Weekly Papers on Quantum Foundations (25)

Authors: Juan CayusoNéstor OrtizLuis Lehner

The question of what gravitational theory could supersede General Relativity has been central in theoretical physics for decades. Many disparate alternatives have been proposed motivated by cosmology, quantum gravity and phenomenological angles, and have been subjected to tests derived from cosmological, solar system and pulsar observations typically restricted to linearized regimes. Gravitational waves from compact binaries provide new opportunities to probe these theories in the strongly gravitating/highly dynamical regimes. To this end however, a reliable understanding of the dynamics in such a regime is required. Unfortunately, most of these theories fail to define well posed initial value problems, which prevents at face value from meeting such challenge. In this work, we introduce a consistent program able to remedy this situation. This program is inspired in the approach to "fixing" viscous relativistic hydrodynamics introduced by Israel and Stewart in the late 70's. We illustrate how to implement this approach to control undesirable effects of higher order derivatives in gravity theories and argue how the modified system still captures the true dynamics of the putative underlying theories in 3+1 dimensions. We sketch the implementation of this idea in a couple of effective theories of gravity, one in the context of Non-commutative geometry, and one in the context of Chern-Simons modified General Relativity.

Authors: Andrew Strominger

We argue that four-dimensional black hole evaporation inevitably produces an infinite number of soft particles in addition to the thermally distributed `hard' Hawking quanta, and moreover that the soft and hard particles are highly correlated. This raises the possibility that quantum purity is restored by correlations between the hard and soft radiation, while inclusive measurements which omit the soft radiation observe the thermal Hawking spectrum. In theories whose only stable particle is the graviton, conservation laws are used to argue that such correlations are in principle sufficient for the soft gravitons to purify the hard thermal ones.

Authors: Matthias LienertRoderich Tumulka

Suppose that particle detectors are placed along a Cauchy surface $\Sigma$ in Minkowski space-time, and consider a quantum theory with fixed or variable number of particles (i.e., using Fock space or a subspace thereof). It is straightforward to guess what Born's rule should look like for this setting: The probability distribution of the detected configuration on $\Sigma$ has density $|\psi_\Sigma|^2$, where $\psi_\Sigma$ is a suitable wave function on $\Sigma$, and the operation $|\cdot|^2$ is suitably interpreted. We call this statement the "curved Born rule." Since in any one Lorentz frame, the appropriate measurement postulates referring to constant-$t$ hyperplanes should determine the probabilities of the outcomes of any conceivable experiment, they should also imply the curved Born rule. This is what we are concerned with here: deriving Born's rule for $\Sigma$ from Born's rule in one Lorentz frame (along with a collapse rule). We describe two ways of defining an idealized detection process, and prove for one of them that the probability distribution coincides with $|\psi_\Sigma|^2$. For this result, we need two hypotheses on the time evolution: that there is no interaction faster than light, and that there is no creation of particles from the Fock vacuum. The wave function $\psi_\Sigma$ can be obtained from the Tomonaga--Schwinger equation, or from a multi-time wave function by inserting configurations on $\Sigma$. Thus, our result establishes in particular how multi-time wave functions are related to detection probabilities.


In this paper, I will argue that metaphysicians ought to utilize quantum theories of gravity (QG) as incubators for a future metaphysics. I will argue why this ought to be done and will present cases studies from the history of science where physical theories have challenged both the dogmatic and speculative metaphysician. I provide two theories of QG and demonstrate the challenge they pose to certain aspects of our current metaphysics; in particular, how they challenge our understanding of the abstract–concrete distinction. I demonstrate how five different accounts of the distinction each fail to hold under the received interpretations of loop quantum gravity and string theory. The central goal of this paper is to encourage metaphysicians to look to physical theories, especially those involving cosmology such as string theory and loop quantum gravity, when doing metaphysics.

