Theory
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Theory has a number of distinct meanings in different fields of knowledge, depending on the context and their methodologies. In common usage, people use the word "theory" to signify "conjecture", "speculation", or "opinion." In this sense, "theories" are opposed to "facts" — parts of the world, or claims about the world, that are real or true regardless of what people think.
In science, a theory is a proposed model, explanation or description of the manner of interaction of a set of natural phenomena, capable of predicting future occurences or observations of the same kind, and capable of being tested through experiment or otherwise verified through empirical observation. It follows from this that for scientists "theory" and "fact" do not necessarily stand in opposition. For example, it is a fact that an apple dropped on earth has been observed to fall towards the center of the planet, and the theory which explains why the apple behaves so is the current theory of gravitation. Template:Wiktionary
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Etymology
The word ‘theory’ derives from the Greek ‘theorein’, which means ‘to look at’. According to some sources, it was used frequently in terms of ‘looking at’ a theatre stage, which may explain why sometimes the word ‘theory’ is used as something provisional or not completely resembling real. The term ‘theoria’ (a noun) was already used by the scholars of ancient Greece. Theorein is built upon 'to theion' (the divine) or 'to theia' (divine things) 'orao' (I see), ie 'contemplate the divine'. 'Divine' was understood as harmony and order (or logos) permeating the real world surrounding us.
Science
In scientific usage, a theory does not mean an unsubstantiated guess or hunch, as it often does in other contexts. A theory is a logically self-consistent model or framework for describing the behavior of a related set of natural or social phenomena, which originates from and/or is supported by experimental evidence (see scientific method). In this sense, a theory is a systematic and formalized expression of all previous observations made that is predictive, logical and testable. In principle, scientific theories are always tentative, and subject to corrections or inclusion in a yet wider theory. Commonly, a large number of more specific hypotheses may be logically bound together by just one or two theories. As a general rule for use of the term, theories tend to deal with much broader sets of universals than do hypotheses, which ordinarily deal with much more specific sets of phenomena or specific applications of a theory.
The term theoretical is sometimes used to describe a result that is predicted by theory but has not yet been adequately confirmed by observation or experiment. It is not uncommon for a theory to produce predictions that are later confirmed by experiment. If enough experiments and observations are made by many researchers, such a theory may become sufficiently verified to be considered thoroughly confirmed, and very dependable, and its premises may after that stage be termed laws Depending on the context, with a well-confirmed theory the terms "theory" and "law" often may be used interchageably without any objection by others familiar with the current state of the research. Indeed in the example given below, electromagnetic theory as a whole is today sufficiently investigated that it is often referred to simply as "electromagnetism" Relativity theory today is often simply referred to as "relativity." As another example, until recently black holes were considered theoretical. Failed predictions, however, also occur, and sometimes work to falsify a theory. Conversely, at any time there can also be confirmed experimental results that are not yet explained by theory.
In physics, the term theory is generally used for a mathematical framework derived from a small set of basic principles (usually symmetries - like equalness of locations in space or in time, or identity of electrons, etc), capable of producing experimental predictions for a given category of physical systems. A good example is electromagnetic theory, which encompasses the results that can be derived from gauge symmetry (sometimes called gauge invariance) in a form of a few equations called Maxwell's equations. Another name for this theory is classical electromagnetism. Within electromagnetic theory generally, there are numerous hypotheses about how electromagnetism applies to specific situations, many already considered adequately confirmed, with new ones always in the making and perhaps yet to be tested.
Usage of the term theory is occasionally stretched to refer to theoretical speculation that is to date still unverifiable. Examples are string theory and various theories of everything. And, in common speech, theory has a far wider and less defined meaning than its use in the sciences.
Theories as "models"
Humans construct theories in order to explain, predict and master phenomena (e.g. inanimate things, events, or the behaviour of animals). In many instances, this is seen to be the construction of models of reality. A theory makes generalizations about observations and consists of an interrelated, coherent set of ideas and models.
According to Stephen Hawking in A Brief History of Time, "a theory is a good theory if it satisfies two requirements: It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations." He goes on to state, "any physical theory is always provisional, in the sense that it is only a hypothesis; you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single repeatable observation that disagrees with the predictions of the theory."
This is a view shared by Isaac Asimov. In Understanding Physics, Asimov spoke of theories as "arguments" where one deduces a "scheme" or model. Arguments or theories always begin with some premises - "arbitrary elements" as Hawking calls them (see above), which are here described as "assumptions". An assumption according to Asimov is "something accepted without proof, and it is incorrect to speak of an assumption as either true or false, since there is no way of proving it to be either. (If there were, it would no longer be an assumption.) It is better to consider assumptions as either useful or useless, depending on whether deductions made from them corresponded to reality. .. On the other hand, it seems obvious that assumptions are the weak points in any argument, as they have to be accepted on faith in a philosophy of science that prides itself on its rationalism. Since we must start somewhere, we must have assumptions, but at least let us have as few assumptions as possible." (See Ockham's razor)
An example of using assumptions to formulate a theory is when Albert Einstein put forth his Special Theory of Relativity. He took two phenomena that had been observed i.e. that the "addition of velocities" is valid (Galilean transformation) and that light did not appear to have an "addition of velocities" (Michelson-Morley experiment). He assumed that both of these were correct and formulated his theory based on these assumptions by simply altering the Galilean transformation to accommodate the lack of addition of velocities with regard to the speed of light. Therefore, the model created in his theory is based on the assumption that light maintains a constant velocity (or more precisely the speed of light is a constant).
