A buddy of mine asked me to explain QM. I don't by any means tout myself as having any sort of worthwhile knowledge about it so I was a little surprised he asked me. But nevertheless, I explained it to the best of my ability. I'm hoping you guys can tell me if I've royally messed anything up here. In the short of it, envision one of these (cubic lattice): http://xpdnc.org/hosted/images/f8ddfdef905744b05298499041caf1f386f940b1.gif In philosophical terms, consider that the above is the matter (conf. materialism) that makes up the entire universe. Everything. The lattice is going to be used to be used to represent what the Copenhagen interpretation (the standard interpretation) calls the "wavefunction." Now imagine that fundamental particles (e.g., photons, electrons) can only be located at one of the points on the lattice. At a macroscopic level, things smooth out (e.g., a beam of light, which appears to travel in a straight line through spacetime at the speed of light), but on a microscopic level, particles are jumping from point to point, never existing in between. There is measurable time between the particle's jump to each point, but it's literally impossible to observe it during that time. The unique quality here is that, for all intents and purposes, their movement is "random." When we try to catch a particle "between" (again, it has fallen out of existence, so it's not "between" anything, in terms of the space part of spacetime) points, we fail. It necessarily jumps to a point. Now, it's most likely to jump to a point nearest to where it last existed (in fact, it's very predictable where the particle will go, but it cannot be deduced), but it can jump to any point on the lattice. Now, the above understanding (Copenhagen's interpretation) relies on Bell's theorem. A well known alternative, and at this point probably considered fringe, is Bohm's (not to be confused with Bohr) interpretation, which is what purports the so-called "hidden variable" theories that would bring the existence of randomness to a grinding halt. To better picture this, there is the famous thought experiment popularly known as "Schrodinger's Cat." In short, there is a chance that a cat that was put into a box is dead (that's a given in the experiment; Schrodinger explains how to yield an increasing probability of a dead cat). The only way to know for sure if the cat is actually alive or dead is to open the box and check it out, but we can't open the box because of the observer effect; when we do open the box, the cat is either alive or dead. Copenhagen interpretation (Bell's theorem) says that we must conclude that the cat is both alive and dead. Bohm interpretation (hidden variable) says that there is a way to figure it out for sure without opening the box, which if we're remaining analogous to the simplicity of the experiment, poses a problem for us. Rather, Bohm is wrong. He went on to ask how the observer effect works, mechanically. I explained that Bell's theorem only actually applies to a closed system, so when we say that a particle falls out of existence, what we really mean is that it has wandered off somewhere, possibly another galaxy, and the term for all of this is "entanglement," and the theory that explains this is known as "quantum information." I'd appreciate any feedback if you have any. I don't want to give this guy wrong information, y'know? edit-- I should add that I've never taken a class or anything on it. That's just based on what I've read on my own. I'd imagine that this is not exactly an area well suited for "self-teaching." Anyway, please be gentle. I don't doubt that I've muddled some concepts somewhere in there.