Authors: M. Rivera-Tapia, A. Delgado, G. F. Rubilar

The technological refinement of experimental techniques has recently allowed the generation of two-photon polarization entangled states at low Earth orbit, which have been subsequently applied to quantum communications. This achievement paves the way to study the interplay between General Relativity and Quantum Mechanics in new setups. Here, we study the generation of two-photon entangled states via large scale Franson and Hugged interferometric arrays in the presence of a weak gravitational field. We show that for certain configurations of the arrays, an entangled state emerges as a consequence of the gravitational time delay. We also show that the aforementioned arrays generate entanglement and violate the Clauser-Horne-Shymony-Holt inequality under suitable conditions even in the presence of frequency dispersion.

Authors: Jacques Pienaar

Modern approaches to causal modeling give a central role to interventions, which require the active input of an observer and introduces an explicit `causal arrow of time’. Causal models typically adopt a mechanistic interpretation, according to which the direction of the causal arrow is intrinsic to the process being studied. Here we investigate whether the direction of the causal arrow might be a contribution from the observer, rather than an intrinsic property of the process. Working within a counterfactual and non-mechanistic interpretation of causal modeling developed in arXiv:1806.00895, we propose a definition of a `quantum observational scheme’ that we argue characterizes the observer-invariant properties of a causal model. By restricting to quantum processes that preserve the maximally mixed state (unbiasedness) we find that the statistics is symmetric under reversal of the time-ordering. The resulting model can therefore accommodate the idea that the causal arrow is observer-dependent, indicating a route towards reconciling the causal arrow with time-symmetric laws of physics.

Publication date: Available online 22 August 2019

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

Author(s): Peter Mättig, Michael Stöltzner

Publication date: Available online 22 August 2019

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

Author(s): Sophie Ritson

Authors: Aurélien Barrau, Killian Martineau, Flora Moulin, Jean-Frédéric Ngono

The idea that dark matter could be made of stable relics of microscopic black holes is not new. In this article, we revisit this hypothesis, focusing on the creation of black holes by the scattering of trans-planckian particles in the early universe. The only new physics required in this approach is an unusually high energy scale for inflation. We show that dark matter emerges naturally and we study the question of fine-tuning. We finally give some lines of thoughts for a possible detection.

Authors: Stefano Viaggiu

In this paper we continue the investigations in \cite{1} concerning the origin of the cosmological constant. First of all, we generalise the results in \cite{1,2} by considering a continuum approximation for a radiation field in a cosmological background. In this way, we clearly show that the bare cosmological constant is obtained with wanishing temperature $T$ and that the specific heat $C$ is zero at the decoherence scale $L_D$. Moreover, we address the issue to fix the parameters present in our model. In particular, we push forward the analogy between our expression for ${\Lambda}_L$ at a given proper scale $L$ and the one extrapolated by the Casimir effect. As a consequence, we can fix the decoherence scale $L_D$ at which we have the crossover to classicality to be of the order of $\sim 10^{-5}$ meters. This implies that the actual observed value of the cosmological constant is fixed (frozen) at this new physical scale.

Author(s): Minyi Huang, Ray-Kuang Lee, Lijian Zhang, Shao-Ming Fei, and Junde Wu

By embedding a PT-symmetric (pseudo-Hermitian) system into a large Hermitian one, we disclose the relations between PT-symmetric quantum theory and weak measurement theory. We show that the weak measurement can give rise to the inner product structure of PT-symmetric systems, with the preselected st…

