Jilin Univ, Sch Phys, Changchun 130023, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
; Jilin Univ, Ctr Theoret Phys, Changchun 130023, Peoples R China
In quantum hadrodynamics there are two methods to take account of the contribution of negative-energy states in the relativistic random phase approximation. Dawson and Furnstahl made the ansatz that the Dirac sea was empty, while according to the Dirac hole theory the sea should be fully occupied. The two methods seem contradictory. Their close relationship and compatibility are explored and in particular the question of the ground-state instability resulting from the Dawson-Furnstanhl ansatz is discussed.