  Using a \emph{gedanken} experiment providing presumably a minimal inaccuracy
the uncertainty contributions to the space-time measurement are precisely
evaluated for clock and mirror respectively. The resulting expression of
minimal uncertainty for the space(time) interval indicates the presence of
minimal Planck scale observable length(time). The synthesis of quantum
mechanics and general relativity predicts the UV and IR scales for Lorentz
invariance violation. The influence of background radiation on the space-time
measurement is estimated. Based on the minimal length uncertainty relation
which takes into account the wavelength of a quantum used for distance
measurement we evaluate the cumulative factor responsible for the magnification
of the space-time fluctuation induced phase incoherence of a light propagating
over a large distance. We notice that in view of the interferometric
observations the quantum fluctuations of space-time in the braneworld model are
enormously increased if the fundamental scale is taken much below the Planck
one. Present approach to the uncertainty in distance measurement leads to new
insight about the bounds of computation. The impact of the space-time
fluctuations on the black hole physics is briefly emphasized.
