I am still in secondary school so I probably shouldn't think about things this complicated (at least that's what it seems to me, complicated), but please correct me if I'm wrong. If I recall correctly, the position of an electron is never certain, and always based on probability, unless observed. Now let's do a though experiment in an isolated system: "The electron of a simple Hydrogen atom is located at 0.1 nm from its single proton when observed, but due to my understanding of how physics works. When - after this observation the electron stays unobserved for a tiny moment of time, and - after that it's been observed at 0.5 nm, it should gain potential enegry fivefold. Also, it's angular momentum should increase, as well as the mass of the entire atom due to E=mc²" I know I'm probably wrong, and it has something to do with the velocity of the electron changing or something like that, but I was wondering what the actual answer would be, and it's fun to think about.