Back in 2011, a survey was taken of various physicists and mathematicians at a conference on "Quantum Physics and the Nature of Reality" in Austria. Thirty-three of the world's top experts were asked to list their favorite interpretation of quantum mechanics.
(On the plus side, the theory turns out to be very, very, very, very accurate in making experimental predictions. So there's that!)
In the video below, Carroll breaks down the basics of why scientists can't seem to agree on how to interpret quantum mechanics — and explains why it's so critical: "What is quantum mechanics, really? I mean, that's like saying 'what is the Universe?' What more important question is there than that?"
It's a little longer and nerdier than our usual Lunch Break videos, but probably worth it in the end.
(Link via io9's Robert Gonzales, who has some additional smart comments.)