QM says that if we have many particles they have a common wavefunction. Also QM says that when you measure a particle or observe it, you collapse its wavefunction. That must be a logical mistake. Now lets look at a laser beam as an example. The laser produces a plane wave which is comprised by many photons. Now if we observe (annihilate) one photon a part of the wavefunction must collapse. But then this means that the wavefunction must be comprised by many individual wavefunctions of any separate photon. So it can not be common but a sum of individual wavefunctions (by the way sphearical in form which overlap to build a plane wave). What is your opinion about this issue?