Editing History of science (section)

==20th century==
{{Further | 20th century in science}}
Science advanced dramatically during the 20th century. There were new and radical developments in the [[physical science|physical]] and [[Life sciences|life]] sciences, building on the progress from the 19th century.<ref>{{Cite book | last = Agar | first = Jon | year = 2012 | title = Science in the Twentieth Century and Beyond | publisher = Polity Press | location = Cambridge | isbn = 978-0-7456-3469-2}}</ref>

===Theory of relativity and quantum mechanics===
[[File:Albert Einstein (Nobel).png|thumb|upright|right|Einstein's official portrait after receiving the 1921 Nobel Prize in Physics]]
The beginning of the 20th century brought the start of a revolution in physics. The long-held theories of Newton were shown not to be correct in all circumstances. Beginning in 1900, [[Max Planck]], [[Albert Einstein]], [[Niels Bohr]] and others developed quantum theories to explain various anomalous experimental results, by introducing discrete energy levels. Not only did [[quantum mechanics]] show that the laws of motion did not hold on small scales, but the theory of [[general relativity]], proposed by Einstein in 1915, showed that the fixed background of [[spacetime]], on which both [[Newtonian mechanics]] and [[special relativity]] depended, could not exist. In 1925, [[Werner Heisenberg]] and [[Erwin Schrödinger]] formulated [[quantum mechanics]], which explained the preceding quantum theories. Currently, general relativity and quantum mechanics are inconsistent with each other, and efforts are underway to unify the two.<ref>{{Cite web|url=https://www.smithsonianmag.com/science-nature/string-theory-about-unravel-180953637/|title=Why String Theory Still Offers Hope We Can Unify Physics|first1=Smithsonian|last1=Magazine|first2=Brian|last2=Greene|website=Smithsonian Magazine}}</ref>

===Big Bang===
The observation by [[Edwin Hubble]] in 1929 that the speed at which galaxies recede positively correlates with their distance, led to the understanding that the universe is expanding, and the formulation of the [[Big Bang]] theory by [[Georges Lemaître]]. [[George Gamow]], [[Ralph Alpher]], and [[Robert Herman]] had calculated that there should be evidence for a [[Big Bang]] in the background temperature of the universe.<ref>{{cite journal | last1=Alpher | first1=Ralph A. | last2=Herman | first2= Robert| year =1948 | title=Evolution of the Universe | journal=[[Nature (journal)|Nature]] | volume=162 | issue=4124| pages=774–775 | doi=10.1038/162774b0 | bibcode=1948Natur.162..774A | s2cid=4113488 }}<br />{{cite journal | last1=Gamow | first1=G. | doi=10.1038/162680a0 | title=The Evolution of the Universe | pmid=18893719 | journal=Nature | year=1948 | volume=162 | issue=4122 | pages=680–682 | bibcode=1948Natur.162..680G | s2cid=4793163 }}</ref> In 1964, [[Arno Penzias]] and [[Robert Woodrow Wilson|Robert Wilson]]<ref>{{cite web|url=http://nobelprize.org/physics/laureates/1978/wilson-lecture.pdf|title=Wilson's 1978 Nobel lecture|website=nobelprize.org|access-date=23 March 2005|archive-date=13 April 2005|archive-url=https://web.archive.org/web/20050413230649/http://nobelprize.org/physics/laureates/1978/wilson-lecture.pdf|url-status=live}}</ref> discovered a 3&nbsp;Kelvin background hiss in their [[Bell Labs]] [[radiotelescope]] (the [[Holmdel Horn Antenna]]), which was evidence for this hypothesis, and formed the basis for a number of results that helped determine the [[age of the universe]].

