Scientific methodThe 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.