I've watched the Susskind lectures on QM and Quantum Entanglements. Susskind seems to avoid many of the interpretation issues inherent in QM. For example, he never talks about the wave function collapsing due to the involvement of "conscious mind". He does show, mathematically, that wave function collapse in the double-slit experiment is a result of particle entanglement with the measuring devices. I'd like to hear from others who can elaborate about Susskind's position in this regard. I don't want to take his explanations solely on his authority. My other question is along the lines of superposition. I have read in many sources that a quantum system "exists in all possible states simultaneously". Susskind doesn't seem to buy this. He seems to discount this by saying that one just can't measure the states of a quanum system in a manner that allows you to say otherwise. So, the question is, is the statement that a quantum system "exists in all possible states simultaneously" a fundamental underpinning of QM or is it just an interpretation of the results of QM predictions?