Can galaxies exist within our particle horizon with Hubble recessional velocities greater than c?

1992 ◽  
Vol 60 (2) ◽  
pp. 142-146 ◽  
Author(s):  
W. M. Stuckey
Keyword(s):  
Particle Horizon

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 On the Necessity of Phantom Fields for Solving the Horizon Problem in Scalar Cosmologies

Universe ◽  
2019 ◽  
Vol 5 (3) ◽  
pp. 76 ◽  
Author(s):  
Davide Fermi ◽  
Massimo Gengo ◽  
Livio Pizzocchero
Keyword(s):  
Arbitrary Dimension ◽  
Energy Conditions ◽  
Solvable Models ◽  
Action Functional ◽  
Spatial Curvature ◽  
Horizon Problem ◽  
Particle Horizon ◽  
Perfect Fluids ◽  
The Universe ◽  
Phantom Fields

We discuss the particle horizon problem in the framework of spatially homogeneous and isotropic scalar cosmologies. To this purpose we consider a Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime with possibly non-zero spatial sectional curvature (and arbitrary dimension), and assume that the content of the universe is a family of perfect fluids, plus a scalar field that can be a quintessence or a phantom (depending on the sign of the kinetic part in its action functional). We show that the occurrence of a particle horizon is unavoidable if the field is a quintessence, the spatial curvature is non-positive and the usual energy conditions are fulfilled by the perfect fluids. As a partial converse, we present three solvable models where a phantom is present in addition to a perfect fluid, and no particle horizon appears.

scholarly journals HOW MANY UNIVERSES DO THERE NEED TO BE?

2006 ◽  
Vol 15 (12) ◽  
pp. 2229-2233 ◽  
Author(s):  
DOUGLAS SCOTT ◽  
J. P. ZIBIN
Keyword(s):  
Cosmological Parameters ◽  
Current Data ◽  
Wilkinson Microwave Anisotropy Probe ◽  
Spatial Curvature ◽  
Observable Universe ◽  
Particle Horizon ◽  
Knowing That ◽  
Density Perturbations ◽  
Best Fit ◽  
The Universe

In the simplest cosmological models consistent with General Relativity, the total volume of the Universe is either finite or infinite, depending on whether or not the spatial curvature is positive. Current data suggest that the curvature is very close to flat, implying that one can place a lower limit on the total volume. In a Universe of finite age, the "particle horizon" defines the patch of the Universe which is observable to us. Based on today's best-fit cosmological parameters it is possible to constrain the number of observable Universe sized patches, NU. Specifically, using the new Wilkinson Microwave Anisotropy Probe (WMAP) data, we can say that there are at least 21 patches out there the same volume as ours, at 95% confidence. Moreover, even if the precision of our cosmological measurements continues to increase, density perturbations at the particle horizon size limit us to never knowing that there are more than about 105 patches out there.

The problems of singularity particle horizon and flatness in quantum cosmology

1983 ◽  
Vol 150 (2) ◽  
pp. 289-306 ◽  
Author(s):  
J.V Narlikar ◽  
T Padmanabhan
Keyword(s):  
Quantum Cosmology ◽  
Particle Horizon

scholarly journals Particle horizon and warped phenomenology

2001 ◽  
Vol 513 (3-4) ◽  
pp. 251-257 ◽  
Author(s):  
Horace Stoica ◽  
S.-H.Henry Tye ◽  
Ira Wasserman
Keyword(s):  
Particle Horizon

The wave vector of light

2018 ◽  
Author(s):  
Nathalie Deruelle ◽  
Jean-Philippe Uzan
Keyword(s):  
Light Source ◽  
Wave Vector ◽  
Light Wave ◽  
Monochromatic Light ◽  
Spectral Shift ◽  
Light Signal ◽  
Particle Horizon ◽  
Alternative Method ◽  
Wave Nature ◽  
Light Signals

This chapter shows how simple world lines of zero length can describe an undulatory aspect of light—namely, its frequency. It first encodes the information about the frequency of a monochromatic light wave in the zeroth component of its wave vector. An alternative method of taking into account the wave nature of light is based on the fact that the emission of successive light corpuscles by the source also defines the period of a light signal. To illustrate, the chapter provides the example of a light source and a receiver moving along the X axis of a frame S. Finally, this chapter illustrates the idea of a particle horizon as well as the limits of validity of the spectral shift formulas introduced in the chapter by the example of two objects which exchange light signals.

scholarly journals Different Faces of Generalized Holographic Dark Energy

Symmetry ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 928
Author(s):  
Shin’ichi Nojiri ◽  
Sergei D. Odintsov ◽  
Tanmoy Paul
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Effective Equation ◽  
Eos Parameter ◽  
Particle Horizon ◽  
The Future ◽  
Expansion Of The Universe ◽  
Entropy Functions ◽  
The Universe ◽  
Future Horizon

In the formalism of generalized holographic dark energy (HDE), the holographic cut-off is generalized to depend upon LIR=LIRLp,L˙p,L¨p,⋯,Lf,L˙f,⋯,a with Lp and Lf being the particle horizon and the future horizon, respectively (moreover, a is the scale factor of the Universe). Based on such formalism, in the present paper, we show that a wide class of dark energy (DE) models can be regarded as different candidates for the generalized HDE family, with respective cut-offs. This can be thought as a symmetry between the generalized HDE and different DE models. In this regard, we considered several entropic dark energy models—such as the Tsallis entropic DE, the Rényi entropic DE, and the Sharma–Mittal entropic DE—and found that they are indeed equivalent with the generalized HDE. Such equivalence between the entropic DE and the generalized HDE is extended to the scenario where the respective exponents of the entropy functions are allowed to vary with the expansion of the Universe. Besides the entropic DE models, the correspondence with the generalized HDE was also established for the quintessence and for the Ricci DE model. In all the above cases, the effective equation of state (EoS) parameter corresponding to the holographic energy density was determined, by which the equivalence of various DE models with the respective generalized HDE models was further confirmed. The equivalent holographic cut-offs were determined by two ways: (1) in terms of the particle horizon and its derivatives, (2) in terms of the future horizon horizon and its derivatives.

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