Realism |

**In General**
> s.a. Ether; mathematics;
Ontology; physics [ultimate theories];
quantum locality; Reality;
Structural Realism.

* __Idea__: Scientific realism is
a view about things, events, processes, that are unobservable either because
they are tiny or because they are past; One can define a realist theory as one
describing a closed system entirely by means of entities and concepts pertaining
to the system (as opposed to operationalism).

* __Microphysical realism__: The view
that the only real entities and properties are found at the most fundamental
level of nature.

@ __General references__: Rohrlich FP(96);
Schmelzer gq/97;
Isham & Butterfield IJTP(98) [presheaf loophole];
Matzkin EJP(02)qp;
Grangier qp/03 [and holism];
Wilholt SHPMP(08) [XIX-century debates over atomism];
Singh a0805-ch [history];
Sánchez-Guillén & Vázquez a0903 [realist world view];
Franson JPA(12)-a1004 [constraint on realistic theories];
d'Espagnat FP(11)-a1101 ['open realism' as restoring a mind-independent reality];
Gisin IJQI-a1401,
Bolotin a1401 [possible definition];
Müller a1712,
a1712 [the physical world as emergent];
Boughn a1903
[the term "reality" should be avoided];
Vickers BJPS(18)-a1912 [defense of realism].

@ __Arguments re local realism__:
Caser PLA(84) [condition];
Hoffmann FP(90);
Bernstein FP(99) [against, simplified GHZ];
Santos qp/01,
SHPMP(05) [pro];
Lan IJTP(08)qp/03 [EPR, pro],
IJTP(08)qp/03 [superpositions and mixtures],
JRLR(05)qp/03 [GHZ, pro];
Adenier AJP(08)feb-a0705 [re Mermin's argument].

@ __Elements of reality__: Peres FP(92);
Marchildon FP(08)-a0802 [Lorentz-invariant];
Grinbaum a1007 [criterion based on algorithmic complexity];
Khalidi PhSc(11) [challenges to microphysical realism].

@ __Philosophical__: Leplin 97;
Psillos BJPS(00) [status];
Turner SHPS(04) [abductive arguments];
McMullin PhSc(03)jul [van Fraassen's],
response van Fraassen PhSc(03)jul;
Lyons BJPS(06) [and dividing systems into constituents];
Sankey 08;
Stanford BJPS(09) [the problem of unconceived alternatives];
Bynum M&M-a1303 [on Informational Structural Realism];
Nanay BJPS(13) [singularist semirealism];
Del Santo a1807 [Einstein and Bohm];
> s.a. philosophy of science.

**In Quantum Theory** > s.a. classical limit;
foundations; hidden variables;
histories in quantum mechanics; interpretations;
relationship with classical mechanics.

* __Idea__: Realism in quantum mechanics is the
view that physical objects have properties that exist even before they are measured.

* __The problem__: Local realism is untenable,
because the Kochen-Specker theorem asserts the impossibility of assigning values to quantum
observables (hidden variables) in a way that preserves functional relations between them
(unless the state space is 2D).

* __Loopholes, way out__: One question is
whether one can formulate a non-local, contextual, holistic one (see Bell's theorem);
It has been claimed that realistic interpretations are wrong because some predictions
derived from a mixture are different from the corresponding ones derived from a
superposition state [but @ see Lan IJTP(08)qp/03];
Then there is the failure of Bell's theorem for Clifford algebra-based local variables.

* __Tests__: It has been argued that local
realism can be tested by considering electroweak CP-violation parameters values in
neutral pseudoscalar meson (*K*^{0}) systems.

@ __General references__: in von Neumann 55;
Gleason JMM(65);
Bell RMP(66);
Van der Merwe et al ed-88;
d'Espagnat FP(90),
qp/98;
Home & Selleri JPA(91) [and kaon physics];
Reid PRA(00)qp,
PRL(00)qp,
qp/01 [and macroscopic fluctuations];
Dieks FP(05) [possibilities];
Belousek FP(05) [underdetermination in quantum mechanics];
Giuliani NCB(07)qp/05;
Norsen FP(07)qp/06 [against the phrase 'local realism'];
Stairs & Bub FP(06) [points of view and apparent conflicts];
Accardi & Khrennikov qp/06-proc [adaptive realism];
Vernette & Caponigro qp/06 ["physical quantity" and "physical reality"];
Gomatam a0708 [connection with observations];
Chaves & Fritz PRA(12) [entropic approach];
Vongehr a1207 [Randi challenge];
Cabello ch(16)-a1612 [non-realism as the key to quantum thory];
Freire & Angelo a1904 [degree of reality for continuous variables].

