Scientific consensus

# Overview
Scientific consensus is the collective judgment, position, and opinion of the community of scientists in a particular field of science at a particular time.  Scientific consensus is not, by itself, a scientific argument, and is not part of the scientific method; however, the content of the consensus may itself be based on both scientific arguments and the scientific method.
Consensus is normally achieved through communication at conferences, the process of publication, and peer review. These lead to a situation where those within the discipline can often recognize such a consensus where it exists, but communicating that to outsiders can be difficult. On occasion, scientific institutes issue position statements intended to communicate a summary of the science from the "inside" to the "outside".  In cases where there is little controversy regarding the subject under study, establishing what the consensus is can be quite straightforward.  Scientific consensus may be invoked in popular or political debate on subjects that are controversial within the public sphere but which are not controversial within the scientific community, such as evolution.

# Philosophy
The issue of consensus is important in the philosophy of science. The view that the goal of science is the creation of such a consensus holds that the scientist is a skeptic using his or her analytical and critical thinking faculties to evaluate all evidence presented before delivering an opinion. Unlike other forms of knowledge, scientific knowledge consists of messages that are consensible  that is they can be mutually understood so that they can be evaluated for agreement or dissent and have the possibility of becoming part of the consensus. Thus, consensibility is a prerequisite for consensuality.
There are always outliers, remaining advocates of earlier ideas which have been superseded, cliques or individuals with unique points of view or with new ideas which have not yet been thoroughly tested, and other dissidents. Each of these groups can be quite forceful in pushing their points of view and often are. As science impinges on society, societal groups become advocates of outlying theories for policy purposes, not scientific ones, which can confuse scientific truth.
A final problem in understanding the value of a consensus is the tendency to exaggerate the number of times that a consensus has been overthrown by an outside theory. By its nature there are many more ideas that fail than those that become established. Since progress is almost always incremental, radically new ideas that become accepted are very rare and often years of stringent testing are required before they do so. There is a natural tendency to overestimate the value of radically new ideas. By their nature newspapers and magazines, looking for good stories do so, as do some of the best scientific publications such as Nature and Science.

# Lack of substantial doubt
In its strongest form, the term is used to assert that on a given question scientists within a particular field of science have reached an agreement of rational opinion without substantial doubt, through a process of experimentation and peer review (see scientific method).
For example, in physics there exists scientific consensus on general relativity and quantum mechanics. Special relativity and quantum mechanics are unified in the framework of quantum field theory (QFT). There exists scientific consensus that QFT is a very useful description, but it is not a final theory.  For example, it does not include gravity. General relativity and quantum mechanics may be unified by superstring theory but there is no consensus whether this candidate unifying theory is the correct description of reality.

# Uncertainty and scientific consensus in policy making
In public policy debates, the assertion that there exists a consensus of scientists in a particular field is often used as an argument for the validity of a theory and as support for a course of action. Similarly arguments for a lack of scientific consensus are often encouraged by sides who stand to gain from a more ambiguous policy.
For example, many people of various backgrounds (political, scientific, media, action groups, and so on) have argued that there is a scientific consensus on the causes of global warming. The historian of science Naomi Oreskes published an article in Science reporting that a survey of the abstracts of 928 science articles published between 1993 and 2003 showed none which disagreed explicitly with the notion of anthropogenic global warming. In an editorial published in the Washington Post, Oreskes claimed that those who opposed these scientific findings are amplifying the normal range of scientific uncertainty about any facts into an appearance that there is a great scientific disagreement, or a lack of scientific consensus..
Many creationist organizations have falsely argued that there is considerable debate over the theory of evolution, and used this to justify their public policy arguments that evolution not be considered the only possibility for education in scientific curriculum. Their argument is not based on scientific methods but only on faith based biblical references. In this case their view doesn't measure up acceptable bilateral contention.
Opponents of these creationists, such as the late biologist Stephen Jay Gould, have claimed that the creationists misunderstand the nature of the debate within the pertinent scientific community, stating that the debate with the scientific community is not about whether "if" evolution occurred, but instead is about "how" it occurred. Again, in this instance "scientific consensus" is seen, if it exists, as mandating a certain form of public policy (i.e., that there is no scientific basis for the teaching of alternatives to Darwinist theories of evolution in public schools), and disputing whether or not a consensus exists in the scientific community is one way of combating this mandate.
The inherent uncertainty in science, where theories are never proven but can only be disproven (see falsifiability), poses a problem for politicians, policymakers, lawyers, and business professionals. Where scientific or philosophical questions can often languish in uncertainty for decades within their disciplinary settings, policymakers are faced with the problems of making sound decisions based on the currently available data, even if it is likely not a final form of the "truth". In this respect, going along with the "scientific consensus" of the day can prove dangerous in some situations: nothing looks worse on a record than making drastic decisions based on theories which later turned out to be false, such as the compulsory sterilization of thousands of mentally ill patients in the US during the 1930s under the false notion that it would end mental illness. Certain domains, such as the approval of certain technologies for public consumption, can have vast and far-reaching political, economic, and human effects should things run awry of the predictions of scientists.
Additionally, because of the inherently uncertain aspect of scientific knowledge, it is easy for political opponents to emphasize the constructed nature of facts employed, making the argument that the claim of "science" is just a way of justifying whatever opinion one wants to go with. As such, the domain of science and policy has been an area of constant controversy since at least the beginning of the twentieth century, but especially so in the period after World War II.

