Science (from meaning "knowledge") is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe. An older and closely related meaning still in use today is that of Aristotle, for whom scientific knowledge was a body of reliable knowledge that can be logically and rationally explained (''see "History and etymology" section below'').

Since classical antiquity science as a type of knowledge was closely linked to philosophy. In the early modern era the two words, "science" and "philosophy", were sometimes used interchangeably in the English language. By the 17th century, "natural philosophy" (which is today called "natural science") had begun to be considered separately from "philosophy" in general. However, "science" continued to be used in a broad sense denoting reliable knowledge about a topic, in the same way it is still used in modern terms such as library science or political science.

In modern use, science is "often treated as synonymous with ‘natural and physical science’, and thus restricted to those branches of study that relate to the phenomena of the material universe and their laws, sometimes with implied exclusion of pure mathematics. This is now the dominant sense in ordinary use." This narrower sense of "science" developed as a part of science became a distinct enterprise of defining "laws of nature", based on early examples such as Kepler's laws, Galileo's laws, and Newton's laws of motion. In this period it became more common to refer to natural philosophy as "natural science". Over the course of the 19th century, the word "science" became increasingly associated with the disciplined study of the natural world including physics, chemistry, geology and biology. This sometimes left the study of human thought and society in a linguistic limbo, which was resolved by classifying these areas of academic study as social science. Similarly, several other major areas of disciplined study and knowledge exist today under the general rubric of "science", such as formal science and applied science.

History and etymology

While descriptions of disciplined empirical investigations of the natural world exist from times at least as early as classical antiquity (for example, by Aristotle and Pliny the Elder), and scientific methods have been employed since the Middle Ages (for example, by Alhazen and Roger Bacon), the dawn of modern science is generally traced back to the early modern period during what is known as the Scientific Revolution of the 16th and 17th centuries. This period was marked by a new way of studying the natural world, by methodical experimentation aimed at defining "laws of nature" while avoiding concerns with metaphysical concerns such as Aristotle's theory of causation.

This modern science developed from an older and broader enterprise. The word "science" is from Old French, and in turn from Latin which was one of several words for "knowledge" in that language. In philosophical contexts, ''scientia'' and "science" were used to translate the Greek word ''epistemē'', which had acquired a specific definition in Greek philosophy, especially Aristotle, as a type of reliable knowledge which is built up logically from strong premises, and can be communicated and taught. In contrast to modern science, Aristotle's influential emphasis was upon the "theoretical" steps of deducing universal rules from raw data, and did not treat the gathering of experience and raw data as part of science itself.

From the Middle Ages to the Enlightenment, science or ''scientia'' continued to be used in this broad sense, which was still common until the 20th century. "Science" therefore had the same sort of very broad meaning that ''philosophy'' had at that time. In other Latin influenced languages, including French, Spanish, Portuguese, and Italian, the word corresponding to ''science'' also carried this meaning.

Prior to the 18th century, the preferred term for the study of nature among English speakers was "natural philosophy", while other philosophical disciplines (e.g., logic, metaphysics, epistemology, ethics and aesthetics) were typically referred to as "moral philosophy". (Today, "moral philosophy" is more-or-less synonymous with "ethics".) Science only became more strongly associated with natural philosophy than other sciences gradually with the strong promotion of the importance of experimental scientific method, by people such as Francis Bacon. With Bacon, begins a more widespread and open criticism of Aristotle's influence which had emphasized theorizing and did not treat raw data collection as part of science itself. An opposed position became common: that what is critical to science at its best is methodical collecting of clear and useful raw data, something which is easier to do in some fields than others.

The word "science" in English was still however used in the 17th century to refer to the Aristotelian concept of knowledge which was secure enough to be used as a prescription for exactly how to accomplish a specific task. With respect to the transitional usage of the term "natural philosophy" in this period, the philosopher John Locke wrote in 1690 that "natural philosophy is not capable of being made a science". However, it may be that Locke was not using the word 'science' in the modern sense, but suggesting that 'natural philosophy' could not be deduced in the same way as mathematics and logic.

Locke's assertion notwithstanding, by the early 19th century natural philosophy had begun to separate from philosophy, though it often retained a very broad meaning. In many cases, ''science'' continued to stand for reliable knowledge about any topic, in the same way it is still used today in the broad sense (see the introduction to this article) in modern terms such as library science, political science, and computer science. In the more narrow sense of ''science'', as natural philosophy became linked to an expanding set of well-defined laws (beginning with Galileo's laws, Kepler's laws, and Newton's laws for motion), it became more popular to refer to natural philosophy as natural science. Over the course of the 19th century, moreover, there was an increased tendency to associate science with study of the natural world (that is, the non-human world). This move sometimes left the study of human thought and society (what would come to be called social science) in a linguistic limbo by the end of the century and into the next.