@ __Realism is untenable__:
Leggett RPP(08);
Bednorz NJP(15)-a1411;
Lapiedra & Pérez a1503 [contradiction without inequalities];
Saldanha BJP(20)-a1805 [example].

@ __Realism is tenable__:
Burgos FP(87) [in defense of realism];
Hájíček & Tolar a0802 [quantum mechanics does not contradict philosophical realism];
Laudisa FP(08)-a0811 [non-local];
Karakostas JGPS(12)-a1202;
Hemmick & Shakur 12;
Dorato & Laudisa a1401-in [various forms of realism, and instrumentalism];
Griffiths a1512;
Hobson a1810,
a1901 [realistic analysis of quantum issues];
Belinsky a1905;
Raymond-Robichaud a2010 [local realistic model];
> s.a. realist interpretations.

@ __Realism vs locality__: Heywood & Redhead FP(83) [impossibility of reconciling];
Chiao & Garrison FP(99)qp/98;
Chen & Zhu a0711;
Jeong et al PRL(09)-a0806;
Gisin FP(12)-a0901;
Wechsler a0903-wd [and non-locality];
Hansson PRI(12)-a1104 [proposed test based on the Ruelle-Takens reconstruction method];
> s.a. quantum locality.

@ __Hardy's theorem__: Clifton & Niemann PLA(92) [and entangled spin-*s* particles];
Pagonis & Clifton PLA(92) [*n* spin-1/2 particles];
> s.a. relativistic quantum mechanics.

@ __And measurement__:
Leggett & Garg PRL(85);
Ballentine PRL(87),
comment Leggett & Garg PRL(87);
Percival & Garraway PLA(07)-a0706.

@ __Other loopholes__:
Kracklauer qp/98 [abandon projection postulate];
Hess & Philipp PNAS(01) [time-correlated],
comment Gill et al PNAS(02),
Suarez qp/02;
Malley PRA(04)qp [observables must commute];
Christian qp/07,
qp/07,
a0707 [Clifford algebra-based variables].

@ __Tests__: Genovese EPJC(05)qp [using CP-violation parameters];
Gröblacher et al Nat(07)-a0704
+ pw(07)apr [non-local];
Suarez a0708 [non-local realism and before-before experiment];
Wilms et al PRA(08) [minimum detector efficiency to see violation];
Zhang et al PRA(13) [quantification];
Arora & Asadian PRA(15)-a1508 [with phase space measurements];
Shalm et al al PRL(15)-a1511 [loophole-free test].

@ __Relativistic__: Nikolić IJQI-a1002 [non-local reality compatible with relativity];
Kent PRA(14)-a1311, PTRS(14)-a1411,
PRA(17)-a1608 [realist, one-world, relativistic framework];
Butterfield & Marsh JPCS(19)-a1902.

@ __Related topics__: Bohm & Hiley PRL(85) [in pilot-wave interpretation];
Jabs BJPS-a1212 [epistemological realism];
Miller PLA(96) [and *t* symmetry];
Vaidman FP(99)qp/98 [GHZ proof];
Nagata et al PRL(04) [constraints from rotational invariance];
Nagata JPSJ-a0705 [local realism and single qubit];
Stairs & Bub SHPMP(07) [and commutativity];
Morgan a0810 [random classical fields vs quantum fields];
Le Bihan SHPMP(09) [Bell inequalities and Fine's theorem];
Gisin a1012-conf [realism and randomness];
Lyre a1408 [Berry phase and ontic structural realism];
Dieks FP(19)-a1905 [Busch's 'unsharp quantum reality'].

**Macroscopic Objects**
> s.a. macroscopic quantum systems.

* __Macrorealism__: A viewpoint which
rests on two assumptions in conflict with quantum theory: An object of sufficiently
large size is always in one place at a time (macroscopic superpositions can't exist) and
the object's location can be determined without disturbing it; Leggett & Garg showed
that if it were true, measurements performed at different times on an object could only
be statistically correlated up to a certain degree, a relation they expressed mathematically
through the Leggett-Garg inequality; Experimental results that violated this inequality
would clearly show macrorealism to be false; Their work inspired a number of experiments;
Later analyses have exposed loopholes in the Leggett-Garg argument, and provided other
arguments against macrorealism.

@ __General references__:
Reid & Deuar AP(98);
Mohrhoff IJQI(04)qp [and spacetime];
Reid PRA(18)-a1612.

@ __ Macrorealism__: Leggett & Garg PRL(85);
Robens et al PRX(15)
+ Knee Phys(15);
Clemente & Kofler PRA(15)-a1501;
Allen et al Quant(17)-a1610 [no-go theorem].

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send feedback and suggestions to bombelli at olemiss.edu – modified 29 oct 2020