  The standard formulation of the cosmological constant problem is based on one
critical assumption---the spacetime is homogeneous and isotropic, which is true
only on cosmological scales. However, this problem is caused by extremely small
scale (Planck scale) quantum fluctuations and at that scale, the spacetime is
highly inhomogeneous and anisotropic. The homogeneous
Friedmann-Lema\^{i}tre-Robertson-Walker metric used in the standard formulation
is inadequate to describe such small scale dynamics of the spacetime. In this
Letter, we reformulate the cosmological constant problem by using a general
inhomogeneous metric. The fine-tuning problem does not arise in the
reformulation since the large gravitational effect of the quantum vacuum is
hidden by small scale spacetime fluctuations. The stress energy tensor
fluctuations of the quantum fields vacuum could serve as "dark energy" to drive
the accelerating expansion of the Universe through a weak parametric resonance
effect.
