Hi My interpretation of how observing the double slit experiment removes the interference pattern was that when (for example) an electron interacts with a photon, the electron is forced to be "at" that position, collapsing it's wavefunction. Then as the electron continues on towards the screen the probability of it going through the other slit is small or negligible from this location (in or next to one of the slits) and so no interference takes place. (this could be way off) Having seen this though http://www.scientificamerican.com/media/inline/DD39218F-E7F2-99DF-39D45DA3DD2602A1_p95.gif I don't know what to think. If by using the magnefying glass the interference pattern can be restored then it's not so much the interaction with the photon, but the existence of certain information that destroys the interference pattern. Does the interaction even collapse the wavefunction as i doubt the collapsed wavefunction could be un-collapsed? Is there a generally excepted interpretation of what is going on here? I assume that if the magnefying glass is placed far enough away so that the electron hits the screen before the photon reaches the magnefying glass then there is no interference pattern? Thanks in advance for any comments ps. I wouldn't have said that after a simple interaction like this the electron and photon would be entangled, but surely they must be here?