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Editorial

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3 pages, 175 KiB

Open AccessEditorial

Current Problems and Recent Advances in Wormhole Physics

by Kirill A. Bronnikov and Sergey V. Sushkov

Universe 2023, 9(2), 81; https://doi.org/10.3390/universe9020081 - 2 Feb 2023

Cited by 2 | Viewed by 1585

Abstract

Wormholes are hypothetical space-time tunnels with nontrivial topologies capable of connecting either two distant regions of the same universe or two different universes [...] Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

Research

Jump to: Editorial, Review

12 pages, 588 KiB

Open AccessArticle

On a Class of Harko-Kovacs-Lobo Wormholes

by Ramis Kh. Karimov, Ramil N. Izmailov and Kamal K. Nandi

Universe 2022, 8(10), 540; https://doi.org/10.3390/universe8100540 - 18 Oct 2022

Cited by 1 | Viewed by 978

Abstract

The Harko, Kovács, and Lobo wormhole (HKLWH) metric contains two free parameters: one is the wormhole throat

r_{0}

, and the other is a dimensionless deviation parameter

γ

with values

0 < γ < 1

, the latter ensuring the needed violation [...] Read more.

The Harko, Kovács, and Lobo wormhole (HKLWH) metric contains two free parameters: one is the wormhole throat

r_{0}

, and the other is a dimensionless deviation parameter

γ

with values

0 < γ < 1

, the latter ensuring the needed violation of the null energy condition at the throat. In this paper, we study the energetics of the HKLWH and the influence of

γ

on the tidal forces in the Lorentz-boosted frame. Finally, we apply a new concept, namely, the probabilistic identity of the object observed by different external observers in terms of the Fresnel coefficients derived by Tangherlini. The intriguing result is that observations can differ depending on the location of the observer, i.e., there is a nonzero probability that the HKLWH will be identified as a black hole even when

γ \neq 0

. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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9 pages, 281 KiB

Open AccessArticle

On Possible Origin of an Artificial Wormhole

by Alexander A. Kirillov and Elena P. Savelova

Universe 2022, 8(8), 428; https://doi.org/10.3390/universe8080428 - 19 Aug 2022

Cited by 4 | Viewed by 1230

Abstract

We assume the picture in which a vacuum is filled with virtual wormholes. The presence of external fields changes the distribution of virtual wormholes and, in principle, allows for the creation of a coherent structure that can work as an actual wormhole or [...] Read more.

We assume the picture in which a vacuum is filled with virtual wormholes. The presence of external fields changes the distribution of virtual wormholes and, in principle, allows for the creation of a coherent structure that can work as an actual wormhole or the Alcubierre bubble. We establish the explicit functional relationship between the external field and the distribution of virtual wormholes in vacuum. This opens a way for examining the question about the possibility of the artificial creation of such objects in a laboratory. We show that weak and quasihomogeneous fields suppress the density of wormholes and cannot be used. We also discuss the existence of a threshold for the intensity of an external field beyond which the formation of wormhole-type structures becomes possible. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

25 pages, 1683 KiB

Open AccessArticle

The “ER = EPR” Conjecture and Generic Gravitational Properties: A Universal Topological Linking Model of the Correspondence between Tripartite Entanglement and Planck-Scale Wormholes

by Elias Zafiris and Albrecht von Müller

Universe 2022, 8(3), 189; https://doi.org/10.3390/universe8030189 - 18 Mar 2022

Cited by 1 | Viewed by 3309

Abstract

The “ER = EPR” conjecture, conceived by Maldacena and Susskind, is grounded on the notion that a gravitational theory in the bulk is dual to the corresponding quantum field theory on the boundary in accordance to the AdS/CFT correspondence. The conjecture pertains to [...] Read more.

