  Several approaches were used to proof the assumption that an universal upper
bound on the entropy to energy ratio (S/E) exists in bounded systems. In 1981
Jacob D. Bekenstein published his findings that S/E is limited by the effective
radius of the system and mentioned various approaches to derive S/E employing
quantum statistics or thermodynamics. It can be shown that similar results are
obtained considering the energetic difference of longitudinal eigenmodes inside
a closed cavity like it was done by Max Planck in 1900 to derive the correct
formula for the spectral distribution of the black-body radiation. Considering
an information theoretical approach this derivation suggests that the variance
of an expectation value is the same like the variance of the probability for
measuring this expectation value. Implications of these findings are shortly
discussed.
