Karri and Mike here:

The first professor who taught me quantum mechanics told us this during the first class: The first time you take quantum mechanics, you don’t quite get it. The second time, you think you understand what’s going on. The third time, you realize that you have no idea. There’s (currently) no good answer to the interpretation question. If Steven Weinberg can honestly tell his students that the next big revolution in physics will be in quantum mechanics, then I think it’s fair to say we don’t really know what’s going on.

As far as what we believe in, I like how the concept of decoherence solves the measurement problem, which is one of the concepts that a lot of people find most problematic when they first come to quantum mechanics. Essentially, the orthodox view (Copenhagen interpretation) says that a particle can be in a superposition of states and that when you measure it, the particle “chooses” one state or the other in a random, probabilistic fashion. Now, we tend to think of this instantaneous “choice” as an effect of the particle becoming entangled with the machine you’re using to measure it. A particle can remain in a quantum superposition (say a quantum coin being both heads-up and tails-up simultaneously) for a relatively long time. When you use a big, classical computer to measure the particle’s state (say the computer beeps if the quantum coin is heads-up), the particle and your computer become entangled (heads+beep or tails+no beep). Since the computer is huge, warm, and noisy, its superposition decoheres almost instantaneously, which forces the particle into one state or the other almost instantaneously.

In terms of our day-to-day work, however, we tend to ascribe to the “shut up and calculate” approach. Though the question is interesting, you generally don’t need to consider the deeper philosophical questions in order to do good work.