I've always though of particles in the following sense: If you do NOT measure/decohere a particle in some way, it exists ONLY as a probability wave--there is no "actual" number for each of its unknown quantity, just a probability of what it will be. There are no "hidden variables" that we don't know and can't find out--the particle has no "actual" value for position, just a probability distribution. One of my friends insists that his quantum physics teacher told him that Quantum Mechanics in fact does have "hidden variables" and that all particles have definite numbers for everything--we just can't know them all at once with complete accuracy. This doesn't make any sense to me--I've read that particles aren't "actually" point particles with positions/velocities/spins that we can't know, but simply have a probability of existing in a particular state and aren't "actually" in a certain state before we measure it. Just like Schrödinger's Cat--who is both dead and alive at the same time until the box is opened (he isn't "actually" dead or alive and we just can't know). So am I correct, and quantum mechanics has no "hidden variables", or is my friend right here?