Since noncommutative measure theory plays a central role in the quantum theory, one might say that quantum mechanics is a new generalized theory of probability. That assertion, however, raises many problems with interpreting quantum probabilities and quantum events. Although one can take a radically instrumentalist or pragmatist approach toward this question, it is much more interesting, both theoretically and heuristically, to adopt a realistic or ontological strategy that treats the quantum measure as an effective parameter of an underlying time-symmetric regime of physical dynamics, which only generates the classical events and probabilities at its limit. It is argued that time-symmetric relativistic reformulations of the quantum theory with time-like nonseparability have important advantages over space-like nonlocal hidden-variable Bohmian-type models, which have Aristotelian spacetime as their natural environment.
Since noncommutative measure theory plays a central role in the quantum theory, one might say that quantum mechanics is a new generalized theory of probability. That assertion, however, raises many problems with interpreting quantum probabilities and quantum events. Although one can take a radically instrumentalist or pragmatist approach toward this question, it is much more interesting, both theoretically and heuristically, to adopt a realistic or ontological strategy that treats the quantum measure as an effective parameter of an underlying time-symmetric regime of physical dynamics, which only generates the classical events and probabilities at its limit. It is argued that time-symmetric relativistic reformulations of the quantum theory with time-like nonseparability have important advantages over space-like nonlocal hidden-variable Bohmian-type models, which have Aristotelian spacetime as their natural environment.
Space, time and probabilities not only form the arena of many physical theories, but also the arena of our everyday life. Therefore, the problem of their ontological status becomes even more interesting. It seems that this problem cannot be solved before we have the final physical theory (theory of everything). However, various methods of looking for such a theory lead to converging results, and are able to elucidate the problem in question. We analyze noncommutative algebraic methods, and show that, when applied to model the fundamental level, they suggest a nonlocal regime in which there is no space and no time, in their usual sense, and which is essentially probabilistic (in a generalized sense). In the noncommutative approach there are many probabilistic measures (not just one as in macroscopic physics), and none of them seems to be distinguished in any way. The tentative conclusion is that space, time and probability are not absolute categories, but rather aspects of the world structure emergent from the fundamental level. One should expect that the ultimate theory will be well off our traditional philosophical categories. This shows that our mind has a peculiar property allowing it to reach far beyond its usual limitations.
This chapter considers a more realistic variation of the measuring procedure, taking into account the fact that the measured particles become entangled with the measuring apparatus at some finite time. The results are also generalized to quantum field theory, where quantum states are represented by wave functions depending on an infinite number of space-time coordinates. Thus, to make Bohmian mechanics covariant, one needs first to reformulate the standard quantum mechanics (QM) in a covariant way such that time is treated on an equal footing with space. Another physically interesting situation is when the entanglement with the environment takes the form, where are coherent states. In general, in the Bohmian interpretation all the other quantities may have a distribution totally different from those predicted by purely probabilistic QM. The space probability density should be generalized to the space-time probability density.
This doctoral thesis in mathematics consists of three articles that explore the probabilistic structure of quantum mechanics and quantization from a novel perspective. The thesis adopts a probabilistic interpretation of quantum mechanics, which views the archetypical quantum experiments of Bell- and double-slit- type as violating the principle of non-contextuality, i.e., the assertion that all events and observables are always representable on one single Kolmogorovian probability space, rather than the principles of realism or locality. This probabilistic interpretation posits that quantum mechanics constitutes a probability theory that adheres to the principle of contextuality, and that quantum events explicitly occur at the level of measurement, rather than the level of that which is measured, as these are traditionally interpreted. The thesis establishes a natural connection between the probabilistic structure of quantum mechanics, specifically Born’s rule, and the frequentist interpretation of probability. The major conceptual step in establishing this connection is to re-identify quantum observables instead as unitary representations of groups, whose irreducible sub-representations correspond to the observable’s different possible outcomes, rather than primarily as self- adjoint operators. Furthermore, the thesis reformulates classical statistical mechanics in the formalism of quantum mechanics, known as the Koopman-von Neumann formulation, to demonstrate that classical statistical mechanics also adheres to the principle of contextuality. This finding is significant because it raises questions about the existence of a hidden-variable model of classical statistical mechanics of the kind as examined in Bell’s theorem, where this presumed hidden-variable model traditionally has been seen as that which distinguishes "classical" from "quantum" probability.A novel reformulation of quantization is proposed considering it rather in terms of the representation theory of Hamiltonian flows and their associated inherent symmetry group of symplectomorphisms. Contrary to the traditional view of quantization, this formulation can be regarded as compatible with the probabilistic interpretation of quantum mechanics and offers a new perspective on the quantization of gravity.
Abstract Some physicists but many philosophers believe that standard Hilbert space quantum mechanics faces a serious measurement problem, whose solution requires a new theory or at least a novel interpretation of standard quantum mechanics. Itamar Pitowsky did not. Instead, he argued in a major essay (Pitowsky 2006) that quantum mechanics offers a new theory of probability. In these and other respects, his views paralleled those of QBists (quantum Bayesians): but their views on the objectivity of measurement outcomes diverged radically. Indeed, Itamar’s view of quantum probability depended on his subtle treatment of the objectivity of outcomes as events whose collective structure underlay this new theory of probability. His thesis is puzzling—that quantum mechanics requires a new theory of probability, as distinct from new ways of calculating probabilities that play the same role as other probabilities in physics and daily life. This essay articulates sources of puzzlement.
Quantum measure theory can be introduced as a histories based reformulation (and generalisation) of Copenhagen quantum mechanics in the image of classical stochastic theories. These classical models lend themselves to a simple interpretation in which a single history (a single element of the sample space) is deemed to be 'real'; we require only that this real history should not be ruled out by the dynamics, the axioms of which ensure that not all histories are precluded. However, applying this interpretation naively to quantum measure theory we can find experimentally realisable systems (notably the Peres-Kochen-Specker system) in which every history is ruled out by the dynamics, challenging us to formulate a deeper realist framework. Our first response is to hold on to our existing interpretative framework and attempt a revision of the dynamics that would reduce quantum measure theory to a classical dynamics. We explore this approach by examining the histories formulation of a stochastic-collapse model on a simple (discrete) null-lattice, concluding that the drawbacks of this approach outweigh the benefits. Our second response is to abandon our classically inspired interpretation in favour of Sorkin's 'co-events', a more general ontology that still allows for strict realism. In this case the 'potentially real' objects of the theory (the 'beables' in Bell's language) are not individual histories but truth valuation maps, or co-events. We develop & evaluate various co-event schemes that have been suggested to date, finally adopting the multiplicative scheme; the current working model of co-event theory and a promising interpretation of quantum measure theory, though still a work in progress. We conclude by exploring the expression of the dynamics & predictions in this new framework.
A unified conceptual foundation of classical and quantum physics is given, free of undefined terms. Ensembles are defined by extending the `probability via expectation' approach of Whittle to noncommuting quantities. This approach carries no connotations of unlimited repeatability; hence it can be applied to unique systems such as the universe. Precise concepts and traditional results about complementarity, uncertainty and nonlocality follow with a minimum of technicalities. Probabilities are introduced in a generality supporting so-called effects (i.e., fuzzy events). States are defined as partial mappings that provide reference values for certain quantities. An analysis of sharpness properties yields well-known no-go theorems for hidden variables. By dropping the sharpness requirement, hidden variable theories such as Bohmian mechanics can be accommodated, but so-called ensemble states turn out to be a more natural realization of a realistic state concept. The weak law of large numbers explains the emergence of classical properties for macroscopic systems.