Through the 19th century, many English speakers were increasingly differentiating science (i.e., the natural sciences) from all other forms of knowledge in a variety of ways. The now-familiar expression “scientific method,” which refers to the ''prescriptive'' part of how to make discoveries in natural philosophy, was almost unused until then, but became widespread after the 1870s, though there was rarely total agreement about just what it entailed. The word "scientist," meant to refer to a systematically working natural philosopher, (as opposed to an intuitive or empirically minded one) was coined in 1833 by William Whewell. Discussion of scientists as a special group of people, who did science, even if their attributes were up for debate, grew in the last half of the 19th century. Whatever people actually meant by these terms at first, they ultimately depicted science, in the narrow sense of the habitual use of the scientific method and the knowledge derived from it, as something deeply distinguished from all other realms of human endeavor.

By the 20th century, the modern notion of science as a special kind of knowledge about the world, practiced by a distinct group and pursued through a unique method was essentially in place. It was used to give legitimacy to a variety of fields through such titles as "scientific" medicine, engineering, advertising, or motherhood. Over the 20th century, links between science and technology also grew increasingly strong. As Martin Rees explains, progress in scientific understanding and technology have been synergistic and vital to one another.

Richard Feynman described science, to his students, as: "The principle of science, the definition, almost, is the following: ''The test of all knowledge is experiment.'' Experiment is the ''sole judge'' of scientific 'truth'. But what is the source of knowledge? Where do the laws that are to be tested come from? Experiment, itself, helps to produce these laws, in the sense that it gives us hints. But also needed is imagination to create from these hints the great generalizations — to guess at the wonderful, simple, but very strange patterns beneath them all, and then to experiment to check again whether we have made the right guess." Feynman also observed, "...there is an expanding frontier of ignorance...things must be learned only to be unlearned again or, more likely, to be corrected."

Branches

Scientific fields are commonly divided into two major groups: natural sciences, which study natural phenomena (including biological life), and social sciences, which study human behavior and societies. These groupings are empirical sciences, which means the knowledge must be based on observable phenomena and capable of being tested for its validity by other researchers working under the same conditions. There are also related disciplines that are grouped into interdisciplinary and applied sciences, such as engineering and medicine. Within these categories are specialized scientific fields that can include parts of other scientific disciplines but often possess their own terminology and expertise.

Mathematics, which is classified as a formal science, has both similarities and differences with the empirical sciences (the natural and social sciences). It is similar to empirical sciences in that it involves an objective, careful and systematic study of an area of knowledge; it is different because of its method of verifying its knowledge, using ''a priori'' rather than empirical methods. The formal sciences, which also include statistics and logic, are vital to the empirical sciences. Major advances in formal science have often led to major advances in the empirical sciences. The formal sciences are essential in the formation of hypotheses, theories, and laws, both in discovering and describing how things work (natural sciences) and how people think and act (social sciences).

Scientific method

A scientific method seeks to explain the events of nature in a reproducible way, and to use these findings to make useful predictions. This is done partly through observation of natural phenomena, but also through experimentation that tries to simulate natural events under controlled conditions. Taken in its entirety, a scientific method allows for highly creative problem solving whilst minimizing any effects of subjective bias on the part of its users (namely the confirmation bias).

Basic and applied research

Although some scientific research is applied research into specific problems, a great deal of our understanding comes from the curiosity-driven undertaking of basic research. This leads to options for technological advance that were not planned or sometimes even imaginable. This point was made by Michael Faraday when, allegedly in response to the question "what is the ''use'' of basic research?" he responded "Sir, what is the use of a new-born child?". For example, research into the effects of red light on the human eye's rod cells did not seem to have any practical purpose; eventually, the discovery that our night vision is not troubled by red light would lead search and rescue teams (among others) to adopt red light in the cockpits of jets and helicopters. In a nutshell: Basic research is the search for knowledge. Applied research is the search for solutions to practical problems using this knowledge. Finally, even basic research can take unexpected turns, and there is some sense in which the scientific method is built to harness luck.

Experimentation and hypothesizing

Based on observations of a phenomenon, scientists may generate a model. This is an attempt to describe or depict the phenomenon in terms of a logical, physical or mathematical representation. As empirical evidence is gathered, scientists can suggest a hypothesis to explain the phenomenon. Hypotheses may be formulated using principles such as parsimony (also known as "Occam's Razor") and are generally expected to seek consilience—fitting well with other accepted facts related to the phenomena. This new explanation is used to make falsifiable predictions that are testable by experiment or observation. When a hypothesis proves unsatisfactory, it is either modified or discarded. Experimentation is especially important in science to help establish causational relationships (to avoid the correlation fallacy). Operationalization also plays an important role in coordinating research in/across different fields.

Once a hypothesis has survived testing, it may become adopted into the framework of a scientific theory. This is a logically reasoned, self-consistent model or framework for describing the behavior of certain natural phenomena. A theory typically describes the behavior of much broader sets of phenomena than a hypothesis; commonly, a large number of hypotheses can be logically bound together by a single theory. Thus a theory is a hypothesis explaining various other hypotheses. In that vein, theories are formulated according to most of the same scientific principles as hypotheses.

While performing experiments, scientists may have a preference for one outcome over another, and so it is important to ensure that science as a whole can eliminate this bias. This can be achieved by careful experimental design, transparency, and a thorough peer review process of the experimental results as well as any conclusions. After the results of an experiment are announced or published, it is normal practice for independent researchers to double-check how the research was performed, and to follow up by performing similar experiments to determine how dependable the results might be.

