scholarly journals Negative energy densities in extended sources generating closed timelike curves in general relativity with and without torsion

1994 ◽  
Vol 49 (2) ◽  
pp. 1124-1125 ◽  
Author(s):  
Harald H. Soleng
Keyword(s):  
General Relativity ◽  
Negative Energy ◽  
Closed Timelike Curves ◽  
Extended Sources

scholarly journals String clouds and radiation flows as sources of gravity in static or rotating cylinders

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040004 ◽  
Author(s):  
K. A. Bronnikov
Keyword(s):  
General Relativity ◽  
Cosmic Strings ◽  
Stationary Solutions ◽  
Negative Energy ◽  
Closed Timelike Curves ◽  
Negative Energy Density ◽  
Cylindrically Symmetric ◽  
All Solutions ◽  
Static Solutions ◽  
Almost All

Static and stationary cylindrically symmetric space-times in general relativity are considered, supported by distributions of cosmic strings stretched in the azimuthal ([Formula: see text]), longitudinal ([Formula: see text]) or radial ([Formula: see text]) directions or and by pairs of mutually opposite radiation flows in any of these directions. For such systems, exact solutions are obtained and briefly discussed, except for radial strings (a stationary solution for them is not found); it is shown that static solutions with [Formula: see text]- and [Formula: see text]-directed radiation flows do not exist while for [Formula: see text]-directed strings a solution is only possible with negative energy density. Almost all solutions under discussion contain singularities, and all stationary solutions have regions with closed timelike curves, hence, most probably, only their well-behaved regions admit application to real physical situations.

scholarly journals Kodama Time, Entropy Bounds, the Raychaudhuri  Equation, and the Quantum Interest Conjecture

2021 ◽  
Author(s):  
◽  
Gabriel Abreu
Keyword(s):  
General Relativity ◽  
Coordinate System ◽  
Negative Energy ◽  
Specific Form ◽  
Einstein Equations ◽  
Surface Gravity ◽  
Quantum Field ◽  
Raychaudhuri Equation ◽  
Dimensional Minkowski Space ◽  
Entropy Bounds

<p>General Relativity, while ultimately based on the Einstein equations, also allows one to quantitatively study some aspects of the theory without explicitly solving the Einstein equations. These geometrical notions of the theory provide an insight to the nature of more general spacetimes. In this thesis, the Raychaudhuri equation, the choice of the coordinate system, the notions of surface gravity and of entropy, and restrictions on negative energy densities on the form of the Quantum Interest Conjecture, will be discussed. First, using the Kodama vector, a geometrically preferred coordinate system is built. With this coordinate system the usual quantities, such as the Riemann and Einstein tensors, are calculated. Then, the notion of surface gravity is generalized in two different ways. The first generalization is developed considering radial ingoing and outgoing null geodesics, in situations of spherical symmetry. The other generalized surface gravity is a three-vector obtained from the spatial components of the redshifted four acceleration of a suitable set of fiducial observers. This vectorial surface gravity is then used to place a bound on the entropy of both static and rotating horizonless objects. This bound is obtain mostly by classical calculations, with a minimum use of quantum field theory in curved spacetime. Additionally, several improved versions of the Raychaudhuri equation are developed and used in different scenarios, including a two congruence generalization of the equation. Ultimately semiclassical quantum general relativity is studied in the specific form of the Quantum Inequalities, and the Quantum Interest Conjecture. A variational proof of a version of the Quantum Interest Conjecture in (3 + 1)–dimensional Minkowski space is provided.</p>

scholarly journals Kodama Time, Entropy Bounds, the Raychaudhuri  Equation, and the Quantum Interest Conjecture

2021 ◽  
Author(s):  
◽  
Gabriel Abreu
Keyword(s):  
General Relativity ◽  
Coordinate System ◽  
Negative Energy ◽  
Specific Form ◽  
Einstein Equations ◽  
Surface Gravity ◽  
Quantum Field ◽  
Raychaudhuri Equation ◽  
Dimensional Minkowski Space ◽  
Entropy Bounds

