Experimentum crucis
Encyclopedia
In the science
s, 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 instancia 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.
Isaac Newton
(1687) presented a disproof of Descartes' vortex theory of the motion of the planets.
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 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 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 in the case of quantum mechanics, it took the confirmation of the theory through new predictions for the theory to gain full acceptance.
For an opposite view putting into question the decisive value of the experimentum crucis in choosing one hypothesis or theory over its rival see Pierre Duhem
.
Science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...
s, an experimentum crucis (English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...
: crucial experiment or critical experiment) is an experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
capable of decisively determining whether or not a particular hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
or theory
Theory
The English word theory was derived from a technical term in Ancient Greek philosophy. The word theoria, , meant "a looking at, viewing, beholding", and referring to contemplation or speculation, as opposed to action...
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
Ceteris paribus
or is a Latin phrase, literally translated as "with other things the same," or "all other things being equal or held constant." It is an example of an ablative absolute and is commonly rendered in English as "all other things being equal." A prediction, or a statement about causal or logical...
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
Francis Bacon
Francis Bacon, 1st Viscount St Albans, KC was an English philosopher, statesman, scientist, lawyer, jurist, author and pioneer of the scientific method. He served both as Attorney General and Lord Chancellor of England...
in his Novum Organum
Novum Organum
The Novum Organum, full original title Novum Organum Scientiarum, is a philosophical work by Francis Bacon, written in Latin and published in 1620. The title translates as new instrument, i.e. new instrument of science. This is a reference to Aristotle's work Organon, which was his treatise on...
first described the concept of a situation in which one theory but not others would hold true, using the name instancia 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
Robert Hooke
Robert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...
and then famously used by Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
.
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.
Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
(1687) presented a disproof of Descartes' vortex theory of the motion of the planets.
A famous example in the 20th century of an experimentum crucis was the expedition led by Arthur Eddington to Principe Island in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
in 1919 to record the positions of stars around the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
during a solar eclipse
Solar eclipse
As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...
. The observation of star positions confirmed predictions of gravitational lensing made by Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
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
Max Planck
Max Karl Ernst Ludwig Planck, ForMemRS, was a German physicist who actualized the quantum physics, initiating a revolution in natural science and philosophy. He is regarded as the founder of the quantum theory, for which he received the Nobel Prize in Physics in 1918.-Life and career:Planck came...
in 1900, to account for the observed black-body spectrum, an experimental result which the existing classical
Classical physics
What "classical physics" refers to depends on the context. When discussing special relativity, it refers to the Newtonian physics which preceded relativity, i.e. the branches of physics based on principles developed before the rise of relativity and quantum mechanics...
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.
For an opposite view putting into question the decisive value of the experimentum crucis in choosing one hypothesis or theory over its rival see Pierre Duhem
Pierre Duhem
Pierre Maurice Marie Duhem was a French physicist, mathematician and philosopher of science, best known for his writings on the indeterminacy of experimental criteria and on scientific development in the Middle Ages...
.