Certainty and science

A scientific theory is empirical, and is always open to falsification if new evidence is presented. That is, no theory is ever considered strictly certain as science accepts the concept of fallibilism. The philosopher of science Karl Popper sharply distinguishes truth from certainty. He writes that scientific knowledge "consists in the search for truth", but it "is not the search for certainty ... All human knowledge is fallible and therefore uncertain."

thumb|left|130px|Although science values legitimate doubt, The Flat Earth Society is still widely regarded as an example of taking skepticism too farTheories very rarely result in vast changes in our understanding. According to psychologist Keith Stanovich, it may be the media's overuse of words like "breakthrough" that leads the public to imagine that science is constantly proving everything it thought was true to be false. While there are such famous cases as the theory of relativity that required a complete reconceptualization, these are extreme exceptions. Knowledge in science is gained by a gradual synthesis of information from different experiments, by various researchers, across different domains of science; it is more like a climb than a leap. Theories vary in the extent to which they have been tested and verified, as well as their acceptance in the scientific community. For example, heliocentric theory, the theory of evolution, and germ theory still bear the name "theory" even though, in practice, they are considered factual. Philosopher Barry Stroud adds that, although the best definition for "knowledge" is contested, being skeptical and entertaining the ''possibility'' that one is incorrect is compatible with being correct. Ironically then, the scientist adhering to proper scientific method will doubt themselves even once they possess the truth. The fallibilist C. S. Peirce argued that inquiry is the struggle to resolve actual doubt and that merely quarrelsome, verbal, or hyperbolic doubt is fruitless—but also that the inquirer should try to attain genuine doubt rather than resting uncritically on common sense. He held that the successful sciences trust, not to any single chain of inference (no stronger than its weakest link), but to the cable of multiple and various arguments intimately connected.

Stanovich also asserts that science avoids searching for a "magic bullet"; it avoids the single cause fallacy. This means a scientist would not ask merely "What is ''the'' cause of...", but rather "What ''are'' the most significant ''causes'' of...". This is especially the case in the more macroscopic fields of science (e.g. psychology, cosmology). Of course, research often analyzes few factors at once, but this always to add to the long list of factors that are most important to consider.

Whether mathematics itself is properly classified as science has been a matter of some debate. Some thinkers see mathematicians as scientists, regarding physical experiments as inessential or mathematical proofs as equivalent to experiments. Others do not see mathematics as a science, since it does not require an experimental test of its theories and hypotheses. Mathematical theorems and formulas are obtained by logical derivations which presume axiomatic systems, rather than the combination of empirical observation and logical reasoning that has come to be known as scientific method. In general, mathematics is classified as formal science, while natural and social sciences are classified as empirical sciences.

Scientific community

The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science.

Fields

Fields of science are widely recognized categories of specialized expertise, and typically embody their own terminology and nomenclature. Each field will commonly be represented by one or more scientific journal, where peer reviewed research will be published.

Institutions

Learned societies for the communication and promotion of scientific thought and experimentation have existed since the Renaissance period. The oldest surviving institution is the in Italy. The respective National Academies of Science are distinguished institutions that exist in a number of countries, beginning with the British Royal Society in 1660 and the French in 1666.

International scientific organizations, such as the International Council for Science, have since been formed to promote cooperation between the scientific communities of different nations. More recently, influential government agencies have been created to support scientific research, including the National Science Foundation in the U.S.

Other prominent organizations include the National Scientific and Technical Research Council in Argentina, the academies of science of many nations, CSIRO in Australia, in France, Max Planck Society and in Germany, and in Spain, CSIC.

Literature

An enormous range of scientific literature is published. Scientific journals communicate and document the results of research carried out in universities and various other research institutions, serving as an archival record of science. The first scientific journals, ''Journal des Sçavans'' followed by the ''Philosophical Transactions'', began publication in 1665. Since that time the total number of active periodicals has steadily increased. As of 1981, one estimate for the number of scientific and technical journals in publication was 11,500. Today Pubmed lists almost 40,000, related to the medical sciences only.

Most scientific journals cover a single scientific field and publish the research within that field; the research is normally expressed in the form of a scientific paper. Science has become so pervasive in modern societies that it is generally considered necessary to communicate the achievements, news, and ambitions of scientists to a wider populace.

Science magazines such as New Scientist, Science & Vie and Scientific American cater to the needs of a much wider readership and provide a non-technical summary of popular areas of research, including notable discoveries and advances in certain fields of research. Science books engage the interest of many more people. Tangentially, the science fiction genre, primarily fantastic in nature, engages the public imagination and transmits the ideas, if not the methods, of science.

Recent efforts to intensify or develop links between science and non-scientific disciplines such as Literature or, more specifically, Poetry, include the ''Creative Writing Science'' resource developed through the Royal Literary Fund.

Women in science

Science is, in general, a male-dominated field. Evidence suggests that this is due to stereotypes (e.g. science as "manly") as well as self-fulfilling prophecies. Experiments have shown that parents challenge and explain more to boys than girls, asking them to reflect more deeply and logically. Physicist Evelyn Fox Keller argues that science may suffer for its manly stereotypes when ego and competitiveness obstruct progress, since these tendencies prevent collaboration and sharing of information. As will be seen in the main article, many women have risen above past prejudices to do great things in science.

