Uniformitarianism, also known as the Doctrine of Uniformity or the Uniformitarian Principle, is the assumption that the same natural laws and processes that operate in our present-day scientific observations have always operated in the universe in the past and apply everywhere in the universe., "The assumption of spatial and temporal invariance of natural laws is by no means unique to geology since it amounts to a warrant for inductive inference which, as Bacon showed nearly four hundred years ago, is the basic mode of reasoning in empirical science. Without assuming this spatial and temporal invariance, we have no basis for extrapolating from the known to the unknown and, therefore, no way of reaching general conclusions from a finite number of observations." It refers to invariance in the metaphysical principles underpinning science, such as the constancy of cause and effect throughout space-time,; "The uniformitarian principle assumes that the behavior of nature is regular and indicative of an objective causal structure in which presently operative causes may be projected into the past to explain the historical development of the physical world and projected into the future for the purposes of prediction and control. In short, it involves the process of inferring past causes from presently observable effects under the assumption that the fundamental causal regularities of the world have not changed over time." but has also been used to describe spatiotemporal invariance of physical laws.Strahler, A.N. 1987. Science and Earth History- The Evolution/Creation Controversy, Prometheus Books, Amherst, New York, USA. p. 194: “Under the updated statement of a useful principle of uniformitarianism it boils down essentially to affirmation of the validity of universal scientific laws through time and space, coupled with a rejection of supernatural causes.” p. 62: “In cosmology, the study of the structure and evolution of the universe, it is assumed that the laws of physics are similar throughout the entire universe.” Though an unprovable postulate that cannot be verified using the scientific method,Rosenberg, Alex. Philosophy of science: A contemporary introduction, 4th ed. Routledge, 2019, 173 some consider that uniformitarianism should be a required first principle in scientific research., "Uniformity is an unprovable postulate justified, or indeed required, on two grounds. First, nothing in our incomplete but extensive knowledge of history disagrees with it. Second, only with this postulate is a rational interpretation of history possible, and we are justified in seeking—as scientists we must seek—such a rational interpretation."
In geology, uniformitarianism has included the gradualistic concept that "the present is the key to the past" and that geological events occur at the same rate now as they have always done, though many modern geologists no longer hold to a strict gradualism.FARIA, Felipe. Actualismo, Catastrofismo y Uniformitarismo. In: Pérez, María Luisa Bacarlett & Caponi, Gustavo. Pensar la vida: Filosofía, naturaleza y evolución. Toluca: Universidad Autónoma del Estado de México, p. 55–80, 2015. Coined by William Whewell, uniformitarianism was originally proposed in contrast to catastrophism, "the idea that Earth was shaped by a series of sudden, short-lived, violent events." by British naturalists in the late 18th century, starting with the work of the geologist James Hutton in his many books including Theory of the Earth. Hutton's work was later refined by scientist John Playfair and popularised by geologist Charles Lyell's Principles of Geology in 1830. Today, Earth's history is considered to have been a slow, gradual process, punctuated by occasional natural catastrophic events.
History
18th century
Abraham Gottlob Werner (1749–1817) proposed Neptunism, where strata represented deposits from shrinking seas precipitated onto primordial rocks such as granite. In 1785 James Hutton proposed an opposing, self-maintaining infinite cycle based on natural history and not on the Biblical account.
Hutton then sought evidence to support his idea that there must have been repeated cycles, each involving deposition on the seabed, uplift with tilting and erosion, and then moving undersea again for further layers to be deposited. At Glen Tilt in the Cairngorm mountains he found granite penetrating metamorphic schists, in a way which indicated to him that the presumed primordial rock had been molten after the strata had formed. Review of Repcheck's The Man Who Found Time He had read about angular unconformities as interpreted by Neptunists, and found an unconformity at Jedburgh where layers of greywacke in the lower layers of the cliff face have been tilted almost vertically before being eroded to form a level plane, under horizontal layers of Old Red Sandstone. In the spring of 1788 he took a boat trip along the Berwickshire coast with John Playfair and the geologist Sir James Hall, and found a dramatic unconformity showing the same sequence at Siccar Point. Playfair later recalled that "the mind seemed to grow giddy by looking so far into the abyss of time", and Hutton concluded a 1788 paper he presented at the Royal Society of Edinburgh, later rewritten as a book, with the phrase "we find no vestige of a beginning, no prospect of an end".