The “ER = EPR” conjecture, conceived by Maldacena and Susskind, is grounded on the notion that a gravitational theory in the bulk is dual to the corresponding quantum field theory on the boundary in accordance to the AdS/CFT correspondence. The conjecture pertains to the idea that Einstein-Rosen (ER) spacetime bridges and Einstein-Podolsky-Rosen (EPR) quantum entanglement may be considered as dually equivalent. Since ER bridges refer to the connectivity between black holes, the “ER = EPR” conjecture implies that black holes connected by ER bridges are entangled, and conversely, that entangled black holes are connected by ER bridges. However, the instance of the maximally entangled tripartite (GHZ) quantum state points to the necessity of devising a model of non-classical Planck scale ER bridges going beyond the standard description of these bridges in spacetime. Based on the topological structure of the maximally entangled GHZ state, we propose that a universal topological link, called the Borromean rings, furnishes a particular linking structure that is able to unravel the equavalence between entanglement and wormholes, and thus, to address the validity of the “ER = EPR” conjecture beyond the initial context of the AdS/CFT correspondence. As a consequence, we propose the explicit construction of distinguishable extensions of the smooth classical spacetime manifold taking place in the transition to the quantum gravity regime according to a naturally induced physical criterion of gravitational generic properties following from this intrinsic topological qualification of the “ER = EPR” conjecture. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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23 pages, 902 KiB

Open AccessArticle

Black Hole and Wormhole Solutions in Einstein–Maxwell Scalar Theory

by Júlio C. Fabris, Tales Augusto Oliveira Gomes and Denis Campos Rodrigues

Universe 2022, 8(3), 151; https://doi.org/10.3390/universe8030151 - 27 Feb 2022

Cited by 3 | Viewed by 2091

Abstract

We classified and studied the charged black hole and wormhole solutions in the Einstein–Maxwell system in the presence of a massless, real scalar field. The possible existence of charged black holes in general scalar–tensor theories was studied in Bronnikov et al., 1999; black [...] Read more.

We classified and studied the charged black hole and wormhole solutions in the Einstein–Maxwell system in the presence of a massless, real scalar field. The possible existence of charged black holes in general scalar–tensor theories was studied in Bronnikov et al., 1999; black holes and wormholes exist for a negative kinetic term for the scalar field. Using a conformal transformation, the static, spherically symmetric possible structures in the minimal coupled system are described. Besides wormholes and naked singularities, only a restricted class of black hole exists, exhibiting a horizon with an infinite surface and a timelike central singularity. The black holes and wormholes defined in the Einstein frame have some specificities with respect to the non-minimal coupling original frame, which are discussed in the text. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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17 pages, 1804 KiB

Open AccessArticle

Magnetized Dusty Black Holes and Wormholes

by Kirill A. Bronnikov, Pavel E. Kashargin and Sergey V. Sushkov

Universe 2021, 7(11), 419; https://doi.org/10.3390/universe7110419 - 3 Nov 2021

Cited by 8 | Viewed by 1296

Abstract

We consider the generalized Tolman solution of general relativity, describing the evolution of a spherical dust cloud in the presence of an external electric or magnetic field. The solution contains three arbitrary functions

f (R)

,

F (R)

and [...] Read more.

We consider the generalized Tolman solution of general relativity, describing the evolution of a spherical dust cloud in the presence of an external electric or magnetic field. The solution contains three arbitrary functions

f (R)

,

F (R)

and

τ_{0} (R)

, where R is a radial coordinate in the comoving reference frame. The solution splits into three branches corresponding to hyperbolic (

f > 0

), parabolic (

f = 0

) and elliptic (

f < 0

) types of motion. In such models, we study the possible existence of wormhole throats defined as spheres of minimum radius at a fixed time instant, and prove the existence of throats in the elliptic branch under certain conditions imposed on the arbitrary functions. It is further shown that the normal to a throat is a timelike vector (except for the instant of maximum expansion, when this vector is null), hence a throat is in general located in a T-region of space-time. Thus, if such a dust cloud is placed between two empty (Reissner–Nordström or Schwarzschild) space-time regions, the whole configuration is a black hole rather than a wormhole. However, dust clouds with throats can be inscribed into closed isotropic cosmological models filled with dust to form wormholes which exist for a finite period of time and experience expansion and contraction together with the corresponding cosmology. Explicit examples and numerical estimates are presented. The possible traversability of wormhole-like evolving dust layers is established by a numerical study of radial null geodesics. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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15 pages, 761 KiB

Open AccessArticle

Epicyclic Oscillations around Simpson–Visser Regular Black Holes and Wormholes

by Zdeněk Stuchlík and Jaroslav Vrba

Universe 2021, 7(8), 279; https://doi.org/10.3390/universe7080279 - 1 Aug 2021

Cited by 33 | Viewed by 2254

Abstract

We study epicyclic oscillatory motion along circular geodesics of the Simpson–Visser meta-geometry describing in a unique way regular black-bounce black holes and reflection-symmetric wormholes by using a length parameter l. We give the frequencies of the orbital and epicyclic motion in a [...] Read more.