Philosophy of science

Philosophy of science seeks to understand the nature and justification of scientific knowledge. Since it is difficult to distinguish science from non-science, there are legitimate arguments about the boundaries between science and non-science. This is known as the problem of demarcation. There is however, a set of core precepts that have broad consensus among philosophers of science and within the scientific community on what constitutes scientific knowledge. For example, it is generally agreed that scientific hypotheses and theories must be capable of being independently tested and verified by other scientists in order to become accepted by the scientific community.

There are different schools of thought in philosophy of science. The most popular position is empiricism, which claims that knowledge is created by a process involving observation and that scientific theories are the result of generalizations from such observations. Empiricism generally encompasses inductivism, a position that tries to explain the way general theories can be justified by the finite number of observations humans can make and the hence finite amount of empirical evidence available to confirm scientific theories. This is necessary because the number of predictions those theories make is infinite, which means that they cannot be known from the finite amount of evidence using deductive logic only. Many versions of empiricism exist, with the predominant ones being bayesianism and the hypothetico-deductive method.

Empiricism has stood in contrast to rationalism, the position originally associated with Descartes, which holds that knowledge is created by the human intellect, not by observation. A significant twentieth century version of rationalism is critical rationalism, first defined by Austrian-British philosopher Karl Popper. Popper rejected the way that empiricism describes the connection between theory and observation. He claimed that theories are not generated by observation, but that observation is made in the light of theories and that the only way a theory can be affected by observation is when it comes in conflict with it. Popper proposed falsifiability as the landmark of scientific theories, and falsification as the empirical method to replace verifiability and induction by purely deductive notions. Popper further claimed that there is only one universal method in science, and that this method is not specific to science: The negative method of criticism, trial and error. It covers all products of the human mind, including science, mathematics, philosophy, and art

Another approach, instrumentalism, colloquially termed "shut up and calculate", emphasizes the utility of theories as instruments for explaining and predicting phenomena. It claims that scientific theories are black boxes with only their input (initial conditions) and output (predictions) being relevant. Consequences, notions and logical structure of the theories are claimed to be something that should simply be ignored and that scientists shouldn't make a fuss about (see interpretations of quantum mechanics).

Finally, another approach often cited in debates of scientific skepticism against controversial movements like creationism, is methodological naturalism. Its main point is that a difference between natural and supernatural explanations should be made, and that science should be restricted methodologically to natural explanations. That the restriction is merely methodological (rather than ontological) means that science should not consider supernatural explanations itself, but should not claim them to be wrong either. Instead, supernatural explanations should be left a matter of personal belief outside the scope of science. Methodological naturalism maintains that proper science requires strict adherence to empirical study and independent verification as a process for properly developing and evaluating explanations for observable phenomena. The absence of these standards, arguments from authority, biased observational studies and other common fallacies are frequently cited by supporters of methodological naturalism as criteria for the dubious claims they criticize not to be true science.

Science policy

Science policy is an area of public policy concerned with the policies that affect the conduct of the science and research enterprise, including research funding, often in pursuance of other national policy goals such as technological innovation to promote commercial product development, weapons development, health care and environmental monitoring. Science policy also refers to the act of applying scientific knowledge and consensus to the development of public policies. Science policy thus deals with the entire domain of issues that involve the natural sciences. Is accordance with public policy being concerned about the well-being of its citizens, science policy's goal is to consider how science and technology can best serve the public.

State policy has influenced the funding of public works and science for thousands of years, dating at least from the time of the Mohists, who inspired the study of logic during the period of the Hundred Schools of Thought, and the study of defensive fortifications during the Warring States Period in China. In Great Britain, governmental approval of the Royal Society in the seventeenth century recognized a scientific community which exists to this day. The professionalization of science, begun in the nineteenth century, was partly enabled by the creation of scientific organizations such as the National Academy of Sciences, the Kaiser Wilhelm Institute, and State funding of universities of their respective nations. Public policy can directly affect the funding of capital equipment, intellectual infrastructure for industrial research, by providing tax incentives to those organizations that fund research. Vannevar Bush, director of the office of scientific research and development for the United States government, the forerunner of the National Science Foundation, wrote in July 1945 that "Science is a proper concern of government"

Science and technology research is often funded through a competitive process, in which potential research projects are evaluated and only the most promising receive funding. Such processes, which are run by government, corporations or foundations, allocate scarce funds. Total research funding in most developed countries is between 1.5% and 3% of GDP. In the OECD, around two-thirds of research and development in scientific and technical fields is carried out by industry, and 20% and 10% respectively by universities and government. The government funding proportion in certain industries is higher, and it dominates research in social science and humanities. Similarly, with some exceptions (e.g. biotechnology) government provides the bulk of the funds for basic scientific research. In commercial research and development, all but the most research-oriented corporations focus more heavily on near-term commercialisation possibilities rather than "blue-sky" ideas or technologies (such as nuclear fusion).