Both Playfair and Hall wrote their own books on the theory, and for decades robust debate continued between Hutton's supporters and the Neptunists. Georges Cuvier's paleontological work in the 1790s, which established the reality of extinction, explained this by local catastrophes, after which other fixed species repopulated the affected areas. In Britain, geologists adapted this idea into "diluvial theory" which proposed repeated worldwide annihilation and creation of new fixed species adapted to a changed environment, initially identifying the most recent catastrophe as the biblical flood.
19th century
From 1830 to 1833 Charles Lyell's multi-volume Principles of Geology was published. The work's subtitle was "An attempt to explain the former changes of the Earth's surface by reference to causes now in operation". He drew his explanations from field studies conducted directly before he went to work on the founding geology text,Wilson, Leonard G. "Charles Lyell" Dictionary of Scientific Biography. Ed. Charles Coulston Gillispie. Vol. VIII. Pennsylvania, Charles Scribner's Sons, 1973 and developed Hutton's idea that the earth was shaped entirely by slow-moving forces still in operation today, acting over a very long period of time. The terms uniformitarianism for this idea, and catastrophism for the opposing viewpoint, was coined by William Whewell in a review of Lyell's book. Principles of Geology was the most influential geological work in the middle of the 19th century.
Systems of inorganic earth history
Geoscientists support diverse systems of Earth history, the nature of which rests on a certain mixture of views about the process, control, rate, and state which are preferred. Because geologists and geomorphologists tend to adopt opposite views over process, rate, and state in the inorganic world, there are eight different systems of beliefs in the development of the terrestrial sphere. All geoscientists stand by the principle of uniformity of law. Most, but not all, are directed by the principle of simplicity. All make definite assertions about the quality of rate and state in the inorganic realm.
Methodologicalassumption concerningkind of processSubstantive claimconcerning state Substantive claimConcerning rate System of InorganicEarth history Promoters Same Kind of processesthat exist todayActualism Steady StateNon-directionalism Constant RateGradualism ActualisticNon-directionalGradualism Most of Hutton, Playfair, Lyell Changing RateCatastrophism ActualisticNon-directionalCatastrophism Hall Changing StateDirectionalism Constant RateGradualism ActualisticDirectionalGradualism Small part of Hutton, Cotta, Darwin Changing RateCatastrophism ActualisticDirectionalCatastrophism Hooke, Steno, Lehmann, Pallas,de Saussure, Werner, and geognosists,Elis de Beaumont and followers Different Kind of processesthan exist todayNon-Actualism Steady StateNon-directionalism Constant RateGradualism Non-ActualisticNon-directionalGradualism Carpenter Changing RateCatastrophism Non-ActualisticNon-directionalCatastrophism Bonnet, Cuvier Changing StateDirectionalism Constant RateGradualism Non-ActualisticdirectionalGradualism De Mallet, Buffon Changing RateCatastrophism Non-ActualisticDirectionalCatastrophism Restoration cosmogonists,English diluvialists,Scriptural geologists
Lyell Lyell's uniformitarianism is a family of four related propositions, not a single idea: Uniformity of law – the laws of nature are constant across time and space. Uniformity of methodology – the appropriate hypotheses for explaining the geological past are those with analogy today. Uniformity of kind – past and present causes are all of the same kind, have the same energy, and produce the same effects. Uniformity of degree – geological circumstances have remained the same over time.
None of these connotations requires another, and they are not all equally inferred by uniformitarians.David Cahan, 2003, From Natural Philosophy to the Sciences, p 95 .
Gould explained Lyell's propositions in Time's Arrow, Time's Cycle (1987), stating that Lyell conflated two different types of propositions: a pair of methodological assumptions with a pair of substantive hypotheses. The four together make up Lyell's uniformitarianism.
Methodological assumptions The two methodological assumptions below are accepted to be true by the majority of scientists and geologists. Gould claims that these philosophical propositions must be assumed before you can proceed as a scientist doing science. "You cannot go to a rocky outcrop and observe either the constancy of nature's laws or the working of unknown processes. It works the other way around." You first assume these propositions and "then you go to the outcrop.". "You first assume."
Uniformity of law across time and space: Natural laws are constant across space and time. The axiom of uniformity of law <ref name=gould1987>, "Making inferences about the past is wrapped up in the difference between studying the observable and the unobservable. In the observable, erroneous beliefs can be proven wrong and be inductively corrected by other observations. This is Popper's principle of falsifiability. However, past processes are not observable by their very nature. Therefore, the invariance of nature's laws must be assumed to come to conclusions about the past."</ref> is necessary in order for scientists to extrapolate (by inductive inference) into the unobservable past. The constancy of natural laws must be assumed in the study of the past; else we cannot meaningfully study it.
Uniformity of process across time and space: Natural processes are constant across time and space.