[Phys. Rev. Lett. 123, 080404] Published Fri Aug 23, 2019

Abstract

In their article, ‘That is not dead which can eternal lie: the aestivation hypothesis for resolving Fermi’s paradox’, Sandberg et al. try to explain the Fermi paradox (we see no aliens) by claiming that Landauer’s principle implies that a civilization can in principle perform far more ( \({\sim } 10^{30}\) times more) irreversible logical operations (e.g., error-correcting bit erasures) if it conserves its resources until the distant future when the cosmic background temperature is very low. So perhaps aliens are out there, but quietly waiting. Sandberg et al. implicitly assume, however, that computer-generated entropy can only be disposed of by transferring it to the cosmological background. In fact, while this assumption may apply in the distant future, our universe today contains vast reservoirs and other physical systems in non-maximal entropy states, and computer-generated entropy can be transferred to them at the adiabatic conversion rate of one bit of negentropy to erase one bit of error. This can be done at any time, and is not improved by waiting for a low cosmic background temperature. Thus aliens need not wait to be active. As Sandberg et al. do not provide a concrete model of the effect they assert, we construct one and show where their informal argument goes wrong.

Abstract

I apply homotopy type theory (HoTT) to the hole argument as formulated by Earman and Norton. I argue that HoTT gives a precise sense in which diffeomorphism-related Lorentzian manifolds represent the same spacetime, undermining Earman and Norton’s verificationist dilemma and common formulations of the hole argument. However, adopting this account does not alleviate worries about determinism: general relativity formulated on Lorentzian manifolds is indeterministic using this standard of sameness and the natural formalization of determinism in HoTT. Fixing this indeterminism results in a more faithful mathematical representation of general relativity as used by physicists. It also gives a substantive notion of general covariance.

Author(s): Nathaniel Rupprecht and Dervis Can Vural

Nearly all theoretical analyses of Maxwell’s demon focus on its energetic and entropic costs of operation. Here, we focus on its rate of operation. In our model, a demon’s rate limitation stems from its finite response time and gate area. We determine the rate limits of mass and energy transfer, as …

[Phys. Rev. Lett. 123, 080603] Published Thu Aug 22, 2019

Abstract

No evidence of “new physics” was found so far by LHC experiments, and this situation has led some voices in the physics community to call for the abandonment of the “naturalness” criterion, while other scientists have felt the need to break a lance in its defense by claiming that, at least in some sense, it has already led to successes and therefore should not be dismissed too quickly, but rather only reflected or reshaped to fit new needs. In our paper we will argue that present pro-or-contra naturalness debates miss the fundamental point that naturalness, despite contrary claims, is essentially a very hazily defined, in a sense even mythical notion which, in the course of more than four decades, has been steadily, and often not coherently, shaped by its interplay with different branches of model-building in high-energy physics and cosmology on the one side, and new incoming experimental results on the other. In our paper we will endeavor to clear up some of the physical and philosophical haze by taking a closer look back at (real or alleged) origin of naturalness in the 1970s and 1980s, with particular attention to the early work of Kenneth Wilson. In doing this, we aim to bring to light how naturalness belongs to a long tradition of present and past physical and philosophical criteria for effectively guiding theoretical reflection and experimental practice in fundamental research.

Author(s): Antoine Tilloy and Thomas M. Stace

Spontaneous wave-function collapse models, like continuous spontaneous localization, are designed to suppress macroscopic superpositions while preserving microscopic quantum phenomena. An observable consequence of collapse models is spontaneous heating of massive objects. We calculate the collapse-i…

[Phys. Rev. Lett. 123, 080402] Published Wed Aug 21, 2019

Abstract

In this short note I reply to criticisms of an argument in my paper (Healey in Found Phys 48:1568–1589, 2018) that appear in comment (Baumann et al. in Found Phys 49:741–749, 2019). Baumann et al. raise one “main criticism” then go on to claim that the argument of Healey contains a series of problems. But their “main criticism” is not an objection to the argument and the problems are of their own making.

