  It is argued that many of the problems and ambiguities of standard cosmology
derive from a single one: violation of conservation of energy in the standard
paradigm. Standard cosmology satisfies conservation of local energy, however
disregards the inherent global aspect of energy. We therefore explore
conservation of the quasi-local Misner-Sharp energy within the causal horizon,
which, as we argue, is necessarily an apparent horizon. Misner-Sharp energy
assumes the presence of arbitrary mass-energy. Its conservation, however,
yields "empty" de Sitter (open, flat, closed) as single cosmological solution,
where Misner-Sharp total energy acts as cosmological constant and where the
source of curvature energy is unidentified. It is argued that de Sitter is only
apparently empty of matter. That is, total matter energy scales as curvature
energy in open de Sitter, which causes evolution of the cosmic potential and
induces gravitational time dilation. Curvature of time accounts completely for
the extrinsic curvature, i.e., renders open de Sitter spatially flat. This
explains the well known, surprising, spatial flatness of Misner-Sharp energy,
even if extrinsic curvature is non-zero. The general relativistic derivation
from Misner-Sharp energy is confirmed by a Machian equation of recessional and
peculiar energy, which explicitly assumes the presence of matter. This
relational model enhances interpretation. Time-dilated open de Sitter is
spatially flat, dynamically close to $\Lambda$CDM, and is shown to be without
the conceptual problems of concordance cosmology.
