# Double-Slit experiment and the role of observation in the distribution

so I am still having difficulty understanding the role of measuring/observing the wave function. Many of the videos I have watched says that when we are not looking at the wave function it makes an interference pattern but when we are looking it makes a normal pattern as we would expect. What I don't get is how do we know there is an interference pattern if it has never been observed (if we would, it would then make the wave function collapse and we would see a normal distribution.). Alsp many people says that observing the wave function doesn't affects the distribution so it is very confusing...

The double slit experiment one electron at a time shows the scattering probability distribution in space for the $Ψ^*Ψ$, the measurable footprint of a wavefunction, and the interference arising from the sinusoidal solution for "electron of specific energy scattering off specific double slits".

so the interference pattern has been measured , contrary to your statement.

You have to realize that the wavefunction is the solution of specific boundary conditions, i.e. constants that have to be introduced to pick up the specific quantum mechanical solution. Any new detection implements entering the measurement, will introduce new boundary conditions changing the constants and the solutions. A careful experiment showed how the detection destroys/changes the conditions of a simle double slit experiment, and the complexity introduced by the detecting method has to be addressed.

Overall, the results suggest that the type of scattering an electron undergoes determines the mark it leaves on the back wall, and that a detector at one of the slits can change the type of scattering. The physicists concluded that, while elastically scattered electrons can cause an interference pattern, the inelastically scattered electrons do not contribute to the interference process.

Your wording is rather imprecise and that leads to problems in understanding here.

You can't "look at" a wave function in any classical sense like you look at your computer screen.

What you can "look at" (i.e., detect) is through which slit each electron goes if you put suitable detectors there (see anna's answer for details). Experiment now shows the following: if you don't put detectors there, you'll get interference with single electrons. If you put detectors there, you don't get interference but the result that is expected by classical, straight propagation of electrons.

The distribution of electrons is influenced by whether or not you look at the slits. The same is true for light. You can either know the path (which-way-information) or get interference, but not both at the same time.

Observing the wave function at the screen, where the interference pattern is, does not destroy the interference pattern. If you observe it earlier, perhaps in an attempt to see which slit the particles went through, that destroys the pattern and that's what these videos are talking about.