<p>General Relativity, while ultimately based on the Einstein equations, also allows one to quantitatively study some aspects of the theory without explicitly solving the Einstein equations. These geometrical notions of the theory provide an insight to the nature of more general spacetimes. In this thesis, the Raychaudhuri equation, the choice of the coordinate system, the notions of surface gravity and of entropy, and restrictions on negative energy densities on the form of the Quantum Interest Conjecture, will be discussed. First, using the Kodama vector, a geometrically preferred coordinate system is built. With this coordinate system the usual quantities, such as the Riemann and Einstein tensors, are calculated. Then, the notion of surface gravity is generalized in two different ways. The first generalization is developed considering radial ingoing and outgoing null geodesics, in situations of spherical symmetry. The other generalized surface gravity is a three-vector obtained from the spatial components of the redshifted four acceleration of a suitable set of fiducial observers. This vectorial surface gravity is then used to place a bound on the entropy of both static and rotating horizonless objects. This bound is obtain mostly by classical calculations, with a minimum use of quantum field theory in curved spacetime. Additionally, several improved versions of the Raychaudhuri equation are developed and used in different scenarios, including a two congruence generalization of the equation. Ultimately semiclassical quantum general relativity is studied in the specific form of the Quantum Inequalities, and the Quantum Interest Conjecture. A variational proof of a version of the Quantum Interest Conjecture in (3 + 1)–dimensional Minkowski space is provided.</p>

scholarly journals SOLUTION TO 2+1 GRAVITY IN DREIBEIN FORMALISM

1994 ◽  
Vol 03 (01) ◽  
pp. 131-137 ◽  
Author(s):  
W.G. UNRUH
Keyword(s):  
General Relativity ◽  
Degrees Of Freedom ◽  
Closed Timelike Curves ◽  
Original Theory ◽  
Arbitrary Genus ◽  
Genus 2 ◽  
Genus Two ◽  
Dynamical Degrees

This paper outlines the reduction of the dreibein formalism of 2+1 General Relativity to the dynamical degrees of freedom for a genus 2 (and by extension for an arbitrary genus) two space. The resulting dynamical variables of the reduced theory are global holonomies and are constants of the motion of the original theory. The relation to geometry and closed timelike curves is briefly described.

scholarly journals CYLINDRICALLY SYMMETRIC SPINNING BRANS–DICKE SPACE–TIMES WITH CLOSED TIMELIKE CURVES

1999 ◽  
Vol 14 (17) ◽  
pp. 1105-1111 ◽  
Author(s):  
LUIS A. ANCHORDOQUI ◽  
SANTIAGO E. PEREZ BERGLIAFFA ◽  
MARTA L. TROBO ◽  
GRACIELA S. BIRMAN
Keyword(s):  
General Relativity ◽  
Exact Solutions ◽  
Cylindrical Symmetry ◽  
Space Time ◽  
Rigid Rotation ◽  
Closed Timelike Curves ◽  
New Exact Solutions ◽  
Cylindrically Symmetric

We present here three new exact solutions of Brans–Dicke theory for a stationary geometry with cylindrical symmetry in the presence of matter in rigid rotation with [Formula: see text]. All the solutions have eternal closed timelike curves in some region of space–time which has a size that depends on ω. Moreover, two of them do not go over a solution of general relativity in the limit ω→∞.

scholarly journals Light Speed Invariant Solution and Its Enlightenment of Field Equation of General Relativity

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Jian Liang Yang
Keyword(s):  
General Relativity ◽  
Gravitational Field ◽  
Field Equation ◽  
Invariant Solution ◽  
Field Approximation ◽  
Weak Field ◽  
Negative Energy ◽  
Precession Angle ◽  
Energy Field ◽  
Light Speed

