scholarly journals Evolution of cosmological horizons of wormhole cosmology

2020 ◽  
Vol 29 (12) ◽  
pp. 2050079
Author(s):  
Sung-Won Kim
Keyword(s):  
Light Cone ◽  
Dynamic Properties ◽  
Field Equations ◽  
The Past ◽  
Particle Horizon ◽  
Proper Distance ◽  
Apparent Horizons ◽  
Spatial Coordinates ◽  
Causal Structures ◽  
Past Light Cone

Recently, we solved Einstein’s field equations to obtain the exact solution of the cosmological model with the Morris–Thorne-type wormhole. We found the apparent horizons and analyzed their geometric natures, including the causal structures. We also derived the Hawking temperature near the apparent cosmological horizon. In this paper, we investigate the dynamic properties of the apparent horizons under the matter-dominated universe and lambda-dominated universe. As a more realistic universe, we also adopt the [Formula: see text]CDM universe which contains both the matter and lambda. The past light cone and the particle horizon are examined for what happens in the case of the model with wormhole. Since the spatial coordinates of the spacetime with the wormhole are limited outside the throat, the past light cone can be operated by removing the smaller-than-wormhole region. The past light cones without wormhole begin to start earlier than the past light cones with wormhole in conformal time-proper distance coordinates. The light cone consists of two parts: the information from our universe and the information from other universe or far distant region through the wormhole. Therefore, the particle horizon distance determined from the observer’s past light cone cannot be defined in a unique way.

scholarly journals Observing relativistic features in large-scale structure surveys – I: Multipoles of the power spectrum

2020 ◽  
Author(s):  
Caroline Guandalin ◽  
Julian Adamek ◽  
Philip Bull ◽  
Chris Clarkson ◽  
L Raul Abramo ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Light Cone ◽  
Large Scale ◽  
Dark Matter Halos ◽  
The Past ◽  
Initial Application ◽  
Correct Estimation ◽  
Number Counts ◽  
Past Light Cone

Abstract Planned efforts to probe the largest observable distance scales in future cosmological surveys are motivated by a desire to detect relic correlations left over from inflation, and the possibility of constraining novel gravitational phenomena beyond General Relativity (GR). On such large scales, the usual Newtonian approaches to modelling summary statistics like the power spectrum and bispectrum are insufficient, and we must consider a fully relativistic and gauge-independent treatment of observables such as galaxy number counts in order to avoid subtle biases, e.g. in the determination of the fNL parameter. In this work, we present an initial application of an analysis pipeline capable of accurately modelling and recovering relativistic spectra and correlation functions. As a proof of concept, we focus on the non-zero dipole of the redshift-space power spectrum that arises in the cross-correlation of different mass bins of dark matter halos, using strictly gauge-independent observable quantities evaluated on the past light cone of a fully relativistic N-body simulation in a redshift bin 1.7 ≤ z ≤ 2.9. We pay particular attention to the correct estimation of power spectrum multipoles, comparing different methods of accounting for complications such as the survey geometry (window function) and evolution/bias effects on the past light cone, and discuss how our results compare with previous attempts at extracting novel GR signatures from relativistic simulations.

scholarly journals Is the Universe homogeneous?

2011 ◽  
Vol 369 (1957) ◽  
pp. 5115-5137 ◽  
Author(s):  
Roy Maartens
Keyword(s):  
Cosmic Microwave Background ◽  
Light Cone ◽  
Space Time ◽  
Gravity Models ◽  
Microwave Background ◽  
The Past ◽  
Galaxy Distribution ◽  
The Galaxy ◽  
The Universe ◽  
Past Light Cone

The standard model of cosmology is based on the existence of homogeneous surfaces as the background arena for structure formation. Homogeneity underpins both general relativistic and modified gravity models and is central to the way in which we interpret observations of the cosmic microwave background (CMB) and the galaxy distribution. However, homogeneity cannot be directly observed in the galaxy distribution or CMB, even with perfect observations, since we observe on the past light cone and not on spatial surfaces. We can directly observe and test for isotropy, but to link this to homogeneity we need to assume the Copernican principle (CP). First, we discuss the link between isotropic observations on the past light cone and isotropic space–time geometry: what observations do we need to be isotropic in order to deduce space–time isotropy? Second, we discuss what we can say with the Copernican assumption. The most powerful result is based on the CMB: the vanishing of the dipole, quadrupole and octupole of the CMB is sufficient to impose homogeneity. Real observations lead to near-isotropy on large scales—does this lead to near-homogeneity? There are important partial results, and we discuss why this remains a difficult open question. Thus, we are currently unable to prove homogeneity of the Universe on large scales, even with the CP. However, we can use observations of the cosmic microwave background, galaxies and clusters to test homogeneity itself.

scholarly journals The volume of the past light-cone and the Paneitz operator

2010 ◽  
Vol 42 (12) ◽  
pp. 2765-2783 ◽  
Author(s):  
Sohyun Park ◽  
R. P. Woodard
Keyword(s):  
Light Cone ◽  
The Past ◽  
Paneitz Operator ◽  
Past Light Cone

CAUSALITY PRINCIPLE AND RETRODICTION IN QUANTUM PHYSICS

1991 ◽  
Vol 06 (21) ◽  
pp. 3843-3852 ◽  
Author(s):  
M.I. SHIROKOV
Keyword(s):  
Quantum Mechanics ◽  
Statistical Physics ◽  
Quantum Physics ◽  
Causality Principle ◽  
Field Equations ◽  
The Past ◽  
Time Arrow ◽  
Time Irreversibility ◽  
Prediction Problems ◽  
Past Light Cone

