Editing Scientific theory (section)

==Modification and improvement==
If experimental results contrary to a theory's predictions are observed, scientists first evaluate whether the experimental design was sound, and if so they confirm the results by independent [[Reproducibility|replication]]. A search for potential improvements to the theory then begins. Solutions may require minor or major changes to the theory, or none at all if a satisfactory explanation is found within the theory's existing framework.<ref>For example, see the article on the [[discovery of Neptune]]; the discovery was based on an apparent violation of the orbit of [[Uranus]] as predicted by Newtonian mechanics. This explanation did not require any modification of the theory, but rather a modification of the hypothesis that there were only seven planets in the Solar System.</ref> Over time, as successive modifications build on top of each other, theories consistently improve and greater predictive accuracy is achieved. Since each new version of a theory (or a completely new theory) must have more predictive and explanatory power than the last, scientific knowledge consistently becomes more accurate over time.{{citation needed|date=March 2023}}

If modifications to the theory or other explanations seem to be insufficient to account for the new results, then a new theory may be required. Since scientific knowledge is usually durable, this occurs much less commonly than modification.<ref name=Project2061/> Furthermore, until such a theory is proposed and accepted, the previous theory will be retained. This is because it is still the best available explanation for many other phenomena, as verified by its predictive power in other contexts. For example, it has been known since 1859 that the observed [[perihelion precession of Mercury]] violates Newtonian mechanics,<ref>U. Le Verrier (1859), (in French), [https://archive.org/stream/comptesrendusheb49acad#page/378/mode/2up "Lettre de M. Le Verrier à M. Faye sur la théorie de Mercure et sur le mouvement du périhélie de cette planète"], Comptes rendus hebdomadaires des séances de l'Académie des sciences (Paris), vol. 49 (1859), pp. 379–83.</ref> but the theory remained the best explanation available until [[Theory of relativity|relativity]] was supported by sufficient evidence. Also, while new theories may be proposed by a single person or by many, the cycle of modifications eventually incorporates contributions from many different scientists.<ref>For example, the modern theory of evolution (the [[modern synthesis (20th century)|modern evolutionary synthesis]]) incorporates significant contributions from [[R. A. Fisher]], [[Ernst Mayr]], [[J. B. S. Haldane]], and many others.</ref>

After the changes, the accepted theory will explain more phenomena and have greater predictive power (if it did not, the changes would not be adopted); this new explanation will then be open to further replacement or modification. If a theory does not require modification despite repeated tests, this implies that the theory is very accurate. This also means that accepted theories continue to accumulate evidence over time, and the length of time that a theory (or any of its principles) remains accepted often indicates the strength of its supporting evidence.{{citation needed|date=March 2023}}

===Unification===
[[File:HAtomOrbitals.png|thumb|200px|In [[quantum mechanics]], the [[electron]]s of an atom occupy [[Atomic orbital|orbitals]] around the [[Atomic nucleus|nucleus]]. This image shows the orbitals of a [[hydrogen]] atom (''s'', ''p'', ''d'') at three different energy levels (1, 2, 3). Brighter areas correspond to higher probability density.]]

In some cases, two or more theories may be replaced by a single theory that explains the previous theories as approximations or special cases, analogous to the way a theory is a unifying explanation for many confirmed hypotheses; this is referred to as ''unification'' of theories.<ref name=Weinberg>Weinberg S (1993). ''Dreams of a Final Theory: The Scientist's Search for the Ultimate Laws of Nature.''</ref> For example, [[electricity]] and [[magnetism]] are now known to be two aspects of the same phenomenon, referred to as [[electromagnetism]].<ref>Maxwell, J. C., & Thompson, J. J. (1892). [https://archive.org/details/atreatiseonelec02thomgoog A treatise on electricity and magnetism]. Clarendon Press series. Oxford: Clarendon.</ref>

