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GianCarlo Ghirardi

Publications and source records attributed to GianCarlo Ghirardi.

44 records · Page 3Linked to original sources
arXiv2000

A General Argument Against the Universal Validity of the Superposition Principle

We reconsider a well known problem of quantum theory, i.e. the so called measurement (or macro-objectification) problem, and we rederive the fact that it gives rise to serious problems of interpretation. The novelty of our approach derives from the fact that the relevant conclusion is obtained in a completely general way, in particular, without resorting to any of the assumptions of ideality which are usually done for the measurement process. The generality and unescapability of our assumptions (we take into account possible malfunctionings of the apparatus, its unavoidable entanglement with the environmment, its high but not absolute reliability, its fundamentally uncontrollable features) allow to draw the conclusion that the very possibility of performing measurements on a microsystem combined with the assumed general validity of the linear nature of quantum evolution leads to a fundamental contradiction.

quant-ph↗
arXiv2000

Local measurements of nonlocal observables and the relativistic reduction process

In this paper we reconsider the constraints which are imposed by relativistic requirements to any model of dynamical reduction. We review the debate on the subject and we call attention on the fundamental contributions by Aharonov and Albert. Having done this we present a new formulation, which is much simpler and more apt for our analysis, of the proposal put forward by these authors to perform measurements of nonlocal observables by means of local interactions and detections. We take into account recently proposed relativistic models of dynamical reduction and we show that, in spite of some mathematical difficulties related to the appearence of divergences, they represent a perfectly appropriate conceptual framework which meets all necessary requirements for a relativistic account of wave packet reduction. Subtle questions like the appropriate way to deal with counterfactual reasoning in a relativistic and nonlocal context are also analyzed in detail.

quant-ph↗
arXiv1999

About the Notion of Truth in the Decoherent Histories Approach: a reply to Griffiths

Griffiths claims that the ``single family rule'', a basic postulate of the decoherent histories approach, rules out our requirement that any decoherent history has a unique truth value, independently from the decoherent family to which it may belong. Here we analyze the reasons which make our requirement indispensable and we discuss the consequences of rejecting it.

quant-ph↗
arXiv1999

Decoherent Histories and Realism

We reconsider the Decoherent Histories approach to Quantum Mechanics and we analyze some problems related to its interpretation which, according to us, have not been adequately clarified by its proponents. We put forward some assumptions which, in our opinion, are necessary for a realistic interpretation of the probabilities that the formalism attaches to decoherent histories. We prove that such assumptions, unless one limits the set of the decoherent families which can be taken into account, lead to a logical contradiction. The line of reasoning we will follow is conceptually different from other arguments which have been presented and which have been rejected by the supporters of the Decoherent Histories approach. The conclusion is that the Decoherent Histories approach, to be considered as an interesting realistic alternative to the orthodox interpretation of Quantum Mechanics, requires the identification of a mathematically precise criterion to characterize an appropriate set of decoherent families which does not give rise to any problem.

quant-ph↗
arXiv1999

More about Dynamical Reduction and the Enumeration Principle

In view of the arguments put forward by Clifton and Monton [1999] in a recent preprint, we reconsider the alleged conflict of dynamical reduction models with the enumeration principle. We prove that our original analysis of such a problem is correct, that the GRW model does not meet any difficulty and that the reasoning of the above authors is inappropriate since it does not take into account the correct interpretation of the dynamical reduction theories.

quant-ph↗
arXiv1999

Can the Decoherent Histories Description of Reality be Considered Satisfactory?

We discuss some features of the Decoherent Histories approach. We consider four assumptions, the first three being in our opinion necessary for a sound interpretation of the theory, while the fourth one is accepted by the supporters of the DH approach, and we prove that they lead to a logical contradiction. We discuss the consequences of relaxing any one of them.

gr-qc↗
arXiv1998

Do dynamical reduction models imply that arithmetic does not apply to ordinary macroscopic objects?

We analyze a recent paper in which an alleged devastating criticism to the so called GRW proposal to account for the objectification of the properties of macroscopic systems has been presented and we show that the author has not taken into account the precise implications of the GRW theory. This fact makes his conclusions basically wrong. We also perform a survey of measurement theory aimed to better focus the physical and the conceptual aspects of the so-called macro-objectification problem.

quant-ph↗