Propagation Speed Of Light Research Articles

Black holes, photon sphere, and cosmology in ghost-free [formula omitted] gravity

The improved version of ghost-free f(G) gravity introduced in Nojiri and Odintsov (2005) is proposed and investigated. It is demonstrated that improved ghost-free f(G) gravity may be consistently applied to describe the expanding universe (with horizon) as well as the static spacetime like black holes. Interestingly, such a theory looks like a close avatar of scalar-Einstein–Gauss–Bonnet gravity with the only difference that the scalar field is not a dynamical one so that many predictions of ghost-free f(G) gravity are very similar to that of sEGB gravity.We discuss the gravitational wave in the improved model with the condition that the propagating speed of the gravitational wave is identical to that of the propagation speed of light. A model that describes inflation in the early universe and could satisfy the observational constraints is also constructed. The solution of ghost-free f(G) gravity realising the given static spacetime with spherical symmetry is proposed. Some of such solutions realise explicitly the Reissner–Nordström black hole or the Hayward black hole, which is a regular black hole without curvature singularity, We also construct a black hole in our theory which contains the Arnowitt–Deser–Misner (ADM) mass, the horizon radius, and the radius of the photon sphere as independent parameters. The radius of the black hole shadow in this model as well as photon sphere radius are estimated. It is shown that there exists a parameter region which satisfies the constraints coming from Event Horizon Telescope observations. Furthermore, we construct model where the radius of the black hole shadow or photon orbit is smaller than the horizon radius supposed from the ADM mass.

Responsive refractive index sensor based on actively tuning liquid crystal topological edge states

In this paper, using the electric field regulation and low loss properties of liquid crystal materials, a tunable polarization-separated liquid crystal (LC) topological edge state is proposed, whose potential in responsive sensors (RSs) is explored. Adjustment of the measuring range and sensitivity of the RS can be realized by controlling the orientation angle of LC and the analyte proportion. In the case of a low ratio of analytes, as the LC orientation angle changes from 18° to 0°, the measurement range will also vary from 1–1.8 RIU (refractive index unit) to 1.8–2.3 RIU. When adding the proportion of analytes and the number of periods, the normalized sensitivity will be increased from 0.0759 c/d/RIU (c is the propagation speed of light in vacuum, and d is the normalized thickness) to 0.299 c/d/RIU, leading to a reduction in the detection limit from 2.75 × 10−4 to 5 × 10−6 RIU, so biological indicators such as bacteria Leptospira in rodent urine can be detected.

Round Trip Time (RTT) Delay in the Internet: Analysis and Trends

Both capacity and latency are crucial performance metrics for the optimal operation of most networking services and applications, from online gaming to futuristic holographic-type communications. Networks worldwide have witnessed important breakthroughs in terms of capacity, including fibre introduction everywhere, new radio technologies and faster core networks. However, the impact of these capacity upgrades on end-toend delay is not straightforward as traffic has also grown exponentially. This article overviews the current status of end-toend latency on different regions and continents worldwide and how far these are from the theoretical minimum baseline, given by the speed of light propagation over an optical fibre.We observe that the trend in the last decade goes toward latency reduction (in spite of the ever-increasing annual traffic growth), but still there are important differences between countries.

All-optical image denoising using a diffractive visual processor

Image denoising, one of the essential inverse problems, targets to remove noise/artifacts from input images. In general, digital image denoising algorithms, executed on computers, present latency due to several iterations implemented in, e.g., graphics processing units (GPUs). While deep learning-enabled methods can operate non-iteratively, they also introduce latency and impose a significant computational burden, leading to increased power consumption. Here, we introduce an analog diffractive image denoiser to all-optically and non-iteratively clean various forms of noise and artifacts from input images – implemented at the speed of light propagation within a thin diffractive visual processor that axially spans <250 × λ, where λ is the wavelength of light. This all-optical image denoiser comprises passive transmissive layers optimized using deep learning to physically scatter the optical modes that represent various noise features, causing them to miss the output image Field-of-View (FoV) while retaining the object features of interest. Our results show that these diffractive denoisers can efficiently remove salt and pepper noise and image rendering-related spatial artifacts from input phase or intensity images while achieving an output power efficiency of ~30–40%. We experimentally demonstrated the effectiveness of this analog denoiser architecture using a 3D-printed diffractive visual processor operating at the terahertz spectrum. Owing to their speed, power-efficiency, and minimal computational overhead, all-optical diffractive denoisers can be transformative for various image display and projection systems, including, e.g., holographic displays.

