There is no "wave function of the universe". Wave functions are for physical systems that can be observed from the outside. This is not the case for the universe.
In case of Universe (free field) equations where number of particles are not constant use of wave function is limited. Still, same equations satisfy for non interaction cases and we reach on some ideal solution. When wave functions used for non relativistic particles in isolated quantum states then probability of true results itself becomes high.
There is no "wave function of the universe". Wave functions are for physical systems that can be observed from the outside. This is not the case for the universe.
In case of Universe (free field) equations where number of particles are not constant use of wave function is limited. Still, same equations satisfy for non interaction cases and we reach on some ideal solution. When wave functions used for non relativistic particles in isolated quantum states then probability of true results itself becomes high.