===Big science===
[[File:Trinity Test Fireball 25ms.jpg|thumb| left | The [[atomic bomb]] ushered in "[[Big Science]]" in physics.]]
In 1938 [[Otto Hahn]] and [[Fritz Strassmann]] [[discovery of nuclear fission|discovered nuclear fission]] with radiochemical methods, and in 1939 [[Lise Meitner]] and [[Otto Robert Frisch]] wrote the first theoretical interpretation of the fission process, which was later improved by [[Niels Bohr]] and [[John A. Wheeler]]. Further developments took place during World War II, which led to the practical application of [[radar]] and the development and use of the [[atomic bomb]]. Around this time, [[Chien-Shiung Wu]] was recruited by the [[Manhattan Project]] to help develop a process for separating uranium metal into U-235 and U-238 isotopes by [[Gaseous diffusion]].<ref>Ronald K. Smeltzer. "Chien-Shiung Wu." Atomic Heritage Foundation, https://www.atomicheritage.org/profile/chien-shiung-wu {{Webarchive|url=https://web.archive.org/web/20190915015223/https://www.atomicheritage.org/profile/chien-shiung-wu |date=15 September 2019 }}. Accessed 26 October 2017.</ref> She was an expert experimentalist in beta decay and weak interaction physics.<ref name="biography.com">Biography.com Editors. "Chien-Shiung Wu." Biography.com, 2 June 2016, https://www.biography.com/people/chien-shiung-wu-053116 {{Webarchive|url=https://web.archive.org/web/20171026054240/https://www.biography.com/people/chien-shiung-wu-053116 |date=26 October 2017 }}.</ref><ref>{{cite journal | doi=10.1063/1.2806727 | title=Chien-Shiung Wu | year=1997 | last1=Garwin | first1=Richard L. | last2=Lee | first2=Tsung-Dao | journal=Physics Today | volume=50 | issue=10 | pages=120–122 | doi-access=free }}</ref> Wu designed an experiment (see [[Wu experiment]]) that enabled theoretical physicists [[Tsung-Dao Lee]] and [[Chen-Ning Yang]] to disprove the law of parity experimentally, winning them a Nobel Prize in 1957.<ref name="biography.com"/>

Though the process had begun with the invention of the [[cyclotron]] by [[Ernest O. Lawrence]] in the 1930s, physics in the postwar period entered into a phase of what historians have called "[[Big Science]]", requiring massive machines, budgets, and laboratories in order to test their theories and move into new frontiers. The primary patron of physics became state governments, who recognized that the support of "basic" research could often lead to technologies useful to both military and industrial applications.

===Advances in genetics===
[[File:Template from Crick and Watson’s DNA molecular model, 1953. (9660573227).jpg|thumb|right|Watson and Crick used many aluminium templates like this one, which is the single base [[Adenine]] (A), to build a physical model of DNA in 1953.]]
In the early 20th century, the study of heredity became a major investigation after the rediscovery in 1900 of the laws of inheritance developed by [[Gregor Mendel|Mendel]].<ref>{{cite book |last=Henig |first=Robin Marantz |title=The Monk in the Garden : The Lost and Found Genius of Gregor Mendel, the Father of Genetics |publisher=Houghton Mifflin |year=2000 |isbn=978-0-395-97765-1 |oclc=43648512 |url=https://archive.org/details/monkingardenlost00heni }}</ref> The 20th century also saw the integration of physics and chemistry, with chemical properties explained as the result of the electronic structure of the atom. [[Linus Pauling]]'s book on ''The Nature of the Chemical Bond'' used the principles of quantum mechanics to deduce [[bond angle]]s in ever-more complicated molecules. Pauling's work culminated in the physical modelling of [[DNA]], ''the secret of life'' (in the words of [[Francis Crick]], 1953). In the same year, the [[Miller–Urey experiment]] demonstrated in a simulation of primordial processes, that basic constituents of proteins, simple [[amino acid]]s, could themselves be built up from simpler molecules, kickstarting decades of research into the [[abiogenesis|chemical origins of life]]. By 1953, [[James D. Watson]] and [[Francis Crick]] clarified the basic structure of DNA, the [[genetic material]] for expressing life in all its forms,<ref name=WastonCrick/> building on the work of [[Maurice Wilkins]] and [[Rosalind Franklin]], suggested that the structure of DNA was a double helix. In their famous paper "[[Molecular structure of Nucleic Acids]]"<ref name=WastonCrick>{{cite journal |doi=10.1038/171737a0 |url=http://www.nature.com/nature/dna50/watsoncrick.pdf |archive-url=https://web.archive.org/web/20171024200745/http://www.nature.com/nature/dna50/watsoncrick.pdf|archive-date=2017-10-24 |title=Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid |year=1953 |last1=Watson |first1=J. D. |last2=Crick |first2=F. H. C. |journal=[[Nature (journal)|Nature]] |volume=171 |issue=4356 |pages=737–738 |pmid=13054692 |bibcode=1953Natur.171..737W |s2cid=4253007 }}</ref> In the late 20th century, the possibilities of [[genetic engineering]] became practical for the first time, and a massive international effort began in 1990 to map out an entire human [[genome]] (the [[Human Genome Project]]). The discipline of [[ecology]] typically traces its origin to the synthesis of [[evolution|Darwinian evolution]] and [[Humboldtian science|Humboldtian]] [[biogeography]], in the late 19th and early 20th centuries.<ref>{{Cite book |last=Cittadino |first=Eugene |title=Nature as the laboratory: Darwinian plant ecology in the German Empire, 1880-1900 |date=2002 |publisher=Cambridge University Press |isbn=978-0-521-52486-5 |location=Cambridge}}</ref> Equally important in the rise of ecology, however, were [[microbiology]] and [[soil science]]—particularly the [[biogeochemical cycle|cycle of life]] concept, prominent in the work of [[Louis Pasteur]] and [[Ferdinand Cohn]].<ref>{{Cite journal |last=Ackert |first=Lloyd T. |date=2007-03-01 |title=The "Cycle of Life" in Ecology: Sergei Vinogradskii's Soil Microbiology, 1885–1940 |url=https://doi.org/10.1007/s10739-006-9104-6 |journal=Journal of the History of Biology|volume=40 |issue=1 |pages=109–145 |doi=10.1007/s10739-006-9104-6 |s2cid=128410978 |issn=1573-0387|url-access=subscription }}</ref> The word ''ecology'' was coined by [[Ernst Haeckel]], whose particularly holistic view of nature in general (and Darwin's theory in particular) was important in the spread of ecological thinking.<ref>{{Cite book |last=Egerton |first=Frank N. |title=Roots of ecology: antiquity to Haeckel |date=2012 |publisher=University of California press |isbn=978-0-520-27174-6 |location=Berkeley}}</ref> The field of [[ecosystem ecology]] emerged in the Atomic Age with the use of radioisotopes to visualize food webs and by the 1970s ecosystem ecology deeply influenced global environmental management.<ref>{{Cite book |last=Martin |first=Laura J. |title=[[Wild by Design]]: The Rise of Ecological Restoration |date=2022 |publisher=Harvard University Press |isbn=978-0-674-97942-0 |location=Cambridge, Massachusetts}}</ref>

