# The gravitational horizon for a Universe with phantom energy

@article{Melia2012TheGH, title={The gravitational horizon for a Universe with phantom energy}, author={Fulvio Melia}, journal={Journal of Cosmology and Astroparticle Physics}, year={2012}, volume={2012}, pages={029-029} }

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 horizon has been called into question, even for cosmologies with an equation-of-state w≡p/ρ ≥ −1, where p and ρ are the total pressure and energy density, respectively. The claim behind this argument is that its radius Rh does not constitute a limit to our observability when the Universe contains…

## 20 Citations

### The apparent (gravitational) horizon in cosmology

- PhysicsAmerican Journal of Physics
- 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…

### Phantom energy and the Cosmic Horizon: Rh is still not a horizon!

- Physics
- 2013

There has been a recent spate of papers on the Cosmic Horizon, an apparently fundamental, although unrecognised, property of the universe. The misunderstanding of this horizon, it is claimed,…

### 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,…

### The cosmic equation of state

- Physics
- 2014

The cosmic spacetime is often described in terms of the Friedmann-Robertson-Walker (FRW) metric, though the adoption of this elegant and convenient solution to Einstein’s equations does not tell us…

### Cosmological perturbations without inflation

- Physics
- 2016

A particularly attractive feature of inflation is that quantum fluctuations in the inflaton field may have seeded inhomogeneities in the cosmic microwave background (CMB) and the formation of…

### Matter matters: unphysical properties of the Rh = ct universe

- Physics
- 2013

It is generally agreed that there is matter in the universe and, in this paper, we show that the existence of matter is extremely problematic for the proposed Rh = ct universe. Considering a dark…

### Why the Rh = ct cosmology is unphysical and in fact a vacuum in disguise like the milne cosmology

- Physics
- 2014

Recently, Melia and his coworkers have proposed the so-called R_h = ct cosmology where the scale factor of the universe is a(t) ∝ t and the spatial part is flat. This model also implies a fixed…

### Observable vacuum energy is finite in expanding space

- Physics
- 2022

In this work I reason that in expanding space only those quantum modes contribute to the measured vacuum energy that do not transcend the observable volume. Since all quantised ﬁeld modes have…

### On recent claims concerning the Rh = ct Universe

- Physics
- 2015

The R_h=ct Universe is a Friedmann-Robertson-Walker (FRW) cosmology which, like LCDM, assumes the presence of dark energy in addition to (baryonic and non-luminous) matter and radiation. Unlike LCDM,…

### A TEST OF COSMOLOGICAL MODELS USING HIGH-z MEASUREMENTS OF H(z)

- Physics
- 2015

The recently constructed Hubble diagram using a combined sample of SNLS and SDSS-II SNe Ia, and an application of the Alcock–Paczyński (AP) test using model-independent Baryon Acoustic Oscillation…

## References

SHOWING 1-10 OF 25 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…

### CONSTRAINTS ON DARK ENERGY FROM THE OBSERVED EXPANSION OF OUR COSMIC HORIZON

- Physics
- 2009

Within the context of standard cosmology, an accelerating universe requires the presence of a third "dark" component of energy, beyond matter and radiation. The available data, however, are still…

### How does the Hubble sphere limit our view of the Universe

- Physics
- 2012

It has recently been claimed that the Hubble sphere represents a previously unknown limit to our view of the universe, with light we detect today coming from a proper distance less than this ‘cosmic…

### 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.…

### The Rh=ct universe

- Physics
- 2011

The backbone of standard cosmology is the Friedmann-Robertson-Walker solution to Einstein's equations of general relativity (GR). In recent years, observations have largely confirmed many of the…

### Scalar–tensor models of normal and phantom dark energy

- Physics
- 2006

We consider the viability of dark energy (DE) models in the framework of the scalar–tensor theory of gravity, including the possibility of having a phantom DE at small redshifts z as admitted by…

### THE COSMOLOGICAL SPACETIME

- Physics
- 2009

We present here the transformations required to recast the Robertson–Walker metric and Friedmann–Robertson–Walker equations in terms of observer-dependent coordinates for several commonly assumed…

### Through the looking glass: why the 'cosmic horizon' is not a horizon

- Physics
- 2010

The present standard model of cosmology, Λ cold dark matter (ΛCDM), contains some intriguing coincidences. Not only are the dominant contributions to the energy density approximately of the same…

### Detecting dark energy in orbit: The cosmological chameleon

- Physics
- 2004

We show that the chameleon scalar field can drive the current phase of cosmic acceleration for a large class of scalar potentials that are also consistent with local tests of gravity. These provide…