Sanders, Ko (2015) What can (mathematical) categories tell us about space-time? In: UNSPECIFIED.
Publication date: Available online 22 June 2017
Source:Physics Reports
Author(s): Luigi Delle Site, Matej Praprotnik
Typical experimental setups for molecular systems must deal with a certain coupling to the external environment, that is, the system is open and exchanges mass, momentum, and energy with its surroundings. Instead, standard molecular simulations are mostly performed using periodic boundary conditions with a constant number of molecules. In this review, we summarize major developments of open simulation methodologies, which, contrary to standard techniques, open up the boundaries of a molecular system and allow for exchange of energy and matter with the environment, in and out of equilibrium. In particular, we construct the review around the open simulation approaches based on the Adaptive Resolution Scheme (AdResS), which seamlessly couples different levels of resolution in molecular simulations. Ideas and theoretical concepts used in its development lie at the crossroad of different fields and disciplines and open many different directions for future developments in molecular simulation. We examine progress related to theoretical as well as novel modeling approaches bridging length scales from quantum to the continuum description and report on their application in various molecular systems. The outlook of the review is dedicated to the perspective of how to further incorporate rigorous theoretical approaches such as the Bergman-Lebowitz and Emch-Sewell models into the molecular simulation algorithms and stimulate further development of open simulation methods and their application.
Menon, Tushar and Moller-Nielsen, Thomas and Read, James (2017) Regarding `Regarding the `Hole Argument''. [Preprint]
Hoehn, Philipp (2017) Reflections on the information paradigm in quantum and gravitational physics. [Preprint]

Huw Price has proposed an argument that suggests a time symmetric ontology for quantum theory must necessarily be retrocausal, i.e. it must involve influences that travel backwards in time. One of Price's assumptions is that the quantum state is a state of reality. However, one of the reasons for exploring retrocausality is that it offers the potential for evading the consequences of no-go theorems, including recent proofs of the reality of the quantum state. Here, we show that this assumption can be replaced by a different assumption, called -mediation, that plausibly holds independently of the status of the quantum state. We also reformulate the other assumptions behind the argument to place them in a more general framework and pin down the notion of time symmetry involved more precisely. We show that our assumptions imply a timelike analogue of Bell's local causality criterion and, in doing so, give a new interpretation of timelike violations of Bell inequalities. Namely, they show the impossibility of a (non-retrocausal) time symmetric ontology.

Bacelar Valente, Mario (2017) Conventionality in Einstein's practical geometry. THEORIA. An International Journal for Theory, History and Foundations of Science, 32 (2). pp. 177-190. ISSN 2171-679X

Authors: Ichiro Oda

An important hurdle to be faced by any model proposing a resolution to the cosmological constant problem is Weinberg's venerable no go theorem. This theorem states that no local field equations including classical gravity can have a flat Minkowski solution for generic values of the parameters, in other words, the no go theorem forbids the existence of any solution to the cosmological constant problem within local field theories without fine tuning. Though the original Weinberg theorem is valid only in classical gravity, in this article we prove that this theorem holds even in quantum gravity. Our proof is very general since it makes use of the BRST invariance emerging after gauge-fixing of general coordinate invariance and does not depend on the detail of quantum gravity.

