Space-time Fluctuations Research Articles

High-resolution remote sensing mapping of global land water

Land water, one of the important components of land cover, is the indispensable and important basic information for climate change studies, ecological environment assessment, macro-control analysis, etc. This article describes the overall study on land water in the program of global land cover remote sensing mapping. Through collection and processing of Landsat TM/ETM+, Chinas HJ-1 satellite image, etc., the program achieves an effective overlay of global multi-spectral image of 30 m resolution for two base years, namely, 2000 and 2010, with the image rectification accuracy meeting the requirements of 1: 200000 mapping and the error in registration of images for the two periods being controlled within 1 pixel. The indexes were designed and selected reasonably based on spectral features and geometric shapes of water on the scale of 30 m resolution, the water information was extracted in an elaborate way by combining a simple and easy operation through pixel-based classification method with a comprehensive utilization of various rules and knowledge through the object-oriented classification method, and finally the classification results were further optimized and improved by the human-computer interaction, thus realizing high-resolution remote sensing mapping of global water. The completed global land water data results, including Global Land 30-water 2000 and Global Land 30-water 2010, are the classification results featuring the highest resolution on a global scale, and the overall accuracy of self-assessment is 96%. These data are the important basic data for developing relevant studies, such as analyzing spatial distribution pattern of global land water, revealing regional difference, studying space-time fluctuation law, and diagnosing health of ecological environment.

Thermal property in Brownian motion of a particle coupled to vacuum fluctuations

We investigate Brownian motions of a particle coupled to vacuum fluctuations of a quantum field. The Unruh effect predicts that an observer in an accelerated motion sees the Minkowski vacuum as thermally excited. This addresses the problem of whether a thermal property appears in a perturbative random motion of a particle in an accelerated motion due to the coupling or not. We revisit this problem by solving the equation of motion of a particle coupled to vacuum fluctuations including the radiation reaction force. We compute a Fourier integral for the variance of the random velocity in a rigorous manner. Similarly, we consider a particle coupled to vacuum fluctuations in de Sitter spacetime motivated by the argument that an observer in de Sitter spacetime sees the Bunch-Davies vacuum as a thermally excited state with the Gibbons-Hawking temperature. Our investigation clarifies the condition that the energy equipartition relation arises in the Brownian motions of a particle.

Reducing space-time to binary information

We present a new description of discrete space-time in 1+1 dimensions in terms of a set of elementary geometrical units that represent its independent classical degrees of freedom. This is achieved by means of a binary encoding that is ergodic in the class of space-time manifolds respecting coordinate invariance of general relativity. Space-time fluctuations can be represented in a classical lattice gas model whose Boltzmann weights are constructed with the discretized form of the Einstein–Hilbert action. Within this framework, it is possible to compute basic quantities such as the Ricci curvature tensor and the Einstein equations, and to evaluate the path integral of discrete gravity. The description as a lattice gas model also provides a novel way of quantization and, at the same time, to quantum simulation of fluctuating space-time.

Explaining Holographic Dark Energy

The possible holographic origin of dark energy is investigated. The main existing explanations, namely the UV/IR connection argument of Cohen et al., Thomas’ bulk holography argument, and Ng’s spacetime foam argument, are shown to be not wholly satisfactory. A new explanation is then proposed based on the ideas of Thomas and Ng. It is suggested that dark energy originates from the quantum fluctuations of spacetime limited by the event horizon of the universe. Several potential problems of the explanation are also discussed.

Toward quantum gravity measurement by cold atoms

AbstractWe propose an experiment for the measurement of gravitational effect on cold atoms by applying a one-dimensional vertically sinusoidal oscillation to the magneto-optical trap, and observe the signature of low quantum energy shift of quantum-bound states as a consequence of gravitational fluctuation. To this end, we present brief details of the experiment on a Bose–Einstein condensate (BEC), and a simplistic calculation of the Gross–Pitaevskii solution using the Thomas–Fermi approximation with focus on the density of the BEC for the time-dependent perturbation. Moreover, we calculate the power induced by quantum gravity on a generic atomic ensemble. We also address the possible challenges for the measurement of the expected results. Finally, we discuss the prospect of further developing this experiment toward measuring the effect of quantum spacetime fluctuations on cold atoms.