# How consensus can change over time
There are many philosophical and historical theories as to how scientific consensus changes over time. Because the history of scientific change is extremely complicated, and because there is a tendency to project "winners" and "losers" onto the past in relation to our current scientific consensus, it is very difficult to come up with accurate and rigorous models for scientific change. This is made exceedingly difficult also in part because each of the various branches of science functions in somewhat different ways with different forms of evidence and experimental approaches.
Most models of scientific change rely on new data produced by scientific experiment. The philosopher Karl Popper proposed that since no amount of experiments could ever prove a scientific theory, but a single experiment could disprove one, all scientific progress should be based on a process of falsification, where experiments are designed with the hope of finding empirical data that the current theory could not account for, indicating its falseness and the requirement for a new theory.
Among the most influential challengers of this approach was the historian Thomas Kuhn, who argued instead that experimental data always provide some data which cannot fit completely into a theory, and that falsification alone did not result in scientific change or an undermining of scientific consensus. He proposed that scientific consensus worked in the form of "paradigms", which were interconnected theories and underlying assumptions about the nature of the theory itself which connected various researchers in a given field. Kuhn argued that only after the accumulation of many "significant" anomalies would scientific consensus enter a period of "crisis". At this point, new theories would be sought out, and eventually one paradigm would triumph over the old one  a cycle of paradigm shifts rather than a linear progression towards truth. Kuhn's model also emphasized more clearly the social and personal aspects of theory change, demonstrating through historical examples that scientific consensus was never truly a matter of pure logic or pure facts.
Lastly, some more radical philosophers, such as Paul Feyerabend, have maintained that scientific consensus is purely idiosyncratic and maintains no relationship to any outside truth. These points of view, while provoking much discussion, have generally not caught on, even with philosophers.

# Scientific consensus and the scientific minority
In a standard application of the psychological principle of confirmation bias, scientific research which supports the existing scientific consensus is usually more favorably received than research which contradicts the existing consensus. In some cases, those who question the current paradigm are at times heavily criticized for their assessments. Research which questions a well supported scientific theory is usually more closely scrutinized in order to assess whether it is well researched and carefully documented. This caution and careful scrutiny is used to ensure that science is protected from a premature divergence away from ideas supported by extensive research and toward new ideas which have yet to stand the testing by extensive research. However, this often results in conflict between the supporters of new ideas and supporters of more dominant ideas, both in cases where the new idea is later accepted and in cases where it is later abandoned. (See: List of minority-opinion scientific theories).
Thomas Kuhn in his 1962 book The Structure of Scientific Revolutions discussed this problem in detail.  Several examples of this are present in the relatively recent history of science. For example:
- the theory of continental drift proposed by Alfred Wegener and supported by Alexander Du Toit and Arthur Holmes but soundly rejected by most geologists until indisputable evidence and an acceptable mechanism was presented after 50 years of rejection.
- the theory of symbiogenesis presented by Lynn Margulis and initially rejected by biologists but now generally accepted.
- the theory of punctuated equilibria proposed by Stephen Jay Gould and Niles Eldredge which is still debated but becoming more accepted in evolutionary theory.
- the theory of prions -proteinaceous infectious particles causing transmissible spongiform encephalopathy diseases- proposed by Stanley B. Prusiner and at first rejected because pathogenicity was believed to depend on nucleic acids now widely accepted due to accumulating evidence.
- the theory of Helicobacter pylori as the cause of stomach ulcers.  This theory was first postulated in 1982 by Barry Marshall and Robin Warren however it was widely rejected by the medical community believing that no bacterium could survive for long in the acidic environment of the stomach.  Marshall demonstrated his findings by drinking a brew of the bacteria and consequently developing ulcers.   In 2005, Warren and Marshall were awarded the Nobel Prize in Medicine for their work on H. pylori
There are also examples of new ideas that were shown to be wrong.  Two of the classics are N rays and polywater.  Although the 2004 DoE panel was divided on the evidence of cold fusion,, most scientists are deeply skeptical.