The discussion about the influence of gravitational time dilation on gravity propagation speed and on light propagation speed

In this article, we will demonstrate, based upon strictly logical reasoning, thought experiment examination, and cosmic observations results, how gravitational time dilation exerts influences upon light propagation and upon gravity propagation. Neutron stars mergers have shown that the speed of gravity coincides with the speed of light (c). However, does gravitational time dilation has the same effect upon the propagation of gravity field as it has on light/electric field/magnetic field? The answer to this question can be concluded by examining such a thought experiment: according to E=mc2, it is theoretically possible to transfer an enormous amount of energy to a place near a black hole and create some matter. Once created, the matter will start to generate both gravity field and light and the gravity field and light will propagate in each direction. The light it generates will NEVER enter into the black hole so it will never interact with the black hole, according to observers on the earth. But, according to current cosmic observation results, the gravity field it generates will quickly enter into the black hole and interact with the black hole, according to observers on the earth. Thus, if gravitational time dilation theory is correct, near a black hole, gravity speed is faster than light speed.

The motion of massless “object” and the physical essence and motion law of light

In this paper, the vacuum absolute static reference system is established by analyzing the motion law of massless “object.” Through the understanding of the physical nature of light, this paper reveals three basic laws of motion of light: First, light always moves in a uniform straight line, independent of the motion of the light source. Second, the speed of light propagation in vacuum is constant relative to the absolute reference system of vacuum. Third, the speed of light propagation in the medium remains constant relative to the inertial frame of the medium. Based on this, we have successfully explained the phenomenon of Michelson‐Morley experiment, Fizeau experiment, and light aberration phenomenon that have long troubled the academic community. Finally, we prove that the two basic assumptions on which special relativity is based are wrong, so the Lorentz transformation and its series of inferences, as the core content of special relativity, are not tenable.

Time‐Lapse Image Classification Using a Diffractive Neural Network

Diffractive deep neural networks (D2NNs), comprised of spatially engineered passive surfaces, collectively process optical input information at the speed of light propagation through a thin diffractive volume, without any external computing power. Diffractive networks were demonstrated to achieve all‐optical object classification and perform universal linear transformations. Herein, a “time‐lapse” image classification scheme using a diffractive network is demonstrated for the first time, significantly advancing its classification accuracy and generalization performance on complex input objects by using the lateral movements of the input objects and/or the diffractive network, relative to each other. In a different context, such relative movements of the objects and/or the camera are routinely being used for image super‐resolution applications; inspired by their success, a time‐lapse diffractive network is designed to benefit from the complementary information content created by controlled or random lateral shifts. The design space and performance limits of time‐lapse diffractive networks are numerically explored, revealing a blind testing accuracy of 62.03% on the optical classification of objects from the CIFAR‐10 dataset. This constitutes the highest inference accuracy achieved so far using a single diffractive network on the CIFAR‐10 dataset. Time‐lapse diffractive networks will be broadly useful for the spatiotemporal analysis of input signals using all‐optical processors.

Using the average air temperature along the trace for atmospheric correction in laser ranging: accuracy analysis

One of the factors affecting the results of laser ranging measurements on ground-level traces is the difference between the speed of light propagation in the Earth’s atmosphere and the speed of light in vacuum. This difference is accounted for by the introduction of a correction for the mean integral refractive index of air along the measured trace. Research to improve the accuracy of such a correction is one of the most important scientific fields in geodesy and metrology. At the same time, the empirical approach to accounting for the atmospheric influence, which does not have a strict justification, is used in geodetic practice and involves determining the mean integral refractive index by the average air temperature along the measured trace. The paper is dedicated to the analysis of the accuracy of this empirical approach and to the estimation of the possibility of its application for providing traceability in the practice of linear measurements.