Bogoliubov space of a Bose–Einstein condensate and quantum spacetime fluctuations

In this work, we consider the role that metric fluctuations could have upon the properties of a Bose–Einstein condensate. In particular, we consider the Bogoliubov space associated with it and show that there are, at least, two independent ways in which the average size of these metric fluctuations could be, experimentally, determined. Indeed, we prove that the pressure and the speed of sound of the ground state define an expression allowing us to determine the average size of these fluctuations. Afterward, an interferometric experiment involving Bogoliubov excitations of the condensate and the pressure (or the speed of sound of the ground state) provides a second and independent way in which this average size could be determined, experimentally.

ANALOGY BETWEEN TURBULENCE AND QUANTUM GRAVITY: BEYOND KOLMOGOROV'S 1941 THEORY

Simple arguments based on the general properties of quantum fluctuations have been recently shown to imply that quantum fluctuations of spacetime obey the same scaling laws of the velocity fluctuations in a homogeneous incompressible turbulent flow, as described by Kolmogorov 1941 (K41) scaling theory. Less noted, however, is the fact that this analogy rules out the possibility of a fractal quantum spacetime, in contradiction with growing evidence in quantum gravity research. In this Note, we show that the notion of a fractal quantum spacetime can be restored by extending the analogy between turbulence and quantum gravity beyond the realm of K41 theory. In particular, it is shown that compatibility of a fractal quantum spacetime with the recent Horava–Lifshitz scenario for quantum gravity, implies singular quantum wavefunctions. Finally, we propose an operational procedure, based on extended self-similarity techniques, to inspect the (multi)-scaling properties of quantum gravitational fluctuations.

Particle Mass from Planck-Scale Fluctuations

In this article we present a theory of particle mass formation. The theory is conceptually based on the ideas that space time fluctuations of very high Planck-scale energy form mass if they exceed a certain threshold value that is a characteristic of the universe. The fluctuations at the length scales that are orders of magnitude smaller than what is currently accessible by direct or indirect experimental methods and of a quantum phenomenonological nature, much inference has to be made of the Planck length scale dynamics that form the observed created particles and their mechanics. Therefore a minimalistic theory should be the starting point, and it is what is proposed here in this rapid communication. Fluctuations of coupled space and time occur, are described statistically and in phase space and therefore are as conjugate variables related by an uncertainty principle the relativistic analogue of the Heisenberg uncertainty principle familiar in low energy quantum mechanics. An information-entropy argument is made for the derivation of the statistical distributions of the fluctuations, that are parametrized by the inverse temperature in order to conveniently connect to thermodynamics. In analogy with 3D 1p time or thermodynamical parameterized condensed matter Schroedinger - like quantum mechanical systems where fluctuations of the system obtain self-energy additional terms to the dispersion relation that describe stable and metastable excitations with mass - like or effective mass, the resulting minimally coupled 4D 1p or 4D-1p equations describing the observed worm-hole mouths obtain self-energy terms to the dispersion relation that derive massive Klein-Gordon - like equations.

Quantum spacetime fluctuations: Lamb shift and hyperfine structure of the hydrogen atom

We consider the consequences of the presence of metric fluctuations upon the properties of a hydrogen atom. Particularly, we introduce these metric fluctuations in the corresponding effective Schr\"odinger equation and deduce the modifications that they entail upon the hyperfine structure related to a hydrogen atom. We will find the change that these effects imply for the ground state energy of the system and obtain a bound for its size comparing our theoretical predictions against the experimental uncertainty reported in the literature. In addition, we analyze the corresponding Lamb shift effect emerging from these fluctuations of spacetime. Once again, we will set a bound to these oscillations resorting to the current experimental outcomes.