Authors: Luis E. IbanezVictor Martin-LozanoIrene Valenzuela

It is known that there are AdS vacua obtained from compactifying the SM to 2 or 3 dimensions. The existence of such vacua depends on the value of neutrino masses through the Casimir effect. Using the Weak Gravity Conjecture, it has been recently argued by Ooguri and Vafa that such vacua are incompatible with the SM embedding into a consistent theory of quantum gravity. We study the limits obtained for both the cosmological constant $\Lambda_4$ and neutrino masses from the absence of such dangerous 3D and 2D SM AdS vacua. One interesting implication is that $\Lambda_4$ is bounded to be larger than a scale of order $m_\nu^4$, as observed experimentally. Interestingly, this is the first argument implying a non-vanishing $\Lambda_4$ only on the basis of particle physics, with no cosmological input. Conversely, the observed $\Lambda_4$ implies strong constraints on neutrino masses in the SM and also for some BSM extensions including extra Weyl or Dirac spinors, gravitinos and axions. We find that experimental neutrino masses are incompatible with Majorana neutrinos unless new physics in the form of at least one Weyl fermion or a multi-axion set are present. Candidates for such particles are sterile neutrinos, axinos or very light gravitinos. Dirac neutrino masses with the lightest of them lighter than $4.1\times 10^{-3} eV$ are still viable with no need of extra BSM particles. We also critically discuss the issue of the stability of these 3D SM vacua, which is required for these bounds to hold.

Authors: Ya XiaoYaron KedemJin-Shi XuChuan-Feng LiGuang-Can Guo

Interpretations of quantum mechanics (QM), or proposals for underlying theories, that attempt to present a definite realist picture, such as Bohmian mechanics, require strong non-local effects. Naively, these effects would violate causality and contradict special relativity. However if the theory agrees with QM the violation cannot be observed directly. Here, we demonstrate experimentally such an effect: we steer the velocity and trajectory of a Bohmian particle using a remote measurement. We use a pair of photons and entangle the spatial transverse position of one with the polarization of the other. The first photon is sent to a double-slit-like apparatus, where its trajectory is measured using the technique of Weak Measurements. The other photon is projected to a linear polarization state. The choice of polarization state, and the result, steer the first photon in the most intuitive sense of the word. The effect is indeed shown to be dramatic, while being easy to visualize. We discuss its strength and what are the conditions for it to occur.

Authors: Angelo BassiAndré GroßardtHendrik Ulbricht

We discuss effects of loss of coherence in low energy quantum systems caused by or related to gravitation, referred to as gravitational decoherence. These effects, resulting from random metric fluctuations, for instance, promise to be accessible by relatively inexpensive table-top experiments, way before the scales where true quantum gravity effects become important. Therefore, they can provide a first experimental view on gravity in the quantum regime. We will survey models of decoherence induced both by classical and quantum gravitational fluctuations; it will be manifest that a clear understanding of gravitational decoherence is still lacking. Next we will review models where quantum theory is modified, under the assumption that gravity causes the collapse of the wave functions, when systems are large enough. These models challenge the quantum-gravity interplay, and can be tested experimentally. In the last part we have a look at the state of the art of experimental research. We will review efforts aiming at more and more accurate measurements of gravity (G and g) and ideas for measuring conventional and unconventional gravity effects on nonrelativistic quantum systems.

Authors: Jonathan OlsonYudong CaoJonathan RomeroPeter JohnsonPierre-Luc Dallaire-DemersNicolas SawayaPrineha NarangIan KivlichanMichael WasielewskiAlán Aspuru-Guzik

The NSF Workshop in Quantum Information and Computation for Chemistry assembled experts from directly quantum-oriented fields such as algorithms, chemistry, machine learning, optics, simulation, and metrology, as well as experts in related fields such as condensed matter physics, biochemistry, physical chemistry, inorganic and organic chemistry, and spectroscopy. The goal of the workshop was to summarize recent progress in research at the interface of quantum information science and chemistry as well as to discuss the promising research challenges and opportunities in the field. Furthermore, the workshop hoped to identify target areas where cross fertilization among these fields would result in the largest payoff for developments in theory, algorithms, and experimental techniques. The ideas can be broadly categorized in two distinct areas of research that obviously have interactions and are not separated cleanly. The first area is quantum information for chemistry, or how quantum information tools, both experimental and theoretical can aid in our understanding of a wide range of problems pertaining to chemistry. The second area is chemistry for quantum information, which aims to discuss the several aspects where research in the chemical sciences can aid progress in quantum information science and technology. The results of the workshop are summarized in this report.

