107 research outputs found
On Closing the Circle
Ghirardi sought to “close the circle”—to find a place for human experience of measurement outcomes within quantum mechanics. I argue that Ghirardi’s spontaneous collapse approach succeeds at this task, and in fact does so even without the postulation of a particular account of “primitive ontology”, such as a mass density distribution or a discrete “flashes”. Nevertheless, I suggest that there is a remaining ontological problem facing spontaneous collapse theories concerning the use of classical concepts like “particle” in quantum mechanical explanation at the micro-level. Neither the mass density nor the flash ontology is any help with this problem
Non-Locality and Theories of Causation
The aim of the paper is to investigate the characterization of an unambiguous
notion of causation linking single space-llike separated events in EPR-Bell
frameworks. This issue is investigated in ordinary quantum mechanics, with some
hints to no collapse formulations of the theory such as Bohmian mechanics.Comment: Presented at the NATO Advanced Research Workshop on Modality,
Probability and Bell's Theorems, Cracow, Poland, August 19-23, 200
Remarks on matter-gravity entanglement, entropy, information loss and events
I recall my 'matter-gravity entanglement hypothesis' and briefly review the
evidence for it, based partly on its seeming ability to resolve a number of
puzzles related to quantum black holes including the black hole information
loss puzzle. I point out that, according to this hypothesis, there is a
quantity, i.e. the universe's 'matter-gravity entanglement entropy' -- which
deserves to be considered the 'entropy of the universe' and which, with
suitable initial conditions, will plausibly increase monotonically with
cosmological time. In the last section, which is more tentative and raises a
number of further puzzles and open questions, I discuss the prospects for a
notion of 'events' which 'happen' whose statistical properties are described by
this entropy of the universe. It is hoped that such a theory of events may be a
step on the way towards explaining how initial quantum fluctuations convert
themselves into inhomogeneities in a seemingly classical universe.Comment: 17 pages, 7 figures. Invited contribution to the proceedings of the
conference "Progress and Visions in Quantum Theory in View of Gravity",
Leipzig, Germany, October 2018, based on part of a talk at the workshop "The
Mysterious Universe: Dark Matter -- Dark Energy -- Cosmic Magnetic Fields"
MITP, Mainz, Germany, June 4, 2019. (v2 No change) v3: References added v4:
typos etc. correcte
Insolubility Theorems and EPR Argument
I wish to thank in particular Arthur Fine for very perceptive comments on a previous draft of this paper. Many thanks also to Theo Nieuwenhuizen for inspiration, to Max Schlosshauer for correspondence, to two anonymous referees for shrewd observations, and to audiences at Aberdeen, Cagliari and Oxford (in particular to Harvey Brown, Elise Crull, Simon Saunders, Chris Timpson and David Wallace) for stimulating questions. This paper was written during my tenure of a Leverhulme Grant on ‘The Einstein Paradox’: The Debate on Nonlocality and Incompleteness in 1935 (Project Grant nr. F/00 152/AN), and it was revised for publication during my tenure of a Visiting Professorship in the Doctoral School of Philosophy and Epistemology, University of Cagliari (Contract nr. 268/21647).Peer reviewedPostprin
Does quantum mechanics tell an atomistic spacetime?
The canonical answer to the question posed is "Yes." -- tacitly assuming that
quantum theory and the concept of spacetime are to be unified by `quantizing' a
theory of gravitation. Yet, instead, one may ponder: Could quantum mechanics
arise as a coarse-grained reflection of the atomistic nature of spacetime? --
We speculate that this may indeed be the case. We recall the similarity between
evolution of classical and quantum mechanical ensembles, according to Liouville
and von Neumann equation, respectively. The classical and quantum mechanical
equations are indistinguishable for objects which are free or subject to
spatially constant but possibly time dependent, or harmonic forces, if
represented appropriately. This result suggests a way to incorporate anharmonic
interactions, including fluctuations which are tentatively related to the
underlying discreteness of spacetime. Being linear and local at the quantum
mechanical level, the model offers a decoherence and natural localization
mechanism. However, the relation to primordial deterministic degrees of freedom
is nonlocal.Comment: Based on invited talks at Fourth International Workshop DICE2008,
held at Castello Pasquini / Castiglioncello, Italy, 22-26 September 2008 and
at DISCRETE'08 - Symposium on Prospects in the Physics of Discrete
Symmetries, held at IFIC, Valencia, Spain, 11-16 December 2008 - to appear in
respective volumes of Journal of Physics: Conference Serie
Classical and quantum: a conflict of interest
We highlight three conflicts between quantum theory and classical general
relativity, which make it implausible that a quantum theory of gravity can be
arrived at by quantising classical gravity. These conflicts are: quantum
nonlocality and space-time structure; the problem of time in quantum theory;
and the quantum measurement problem. We explain how these three aspects bear on
each other, and how they point towards an underlying noncommutative geometry of
space-time.Comment: 15 pages. Published in `Gravity and the quantum' [Essays in honour of
Thanu Padmanabhan on the occasion of his sixtieth birthday] Eds. Jasjeet
Singh Bagla and Sunu Engineer (Springer, 2017
Towards a realistic interpretation of quantum mechanics providing a model of the physical world
It is argued that a realistic interpretation of quantum mechanics is possible
and useful. Current interpretations, from Copenhagen to many worlds are
critically revisited. The difficulties for intuitive models of quantum physics
are pointed out and possible solutions proposed. In particular the existence of
discrete states, the quantum jumps, the alleged lack of objective properties,
measurement theory, the probabilistic character of quantum physics, the
wave-particle du- ality and the Bell inequalities are analyzed. The sketch of a
realistic picture of the quantum world is presented. It rests upon the assump-
tion that quantum mechanics is a stochastic theory whose randomness derives
from the existence of vacuum fields. They correspond to the vacuum fluctuations
of quantum field theory, but taken as real rather than virtual.Comment: 43 pages, paper throughout revised and somewhat enlarged, sections on
the Bell inequalities and on the sketch of a picture of the quantum world
rewritten, new references adde
Free Will in a Quantum World?
In this paper, I argue that Conway and Kochen’s Free Will Theorem (1,2) to the conclusion that quantum mechanics and relativity entail freedom for the particles, does not change the situation in favor of a libertarian position as they would like. In fact, the theorem more or less implicitly assumes that people are free, and thus it begs the question. Moreover, it does not prove neither that if people are free, so are particles, nor that the property people possess when they are said to be free is the same as the one particles possess when they are claimed to be free. I then analyze the Free State Theorem (2), which generalizes the Free Will Theorem without the assumption that people are free, and I show that it does not prove anything about free will, since the notion of freedom for particles is either inconsistent, or it does not concern our common understanding of freedom. In both cases, the Free Will Theorem and the Free State Theorem do not provide any enlightenment on the constraints physics can pose on free will
From Quantum to Classical: the Quantum State Diffusion Model
Quantum mechanics is nonlocal. Classical mechanics is local. Consequently classical mechanics can not explain all quantum phenomena. Conversely, it is cumbersome to use quantum mechanics to describe classical phenomena. Not only are the computations more complex, but - and this is the main point - it is conceptually more difficult: one has to argue that nonlocality, entanglement and the principle of superposition can be set aside when crossing the "quantum principle of superposition should become irrelevant in the classical limit. But why should one argue? Shouldn't it just come out of the equations? Does it come out of the equations? This contribution is about the last question. And the answer is: "it depends on which equation"
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