No quantum gravity signature from the farthest quasars

Context: Strings and other alternative theories describing the quantum properties of space-time suggest that space-time could present a foamy structure and also that, in certain cases, quantum gravity (QG) may manifest at energies much below the Planck scale. One of the observable effects could be the degradation of the diffraction images of distant sources. Aims: We searched for this degradation effect, caused by QG fluctuations, in the light of the farthest quasars (QSOs) observed by the Hubble Space Telescope with the aim of setting new limits on the fluctuations of the space-time foam and QG models. Methods: We developed a software that estimates and compares the phase variation in the interference patterns of the high-redshift QSOs, taken from the snapshot survey of HST-SDSS, with those of stars that are expected to not be affected by QG effects. We used a two-parameter function to determine, for each test star and QSO, the maximum of the diffraction pattern and to calculate the Strehl ratio. Results: Our results go far beyond those already present in the literature. By adopting the most conservative approach where the correction terms, that describe the possibility for space-time fluctuations cumulating across long distances and partially compensate for the effects of the phase variations, are taken into account. We exclude the random walk model and most of the holographic models of the space-time foam. Without considering these correction terms, all the main QG scenarios are excluded. Finally, our results show the absence of any directional dependence of QG effects and the validity of the cosmological principle with an independent method; that is, viewed on a large scale, the properties of the Universe are the same for all observers, including the effects of space-time fluctuations.

Extreme Physics and Informational/Computational Limits

A sector of the current theoretical physics, even called "extreme physics", deals with topics concerning superstring theories, multiverse, quantum teleportation, negative energy, and more, that only few years ago were considered scientific imaginations or purely speculative physics. Present experimental lines of evidence and implications of cosmological observations seem on the contrary support such theories. These new physical developments lead to informational limits, as the quantity of information, that a physical system can record, and computational limits, resulting from considerations regarding black holes and space-time fluctuations. In this paper I consider important limits for information and computation resulting in particular from string theories and its foundations.

Fluctuations of spacetime and holographic noise in atomic interferometry

Space--time can be understood as some kind of space--time foam of fluctuating bubbles or loops which are expected to be an outcome of a theory of quantum gravity. One recently discussed model for this kind of space--time fluctuations is the holographic principle which allows to deduce the structure of these fluctuations. We review and discuss two scenarios which rely on the holographic principle leading to holographic noise. One scenario leads to fluctuations of the space--time metric affecting the dynamics of quantum systems: (i) an apparent violation of the equivalence principle, (ii) a modification of the spreading of wave packets, and (iii) a loss of quantum coherence. All these effects can be tested with cold atoms. These tests would supplement measurements of a so called ``mystery noise'' at the gravitational wave detector GEO600 which was recently speculated to have its origin in holographic noise.

On the creation of spacetime volume and gravity in loop gravity

Using the 4-simplex and its dual-skeleton spin networks, a quantum transition of pure spacetime is described. The change of vertex volumes between successive steps of the transition of the three-dimensional space woven by spin networks is demonstrated. At the same time, a model of quantum flate fluctuation of the four-dimensional spacetime is given. Employing the excitations created when the loops on the edges of spin network pierce sarfaces, a 2 order symmerric tensor hab is obtained in three-dimensional space. Based on the viewpoint that the spacetime is excitation and transition system, the creation and the change mechanisms of the gravitational field h are investigated.

A NOTE ON THE ANALOGY BETWEEN KOLMOGOROV TURBULENCE AND QUANTUM GRAVITY

Based on a formal analogy between space-time quantum fluctuations and classical Kolmogorov fluid turbulence, we suggest that the dynamic growth of the Universe from Planckian to macroscopic scales should be characterized by the presence of a fluctuating volume-flux (FVF) invariant. The existence of such an invariant could be tested in numerical simulations of quantum gravity, and may also stimulate the development of a new class of hierarchical models of quantum foam, similar to those currently employed in modern phenomenological research on fluid turbulence. The use of such models shows that the simple analogy with Kolmogorov turbulence is not compatible with a fine-scale fractal structure of quantum space-time. Hence, should such theories prove correct, they would imply that the scaling properties of quantum fluctuations of space-time are subtler than those described by the simple Kolmogorov analogy.

New agegraphic dark energy as a rolling tachyon

Combining the general relativity and the uncertainty relation in quantum mechanics, the energy density of quantum fluctuations of space-time can be viewed as dark energy. The so-called agegraphic dark energy model is just based on this viewpoint, in which the age of the universe is introduced as the length measure. Recently, the new agegraphic dark energy model was proposed, where the dynamical dark energy is measured by the conformal age of the universe. On the other hand, scalar-field dark energy models like tachyons are often regarded as an effective description of some underlying theory of dark energy. In this paper, we show that the new agegraphic dark energy can be described completely by a tachyon scalar-field. We thus reconstruct the potential and the dynamics of the tachyon scalar-field, according to the evolution of the new agegraphic dark energy.

