# 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} }

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…

## 15 Citations

### A Cosmological Basis for E = mc 2

- PhysicsInternational Journal of Modern Physics A
- 2019

The Universe has a gravitational horizon with a radius [Formula: see text] coincident with that of the Hubble sphere. This surface separates null geodesics approaching us from those receding, and as…

### Tantalizing new physics from the cosmic purview

- PhysicsModern Physics Letters A
- 2019

The emergence of a highly improbable coincidence in cosmological observations speaks of a remarkably simple cosmic expansion. Compelling evidence now suggests that the Universe’s gravitational…

### Thermodynamics of the $$R_{\mathrm{h}}=ct$$ Universe: a simplification of cosmic entropy

- Physics
- 2021

In the standard model of cosmology, the Universe began its expansion with an anomalously low entropy, which then grew dramatically to much larger values consistent with the physical conditions at…

### Particle and entropy production in the running vacuum universe

- PhysicsGeneral Relativity and Gravitation
- 2020

We study particle production and the corresponding entropy increase in the context of cosmology with dynamical vacuum. We focus on the particular form that has been called “running vacuum model”…

### Exact model for evaporating primordial black holes in a cosmological spacetime

- PhysicsPhysical Review D
- 2022

Primordial black holes (PBHs) in the mass range 10 17 − 10 23 gm are considered as possible dark matter candidates as they are not subject to big-bang nucleosynthesis constraints and behave like cold…

### Classicalization of Quantum Fluctuations at the Planck Scale in the Rh=ct Universe

- PhysicsPhysics Letters B
- 2021

### Testing viable f(R) models with the angular-diameter distance to compact quasar cores.

- PhysicsPhysical review. D.
- 2019

The results show that, while the most popular f(R) models today are consistent with this measurement to within 1σ, the turning point z max will allow us to prioritize these alternative gravity theories as the measurement precision continues to improve, particularly with regard to how well they mitigate the tension between the predictions of ΛCDM and the observations.

### Fundamentals of Relativistic Cosmology

- Physics
- 2018

This chapter provides a concise introduction to the basic notions of Cosmology. Starting from the Cosmological Principle, the Weyl’s Postulate, and the Einstein’s equations, this chapter goes on to…

### A resolution of the trans‐Planckian problem in the R h = ct universe

- Physics
- 2020

The recent measurement of a cutoff k_min in the fluctuation power spectrum P(k) of the cosmic microwave background may vitiate the possibility that slow-roll inflation can simultaneously solve the…

## References

SHOWING 1-10 OF 49 REFERENCES

### The cosmic horizon

- Physics
- 2007

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

- Physics
- 2012

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

- Physics
- 2013

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

- Physics
- 2012

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

- Physics
- 2016

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

- Physics
- 2009

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

- Physics
- 2011

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

- Physics
- 2009

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

- Physics
- 1996

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

- Physics
- 2016

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,…