  It is shown that the dark energy presently observed in our universe can be
regarded as the energy of a scalar field driving an inflation-like expansion of
a multiverse with ours being a subuniverse among other parallel universes. A
simple model of this multiverse is elaborated: Assuming closed space geometry,
the origin of the multiverse can be explained by quantum tunneling from
nothing; subuniverses are supposed to emerge from local fluctuations of
separate inflation fields. The standard concept of tunneling from nothing is
extended to the effect that in addition to an inflationary scalar field, matter
is also generated, and that the tunneling leads to an (unstable) equilibrium
state. The cosmological principle is assumed to pertain from the origin of the
multiverse until the first subuniverses emerge. With increasing age of the
multiverse, its spatial curvature decays exponentially so fast that, due to
sharing the same space, the flatness problem of our universe resolves by
itself. The dark energy density imprinted by the multiverse on our universe is
time-dependent, but such that the ratio $w{=}\varrho/(c^2p)$ of its mass
density and pressure (times $c^2$) is time-independent and assumes a value
$-1{+}\epsilon$ with arbitrary $\epsilon{>}0$. $\epsilon$ can be chosen so
small, that the dark energy model of this paper can be fitted to the current
observational data as well as the cosmological constant model.