Authors: Dharam Vir Ahluwalia

A broad brush impressionistic view of physics from the vantage point of she living on a nearby dark-planet Zimpok is presented so as to argue that the observed and the observer are reflected in quantum gravity through a universal mass shared by neurones and a unification scale of the high energy physics.

Authors: Pierre-Henri Chavanis

Using Nottale's theory of scale relativity, we derive a generalized Schr\"odinger equation applying to dark matter halos. This equation involves a logarithmic nonlinearity associated with an effective temperature and a source of dissipation. Fundamentally, this wave equation arises from the nondifferentiability of the trajectories of the dark matter particles whose origin may be due to ordinary quantum mechanics, classical ergodic (or almost ergodic) chaos, or to the fractal nature of spacetime at the cosmic scale. The generalized Schr\"odinger equation involves a coefficient ${\cal D}$, possibly different from $\hbar/2m$, whose value for dark matter halos is ${\cal D}=1.02\times 10^{23}\, {\rm m^2/s}$. We suggest that the cold dark matter crisis may be solved by the fractal (nondifferentiable) structure of spacetime at the cosmic scale, or by the chaotic motion of the particles on a very long timescale, instead of ordinary quantum mechanics. The equilibrium states of the generalized Schr\"odinger equation correspond to configurations with a core-halo structure. The quantumlike potential generates a solitonic core that solves the cusp problem of the classical cold dark matter model. The logarithmic nonlinearity accounts for the presence of an isothermal halo that leads to flat rotation curves. The damping term ensures that the system relaxes towards an equilibrium state. This property is guaranteed by an $H$-theorem satisfied by a Boltzmann-like free energy functional. In our approach, the temperature and the friction arise from a single formalism. They correspond to the real and imaginary parts of the complex friction coefficient present in the scale covariant equation of dynamics that is at the basis of Nottale's theory of scale relativity.

Authors: Furkan Semih DündarMetin Arik

In this paper, we investigated the role of accelerated observers in observing the Unruh radiation in the Bohmian field theory on a shape dynamics background setting. Since metric and metric momentum are real quantities, the integral kernel to invert the Lichnerowicz-York equation for first order deviations due to existence of matter terms turns out to be real. This fact makes the interaction Hamiltonian real. On the other hand, since the ground state wave functional for rectilinear observers is also real, the jump rate of the Bohmian field theory turns out to vanish. Hence we conclude that Unruh effect in Bohmian field theory on a shape dynamics background setting is non-existent. It is also found out that the non-existence of Unruh radiation is independent from the compact nature of space in shape dynamics. Therefore, observation of Unruh radiation may be a test for quantum field theory and Bohmian field theory on a shape dynamics background.


In an accompanying paper Gomes (arXiv:1504.02818, 2015), we have put forward an interpretation of quantum mechanics based on a non-relativistic, Lagrangian 3+1 formalism of a closed Universe M, existing on timeless configuration space \mathcal {Q} of some field over M. However, not much was said there about the role of locality, which was not assumed. This paper is an attempt to fill that gap. Locality in full can only emerge dynamically, and is not postulated. This new understanding of locality is based solely on the properties of extremal paths in configuration space. I do not demand locality from the start, as it is usually done, but showed conditions under which certain systems exhibit it spontaneously. In this way we recover semi-classical local behavior when regions dynamically decouple from each other, a notion more appropriate for extension into quantum mechanics. The dynamics of a sub-region O within the closed manifold M is independent of its complement, M-O , if the projection of extremal curves on \mathcal {Q} onto the space of extremal curves intrinsic to O is a surjective map. This roughly corresponds to e^{i\hat{H}t}\circ \mathsf {pr}_{\mathrm{O}}= \mathsf {pr}_{\mathrm{O}}\circ e^{i\hat{H}t} , where \mathsf {pr}_{\mathrm{O}}:\mathcal {Q}\rightarrow \mathcal {Q}_O^{\partial O} is a linear projection. This criterion for locality can be made approximate—an impossible feat had it been already postulated—and it can be applied for theories which do not have hyperbolic equations of motion, and/or no fixed causal structure. When two regions are mutually independent according to the criterion proposed here, the semi-classical path integral kernel factorizes, showing cluster decomposition which is the ultimate aim of a definition of locality.

