Related papers: About apparent superluminal drives in generic grav…
Warp drives in Einstein's general theory of relativity provide a unique mechanism for manned interstellar travel. It is well-known that the classical superluminal soliton spacetimes require negative energy densities, likely sourced by…
When angular objects in lensing are considered as linear objects, interesting phenomena start happening. Tachyonic caustics are one example. We review that the intrinsic variables of the lens equation are angular variables. We argue that…
In general relativity (GR) no observer is physically privileged. As a strict consequence, it can be shown that the physical generation of gravitational waves (GW's) is quite impossible.
While General Relativity ranks undoubtedly among the best physics theories ever developed, it is also among those with the most striking implications. In particular, General Relativity admits solutions which allow faster than light motion…
We first take a closer look at the original warp drive proposal by Alcubierre, examine its kinematics in the context of a covariant 3+1 setting, and explain some drawbacks of this construction. In this model, changes of the velocity profile…
A recent paper by Ahluwalia-Khalilova (astro-ph/0601489) is examined where he claims that the standard FRW cosmology with a $\Lambda$ predicts existence of dark matter without invoking the data on galactic rotation curves and gravitational…
We construct the Green-Schwarz terms of six-dimensional supergravity theories on spacetimes with non-trivial topology and gauge bundle. We prove the cancellation of all global gauge and gravitational anomalies for theories with gauge groups…
A scalar-tensor theory of gravity is formulated in which $G$ and particle masses are allowed to vary. The theory yields a globally static cosmological model with no evolutionary timescales, no cosmological coincidences, and no flatness and…
Warp-drives are solutions of general relativity widely considered unphysical due to high negative energy requirements. While the majority of the literature has focused on macroscopic solutions towards the goal of interstellar travel, in…
In the present work some generalizations of the Hawking singularity theorems in the context of $f(R)$ theories are presented. The assumptions are of these generalized theorems is that the matter fields satisfy the conditions…
I show how a minor modification of the Alcubierre geometry can dramatically improve the total energy requirements for a `warp bubble' that can be used to transport macroscopic objects. A spacetime is presented for which the total negative…
In General Relativity without a cosmological constant a non-positive contribution from the space-time geometry to Raychaudhuri equation is found provided that particular energy conditions are assumed and regardless the considered solution…
In this paper the problem of the quantum stability of the two-dimensional warp drive spacetime moving with an apparent faster than light velocity is considered. We regard as a maximum extension beyond the event horizon of that spacetime its…
A number of theories of gravity have been proposed as proxies for dark matter in the regime of galaxies and cosmology. The recent observations of gravitational waves (GW170817) from the merger of two neutron stars, followed by an…
We derive general conditions under which geodesics of stationary spacetimes resemble trajectories of charged particles in an electromagnetic field. For large curvatures (analogous to strong magnetic fields), the quantum mechanicical states…
We discuss the possibility of obtaining the present acceleration of the universe via f(R) gravity theories which recently attracted much attention. It is known that f(R) theories generally have room for this. In this work we stress that the…
The direct detection of gravitational waves (GWs) is an invaluable new tool to probe gravity and the nature of cosmic acceleration. A large class of scalar-tensor theories predict that GWs propagate with velocity different than the speed of…
We propose an alternative theory of gravity which assumes that background geometry of the Universe is fixed four dimensional Euclidean space and gravity is a vector field $A_k$ in this space which breaks the Euclidean symmetry. Direction of…
As an alternative to dark energy that explains the observed acceleration of the universe, it has been suggested that we may be at the center of an inhomogeneous isotropic universe described by a Lemaitre-Tolman-Bondi (LTB) solution of…
We investigate here the local versus global visibility of a space-time singularity formed due to the gravitational collapse of a spherically symmetric dust cloud having a non-zero velocity function. The conditions are investigated that…