# Double slit experiments - basic pondering

I have some ponderings about the double slit experiment(s) and mainly their interpretations. Some of my questions may exhibit insufficient scholarship so please bear along, or please point out the fallacies wherever they are instead.

1. Why is it commonly said that it is impossible to know in advance which slit any single particle will go through, and all that can be said is that there will be a probability distribution that can describe many particle's aggregate behavior. Isn't it more humbly correct to say that we just don't know how to predict that?

2. Say that the experiment is held with electrons. And photons are used to detect whether an electron passed through one of the slits. And of course, this detection collapses the wave function etc. What however should be the effect of the photons on the electron? is an electron totally and entirely oblivious to having interacted with a photon? is only the photon affected by an electron (in the classical model to start with) and not vice versa?

3. When the particle beam is being shot, or a a single particle is shot at a time, what can be said about the direction of the particles or the angle of the beam? are those of a probabilistic nature, and what would happen if they are not probabilistic but rather if the direction of each particle is known in advance? this is probably the most straightforward to answer of my questions.

Thanks! I just find it very interesting, and yet in a sense basic.

3. The direction of the particle's motion, i.e. given by $\vec p / |\vec p|$, is an observable and like every other observable in any system obeying the laws of quantum mechanics, this observable is mathematically represented by a linear operator on the Hilbert space which means that one can only make probabilistic predictions about its values (unless the predicted probabilities of certain properties are 0 or 100 percent which is extremely rare and surely can't occur in a double slit experiment).