Wave-Function
Collapse as a Dynamical Process |

**In General** > s.a. wave-function
collapse [including some models]; zeno
effect.

* __Idea__: The point
of view according to which wave-function collapse (quantum-state
reduction) is a physical process, as opposed to just being related to our
knowledge and description of the system; In a relativistic scenario the
collapse will then happen at a finite speed, as opposed to the
instantaneous collapse of the conventional view.

* __Tests__: One way to
test it is to look for quantum behaviour in
larger and larger objects; If collapse models are correct, then quantum
effects will not be apparent above a certain mass;
2015, Physicists have already carried out double-slit interference
experiments with large molecules; Various groups are
planning to search for such a cut-off using metal clusters and
nanoparticles, and hope to see results within a decade.

* __Motivation__: Using
this point of view it becomes easier to explain
how quantum fluctuations in the early universe might have become
classical.

@ __General references__: Lewin FP(09)
[as
an effect of field quantization]; Omnčs a1006,
a1601
[derivation of collapse from quantum dynamics].

@ __Speed / time for collapse__: Squires PLA(90);
Pegg
PLA(91);
Zurek
qp/03
["decoherence timescale"];
Ohanian a1311
[atom-interferometer test].

@ __State recovery / uncollapse__: Katz et al PRL(08)-a0806;
Jordan & Korotkov CP(10)-a0906
[undoing
quantum measurements]; news PhysOrg(13)nov.

@ __Objective collapse, and retina / mind__: Georgiev qp/02;
Thaheld qp/06/PRA,
BioSys(08)qp/06;
Ghirardi & Romano JPCS-a1401
[collapse models and perceptual processes]; Ghirardi IJTP(15)-a1411
[reply to Elio Conte].

@ __Constraints__: Jones et al FP(04)qp
[SNO experiment]; Curceanu et al JAP(15)-a1502
[from X-ray experiments]; Helou et al PRD(17)-a1606,
Carlesso et al PRD(16)-a1606
[from gravitational-wave detectors].

@ __Other phenomenology__: Squires PLA(91),
Pearle
et al FP(99)qp/00
[and
radiation]; Pearle FP(12)-a1003
[and cosmogenesis];
Donadi et al FP(13)-a1207
[and neutrino oscillations], FP(13)-a1207
[and flavor oscillations]; Okon & Sudarsky FP(14)-a1309
[advantages for cosmology and quantum gravity];
Donadi & Bassi JPA(15)-a1408
[and electromagnetic radiation]; Toroš & Bassi a1601
[and matter-wave interferometry]; Simonov & Hiesmayr a1606
[and neutral meson flavor oscillations].

@ __Collapse over a finite time__: Marchewka & Schuss a1103;
Ignatiev JPCS(13)-a1204.

@ __Related topics__: Bassi et al JPA(05)qp
[and *E* non-conservation], JPA(07)
[and
Hilbert space operator formalism]; Bondoni a1006-wd
[measurement
as mathematical
vs phenomenological.process]; Tumulka a1102
[paradoxes and primitive ontology];
Brouzakis et al PLB(12)-a1109;
Weinberg PRA(12)-a1109;
Rizos & Tetradis JHEP(12)-a1112;
Simpson FP(11);
Melkikh
a1311 [and
quantum field theory]; McQueen SHPMP(15)-a1501
[four tails problems]; Yun a1606
[entangling-speed threshold]; Bedingham & Maroney PRA(17)-a1607
[and time-reversal symmetry].

**And Gravity** > s.a. models
of decoherence [gravity-related].

* __History__: In the
first lecture of his 1962 course on gravitation Feynman speculated that
gravity would enforce classical behavior for masses larger than the Planck
mass; The idea is related to work on the quantum-classical divide and
attempts at building and experimenting with hybrid quantum-classical
devices.

* __Gravity produces wave function collapse__: A wave
function collapses under the influence of gravity in a region where the
matter density reaches a certain value (masses and lengths of the order of
bacterial scales); Gravity provides a decoherence mechanism; Penrose's
proposal is motivated by a fundamental conflict between the superposition
principle of quantum mechanics and the principle of general covariance.

* __Wave function collapse produces gravity__: 2017, An idea proposed by Antoine Tilloy is that when a GRW-type flash collapses a wave function and causes a particle to be localized in one place, it creates a gravitational field at that event; Gravity remains classical.

@ __General references__: Károlyházy NC(66);
Diósi PLA(84)-a1412;
Károlyházy in(85),
et al in(86);
Diósi PRA(89);
Ellis et al PLB(89);
Fivel qp/97;
Anandan FP(99)gq/98;
Christian gq/98-ch;
De Filippo qp/00,
qp/01;
De Filippo et al PhyA(03)qp
[simulation]; Mureika PRD(06)
[and large extra dimensions]; Adler JPA(07)qp/06;
Salart et al PRL(08)-a0803
[and Bell inequalities]; Diósi JPCS(09)-a0902
[collapse causes gravity]; Diósi JPCS(13)-a1302;
Sharma & Singh GRG(14)-a1403
[Ricci identities and Dirac equations]; Diósi FP(14),
NJP(14)-a1404
[in bulk matter]; Singh JPCS-a1503
[survey]; Banerjee et al IJMPD(15)-a1505-GRF
[and the cosmological constant and time].

