Is the Observational Dark Energy Universe Completely a Coincidence?
Abstract:
In this article, we propose a new cosmological model called ‘Fractal Cosmology’ based on two pos- tulates that gives a ‘not really’ answer to the question in the title: At any epoch of the universe, for an arbitrary local observer living well below the scale of Hubble horizon, the observational universe centered on this observer appears to be accelerated expanding. The anthropic principle is thus un- necessary for our current observation of an accelerat ed expanding universe. We will argue how such a story is qualitatively compatible with the CMB and low-redshift observations on the expansion history. Moreover, Fractal Cosmology implies four characteristic signals that could substantially distinguish it from the standard ΛCDM cosmology: 1) Unlike the prediction in ΛCDM, in Fractal Cos mology, the local Hubble rate will be positively correlated with regional matter overdensities. 2) In a conventional expansion history data analysis of modern cosmology, effectively, dynamical dark energy will show phantom behav ior. 3) Over-aged high-redshift astronomical objects/events will generally exist in the observation samples, where ‘over-aged’ specifically means that the astronomi- cally (local physics) derived event age is longer than the ΛCDM predicted universe age at the event redshift. 4) Astronomical events with a characteristic time, for example the type Ia supernovae light curves, are subject to a growing characteristic time scattering (variance) with their redshifts, even after being modulated by the (1 + z) factor expected in standard cosmology; On the contrary, in for example ΛCDM, no known effect would lead to such a redshift-dependent trend of the characteristic time variance of the same type of events. Each of those four signals has either inconclusively shown some hints in recent observation or is feasible to be tested with current and near-future available data.