Pseudoscience, fringe science, and junk science

An area of study or speculation that masquerades as science in an attempt to claim a legitimacy that it would not otherwise be able to achieve is sometimes referred to as pseudoscience, fringe science, or "alternative science". Another term, junk science, is often used to describe scientific hypotheses or conclusions which, while perhaps legitimate in themselves, are believed to be used to support a position that is seen as not legitimately justified by the totality of evidence. Physicist Richard Feynman coined the term "cargo cult science" in reference to pursuits that have the formal trappings of science but lack "a principle of scientific thought that corresponds to a kind of utter honesty" that allows their results to be rigorously evaluated. Various types of commercial advertising, ranging from hype to fraud, may fall into these categories.

There also can be an element of political or ideological bias on all sides of such debates. Sometimes, research may be characterized as "bad science", research that is well-intentioned but is seen as incorrect, obsolete, incomplete, or over-simplified expositions of scientific ideas. Doctor Hugh O'Connor coined the term "scientific misconduct" which refers to where researchers have intentionally misrepresented their published data or have purposely given credit for a discovery to the wrong person.

Critiques

Philosophical critiques

Historian Jacques Barzun termed science "a faith as fanatical as any in history" and warned against the use of scientific thought to suppress considerations of meaning as integral to human existence. Many recent thinkers, such as Carolyn Merchant, Theodor Adorno and E. F. Schumacher considered that the 17th century scientific revolution shifted science from a focus on understanding nature, or wisdom, to a focus on manipulating nature, i.e. power, and that science's emphasis on manipulating nature leads it inevitably to manipulate people, as well. Science's focus on quantitative measures has led to critiques that it is unable to recognize important qualitative aspects of the world.

Philosopher of science Paul K Feyerabend advanced the idea of epistemological anarchism, which holds that there are no useful and exception-free methodological rules governing the progress of science or the growth of knowledge, and that the idea that science can or should operate according to universal and fixed rules is unrealistic, pernicious and detrimental to science itself. Feyerabend advocates treating science as an ideology alongside others such as religion, magic and mythology, and considers the dominance of science in society authoritarian and unjustified. He also contended (along with Imre Lakatos) that the demarcation problem of distinguishing science from pseudoscience on objective grounds is not possible and thus fatal to the notion of science running according to fixed, universal rules.

Feyerabend also criticized science for not having evidence for its own philosophical precepts. Particularly the notion of Uniformity of Law and the Uniformity of Process across time and space. "We have to realize that a unified theory of the physical world simply does not exist" says Feyerabend, "We have theories that work in restricted regions, we have purely formal attempts to condense them into a single formula, we have lots of unfounded claims (such as the claim that all of chemistry can be reduced to physics), phenomena that do not fit into the accepted framework are suppressed; in physics, which many scientists regard as the one really basic science, we have now at least three different points of view...without a promise of conceptual (and not only formal) unification".

Sociologist Stanley Aronowitz scrutinizes science for operating with the presumption that the only acceptable criticisms of science are those conducted within the methodological framework that science has set up for itself. That science insists that only those who have been inducted into its community, through means of training and credentials, are qualified to make these criticisms. Aronowitz also alleges that while scientists consider it absurd that Fundamentalist Christianity uses biblical references to bolster their claim that the Bible is true, scientists pull the same tactic by using the tools of science to settle disputes concerning its own validity.

Psychologist Carl Jung believed that though science attempted to understand all of nature, the experimental method imposed artificial and conditional questions that evoke equally artificial answers. Jung encouraged, instead of these 'artificial' methods, empirically testing the world in a holistic manner. David Parkin compared the epistemological stance of science to that of divination. He suggested that, to the degree that divination is an epistemologically specific means of gaining insight into a given question, science itself can be considered a form of divination that is framed from a Western view of the nature (and thus possible applications) of knowledge.

Several academics have offered critiques concerning ethics in science. In ''Science and Ethics'', for example, the philosopher Bernard Rollin examines the relevance of ethics to science, and argues in favor of making education in ethics part and parcel of scientific training.

Media perspectives

The mass media face a number of pressures that can prevent them from accurately depicting competing scientific claims in terms of their credibility within the scientific community as a whole. Determining how much weight to give different sides in a scientific debate may require considerable expertise regarding the matter. Few journalists have real scientific knowledge, and even beat reporters who know a great deal about certain scientific issues may be ignorant about other scientific issues that they are suddenly asked to cover.

Politics and public perception of science

Many issues damage the relationship of science to the media and the use of science and scientific arguments by politicians. As a very broad generalisation, many politicians seek certainties and ''facts'' whilst scientists typically offer probabilities and caveats. However, politicians' ability to be heard in the mass media frequently distorts the scientific understanding by the public. Examples in Britain include the controversy over the MMR inoculation, and the 1988 forced resignation of a Government Minister, Edwina Currie for revealing the high probability that battery farmed eggs were contaminated with ''Salmonella''.

See also

Protoscience

Outline of science

Science wars

Antiquarian science books

Notes

References

Feyerabend, Paul (2005). ''Science, history of the philosophy'', as cited in of.'' Oxford Companion to Philosophy. Oxford. Papineau, David. (2005). ''Science, problems of the philosophy of.'', as cited in }}.

