- Predictive power
The predictive power of a
scientific theory refers to its ability to generate testable predictions. Theories with strong predictive power are highly valued, because the predictions can often encourage the falsification of the theory. The concept of predictive power differs from explanatory or descriptive power (where phenomena that are already known are retrospectively explained by a given theory) in that it allows a prospective test of theoretical understanding.Scientific ideas that do not confer any predictive power are considered at best "
conjecture s", or at worst "pseudoscience ". Because they cannot be tested or falsified in any way, there is no way to determine whether they are true or false, and so they do not gain the status of "scientific theory".Theories whose "predictive power" presupposes technologies that are not currently possible constitute something of a grey area. For example, certain aspects of
string theory have been labeled as predictive, but only through the use of machines that have not yet been built and in some cases may never be possible. Whether or not this sort of theory can or should be considered "truly" predictive is a matter of scientific and philosophical debate.Examples
A classic example of the predictive power of a theory is the
Discovery of Neptune as a result of predictions made by mathematiciansJohn Couch Adams andUrbain Le Verrier , based on Newton's theory of gravity.Other examples of predictive power of theories or models include
Dmitri Mendeleev 's use of hisperiodic table to predict previously undiscoveredchemical element s and their properties (though largely correct, he misjudged the relative atomic masses oftellurium andiodine ), andCharles Darwin 's use of his knowledge ofevolution bynatural selection to predict that because there existed a plant ("Angraecum ") with a long spur in its flowers, a complementary animal with a 30 cmproboscis must also exist to feed on and pollinate it (twenty years after his death, a form ofhawk moth was found which did just that).Another example of predictive power is the prediction of Einstein's
General Theory of Relativity that the path of light would bend in the presence of a strong gravitational field. This was experimentally verified by an expedition toSobral inBrazil and the Atlantic island ofPríncipe to measure star positions during the solar eclipse ofMay 29 ,1919 , when observations made by the astrophysicistArthur Eddington seemed to confirm Einstein's predictions [F. W. Dyson, A. S. Eddington, and C. Davidson, "A Determination of the Deflection of Light by the Sun's Gravitational Field, from Observations Made at the Total Eclipse of May 29, 1919," "Philosophical Transactions of the Royal Society of London. Series A," Volume 220 (1920) pp. 291-333 (available [http://www.journals.royalsoc.ac.uk/content/l30l04qu5m012r87/ online from the Royal Society] )] . Although the measurements have been criticized by some as utilizing flawed methodology [Harry Collins andTrevor Pinch , "The Golem: What Everyone Should Know About Science," Cambridge University Press, 1993. (ISBN 0521477360)] , modern reanalysis of the data [Daniel Kennefick, "Not Only Because of Theory: Dyson, Eddington and the Competing Myths of the 1919 Eclipse Expedition," "Proceedings of the 7th Conference on the History of General Relativity", Tenerife, 2005; available [http://xxx.arxiv.org/abs/0709.0685 online from ArXiv] ] [Phillip Ball, "Arthur Eddington Was Innocent," "Nature," 7 September 2007, doi:10.1038/news070903-20 (available [http://philipball.blogspot.com/2007/09/arthur-eddington-was-innocent-this-is.html online] 2007)] suggests that Eddington's analysis of the data was accurate. Later, more precise measurements taken by radiointerferometry confirmed the predictions to a high degree of accuracy.Applications
The predictive power of a theory is closely related to applications.
General relativity not only predicts the bending of light, but also predicts several other phenomena. Recently, the calculation of
proper time ofsatellite s has been a successfully-measured prediction, now incorporated into the method used to calculate positions viaGPS .If a theory has no predictive power, it cannot be used for applications.
References
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