Significance of Negative Energy States in Quantum Field Theory $(1) $
  We suppose that there are both particles with negative energies described by L_{W} and particles with positive energies described by L_{F}, L_{W} and L_{F} are independent of each other before quantization, dependent on each other after quantization and symmetric, and L=L_{W} + L_{F}. From this we present a new quantization method for QED. That the energy of the vacuum state is equal to zero is naturally obtained. Thus we can easily determine the cosmological constant according to data of astronomical observation, and it is possible to correct nonperturbational methods which depend on the energy of the ground state in quantum field theory. 
Shi-Hao Chen