Scientific method

The scientific method is the term usually used to refer to either a series, or a collection, of processes that are considered characteristic of scientific investigation and of the acquisition of new scientific knowledge.

Philosophers, historians, sociologists, and even scientists have found many ways to describe how science works. Often when someone describes how they think science is done, they are describing how they think science may be best or most reliably done. Since many people, including many scientists, are not particularly observant of their thinking, there are strong opinions about this. Not all are compatible. As a result, discussions of scientific method are frequently partisan. Indeed, there are perhaps as many methods of doing science as there are scientists, and almost certainly as many as as there are method theorists. Usually, the scientific method refers more to the "scientific attitude" and not a set order of doing things, as a step-by-step procedure is not always necessary (such as when something is discovered by accident or fluke). Astronomy, for example, consists of observervation and usually not experimentation.

Nevertheless, some philosophers, and many scientists, have tried to distinguish what it is that is characteristic of science, as opposed to art or engineering or literature or theology. As science has come to occupy a central place in the way humans interact with the world and, to some extent, with each other, more and more people have come to think it important to understand what science is and how it works. With more interest have come more opinions and more approaches. This article is an attempt to summarize the most common views.

Table of contents

1 Introduction 2 The idealized scientific method 2.1 Observation 2.2 Hypothesis 2.3 Prediction 2.4 Verification 2.5 Evaluation 3 Other aspects of the scientific method 4 Annotated list of related issues 5 See Also 6 Collateral topics 7 External links

Introduction

The enunciation of a 'scientific method' by Roger Bacon in the thirteenth century described a repeating cycle of observation, hypothesis, experimentation and the need for independent verification. This view, itself inspired by an Arab alchemical tradition with which Christian ecclesiastical authority was uncomfortable, and based on an essentially Aristolean view of induction, led to Sir Francis Bacon (in 1620 with the New Organon) laying down some methods for identifying causation between phenomena. Analogical arguments became less and less acceptable in explaining what science was.

It is common to speak as if a single approach of this type were how scientists always operate. Many historians, philosophers and sociologists regard this perspective as naïve, and see the actual operation of science as more complicated and haphazard. How scientists actually operate (ie, design experiments, come up with theories, and choose among them) clearly differs from scientist to scientist. A single, formal process cannot fully account for 'the' scientific method in this sense. However, science differs from politics and other aspects of culture in that scientists refer to experiments to 'vet' theories in a way that politics and culture do not. If they did, one supposes they might have become scientific. Many, within science and without, believe that this is the core of the difference.

The question of how science operates is important well beyond scientific circles or the academic community. In the judicial system and in public policy controversies, for example, a study's deviation from accepted scientific practice is grounds to reject it as "junk science." For some decades, the world has been in the midst of such a debate about global warming with studies claimed to 'support' one side or another brandished by advocates of one or another policy. A policy recommendation based on a theory which is not 'generally accepted science' may be rejected by courts, legislators, public officials, or even the public. Whether strictly formularizable or not, scientific method is a usable standard of proficiency and reliability, as are generally accepted scientific theories. This is due at least in part to the way scientists work, that is to 'the scientific method'.

The idealized scientific method

The essential elements of the scientific method are traditionally described as follows:

• Observe: Observe or read about a phenomenon.
• Hypothesize: Wonder about your observations, and invent a hypothesis, (sometimes a 'guess'), which could explain the phenomenon or set of facts that you have observed.
• Test an hypothesis
  • Predict: Use the logical consequences of your hypothesis to predict results (eg, measurement values) which must be seen if the hypothesis is correct -- whether it is 'complete' or not.
  • Experiment: Perform experiments to test those predictions; note that accuracy might be important or might not.
• Conclude: Failure to see the predicted results from a well designed and implemented experiment is clear indication that the hypothesis is defective. Try again. Seeing the predicted results is an indication that the hypothesis is acceptable though not 'confirmation' or 'proof' of its correctness.
  • Evaluate: Search for other possible explanations of the result until you can propose no better account of your data.
• Formulate a new hypothesis which may better explain the experimental data and the original observation.
• Repeat

These activities do not describe all that scientists do. This simplified method is useful for teaching, since it describes the way in which scientists often think of themselves as acting.