The causality principle (CP) states that the cause can only be inside the past light cone of an effect. The principle is used in choosing retarded solutions to field equations and also in the Bogoliubov derivation of dispersion relations. However, using CP leads to the following problem: CP determines a “time arrow” in microphysics and shuts out other ways of explaining time irreversibility in Nature (based on statistical physics, cosmology, etc). It is shown that CP can be replaced by the condition that we consider only prediction problems, sometimes together with the use of a principle which is weaker than CP: the cause cannot be outside an effect’s light cones. The retrodiction problem and verification of CP in quantum mechanics are discussed.

scholarly journals Collinder 135 and UBC 7: A physical pair of open clusters

2020 ◽  
Vol 642 ◽  
pp. L4
Author(s):  
Dana A. Kovaleva ◽  
Marina Ishchenko ◽  
Ekaterina Postnikova ◽  
Peter Berczik ◽  
Anatoly E. Piskunov ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Observational Evidence ◽  
Open Clusters ◽  
Line Of Sight ◽  
Kinematic Parameters ◽  
Current Line ◽  
Chance Coincidence ◽  
The Past ◽  
Link Type ◽  
Spatial Coordinates

Context. Given the closeness of the two open clusters Collinder 135 and UBC 7 on the sky, we investigate the possibility that the two clusters are physically related. Aims. We aim to recover the present-day stellar membership in the open clusters Cr 135 and UBC 7 (300 pc from the Sun) in order to constrain their kinematic parameters, ages, and masses and to restore their primordial phase space configuration. Methods. The most reliable cluster members are selected with our traditional method modified for the use of Gaia DR2 data. Numerical simulations use the integration of cluster trajectories backwards in time with our original high-order Hermite4 code φ−GRAPE. Results. We constrain the age, spatial coordinates, velocities, radii, and masses of the clusters. We estimate the actual separation of the cluster centres equal to 24 pc. The orbital integration shows that the clusters were much closer in the past if their current line-of-sight velocities are very similar and the total mass is more than seven times larger than the mass of the most reliable members. Conclusions. We conclude that the two clusters Cr 135 and UBC 7 might very well have formed a physical pair based on the observational evidence as well as numerical simulations. The probability of a chance coincidence is only about 2%.

Time Travelers

2018 ◽  
Vol 3 (4) ◽  
Author(s):  
Alasdair Richmond
Keyword(s):  
Einstein Field Equations ◽  
Field Equations ◽  
The Past

Within Kurt Gödel’s rotating universes, it is possible to revisit the past, a prospect that immediately prompts a sense of paradox. Alasdair Richmond examines the unusual implications of Gödel’s solution of the Einstein field equations.

scholarly journals Cliques Are Bricks for k-CT Graphs

Mathematics ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1160
Author(s):  
Václav Snášel ◽  
Pavla Dráždilová ◽  
Jan Platoš
Keyword(s):  
Complex Networks ◽  
Simplicial Complex ◽  
Dynamic Properties ◽  
Simplicial Complexes ◽  
Many Body ◽  
Chemistry Industry ◽  
The Past ◽  
Pairwise Interactions ◽  
The Many ◽  
Many Body Interactions

Many real networks in biology, chemistry, industry, ecological systems, or social networks have an inherent structure of simplicial complexes reflecting many-body interactions. Over the past few decades, a variety of complex systems have been successfully described as networks whose links connect interacting pairs of nodes. Simplicial complexes capture the many-body interactions between two or more nodes and generalized network structures to allow us to go beyond the framework of pairwise interactions. Therefore, to analyze the topological and dynamic properties of simplicial complex networks, the closed trail metric is proposed here. In this article, we focus on the evolution of simplicial complex networks from clicks and k-CT graphs. This approach is used to describe the evolution of real simplicial complex networks. We conclude with a summary of composition k-CT graphs (glued graphs); their closed trail distances are in a specified range.

scholarly journals THERMODYNAMICS OF BLACK HOLE IN (N+3) DIMENSIONS FROM EUCLIDEAN N-BRANE THEORY

1995 ◽  
Vol 10 (36) ◽  
pp. 2775-2782 ◽  
Author(s):  
ICHIRO ODA
Keyword(s):  
Black Hole ◽  
Event Horizon ◽  
Three Dimensional ◽  
Black Hole Entropy ◽  
Particle Model ◽  
Field Equations ◽  
3 Dimensional ◽  
The Past ◽  
Dimensional Black Hole ◽  
Brane Theory

In this letter we consider an N-brane description of an (N+3)-dimensional black hole horizon. First of all, we start by examining in more detail a previous work where a string theory is used in describing the dynamics of the event horizon of a four-dimensional black hole. This is an attempt to understand the black hole thermodynamics by an effective two-dimensional field theory of the event horizon of a black hole. Then we consider a particle model defined on one-dimensional Euclidean line in a three-dimensional black hole as a target spacetime metric. By solving the field equations we find a “worldline instanton” which connects the past event horizon with the future one. This solution gives us the exact value of the Hawking temperature and to leading order the Bekenstein-Hawking formula of black hole entropy. We also show that this formalism is extensible to an arbitrary spacetime dimension. Finally we make a comment of many recent works of one-loop quantum correction to the black hole entropy.

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