Realism |

**In General** > s.a. Ether; mathematics; physics [ultimate theories]; quantum
locality; 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 a1401, Bolotin a1401 [possible definition].

@ __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]; > s.a. philosophy of science.

**In Quantum Theory** > s.a. classical
limit; foundations;
hidden variables;
histories in quantum mechanics; 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]; Wechsler a0903-wd [and non-locality]; Caves & Fritz PRA(12) [entropic approach]; Vongehr a1207 [Randi challenge]; Cabello ch(16)-a1612 [non-realism as the key to quantum thory].

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

@ __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.

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

@ __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 a1508 [with phase space measurements]; Shalm et al al a1511 [loophole-free test].

@ __Relativistic__: Nikolić IJQI-a1002 [non-local
reality compatible with relativity]; Kent PRA(14)-a1311 [solution to the Lorentzian quantum reality problem].

@ __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].

**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 a1612.

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

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