This idealised process is often misinterpreted as applying to scientists individually rather than to the scientific enterprise as a whole. Science is a social activity, and one scientist's theory or proposal cannot become accepted unless it has become knonw to others (usually via publication, ideally peer reviewed publication), criticised, and finally accepted by the scientific community.

Observation

The scientific method begins with observation. Observation often demands careful measurement. It also requires the establishment of operational definitions of measurements and other relevant concepts. Definitions are not scientific hypotheses; they are not "falsifiable"; they are simply a way to ensure that everyone is talking about, experimentally testing, etc the same thing. Definitions condense a number of ideas into a single word or phrase. That being said, an observer's definition could differ significantly from commonly understood concepts of a term, and still be correct. Such a definition, however, would as 'private speech' always does, carry greater risk of being misunderstood. These definitions are operational in that they may differ with the context of a hypothesis, and they may be refined when the hypothesis is refined.

For example, the term "day" is useful in ordinary life, and its meaning may vary with the context. (Do we mean a 24 hour period or do we mean the time between sunrise and sunset?) We don't always have to define it with quantitative precision to make use of it. In many contexts, it is precisely 86,400 atomic seconds. In studying the motion of the Earth, we may use two distinct operational definitions: a solar day is the time between two successive observations of the sun at the same position in the sky; a sidereal day is the time between two successive observations of a specific star in the sky at the same position. The length of these two kinds of day differs by about four minutes and is due to the motion of the Earth along its orbit around the Sun during a 'day'.

Slight differences between operational definitions are often important, as they are needed to make experiments precise enough to distinguish subtle underlying phenomena. Another example of this lies in choosing the appropriate segmentation in the statistical analysis of data.

Distinctions in operational definitions can also reflect important conceptual differences: for example, mass and weight are quite different concepts in science, but the distinction is often ignored in everyday life.

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.

In the twentieth century Karl Popper introduced the idea that a hypothesis must be falsifiable; that is, it must be capable of being demonstrated wrong. He was, in this, following the lead of C S Peirce a generation earlier. Paul Feyerabend argued against this position, providing examples of falsified scientific theories that nevertheless had a vital role in the progress of scientific understanding.

Of course, it is impossible for a scientist to be impartial, considering all known evidence, and not merely evidence which supports the hypothesis under development. Scientists are, like everyone else, human. But by submitting their theories and the evidence for or against them for peer review, scientists can at least make it more likely that the hypotheses formed will be relevant and useful, or at least get others to agree with it.

In those 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 (there are several spellings). One chooses the simplest explanation for all the available evidence, in whatever sense "simple" is appropriate in the context. The usual meaning is 'conceptually simple'. An example might be an ancient theory of how the Earth is supported. It was believed that it rested on the back of a giant turtle. The moment one asks what supports the turtle, the issue of infinite regress ("Why, sonny, it's turtles all the way down!" is a famous retort) arises, and any explanation not involving an infinite turtle stack becomes 'simpler'. In other cases, it is 'mathematical simplicity'. For example, James Maxwell developed a mathematically quite elegant, and structually simple, account of electromagnetic radiation (light, X-rays, radio, radar, ...) which involved dual magnetic and electric fields and their interactions about 1860. It was surely less simple in many ways than vibrations of the ether 'carrying' electromagnetic radiation. Unfortunately for the simpler luminiferous ether theory, the Michelson-Morley experiment of 1887 made any account including both the ether and their experimental results more complicated still. Both continued for some decades to ponder the problem in an attempt to reconcile the result with the existence of an ether; neither they nor anyone else has succeeded. Ernst Mach may have been the first to explicitly abandon the ether as a result. Maxwell's hypothesis became, rather quickly, the simplest available account. With modifications required by Relativity, it still is.

