Really interesting indeed. Although I will need to digest it (and maybe put up a little fight with my QM professor) in order to understand better. I thought that this question was just something which I was calculating or interpreting wrong, but seems that it touches something more complicated...
That means that the measurement postulate about projection of the states only works in specific situations? I thought it was a basic postulate of quantum mechanics. But this means that such an experimental simple set up like measuring the momentum of a particle inside a box cannot be realized?
This may sound very basic, but I've just learned about the potential well with infinite barriers at +a and -a and I had a doubt. If we measure the momentum of a particle inside the well, it collapses to an eigenstate of the momentum operator, so, the uncertainty will be zero. Accordingly, the...