If we try to an electron with a high energy photon, we precisely detect its position, while its momentum becomes totally uncertain. On the other hand, if we detect it using a low energy photon, its momentum is detected, while the position becomes uncertain. Now, if, during a double slit experiment of electrons, we try to detect the electron with low energy photons, we will still remain uncertain about its which-path information. Should it still collapse its wave function? Should the interference pattern disappear?