A systematic examination of the basic theory of general relativity is made, the meaning of coordinates again is emphasized, the confusion caused by unclear meaning of coordinates in the past is corrected, and the expression of the theory is made more accurate. Firstly, the equation of Einstein’s gravitational field is solved in the usual coordinate system, the existence of light speed invariant solution in the spherically symmetric gravitational field is proved, and in the same time, the solution is determined. It turns out that black holes are not an inevitable prediction of general relativity. The more exact formulas for calculating the curvature of light on the surface of the Sun and the precession angle of the orbit of Mercury are given, and the convergence of general relativistic gravity and special relativistic mechanics under the weak field approximation is realized. Finally, it is shown that the coupling coefficient of the gravitational field equation is not unique. Modifying this coefficient is an ideal project to eliminate the singularities of general relativity on the condition keeping the field equation concise and elegant, and moreover, it reveals that dark matter and dark energy are the negative energy field in the matter, the expansion of the universe is the appearance of the gradual formation of galaxies in accordance with fractal rules, not only the space between galaxies is expanding but also the galaxies themselves are also expanding, new matter is continuously generated in the celestial bodies, for the first time, the unity of fractal geometry and cosmic dynamics of general relativity is realized, and the formation and evolution of galaxies are brought into the fractal generation mode. This is a living and vivacious universe in which all aspects are gradually strengthening, in sharp contrast to the dying universe under the current cosmological framework.

scholarly journals CLOSED TIMELIKE CURVES IN CLASSICAL RELATIVITY

2003 ◽  
Vol 12 (09) ◽  
pp. 1705-1708 ◽  
Author(s):  
W. B. BONNOR
Keyword(s):  
General Relativity ◽  
Laboratory Experiments ◽  
Closed Timelike Curves ◽  
Realistic Interpretation ◽  
New Type

Spacetimes of general relativity containing closed timelike curves (CTC) are usually dismissed as non-physical. However, it is now known that CTC may appear in spacetimes modelling simple laboratory experiments, and two such experiments are described in this essay. We therefore need a realistic interpretation of CTC. I suggest that a region containing CTC may represent a new type of singularity, called a torsion singularity.

scholarly journals Replicating the benefits of Deutschian closed timelike curves without breaking causality

2015 ◽  
Vol 1 (1) ◽  
Author(s):  
Xiao Yuan ◽  
Syed M Assad ◽  
Jayne Thompson ◽  
Jing Yan Haw ◽  
Vlatko Vedral ◽  
...  
Keyword(s):  
General Relativity ◽  
Quantum States ◽  
Quantum Computers ◽  
Closed Timelike Curves ◽  
Classical Level ◽  
The Past ◽  
Complete Problems ◽  
Np Complete ◽  
The Many ◽  
Arbitrary Quantum

AbstractIn general relativity, closed timelike curves can break causality with remarkable and unsettling consequences. At the classical level, they induce causal paradoxes disturbing enough to motivate conjectures that explicitly prevent their existence. At the quantum level such problems can be resolved through the Deutschian formalism, however this induces radical benefits—from cloning unknown quantum states to solving problems intractable to quantum computers. Instinctively, one expects these benefits to vanish if causality is respected. Here we show that in harnessing entanglement, we can efficiently solve NP-complete problems and clone arbitrary quantum states—even when all time-travelling systems are completely isolated from the past. Thus, the many defining benefits of Deutschian closed timelike curves can still be harnessed, even when causality is preserved. Our results unveil a subtle interplay between entanglement and general relativity, and significantly improve the potential of probing the radical effects that may exist at the interface between relativity and quantum theory.

On the avoidance of singularities in C -field cosmology

1964 ◽  
Vol 278 (1375) ◽  
pp. 465-478 ◽  
Keyword(s):  
General Relativity ◽  
Energy Density ◽  
Negative Energy ◽  
The Body ◽  
Spherically Symmetric ◽  
Time Singularity ◽  
Negative Energy Density ◽  
Energy Field ◽  
Internal Pressures ◽  
Creation Of Matter

It is well known that a spherically symmetric imploding cold body collapses into a space-time singularity in general relativity. The singularity does not arise, however, in the modification of the theory proposed in C -field cosmology. Although the C -field has been used to represent creation of matter, the prevention of singularities does not depend on the creation property of the field, but on its negative energy density. It does not seem that singularities can be prevented except by a negative energy field. Internal pressures of the ordinary kind fail to provide support against gravitation provided the mass of the body is sufficiently large.

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