We study epicyclic oscillatory motion along circular geodesics of the Simpson–Visser meta-geometry describing in a unique way regular black-bounce black holes and reflection-symmetric wormholes by using a length parameter l. We give the frequencies of the orbital and epicyclic motion in a Keplerian disc with inner edge at the innermost circular geodesic located above the black hole outer horizon or on the our side of the wormhole. We use these frequencies in the epicyclic resonance version of the so-called geodesic models of high-frequency quasi-periodic oscillations (HF QPOs) observed in microquasars and around supermassive black holes in active galactic nuclei to test the ability of this meta-geometry to improve the fitting of HF QPOs observational data from the surrounding of supermassive black holes. We demonstrate that this is really possible for wormholes with sufficiently high length parameter l. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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14 pages, 769 KiB

Open AccessArticle

Possible Effects of the Fractal Distribution of Relic Wormholes

by Alexander A. Kirillov, Elena P. Savelova and Polina O. Vladykina

Universe 2021, 7(6), 178; https://doi.org/10.3390/universe7060178 - 3 Jun 2021

Cited by 7 | Viewed by 2292

Abstract

We discuss the possibility that the distribution of relic wormholes may possess fractal properties. Relic wormholes and their fractal distributions are predicted in a natural way by lattice quantum gravity models. This provides a new approach to some long standing problems. That is [...] Read more.

We discuss the possibility that the distribution of relic wormholes may possess fractal properties. Relic wormholes and their fractal distributions are predicted in a natural way by lattice quantum gravity models. This provides a new approach to some long standing problems. That is the nature of dark matter phenomena, the origin of Faber-Jackson and Tully-Fisher relations and the observed deficit of baryons. We derive corrections to the Newton’s potential caused by the presence of relic wormholes and show that the analysis of dark matter distribution in galaxies allows us to fix the parameters of the fractal distribution of wormholes. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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13 pages, 1668 KiB

Open AccessArticle

Accretion Flow onto Ellis–Bronnikov Wormhole

by Rosaliya M. Yusupova, Ramis Kh. Karimov, Ramil N. Izmailov and Kamal K. Nandi

Universe 2021, 7(6), 177; https://doi.org/10.3390/universe7060177 - 2 Jun 2021

Cited by 9 | Viewed by 2007

Abstract

Study of accretion onto wormholes is rather rare compared to that onto black holes. In this paper, we consider accretion flow of cosmological dark energy modeled by barotropic fluid onto the celebrated Ellis–Bronnikov wormhole (EBWH) built by Einstein minimally coupled scalar field

ϕ

[...] Read more.

Study of accretion onto wormholes is rather rare compared to that onto black holes. In this paper, we consider accretion flow of cosmological dark energy modeled by barotropic fluid onto the celebrated Ellis–Bronnikov wormhole (EBWH) built by Einstein minimally coupled scalar field

ϕ

, violating the null energy condition. The accreting fluid is assumed to be phantom, quintessence, dust and stiff matter. We begin by first pointing out a mathematical novelty showing how the EBWH can lead to the Schwarzschild black hole under a complex Wick rotation. Then, we analyze the profiles of fluid radial velocity, density and the rate of mass variation of the EBWH due to accretion and compare the profiles with those of the Schwarzschild black hole. We also analyze accretion to the massless EBWH that has zero ADM mass but has what we call nonzero Wheelerian mass (“mass without mass”), composed of the non-trivial scalar field, that shows gravitational effects. Our conclusion is that the mass of SBH due to phantom accretion decreases consistently with known results, while, in contrast, the mass of EBWH increases. Exactly an opposite behavior emerges for non-phantom accretion to these two objects. Accretion to massless EBWH (i.e., to nonzero Wheelerian mass) shares the same patterns as those of the massive EBWH; hence there is no way to distinguish massive and massless cases by means of accretion flow. The contrasting mass variations due to phantom accretion could be a reflection of the distinct topology of the central objects. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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15 pages, 1323 KiB

Open AccessArticle

Astrophysical Wormholes

by Cosimo Bambi and Dejan Stojkovic

Universe 2021, 7(5), 136; https://doi.org/10.3390/universe7050136 - 8 May 2021

Cited by 67 | Viewed by 5902

Abstract

Wormholes are hypothetical topologically-non-trivial structures of spacetime. From the theoretical point of view, the possibility of their existence is challenging but cannot be ruled out. This article is a compact and non-exhaustive review of past and current efforts to search for astrophysical wormholes [...] Read more.

