In the canonical quantum gravity, Hamiltonian equal zero, why? Since the split is space, the time is a constant? or the space-time is Ricci-flat?
In other words, if the space-time is Ricci-flat whether time supersurface, Hamiltonian equal zero?
I study in graduate school. My major is higher dimension cosmology. I want to study the quantum cosmology with extra dimension. So I should know what had been done in standard model.