RST analysis of MSG-SEVIRI TIR radiances at the time of the Abruzzo 6 April 2009 earthquake

Abstract. Space-time fluctuations of Earth's emitted Thermal Infrared (TIR) radiation have been observed from satellite months to weeks before earthquakes occurrence. The general RST approach has been proposed in order to discriminate normal (i.e. related to the change of natural factor and/or observation conditions) TIR signal fluctuations from anomalous signal transient possibly associated to earthquake occurrence. In this work RST approach is applied to the Abruzzo 6 April 2009 event (ML=5.8) by using for the first time MSG-SEVIRI (Meteosat Second Generation -Spinning Enhanced Visible and Infrared Imager) thermal infrared observations. A validation/confutation analysis has been performed in order to verify the presence/absence of anomalous space-time TIR transients in the presence/absence of significant seismic activity. March–April 2009 has been analyzed for validation purposes. Relatively unperturbed periods (no earthquakes with ML≥5) have been taken for confutation. A specific TIR anomalies space-time persistence analysis as well as a cloud coverage distribution test have been introduced in order to eliminate artifacts and outliers both in the validation and confutation phases. Preliminary results show clear differences in TIR anomalies occurrence during the periods used for validation and confutation purposes. Quite clear TIR anomalies appear also to mark main tectonic lines related to the preparatory phases of others, low magnitude (ML~4) earthquakes, occurred in the area.

Spacetime fluctuations and the spreading of wavepackets

Using a density matrix description in space we study the evolution of wavepackets in a fluctuating spacetime background. We assume that spacetime fluctuations manifest as classical fluctuations of the metric. From the non-relativistic limit of a non-minimally coupled Klein–Gordon equation, we derive a Schrödinger equation with an additive Gaussian random potential. This is transformed into an effective master equation for the density matrix. The solutions of this master equation allow us to study the dynamics of wavepackets in a fluctuating spacetime, depending on the fluctuation scenario. We show how different scenarios alter the diffusion properties of wavepackets.

Dynamics of the Petal-like Patterns in a Liquid Crystal Light Valve with Rotational Optical Feedback

The bifurcation from the static petal pattern to the fluctuating petal pattern in a liquid crystal light valve with optical rotational feedback is investigated experimentally. At a threshold voltage of the bifurcation, rotationally propagating patches arises on the petals. When increasing the applied voltage, the motion of the patches becomes irregular and the pattern develops into space-time fluctuations. By measuring the time correlation function for the major spatial wave numbers, the characteristic features of the spatiotemporal fluctuations are analyzed in detail.

Reduced-order modelling of vortex-induced vibration of catenary riser

A new reduced-order model capable of analyzing the vortex-induced vibration of catenary riser in the ocean current has been developed. This semi analytical–numerical approach is versatile and allows for a significant reduction in computational effort for the analysis of fluid–riser interactions. The incoming current flow is assumed to be steady, uniform, unidirectional and perpendicular to the riser plane of initial equilibrium curvatures. The equations of riser 3-D motion are based on a pinned–pinned, tensioned-beam or flexural cable, modelling which accounts for overall effects of riser bending, extensibility, sag, inclination and structural nonlinearities. The unsteady hydrodynamic forces associated with cross-flow and in-line vibrations are modelled as distributed van der Pol wake oscillators. This hydrodynamic model has been modified in order to capture the effect of varying initial curvatures of the inclined flexible cylinder and to describe the space-time fluctuation of lift and drag forces. Depending on the vortex-excited in-plane/out-of-plane modes and system fluid–structure parameters, the parametric studies are carried out to determine the maximum response amplitudes of catenary risers, along with the occurrence of uni-modal lock-in phenomenon. The obtained results highlight the effect of initial curvatures and geometric nonlinearities on the nonlinear dynamics of riser undergoing vortex-induced vibration.

Analogue Hawking Radiation in a dc-SQUID Array Transmission Line

We propose the use of a superconducting transmission line formed from an array of direct-current superconducting quantum interference devices for investigating analogue Hawking radiation. Biasing the array with a space-time varying flux modifies the propagation velocity of the transmission line, leading to an effective metric with a horizon. Being a fundamentally quantum mechanical device, this setup allows for investigations of quantum effects such as backreaction and analogue space-time fluctuations on the Hawking process.