Dark Energy in Light of the Cosmic Horizon

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Discussion Overview

The discussion centers around the implications of dark energy in cosmology, particularly in light of the cosmic horizon as presented in a paper by Fulvio Melia. Participants explore the relationship between dark energy, the universe's expansion, and the age of the universe, while examining the validity of the proposed models against observational data.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • Some participants note that the paper suggests a universe age of ~16.9 billion years, which could resolve several cosmological issues, including the early appearance of supermassive black holes.
  • Others express skepticism about the model, pointing out that it requires a significant energy density of dark energy at recombination, which contradicts observed CMB data.
  • A participant challenges the claim that the proposed model resolves the substructure problem, arguing that it lacks detailed explanation and fails to align with existing observational data.
  • Some participants highlight the methodological concerns in the paper, suggesting that rejecting the LCDM model based on perceived special numbers is not scientifically rigorous.
  • Another viewpoint is that the paper does not introduce new models but critiques existing ones, particularly focusing on the peculiar nature of certain values being significant only at the present time.
  • There is a discussion about whether the proposed model can adequately account for the hierarchical merging of dwarf galaxies, with uncertainty about the sufficiency of the time frame suggested.
  • One participant emphasizes that any new cosmological model must address multiple observational pillars, including distance-redshift measurements, the CMB, and large-scale structure, rather than focusing on a single aspect.
  • Another participant questions the notion of special numbers in cosmology, suggesting that the significance attributed to the number one is based on preconceived notions rather than empirical evidence.

Areas of Agreement / Disagreement

Participants express a mix of skepticism and intrigue regarding the proposed model, with no clear consensus on its validity or implications. Disagreements persist about the adequacy of the model in addressing existing cosmological problems and its alignment with observational data.

Contextual Notes

Participants note limitations in the proposed model's ability to explain all relevant data, particularly concerning the CMB and large-scale structure. There are also unresolved questions about the implications of the cosmic horizon and the assumptions underlying the proposed age of the universe.

  • #31
Recent post on this issue: http://xxx.lanl.gov/abs/1001.4795

Interestingly (and I say so as an author), the time average of the deceleration parameter
appears to be very close to zero.


Through the Looking Glass: Why the "Cosmic Horizon" is not a horizon
Authors: Pim van Oirschot, Juliana Kwan, Geraint F. Lewis
(Submitted on 26 Jan 2010)

Abstract: The present standard model of cosmology, $\Lambda$CDM, contains some intriguing coincidences. Not only are the dominant contributions to the energy density approximately of the same order at the present epoch, but we note that contrary to the emergence of cosmic acceleration as a recent phenomenon, the time averaged value of the deceleration parameter over the age of the universe is nearly zero. Curious features like these in $\Lambda$CDM give rise to a number of alternate cosmologies being proposed to remove them, including models with an equation of state w = -1/3. In this paper, we examine the validity of some of these alternate models and we also address some persistent misconceptions about the Hubble sphere and the event horizon that lead to erroneous conclusions about cosmology.

Comments: Accepted for publication by MNRAS, 6 pages, 3 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1001.4795v1 [astro-ph.CO]
 

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