Space-time curvature due to quantum vacuum fluctuations: An alternative
  to dark energy?
  It is pointed out that quantum vacuum fluctuations may give rise to a
curvature of space-time equivalent to the curvature currently attributed to
dark energy. A simple calculation is made, which suggests that the value of the
dark energy density is roughly given by the product of Newton constant time the
quantity m^6 c^4 h^-4, m being a typical mass of elementary particles. The
estimate is compatible with observations.
