# Weekly Papers on Quantum Foundations (19)

Einstein’s Oxford Blackboard: A Unique Historical Artefact. (arXiv:2205.02539v1 [physics.hist-ph])

Authors: Cormac O’Raifeartaigh

Einstein’s blackboard is a well-known exhibit at the History of Science Museum at Oxford University. However, it is much less well known that the writing on the board provides a neat summary of a work of historic importance, Einstein’s 1931 model of the expanding universe. As a visual representation of one of the earliest models of the universe to be proposed in the wake of Hubble’s observations of the nebulae, the blackboard provides an intriguing snapshot of a key moment in modern astronomy and cosmology. In addition, one line on the blackboard that is not in Einstein’s 1931 paper casts useful light on some anomalies in the calculations of that paper.

Quantum computers as an amplifier for existential risk. (arXiv:2205.02761v1 [physics.soc-ph])

Authors: Benjamin F. Schiffer

Quantum computing is expected to have a profound impact on society. In this work we discuss the potential consequences on existential risk for humanity. Even with the timeline for large-scale fault-tolerant quantum computing still unclear, it is highly likely that quantum computers will eventually realize an exponential speedup for certain practical applications. We identify quantum simulation as the most relevant application in this regard and we qualitatively outline different risk trajectories. Both amplifying and mitigating effects of quantum computing for existential risk are anticipated. In order to prevent quantum computing from being an amplifier of existential risk, we call for increased efforts by the scientific community towards reducing potential future quantum risk. This viewpoint seeks to add a new perspective to the discussion on technological risk of quantum computing.

An analogue of the Riemann Hypothesis via quantum walks. (arXiv:2204.00765v2 [quant-ph] UPDATED)

We consider an analogue of the well-known Riemann Hypothesis based on quantum walks on graphs with the help of the Konno-Sato theorem. Furthermore, we give some examples for complete, cycle, and star graphs.

When does a particle arrive?. (arXiv:2205.02219v2 [quant-ph] UPDATED)

We compare the different proposals that have appeared in the literature to describe a measurement of the time of arrival of a quantum particle at a detector. We show that there are multiple regimes where different proposals give inequivalent, experimentally discriminable, predictions. This analysis paves the way for future experimental tests.

Extreme events in dynamical systems and random walkers: A review

Publication date: 5 July 2022

Source: Physics Reports, Volume 966

Author(s): Sayantan Nag Chowdhury, Arnob Ray, Syamal K. Dana, Dibakar Ghosh

Measuring the distortion of time with relativistic effects in large-scale structure. (arXiv:2205.02567v1 [astro-ph.CO])

Authors: Daniel Sobral-BlancoCamille Bonvin

To test the theory of gravity one needs to test, on one hand, how space and time are distorted by matter and, on the other hand, how matter moves in a distorted space-time. Current observations provide tight constraints on the motion of matter, through the so-called redshift-space distortions, but they only provide a measurement of the sum of the spatial and temporal distortions, via gravitational lensing. In this Letter, we develop a method to measure the time distortion on its own. We show that the coming generation of galaxy surveys, like the Square Kilometer Array, will allow us to measure the distortion of time with an accuracy of 10-30\%. Such a measurement will be essential to test deviations from General Relativity in a fully model-independent way. In particular, it can be used to compare the spatial and temporal distortions of space-time, that are predicted to be the same in $\Lambda$CDM but generically differ in modified theories of gravity.

