The apparent (gravitational) horizon in cosmology

@article{Melia2018TheA,
  title={The apparent (gravitational) horizon in cosmology},
  author={Fulvio Melia},
  journal={American Journal of Physics},
  year={2018}
}
  • F. Melia
  • Published 19 July 2018
  • Physics
  • American Journal of Physics
In general relativity, a gravitational horizon (more commonly known as the “apparent horizon”) is an imaginary surface beyond which all null geodesics recede from the observer. The Universe has an apparent (gravitational) horizon, but unlike its counterpart in the Schwarzschild and Kerr metrics, it is not static. It may eventually turn into an event horizon—an asymptotically defined membrane that forever separates causally connected events from those that are not—depending on the equation of… 

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References

SHOWING 1-10 OF 49 REFERENCES

The cosmic horizon

The cosmological principle, promoting the view that the Universe is homogeneous and isotropic, is embodied within the mathematical structure of the Robertson‐Walker (RW) metric. The equations derived

The gravitational horizon for a Universe with phantom energy

The Universe has a gravitational horizon, coincident with the Hubble sphere, that plays an important role in how we interpret the cosmological data. Recently, however, its significance as a true

Proper size of the visible Universe in FRW metrics with a constant spacetime curvature

In this paper, we continue to examine the fundamental basis for the Friedmann–Robertson–Walker (FRW) metric and its application to cosmology, specifically addressing the question: What is the proper

Photon geodesics in Friedmann–Robertson–Walker cosmologies

The Hubble radius is a particular manifestation of the Universe’s gravitational horizon, Rh(t0) ≡c/H0, the distance beyond which physical processes remain unobservable to us at the present epoch.

Physical basis for the symmetries in the Friedmann–Robertson–Walker metric

Modern cosmological theory is based on the Friedmann–Robertson–Walker (FRW) metric. Often written in terms of co-moving coordinates, this well-known solution to Einstein’s equations owes its elegant

Interpretation of the cosmological metric

The cosmological Robertson–Walker metric of general relativity is often said to have the consequences that (1) the recessional velocity v of a galaxy at proper distance l obeys the Hubble law v=Hl,

The R h = ct universe

The backbone of standard cosmology is the Friedmann–Robertson–Walker solution to Einstein’s equations of general relativity(GR). Inrecent years, observations havelargelyconfirmed many of the

The kinematic origin of the cosmological redshift

A common belief about big-bang cosmology is that the cosmological redshift cannot be properly viewed as a Doppler shift (that is, as evidence for a recession velocity) but must be viewed in terms of

Cosmological Schwarzschild radii and Newtonian gravitational theory

We describe Friedmann–Robertson–Walker zero‐pressure dust‐filled universes using a Schwarzschild‐like curvature spatial coordinate R along with the usual cosmological time coordinate t. In terms of

The zero active mass condition in Friedmann–Robertson–Walker cosmologies

Many cosmological measurements today suggest that the Universe is expanding at a constant rate. This is inferred from the observed age versus redshift relationship and various distance indicators,