We consider some formulations of the entropy bounds at the semiclassical
level. The entropy S(V) localized in a region V is divergent in quantum field
theory (QFT). Instead of it we focus on the mutual information
I(V,W)=S(V)+S(W)-S(V\cup W) between two different non-intersecting sets V and
W. This is a low energy quantity, independent of the regularization scheme. In
addition, the mutual information is bounded above by twice the entropy
corresponding to the sets involved. Calculations of I(V,W) in QFT show that the
entropy in empty space cannot be renormalized to zero, and must be actually
very large. We find that this entropy due to the vacuum fluctuations violates
the FMW bound in Minkowski space. The mutual information also gives a precise,
cutoff independent meaning to the statement that the number of degrees of
freedom increases with the volume in QFT. If the holographic bound holds, this
points to the essential non locality of the physical cutoff. Violations of the
Bousso bound would require conformal theories and large distances. We speculate
that the presence of a small cosmological constant might prevent such a
violation.Comment: 10 pages, 2 figures, minor change