Abstract

We argue that causal decision theory (CDT) is no worse off than evidential decision theory (EDT) in handling entanglement, regardless of one’s preferred interpretation of quantum mechanics. In recent works, Ahmed (Evidence, decision, and causality, Cambridge University Press, Cambridge, 2014) and Ahmed and Caulton (Synthese, 191(18): 4315–4352, 2014) have claimed the opposite; we argue that they are mistaken. Bell-type experiments are not instances of Newcomb problems, so CDT and EDT do not diverge in their recommendations. We highlight the fact that a Causal Decision Theorist should take all lawlike correlations into account, including potentially acausal entanglement correlations. This paper also provides a brief introduction to CDT with a motivating “small” Newcomb problem. The main point of our argument is that quantum theory does not provide grounds for favouring EDT over CDT.

Publication date: Available online 1 August 2019

Source: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics

Author(s): Olivier Darrigol

Authors: Nengkun Yu

In this paper, we introduce a model of quantum concurrent program, which can be used to model the behaviour of reactive quantum systems and to design quantum compilers. We investigate quantum temporal logic, QTL, for the specification of quantum concurrent systems by suggesting the time-dependence of events. QTL employs the projections on subspaces as atomic propositions, which was established in the Birkhoff and von Neumann’s classic treatise on quantum logic. For deterministic functional quantum program, We prove a quantum B\”{o}hm-Jacopini theorem which states that any such program is equivalent to a Q-While program. The decidability of basic QTL formulae for general quantum concurrent program is studied.

Authors: Indrajit Sen

The possibility of using retrocausality to obtain a fundamentally relativistic account of the Bell correlations has gained increasing recognition in recent years. It is not known, however, the extent to which these models can make use of their relativistic properties to account for relativistic effects on entangled systems. We consider here a hypothetical relativistic Bell experiment, where one wing of the experiment is located in a lab on Earth, whereas the other wing is located inside a relativistic rocket, initially grounded adjacent to the lab. The Stern-Gerlach magnets in both the wings are turned on simultaneously as the rocket lifts off into orbit, and turned off when the rocket returns after a certain duration to its original spot. We show that the retrocausal Brans model (Found. Phys, 49(2), 2019) can be easily generalised to analyse this setup, and that it predicts less separation of eigenpackets in the rocket compared to the stationary lab. This causes the particle distribution patterns on the photographic plates to differ between the wings – an experimentally testable prediction of the model. We argue that the description of the experiment and the verification of this prediction using quantum field theory is a challenging task, in contrast to the ease of handling in the retrocausal Brans model. We mention the implications of our hypothetical experiment for hidden variable models in general.

Authors: Michael Vogl, Pontus Laurell, Aaron D. Barr, Gregory A. Fiete

In this paper we develop an analogue of Hamilton-Jacobi theory for the time-evolution operator of a quantum many-particle system. The theory offers a useful approach to develop approximations to the time-evolution operator, and also provides a unified framework and starting point for many well-known approximations to the time-evolution operator. In the important special case of periodically driven systems at stroboscopic times, we find relatively simple equations for the coupling constants of the Floquet Hamiltonian, where a straightforward truncation of the couplings leads to a powerful class of approximations. Using our theory, we construct a flow chart that illustrates the connection between various common approximations, which also highlights some missing connections and associated approximation schemes. These missing connections turn out to imply an analytically accessible approximation that is the “inverse” of a rotating frame approximation and thus has a range of validity complementary to it. We numerically test the various methods on the one-dimensional Ising model to confirm the ranges of validity that one would expect from the approximations used. The theory provides a map of the relations between the growing number of approximations for the time-evolution operator. We describe these relations in a table showing the limitations and advantages of many common approximations, as well as the new approximations introduced in this paper.

Authors: Ramón Ramos, David Spierings, Isabelle Racicot, Aephraim M. Steinberg

Tunnelling is one of the most paradigmatic and evocative phenomena of quantum physics, underlying processes such as photosynthesis and nuclear fusion, as well as devices ranging from SQUID magnetometers to superconducting qubits for quantum computers. The question of how long a particle takes to tunnel, however, has remained controversial since the first attempts to calculate it, which relied on the group delay. It is now well understood that this delay (the arrival time of the transmitted wave packet peak at the far side of the barrier) can be smaller than the barrier thickness divided by the speed of light, without violating causality. There have been a number of experiments confirming this, and even a recent one claiming that tunnelling may take no time at all. There have also been efforts to identify another timescale, which would better describe how long a given particle spends in the barrier region. Here we present a direct measurement of such a time, studying Bose-condensed $^{87}$Rb atoms tunnelling through a 1.3-${\mu}$m thick optical barrier. By localizing a pseudo-magnetic field inside the barrier, we use the spin precession of the atoms as a clock to measure the time it takes them to cross the classically forbidden region. We find a traversal time of 0.62(7) ms and study its dependence on incident energy. In addition to finally shedding light on the fundamental question of the tunnelling time, this experiment lays the groundwork for addressing deep foundational questions about history in quantum mechanics: for instance, what can we learn about where a particle was at earlier times by observing where it is now?

