Search results for "Spacetime"
showing 9 items of 159 documents
Seeing reality through Einstein's eyes: a teaching proposal for special relativity
2021
The teaching of Special Relativity is still a critical issue not only for students but also for teachers. In this paper, we describe the trial of a learning unit on the Special Relativity topic based on Minkowski's approach through spacetime diagrams, following the results in pedagogical researches in this field. The main innovation of our project consists of a mechanical instrument: it allows to physically and mechanically represent Lorentz’s transformations by hands, exploring the effects of a change of the reference frame. Teachers and students can deal “by eye” with unusual phenomena as the loss of simultaneity, time dilation, length contraction, relativistic addition of velocities and …
Thermodynamic class II Szekeres-Szafron solutions. Singular models
2019
A family of parabolic Szekeres-Szafron class II solutions in local thermal equilibrium is studied and their associated thermodynamics are obtained. The subfamily with the hydrodynamic behavior of a generic ideal gas (defined by the equation of state $p = k n \Theta$) results to be an inhomogeneous generalization of flat FLRW $\gamma$-law models. Three significative interpretations that follow on from the choice of three specific thermodynamic schemes are analyzed in depth. First, the generic ideal gas in local thermal equilibrium; this interpretation leads to an inhomogeneous temperature $\Theta$. Second, the thermodynamics with homogeneous temperature considered by Lima and Tiomno (CQG 6 1…
A Numbers-Based Approach to a Free Particle's Spacetime
2020
A possibility is proposed to define the proper spacetime of a free nonzerorest- mass m_0 particle based on the connection of its lasting proper time to an open sequence of natural numbers counting de Broglie time periods (h/c^2)(m^(-1)_ 0 ) [see R. Ferber, A Missing Link: What is Behind de Broglie's" Periodic Phenomenon"?, Foundations of Physics Letters 9, 575 (1996)]. It is suggested to define a set of twodirectional intervals of the particle's proper space (proper distances) following the construction of positive and negative integers from the ordered pairs of the natural numbers, which belong to the sequence 1, 2, ..., n defining the elapsed interval of de Broglie time t_n. Corresponding…
Handling of Small Scale Structures of the Irradiance Field for Solar Energy System Analysis – A Review
2016
Abstract Satellite derived irradiance information currently approaches a status as standard input for solar energy system analysis. Due to intrinsic limitations in spatial and temporal resolution, these data fail to give information of the full dynamics of the irradiance field in space and time. The analysis of systems with sensibility to details of the temporal evolution of the irradiance field and systems with sensibility to the spatial inhomogeneity of the field require knowledge of its fine-structured. Thus, methods for a respective enhancement of the satellite derived data are needed. This contribution presents various approaches discussed for setting up respective input data.
Distributed n-player approachability via time and space average consensus
2012
Abstract In this paper we consider repeated coalitional games with transferable utilities (TU) over networks. Namely, we consider a set of n players that have to distribute among themselves a vector of rewards (one for each player). In our network version there is no coordinator allocating the rewards, but the agents have to agree on a common time-averaged vector by updating the local estimates of the reward vector. The common time-averaged reward vector has to approach a suitable constraint set, called core of the game, that guarantees that no agents benefit from quitting the grand coalition. We propose a doubly (over time and space) averaging distributed algorithm. At every iteration, eac…
Quantum aspects originated by Gravitation: from cosmology to astrophysics
2018
El estudio de campos cuánticos que se propagan en espacio-tiempos clásicos, curvos y dinámicos, ofrece una primera manera de evaluar las consecuencias de la teoría cuántica cuando los fenómenos gravitatorios no son despreciables. Esta es una cuestión importante que debe ser abordada cuando un campo gravitatorio intenso juega un papel principal en la dinámica de un sistema físico, tal como ocurre durante el universo temprano (inflación cósmica) o en la formación de agujeros negros astrofísicos. Una de las características más sorprendentes de esta materia es quizás el hecho de que el cálculo de observables físicos, incluso para campos sin interacción, frecuentemente involucra operadores cuadr…
Pseudospectrum of Reissner-Nordström black holes: Quasinormal mode instability and universality
2021
Black hole spectroscopy is a powerful tool to probe the Kerr nature of astrophysical compact objects and their environment. The observation of multiple ringdown modes in gravitational waveforms could soon lead to high-precision gravitational spectroscopy, so it is critical to understand if the quasinormal mode spectrum is stable against perturbations. It was recently shown that the pseudospectrum can shed light on the spectral stability of black hole quasinormal modes. We study the pseudospectrum of Reissner-Nordstr\"om spacetimes and we find a spectral instability of scalar and gravitoelectric quasinormal modes in subextremal and extremal black holes, extending similar findings for the Sch…
Scattering of Co-Current Surface Waves on an Analogue Black Hole
2018
We report on what is to our knowledge the first scattering experiment of surface waves on an accelerating transcritical flow, which in the analogue gravity context is described by an effective spacetime with a black-hole horizon. This spacetime has been probed by an incident co-current wave, which partially scatters into an outgoing countercurrent wave on each side of the horizon. The measured scattering amplitudes are compatible with the predictions of the hydrodynamical theory, where the kinematical description in terms of the effective metric is exact.
$$\mathscr {K}$$-Convergence of Finite Volume Solutions of the Euler Equations
2020
We review our recent results on the convergence of invariant domain-preserving finite volume solutions to the Euler equations of gas dynamics. If the classical solution exists we obtain strong convergence of numerical solutions to the classical one applying the weak-strong uniqueness principle. On the other hand, if the classical solution does not exist we adapt the well-known Prokhorov compactness theorem to space-time probability measures that are generated by the sequences of finite volume solutions and show how to obtain the strong convergence in space and time of observable quantities. This can be achieved even in the case of ill-posed Euler equations having possibly many oscillatory s…