Howard Barnum, Perimeter Institute
Probabilities from Quantum States, or Quantum States from Probabilities?
I will consider various attempts to derive the quantum probabilities from the HIlbert space formalism within the many-worlds interpretation, and argue that they either fail, or depend on tacit probabilistic assumptions.   The main problem with the project is that it is difficult to understand what the state of system X is psi even *means* without already supposing some probabilistic link to definite observed or observable phenomena involving X.  I will argue it is better to conceive of quantum states as *representations* of empirically inferred probabilities for quantum processes associated with definite observable phenomena, accepting all the issues this raises concerning what exactly are to count as observable outcomes, and relatedly, what as real, as an unavoidable conundrum but also a potential source of progress in the evolution of physical theory.

Chris Dewdney, University of Portsmouth
A methodology for the development of relativistically covariant interpretations of quantum theory of the de Broglie-Bohm type based on the definition of intrinsic time-like flows of energy-momentum.
We discuss the context in which realist interpretations of quantum theory of the de Broglie-Bohm type cope with the tensions stemming from the configuration-space character of the wave function and from the necessary coexistence of quantum non locality and relativistic invariance. Within this context, our recent work has been motivated by the desire to formulate a relativistically covariant  theory of the well-defined processes occurring in a de Broglie-Bohm type of theory  which enables the inclusion of gravity ( at least in a non-quantized form) and in which the extra structure necessary for the extension of the approach emerges in a natural and intrinsic way . We would also like to produce an approach that can equally well be applied to bosons and fermions and we have no particular predilection for particle or field ontologies.  In this talk we will describe our partial progress along this path inspired by the demonstration by Edelen (following a line of thought initiated by Synge) that in the classical case, the Einstein field equations yield a mechanics of continuous media that can be viewed as describing the flow of an intrinsic and unique rest energy under the natural requirement that a region of an Einstein-Riemann space filled by a material medium is such that its associated energy-momentum tensor admits a unique time-like eigen vector. The intrinsic four vector W^μ that defines the flows of the intrinsic rest energy density λ is provided by the matter field itself in its local  through the eigen value equation

T^μ_υ W^υ=λW^μ

and given the unique  W^μ a conserved density exists such that

(ρW^μ)_;μ=0

Initially we use the approach to develop an intrinsic trajectory interpretation for the massive Klein-Gordon field. The trajectory approach may also be extended to cover the massive vector field.  We then examine a possible way in which the approach could be used to provide a Lorentz invariant methodology for the calculation of many-particle trajectories in the many-time formalism. (A specific implementation of an idea proposed by DÏ‹rr et al.) However, not being wedded to the idea of describing many particle systems through trajectories, we also examine the way in which the basic idea could be used to provide a covariant version of Bohm’s  pure field ontology for the quantized scalar field.

Chris Fuchs, Perimeter Institute
Texas-Bavarian Home Cooking:  A Quantum Bayesian Reply to Bell’s (and Norsen’s) la Nouvelle Cuisine

Philip Goyal, Perimeter Institute
Quantum Theory from Complementarity, and its Implications
Complex numbers are an intrinsic part of the mathematical formalism of quantum theory, and are perhaps its most mysterious feature.   In this talk, we show how it is possible to derive the complex nature of the quantum formalism directly  from the assumption that  a pair of real numbers is associated with each sequence of measurement outcomes, and that the probability of this sequence is a real-valued function of this number pair.  By making use of elementary symmetry and consistency conditions, and without assuming that these real number pairs have any other algebraic structure, we show that these pairs must be manipulated according to the rules of complex arithmetic. We demonstrate that these complex numbers combine according to Feynman's sum and product rules, with the modulus-squared yielding the probability of a sequence of outcomes.  We then discuss how complementarity --- the key guiding idea in the derivation ---  can be understood as a consequence of the intrinsically relational nature of measurement, and discuss the implications of this for our understanding of the status of the quantum state.

Brian R. La Cour, The University of Texas at Austin
Reconciling the ontic and epistemic views in quantum contextuality
The classic debate between Einstein and Bohr over a realistic interpretation of quantum mechanics can be cast in terms of the measurement problem: Is there an underlying ontic state prior to measurement which maps deterministically to the measured outcome? According to the Kochen-Specker theorem, such a view is patently inconsistent with quantum theory, leading to the paradox of quantum contextuality.  This result, however, relies upon the (arguably unwarranted) assumption that the ontic state remains unchanged through the process of measurement and attendant interaction with the measuring device.  By relaxing this assumption, it will be shown that one is able to maintain a realistic view of a pre-existing ontic state, as Einstein insisted, while allowing for changes in that ontic state relative to the chosen measurement, in accordance with Bohr.  In this view, the wavefunction respresents an epistemic ensemble of ontological states, corresponding to, say, a particular preparation procedure, and its collapse is a selection of and dynamical process on one member of that ensemble.  The specific case of the Mermin-Peres square will be considered, both for its simplicity and its connection to recent experimental tests of quantum contextuality.

Dean Rickles, University of Sydney
Correlations all the way Down?
I give a review and assessment of relational approaches to quantum theory – that is, approaches that view QM “as an account of the way distinct physical systems affect each other when they interact – and not the way physical systems ‘are’”. I argue that the “relational QM” is a misnomer: the correct way to understand these approaches is in terms of structuralism, whereby the correlations themselves are fundamental. I then argue that the connection to gravitational physics and gauge symmetries has a crucial impact on the attractiveness of such approaches.

Ken Wharton, San Jose State U.
Mapping classical fields to quantum states
Efforts to extrapolate non-relativistic (NR) quantum mechanics to a covariant framework encounter well-known problems, implying that an alternate view of quantum states might be more compatible with relativity.  This talk will reverse the usual extrapolation, and examine the NR limit of a real, classical scalar field.  A complex scalar \psi that obeys the Schrodinger equation naturally falls out of the analysis.  One can also replace the usual operator-based measurement theory with classical measurement theory on the scalar field, and examine the NR limit of this as well.  In this limit, the local energy density of the field scales as |\psi|^2, adding credibility to this approach.  With the added postulate that "all measurements correspond to boundary conditions that extremize the classical action" (see arXiv:0906.5409), additional quantitative comparisons emerge between this \psi and the standard quantum wavefunction.  Uncertainty can then be introduced (along with a "collapse" due to Bayesian updating) by simply giving the classical scalar field two components instead of one, leading to an intriguing \psi-epistemic model.