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Black Hole Incident, Calcutta, India, 1756.

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There are fundamental problems and tensions in cosmology that suggest that our current formalism for the description of the Universe is the approximation of a better story. The main motivation of this work is related to the efficient resolution of some current cosmological problems associated with the initial conditions of our Universe. With the current formalism, today’s Universe
had to start in an extremely particular state. A minor deviation from its initial conditions would not support the current phenomenological data. In the present work, we study a cosmological model solely based on general relativity, referred to as the reversed black hole Universe. The Universe is modelled by a dust-filled Friedmann model with two extra components. First, the Universe is assumed to be inside a Schwarzschild black hole. Second, observers in the black hole Universe see a time flow that goes in the opposite direction to that of the observers outside the black hole. With time flowing in the opposite direction in the interior, however, the precise fine-tuning of the initial conditions is equivalent, from the exterior, to a Universe which ends up in a very particular final state, which is no longer a problem in itself.

black holes --- cosmological model --- black hole Universe --- reversed time --- reversed black hole Universe model --- Physique, chimie, mathématiques & sciences de la terre > Aérospatiale, astronomie & astrophysique

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The year 2019 saw the centenary of Eddington's eclipse expeditions and the corroboration of Einstein's general relativity by gravitational lensing. To mark the occasion, a Special Issue of Universe has been dedicated to the theoretical aspects of strong gravitational lensing. The articles assembled in this volume contain original research and reviews and apply a variety of mathematical techniques that have been developed to study this effect, both in 3-space and in spacetime. These include: · Mathematical properties of the standard thin lens approximation, in particular caustics; · Optical geometry, the Gauss–Bonnet method and related approaches; · Lensing in the spacetime of general relativity and modified theories; black hole shadows.

Research & information: general --- Mathematics & science --- gravitational lensing --- weak deflection --- dark matter --- Gauss–Bonnet theorem --- black hole --- wormhole --- strong gravitational lensing --- magnification cross sections --- caustics --- gravitational lens --- general relativity --- ultralight particles --- black hole shadow --- event horizon telescope --- rotating black hole --- global monopole --- perfect fluid --- scalar field --- shadows --- black holes --- wormholes --- galaxies

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Astronomical observations have confirmed dark matter's existence, but what exactly is dark matter? Particle physicist Peter Fisher introduces readers to one of the most intriguing frontiers of physics. We cannot actually see dark matter, a mysterious, nonluminous form of matter that is believed to account for about 27 percent of the mass-energy balance in the universe. But we know dark matter is present by observing its ghostly gravitational effects on the behavior and evolution of galaxies. Fisher brings readers quickly up to speed regarding the current state of the dark matter problem, offering relevant historical context as well as a close look at the cutting-edge research focused on revealing dark matter's true nature.

Dark matter (Astronomy) --- Dark matter (Astronomy). --- SCIENCE / Physics / Condensed Matter. --- (MOND). --- Axion. --- Big Bang. --- Black hole. --- Cosmic microwave. --- Cosmology. --- Dark energy. --- Dark matter. --- Fritz Zwicky. --- Galaxy. --- George Smoot. --- Gravitational lensing. --- Gravity. --- Jim Peebles. --- Modified Newtonian Dynamics. --- Primordial black hole. --- Vera Rubin. --- WIMP. --- radiation. --- Nonluminous matter (Astronomy) --- Unobserved matter (Astronomy) --- Unseen matter (Astronomy) --- Interstellar matter

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Dive into a mind-bending exploration of the physics of black holesBlack holes, predicted by Albert Einstein's general theory of relativity more than a century ago, have long intrigued scientists and the public with their bizarre and fantastical properties. Although Einstein understood that black holes were mathematical solutions to his equations, he never accepted their physical reality-a viewpoint many shared. This all changed in the 1960s and 1970s, when a deeper conceptual understanding of black holes developed just as new observations revealed the existence of quasars and X-ray binary star systems, whose mysterious properties could be explained by the presence of black holes. Black holes have since been the subject of intense research-and the physics governing how they behave and affect their surroundings is stranger and more mind-bending than any fiction.After introducing the basics of the special and general theories of relativity, this book describes black holes both as astrophysical objects and theoretical "laboratories" in which physicists can test their understanding of gravitational, quantum, and thermal physics. From Schwarzschild black holes to rotating and colliding black holes, and from gravitational radiation to Hawking radiation and information loss, Steven Gubser and Frans Pretorius use creative thought experiments and analogies to explain their subject accessibly. They also describe the decades-long quest to observe the universe in gravitational waves, which recently resulted in the LIGO observatories' detection of the distinctive gravitational wave "chirp" of two colliding black holes-the first direct observation of black holes' existence.The Little Book of Black Holes takes readers deep into the mysterious heart of the subject, offering rare clarity of insight into the physics that makes black holes simple yet destructive manifestations of geometric destiny.

Black holes (Astronomy) --- Frozen stars --- Compact objects (Astronomy) --- Gravitational collapse --- Stars --- A-frame. --- Acceleration. --- Accretion disk. --- Alice and Bob. --- Angular momentum. --- Astronomer. --- Atomic nucleus. --- Binary black hole. --- Binary star. --- Black hole information paradox. --- Black hole thermodynamics. --- Black hole. --- Calculation. --- Circular orbit. --- Classical mechanics. --- Closed timelike curve. --- Cosmological constant. --- Curvature. --- Cygnus X-1. --- Degenerate matter. --- Differential equation. --- Differential geometry. --- Doppler effect. --- Earth. --- Einstein field equations. --- Electric charge. --- Electric field. --- Electromagnetism. --- Ergosphere. --- Escape velocity. --- Event horizon. --- Excitation (magnetic). --- Frame-dragging. --- Galactic Center. --- General relativity. --- Gravitational acceleration. --- Gravitational collapse. --- Gravitational constant. --- Gravitational energy. --- Gravitational field. --- Gravitational redshift. --- Gravitational wave. --- Gravitational-wave observatory. --- Gravity. --- Hawking radiation. --- Inner core. --- Kerr metric. --- Kinetic energy. --- LIGO. --- Length contraction. --- Lorentz transformation. --- Magnetic field. --- Mass–energy equivalence. --- Maxwell's equations. --- Metric expansion of space. --- Metric tensor. --- Milky Way. --- Minkowski space. --- Negative energy. --- Neutrino. --- Neutron star. --- Neutron. --- Newton's law of universal gravitation. --- No-hair theorem. --- Nuclear fusion. --- Nuclear reaction. --- Orbit. --- Orbital mechanics. --- Orbital period. --- Penrose process. --- Photon. --- Physicist. --- Primordial black hole. --- Projectile. --- Quantum entanglement. --- Quantum gravity. --- Quantum mechanics. --- Quantum state. --- Quasar. --- Ray (optics). --- Rotational energy. --- Roy Kerr. --- Schwarzschild metric. --- Schwarzschild radius. --- Solar mass. --- Special relativity. --- Star. --- Stellar mass. --- Stephen Hawking. --- Stress–energy tensor. --- String theory. --- Supermassive black hole. --- Temperature. --- Theory of relativity. --- Thought experiment. --- Tidal force. --- Time dilation. --- Wavelength. --- White hole. --- Wormhole.