On Spontaneous Wave Function Collapse and Quantum Field Theory

One way of obtaining a version of quantum mechanics without observers, and thus of solving the paradoxes of quantum mechanics, is to modify the Schroedinger evolution by implementing spontaneous collapses of the wave function. An explicit model of this kind was proposed in 1986 by Ghirardi, Rimini, and Weber (GRW), involving a nonlinear, stochastic evolution of the wave function. We point out how, by focussing on the essential mathematical structure of the GRW model and a clear ontology, it can be generalized to (regularized) quantum field theories in a simple and natural way.Comment: 14 pages LaTeX, no figures; v2 minor improvement

Does quantum nonlocality irremediably conflict with Special Relativity?

We reconsider the problem of the compatibility of quantum nonlocality and the requests for a relativistically invariant theoretical scheme. We begin by discussing a recent important paper by T. Norsen [arXiv:0808.2178] on this problem and we enlarge our considerations to give a general picture of the conceptually relevant issue to which this paper is devoted.Comment: 18 pages, 1 figur

Relativistic state reduction dynamics

A mechanism describing state reduction dynamics in relativistic quantum field theory is outlined. The mechanism involves nonlinear stochastic modifications to the standard description of unitary state evolution and the introduction of a relativistic field in which a quantized degree of freedom is associated to each point in spacetime. The purpose of this field is to mediate in the interaction between classical stochastic influences and conventional quantum fields. The equations of motion are Lorentz covariant, frame independent, and do not result in divergent behavior. It is shown that the mathematical framework permits the specification of unambiguous local properties providing a connection between the model and evidence of real world phenomena. The collapse process is demonstrated for an idealized example.Comment: 20 pages, 2 figures, replacement with minor correction

On a recent proof of nonlocality without inequalities

Recently a quite stimulating paper [1] dealing with the possibility of exploiting the nonlocal aspects of a superposition of states of a single photon appeared. We regard as greatly relevant the results which have been obtained. However we think that the presentation of the matter and the way to derive the conclusion are not fully satisfactory and do not put the necessary emphasis on some subtle basic aspects like locality and realism. In view of its interest we consider it useful to reconsider the line of reasoning of ref.[1] and to derive once more its results by following a procedure which seems to us more lucid and which makes fully clear the role of the various conceptual aspects of the treatment. We hope that our analysis will contribute to clarify and to deepen the interesting results of ref.[1]

The Conway-Kochen argument and relativistic GRW models

In a recent paper, Conway and Kochen proposed what is now known as the "Free Will theorem" which, among other things, should prove the impossibility of combining GRW models with special relativity, i.e., of formulating relativistically invariant models of spontaneous wavefunction collapse. Since their argument basically amounts to a non-locality proof for any theory aiming at reproducing quantum correlations, and since it was clear since very a long time that any relativistic collapse model must be non-local in some way, we discuss why the theorem of Conway and Kochen does not affect the program of formulating relativistic GRW models.Comment: 16 pages, RevTe

EPR-Bell Nonlocality, Lorentz Invariance, and Bohmian Quantum Theory

We discuss the problem of finding a Lorentz invariant extension of Bohmian mechanics. Due to the nonlocality of the theory there is (for systems of more than one particle) no obvious way to achieve such an extension. We present a model invariant under a certain limit of Lorentz transformations, a limit retaining the characteristic feature of relativity, the non-existence of absolute time resp. simultaneity. The analysis of this model exemplifies an important property of any Bohmian quantum theory: the quantum equilibrium distribution $\rho = |\psi |^2$ cannot simultaneously be realized in all Lorentz frames of reference.Comment: 24 pages, LaTex, 4 figure

Real World Interpretations of Quantum Theory

I propose a new class of interpretations, {\it real world interpretations}, of the quantum theory of closed systems. These interpretations postulate a preferred factorization of Hilbert space and preferred projective measurements on one factor. They give a mathematical characterisation of the different possible worlds arising in an evolving closed quantum system, in which each possible world corresponds to a (generally mixed) evolving quantum state. In a realistic model, the states corresponding to different worlds should be expected to tend towards orthogonality as different possible quasiclassical structures emerge or as measurement-like interactions produce different classical outcomes. However, as the worlds have a precise mathematical definition, real world interpretations need no definition of quasiclassicality, measurement, or other concepts whose imprecision is problematic in other interpretational approaches. It is natural to postulate that precisely one world is chosen randomly, using the natural probability distribution, as the world realised in Nature, and that this world's mathematical characterisation is a complete description of reality.Comment: Minor revisions. To appear in Foundations of Physic

Explaining the unobserved: why quantum mechanics is not only about information

A remarkable theorem by Clifton, Bub and Halvorson (2003)(CBH) characterizes quantum theory in terms of information--theoretic principles. According to Bub (2004, 2005) the philosophical significance of the theorem is that quantum theory should be regarded as a ``principle'' theory about (quantum) information rather than a ``constructive'' theory about the dynamics of quantum systems. Here we criticize Bub's principle approach arguing that if the mathematical formalism of quantum mechanics remains intact then there is no escape route from solving the measurement problem by constructive theories. We further propose a (Wigner--type) thought experiment that we argue demonstrates that quantum mechanics on the information--theoretic approach is incomplete.Comment: 34 Page

Quantum measurement in a family of hidden-variable theories

The measurement process for hidden-configuration formulations of quantum mechanics is analysed. It is shown how a satisfactory description of quantum measurement can be given in this framework. The unified treatment of hidden-configuration theories, including Bohmian mechanics and Nelson's stochastic mechanics, helps in understanding the true reasons why the problem of quantum measurement can succesfully be solved within such theories.Comment: 16 pages, LaTeX; all special macros are included in the file; a figure is there, but it is processed by LaTe

Cosmological Surrealism: More than ``Eternal Reality" is Needed

Inflationary Cosmology makes the universe ``eternal" and provides for recurrent universe creation, ad infinitum -- making it also plausible to assume that ``our" Big Bang was also preceeded by others, etc.. However, GR tells us that in the ``parent" universe's reference frame, the newborn universe's expansion will never start. Our picture of ``reality" in spacetime has to be enlarged.Comment: 7 pages, TAUP N23