Editing Philosophy of physics (section)

===Interpretations of quantum mechanics===
{{Main|Interpretation of quantum mechanics}}
In March 1927, working in [[Niels Bohr]]'s institute, [[Werner Heisenberg]] formulated the principle of uncertainty thereby laying the foundation of what became known as the [[Copenhagen interpretation]] of quantum mechanics. Heisenberg had been studying the papers of [[Paul Dirac]] and [[Pascual Jordan]].  He discovered a problem with measurement of basic variables in the equations. His analysis showed that uncertainties, or imprecisions, always turned up if one tried to measure the position and the momentum of a particle at the same time. Heisenberg concluded that these uncertainties or imprecisions in the measurements were not the fault of the experimenter, but fundamental in nature and are inherent mathematical properties of operators in quantum mechanics arising from definitions of these operators.<ref>Niels Bohr, ''Atomic Physics and Human Knowledge'', p. 38</ref>

The Copenhagen interpretation is somewhat loosely defined, as many physicists and philosophers of physics have advanced similar but not identical views of quantum mechanics. It is principally associated with Heisenberg and Bohr, despite their philosophical differences.<ref name="Faye-Stanford">{{Cite book|last=Faye|first=Jan|title=[[Stanford Encyclopedia of Philosophy]]|publisher=Metaphysics Research Lab, Stanford University|year=2019|editor-last=Zalta|editor-first=Edward N.|chapter=Copenhagen Interpretation of Quantum Mechanics|author-link=Jan Faye|chapter-url=https://plato.stanford.edu/entries/qm-copenhagen/}}</ref><ref name="camilleri2015">{{cite journal|first1=K. |last1=Camilleri |first2=M. |last2=Schlosshauer |title=Niels Bohr as Philosopher of Experiment: Does Decoherence Theory Challenge Bohr's Doctrine of Classical Concepts? |arxiv=1502.06547 |journal=Studies in History and Philosophy of Modern Physics |volume=49 |pages=73–83 |year=2015 |doi=10.1016/j.shpsb.2015.01.005|bibcode=2015SHPMP..49...73C |s2cid=27697360 }}</ref> Features common to Copenhagen-type interpretations include the idea that quantum mechanics is intrinsically indeterministic, with probabilities calculated using the [[Born rule]], and the principle of [[Complementarity (physics)|complementarity]], which states that objects have certain pairs of complementary properties that cannot all be observed or measured simultaneously.<ref>{{cite book|last=Omnès |first=Roland |author-link=Roland Omnès |chapter=The Copenhagen Interpretation |title=Understanding Quantum Mechanics |publisher=Princeton University Press |year=1999 |pages=41–54 |doi=10.2307/j.ctv173f2pm.9 |s2cid=203390914 |quote=Bohr, Heisenberg, and Pauli recognized its main difficulties and proposed a first essential answer. They often met in Copenhagen ... 'Copenhagen interpretation has not always meant the same thing to different authors. I will reserve it for the doctrine held with minor differences by Bohr, Heisenberg, and Pauli.}}</ref> Moreover, the act of "observing" or "measuring" an object is irreversible, and no truth can be attributed to an object, [[counterfactual definiteness|except according to the results of its measurement]]. Copenhagen-type interpretations hold that quantum descriptions are objective, in that they are independent of any arbitrary factors in the physicist's mind.<ref name="omnes">{{cite book|first=R. |last=Omnès |author-link=Roland Omnès |title=The Interpretation of Quantum Mechanics |publisher=Princeton University Press |year=1994 |isbn=978-0-691-03669-4 |oclc=439453957 }}</ref>{{Rp|85–90}}

The [[many-worlds interpretation of quantum mechanics]] by [[Hugh Everett III]] claims that the wave-function of a quantum system is telling us claims about the reality of that physical system. It denies wavefunction collapse, and claims that [[superposition principle|superposition]] states should be interpreted literally as describing the reality of many-worlds where objects are located, and not simply indicating the indeterminacy of those variables. This is sometimes argued as a corollary of [[scientific realism]],<ref>David Wallace, 'The Emergent Multiverse', pp. 1–10</ref> which states that scientific theories aim to give us literally true descriptions of the world.

One issue for the Everett interpretation is the role that probability plays on this account. The Everettian account is completely deterministic, whereas probability seems to play an ineliminable role in quantum mechanics.<ref>David Wallace, 'The Emergent Multiverse', pp. 113–117</ref> Contemporary Everettians have argued that one can get an account of probability that follows the Born rule through certain decision-theoretic proofs,<ref>David Wallace, 'The Emergent Multiverse', pg. 157–189</ref> but there is as yet no consensus about whether any of these proofs are successful.<ref name=kent2009>{{Cite book|arxiv=0905.0624|last1=Kent|first1=Adrian|chapter=One world versus many: The inadequacy of Everettian accounts of evolution, probability, and scientific confirmation|title=Many Worlds? Everett, Quantum Theory and Reality |editor=S. Saunders |editor2=J. Barrett |editor3=A. Kent |editor4=D. Wallace |publisher=Oxford University Press|year=2010|bibcode=2009arXiv0905.0624K}}</ref><ref>{{cite journal | last1 = Kent | first1 = Adrian | year = 1990 | title = Against Many-Worlds Interpretations | arxiv = gr-qc/9703089 | journal = International Journal of Modern Physics A | volume = 5 | issue = 9| pages = 1745–1762 |bibcode = 1990IJMPA...5.1745K |doi = 10.1142/S0217751X90000805 | s2cid = 14523184 }}</ref><ref>{{Cite book| last1=Price |first1=Huw | chapter=Decisions, Decisions, Decisions: Can Savage Salvage Everettian Probability?|title=Many Worlds? Everett, Quantum Theory and Reality |editor=S. Saunders |editor2=J. Barrett |editor3=A. Kent |editor4=D. Wallace |publisher=Oxford University Press|year=2010|arxiv = 0802.1390}}</ref>

Physicist [[Roland Omnès]] noted that it is impossible to experimentally differentiate between Everett's view, which says that as the wave-function decoheres into distinct worlds, each of which exists equally, and the more traditional view that says that a decoherent wave-function leaves only one unique real result. Hence, the dispute between the two views represents a great "chasm". "Every characteristic of reality has reappeared in its reconstruction by our theoretical model; every feature except one: the uniqueness of facts."<ref>{{cite book|last1=Omnès|first1=Roland|title=Quantum philosophy : understanding and interpreting contemporary science|date=2002|publisher=Princeton University Press|location=Princeton|isbn=978-1400822867|page=213|edition=1st paperback |others=Arturo Spangalli (transl.)|language=fr|chapter=11}}</ref>