An example of how theories are models can be seen from theories on the planetary system. The Greeks formulated theories that were recorded by the astronomer Ptolemy. In Ptolemy's planetary model, the earth was at the center, the planets and the sun made circular orbits around the earth, and the stars were on a sphere outside of the orbits of the planet and the earth. Retrograde motion of the planets was explained by smaller circular orbits of individual planets. This could actually be built into a literal model and illustrated as a model. Mathematical calculations could be made for the prediction of where the planets would be to a great degree of accuracy, so that this model of the planetary system survived over 1500 years until the time of Copernicus. So one can see how a theory is a model of reality that explains certain scientific facts yet may not be a true picture of reality and another more accurate theory can later replace the previous model.
In engineering practise there is a distinction between "mathematical models" and "physical models" (e.g., the winged rockets built by Convair to test the Whitcomb area rule for the F-106 supersonic aircraft).
Characteristics
In science, a body of descriptions of knowledge is usually only called a theory once it has a firm empirical basis, i.e., it
- is consistent with pre-existing theory to the extent that the pre-existing theory was experimentally verified, though it will often show pre-existing theory to be wrong in an exact sense,
- is supported by many strands of evidence rather than a single foundation, ensuring that it probably is a good approximation if not totally correct,
- makes predictions that might someday be used to disprove the theory,
- is tentative, correctable and dynamic, in allowing for changes to be made as new data is discovered, rather than asserting certainty, and
- is the most parsimonious explanation, sparing in proposed entities or explanations, commonly referred to as passing Ockham's razor.
This is true of such established theories as special and general relativity, quantum mechanics, plate tectonics, evolution, etc. Theories considered scientific meet at least most, but ideally all, of the above criteria. The fewer which are matched, the less scientific it is; those that meet only several or none at all, cannot be said to be scientific in any meaningful sense of the word.
Karl Popper described the characteristics of a scientific theory as:
1. It is easy to obtain confirmations, or verifications, for nearly every theory — if we look for confirmations.
2. Confirmations should count only if they are the result of risky predictions; that is to say, if, unenlightened by the theory in question, we should have expected an event which was incompatible with the theory — an event which would have refuted the theory.
3. Every "good" scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is.
4. A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.
5. Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks.
6. Confirming evidence should not count except when it is the result of a genuine test of the theory; and this means that it can be presented as a serious but unsuccessful attempt to falsify the theory. (I now speak in such cases of "corroborating evidence.")
7. Some genuinely testable theories, when found to be false, are still upheld by their admirers — for example by introducing ad hoc some auxiliary assumption, or by reinterpreting the theory ad hoc in such a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroying, or at least lowering, its scientific status. (I later described such a rescuing operation as a "conventionalist twist" or a "conventionalist stratagem.").
One can sum up all this by saying that the criterion of the scientific status of a theory is its falsifiability, or refutability, or testability."--end quote
Mathematics
In mathematics, the word theory is used informally to refer to certain distinct bodies of knowledge about mathematics. This knowledge consists of axioms, definitions, theorems and computational techniques, all related in some way by tradition or practice. Examples include group theory, set theory, Lebesgue integration theory and field theory.
The term theory also has a precise technical usage in mathematics, particularly in mathematical logic and model theory. A theory in this sense is a set of statements in a formal language, which is closed upon application of certain procedures called rules of inference. A special case of this, an axiomatic theory, consists of axioms and rules of inference. A theorem is a statement which can be derived from those axioms by application of these rules of inference. Theories used in applications are abstractions of observed phenomena and the resulting theorems provide solutions to real-world problems. Obvious examples include arithmetic (abstracting concepts of number), geometry (concepts of space), and probability (concepts of randomness and likelihood).
Gödel's incompleteness theorem shows that no consistent computably enumerable theory capable of defining the concept of natural numbers can derive all true statements about them. This makes it impossible to formalize accurately and completely some domains of knowledge as mathematical theories. Formalizing accurately and completely means here that all true propositions and only true propositions are derivable within the mathematical system. This however, in no way precludes the construction of mathematical theories that formalize large bodies of scientific knowledge.
Other fields
Theories exist not only in the so-called hard sciences, but in all fields of academic study, from philosophy to music to literature. In the humanities, theory is often used as an abbreviation for critical theory or literary theory, referring to continental philosophy's aesthetics or its attempts to understand the structure of society and to conceptualize alternatives. In philosophy, theoreticism refers to the overuse of theory.
List of notable theories
- Biology: Evolution by natural selection — Cell theory
- Chemistry: Atomic theory — Kinetic theory of gases
- Climatology: Global warming
- Computer science: Algorithmic information theory — Computation theory
- Economics: Decision theory
- Engineering: Circuit theory — Control theory — Signal theory - Systems theory
- Games: Rational choice theory — Game theory
- Geology: Continental drift — Plate tectonics
- Humanities: Critical theory
- Literature: Literary theory
- Mathematics: Catastrophe theory — Category theory — Chaos theory — Graph theory — Number theory — Probability theory — Set theory
- Music: Music theory
- Philosophy: Proof theory — Speculative reason — Theory of truth - Type theory - Value theory — Virtue theory
- Physics: Theory of relativity — Special relativity — General relativity - Quantum field theory — Acoustic theory — Antenna theory
- Planetary science: Giant impact theory
- Sociology: Social theory — Critical social theory
- Statistics : Extreme value theory
See also
References
- Karl Popper. Conjectures and Refutations. London: Routledge and Kegan Paul, 1963, pp. 33–39; from Theodore Schick, ed., Readings in the Philosophy of Science, Mountain View, CA: Mayfield Publishing Company, 2000, pp. 9–13.ar:نظرية
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