TO THE METHOD OF STUDYING THE BASICS OF SPECIAL THEORY OF RELATIVITY

Special Theory of Relativity (STR) is a fundamental physical theory that underlies modern physics andhas enormous worldview potential. At the same time, in the process of teaching (studying) the elementsof STR in school and higher education institutions face a number of problems. These problems areprimarily related to the complex mathematical apparatus that describes it; consideration of imaginarymodel representations that do not really exist in nature; formation of the concept of “event” anddistinguishing under different initial conditions of the concepts of “relative”, “portable” and“absolute” movements, etc. In this regard, it is important to find ways to improve the methodology ofstudying the elements of STR, which is what this article is about.The article offers one of the tested options for studying the main provisions of the special theory ofrelativity in the general course of physics, which is taught in the programs of physical andmathematical specialties of pedagogical universities. The main approaches on which the proposedmethodology is based are the reference to the principle of conformity in the transformation of physicaltheories from their partial cases to more general ones. In this regard, the limits of application ofclassical Galilean-Newton mechanics in the plane of absolutization by this theory of categories of spaceand time, the simultaneity of events in a different frame of reference, the instantaneous transmission ofinteractions between bodies at a distance, etc. are analyzed.The physical meaning of Einstein’s postulates, which underlie the theory of relativity, regarding thespecial status of the speed of light propagation as a natural phenomenon is clarified. On the basis ofthese postulates, the formulas of the Lorentz coordinate and time transformations are deduced. Aconsistent, detailed derivation of the formula for the transition coefficient from the Galilean coordinateand time transformations (for the transition from one inertial frame of reference to another) to theLorentz coordinate and time transformations, which reflects their relativistic content, is given. Theestablishment of these formulas is based on the mathematical apparatus, which corresponds to the levelof school mathematical training of participants in the educational process. Based on the obtainedresults on the formulas of Lorentz transformations, the relativity of the concepts of “duration ofevents”, “time intervals”, “changes in size and shape of bodies”, etc. is demonstrated mathematically,if they are considered in reference systems that are in motion relative to each other.&#x0D; Keywords: classical mechanics; reference system; the principle of relativity; space-time invariant;coordinate and time conversion.

Computer-Free, All-Optical Reconstruction of Holograms Using Diffractive Networks

Reconstruction of in-line holograms of unknown objects in general suffers from twin-image artifacts due to the appearance of an out-of-focus image overlapping with the desired image to be reconstructed. Computer-based iterative phase retrieval algorithms and learning-based methods have been used for the suppression of such image artifacts in digital holography. Here we report an all-optical hologram reconstruction method that can instantly retrieve the image of an unknown object from its in-line hologram and eliminate twin-image artifacts without using a digital processor or a computer. Multiple transmissive diffractive layers are trained using deep learning so that the diffracted light from an arbitrary input hologram is processed all-optically, through light-matter interaction, to reconstruct the image of an unknown object at the speed of light propagation and without the need for any external power. This passive all-optical processor composed of spatially-engineered transmissive layers forms a diffractive network, which successfully generalizes to reconstruct in-line holograms of unknown, new objects and exhibits improved diffraction efficiency as well as extended depth-of-field at the hologram recording distance. This all-optical hologram processor and the underlying design framework can find numerous applications in coherent imaging and holographic display-related applications owing to its major advantages in terms of image reconstruction speed and computer-free operation.

Time-Resolved Far Infrared Light Transport Decomposition for Thermal Photometric Stereo.

We present a novel time-resolved light transport decomposition method using thermal imaging. Because the speed of heat propagation is much slower than the speed of light propagation, the transient transport of far infrared light can be observed at a video frame rate. A key observation is that the thermal image looks similar to the visible light image in an appropriately controlled environment. This implies that conventional computer vision techniques can be straightforwardly applied to the thermal image. We show that the diffuse component in the thermal image can be separated, and therefore, the surface normals of objects can be estimated by the Lambertian photometric stereo. The effectiveness of our method is evaluated by conducting real-world experiments, and its applicability to black body, transparent, and translucent objects is shown.

On the dependence of the speed of light in vacuum on temperature

It is shown that the interaction of the electromagnetic field with the vacuum of the electron-positron field gives rise to dependence of the speed of light propagation on the radiation temperature. Estimation show that in the modern epoch, even at very high temperatures, such for example which exist in the star interiors, the temperature-dependent correction to the speed of light proves to be extremtly small. But in the cosmological model of the hot Universe, in the first instances after the Big Bang the temperature was so high that the speed of light exceeded its present value by many orders of magnitude. The effect of dependence of the speed of light on temperature must be important for understanding the early evolution of the Universe.

