Papers by Giancarlo Ghirardi
Fortschritte der Physik, 1972
We reconsider the problem of the compatibility of our definite perceptions with the linear nature... more We reconsider the problem of the compatibility of our definite perceptions with the linear nature of quantum theory. We review some proposed solutions to the puzzling situation implied by the possible occurrence of superpositions of different perceptions and we argue that almost all are not satisfactory. We then discuss the way out which makes explicit reference to consciousness and we underline its pros and cons. In the second part of the paper we reconsider this problem in the light of the recently proposed collapse models, which overcome the difficulties of the standard theory by adding nonlinear and stochastic terms to the evolution equation and, on the basis of a unique dynamical principle, account both for the wavy behaviour of microsystems as well as for definite macroscopic events. By taking into account that different microscopic situations can trigger different displacements of an enormous number of particles in our brains which, in turn, lead to different and definite perceptions, we make plausible that such models do not assign a peculiar role to the conscious observer. Simply, the characteristic amplification mechanism leading to the collapse implies the suppression of all but one of the nervous stimuli corresponding to different perceptions. Thus, collapse models, at the nonrelativistic level, qualify themselves as theories which can consistently account for all natural processes, among them our definite perceptions.
We analyze critically a recent proposal of faster than light communication.
By taking advantage of my long lasting research activity on the conceptual foundations of quantum... more By taking advantage of my long lasting research activity on the conceptual foundations of quantum mechanics I reconsider some of the basic problems which have been at the centre of the recent debate on this theory. Specific attention is given to topics like quantum nonlocality, the impossibility of faster than light communication and the so-called measurement or macroobjectification problem. A large part of the paper deals with the dynamical reduction program and discusses its merits and achievements, as well as its limitations. The above considerations lead me in a natural way to express my personal views on the present status of the foundational studies.
Lecture Notes in Physics, 2003
ABSTRACT
Quantum [Un]speakables, 2002
Advances in Quantum Mechanics, 2013
Physical Review, 1963
... Rev. 79, 238 (1950). ' F. W. Fenning and F. R. Holt, Nature 165, 722 (1950}. K. M. Watso... more ... Rev. 79, 238 (1950). ' F. W. Fenning and F. R. Holt, Nature 165, 722 (1950}. K. M. Watson and R. N. Stuart, Phys. Rev. 82, 738 (1952). ... (2.3) Page 3. ALZ ETTA, GH I RARD I, AN D III MI N I d'pfi'(p) 2x2p~a~' E'+' Ei(p'/21 i) Pi(Pi ~T21 i(EEi)]")' if E&E)) 2&2P lo,l2 if E(EE. ...
Annals of the New York Academy of Sciences, 1995
ABSTRACT This article has taken into account the main conceptual difficulties met by standard qua... more ABSTRACT This article has taken into account the main conceptual difficulties met by standard quantum mechanics in dealing with physical processes involving macroscopic systems. An idea stressed has been how J. A. Wheeler's remarks and lucid analysis have been relevant in pinpointing and bringing to its extreme consequences the puzzling aspects of quantum phenomena. The recently proposed models of spontaneous dynamical reduction shown represent a consistent way to overcome the conceptual difficulties of the standard theory. Obviously, many nontrivial problems remain open, the first and more relevant one being that of generalizing the model theories considered to the relativistic case. This is the challenge of the dynamical reduction program.
Physics Letters a, Jun 1, 1992
We explain how the idea of an element of physical reality, appropriately formulated for a relativ... more We explain how the idea of an element of physical reality, appropriately formulated for a relativistically invariant theory of statevector collapse, in a quite natural way leads one to model (as Squires wishes to do) a small brain's “perception by the mind”, without entailing superluminal communication.
Found Phys, 1998
We consider the problem of whether there are deterministic theories describing the evolution of a... more We consider the problem of whether there are deterministic theories describing the evolution of an individual physical system in terms of the definite trajectories of its constituent particles and which stay in the same relation to Quantum Mechanics as Bohmian Mechanics but which differ from the latter for what concerns the trajectories followed by the particles. Obviously, one has to impose on the hypothetical alternative theory precise physical requirements. We analyse various such constraints and we show step by step how to meet them. This way of attacking the problem turns out to be useful also from a pedagogical point of view since it allows to recall and focus on some relevant features of Bohm's theory. One of the central requirements we impose on the models we are going to analyse has to do with their transformation properties under the transformations of the extended Galilei group. In a context like the one we are interested in one can put forward various requests that we refer to as physical and genuine covariance and invariance. Other fundamental requests are that the theory allows the description of isolated physical systems as well as that it leads to a solution (in the same sense as Bohmian Mechanics) of the measurement problem.We show that, even when all above conditions are taken into account, there are infinitely many inequivalent (from the point of view of the trajectories) bohmian-like theories reproducing the predictions of Quantum Mechanics. This raises some interesting questions about the meaning of Bohmian Mechanics.
Journal of Statistical Physics, 2000
Unknown, Jun 1, 1994
This article has taken into account the main conceptual difficulties met by standard quantum mech... more This article has taken into account the main conceptual difficulties met by standard quantum mechanics in dealing with physical processes involving macroscopic systems. An idea stressed has been how J. A. Wheeler's remarks and lucid analysis have been relevant in pinpointing and bringing to its extreme consequences the puzzling aspects of quantum phenomena. The recently proposed models of spontaneous dynamical reduction shown represent a consistent way to overcome the conceptual difficulties of the standard theory. Obviously, many nontrivial problems remain open, the first and more relevant one being that of generalizing the model theories considered to the relativistic case. This is the challenge of the dynamical reduction program.
Nuovo Cimento a Nucl Part F, 1968
We shall focus on the relations between irreversibility and the foundations of quantum mechanics,... more We shall focus on the relations between irreversibility and the foundations of quantum mechanics, with particular attention to the macro-objectification problem.
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Papers by Giancarlo Ghirardi