Author(s): Stephen L. Adler

Assuming the standard axioms for quaternionic quantum theory and a spatially localized scattering interaction, the S matrix in quaternionic quantum theory is complex valued, not quaternionic. Using the standard connections between the S matrix, the forward scattering amplitude for electromagnetic wa…
[Phys. Rev. A 95, 060101(R)] Published Mon Jun 19, 2017

Authors: Wen-ge Wang

A method is proposed for the formulation of the quantum electrodynamics, which is completely quantum mechanical and does not make use of gauge symmetry of the corresponding classical fields. In this formulation, photon states are introduced based on a geometric property of the quantum state space for one electron and one positron, and an interaction Hamiltonian appears as an operator, which maps in a most natural way the quantum state space for electron and positron to the quantum state space for photon. This method could be useful in the search for a description of the three interactions (electromagnetic, weak, and strong), which is more unified than that given in the standard model.

Authors: Jerome MartinVincent Vennin

We present a general and systematic study of how a Bell experiment on the cosmic microwave background could be carried out. We introduce different classes of pseudo-spin operators and show that, if the system is placed in a two-mode squeezed state as inflation predicts, they all lead to a violation of the Bell inequality. However, we also discuss the obstacles that one faces in order to realize this program in practice and show that they are probably insurmountable. We suggest alternative methods that would reveal the quantum origin of cosmological structures without relying on Bell experiments.

Authors: Catarina MoreiraAndreas Wichert

The application of principles of Quantum Mechanics in areas outside of physics has been getting increasing attention in the scientific community in an emergent disciplined called Quantum Cognition. These principles have been applied to explain paradoxical situations that cannot be easily explained through classical theory. In quantum probability, events are characterised by a superposition state, which is represented by a state vector in a $N$-dimensional vector space. The probability of an event is given by the squared magnitude of the projection of this superposition state into the desired subspace. This geometric approach is very useful to explain paradoxical findings that involve order effects, but do we really need quantum principles for models that only involve projections?

This work has two main goals. First, it is still not clear in the literature if a quantum projection model has any advantage towards a classical projection. We compared both models and concluded that the Quantum Projection model achieves the same results as its classical counterpart, because the quantum interference effects play no role in the computation of the probabilities. Second, it intends to propose an alternative relativistic interpretation of rotation parameters that are involved in both classical and quantum models. In the end, instead of interpreting these parameters as a similarity measure between questions, we propose that they emerge due to the lack of knowledge concerned with a personal basis state and also due to uncertainties towards the state of the world and towards the context of the questions.

Volume 3, Issue 3, pages 78-99

Tom Campbell [Show Biography], Houman Owhadi [Show Biography], Joe Sauvageau [Show Biography], andDavid Watkinson [Show Biography]






