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We explore the tripartite entropic uncertainty and genuine tripartite quantumness of Dirac fields in the background of the Garfinkle–Horowitz–Strominger (GHS) dilation space-time. It is interesting to note that Hawking radiation leads to the decay of quantum nonlocality in the physically accessible region while preserving its total coherence. More importantly, it demonstrates an intrinsic trade-off relationship between the coherences of physically accessible and inaccessible regions. Moreover, we examine the effect of Hawking radiation on entropy-based measured uncertainty and find that stronger Hawking radiation causes the uncertainty in physically accessible regions to increase while decreasing the uncertainty in physically inaccessible regions. Therefore, our investigations may be beneficial to a better understanding of the system's quantumness in a curved space-time. Combining relativity theory with quantum information science offers new avenues for comprehending the information paradoxes involving black holes. [ABSTRACT FROM AUTHOR]

In general relativity, gravitational collapse of matter fields ends with the formation of a spacetime singularity, where the matter density becomes infinite and standard physics breaks down. According to the weak cosmic censorship conjecture, singularities produced in the gravitational collapse cannot be seen by distant observers and must be hidden within black holes. The validity of this conjecture is still controversial and at present we cannot exclude that naked singularities can be created in our Universe from regular initial data. In this paper, we study the radiation emitted by a collapsing cloud of dust and check whether it is possible to distinguish the birth of a black hole from the one of a naked singularity. In our simple dust model, we find that the properties of the radiation emitted in the two scenarios is qualitatively similar. That suggests that observational tests of the cosmic censorship conjecture may be very difficult, even in principle. [ABSTRACT FROM AUTHOR]

We consider a free particle in a de Sitter spacetime. We use a picture in which the analogs of the Schrödinger operators of the particle are independent of both the time and the space coordinates. These operators induce operators which are related to Killing vectors of the de Sitter spacetime. [ABSTRACT FROM AUTHOR]

Any spacetime containing a degenerate Killing horizon, such as an extremal black hole, possesses a well-defined notion of a near-horizon geometry. We review such near-horizon geometry solutions in a variety of dimensions and theories in a unified manner. We discuss various general results including horizon topology and near-horizon symmetry enhancement. We also discuss the status of the classification of near-horizon geometries in theories ranging from vacuum gravity to Einstein--Maxwell theory and supergravity theories. Finally, we discuss applications to the classification of extremal black holes and various related topics. Several new results are presented and open problems are highlighted throughout. [ABSTRACT FROM AUTHOR]

We study static spherically symmetric spacetime to describe compact objects with anisotropic matter distribution. We express the system of Einstein field equations as a new system of differential equations using a coordinate transformation, and then write the system in another form with polytropic equation of state and obtain two classes of exact models. The models satisfy all major physical features expected in a realistic star. For polytropic index n = 2, we obtain expressions for mass and density which are comparable with the reported experimental observations. [ABSTRACT FROM AUTHOR]

A conclusion drawn after a conference devoted (in 1995) to the “arrow of time” was the following: “Indeed, it seems not a very great exaggeration to say that the main problem with “the problem of the direction of time” is to figure out exactly what the problem is supposed to be !” What does that mean? That more than 130 years after the work of Ludwig Boltzmann on the interpretation of irreversibility of physical phenomena, and that one century after Einstein’s formulation of Special Relativity, we are still not sure what we mean when we talk of “time” or “arrow of time”. We shall try to show that one source of this difficulty is our tendency to confuse, at least verbally, time and becoming, i.e. the course of time and the arrow of time, two concepts that the formalisms of modern physics are careful to distinguish. [ABSTRACT FROM AUTHOR]

Einstein's field equations are considered for a locally rotationally symmetric Bianchi Type-II space--time in the presence of a massless scalar field with a scalar potential. Exact solutions of scale factors and other physical parameters are obtained by using a special law of variation for Hubble's parameter that yields a constant value of deceleration parameter. To get inflationary solutions, a flat region is considered in which the scalar potential is constant. Power-law and exponential cases are studied and in both solutions there is an anisotropic expansion of the cosmic fluid, but the fluid has vanishing vorticity. A detailed study of geometrical and kinematical properties of solutions has been carried out. [ABSTRACT FROM AUTHOR]

