Hey everyone - just a bit of a conceptual question regarding the sudden approximation for a particle in an infinite square well. In theory, if we were to suddenly decrease the width of the potential from say L, to L' << L, in a very quick period of time - wouldn't this in some sense constitute a "measurement" of the particle's position in that you would now have a very good idea of where it was (especially if L' is very small) - at what point does the "collapse" of the wavefunction occur? would it be at the point at which the well length L was infinitely small (ie, a delta function potential?). When does collapsing of the wavefunction occur - what I don't understand is that since any measurement of position in the lab has some level of error (We can never pinpoint the particle's position exactly) how could a wavefunction ever truly "collapse" to a delta function? I imagine it doesn't and if anything this is as usual just an approximation of reality. Many thanks for help clearing up the confusion.