===Space exploration===
In 1925, [[Cecilia Payne-Gaposchkin]] determined that stars were composed mostly of hydrogen and helium.<ref>Erik Gregersen. "Cecilia Payne-Gaposchkin | American Astronomer." Encyclopædia Britannica, https://www.britannica.com/biography/Cecilia-Payne-Gaposchkin {{Webarchive|url=https://web.archive.org/web/20181008214403/https://www.britannica.com/biography/Cecilia-Payne-Gaposchkin |date=8 October 2018 }}.</ref> She was dissuaded by astronomer [[Henry Norris Russell]] from publishing this finding in her PhD thesis because of the widely held belief that stars had the same composition as the Earth.<ref name="newn.cam.ac.uk">Rachael Padman. "Cecilia Payne-Gaposchkin (1900–1979)." Newnham College Biographies, 2004, http://www.newn.cam.ac.uk/about/history/biographies/ {{Webarchive|url=https://web.archive.org/web/20170325225822/http://www.newn.cam.ac.uk/about/history/biographies/ |date=25 March 2017 }}.</ref> However, four years later, in 1929, [[Henry Norris Russell]] came to the same conclusion through different reasoning and the discovery was eventually accepted.<ref name="newn.cam.ac.uk"/>

In 1987, supernova [[SN 1987A]] was observed by astronomers on Earth both visually, and in a triumph for [[neutrino astronomy]], by the solar neutrino detectors at [[Kamiokande]]. But the solar neutrino flux was [[solar neutrino problem|a fraction of its theoretically expected value]]. This discrepancy forced a change in some values in the [[standard model]] for [[particle physics]].

===Neuroscience as a distinct discipline===
The understanding of neurons and the nervous system became increasingly precise and molecular during the 20th century. For example, in 1952, [[Alan Lloyd Hodgkin]] and [[Andrew Huxley]] presented a mathematical model for transmission of electrical signals in neurons of the giant axon of a squid, which they called "[[action potentials]]", and how they are initiated and propagated, known as the [[Hodgkin–Huxley model]]. In 1961–1962, Richard FitzHugh and J. Nagumo simplified Hodgkin–Huxley, in what is called the [[FitzHugh–Nagumo model]]. In 1962, [[Bernard Katz]] modeled [[neurotransmission]] across the space between neurons known as [[synapses]]. Beginning in 1966, Eric Kandel and collaborators examined biochemical changes in neurons associated with learning and memory storage in ''[[Aplysia]]''. In 1981 Catherine Morris and Harold Lecar combined these models in the [[Morris–Lecar model]]. Such increasingly quantitative work gave rise to numerous [[biological neuron model]]s and [[models of neural computation]]. [[Neuroscience]] began to be recognized as a distinct academic discipline in its own right. [[Eric Kandel]] and collaborators have cited [[David Rioch]], [[Francis O. Schmitt]], and [[Stephen Kuffler]] as having played critical roles in establishing the field.<ref name=Rioch>{{Cite journal|last1=Cowan|first1=W.M. |last2=Harter|first2=D.H.|last3=Kandel|first3=E.R.|date=2000|title=The emergence of modern neuroscience: Some implications for neurology and psychiatry|journal=Annual Review of Neuroscience|volume=23|pages=345–346 |doi=10.1146/annurev.neuro.23.1.343|pmid=10845068}}</ref>

