  We determine the non-local in time and space current-current cross correlator
$<\hat{I}(x_1,t_1) \hat{I}(x_2,t_2)>$ in a mesoscopic conductor with a
scattering center at the origin. Its excess part appearing at finite voltage
exhibits a unique dependence on the retarded variable $t_1-t_2-(|x_1|-|x_2|)/
v_{\rm\scriptscriptstyle F}$, with $v_{\rm\scriptscriptstyle F}$ the Fermi
velocity. The non-monotonic dependence of the retardation on $x_1$ and its
absence at the symmetric position $x_1 = -x_2$ is a signature of the wave
function collapse, which thus becomes amenable to observation in a mesoscopic
solid state device.