Wormholes are hypothetical topologically-non-trivial structures of spacetime. From the theoretical point of view, the possibility of their existence is challenging but cannot be ruled out. This article is a compact and non-exhaustive review of past and current efforts to search for astrophysical wormholes in the Universe. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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10 pages, 284 KiB

Open AccessCommunication

Determining the Topology and Deflection Angle of Ringholes via Gauss-Bonnet Theorem

by Kimet Jusufi

Universe 2021, 7(2), 44; https://doi.org/10.3390/universe7020044 - 16 Feb 2021

Cited by 2 | Viewed by 1655

Abstract

In this letter, we use a recent wormhole metric known as a ringhole [Gonzalez-Diaz, Phys. Rev. D 54, 6122, 1996] to determine the surface topology and the deflection angle of light in the weak limit approximation using the Gauss-Bonnet theorem (GBT). We [...] Read more.

In this letter, we use a recent wormhole metric known as a ringhole [Gonzalez-Diaz, Phys. Rev. D 54, 6122, 1996] to determine the surface topology and the deflection angle of light in the weak limit approximation using the Gauss-Bonnet theorem (GBT). We apply the GBT and show that the surface topology at the wormhole throat is indeed a torus by computing the Euler characteristic number. As a special case of the ringhole solution, one can find the Ellis wormhole which has the surface topology of a 2-sphere at the wormhole throat. The most interesting results of this paper concerns the problem of gravitational deflection of light in the spacetime of a ringhole geometry by applying the GBT to the optical ringhole geometry. It is shown that, the deflection angle of light depends entirely on the geometric structure of the ringhole geometry encoded by the parameters

b_{0}

and a, being the ringhole throat radius and the radius of the circumference generated by the circular axis of the torus, respectively. As special cases of our general result, the deflection angle by Ellis wormhole is obtained. Finally, we work out the problem of deflection of relativistic massive particles and show that the deflection angle remains unaltered by the speed of the particles. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

33 pages, 7518 KiB

Open AccessArticle

Curvature Invariants for the Alcubierre and Natário Warp Drives

by Brandon Mattingly, Abinash Kar, Matthew Gorban, William Julius, Cooper K. Watson, MD Ali, Andrew Baas, Caleb Elmore, Jeffrey S. Lee, Bahram Shakerin, Eric W. Davis and Gerald B. Cleaver

Universe 2021, 7(2), 21; https://doi.org/10.3390/universe7020021 - 20 Jan 2021

Cited by 10 | Viewed by 3932

Abstract

A process for using curvature invariants is applied to evaluate the metrics for the Alcubierre and the Natário warp drives at a constant velocity. Curvature invariants are independent of coordinate bases, so plotting these invariants will be free of coordinate mapping distortions. As [...] Read more.

A process for using curvature invariants is applied to evaluate the metrics for the Alcubierre and the Natário warp drives at a constant velocity. Curvature invariants are independent of coordinate bases, so plotting these invariants will be free of coordinate mapping distortions. As a consequence, they provide a novel perspective into complex spacetimes, such as warp drives. Warp drives are the theoretical solutions to Einstein’s field equations that allow for the possibility for faster-than-light (FTL) travel. While their mathematics is well established, the visualisation of such spacetimes is unexplored. This paper uses the methods of computing and plotting the warp drive curvature invariants to reveal these spacetimes. The warp drive parameters of velocity, skin depth and radius are varied individually and then plotted to see each parameter’s unique effect on the surrounding curvature. For each warp drive, this research shows a safe harbor and how the shape function forms the warp bubble. The curvature plots for the constant velocity Natário warp drive do not contain a wake or a constant curvature, indicating that these are unique features of the accelerating Natário warp drive. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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9 pages, 236 KiB

Open AccessCommunication

New Scenarios of High-Energy Particle Collisions Near Wormholes

by Oleg B. Zaslavskii

Universe 2020, 6(12), 227; https://doi.org/10.3390/universe6120227 - 30 Nov 2020

Cited by 2 | Viewed by 1382

Abstract

We suggest two new scenarios of high-energy particle collisions in the background of a wormhole. In scenario 1, the novelty consists of the fact that the effect does not require two particles coming from different mouths. Instead, all such scenarios of high energy [...] Read more.