When the predictions of different theories appear to contradict each other, this is also resolved by either further evidence or unification. For example, physical theories in the 19th century implied that the [[Sun]] could not have been burning long enough to allow certain geological changes as well as the [[evolution]] of life. This was resolved by the discovery of [[nuclear fusion]], the main energy source of the Sun.<ref>{{cite web|url=https://www.nobelprize.org/nobel_prizes/physics/articles/fusion/#1|title=How the Sun Shines|website=www.nobelprize.org}}</ref> Contradictions can also be explained as the result of theories approximating more fundamental (non-contradictory) phenomena. For example, [[atomic theory]] is an approximation of [[quantum mechanics]]. Current theories describe three separate [[Fundamental interaction|fundamental phenomena]] of which all other theories are approximations;<ref>The [[strong force]], the [[electroweak force]], and [[gravity]]. The electroweak force is the unification of [[electromagnetism]] and the [[weak force]]. All observed causal interactions are understood to take place through one or more of these three mechanisms, although most systems are far too complicated to account for these except through the successive approximations offered by other theories.</ref> The potential unification of these is sometimes called the [[Theory of Everything]].<ref name=Weinberg/>

===Example: Relativity===

In 1905, [[Albert Einstein]] published the theory of [[special relativity]].<ref>[[Albert Einstein]] (1905) "[http://www.pro-physik.de/Phy/pdfs/ger_890_921.pdf ''Zur Elektrodynamik bewegter Körper''] {{webarchive|url=https://web.archive.org/web/20091229162203/http://www.pro-physik.de/Phy/pdfs/ger_890_921.pdf |date=2009-12-29 }}", ''Annalen der Physik'' 17: 891; English translation [http://www.fourmilab.ch/etexts/einstein/specrel/www/ On the Electrodynamics of Moving Bodies] by [[George Barker Jeffery]] and Wilfrid Perrett (1923); Another English translation [[s:On the Electrodynamics of Moving Bodies|On the Electrodynamics of Moving Bodies]] by [[Megh Nad Saha]] (1920).</ref>
He started with a principle known for three hundred years, since the time of [[Galileo Galilei]]: the principle of relativity and a prediction from a well established theory for electromagnetism known as [[Maxwell's equations]], the prediction that the speed of light in a vacuum does not depend on relative motion of the source and receiver. Einstein proposed, or hypothesized, that the concept of [[Galilean relativity]] should be modified to align mechanical physics with electromagnetism.<ref name=Weinberg-1972>{{cite book |last=Weinberg |first=Steven |url=https://archive.org/details/gravitationcosmo00stev_0 |title=Gravitation and cosmology |date=1972 |publisher=John Wiley & Sons |isbn=9780471925675 |author-link=Steven Weinberg |url-access=registration}}.</ref>{{rp|17}} In addition to unifying two branches of physics, this modification lead to specific consequences such as  [[time dilation]] and [[length contraction]]. Careful, repeated experiments have both confirmed Einstein's postulates are valid and that the predictions of the special theory of relativity match experiement.<ref>Will, C. M. (2005). Special relativity: a centenary perspective. In Einstein, 1905–2005: Poincaré Seminar 2005 (pp. 33-58). Basel: Birkhäuser Basel.</ref> 

Einstein next sought to generalize the invariance principle to all reference frames, whether inertial or accelerating.<ref name=Torrettipp289-90/> Rejecting Newtonian gravitation—a [[central force]] [[action at a distance|acting instantly at a distance]]—Einstein presumed a gravitational field. In 1907, Einstein's [[equivalence principle]] implied that a free fall within a uniform gravitational field is equivalent to [[inertial]] motion.<ref name=Torrettipp289-90>Roberto Torretti, ''The Philosophy of Physics'' (Cambridge: Cambridge University Press, 1999), [https://books.google.com/books?id=vg_wxiLRvvYC&pg=PA289&dq=Newtownian+Relativity+Equivalence#v=twopage pp. 289–90].</ref> By extending special relativity's effects into three dimensions, [[general relativity]] extended length contraction into [[space contraction]], conceiving of 4D space-time as the gravitational field that alters geometrically and sets all local objects' pathways.  Even massless energy exerts gravitational motion on local objects by "curving" the geometrical "surface" of 4D space-time. Yet unless the energy is vast, its relativistic effects of contracting space and slowing time are negligible when merely predicting motion. Although general relativity is embraced as the more explanatory theory via ''[[scientific realism]]'', Newton's theory remains successful as merely a predictive theory via ''[[instrumentalism]]''. To calculate trajectories, engineers and NASA still use Newton's equations, which are simpler to operate.<ref name=Project2061/>