In science, an experimentum crucis (English: crucial experiment or critical experiment) is an experiment capable of decisively determining whether or not a particular hypothesis or theory is superior to all other hypotheses or theories whose acceptance is currently widespread in the scientific community. In particular, such an experiment must typically be able to produce a result that rules out all other hypotheses or theories if true, thereby demonstrating that under the conditions of the experiment (i.e., under the same external circumstances and for the same "input variables" within the experiment), those hypotheses and theories are proven false but the experimenter's hypothesis is not ruled out.
Francis Bacon in his Novum Organum first described the concept of a situation in which one theory but not others would hold true, using the name instantia crucis; the phrase experimentum crucis, denoting the deliberate creation of such a situation for the purpose of testing the rival theories, was later coined by Robert Hooke and then famously used by Isaac Newton.
The production of such an experiment is considered necessary for a particular hypothesis or theory to be considered an established part of the body of scientific knowledge. It is not unusual in the history of science for theories to be developed fully before producing a critical experiment. A given theory which is in accordance with known experiment but which has not yet produced a critical experiment is typically considered worthy of exploration in order to discover such an experimental test.
Examples
Robert Boyle was the first person to hail an experiment as experimentum crucis when he referred to the famous mercury barometer experiment on Puy-de-Dome in 1648. This experiment settled the question: Was there some natural resistance to the creation of an apparently empty space at the top of the tube, or was the height of the mercury determined solely by the weight of the air?[1]
Isaac Newton performing his crucial prism experiment – the 'experimentum crucis' – in his Woolsthorpe Manor bedroom. Acrylic painting by Sascha Grusche (17 Dec 2015)
A 19th-century example was the prediction by Poisson, based on Fresnel's mathematical analysis, that the wave theory of light predicted a bright spot in the center of the shadow of a perfectly circular object, a result that could not be explained by the (then current) particle theory of light. An experiment by François Arago showed the existence of this effect, now called the Arago spot, or "Poisson's bright spot", which led to the acceptance of the wave theory.
In some cases, a proposed theory can account for existing anomalous experimental results for which no other existing theory can furnish an explanation. An example would be the ability of the quantum hypothesis, proposed by Max Planck in 1900, to account for the observed black-body spectrum, an experimental result that the existing classicalRayleigh–Jeans law could not predict. Such cases are not considered strong enough to fully establish a new theory, however, and in the case of quantum mechanics, it took the confirmation of the theory through new predictions for the theory to gain full acceptance.
In the 21st century, the discovery of the Tanis fossil site, a killing field in the Hell Creek formation of North Dakota, proved that the K-T boundary (now known as the KPg, or the Cretaceous–Paleogene extinction event)[4] was the same event (the Chicxulub impact) which killed off the dinosaurs. This impact event was previously hypothesized from the global existence of iridium deposits (a rare element on Earth). In this case, the existence of a microtektite layer raining down upon the multiple intermixed species (including a Triceratops)[5] which were found at the site (the Tanis Konservat-Lagerstätte)[4]:page 7 served as the conclusive witness,[4] as cited in Science Daily.[5] Based on the dating of the Tanis, the event occurred 65.76 million years ago (± 0.15 My).[4]
Theory of Experimentum Crucis
There's an emerging scholarship extending understanding and evaluation of experiments that fit into this category. J. A. Lohne tracks the development of the idea from Francis Bacon's 1620 Instantie Crucis through the various prismoptics experiments and discussions of 1722 [6].
↑ Wootton, David, 1952- (8 December 2015). The invention of science: a new history of the scientific revolution (First U.S.ed.). New York, NY. p.311. ISBN978-0-06-175952-9. OCLC883146361.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
↑ Isaac Newton (1687), Principia Mathematica Book iii, Proposition 43, General Scholium and Book ii, Section ix, Proposition 53, as referenced by William Stanley Jevons (1874), The Principles of Science: A Treatise on Logic and Scientific Method p. 517.
↑ J. A. Lohne, Experimentum Crucis, Notes and Records of the Royal Society of London, Dec., 1968, Vol. 23, No. 2 (Dec., 1968), pp. 169-199 https://www.jstor.org/stable/530985
↑ William L. Reese, The "Experimentum Crucis" In Locke's Doctrine of Abstraction, Philosophy and Phenomenological Research, Jun., 1961, Vol. 21, No. 4 (Jun., 1961), pp. 490-500. https://www.jstor.org/stable/2105018
↑ Lorne Falkenstein, Dualism And The Experimentum Crucis, Philosophy and Phenomenological Research, JULY, 2016, Vol. 93, No. 1 (JULY, 2016), pp. 212-217. https://www.jstor.org/stable/10.2307/48579468
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