===Plate tectonics===
[[File:Wegener Expedition-1912 008.jpg|thumb|right|[[Alfred Wegener]] in Greenland in the winter of 1912–13. He is most remembered as the originator of [[continental drift]] hypothesis by suggesting in 1912 that the [[continent]]s are slowly drifting around the Earth.]]
Geologists' embrace of [[plate tectonics]] became part of a broadening of the field from a study of rocks into a study of the Earth as a planet. Other elements of this transformation include: [[Geophysics|geophysical studies]] of the interior of the Earth, the grouping of geology with [[meteorology]] and [[oceanography]] as one of the "[[earth science]]s", and comparisons of Earth and the solar system's other rocky planets.

===Applications===
In terms of applications, a massive number of new technologies were developed in the 20th century. Technologies such as [[electricity]], the [[incandescent light bulb]], the [[automobile]] and the [[phonograph]], first developed at the end of the 19th century, were perfected and universally deployed. The first car was introduced by Karl Benz in 1885.<ref>American Society of Mechanical Engineers. [https://www.asme.org/topics-resources/content/karl-benz Karl Benz] {{Webarchive|url=https://web.archive.org/web/20211128084747/https://www.asme.org/topics-resources/content/karl-benz |date=28 November 2021 }}.</ref> The first [[airplane]] flight occurred in 1903, and by the end of the century [[airliner]]s flew thousands of miles in a matter of hours. The development of the [[radio]], [[television]] and [[computers]] caused massive changes in the dissemination of information. Advances in biology also led to large increases in food production, as well as the elimination of diseases such as [[polio]] by [[Jonas Salk|Dr. Jonas Salk]]. Gene mapping and gene sequencing, invented by Drs. Mark Skolnik and Walter Gilbert, respectively, are the two technologies that made the [[Human Genome Project]] feasible. Computer science, built upon a foundation of [[theoretical linguistics]], [[discrete mathematics]], and [[electrical engineering]], studies the nature and limits of computation. Subfields include [[Computability theory (computer science)|computability]], [[Computational complexity theory|computational complexity]], [[database]] design, [[computer networking]], artificial intelligence, and the design of [[computer hardware]]. One area in which advances in computing have contributed to more general scientific development is by facilitating large-scale [[Scientific data archiving|archiving of scientific data]]. Contemporary computer science typically distinguishes itself by emphasizing mathematical 'theory' in contrast to the practical emphasis of [[software engineering]].<ref>{{Cite web|url=https://www.springboard.com/blog/software-engineering/computer-science-vs-software-engineering/#:~:text=Yes%2C%20there%20is%20a%20difference,emphasizing%20engineering%20principles%20and%20practices|title=Computer Science vs. Software Engineering [Comparison Guide]|date=5 February 2024 }}</ref>

Einstein's paper "On the Quantum Theory of Radiation" outlined the principles of the stimulated emission of photons. This led to the invention of the [[Laser]] (light amplification by the stimulated emission of radiation) and the [[optical amplifier]] which ushered in the [[Information Age]].<ref>{{Cite news|last=Hecht|first=Jeff|date=10 August 2016|title=The Bandwidth Bottleneck That is Throttling the Internet .|work=Scientific American}}</ref> It is optical amplification that allows [[Fiber-optic network|fiber optic networks]] to transmit the massive capacity of the [[Internet]].

Based on wireless transmission of electromagnetic radiation and global networks of cellular operation, the mobile phone became a primary means to access the internet.<ref>{{cite news |last1=Handley |first1=Lucy |title=Nearly three quarters of the world will use just their smartphones to access the internet by 2025 |url=https://www.cnbc.com/2019/01/24/smartphones-72percent-of-people-will-use-only-mobile-for-internet-by-2025.html |access-date=28 September 2022 |work=CNBC |archive-date=28 September 2022 |archive-url=https://web.archive.org/web/20220928214700/https://www.cnbc.com/2019/01/24/smartphones-72percent-of-people-will-use-only-mobile-for-internet-by-2025.html |url-status=live }}</ref>