Two Novel Observational Tests of General Relativity. (arXiv:2205.02746v1 [gr-qc])

Authors: Abraham Loeb (Harvard)

We propose two novel observational tests of general relativistic predictions: (i) Detecting the memory effect from a massive black hole merger at the Galactic Center through Lunar Ranging; and (ii) Violation of a limiting flux versus redshift as a flag of new physics. First, I show that a gravitational wave pulse from a major merger of massive black holes at the Galactic center induces a permanent increase in the Earth-Moon separation. For black holes of millions of solar masses, the shift in the local gravitational potential is comparable to the Earth-Moon potential, leading to the Moon being perturbed relative to the Earth during the passage of the pulse. The permanent increase in the Earth-Moon separation is a fraction of a millimeter, measurable by lunar ranging for future merger events. Second, I show that General Relativity sets an absolute upper limit on the energy flux observed from a cosmological source as a function of its redshift. Detecting a brighter source in gravitational waves, neutrinos or light, would flag new physics. The derived flux limit can also be used to determine the maximum redshift possible for any source with an unknown origin.

Alcubierre Warp Drive in Bohmian Quantum Gravity. (arXiv:2205.02780v1 [physics.gen-ph])

Authors: Sijo K. Joseph

Alcubierre warp drive metric is coupled to quantum mechanical scalar matter field. The requirement of the exotic matter for the warp drive is mapped into a conformal wave equation. This result into a fourth order partial differential equation in terms of the quantum mechanical density. Finding a proper quantum mechanical density obeying the proposed partial differential equation will be a resolution to the exotic matter problem of Alcubierre warp drive in Bohmian Quantum Gravity context.

The Penrose Property with a Cosmological Constant. (arXiv:2106.02536v2 [gr-qc] UPDATED)

Authors: Peter Cameron

A spacetime satisfies the non-timelike boundary version of the Penrose property if the timelike future of any point on $\mathcal{I}^-$ contains the whole of $\mathcal{I}^+$. This property was first discussed for asymptotically flat spacetimes by Penrose, along with an equivalent definition (the finite version). In this paper we consider the Penrose property in greater generality. In particular we consider spacetimes with a non-zero cosmological constant and we note that the two versions of the property are no longer equivalent. In asymptotically AdS spacetimes it is necessary to re-state the property in a way which is more suited to spacetimes with a timelike boundary. We arrive at a property previously considered by Gao and Wald. Curiously, this property was shown to fail in spacetimes which focus null geodesics. This is in contrast to our findings in asymptotically flat and asymptotically de Sitter spacetimes. We then move on to consider some further example spacetimes (with zero cosmological constant) which highlight features of the Penrose property not previously considered. We discuss spacetimes which are the product of a Lorentzian and a compact Riemannian manifold. Perhaps surprisingly, we find that both versions of the Penrose property are satisfied in this product spacetime if and only if they are satisfied in the Lorentzian spacetime only. We also discuss the Ellis-Bronnikov wormhole (an example of a spacetime with more than one asymptotically flat end) and the Hayward metric (an example of a non-singular black hole spacetime).

Quantum evolution of the Hawking state for black holes. (arXiv:2204.13126v1 [hep-th] CROSS LISTED)

Authors: Steven B. GiddingsJulie Perkins

We give a general description of the evolving quantum state of a Schwarzschild black hole, in the quantum field theory approximation. Such a time-dependent description is based on introducing a choice of time slices. We in particular consider slices that smoothly cross the horizon, and introduction of “stationary” such slices simplifies the analysis. This analysis goes beyond standard derivations of Hawking radiation that focus on asymptotic excitations, and in particular gives an evolving state that is regular at the horizon, with no explicit transplanckian dependence, and that can in principle be generalized to incorporate interacting fields. It is also expected to be useful in connecting to information-theoretic investigation of black hole evolution. The description of the evolving state depends on the choice of slices as well as coordinates on the slices and mode bases; these choices give different “pictures” analogous to that of Schr\”odinger. Evolution does have a simpler appearance in an energy eigenbasis, but such a basis is also singular at the horizon; evolution of regular modes has a more complicated appearance, whose properties may be inferred by comparing with the energy eigenbasis. In a regular description, Hawking quanta are produced in a black hole atmosphere, at scales comparable to the horizon size. This approach is also argued to extend to more general asymptotics, such as that of anti de Sitter space. In the latter context, this analysis provides a description of the hamiltonian and evolution of a black hole that may be compared to the large-$N$ dynamics of the proposed dual CFT.

