many experiments and usages of
Newtonian theory should not have been interpreted as confirming it's
absolute truth.

Evaluation

Any hypothesis, no matter how respected or time-honored, must be discarded
once it is contradicted by new reliable evidence. Hence all scientific
knowledge is always in a state of flux, for at any time new evidence could
be presented that contradicts long-held hypotheses. A classic example is the
explanation of light. Isaac Newton's particle paradigm was overturned by the
wave theory of light, which explained diffraction, and which was held to be
incontrovertible for many decades.The wave paradigm, in turn was refuted by
the discovery of the photoelectric effect. The currently held theory of
light holds that photons (the 'particles' of light) are both waves and
particles; experiments have been performed which demonstrate that light has
both particle and wave properties.

The experiments that reject a hypothesis should be performed by many
different scientists to guard against bias, mistake, misunderstanding, and
fraud. Scientific journals use a process of peer review, in which scientists
submit their results to a panel of fellow scientists (who may or may not
know the identity of the writer) for evaluation. Scientists are rightly
suspicious of results that do not go through this process; for example, the
cold fusion experiments of Fleischmann and Pons were never peer reviewed --
they were announced directly to the press, before any other scientists had
tried to reproduce the results or evaluate their efforts. They have not been
reproduced elsewhere as yet; and the press announcement was regarded, by
most nuclear physicists, as very likely wrong. Proper peer review would
have, most likely, turned up problems and led to a closer examination of the
experimental evidence Fleischmann, Pons, et al believed they had. Much
embarrassment, and wasted effort worldwide, would have been avoided.

The scientific method in practice

Most philosophers of science are agreed that there are no definitive
guidelines for the production of new hypotheses. The history of science is
filled with stories of scientists describing a "flash of inspiration", or a
hunch, which then motivated them to look for evidence to support or refute
their idea. The anecdote that an apple falling on Isaac Newton's head
inspired his theory of gravity is a popular example of this (there is no
evidence that the apple fell on his head; all Newton said was that his ideas
were inspired "by the fall of an apple.") Kekule's account of the
inspiration for his hypothesis of the structure of the benzene-ring
(dreaming of snakes biting their own tails) is better attested.

Scientists tend to look for theories that are "elegant" or "beautiful"; in
contrast to the usual English use of these terms, scientists have a more
specific meaning in mind. "Elegance" (or "beauty") refers to the ability of
a theory to neatly explain all known facts as simply as possible, or in a
manner consistent with Occam's Razor.

In 1962 Thomas Kuhn published his essay The Structure of Scientific
Revolutions, a seminal work on the practice and process of science. Kuhn
suggested that sociological mechanisms significantly affect the rejection of
older scientific theories and the acceptance of new ones. According to Kuhn,
when a scientist encounters an anomaly that is not explained by the
scientific community's currently accepted general paradigm or theory, that
community can ignore it (the increasing problems with Ptolemaic epicycles in
accounting for the motion of the planets was a long standing case), but is
often compelled to accommodate it by either modifying the existing theory or
replacing it with a new one. A paradigm shift occurs when a new paradigm
gains wider acceptance than a pre-existing one. It is at this point that
sociological factors may partly influence that abandonment. Kuhn postulates
that "normal science" continues on after the adoption of a new paradigm,
punctuated with occasional scientific revolutions as later anomalies arise
and paradigm shifts occur. History is replete with examples of accurate
theories ignored by peers, and inaccurate ones propagated unduly, due to
social factors.

The typical example used in Kuhnian explanations is the development of
astronomical theory that began, more or less, with the Aristotelian model of
the universe: "The earth is the center of a pristine, perfect universe," and
all motions in such a universe must be circular. The Aristotelian model was
afflicted with various anomalies, such as the apparent retrograde motion of
the planets, which were accommodated by modifications of the model. Nicolaus
Copernicus's model differed by placing the sun at the center of planetary
motion. Both Kepler and Galileo found evidence that supported the
heliocentric model. Aristotle's laws were replaced by Isaac Newton, and
eventually by Albert Einstein's General Relativity. This example
demonstrates that much time may pass before a substitute paradigm is widely
accepted. The Aristotelian model dominated Western thought for more than
2000 years before Newton's viewpoint took its place.

Late 20th century study on the scientific method has focused on
quasi-empirical methods, such as peer review, the spread of notations, which
are the key common concern of philosophy of science, and the philosophy of mathematics.