Estimating snow depth over Arctic sea ice from calibrated dual-frequency radar freeboards

Abstract. Snow depth on sea ice remains one of the largest uncertainties in sea ice thickness retrievals from satellite altimetry. Here we outline an approach for deriving snow depth that can be applied to any coincident freeboard measurements after calibration with independent observations of snow and ice freeboard. Freeboard estimates from CryoSat-2 (Ku band) and AltiKa (Ka band) are calibrated against data from NASA's Operation IceBridge (OIB) to align AltiKa with the snow surface and CryoSat-2 with the ice–snow interface. Snow depth is found as the difference between the two calibrated freeboards, with a correction added for the slower speed of light propagation through snow. We perform an initial evaluation of our derived snow depth product against OIB snow depth data by excluding successive years of OIB data from the analysis. We find a root-mean-square deviation of 7.7, 5.3, 5.9, and 6.7 cm between our snow thickness product and OIB data from the springs of 2013, 2014, 2015, and 2016 respectively. We further demonstrate the applicability of the method to ICESat and Envisat, offering promising potential for the application to CryoSat-2 and ICESat-2, which launched in September 2018.

Experimental study of the propagation of scintillation light in Liquid Argon

Properties of the propagation of scintillation light in liquid argon (LAr), at λ ∼ 128 nm wavelength, have been experimentally investigated in a dedicated setup at CERN. The speed of scintillation photons has been measured for the first time in this medium, refractive index and the Rayleigh scattering are being studied as well. Such measurement provides a key ingredient for the interpretation of data from the current and next generation large mass LAr detectors as those dedicated to the search for rare events such as neutrinos or Dark Matter. Furthermore the improvement on the understanding of the scintillation light propagation represent a benchmark for the multiple theoretical models and simulations for the next generation of detectors which are now based on still incomplete measurements and calculations. • Measurement of the scintillation light propagation speed in liquid argon. • Optical properties as refractive index and Rayleigh Scattering ( λ =128 nm) are derived. • Measurement of interest for LAr-based large scale future experimental setups. • Results can be used to improve current Monte Carlo simulations.

Research on the speed of light transmission in a dual-frequency laser pumped single fiber with two directions

In this article a general theory of the coherent population oscillation effect in an erbium-doped fiber at room temperature is presented. We use dual pumping light waves with a simplified two-level system. Thus the time delay equations can be calculated from rate equations and the transmission equation. Using numerical simulation, in the case of dual-frequency pump light waves (1480 nm and 980 nm) with two directions, we analyze the influence of the pump power ratio on the group speed of light propagation. In addition, we compare slow light propagation with a single-pumping light and slow light propagation with a dual-pumping light at room temperature. The discussion shows that a larger time delay of slow light propagation can be obtained with a dual-frequency pumping laser. Compared to previous research methods, a dual-frequency laser pumped fiber with two directions is more controllable. Moreover, we conclude that the group velocity of light can be varied by changing the pump ratio.

Optical-density-enhanced squeezed-light generation without optical cavities

To achieve high degree of quantum noise squeezing, an optical cavity is often employed to enhance the interaction time between light and matter. Here, we propose to utilize the effect of coherent population trapping (CPT) to directly generate squeezed light without any optical cavity. Combined with the slow propagation speed of light in a CPT medium, a coherent state passing through an atomic ensemble with a high optical density (OD) can evolve into a highly squeezed state even in a single passage. Our study reveals that noise squeezing of more than $10$ dB can be achieved with an OD of 1,000, which is currently available in experiments. A larger OD can further increase the degree of squeezing. As the light intensity and two-photon detuning are key factors in the CPT interaction, we also demonstrate that the minimum variance at a given OD can be reached for a wide range of these two factors, showing the proposed scheme is flexible and robust. Furthermore, there is no need to consider the phase-matching condition in the CPT scheme. Our introduction of high OD in atomic media not only brings a long light-matter interaction time comparable to optical cavities, but also opens new avenue in the generation of squeezed light for quantum interface.

