  Based on the cosmic holographic conjecture of Fischler and Susskind, we point
out that the average energy density of the universe is bound from above by its
entropy limit. Since Friedmann's equation saturates this relation, the measured
value of the cosmological energy density is completely natural in the framework
of holographic thermodynamics: vacuum energy density fills the available
quantum degrees of freedom allowed by the holographic bound. This is in strong
contrast with traditional quantum field theories where, since no similar bound
applies, the natural value of the vacuum energy is expected to be 123 orders of
magnitude higher than the holographic value. Based on our simple calculation,
holographic thermodynamics, and consequently any future holographic quantum
(gravity) theory, resolves the vacuum energy puzzle.
