Orthodox Quantum Research Articles

Partial and unsharp quantum logics

The total and the sharp character of orthodox quantum logic has been put in question in different contexts. This paper presents the basic ideas for a unified approach to partial and unsharp forms of quantum logic. We prove a completeness theorem for some partial logics based on orthoalgebras and orthomodular posets. We introduce the notion of unsharp orthoalgebra and of generalized MV algebra. The class of all effects of any Hilbert space gives rise to particular examples of these structures. Finally, we investigate the relationship between unsharp orthoalgebras, generalized MV algebras, and orthomodular lattices.

Theoretical model of a purported empirical violation of the predictions of quantum theory.

A generalization of Weinberg's nonlinear quantum theory is used to model a reported violation of the predictions of orthodox quantum theory.

Particle creation as the quantum condition for probabilistic events to occur

A new version of non-relativistic quantum theory is proposed, according to which probabilistic events occur whenever new stationary or bound states are created as a result of inelastic collisions. The new theory recovers the experimental success of orthodox quantum theory, but differs from the orthodox theory for as yet unperformed experiments.

The joint measurement problem

According to orthodox quantum theory, the joint measurement of noncommuting observables is impossible. It has been claimed recently that such joint measurements are admitted in a generalized formalism for quantum theory developed by Ludwig and Davies, by means of so-called ‘unsharp observables.’ It is argued in this paper that this claim has not been substantiated.

Comment on "Surrealistic Bohm Trajectories"

Abstract From the perspective of orthodox quantum theory, no meaning can be assigned to the notion of the "slit" through which the atom passed in the experiments under discussion in this paper. From a Bohmian perspective this notion does have meaning. Moreover, when we compare the answer provided by BM with the answer provided, not by orthodox quantum theory, but by a naive, largely incoherent operationalism, we obtain different answers. So what?

Reply to Comment on "Surrealistic Bohm Trajectories"

Let us begin with a response to the summary of the Comment by D. Durr, W. Fusseder, S. Goldstein, and N. Zanghi [1]. We are accused to not stay inside orthodox quantum but to employ a naive, largely incoherent operationalism instead. We think that this charge is not justified, because we did apply standard quantum theory correctly and also followed the rules of Bohmian Mechanics (BM) carefully. In the following we react to the more essential points of the Comment in some detail. The Comment suggests that we have conceded many virtues to BM and that we have admitted that standard quantum theory is plagued by notorious conceptual difficulties. This is not the case. On the contrary, we maintain that BM is not needed to have the Schrodinger equation embedded into a physical theory. Standard quantum theory has already clarified the significance of Schrodinger's wave function as a tool used by theoreticians to arrive at probabalistic predictions. It is quite unnecessary, and indeed dangerous, to attribute any additional meaning to the (/^-function. The semantic difference between inconsistent and surrealistic is not the issue. It is the purpose of our paper to show clearly that the interpretation of the Bohm trajectory as the real retrodicted history of the atom observed on the screen is implausible, because this trajectory can be macroscopically at variance with the detected, actual way through the interferometer. And yes, we do have a framework to talk about path detection; it is based upon the local interaction of

Does Orthodox Quantum Theory Undermine, or Support, Scientific Realism?

It is usually taken for granted that orthodox quantum theory poses a serious problem for scientific realism, in that the theory is empirically extraordinarily successful, and yet has instrumentalism built into it. This paper stand this view on its head. I argue that orthodox quantum theory suffers from a number of serious (if not always noticed) defects precisely because of its inbuilt instrumentalism. This defective character of orthdoox quantum theory thus undermines instrumentalism, and supports scientific realism. I go on to consider whether there is here the basis of a general argument against instrumentalism.