Further reading

Augros, Robert M., Stanciu, George N., "The New Story of Science: mind and the universe", Lake Bluff, Ill.: Regnery Gateway, c1984. ISBN 0-89526-833-7

Baxter, Charles

Cole, K. C., ''Things your teacher never told you about science: Nine shocking revelations'' Newsday, Long Island, New York, March 23, 1986, pg 21+

Feynman, Richard "Cargo Cult Science"

Gopnik, Alison, "Finding Our Inner Scientist", Daedalus, Winter 2004.

Krige, John, and Dominique Pestre, eds., ''Science in the Twentieth Century'', Routledge 2003, ISBN 0-415-28606-9

Kuhn, Thomas, ''The Structure of Scientific Revolutions'', 1962.

McComas, William F. Rossier School of Education, University of Southern California. Direct Instruction News. Spring 2002 24–30.

Levin, Yuval (2008). ''Imagining the Future: Science and American Democracy''. New York, Encounter Books. ISBN 1-59403-209-2

Stephen Gaukroger. ''The Emergence of a Scientific Culture: Science and the Shaping of Modernity 1210–1685.'' Oxford, Clarendon Press, 2006, 576 pp.

External links

Publications

"''GCSE Science textbook''". Wikibooks.org

News

Nature News. Science news by the journal ''Nature''

New Scientist. An weekly magazine published by Reed Business Information

ScienceDaily

Science Newsline

Sciencia

Discover Magazine

Irish Science News from Discover Science & Engineering

Science Stage Scientific Videoportal and Community

Resources

Euroscience:

* Euroscience Open Forum (ESOF)

Science Council

Science Development in the ''Latin American docta''

Classification of the Sciences in ''Dictionary of the History of Ideas''. (Dictionary's new electronic format is badly botched, entries after "Design" are inaccessible. ''Internet Archive'' old version).

"Nature of Science" University of California Museum of Paleontology

United States Science Initiative. Selected science information provided by U.S. Government agencies, including research and development results.

af:Wetenskap am:ሳይንስ ang:Witancræft ar:علم an:Sciencia as:বিজ্ঞান ast:Ciencia ay:Yatxatawi az:Elm bm:Dɔnniya bn:বিজ্ঞান zh-min-nan:Kho-ha̍k map-bms:Ilmu ba:Фән be:Навука be-x-old:Навука bar:Wissnschåft bo:ཚན་རིག bs:Nauka br:Skiant bg:Наука ca:Ciència cv:Ăслăх ceb:Kaalamdag cs:Věda cy:Gwyddoniaeth da:Videnskab de:Wissenschaft et:Teadus el:Επιστήμη es:Ciencia eo:Scienco ext:Céncia eu:Zientzia fa:علم hif:Vigyan fr:Science fy:Wittenskip fur:Sience ga:Eolaíocht gd:Saidheans gl:Ciencia gan:科學 gu:વિજ્ઞાન hak:Khô-ho̍k ko:과학 haw:Akeakamai hy:Գիտություն hi:विज्ञान hr:Znanost io:Cienco ig:Amamihe bpy:বিজ্ঞান id:Ilmu ia:Scientia os:Зонад xh:ISyensya is:Vísindi it:Scienza he:מדע jv:Èlmu kn:ವಿಜ್ಞಾನ krc:Илму ka:მეცნიერება csb:Ùczba kk:Ғылым kw:Godhonieth ky:Илим sw:Sayansi kg:Kizabu ht:Syans ku:Zanist la:Scientia lv:Zinātne lb:Wëssenschaft lt:Mokslas li:Weitesjap jbo:saske lmo:Scienza hu:Tudomány mk:Наука mg:Siansa ml:ശാസ്ത്രം mt:Xjenza mr:विज्ञान arz:علم ms:Sains mwl:Ciéncia mn:Шинжлэх ухаан my:သိပ္ပံပညာ nah:Tlamatiliztli nl:Wetenschap nds-nl:Wetenschop ne:विज्ञान new:विज्ञान ja:科学 ce:Iилм pih:Saiens no:Vitenskap nn:Vitskap nrm:Scienche oc:Sciéncia mhr:Шанче or:ବିଜ୍ଞାନ uz:Fan pnb:سائنس pap:Siencia pms:Siensa nds:Wetenschop pl:Nauka pt:Ciência crh:İlim ro:Știință qu:Hamut'ay rue:Наука ru:Наука sah:Үөрэх sm:Saienisi sa:विज्ञानम् sc:Iscièntzia sco:Science st:Sayense sq:Shkencëtari scn:Scienza si:බටහිර-විද්‍යාව simple:Science ss:Isayensi sk:Veda sl:Znanost so:Saynis ckb:زانست srn:Skoro sr:Наука sh:Nauka su:Élmu fi:Tiede sv:Vetenskap tl:Agham ta:அறிவியல் tt:Фән te:విజ్ఞానశాస్త్రం th:วิทยาศาสตร์ tg:Илм ve:Saintsi tr:Bilim bug:ᨔᨕᨗᨊᨔ uk:Наука ur:سائنس za:Gohyoz vec:Sienza vi:Khoa học fiu-vro:Tiidüs wa:Syince zh-classical:格致 war:Syensya wo:Xam-xam ts:Sciences yi:וויסנשאפט yo:Sáyẹ́nsì zh-yue:科學 bat-smg:Muokslos zh:科学

Carbon fiber (carbon fibre), alternatively graphite fiber, carbon graphite or CF, is a material consisting of extremely thin fibers about 0.005–0.010 mm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fiber. The crystal alignment makes the fiber very strong for its size. Several thousand carbon fibers are twisted together to form a yarn, which may be used by itself or woven into a fabric.

