An Uncertainty Relation of Space-Time

We propose an uncertainty relation of space-time. It is characterized by G scale and a spatial volume, respectively. Using this uncertainty relation, we give qualitative estimations for the entropies of a black hole and our universe. We obtain qualitative agreements with the known results. The holographic principle of 't Hooft and Susskind is reproduced. We also discuss the cosmology and show a relation to the cosmic holographic principle of Fischler and Susskind. However, as for the maximal entropy of a system with an energy E, we obtain a formula \√E V / G \^2 with V denoting the volume of the system, which is distinct from the Bekenstein entropy formula E R /