  Standard cosmology has long been plagued by a number of persistent problems.
The origin of the apparent acceleration of the cosmic expansion remains
enigmatic. The cosmological constant has been reintroduced as a free parameter
with a value in energy density units that ``happens'' to be of the same order
as the present matter energy density. There is an internal inconsistency with
regards to the Hubble constant, the so-called $H_0$ tension. The derived value
of $H_0$ depends on the type of data that is used. With supernovae as standard
candles one gets a $H_0$ that is 4-5 $\sigma$ larger than the value that one
gets from CMB (Cosmic Microwave Background) data for the early universe. Here
we show that these problems are related and can be solved if the cosmological
constant represents a covariant integration constant that arises from a spatial
boundary condition, instead of being a new type of hypothetical physical field,
``dark energy'', as assumed by standard cosmology. The boundary condition only
applies to the bounded 3D subspace that represents the observable universe, the
hypersurface of the past light cone.
