Pressure of Cosmic Voids: A Possible Source for Dark Matter and Dark
  Energy
  The cosmological constant is obtained by considering the surface tension of
vast voids in a void-dominated cosmic fluid by which we can get a possible
unifying solution to both dark matter and dark energy problems. Looking at
voids as bubbles, we define the concept of surface tension which is shown to
have almost constant value at large scale. The surface tensions of the cosmic
voids are computed by dimensional method for galaxies, clusters and
super-clusters with different values for each group. At large scale which vast
voids are dominant the positive cosmological constant obtained of order $
(\simeq+10^{-52} m^{-2})$, which are very close to those given by $Planck$
2018. However, on local scales we are led to a larger cosmological constant $
(\simeq -10^{-49} m^{-2})$ with negative sign. Also, we will show that by
adding the local negative cosmological constant to the Kepler formula, the
velocity rotation curves of the galaxies will flatten out to several tens of
$kpc$, which is consistent with \emph{SPARC} database and justifies dark matter
problem. Finally, the model predicts that galaxies without dark matter should
be in the inner regions of cosmic voids.
