In the sciences, an experimentum crucis, or critical experiment, is an experiment capable of decisively determining whether or not a particular hypothesis or theory is correct. In particular, such an experiment must typically be able to produce a predictable result that no established hypothesis or theory is capable of producing. // What is science? There are different theories of what science is. ... From Latin ex- + -periri (akin to periculum attempt). ... A hypothesis (assumption in ancient Greek) is a proposed explanation for a phenomenon. ... Theory has a number of distinct meanings, depending on the context. ...

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.

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. 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 the Einstein's theory. (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901–2000 in the sense of the Gregorian calendar (1900–1999 in the... One of Sir Arthur Stanley Eddingtons papers announced Einsteins theory of general relativity to the English-speaking world. ... Africa is the worlds second-largest continent and second most populous after Asia. ... 1919 was a common year starting on Wednesday (see link for calendar). ... By ancient tradition, the Sun is the light in the heavens whose presence is day and whose absence is night. ... Photo taken by John Walker during the Zambia 2001 eclipse A solar eclipse occurs when the Moon passes in front of the Sun and obscures it totally or partially. ... A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a massive galaxy) between the source object and the observer. ... Albert Einstein, by Yousuf Karsh Albert Einstein (March 14, 1879 – April 18, 1955) was a German-born Jewish theoretical physicist of Swiss and American citizenship, who is widely regarded as the greatest scientist of the 20th century. ... General relativity (GR) or general relativity theory (GRT) is the theory of gravitation published by Albert Einstein in 1915. ... 1915 was a common year starting on Friday (see link for calendar). ...

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 which the existing classical Rayleigh-Jeans law could not predict. Such cases are not considered strong enough to fully establish a new theory, however, and the case of quantum mechanics, it took the confirmation of the theory through new predictions for the theory to gain full acceptance. Max Planck This article is about Planck, the German physicist. ... 1900 is a common year starting on Monday. ... Classical physics is physics based on principles developed before the rise of quantum theory, including the special theory of relativity. ... In physics, the Rayleigh-Jeans Law, first proposed in the early 20th century, expresses the energy density of blackbody radiation of wavelength λ as where T is the temperature in kelvins, and k is Boltzmanns constant. ...