Abstract

In quantum field theory, coherent states can be created that have negative energy density, meaning it is below that of empty space, the free quantum vacuum. If no restrictions existed regarding the concentration and permanence of negative energy regions, it might, for example, be possible to produce exotic phenomena such as Lorentzian traversable wormholes, warp drives, time machines, violations of the second law of thermodynamics, and naked singularities. Quantum Inequalities (QIs) have been proposed that restrict the size and duration of the regions of negative quantum vacuum energy that can be accessed by observers. However, QIs generally are derived for situations in cosmology and are very difficult to test. Direct measurement of vacuum energy is difficult and to date no QI has been tested experimentally. We test a proposed QI for squeezed light by a meta-analysis of published data obtained from experiments with optical parametric amplifiers and balanced homodyne detection. Over the last three decades, researchers in quantum optics have been trying to maximize the squeezing of the quantum vacuum and have succeeded in reducing the variance in the quantum vacuum fluctuations to \(-\,15\) dB. To apply the QI, a time sampling function is required. In our meta-analysis different time sampling functions for the QI were examined, but in all physically reasonable cases the QI is violated by much or all of the measured data. This brings into question the basis for QI. Possible explanations are given for this surprising result.

Authors: K. Urbanowski

The Heisenberg and Mandelstam-Tamm time-energy uncertainty relations are analyzed. The conlusion resulting from this analysis is that within the Quantum Mechanics of Schr\”{o}dinger and von Neumann, the status of these relations can not be considered as the same as the status of the position-momentum uncertainty relations, which are rigorous. The conclusion is that the time–energy uncertainty relations can not be considered as universally valid.

Authors: Manus R. Visser

This dissertation investigates thermodynamic, emergent and holographic aspects of gravity in the context of causal diamonds. We obtain a gravitational first law for causal diamonds in maximally symmetric spacetimes and argue that these diamonds are in thermodynamic equilibrium at negative temperature. Further, gravitational field equations, including higher curvature corrections, are derived from an equilibrium condition on the generalized entropy of small maximally symmetric diamonds. Finally, we assign three holographic microscopic quantities to causal diamonds in spherically symmetric spacetimes, and for non-AdS geometries we interpret them in terms of the long string degrees of freedom of symmetric product conformal field theories.

Authors: Daniel G. Figueroa, Erwin H. Tanin

The expansion history of the Universe between the end of inflation and the onset of radiation-domination (RD) is currently unknown. If the equation of state during this period is stiffer than that of radiation, $w > 1/3$, the gravitational wave (GW) background from inflation acquires a blue-tilt ${d\log\rho_{\rm GW}\over d\log f} = {2(w-1/3)\over (w+1/3)} > 0$ at frequencies $f \gg f_{\rm RD}$ corresponding to modes re-entering the horizon during the stiff-domination (SD), where $f_{\rm RD}$ is the frequency today of the horizon scale at the SD-to-RD transition. We characterized in detail the transfer function of the GW energy density spectrum, considering both ‘instant’ and smooth modelings of the SD-to-RD transition. The shape of the spectrum is controlled by $w$, $f_{\rm RD}$, and $H_{\rm inf}$ (the Hubble scale of inflation). We determined the parameter space compatible with a detection of this signal by LIGO and LISA, including possible changes in the number of relativistic degrees of freedom, and the presence of a tensor tilt. Consistency with upper bounds on stochastic GW backgrounds, however, rules out a significant fraction of the observable parameter space. We find that this renders the signal unobservable by Advanced LIGO, in all cases. The GW background remains detectable by LISA, though only in a small island of parameter space, corresponding to scenarios with an equation of state in the range $0.46 \lesssim w \lesssim 0.56$ and a high inflationary scale $H_{\rm inf} \gtrsim 10^{13}~{\rm GeV}$, but low reheating temperature $1~{\rm MeV} \lesssim T_{\rm RD} \lesssim 150~{\rm MeV}$ (equivalently, $10^{-11}~{\rm Hz} \lesssim f_{\rm RD} \lesssim 3.6\cdot10^{-9}~{\rm Hz}$). Implications for early Universe scenarios resting upon an SD epoch are briefly discussed.