@ __Relativistic models__: Quandt-Wiese a0912;
Stoica Quanta(16)-a1601
[continuous evolution]; Quandt-Wiese a1701 , a1701 [from semiclassical gravity, wave function evolution in a dynamically expanding spacetime]; Gasbarri et al a1701 [mechanism]; Okon & Sudarsky a1701 [in cosmology and quantum gravity].

@ __Other models__: Melko & Mann gq/00 [*D*-dimensional Schrödinger-Newton equations]; Gao IJTP(10)-a1001 [and spacetime discreteness]; Adler a1401-ch
[state vector reduction as driven by spacetime foam]; Bera et al a1608 [stochastic modification of the Schrödinger-Newton equation]; Brody & Hughston a1611 [energy-driven stochastic master equation for the density matrix]; Korbicz & Tuziemski a1612; Tilloy a1709 [GRW with massive flashes].

@ __Penrose's proposal__: Penrose in(81),
in(86);
Penrose GRG(96);
Penrose in(00);
Gao SHPMP(13)-a1305
[critique]; Oosterkamp & Zaanen a1401-conf
[thought experiment]; Penrose FP(14);
Bahrami et al PRA(14)-a1408
[cutoff, and dissipative generalization].

@ __Gravitational self-interaction__: Colin et al CQG(14)-a1403
[approximate dynamics and experimental setting].

@ __Tests__: Christian PRL(05)qp
[with cosmic neutrinos]; van Wezel et al PhilM(08)-a0706
[towards
an experimental test]; Quandt-Wiese a1701 [proposal].

> __Phenomenology__:
see matter phenomenology in quantum
gravity; models
of dark energy; quantum
cosmological perturbations.

**Continuous Spontaneous Localization**

* __Idea__: Models of
spontaneous wave function collapse modify the linear Schrödinger equation
by adding stochastic non-linear terms to it, which leads to
non-conservation of energy for the system under consideration; The larger
a system is, the faster a state superposition will collpase;
> s.a. schrödinger equation.

* __GRW mechanism__:
Gives a quantum theory without observers; In fact, two different ones by
using either the matter density ontology (GRWm) or the flash ontology
(GRWf); Testable deviations from quantum mechanics are known for both
theories, but the difference is so small that no decisive experiment has
been performed (2007).

@ __General references__: Pearle IJTP(79),
PRA(89)
[randomly fluctuating interaction]; Pearle & Soucek FPL(89)
[path integral]; Ghirardi & Pearle in(90);
Nicrosini & Rimini FP(90)
[stochastic processes in \(\cal H\)]; Squires PLA(91)
[without stochastic field]; Pearle in(97)qp/98,
in(97)qp/98,
LNP(99)qp,
PRA(99)qp,
FP(00)qp
[and conservation laws], PRA(04)qp/03
[energy-driven]; Santos & Escobar qp/98
[beable interpretation]; Hansson qp/00
[from non-abelian non-linearity]; Bassi & Ghirardi PRP(03)qp;
Bassi JPA(05)qp/04
[single free particle]; Dowker & Herbauts FPL(05)qp/04
[without wave function]; Pearle PRA(05)qp
[quasirelativistic quasilocal model]; Lewis SHPMP(05)
[interpretation]; Morikawa & Nakamichi PTP(06)qp/05
[as spontaneous symmetry breaking]; Pearle JPA(07)qp/06,
qp/06
[overview]; Bassi JPCS(07)qp
[rev]; Bassi et al RMP(13)-a1204
[rev, and tests], a1212/RMP
[stochastic methods]; Bassi & Ulbricht JPCS(14)-a1401
[rev].

@ __GRW mechanism__: Ghirardi et al PRA(90);
Tessieri
et al PRA(95);
Clifton & Monton BJPS(99),
Bassi & Ghirardi BJPS(99),
BJPS(99)
[and enumeration principle]; Monton SHPMP(04)
[interpretation];
Allori et al BJPS(08)qp/06
[and
pilot-wave theory]; Vacchini JPA(07)
[GRW
master equation and decoherence]; Frigg & Hoefer SHPMP(07)
[and
probabilities]; Goldstein et al JSP(12)-a0710
[testable
predictions]; Tumulka RVMP(09)-a0711
[flash
ontology]; Bedingham JPA(11)
[hidden-variable interpretation]; Esfeld & Gisin a1310
[John Bell's GRW flash theory]; Wallace a1407
[tails of the GRW wave function].

@ __GRW mechanism, variations__: Smirne et al PRA(14)-a1408
[dissipative extension]; Egg & Esfeld a1410
[GRW matter density theory (GRWm)].

@ __For quantum field theory__: Tumulka PRS(06)qp/05
[GRW]; Diósi AIP(06)qp
[QED]; Derakhshani PLA(13)-a1304
[Newtonian theory of semiclassical gravity]; Pearle a1404-wd,
PRD(15)-a1412
[scalar field, relativistic model]; Pearle a1610-in [for photons].

@ __Phenomenology__: Nimmrichter et al PRA(11)
[tests with matter-wave interferometry]; Lochan et al PRD(12)
[constraints from cmb spectral distortions]; Das et al a1302-MG13
[cosmology]; Laloë et al PRA(14)-a1409
[trapped ultra-cold atoms]; Diósi PRL(15)-a1411
[classical mechanical oscillators]; > s.a. black-hole
information.

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