Tom Campbell, born in the USA in 1944, earned his BS degree (Cum Laude) in 1966 with majors in both Mathematics and Physics. While an undergraduate, Tom became the president of his fraternity and chief Justice of the college’s student court.  Tom was awarded a master’s degree in Physics from Purdue university in 1968 after which PhD work commenced at the University of Virginia with a specialization in experimental nuclear physics.  Campbell was an analyst with Army technical intelligence for a decade before moving into the research and development of technology supporting defensive missile systems.  He also worked as a consultant for NASA within the Ares I program assessing and solving problems of system risk and survivability to insure crew survivability and mission success.  Campbell published a trilogy My Big TOE (MBT) in 2003 that offered a fully complete cosmology based on the simulation hypothesis including a theory of consciousness, and a derivation of both relativity and Quantum Mechanics from one overarching set of principles.  Furthermore, Campbell’s theory eliminates any nonlocal "weirdness"…. replacing it with a completely rational and logical causal process as found in all other subsets of science.  MBT has been successful at solving many outstanding fundamental paradoxes within physics in particular, science in general, and within several other major fields of study including: philosophy (cosmology, epistemology, ontology), psychology (mind models), mathematics (cellular automata and evolution as process fractals), medicine (mind-body connection), biology (math & other anomalies), and theology (source). In October 2016, Campbell presented, in Los Angeles CA (MBT-LA), a set of quantum experiments that would support his theory if they worked as predicted (available on DVD upon request or on YouTube).   Fortunately, these experiments are relatively inexpensive and not particularly difficult to perform.

Houman Owhadi is Professor of Applied & Computational Mathematics and Control and Dynamical Systems in the Computing and Mathematical Sciences Department at the California Institute of Technology. His work lies at the interface between applied mathematics, probability and statistics. At the center of his work are fundamental problems such as the optimal quantification of uncertainties in presence of limited information, statistical inference/game theoretic approaches to numerical approximation and algorithm design, multiscale analysis with non-separated scales, and the geometric integration of structured stochastic systems.

Joe Sauvageau received a M.A, and Ph.D. from Stony Brook University in New York in Applied Physics in 1987. He is currently serving as a Senior Systems Manager at the NASA Jet Propulsion Laboratory in Pasadena, CA in the Astronomy, Physics and Space Technology Office. His career experience has spanned scientific pursuits as a government scientist at NIST studying superconducting quantum devices; industrial physics and engineering development in the semiconductor, optoelectronics and photonics industries; and leading the optical engineering design, development and deployment of next generation optical instruments including visible and infrared imaging sensors for space and airborne applications. He was the recipient of the Rotary National Award for Space Achievement (RNASA) Stellar Award in 2013, Aviation Week Technical Program Excellence Award and an IEEE Outstanding Engineer of the Year Award in 2012 associated with the design and development of a multispectral sensor payload currently in geosynchronous orbit. He has also served in various senior management positions ranging from start-ups through Fortune 500 companies and he has held positions on several Technical Advisory Boards. His publication portfolio includes four patents and a multitude of articles and technical reports in journals.

In 1964, David Watkinson went to the University of North Carolina on a navy scholarship to major in physics and mathematics. In his junior year, he visited Dr. J. B. Rhine’s Parapsychology laboratory at nearby Duke University and became so interested in that field of study that he graduated with a degree in psychology. Having developed programming and 2D/3D animation skills, Watkinson was recruited to work on feature films which led to a long career in Hollywood and some time as a Visiting Assistant Professor in the UCLA Graduate School of Film. During that time, Watkinson became interested in virtual reality technology while writing about it for Videography Magazine. Watkinson was finally able to combine his interest in virtual reality simulations, parapsychology and physics when he formed a group to study physicist Tom Campbell’s TOE which unifies all three fields. In pursuing that study, Watkinson visited physicist Marlan Scully and his team at Texas A&M to discuss Scully’s Delayed Choice Quantum Eraser. During the visit, Watkinson became aware of an important variation of the Double Slit experiment that had never been performed. That led Watkinson to get involved with Campbell and the other authors in an effort to promote interest in performing multiple experiments to test the simulation hypothesis.

Can the theory that reality is a simulation be tested? We investigate this question based on the assumption that if the system performing the simulation is finite (i.e. has limited resources), then to achieve low computational complexity, such a system would, as in a video game, render content (reality) only at the moment that information becomes available for observation by a player and not at the moment of detection by a machine (that would be part of the simulation and whose detection would also be part of the internal computation performed by the Virtual Reality server before rendering content to the player). Guided by this principle we describe conceptual wave/particle duality experiments aimed at testing the simulation theory.

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