How Recent Is Cosmic Acceleration?

Abstract

Possibly the most peculiar expectation of the standard fine-tuned cosmological paradigm is that cosmic acceleration is to only be a very recent (z < 1) phenomenon, with the universe being required to be decelerating at all higher redshifts. Detailed exploration of the Hubble plot out to z = 2 or so will not only provide an absolute test of this expectation but will also allow for testing of conformal gravity, a non fine-tuned alternate cosmological theory which provides equally good fitting to the current z < 1 Hubble plot data while requiring the universe to be accelerating at higher z instead. With both standard and conformal gravity being found to be compatible with a very recently reported z = 1.7 data point, additional data points will thus be needed to determine whether the universe is accelerating or decelerating above z = 1. I. THE HUBBLE PLOT OF STANDARD COSMOLOGYA variety of recent observational measurements [1][2][3][4] have sharply constrained the space available to the standard model cosmological parameters. Specifically, phenomenological data fitting using the standard Einstein-Friedmann cosmological evolution equatioṅ(where Ω M (t) = 8πGρ M (t)/3c 2 H 2 (t) is due to ordinary ρ M (t) ∼ 1/R n (t) matter and where Ω Λ (t) = 8πGΛ/3cH 2 (t) is due to a cosmological constant cΛ) is found to favor current era values Ω M (t 0 ) ≃ 0.3 and Ω Λ (t 0 ) ≃ 0.7, with the current era deceleration parameter q 0 = q(t 0 ) = (n/2 − 1)Ω M (t 0 ) − Ω Λ (t 0 ) then having to be of order −1/2. While these values are very supportive of the flat Ω k (t) = −kc 2 /Ṙ 2 (t) = 1 − Ω M (t) − Ω Λ (t) = 0 inflationary universe paradigm [5], they are nonetheless extremely troubling. Specifically, solving Eq. (1) for ρ M (t) = B/R 3 (t) and k = 0 yields R(t) = (B/cΛ) 1/3 sinh 2/3 (3D 1/2 t/2) where D = 8πGΛ/3c, so that Ω Λ (t) = D/H 2 (t) = 1 − Ω M (t) = tanh 2 (3D 1/2 t/2).(2) *

Revised Concepts for Cosmic Vacuum Energy and Binding Energy: Innovative Cosmology

“…There are also recent studies by Mannheim (2001;2003; in the literature which point into a similar direction. Mannheim (2006) investigates the logical independence of the general covariance principle, the equivalence principle and the Einstein GRT field equations and manifests several restrictions in the present-day formulation of the energy-momentum tensor which can shed light to why at present the standard cosmology is in troubles.…”

Alternatives to dark matter and dark energy

“…of order 0.01 at the current time t 0 39. Such a value for Ω M (t 0 ) is quite close to the critical value Ω M = 1, the value at which the Friedmann equation would require the parameter k to be zero (flat universe) 40.…”

“…Specifically, regardless of the value of k, the use of the above normal matter equations of state in the Friedmann equation leads to the occurrence of a big bang singularity in the early universe, withṘ(t = 0) diverging at t = 0. Near to such a singularity the same Friedmann equation then requires that Ω M (t = 0) be incredibly close to one, again regardless of the choice of k. Then, with Ω M (t = 0) being close to one in the early universe, and with the universe then expanding for an entire Hubble time (1/H (t 0 ) ∼ 10 10 years), it is very hard to39 Since such inventorying does not undercount, 0.01 thus serves as a lower bound on Ω M (t 0 ). 40 It is called the critical value since the sign of the three-curvature k of the universe has the same sign as Ω M (t 0 ) − 1.…”

Fourth order Weyl gravity

“…In the fourth order Weyl theory of gravity [1,2,3,4,5,6,7,8,9], the Einstein-Hilbert action is replaced by a term proportional to the square of the Weyl tensor, and the action of the standard model of particle physics is modified to make it be conformally invariant. For simplicity and following Ref.…”

“…Refs. [7,8,9] argue that Weyl gravity yields a viable model of the acceleration of the Universe, removing the need for dark energy. Further studies of the theory can be found in Refs.…”