Currently, a theory (or several theories in a family) is developing which will require 11 dimensions to account for the phenomena being described (elementary particles and their interactions plus gravity). The necessity appears, to outsiders, to be both mathematical and excessively complicated. But it may be, when the dust settles, that superstrings with 11 dimensions may be the simplest available theory which satisfies the Razor. Or something else altogether (turtles redux, perhaps).

Prediction

An hypothesis must make specific predictions; these predictions can be tested with concrete measurements to support or refute the hypothesis. In Popper's view, any hypothesis that does not, is simply not science. Something else useful and valuable perhaps (or perhaps not), but not science. For instance, Albert Einstein's General Relativity makes several specific predictions about the structure of space-time, such as a prediction that light bends in a strong gravitational field, and that the amount of bending depends in a precise way on the strength of the gravitational field. Observations made during a 1919 solar eclipse supported the hypothesis (i.e., General Relativity) as against those of other hypotheses which predicted different results, and falsified any theory which predicted something else, eg Newtonian gravitation. (Later observations provided other fits with GR predictions. So far, no observation has contradicted a GR prediction; but note that there have been developed several alternative theories to GR, none of which has, to date, done better.)

On the other hand, no one has succeeded in finding any of those giant turtles. By now, observation has established that they must be invisible, allow undetectable penetration by spacecraft, and probably have giant rollers in the backs to allow for the Earth's rotation, else they would have been noticed by now, one way or another. Any turtle theory suggesting otherwise has been demonstrated to be wrong. The turtle theory (as modified to account for new info) is getting more and more complicated. Occam would suggest its rejection.

Deductive reasoning is the way in which predictions are used to test a hypothesis.

Verification

Probably the most important aspect of scientific reasoning is verification: One's experimental observations must be verified. Verification is the process of determining whether the hypothesis is in accord with empirical evidence, both newly acquired and existing.

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 many 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.

Evaluation

Falsificationism suggests that any hypothesis, no matter how respected or time-honoured, be discarded once it is contradicted by reliable evidence, usually from new experiments. This is something of an oversimplification, since individual scientists will often hold on to their pet theory long after contrary evidence has been found. Planck is said to have suggested that new scientific theories are adopted when today's scientists finally die. This is not always a bad thing -- delayed adoption, not scientist mortality. Any theory can be made to correspond to the facts, simply by making a few adjustments—called "auxiliary hypothesis"—so as to bring it into correspondence with the accepted observations. Additions to the turtle theory (invisibility, non-corporality, ...) are an example. When to reject one theory and accept another ('better' one) is dependent on the judgement of individual scientists, rather than some law or authority. As for the turtles, the members of the Flat Earth Society apparently still regard it as a tenable hypothesis, despite any changes in the last few thousand years.

All scientific knowledge is thus always in a state of flux, for at any time new evidence could be presented/discovered/developed that contradicts a long-held hypothesis. A particularly clear example is the theory of light. Light had long been imagined to be made of particles. Isaac Newton was convinced it was so, but his light_is_particles account was overturned by evidence in favor of a wave theory of light, which explained diffraction and interference, and which was widely held to be incontrovertible for most of the 19th century. Evidence, accounted for by Max Planck's quantum theory (including the photoelectric effect and Brownian motion -- both from Albert Einstein) finally made the pure wave theory untenable. The currently held theory of light, dating from the first decades of the 20th century, 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, and so any theory holding one way or the other is unacceptable.

The experiments that force rejection of an 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 papers describing experimental results and their consequences 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 were able 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. Peer review may well have turned up problems and led to a closer examination of the experimental evidence Fleischmann, Pons, et al believed they had. Paul Kammerer's experiments on developing traits in amphibians (described in Arthur Koestler's The Midwife Toad) seem to have been deliberate fraud, while the confusion in the 60s and 70s about 'polywater' seems to have the result of micro contamination (and maybe some Cold War political oneupsmanship). Much embarrassment, and wasted effort, might have been avoided by proper peer review in many of these cases.