The properties of carbon fibers such as high flexibility, high tensile strength, low weight, high temperature tolerance and low thermal expansion make them very popular in aerospace, civil engineering, military, and motorsports, along with other competition sports. However, they are relatively expensive when compared to similar fibers for example glass fibers or plastic fibers.

Carbon fibers are usually combined with other materials to form a composite. When combined with a plastic resin and wound or molded it forms carbon fiber reinforced plastic (often referred to also as carbon fiber) which is a very high strength-to-weight, extremely rigid, although somewhat brittle material. However, carbon fibers are also composed with other materials, such as with graphite to form carbon-carbon composites, which have a very high heat tolerance.

History of carbon fiber

In 1958, Roger Bacon created high-performance carbon fibers at the Union Carbide Parma Technical Center, now GrafTech International Holdings, Inc., located outside of Cleveland, Ohio. Those fibers were manufactured by heating strands of rayon until they carbonized. This process proved to be inefficient, as the resulting fibers contained only about 20% carbon and had low strength and stiffness properties. In the early 1960s, a process was developed by Dr. Akio Shindo at Agency of Industrial Science and Technology of Japan, using polyacrylonitrile (PAN) as a raw material. This had produced a carbon fiber that contained about 55% carbon.

The high potential strength of carbon fiber was realized in 1963 in a process developed at the Royal Aircraft Establishment at Farnborough, Hampshire. The process was patented by the UK Ministry of Defence then licensed by the National Research Development Corporation (NRDC) to three British companies: Rolls-Royce, already making carbon fiber, Morganite and Courtaulds. They were able to establish industrial carbon fiber production facilities within a few years, and Rolls-Royce took advantage of the new material's properties to break into the American market with its RB-211 aero-engine.

Public concern arose over the ability of British industry to make the best of this breakthrough. In 1969 a House of Commons select committee inquiry into carbon fiber prophetically asked: "How then is the nation to reap the maximum benefit without it becoming yet another British invention to be exploited more successfully overseas?" Ultimately, this concern was justified. One by one the licensees pulled out of carbon-fiber manufacture. Rolls-Royce's interest was in state-of-the-art aero-engine applications. Its own production process was to enable it to be leader in the use of carbon-fiber reinforced plastics. In-house production would typically cease once reliable commercial sources became available.

Unfortunately, Rolls-Royce pushed the state-of-the-art too far, too quickly, in using carbon fiber in the engine's compressor blades, which proved vulnerable to damage from bird impact. What seemed a great British technological triumph in 1968 quickly became a disaster as Rolls-Royce's ambitious schedule for the RB-211 was endangered. Indeed, Rolls-Royce's problems became so great that the company was eventually nationalized by the British government in 1971 and the carbon-fiber production plant was sold off to form "Bristol Composites".

Given the limited market for a very expensive product of variable quality, Morganite also decided that carbon-fiber production was peripheral to its core business, leaving Courtaulds as the only big UK manufacturer.

The company continued making carbon fiber, developing two main markets: aerospace and sports equipment. The speed of production and the quality of the product were improved.

Continuing collaboration with the staff at Farnborough proved helpful in the quest for higher quality, but, ironically, Courtaulds's big advantage as manufacturer of the "Courtelle" precursor now became a weakness. Low cost and ready availability were potential advantages, but the water-based inorganic process used to produce Courtelle made it susceptible to impurities that did not affect the organic process used by other carbon-fiber manufacturers.

Nevertheless, during the 1980s Courtaulds continued to be a major supplier of carbon fiber for the sports-goods market, with Mitsubishi its main customer. But a move to expand, including building a production plant in California, turned out badly. The investment did not generate the anticipated returns, leading to a decision to pull out of the area. Courtaulds ceased carbon-fiber production in 1991, though ironically the one surviving UK carbon-fiber manufacturer continued to thrive making fiber based on Courtaulds's precursor. Inverness-based RK Carbon Fibres Ltd has concentrated on producing carbon fiber for industrial applications, and thus does not need to compete at the quality levels reached by overseas manufacturers.

During the 1970s, experimental work to find alternative raw materials led to the introduction of carbon fibers made from a petroleum pitch derived from oil processing. These fibers contained about 85% carbon and had excellent flexural strength.

Structure and properties

Each carbon filament thread is a bundle of many thousand carbon filaments. A single such filament is a thin tube with a diameter of 5–8 micrometers and consists almost exclusively of carbon. The earliest generation of carbon fibers (i.e., T300, and AS4) had diameters of 7-8 micrometers. Later fibers (i.e., IM6) have diameters that are approximately 5 micrometers.