An apparent conflict between the de Broglie-Bohm model and orthodoxy in quantum cosmology

If the wave function of the universe is a real solution of the Wheeler-deWitt equation, then the de Broglie-Bohm model predicts a static universe for all time, in contrast to the prediction of orthodox quantum theory as used for example in the model of Gell-Mann and Hartle. The reason for this conflict is located in the fact that orthodox quantum theory does not give a unique prescription. Two particular methods of completing the theory, however, are shown to give rise to the same discrepancy.

Does quantum mechanics carry the seeds of its own destruction?

Quantum mechanics is the most powerful theory of physics. It was John Bell's view, however, that no formulation of orthodox quantum mechanics is free of fatal flaws. While fully recognising the theory's indisputable utilitarian success, Bell was convinced that its failings meant that “something is rotten in the state of Denmark”. Indeed, as many know from personal experience, he was in the habit of proclaiming that quantum mechanics is “rotten”. What I do not know is whether he chose this particular adjective as a veiled condemnation of the House of Bohr.

Towards objectification of measurement in an orthodox but incomplete quantum mechanics

The problem of objectification of measurement is investigated in orthodox quantum mechanics, that is assuming the validity of the Schrodinger equation (and the other postulates) for the composite object-plus-measuring-instrument system. It is argued that by giving physical meaning to basic entities, the positivist and the realist positions must be explicitly distinguished. It is shown that the objectification problem is satisfactorily solved within quantum mechanics for the positivist, but not for the realist. For the latter, a partially satisfactory solution is obtained by assuming that the quantum mechanical description of individual systems is incomplete and, by assuming further, that the pointer observable has definite values prior to any measurement in any quantum state (a so-called beable).

EPR and Bell's theorem: A critical review

The argument of Einstein, Podolsky, and Rosen is reviewed with attention to logical structure and character of assumptions. Bohr's reply is discussed. Bell's contribution is formulated without use of hidden variables, and efforts to equate hidden variables to realism are critically examined. An alternative derivation of nonlocality that makes no use of hidden variables, microrealism, counterfactual definiteness, or any other assumption alien to orthodox quantum thinking is described in detail, with particular attention to the quartet or broken-square question.

Quantum Propensiton Theory: A Testable Resolution of the Wave/Particle Dilemma

In this paper I put forward a new micro realistic, fundamentally probabilistic, propensiton version of quantum theory. According to this theory, the entities of the quantum domain - electrons, photons, atoms - are neither nor fields, but a new kind of fundamentally probabilistic entity, the propensiton - entities which interact with one another probabilistically. This version of quantum theory leaves the Schroedinger equation unchanged, but reinterprets it to specify how propensitons evolve when no probabilistic transitions occur. Probabilisitic transitions occur (...) when new particles are created as a result of inelastic interactions. All measurements are just special cases of this. This propensiton version of quantum theory, I argue, solves the wave/particle dilemma, is free of conceptual problems that plague orthodox quantum theory, recovers all the empirical success of orthodox quantum theory, and at the same time yields as yet untested predictions that differ from those of orthodox quantum theory

An objective formulation of orthodox quantum mechanics

Relying on some concepts introduced in a companion paper, we set foth in this article a formulation of quantum theory that yields the same experimental predictions as those obtained from von Neumann's formulation. Moreover, this is accomplished in such a manner as to obviate the need for observer intervention.

Properties and operational propositions in quantum mechanics

In orthodox quantum mechanics, it has virtually become the custom to identify properties of a physical system with operationally testable propositions about the system. The causes and consequences of this practice are explored mathematically in this paper. Among other things, it is found that such an identification imposes severe constraints on the admissible states of the physical system.

Nonreduction of the state vector in quantum measurement

We describe a formalism which allows us to regard the quantum-mechanical state vector as developing solely according to the Schrödinger equation and not being subject to any reduction or collapse upon measurement. On the other hand, our relationship, as observers, to the state is revised upon our learning the results of measurements. By introducing joint probability operators, whose expectation values in the unreduced state yield the probabilities of obtaining specified measurement results sequentially, we are able to reproduce the predictions of orthodox quantum theory for all testable quantities.

