The Trouble with Many Worlds
Something that never made sense to me is why people think of Quantum Mechanics (the non-relativistic classical one) as fundamental. While some of its principles certainly are, clearly QFT (quantum field theory) is fundamental. From the perspective of quantum field theory there really is no observer just different field that couple to each other. Something like a measurement can in principle be described by a complicated interaction of fields (think of shining light at a double slit). The big mistery is I would rather say why the path-integral formulation of QFT (of which the principle of least action is the classical limit) agrees so well with reality.