An obstruction based approach to the Kochen-Specker theorem

In [1] it was shown that the Kochen Specker theorem can be written in terms of the non-existence of global elements of a certain varying set over the partially ordered set of boolean subalgebras of projection operators on some Hilbert space. In this paper, we show how obstructions to the construction of such global elements arise, and how this provides a new way of looking at proofs of the theorem.Comment: 14 pages, 6 figure

Mass influx obtained from low-light-level television observations of faint meteors

Low light level television systems offer the ability to observe meteors as faint as 10th magnitude which allows the extension of optical meteor data to masses as small as 0.0001 gram. The results of these observations, using image orthicons and intensified vidicons, are presented along with an interpretation in terms of mass flux. This interpretation includes the development of a relationship between peak luminosity of a meteor and mass, velocity, and zenith angle that was derived from single body meteor theory and compares favorably with results obtained from the artificial meteor program. Also included in the mass flux interpretation is an analysis of the observation response of a LLLTV system to fixed and moving point sources

Lorentz-Invariant "Elements of Reality" and the Question of Joint Measurability of Commuting Observables

It is shown that the joint measurements of some physical variables corresponding to commuting operators performed on pre- and post-selected quantum systems invariably disturb each other. The significance of this result for recent proofs of the impossibility of realistic Lorentz invariant interpretation of quantum theory (without assumption of locality) is discussed.Comment: 15 page

Decoherence of multi-dimensional entangled coherent states

For entangled states of light both the amount of entanglement and the sensitivity to noise generally increase with the number of photons in the state. The entanglement-sensitivity tradeoff is investigated for a particular set of states, multi-dimensional entangled coherent states. Those states possess an arbitrarily large amount of entanglement $E$ provided the number of photons is at least of order $2^{2E}$. We calculate how fast that entanglement decays due to photon absorption losses and how much entanglement is left. We find that for very small losses the amount of entanglement lost is equal to $2/\log(2)\approx 2.89$ ebits per absorbed photon, irrespective of the amount of pure-state entanglement $E$ one started with. In contrast, for larger losses it tends to be the remaining amount of entanglement that is independent of $E$. This may provide a useful strategy for creating states with a fixed amount of entanglement.Comment: 6 pages, 5 figure

Hiding Private Locations by Anonymizing Data

Researchers explore ways of masking private locations in the interest of making useful data publicly available

Generic Bell correlation between arbitrary local algebras in quantum field theory

We prove that for any two commuting von Neumann algebras of infinite type, the open set of Bell correlated states for the two algebras is norm dense. We then apply this result to algebraic quantum field theory -- where all local algebras are of infinite type -- in order to show that for any two spacelike separated regions, there is an open dense set of field states that dictate Bell correlations between the regions. We also show that any vector state cyclic for one of a pair of commuting nonabelian von Neumann algebras is entangled (i.e., nonseparable) across the algebras -- from which it follows that every field state with bounded energy is entangled across any two spacelike separated regions.Comment: Third version; correction in the proof of Proposition

Dynamics of a lattice Universe

We find a solution to Einstein field equations for a regular toroidal lattice of size L with equal masses M at the centre of each cell; this solution is exact at order M/L. Such a solution is convenient to study the dynamics of an assembly of galaxy-like objects. We find that the solution is expanding (or contracting) in exactly the same way as the solution of a Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average density as our model. This points towards the absence of backreaction in a Universe filled with an infinite number of objects, and this validates the fluid approximation, as far as dynamics is concerned, and at the level of approximation considered in this work.Comment: 14 pages. No figure. Accepted version for Classical and Quantum Gravit

Volume Weighted Measures of Eternal Inflation in the Bousso-Polchinski Landscape

We consider the cosmological dynamics associated with volume weighted measures of eternal inflation, in the Bousso-Polchinski model of the string theory landscape. We find that this measure predicts that observers are most likely to find themselves in low energy vacua with one flux considerably larger than the rest. Furthermore, it allows for a satisfactory anthropic explanation of the cosmological constant problem by producing a smooth, and approximately constant, distribution of potentially observable values of Lambda. The low energy vacua selected by this measure are often short lived. If we require anthropically acceptable vacua to have a minimum life-time of 10 billion years, then for reasonable parameters a typical observer should expect their vacuum to have a life-time of approximately 12 billion years. This prediction is model dependent, but may point toward a solution to the coincidence problem of cosmology.Comment: 35 pages, 8 figure

Non-local Correlations are Generic in Infinite-Dimensional Bipartite Systems

It was recently shown that the nonseparable density operators for a bipartite system are trace norm dense if either factor space has infinite dimension. We show here that non-local states -- i.e., states whose correlations cannot be reproduced by any local hidden variable model -- are also dense. Our constructions distinguish between the cases where both factor spaces are infinite-dimensional, where we show that states violating the CHSH inequality are dense, and the case where only one factor space is infinite-dimensional, where we identify open neighborhoods of nonseparable states that do not violate the CHSH inequality but show that states with a subtler form of non-locality (often called "hidden" non-locality) remain dense.Comment: 8 pages, RevTe

Constraints on the Variation of G from Primordial Nucleosynthesis

We study here the effect of a varying G on the evolution of the early Universe and, in particular, on primordial nucleosynthesis. This variation of G is modelled using the Brans-Dicke theory as well as a more general class of scalar-tensor theories. Modified nucleosynthesis codes are used to investigate this effect and the results obtained are used to constrain the parameters of the theories. We extend previous studies of primordial nucleosynthesis in scalar-tensor theories by including effects which can cause a slow variation of G during radiation domination and by including a late-time accelerating phase to the Universe's history. We include a brief discussion on the epoch of matter-radiation equality in Brans-Dicke theory, which is also of interest for determining the positions of the cosmic microwave background power-spectrum peaks.Comment: 10 pages, 7 figures. Published versio