Authors: Venkatesa Chandrasekaran, Kartik Prabhu

We study the covariant phase space of vacuum general relativity at the null boundary of causal diamonds. The past and future components of such a null boundary each have an infinite-dimensional symmetry algebra consisting of diffeomorphisms of the $2$-sphere and boost supertranslations corresponding to angle-dependent rescalings of affine parameter along the null generators. Associated to these symmetries are charges and fluxes obtained from the covariant phase space formalism using the prescription of Wald and Zoupas. By analyzing the behavior of the spacetime metric near the corners of the causal diamond, we show that the fluxes are also Hamiltonian generators of the symmetries on the phase space. In particular, the supertranslation fluxes yield an infinite family of boost Hamiltonians acting on the gravitational data of causal diamonds. We show that the smoothness of the vector fields representing such symmetries at the bifurcation edge of the causal diamond implies suitable matching conditions between the symmetries on the past and future components of the null boundary. Similarly, the smoothness of the spacetime metric implies that the fluxes of all such symmetries is conserved between the past and future components of the null boundary. This establishes an infinite set of conservation laws for finite subregions in gravity analogous to those at null infinity. We also show that the symmetry algebra at the causal diamond has a non-trivial center corresponding to constant boosts. The central charges associated to these constant boosts are proportional to the area of the bifurcation edge, for any causal diamond, in analogy with the Wald entropy formula.

Authors: Cristhian Garcia-Quintero, Mustapha Ishak, Logan Fox, Jason Dossett

We introduce a new version of the Integrated Software in Testing General Relativity (ISiTGR) which is a patch to the software CAMB and CosmoMC. ISiTGR is intended to test deviations from GR at cosmological scales using cosmological data sets. While doing so, it allows for various extensions to the standard flat $\Lambda$CDM model. In this new release, we have support for the following: 1) dynamical dark energy parametrizations with a constant or time-dependant equation of state; 2) a consistent implementation of anisotropic shear to model massive neutrinos throughout the full formalism; 3) multiple commonly-used parametrizations of modified growth (MG) parameters; 4) functional, binned and hybrid time- and scale-dependencies for all MG parameters; 5) spatially flat or curved backgrounds. ISiTGR is designed to allow cosmological analyses to take full advantage of ongoing and future surveys to test simultaneously or separately various extensions to the standard model. We describe here the formalism and its implementation in the CMB code, the Integrated Sachs-Wolfe (ISW) effect, and the 3×2 point statistics. Next, we apply ISiTGR to current data sets from Planck2015, Dark Energy Survey YR1 release, Baryonic Acoustic Oscillations (BAO), Redshift Space Distortions (RSD) from the BOSS Data Release 12, the 6DF Galaxy Survey and the SDSS Data Release 7 Main Galaxy Sample, and Supernova from the Pantheon compilation, joint SNLS/SDSS data analysis and the Hubble Space Telescope. We derive constraints on MG parameters for various combinations of the five features above and find that GR is consistent with current data sets in all cases. The code is made publicly available at https://github.com/mishakb/ISiTGR

Sullivan, Emily (2019) Universality Caused: The case of renormalization group explanation. European Journal for Philosophy of Science, 9 (36). ISSN 1879-4912

Letertre, Laurie (2019) Causal nonseparability and the structure of spacetime. In: UNSPECIFIED.

Driessen, Alfred (2019) Aristotle and the Foundation of Quantum Mechanics. [Preprint]

Gomez-Marin, Alex and Arnau, Juan (2019) When the part mirrors the whole: interactions beyond simple location. [Preprint]

Landsman, Klaas (2019) Randomness? What randomness? [Preprint]

Teh, Nicholas and Schenkel, Alexander and Wells, Laura and Mathieu, Philippe (2019) Homological perspective on edge modes in linear Yang-Mills theory. [Preprint]

Slavov, Matias (2019) Book review: The Order of Time by Carlo Rovelli. European Journal of Analytic Philosophy, 15 (1). pp. 71-75.

Thebault, Karim P Y (2016) What Can We Learn From Analogue Experiments? [Preprint]

Abstract

In this paper I report a public discussion with E.P. Wigner that took place in 1987 at a conference on fundamental problems in Quantum Mechanics. In it Wigner clarified an idea that was widely attributed to him about consciousness playing a direct role in the quantum measurement process. He significantly revised that idea, and distanced himself from the earlier notion that consciousness plays a direct role.

Abstract

I try to revive, and possibly reconcile, a debate started a few years ago, about the relative roles of a bare cosmological constant and of a vacuum energy, by taking the attitude to try to get the most from the physics now available as established. I notice that the bare cosmological constant of the Einstein equations, which is there ever since GR emerged, is actually constrained (if not measured) indirectly combining the effective cosmological constant observed now, as given by ΛCDM Precision Cosmology, with the cumulative vacuum contribution of the particles of the Standard Model, SM. This comes out when the vacuum energy is regularized, as given by many Authors, still within well established Quantum Field Theory, QFT, but without violating Lorentz invariance. The fine tuning, implied by the compensation to a small positive value of the two large contributions, could be seen as offered by Nature, which provides one more fundamental constant, the bare Lambda. The possibility is then discussed of constraining (measuring) directly such a bare cosmological constant by the features of primordial gravitational wave signals coming from epoch’s precedent to the creation of particles. I comment on possibilities that would be lethal, that is if the vacuum does not gravitate. This last issue is often raised, and I discuss the current situation about. Finally a hint is briefly discussed for a possible “bare Lambda inflation” process.