What is the state of the art (potential) answers to the measurement problem of quantum mechanics? I recently finished my undergraduate quantum mechanics course, and we used Griffiths' introductory textbook. One of the "open questions" within the book (and the course overall), was that of the "measurement problem," which refers to the apparent collapse of the wave function of the system upon observation of the system.
However, obviously, it was all relatively low level (never thought I'd say that about quantum mechanics), and I was curious if the measurement problem is still considered an open problem of quantum mechanics? What are the most recent, or most "state of the art," answers or possible answers to the measurement problem? I'm vaguely aware of the ideas of quantum decoherence, the De Broglie–Bohm theory, and objective-collapse models, all as tentative or partial explanations. Is there any consensus, or other possible explanations that answer the measurement problem?
 A: There is no consensus on a solution to the measurement problem, nor even consensus it constitutes an "open problem" in the strict sense.
The various viewpoints on how to make peace with the measurement problem are called quantum interpretations and have various levels of support - by people and rather philosophical arguments, not by experiment, since most of these are metaphysics in the original sense in that they do not differ in the experimental predictions they make. There are rather many of them beyond the ones you already named in your question, and they vary widely in acceptance.
The interpretation that regularly enjoys the greatest support in polls among physicists is the Copenhagen interpretation, but is also the one interpretation without a formal statement - it's the one many lectures and books pay lip service to when they want to not worry about debating interpretations, but you'll get a wide range of responses when you ask people to actually state what it says.
These two things together - a wide array of possible resolutions that are experimentally indistinguishable and a majority view that is essentially "Please don't bother me too much about this, something something Copenhagen" or possibly even "Shut up and calculate" - are why I'd hesitate to call this an "open problem" in physics, and more a frequently debated question in the philosophy of physics.