The atomic structure of carbon fiber is similar to that of graphite, consisting of sheets of carbon atoms (graphene sheets) arranged in a regular hexagonal pattern. The difference lies in the way these sheets interlock. Graphite is a crystalline material in which the sheets are stacked parallel to one another in regular fashion. The intermolecular forces between the sheets are relatively weak Van der Waals forces, giving graphite its soft and brittle characteristics. Depending upon the precursor to make the fiber, carbon fiber may be turbostratic or graphitic, or have a hybrid structure with both graphitic and turbostratic parts present. In turbostratic carbon fiber the sheets of carbon atoms are haphazardly folded, or crumpled, together. Carbon fibers derived from Polyacrylonitrile (PAN) are turbostratic, whereas carbon fibers derived from mesophase pitch are graphitic after heat treatment at temperatures exceeding 2200 C. Turbostratic carbon fibers tend to have high tensile strength, whereas heat-treated mesophase-pitch-derived carbon fibers have high Young's modulus and high thermal conductivity.

Applications

Carbon fiber is most notably used to reinforce composite materials, particularly the class of materials known as Carbon fiber or graphite reinforced polymers. Non-polymer materials can also be used as the matrix for carbon fibers. Due to the formation of metal carbides and corrosion considerations, carbon has seen limited success in metal matrix composite applications. Reinforced carbon-carbon (RCC) consists of carbon fiber-reinforced graphite, and is used structurally in high-temperature applications. The fiber also finds use in filtration of high-temperature gases, as an electrode with high surface area and impeccable corrosion resistance, and as an anti-static component. Molding a thin layer of carbon fibers significantly improves fire resistance of polymers or thermoset composites because a dense, compact layer of carbon fibers efficiently reflects heat.

Synthesis

Each carbon filament is produced from a precursor polymer. The precursor polymer is commonly rayon, polyacrylonitrile (PAN) or petroleum pitch. For synthetic polymers such as rayon or PAN, the precursor is first spun into filaments, using chemical and mechanical processes to initially align the polymer atoms in a way to enhance the final physical properties of the completed carbon fiber. Precursor compositions and mechanical processes used during spinning may vary among manufacturers. After drawing or spinning, the polymer fibers are then heated to drive off non-carbon atoms (carbonization), producing the final carbon fiber. The carbon fibers may be further treated to improve handling qualities, then wound on to bobbins. Wound bobbins are then used to supply machines that produce carbon fiber threads or yarn.

A common method of manufacture involves heating the spun PAN filaments to approximately 300 °C in air, which breaks many of the hydrogen bonds and oxidizes the material. The oxidized PAN is then placed into a furnace having an inert atmosphere of a gas such as argon, and heated to approximately 2000 °C, which induces graphitization of the material, changing the molecular bond structure. When heated in the correct conditions, these chains bond side-to-side (ladder polymers), forming narrow graphene sheets which eventually merge to form a single, columnar filament. The result is usually 93–95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of PAN. The carbon can become further enhanced, as high modulus, or high strength carbon, by heat treatment processes. Carbon heated in the range of 1500-2000 °C (carbonization) exhibits the highest tensile strength (820,000 psi, 5,650 MPa or N/mm²), while carbon fiber heated from 2500 to 3000 °C (graphitizing) exhibits a higher modulus of elasticity (77,000,000 psi or 531 GPa or 531 kN/mm²).

Textile

Precursors for carbon fibers are polyacrylonitrile (PAN), rayon and pitch. Carbon fiber filament yarns are used in several processing techniques: the direct uses are for prepregging, filament winding, pultrusion, weaving, braiding, etc. Carbon fiber yarn is rated by the linear density (weight per unit length, i.e. 1 g/1000 m = 1 tex) or by number of filaments per yarn count, in thousands. For example, 200 tex for 3,000 filaments of carbon fiber is three times as strong as 1,000 carbon fibers, but is also three times as heavy. This thread can then be used to weave a carbon fiber filament fabric or cloth. The appearance of this fabric generally depends on the linear density of the yarn and the weave chosen. Some commonly used types of weave are twill, satin and plain. Carbon fibers can be also knitted or braided.

See also

Carbon fiber reinforced polymer

Carbon fiber reinforced ceramic material

Carbon nanotube

References

External links

Making Carbon Fiber

How carbon fiber is made

Carbon Fibres - the First Five Years A 1971 ''Flight'' article on carbon fibre in the aviation field

Category:Carbon forms Category:Synthetic fibers Category:Woven fabrics Category:Nonwoven fabrics Category:Net fabrics

ar:ألياف الكربون bg:Въглеродно влакно ca:Fibra de carboni cs:Uhlíkové vlákno da:Kulfiber de:Kohlenstofffaser es:Fibra de carbono fa:الیاف کربن fr:Fibre de carbone ko:탄소 섬유 is:Koltrefjar it:Fibra di carbonio he:סיב פחמן hu:Szénszál nl:Koolstofvezel ja:炭素繊維 no:Karbonfiber oc:Fibra de carbòni pl:Włókno węglowe pt:Fibra de carbono ro:Fibră de carbon ru:Углеродное волокно simple:Carbon fiber fi:Hiilikuitu sv:Kolfiber tr:Karbon fiber uk:Вуглеволокно zh-yue:碳纖維 zh:碳纖維