Reassessing the Notion of a Kuhnian Revolution What Happened in Twentieth-Century Chemistry

Scerri, Eric (2021) Reassessing the Notion of a Kuhnian Revolution What Happened in Twentieth-Century Chemistry. B. Wray (ed.), Interpreting Kuhn,. pp. 124-141.

A (strictly) contemporary perspective on trans-Planckian censorship

Schneider, Mike D. (2022) A (strictly) contemporary perspective on trans-Planckian censorship. [Preprint]

Idealisations and the No-Miracle Argument

Ruyant, Quentin (2022) Idealisations and the No-Miracle Argument. [Preprint]

The introduction of topology into analytic philosophy: two movements and a coda

Abstract

Both early analytic philosophy and the branch of mathematics now known as topology were gestated and born in the early part of the 20th century. It is not well recognized that there was early interaction between the communities practicing and developing these fields. We trace the history of how topological ideas entered into analytic philosophy through two migrations, an earlier one conceiving of topology geometrically and a later one conceiving of topology algebraically. This allows us to reassess the influence and significance of topological methods for philosophy, including the possible fruitfulness of a third conception of topology as a structure determining similarity.

The Inaccessibility of the Past is not Statistical

Emily, Adlam (2022) The Inaccessibility of the Past is not Statistical. [Preprint]

The sky is blue, and other reasons quantum mechanics is not underdetermined by evidence

Wallace, David (2022) The sky is blue, and other reasons quantum mechanics is not underdetermined by evidence. [Preprint]

Understanding Time Reversal in Quantum Mechanics: A Full Derivation

Gao, Shan (2022) Understanding Time Reversal in Quantum Mechanics: A Full Derivation. [Preprint]

Variable relativity of causation is good

Abstract

Interventionism is a theory of causation with a pragmatic goal: to define causal concepts that are useful for reasoning about how things could, in principle, be purposely manipulated. In its original presentation, Woodward’s (2003) interventionist definition of causation is relativized to an analyzed variable set. In Woodward (2008), Woodward changes the definition of the most general interventionist notion of cause, contributing cause, so that it is no longer relativized to a variable set. This derelativization of interventionism has not gathered much attention, presumably because it is seen as an unproblematic way to save the intuition that causal relations are objective features of the world. This paper first argues that this move has problematic consequences. Derelativization entails two concepts of unmediated causal relation that are not coextensional, but which nonetheless do not entail different conclusions about manipulability relations within any given variable set. This is in conflict with the pragmatic orientation at the core of interventionism. The paper then considers various approaches for resolving this tension but finds them all wanting. It is concluded that interventionist causation should not be derelativized in the first place. Various considerations are offered rendering that conclusion acceptable.

Not so distinctively mathematical explanations: topology and dynamical systems

Abstract

So-called ‘distinctively mathematical explanations’ (DMEs) are said to explain physical phenomena, not in terms of contingent causal laws, but rather in terms of mathematical necessities that constrain the physical system in question. Lange argues that the existence of four or more equilibrium positions of any double pendulum has a DME. Here we refute both Lange’s claim itself and a strengthened and extended version of the claim that would pertain to any n-tuple pendulum system on the ground that such explanations are actually causal explanations in disguise and their associated modal conditionals are not general enough to explain the said features of such dynamical systems. We argue and show that if circumscribing the antecedent for a necessarily true conditional in such explanations involves making a causal analysis of the problem, then the resulting explanation is not distinctively mathematical or non-causal. Our argument generalises to other dynamical systems that may have purported DMEs analogous to the one proposed by Lange, and even to some other counterfactual accounts of non-causal explanation given by Reutlinger and Rice.

Dystopian or Utopian? Two Images of Alan Turing

Gonçalves, Bernardo (2020) Dystopian or Utopian? Two Images of Alan Turing. [Preprint]