6 research outputs found
Dynamics & Predictions in the Co-Event Interpretation
Sorkin has introduced a new, observer independent, interpretation of quantum
mechanics that can give a successful realist account of the 'quantum
microworld' as well as explaining how classicality emerges at the level of
observable events for a range of systems including single time 'Copenhagen
measurements'. This 'co-event interpretation' presents us with a new ontology,
in which a single 'co-event' is real. A new ontology necessitates a review of
the dynamical & predictive mechanism of a theory, and in this paper we begin
the process by exploring means of expressing the dynamical and predictive
content of histories theories in terms of co-events.Comment: 35 pages. Revised after refereein
Distinguishing Initial State-Vectors from Each Other in Histories Formulations and the PBR Argument
Following the argument of Pusey, Barrett and Rudolph (Nature Phys. 8:476,
2012), new interest has been raised on whether one can interpret state-vectors
(pure states) in a statistical way (-epistemic theories), or if each of
them corresponds to a different ontological entity. Each interpretation of
quantum theory assumes different ontology and one could ask if the PBR argument
carries over. Here we examine this question for histories formulations in
general with particular attention to the co-event formulation. State-vectors
appear as the initial state that enters into the quantum measure. While the PBR
argument goes through up to a point, the failure to meet some of the
assumptions they made does not allow one to reach their conclusion. However,
the author believes that the "statistical interpretation" is still impossible
for co-events even if this is not proven by the PBR argument.Comment: 25 pages, v2 published versio
Spacelike distance from discrete causal order
Any discrete approach to quantum gravity must provide some prescription as to
how to deduce continuum properties from the discrete substructure. In the
causal set approach it is straightforward to deduce timelike distances, but
surprisingly difficult to extract spacelike distances, because of the unique
combination of discreteness with local Lorentz invariance in that approach. We
propose a number of methods to overcome this difficulty, one of which
reproduces the spatial distance between two points in a finite region of
Minkowski space. We provide numerical evidence that this definition can be used
to define a `spatial nearest neighbor' relation on a causal set, and conjecture
that this can be exploited to define the length of `continuous curves' in
causal sets which are approximated by curved spacetime. This provides evidence
in support of the ``Hauptvermutung'' of causal sets.Comment: 32 pages, 16 figures, revtex4; journal versio
Twistor form of massive 6D superparticle
The massive six-dimensional (6D) superparticle with manifest (n, 0) supersymmetry is shown to have a supertwistor formulation in which its “hidden” (0, n) supersymmetry is also manifest. The mass-shell constraint is replaced by Spin(5) spin-shell constraints which imply that the quantum superparticle has zero superspin; for n = 1 it propagates the 6D Proca supermultiplet.PKT acknowledges support from the UK Science and Technology Facilities Council (grant ST/L000385/1). AJR is supported by a grant from the London Mathematical Society.This is the final version of the article. It was first available from IOP Science via http://dx.doi.org/10.1088/1751-8113/49/2/02540
Stable Homology as an Indicator of Manifoldlikeness in Causal Set Theory
We present a computational tool that can be used to obtain the "spatial"
homology groups of a causal set. Localisation in the causal set is seeded by an
inextendible antichain, which is the analog of a spacelike hypersurface, and a
one parameter family of nerve simplicial complexes is constructed by
"thickening" this antichain. The associated homology groups can then be
calculated using existing homology software, and their behaviour studied as a
function of the thickening parameter. Earlier analytical work showed that for
an inextendible antichain in a causal set which can be approximated by a
globally hyperbolic spacetime region, there is a one parameter sub-family of
these simplicial complexes which are homological to the continuum, provided the
antichain satisfies certain conditions. Using causal sets that are approximated
by a set of 2d spacetimes our numerical analysis suggests that these conditions
are generically satisfied by inextendible antichains. In both 2d and 3d
simulations, as the thickening parameter is increased, the continuum homology
groups tend to appear as the first region in which the homology is constant, or
"stable" above the discreteness scale. Below this scale, the homology groups
fluctuate rapidly as a function of the thickening parameter. This provides a
necessary though not sufficient criterion to test for manifoldlikeness of a
causal set.Comment: Latex, 46 pages, 43 .eps figures, v2 numerous changes to content and
presentatio