Time, Information and Perspective in the
Quantum World

Wednesday 14 December 
Thursday 15 December 
9:30  11:00 Huw Price 
9:30  11:00 Amit Hagar 
Morning Tea 

11:30  1:00 Rod Sutherland 
11:30  1:00 Guido Bacciagaluppi 
Lunch 

2:30  3:30 Veiko Palge 
2:30  4:00 Alexei Grinbaum 
Afternoon Tea 

4:00  5:30 Guido Bacciagaluppi 
4:30  6:00 Michael Dickson 
7:00  bedtime 

Huw Price
To Be Announced: the Ontological Significance of Ignorance About the Future
slides
According to an appealing conception, physics aims for a complete, perspectivefree description of physical reality; or at least for theories couched in the right conceptual vocabulary for such a description (leaving the details to be filled in by God). However, we human practitioners of physics are chronically ignorant, in two senses. Firstly, obviously, we'll never know more than a tiny fraction of the available facts (hence the task for God). Secondly, and more interestingly, our epistemic viewpoint is chronically or temporally constrained, in striking ways: in particular, we're especially ignorant about the future.
In this talk I argue that the second kind of ignorance is still deeply embedded in the conceptual foundations of physics (of contemporary theoretical physics, including quantum mechanics, as well as of folk physics). In particular, I argue that dispositionsal and counterfactual facts are fundamentally epistemic. From the point of view of God, for whom nothing is ever TBA, there are no facts of this kind.
Rod Sutherland
A Timesymmetric Bohm Model
A timesymmetric version of David Bohm’s wellknown model will be summarized as an explicit example of a theory involving backwardsintime effects. The rationale is that such effects can be examined more easily in the context of a specific model. Furthermore, the fairly classical ontology employed in Bohmtype models helps to highlight more clearly the consequences of imposing timesymmetry. In particular, it is seen that we are able to (i) avoid a preferred reference frame, (ii) explain EPR nonlocality and (iii) work with separate 3D wavefunctions in the correlated multiparticle case. Of course, there are tradeoffs and the pros and cons of the timesymmetric versus the usual Bohm model will be compared.
Veiko Palge
Open future and quantum delayed choice experiments in McCall's
Universe
In the debate between the A and Btheory of time, the Atheory is associated with ontological becoming and open future. McCall proposes a treelike model of the Universe which seeks to do justice to both these features. The goal is to give a representation of a world in which objective chance arises out of branching spacetime structure. In such a world, an indeterministic process like quantum measurement results in the world's choosing a particular path through the treelike structure. In this paper, we discuss compatibility of McCall's model with quantum delayed choice experiments.
Michael Dickson
The Role of the Observer in Quantum Computation
slides
The main point of this talk is to say something preliminary, from a philosopher's point of view, about the role of the observer in quantum computation. I will begin with some more abstract considerations about the nature and role of observers in quantum theory generally, reviewing a grouptheoretic account of the notion of an observer based in part on Mackey's imprimitivity theorem. I will then say something about the application of this general account to the case of quantum computation. This talk is thus intended to be a philosophical commentary on the question that is often put in terms of 'the role of measurement in quantum computation'. Given time, I will comment on recent movements in quantum computation that speak to this issue: 'measurementbased quantum computation', and specifically 'oneway quantum computation'.
Guido Bacciagaluppi
Probability, arrow of time and decoherence
slides
This paper relates both to the metaphysics of probability and to the physics of time asymmetry. It investigates whether and how intuitions about 'open future' often associated with probability might be justified in the context of the decoherent histories formalism of quantum mechanics. At the same time it investigates whether and if so under which conditions time asymmetry at the level of histories can be said to emerge from time symmetry at the level of the universal Schroedinger equation.
Amit Hagar
Quantum Computing: Lessons from two Halting Problems
slides
Starting as a visionary idea, quantum computing has become a small industry; by far one of the most fascinating domains in quantum mechanics to this date. The common view is that by harnessing some essentially quantum features, quantum computers, if built, may solve computational problems that are believed to be intractable for classical computers. Concentrating on theoretical aspects rather than on practical ones, I shall discuss two halting problems that constrain any attempt to rewrite the abstract notion of computability using quantum mechanics. I will then use these problems to raise some good natured philosophical doubts about the putative power of quantum computers.
Guido Bacciagaluppi
Timesymmetry argument for v being a gradient in Nelson's theory
Nelson aims to derive the wave function and the Schroedinger equation from conditions on a timesymmetric diffusion process in configuration space. One of the assumptions that are needed is that the current velocity v of the process be the gradient of some function S. We give a new interpretation of this assumption as a further timesymmetry condition. This talk is work in progress.
Alexei Grinbaum
Informationtheoretic derivation of quantum theory via
quantum logic
slides  papers
In this paper we look at quantum mechanics as a theory about information. We propose a system of informationtheoretic axioms and we use quantum logical techniques for deriving the Hilbert space structure. Lattice orthomodularity follows from the postulate of finite amount of relevant information, while quantumness is shown to be due to the postulated possibility to obtain new information. Reconstruction of the formalism is completed by a derivation of the state space and the time evolution from informationtheoretically intepreted principles.