Conditional wave function ($\psi (x,t)\propto \Psi (x,Y(t),t)$)

In the spinless version of Bohmian mechanics, insert the actual environment configuration $Y(t)$ into a total wave function $\Psi (x,y,t)$ to obtain a subsystem's conditional wave function, when that slice is nonzero. It encodes the actual environment relevant to the subsystem's guiding dynamics. It need not satisfy an autonomous subsystem Schrödinger equation; further separation conditions are needed for an effective wave function.^[ref]

If total-wave branches become disjoint in the relevant environment configuration variables and the actual environment lies within one branch, the subsystem's conditional wave function is proportional to that branch's subsystem factor. Persistent separation makes its autonomous use an effective description. No term of the universal wave function has literally been deleted. Possible recombination prevents treating every temporary packet separation as irreversible collapse.^[ref]