Instead of particles and fields: A micro realistic quantum ?smearon? theory

A fully micro realistic, propensity version of quantum theory is proposed, according to which fundamental physical entities—neither particles nor fields—have physical characteristics which determine probabilistically how they interact with one another (rather than with measuring instruments). The version of quantum “smearon” theory proposed here does not modify the equations of orthodox quantum theory: rather it gives a radically new interpretation to these equations. It is argued that (i) there are strong general reasons for preferrring quantum “smearon” theory to orthodox quantum theory; (ii) the proposed change in physical interpretation leads quantum “smearon” theory to make experimental predictions subtly different from those of orthodox quantum theory. Some possible crucial experiments are considered.

Quantum Logic and the Interpretation of Quantum Mechanics

There is no such thing as “The Quantum Logical Interpretation of Quantum Mechanics”. Rather, there is a cluster of interpretations, all of which can be described as “quantum logical”. Here I provide a general framework for discussing interpretations of this kind, and then locate various suggestions within it. The presentation owes much to van Fraassen (see, in particular, van Fraassen 1974 ); his “modal interpretation” is one of those I discuss, along with those of Jauch, Putnam and Kochen. I begin by rehearsing some orthodox quantum theory.Within quantum mechanics we deal with a set 0 of measurable quantities, or observables (position, momentum, components of spin and so on). Experiment can determine the value of an observable for a given system: the values so determined will be real numbers. A maximal amount of information about what the result would be for a given system, whatever experiment we chose to perform on it, is available once we know the state of the system.

Bouncing Quantum Cosmologies

Spatially homogeneous cosmological models of Bianchi types I, V and IX (as well as their isotropic counterparts : the Einstein-de Sitter, open and closed Friedmann-Robertson-Walker (FRW) models, respectively), filled with a perfect fluid with an equation of state of the type p = (γ - 1 )ρ (γ = constant comprised between 1 and 2) are quantized in the framework of an ADM-type canonical quantization scheme introduced by Demaret and Moncrief. This method which generalizes a method due to Lund and originally restricted to space-times filled with a pressureless fluid (p = 0) is based on Schutz's Hamiltonian theory of a relativistic perfect fluid, extending to general relativity Seliger and Whitham's velocity-potential version of classical hydrodynamics. It leads to a Schrödinger-like equation for the wave function of the universe, which admits a true physical interpretation in terms of probability as in orthodox quantum mechanics. Contrary to Misner's early results based on a different quantization scheme, our method leads to the conclusion that, apart from a set of measure zero of models comprising FRW models as well as Bianchi models filled with a fluid with a stiff equation of state (p = ρ), all Bianchi models are non-singular, in the sense that the quantum wave function becomes zero at the classical singularity. Such a non-singular model can be interpreted as a contracting universe bouncing into an expanding universe, due to quantum gravitational fluctuations. A similar conclusion of non-singularity of a quantum Bianchi I universe has recently been obtained by Narlikar by using a different method of quantization, i.e. the method of path integration.

Alpha particle emission and the orthodox interpretation of quantum mechanics

It is argued that Robinson's attempt to show that α-particle emission contradicts orthodox quantum mechanics does not succeed. However, the possibility remains that α-emission does contradict quantum mechanics.

A New Look at the Quantum Mechanical Problem of Measurement

According to orthodox quantum mechanics, state vectors change in two incompatible ways: “deterministically” in accordance with Schr0̈dinger's time-dependent equation, and probabilistically if and only if a measurement is made. It is argued here that the problem of measurement arises because the precise, mutually exclusive conditions for these two types of transitions to occur are not specified within orthodox quantum mechanics. Fundamentally, this is due to an inevitable ambiguity in the notion of “measurement” itself. Hence, if the problem of measurement is to be resolved, a new, fully objective version of quantum mechanics needs to be developed which does not incorporate the notion of measurement in its basic postulates at all.