In the present article, we derive the space-time action of the bosonic string in terms of geometrical quantities. First, we study the space-time geometry felt by a probe bosonic string moving in antisymmetric and dilaton background fields. We show that the presence of the antisymmetric field leads to space-time torsion, and the presence of the dilaton field leads to space-time non-metricity. Using these results we obtain the integration measure for space-time with stringy non-metricity, requiring its preservation under parallel transport. We derive the Lagrangian depending on stringy curvature, torsion and non-metricity. [ABSTRACT FROM AUTHOR]

At the beginning of the 20th century, Einstein revolutionized the notions of space and time, first through special relativity and then, a decade later, through general relativity. Conceptual ideas underlying general relativity are explained and its physical ramifications summarized in general terms, without recourse to advanced mathematics. This theory is perhaps the most sublime creation of the human mind. Nonetheless, it has become increasingly clear that it too has serious limitations which can be overcome only through another dramatic revision of our notions of space and time. The article concludes by providing glimpse of what awaits us in the 21st century. [ABSTRACT FROM AUTHOR]

This paper shows that the properties of space-time that constitutes the background of the theory of special relativity, namely its dimensionality, the correct partition of dimensions between one time-type and three space-type dimensions and the Minkowski metrics, may emerge from a set of completely interacting binary units structured by a noise defined in a Landau-type free energy of Fliggs fields and by gauge symmetries, in particular those related to the permutation group of four objects. [ABSTRACT FROM AUTHOR]

I examine the issue of persistence over time in thecontext of the special theory of relativity (SR). Thefour-dimensional ontology of perduring objects isclearly favored by SR. But it is a different questionif and to what extent this ontology is required, andthe rival endurantist ontology ruled out, by thistheory. In addressing this question, I take theessential idea of endurantism, that objects are whollypresent at single moments of time, and argue that itcommits one to unacceptable conclusions regardingcoexistence, in the context of SR. I then propose anddiscuss a plausible account of coexistence forperduring objects, which is free of these defects. This leaves the endurantist room for some maneuvers. I consider them and show that they do not really helpthe endurantist out. She can accommodate the notionof coexistence in the relativistic framework only atthe cost of renouncing central endurantist intuitions. [ABSTRACT FROM AUTHOR]

It is often stated in the physics literature that maximally-spinning Kerr black-hole spacetimes are characterized by near-horizon co-rotating circular geodesics of radius rcircular with the property rcircular→rH+, where rH is the horizon radius of the extremal black hole. Based on the famous Thorne hoop conjecture, in the present compact paper we provide evidence for the existence of a non-trivial lower bound rcircular-rHrH≳(μ/M)1/2 on the radii of circular orbits in the extremal Kerr black-hole spacetime, where μ/M is the dimensionless mass ratio which characterizes the composed black-hole-orbiting-particle system. [ABSTRACT FROM AUTHOR]

We numerically integrate the Einstein’s equations for a spatially flat Friedmann-Lemaire-Robertson-Walker (FLRW) background spacetime with a spatial curvature perturbation and evolving primordial tensor perturbations using the Einstein Toolkit. We find that although the primordial tensor perturbation does not play an important role in the evolution of the overdensity produced by the scalar perturbation, there is an obvious imprint left by the primordial tensor perturbation on the distribution of the fractional density perturbation in the nonlinear region. This imprint may be a possible probe of a gravitational waves background in the future. [ABSTRACT FROM AUTHOR]

The article discusses the string theory known as the anti-de-Sitter space/conformal field theory correspondence which demonstrates an intimate connection between Einstein's general theory of relativity and quantum physics. It is said that string theory might be used to in such far-flung fields as superconductivity and the quark-gluon plasma to explain some properties of exotic matter phases such as some peculiarities of high-temperature superconductors. A study shows that the easiest path to enlightenment on the mysterious phenomena of superconduction and the quark-gluon plasma leads through a black hole, which is a negatively curved space-time with an extra dimension.

Examines the origin and formation of the Universe. Description of the nature of space and time; Combination of general relativity and quantum theory; Determination of atomic structure.