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((Short description|Critical experiment))
((More references|date=August 2017))
((DISPLAYTITLE:''Experimentum crucis''))
In science, an '''''experimentum crucis''''' ([[English language|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.'', [[Ceteris paribus|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''. 

An opposite view, rejecting the decisive value of the ''experimentum crucis'' in choosing one hypothesis or theory over its rivals, is the [[Duhem–Quine thesis]]; see also ((Section link|Pierre Duhem|Philosophy of science)).

==History==
[[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?<ref>((Cite book|last=Wootton, David, 1952-|title=The invention of science : a new history of the scientific revolution|date=8 December 2015|isbn=978-0-06-175952-9|edition=First U.S.|location=New York, NY|pages=311|oclc=883146361))</ref> 

In his ''[[Philosophiæ Naturalis Principia Mathematica]]'', [[Isaac Newton]] (1687) presents a disproof of [[Descartes' vortex theory]] of the motion of the planets.<ref>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.</ref> In his ''[[Opticks]]'', Newton describes an optical ''experimentum crucis'' in the ''First Book, Part I, Proposition II, Theorem II, Experiment 6'', to prove that sunlight consists of rays that differ in their [[index of refraction]].

[[File:Newton's Experimentum Crucis (Grusche 2015).jpg|thumb|upright=2.25|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 [[Siméon Denis Poisson|Poisson]], based on [[Augustin-Jean Fresnel|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.

A famous example in the 20th century of an ''experimentum crucis'' was the expedition led by [[Arthur Eddington]] to [[Principe Island]] in [[Africa]] in 1919 to record the positions of stars around the [[Sun]] during a [[solar eclipse]] (see [[Eddington experiment]]). The observation of star positions confirmed predictions of [[gravitational lensing]] made by [[Albert Einstein]] in the [[general theory of relativity]] published in 1915. Eddington's observations were considered to be the first solid evidence in favor of Einstein's 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 [[classical physics|classical]] [[Rayleigh–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.
===DNA, experimentum crucis===
:''See [[Scientific method#Context|§Context for crucial experiment]] in the discovery of the [[Scientific method#Crucial experiment|§structure of DNA]], and [[List of experiments#Biology|§List of experiments in biology]]''
In [[DNA#History|the discovery of the significance of the structure of DNA]], the fact that DNA was a double helix enabled the discoverers, Francis Crick and James Watson, to suggest that one strand of the double helix could serve as the template for the second strand, as the second strand was being duplicated. This explained the ''secret of life'',<ref>((cite book | last = Regis | first = Ed | name-list-style = vanc | date = 2009 | title = What Is Life?: investigating the nature of life in the age of synthetic biology | location = Oxford | publisher = [[Oxford University Press]] | isbn = 978-0-19-538341-6 | page = 52 ))</ref> how the structure of DNA could serve as the [[nanomotor|mechanism]] for the [[gene]] (the [[genetic code]]), in which four [[nucleotide]]s serve to encode the sequence of [[enzyme]]s needed [[enzyme catalysis|to catalyze]] the production of macromolecules in the cell, and which led to its application in [[synthetic biology]], in [[genetic engineering]], in [[forensics]], [[genetic testing]], [[genomics]] and [[pharmaceutical]]s, among other industries.

===Tanis fossil site===
((main|Tanis (fossil site)))
In the 21st century, the discovery of the [[Tanis (fossil site)|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]])<ref name=KPg21stC /> was the same event (the [[Chicxulub impact]]) which killed off the [[dinosaur]]s. 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]])<ref name=SD /> which were found at the site (the Tanis Konservat-Lagerstätte)<ref name=KPg21stC />((rp|page 7)) served as the conclusive witness,<ref name=KPg21stC >((Cite journal|doi = 10.1073/pnas.1817407116|title = A seismically induced onshore surge deposit at the KPG boundary, North Dakota|year = 2019|last1 = Depalma|first1 = Robert A.|last2 = Smit|first2 = Jan|last3 = Burnham|first3 = David A.|last4 = Kuiper|first4 = Klaudia|last5 = Manning|first5 = Phillip L.|last6 = Oleinik|first6 = Anton|last7 = Larson|first7 = Peter|last8 = Maurrasse|first8 = Florentin J.|last9 = Vellekoop|first9 = Johan|last10 = Richards|first10 = Mark A.|last11 = Gurche|first11 = Loren|last12 = Alvarez|first12 = Walter|journal = Proceedings of the National Academy of Sciences|volume = 116|issue = 17|pages = 8190–8199|pmid = 30936306|pmc = 6486721|bibcode = 2019PNAS..116.8190D|doi-access = free))</ref>  as cited in ''Science Daily''.<ref name=SD >[https://www.sciencedaily.com/releases/2019/03/190329144223.htm University of California - Berkeley: (29 March 2019) 66-million-year-old deathbed linked to dinosaur-killing meteor]</ref> Based on the dating of the Tanis, the event occurred 65.76 million years ago  (± 0.15 My).<ref name=KPg21stC />

=== 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 [[Prism (optics)|prism]] [[optics]] experiments and discussions of 1722.<ref>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</ref> 

An early indicator of a theory of Experimentum Crucis appears in [[John Locke]]'s [[Doctrine of Abstraction]]<ref>
 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</ref>

Lorne Falkenstein, reviewing  Van Cleve expands the discussion  of Experimentum crucis to the more general philosophical realm of [[Property dualism]]
<ref>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 </ref>

==See also ==
* [[Contraposition]] in logic, the formal basis of an ''experimentum crucis''
* [[Cross-validation (disambiguation)]]
* [[Falsifiability]]
* [[Material conditional]]
* [[Q.E.D.]]
* [[Scientific method]]
* [[Smoking gun]]
* [[Therefore sign]]

==Notes==
((Reflist))

((Authority control))
[[Category:Scientific method]]

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