The state of a quantum mechanical system is completely
specified by a function Ψ(r, t) that depends upon the coordinates of the
particle(s) and on time. This function, called the wavefunction or state
function, has the important property that |Ψ(r, t)|
2 dr represents the
probability that the particle lies in the volume element dr ≡ ddr located
at position r at time t.
The wavefunction must satisfy certain mathematical conditions because
of this probabilistic interpretation. For the case of a single particle, the
net probability of finding it at some point in space must be unity leading
to the normalization condition, ' ∞
−∞ |Ψ(r, t)|
2 dr = 1. It is customary to
also normalize many-particle wavefunctions to unity. The wavefunction
must also be single-valued, continuous, and finite.