Publications & Presentations
- D. Almada, K. Ch'ng, S. Kintner, B. Morrison, K.B. Wharton, "Are Retrocausal Accounts of Entanglement Unnaturally Fine-Tuned?" accepted for publication, International Journal of Quantum Foundations (2016).
Abstract: An explicit retrocausal model is used to analyze the general Wood-Spekkens argument that any causal explanation of Bell-inequality violations must be unnaturally fine-tuned to avoid signaling. The no-signaling aspects of the model turn out to be robust under variation of the only free parameter, even as the probabilities deviate from standard quantum theory. The ultimate reason for this robustness is then traced to a symmetry assumed by the original model. A broader conclusion is that symmetry-based restrictions seem a natural and acceptable form of fine-tuning, not an unnatural model-rigging. And if the Wood-Spekkens argument is indicating the presence of hidden symmetries, this might even be interpreted as supporting time-symmetric retrocausal models.
- K.B. Wharton and D. Koch, "Unit Quaternions and the Bloch Sphere" Journal of Physics A, v48 (2015). p.235302
Abstract: The spinor representation of spin-1/2 states can equally well be mapped to a single unit quaternion, yielding a new perspective despite the equivalent mathematics. This paper first demonstrates a useable map that allows Bloch-sphere rotations to be represented as quaternionic multiplications, simplifying the form of the dynamical equations. Left-multiplications generally correspond to non-unitary transformations, providing a simpler (essentially classical) analysis of time-reversal. But the quaternion viewpoint also reveals a surprisingly large broken symmetry, as well as a potential way to restore it, via a natural expansion of the state space that has parallels to second order fermions. This expansion to "second order qubits" would imply either a larger gauge freedom or a natural space of hidden variables.
- Ken Wharton. "Quantum States as Ordinary Information" Information, v5 (2014). pp.190-208.
Abstract: Despite various parallels between quantum states and ordinary information, quantum no-go-theorems have convinced many that there is no realistic framework that might underly quantum theory, no reality that quantum states can represent knowledge *about*. This paper develops the case that there is a plausible underlying reality: one actual spacetime-based history, although with behavior that appears strange when analyzed dynamically (one time-slice at a time). By using a simple model with no dynamical laws, it becomes evident that this behavior is actually quite natural when analyzed "all-at-once" (as in classical action principles). From this perspective, traditional quantum states would represent incomplete information about possible spacetime histories, conditional on the future measurement geometry. Without dynamical laws imposing additional restrictions, those histories can have a classical probability distribution, where exactly one history can be said to represent an underlying reality.
- Peter Evans, Huw Price, and K.B. Wharton. "New Slant on the EPR-Bell Experiment" Brit. J. Phil. Sci.. Article. Vol. 64. Issue 2. Brit. J. Phil. Sci., (2013). pp.297.
Abstract: The best case for thinking that quantum mechanics is nonlocal rests on Bell's Theorem, and later results of the same kind. However, the correlations characteristic of EPR-Bell (EPRB) experiments also arise in familiar cases elsewhere in QM, where the two measurements involved are timelike rather than spacelike separated; and in which the correlations are usually assumed to have a local causal explanation, requiring no action-at-a-distance. It is interesting to ask how this is possible, in the light of Bell's Theorem. We investigate this question, and present two options. Either (i) the new cases are nonlocal, too, in which case action-at-a-distance is more widespread in QM than has previously been appreciated (and does not depend on entanglement, as usually construed); or (ii) the means of avoiding action-at-a-distance in the new cases extends in a natural way to EPRB, removing action-at-a-distance in these cases, too. There is a third option, viz., that the new cases are strongly disanalogous to EPRB. But this option requires an argument, so far missing, that the physical world breaks the symmetries which otherwise support the analogy. In the absence of such an argument, the orthodox combination of views -- action-at-a-distance in EPRB, but local causality in its timelike analogue -- is less well established than it is usually assumed to be.
- K.B. Wharton, D.J. Miller, and Huw Price. "Action Duality: A Constructive Principle for Quantum Foundations" Symmetry. v3 (2011). pp.524.
Abstract: An analysis of the path-integral approach to quantum theory motivates the hypothesis that two experiments with the same classical action should have dual ontological descriptions. If correct, this hypothesis would not only constrain realistic interpretations of quantum theory, but would also act as a constructive principle, allowing any realistic model of one experiment to generate a corresponding model for its action-dual. Two pairs of action-dual experiments are presented, including one experiment that violates the Bell inequality and yet is action-dual to a single particle. The implications generally support retrodictive and retrocausal interpretations
K.B. Wharton. "A novel interpretation of the Klein-Gordon equation" Foundations of Physics. v40 (2010). pp.313.
Abstract: The covariant Klein-Gordon equation requires twice the boundary conditions of the Schr\"odinger equation and does not have an accepted single-particle interpretation. Instead of interpreting its solution as a probability wave determined by an initial boundary condition, this paper considers the possibility that the solutions are determined by both an initial and a final boundary condition. By constructing an invariant joint probability distribution from the size of the solution space, it is shown that the usual measurement probabilities can nearly be recovered in the non-relativistic limit, provided that neither boundary constrains the energy to a precision near hbar/t_0 (where t_0 is the time duration between the boundary conditions). Otherwise, deviations from standard quantum mechanics are predicted.
- Ken Wharton. "Time-Symmetric Boundary Conditions and Quantum Foundations" Symmetry, v2 (2010). pp.272.
Abstract: Despite the widely-held premise that initial boundary conditions (BCs) corre- sponding to measurements/interactions can fully specify a physical subsystem, a literal read- ing of Hamilton’s principle would imply that both initial and final BCs are required (or more generally, a BC on a closed hypersurface in spacetime). Such a time-symmetric perspective of BCs, as applied to classical fields, leads to interesting parallels with quantum theory. This paper will map out some of the consequences of this counter-intuitive premise, as applied to covariant classical fields. The most notable result is the contextuality of fields constrained in this manner, naturally bypassing the usual arguments against so-called “realistic” interpretations of quantum phenomena.
- K.B. Wharton. "Time Symmetric Quantum Mechanics" Foundations of Physics, v37 (2007). pp.159.
Abstract: A time-symmetric formulation of nonrelativistic quantum mechanics is developed by applying two consecutive boundary conditions onto solutions of a time-symmetrized wave equation. From known probabilities in ordinary quantum mechanics, a time-symmetric parameter $P_0$ is then derived that properly weights the likelihood of any complete sequence of measurement outcomes on a quantum system. The results appear to match standard quantum mechanics, but do so without requiring a time-asymmetric collapse of the wavefunction upon measurement, thereby realigning quantum mechanics with an important fundamental symmetry.