i was wondering, if we can arrange this kind of experiment.... What we do is this, we send photons (or whatever u choose) directly opposite to each other of which the energy is exactly the same such that if there is nothing is in their path the would anihialate each other. Now, if something was in their path although... the following would happen..... We have two photons lets name them 1 and 2. Now, we know where the atom is so we position both the phtons equidistant from each other. Photon 1 and 2 hits the electron at the same time and therefore there is no change in the position of the particle. Even if there is as in if 1 hits first and then 2 although we might have displaced it we know its present position now thanks to diffrence in wavelength of the photons. And with another pair we can set it back to its original place. So in essence there should be no change in their position and we should be able to calculate the velocity in the same way, right...?