Computational electrodynamics in material media with constraint-preservation, multidimensional Riemann solvers and sub-cell resolution – Part I, second-order FVTD schemes

While classic finite-difference time-domain (FDTD) solutions of Maxwell's equations have served the computational electrodynamics (CED) community very well, formulations based on Godunov methodology have begun to show advantages. We argue that the formulations presented so far are such that FDTD schemes and Godunov-based schemes each have their own unique advantages. However, there is currently not a single formulation that systematically integrates the strengths of both these major strains of development. While an early glimpse of such a formulation was offered in Balsara et al. [16], that paper focused on electrodynamics in plasma. Here, we present a synthesis that integrates the strengths of both FDTD and Godunov-based schemes into a robust single formulation for CED in material media.Three advances make this synthesis possible. First, from the FDTD method, we retain (but somewhat modify) a spatial staggering strategy for the primal variables. This provides a beneficial constraint preservation for the electric displacement and magnetic induction vector fields via reconstruction methods that were initially developed in some of the first author's papers for numerical magnetohydrodynamics (MHD). Second, from the Godunov method, we retain the idea of upwinding, except that this idea, too, has to be significantly modified to use the multi-dimensionally upwinded Riemann solvers developed by the first author. Third, we draw upon recent advances in arbitrary derivatives in space and time (ADER) time-stepping by the first author and his colleagues. We use the ADER predictor step to endow our method with sub-cell resolving capabilities so that the method can be stiffly stable and resolve significant sub-cell variation in the material properties within a zone.Overall, in this paper, we report a new scheme for numerically solving Maxwell's equations in material media, with special attention paid to a second-order-accurate formulation. Several numerical examples are presented to show that the proposed technique works. Because of its sub-cell resolving ability, the new method retains second-order accuracy even when material permeability and permittivity vary by an order-of-magnitude over just one or two zones. Furthermore, because the new method is also unconditionally stable in the presence of stiff source terms (i.e., in problems involving giant conductivity variations), it can handle several orders-of-magnitude variation in material conductivity over just one or two zones without any reduction of the time–step. Consequently, the CFL depends only on the propagation speed of light in the medium being studied.

The use of metamaterials to control the speed of light propagation in optical structures

In the article we show in the geometric approximation the possibility of slowing down the light propagating along the axis of an optical waveguide structure by using metamaterials as optical structure elements. We study features of light propagation using a plane model of a fiber optic line whose cladding material has a negative refractive index. It is shown that by introducing a metamaterial, the propagation of light waves in the structure can be changed so that the light is decelerated along the structure axis to the extent that it stops, before starting to propagate in the opposite direction. We derive relationships for calculating the delay time as a function of geometrical and optical parameters of the structure, relationships for calculating critical parameters, and conditions for stopping the lighth.

Light Propagation and Photoactuation in Densely Cross-Linked Azobenzene-Functionalized Liquid-Crystalline Polymers: Contribution of Host and Concerted Isomerism

The photomechanical behavior of azobenzene-functionalized liquid-crystalline polymers (azo-LCPs) is closely related to UV light propagation. Here, we report the effect of light absorption by the LC host and the concerted isomerism of azobenzene on this property. In situ measurements of light absorptivity and computer simulations revealed that the light propagation of a liquid-crystalline polymer is affected by the UV absorption of the LC host under the same concerted isomerism of azobenzene. The lower UV light absorption of the LC host results in deeper UV light propagation and a sharper isomerization profile, which eventually induces faster bending when compared to the higher UV light absorption of the LC host. On the other hand, increasing the azobenzene concentration in the polymer greatly decreases the speed of light propagation, which is regarded as one of the factors inhibiting further increases in the bending speed of azo-LCP films.

Experimental demonstration of superluminal space-to-time mapping in long period gratings

We experimentally demonstrate a superluminal space-to-time mapping process in grating-assisted (GA) codirectional coupling devices, particularly fiber long period gratings (LPGs). Through this process, the grating complex (amplitude and phase) apodization profile is directly mapped into the device's temporal impulse response. In contrast to GA counterdirectional couplers, e.g., Bragg gratings, this mapping occurs with a space-to-time scaling factor that is much higher than the propagation speed of light in vacuum. This phenomenon has been used for synthesizing customized complex optical pulse data sequences with femtosecond features (3.5 Tbit/s data rate) using readily feasible fiber LPG designs, e.g., with subcentimeter resolutions.