I have not started studying quantum mechanics in depth (so I don't know too much of the math behind it). But I read about the Schrodinger's wave equation and how it can be applied to a system when there are more than one particle (for example, hydrogen atom, a molecule etc). However, if the events in the whole universe was concerned, then wouldn't every single particle in the universe have to be in the equation? Then would the final wave function be the complete description of the whole universe? I have another part to the question concerning the double split experiment. I read that if a detector is placed then the wave nature of the particle disappears apparently because the device is measuring the position of the particle. However, what is the definition of measurement in this case? What is the exact interaction in the device with the particle that collapses the wave function. (and how could that be possible if the explanation for the whole universe is just one gigantic wave function?) Is it a photon just hitting an electron (if that is the particle used) that collapses the wave function? Finally, if the wave function of the whole universe is known (or at least a wave function of all the particles involved in the experiment), then when the device is placed at the slits, wouldn't the wave function perfectly predict the way the electron will hit the screen (just one strip of dots where electrons hit instead of interference)?