We suggest two new scenarios of high-energy particle collisions in the background of a wormhole. In scenario 1, the novelty consists of the fact that the effect does not require two particles coming from different mouths. Instead, all such scenarios of high energy collisions develop, when an experimenter sends particles towards a wormhole from the same side of the throat. For static wormholes, this approach leads to indefinitely large energy in the center of mass. For rotating wormholes, it makes possible the super-Penrose process (unbounded energies measured at infinity). In scenario 2, one of colliding particles oscillates near the wormhole throat from the very beginning. In this sense, scenario 2 is intermediate between the standard one and scenario 1 since the particle under discussion does not come from infinity at all. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

15 pages, 271 KiB

Open AccessArticle

CPTM Discrete Symmetry, Quantum Wormholes and Cosmological Constant Problem

by Sergey Bondarenko

Universe 2020, 6(8), 121; https://doi.org/10.3390/universe6080121 - 11 Aug 2020

Cited by 9 | Viewed by 1962

Abstract

We discuss the consequences of the charge, parity, time, and mass (CPTM) extended reversal symmetry for the problems of the vacuum energy density and value of the cosmological constant. The results obtained are based on the framework with the separation of extended space-time [...] Read more.

We discuss the consequences of the charge, parity, time, and mass (CPTM) extended reversal symmetry for the problems of the vacuum energy density and value of the cosmological constant. The results obtained are based on the framework with the separation of extended space-time of the interest on the different regions connected by this symmetry with the action of the theory valid for the full space-time and symmetrical with respect to the extended CPTM transformations. The cosmological constant is arising in the model due the gravitational interactions between the different parts of the space-time trough the quantum non-local vertices. It is proposed that the constant’s value depends on the form and geometry of the vertices that glue the separated parts of the extended solution of Einstein equations determining, in turn, its classical geometry. The similarity of the proposed model to the bimetric theories of gravitation is also discussed. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

Review

Jump to: Editorial, Research

40 pages, 1871 KiB

Open AccessReview

Thin-Shell Wormholes in Einstein and Einstein–Gauss–Bonnet Theories of Gravity

by Takafumi Kokubu and Tomohiro Harada

Universe 2020, 6(11), 197; https://doi.org/10.3390/universe6110197 - 26 Oct 2020

Cited by 7 | Viewed by 2029

Abstract

We review recent works on the possibility for eternal existence of thin-shell wormholes on Einstein and Einstein–Gauss–Bonnet gravity. We introduce thin-shell wormholes that are categorized into a class of traversable wormhole solutions. After that, we discuss stable thin-shell wormholes with negative-tension branes in [...] Read more.

We review recent works on the possibility for eternal existence of thin-shell wormholes on Einstein and Einstein–Gauss–Bonnet gravity. We introduce thin-shell wormholes that are categorized into a class of traversable wormhole solutions. After that, we discuss stable thin-shell wormholes with negative-tension branes in Reissner–Nordström–(anti) de Sitter spacetimes in d-dimensional Einstein gravity. Imposing

Z_{2}

symmetry, we construct and classify traversable static thin-shell wormholes in spherical, planar and hyperbolic symmetries. It is found that the spherical wormholes are stable against spherically symmetric perturbations. It is also found that some classes of wormholes in planar and hyperbolic symmetries with a negative cosmological constant are stable against perturbations preserving symmetries. In most cases, stable wormholes are found with the appropriate combination of an electric charge and a negative cosmological constant. However, as special cases, there are stable wormholes even with a vanishing cosmological constant in spherical symmetry and with a vanishing electric charge in hyperbolic symmetry. Subsequently, the existence and dynamical stability of traversable thin-shell wormholes with electrically neutral negative-tension branes is discussed in Einstein–Gauss–Bonnet theory of gravitation. We consider radial perturbations against the shell for the solutions, which have the

Z_{2}

symmetry. The effect of the Gauss–Bonnet term on the stability depends on the spacetime symmetry. Full article

(This article belongs to the Special Issue Recent Advances in Wormhole Physics)

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