  In an effective field theory model with an ultraviolet momentum cutoff, there
is a relation between the effective equation of state of dark energy and the
ultraviolet cutoff scale. It implies that a measure of the equation of state of
dark energy different from minus one, does not rule out vacuum energy as dark
energy. It also indicates an interesting possibility that precise measurements
of the infrared properties of dark energy can be used to probe the ultraviolet
cutoff scale of effective quantum field theory coupled to gravity. In a toy
model with a vacuum energy dominated universe with a Planck scale cutoff, the
dark energy effective equation of state is -0.96.
