Weekly Papers on Quantum Foundations (6)

Authors: Rodolfo GambiniJorge Pullin

In the 1960's, Mandelstam proposed a new approach to gauge theories and gravity based on loops. The program for gauge theories was completed for Yang--Mills theories by Gambini and Trias in the 1980's. Gauge theories could be understood as representations of certain group: the group of loops. The same formalism could not be implemented at that time for the gravitational case. Here we would like to propose an extension to the case of gravity. The resulting theory is described in terms of loops and open paths and can provide the underpinning for a new quantum representation for gravity distinct from the one used in loop quantum gravity or string theory. In it, space-time points are emergent entities that would only have quasi-classical status. The formulation may be given entirely in terms of Dirac observables that form a complete set of gauge invariant functions that completely define the Riemannian geometry of the spacetime. At the quantum level this formulation will lead to a reduced phase space quantization free of any constraints.

Authors: Denis Bashkirov

We suggest an interpretation of Einstein Equations of General Relativity at large scales in which the Cosmological constant is exactly zero in the limit of zero spacetime variations of fundamental constants. We argue that in a quasiclassical Universe such variation should be tiny which leads to a tiny value for the Dark Energy. Next, we suggest that the are two sources of the Dark Energy. The first is the variation in Newton's constant $G_N$. It is a form of Dark Energy in that it has negative pressure, but it differs from the Cosmological Constant by a negative contribution to the energy. The second is the contribution of (causal) nonlocalities to the Dark Energy.

This comes together with a particular view of Quantum Mechanics and the wavefunction collapse, in particular. The collapse is neither dynamical nor subjective.

Many of those involved in the race to unleash the power of quantum computing predict it will happen soon. Here's why, says Graeme Malcolm
Research could lead to more robust quantum-information systems

Author(s): Robert B. Griffiths

While much of the technical analysis in the preceding Comment is correct, in the end it confirms the conclusion reached in my previous work [Phys. Rev. A 94, 032115 (2016)]: A consistent histories analysis provides no support for the claim of counterfactual quantum communication put forward by Salih...
[Phys. Rev. A 97, 026102] Published Fri Feb 09, 2018

Castellani, Elena (2018) Scientific Methodology: A View from Early String Theory. [Preprint]
Moulavi Ardakani, Reza (2017) Time Reversal Invariance in Quantum Mechanics. UNSPECIFIED.

Abstract

A proposal is made for a fundamental theory, in which the history of the universe is constituted of diverse views of itself. Views are attributes of events, and the theory’s only be-ables; they comprise information about energy and momentum transferred to an event from its causal past. A dynamics is proposed for a universe constituted of views of events, which combines the energetic causal set dynamics with a potential energy based on a measure of the distinctiveness of the views, called the variety (Smolin in Found Phys 46(6):736–758, 2016). As in the real ensemble formulation of quantum mechanics (Barbour and Smolin in Variety, complexity and cosmology, arXiv: hep-th/9203041), quantum pure states are associated to ensembles of similar events; the quantum potential of Bohm then arises from the variety.

ROVELLI, Carlo (2018) Space and Time in Loop Quantum Gravity. [Preprint]
Cuffaro, Michael E. (2018) Causality and Complementarity in Kant, Hermann, and Bohr. [Preprint]
Johns, Richard (2018) Epistemic Theories of Objective Chance. [Preprint]
Oldofredi, Andrea (2018) Stochasticity and Bell-type Quantum Field Theory. [Preprint]
Farr, Matt (2015) Review of Tim Maudlin, "Philosophy of Physics: Space and Time". Philosophy in Review, Vol 35 (4).
Vickers, Peter (2018) Disarming the Ultimate Historical Challenge to Scientific Realism. The British Journal for the Philosophy of Science.

Abstract

Various claims regarding intertheoretic reduction, weak and strong notions of emergence, and explanatory fictions have been made in the context of first-order thermodynamic phase transitions. By appealing to John Norton’s recent distinction between approximation and idealization, I argue that the case study of anyons and fractional statistics, which has received little attention in the philosophy of science literature, is more hospitable to such claims. In doing so, I also identify three novel roles that explanatory fictions fulfill in science. Furthermore, I scrutinize the claim that anyons, as they are ostensibly manifested in the fractional quantum Hall effect, are emergent entities and urge caution. Consequently, it is suggested that a particular notion of strong emergence signals the need for the development of novel physical–mathematical research programs.

Abstract

The formulation of quantum mechanics developed by Bohm, which can generate well-defined trajectories for the underlying particles in the theory, can equally well be applied to relativistic quantum field theories to generate dynamics for the underlying fields. However, it does not produce trajectories for the particles associated with these fields. Bell has shown that an extension of Bohm’s approach can be used to provide dynamics for the fermionic occupation numbers in a relativistic quantum field theory. In the present paper, Bell’s formulation is adopted and elaborated on, with a full account of all technical detail required to apply his approach to a bosonic quantum field theory on a lattice. This allows an explicit computation of (stochastic) trajectories for massive and massless particles in this theory. Also particle creation and annihilation, and their impact on particle propagation, is illustrated using this model.

Abstract

We propose that observables in quantum theory are properly understood as representatives of symmetry-invariant quantities relating one system to another, the latter to be called a reference system. We provide a rigorous mathematical language to introduce and study quantum reference systems, showing that the orthodox “absolute” quantities are good representatives of observable relative quantities if the reference state is suitably localised. We use this relational formalism to critique the literature on the relationship between reference frames and superselection rules, settling a long-standing debate on the subject.

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