Other aspects of the scientific method

There are no definitive guidelines for the production of new hypotheses. The history of science is filled with stories of scientists claiming a "flash of inspiration", or a hunch, which then motivated them to look for evidence to support or refute their idea. Michael Polanyi made such creativity the centrepiece of his methodology. The story about an apple falling on Isaac Newton's head and inspiring his theory of gravity is a popular example of this; there is no evidence that an apple actually fell on his head. All Newton said was that his ideas were inspired "by the fall of an apple." In contrast, Kekule's account of the inspiration (in the mid 19th century) for his hypothesis of the structure of the benzene-ring (day dreaming of snakes biting their own tails while dozing in an omnibus) is better attested, in his own words from the time. And, though primarily an engineer and not a scientist, Thomas Edison was famously quoted in the 20th century as saying that "inspiration is 99% perspiration". Hypotheses come from many sources and there is no method known which always generates 'good' ones.

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. This is primarily a psychological bias, however often useful, as 'more complex' (and less psychologically satisfying) theories have often been required 'to account for the phenomena'. Superstring theory (with all those dimensions) may turn out to be one such.

Aristotle's model of the universe suggested that the earth is the centre of a pristine, perfect universe, and that all motions in the perfect portion of such a universe be circular. In its most developed form, the Ptolemaic model, this model quantitatively explained the motion of the planets, including the retrograde motion of some of them, by introducing epicycles -- ie, circles on circles. Nicolaus Copernicus' model placed the sun at the centre of planetary motion, but also assumed that the planets moved in perfect circles. He also found it necessary to make use of epicycles, and jhis theory was as complex as -- yet less accurate when proposed -- than Ptolemy's heliocentric/epicyclic model was when it was designed. Improvement in the fit of Copernicus' model to actual observation depended on developing a mathematics of elliptical orbits to replace the epicycles; but it did not achieve near universal acceptance until a conceptual change in the way in which gravitational motion was understood. Tycho Brahe made unprecedentedly accurate observations after Copernicus, but did himself not reject the geocentric model. His own was a modification of Ptolemy. It took Johannes Kepler 20 years to develop a mathematical account of planetary motion (ie, heliocentric elliptical orbits with equal areas swept in equal times) which was compatible with Tycho Brahe's observations.

In turn, Sir Isaac Newton's System of the World unified Kepler's mathematical description of the observed motion with Galileo's studies of acceleration, and produced a comprehensive account of motion and gravity. It has remained in most respects the best available theory of both, since it was developed. The corrections imposed by Einstein's General Relativity (forced by such things as the motion of Mercury) apply only at high velocities and in the close neighborhood of intense gravitational fields; no human being has ever yet directly experienced either to a noticeable extent.

Dogged adherence to any method can be counterproductive in science as in any discipline. Imagination is hardly to be neglected.

History relates several examples of theories which were first ignored by others, including scientists, but later widely seen to have been better theories. Examples include

• the motion of the continents (now called plate tectonics, which was not taken seriously by almost anyone (despite what are, in retrospect only, plain hints in some of the available data) until still more blatant evidence was (literally) unearthed of ocean floor spreading,
• generation of new life requiring existing life (not believed by most observers; certainly not for such things as maggots and, later, bacteria which were thought to spontaneously generate), which were not seriously regarded until Francesco Redi, Lazzaro Spallanzani, and Louis Pasteur designed and carried out experiements demonstrating that mice, maggots, and bacteria required progenitors; it's instructive to note how many decades came between the first and last of these experiments (about 20!),
• protein as a carrier of genetic traits, widely thought a plausible theory as protein was the only known biological chemical with 'sufficient complexity to carry genetic information' until Oswald Avery's experiment involving salmon just prior to WWII demonstrated that nucleic acid was the genetic information carrier.