===Developments in political science and economics===
In political science during the 20th century, the study of ideology, behaviouralism and international relations led to a multitude of 'pol-sci' subdisciplines including [[rational choice theory]], [[voting theory]], [[game theory]] (also used in economics), [[psephology]], [[political geography]]/[[geopolitics]], [[political anthropology]]/[[political psychology]]/[[political sociology]], political economy, [[policy analysis]], public administration, comparative political analysis and [[peace studies]]/conflict analysis. In economics, [[John Maynard Keynes]] prompted a division between [[microeconomics]] and [[macroeconomics]] in the 1920s. Under [[Keynesian economics]] macroeconomic trends can overwhelm economic choices made by individuals. Governments should promote [[aggregate demand]] for goods as a means to encourage economic expansion. Following World War II, [[Milton Friedman]] created the concept of [[monetarism]]. Monetarism focuses on using the supply and demand of money as a method for controlling economic activity. In the 1970s, monetarism has adapted into [[supply-side economics]] which advocates reducing taxes as a means to increase the amount of money available for economic expansion. Other modern schools of economic thought are [[New Classical economics]] and [[New Keynesian economics]]. New Classical economics was developed in the 1970s, emphasizing solid microeconomics as the basis for macroeconomic growth. New Keynesian economics was created partially in response to New Classical economics. It shows how imperfect competition and market rigidities, means monetary policy has real effects, and enables analysis of different policies.<ref>{{Cite journal|url=https://pubs.aeaweb.org/doi/10.1257/jep.32.3.87|title=The State of New Keynesian Economics: A Partial Assessment|first=Jordi|last=Galí|date=1 August 2018|journal=Journal of Economic Perspectives|volume=32|issue=3|pages=87–112|via=CrossRef|doi=10.1257/jep.32.3.87|hdl=10230/35942|hdl-access=free}}</ref>

===Developments in psychology, sociology, and anthropology===
Psychology in the 20th century saw a rejection of Freud's theories as being too unscientific, and a reaction against [[Edward Titchener]]'s atomistic approach of the mind. This led to the formulation of [[behaviorism]] by [[John B. Watson]], which was popularized by [[B.F. Skinner]]. Behaviorism proposed [[epistemology|epistemologically]] limiting psychological study to overt behavior, since that could be reliably measured. Scientific knowledge of the "mind" was considered too metaphysical, hence impossible to achieve. The final decades of the 20th century have seen the rise of [[cognitive science]], which considers the mind as once again a subject for investigation, using the tools of psychology, [[linguistics]], [[computer science]], philosophy, and [[neurobiology]]. New methods of visualizing the activity of the brain, such as [[PET scan]]s and [[CAT scan]]s, began to exert their influence as well, leading some researchers to investigate the mind by investigating the brain, rather than cognition. These new forms of investigation assume that a wide understanding of the human mind is possible, and that such an understanding may be applied to other research domains, such as [[artificial intelligence]]. Evolutionary theory was applied to behavior and introduced to anthropology and psychology, through the works of [[cultural anthropologist]] [[Napoleon Chagnon]]. Physical anthropology would become [[biological anthropology]], incorporating elements of evolutionary biology.<ref>{{Cite journal|url=https://onlinelibrary.wiley.com/doi/10.1002/ajpa.21438|title=The new biological anthropology: Bringing Washburn's new physical anthropology into 2010 and beyond-The 2008 AAPA luncheon lecture|first=Agustin|last=Fuentes|date=6 January 2010|journal=American Journal of Physical Anthropology|volume=143|issue=S51|pages=2–12|via=CrossRef|doi=10.1002/ajpa.21438|pmid=21086524 }}</ref>

American sociology in the 1940s and 1950s was dominated largely by [[Talcott Parsons]], who argued that aspects of society that promoted structural integration were therefore "functional". This structural functionalism approach was questioned in the 1960s, when sociologists came to see this approach as merely a justification for inequalities present in the status quo. In reaction, [[conflict theory]] was developed, which was based in part on the philosophies of Karl Marx. Conflict theorists saw society as an arena in which different groups compete for control over resources. Symbolic interactionism also came to be regarded as central to sociological thinking. [[Erving Goffman]] saw social interactions as a stage performance, with individuals preparing "backstage" and attempting to control their audience through [[impression management]].<ref>{{cite web | url=https://opentextbc.ca/introductiontosociology2ndedition/chapter/chapter-22-social-interaction/ | title=Chapter 22: Social Interaction | date=5 October 2016 | last1=Little | first1=William }}</ref> While these theories are currently prominent in sociological thought, other approaches exist, including [[feminist theory]], [[post-structuralism]], rational choice theory, and [[postmodernism]].

In the mid-20th century, much of the methodologies of earlier anthropological and ethnographical study were reevaluated with an eye towards research ethics, while at the same time the scope of investigation has broadened far beyond the traditional study of "primitive cultures".