Past light cone shape and refocusing in cosmology, A Response to Michael Rauch’s ‘‘Comments on ‘Lost Horizons’ ’’ [Am. J. Phys. 63, 87 (1995)]

1995 ◽  
Vol 63 (1) ◽  
pp. 88-89 ◽  
Author(s):  
G. F. R. Ellis ◽  
Tony Rothman
Keyword(s):  
Light Cone ◽  
Past Light Cone

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

scholarly journals Radiation from a D-dimensional collision of shock waves: Two-dimensional reduction and Carter–Penrose diagram

2016 ◽  
Vol 25 (09) ◽  
pp. 1641010
Author(s):  
Flávio S. Coelho ◽  
Marco O. P. Sampaio
Keyword(s):  
Shock Waves ◽  
Light Cone ◽  
Causal Structure ◽  
Parametric Representation ◽  
Two Dimensional ◽  
Penrose Diagram ◽  
Hyperbolic Form ◽  
Higher Order Corrections ◽  
Past Light Cone ◽  
Characteristic Coordinates

We analyze the causal structure of the two-dimensional (2D) reduced background used in the perturbative treatment of a head-on collision of two [Formula: see text]-dimensional Aichelburg–Sexl gravitational shock waves. After defining all causal boundaries, namely the future light-cone of the collision and the past light-cone of a future observer, we obtain characteristic coordinates using two independent methods. The first is a geometrical construction of the null rays which define the various light cones, using a parametric representation. The second is a transformation of the 2D reduced wave operator for the problem into a hyperbolic form. The characteristic coordinates are then compactified allowing us to represent all causal light rays in a conformal Carter–Penrose diagram. Our construction holds to all orders in perturbation theory. In particular, we can easily identify the singularities of the source functions and of the Green’s functions appearing in the perturbative expansion, at each order, which is crucial for a successful numerical evaluation of any higher order corrections using this method.

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