ACAD SINICA,INST HIGH ENERGY PHYS,BEIJING 100039,PEOPLES R CHINA
; SHANDONG TEACHERS UNIV,CTR STRING THEORY,SHANGHAI 200234,PEOPLES R CHINA
The problem of what is observable in general relativity is investigated. With the help of Landau's observable space interval. the observational frames for individual observers are established. Within the Ashtekar formulation of general relativity, we argue from the nonvanishing Poisson brackets of the Yang-Mills fi-ld and the constraints that Dirac observability does not apply to gravitational systems.