The measurement problem? No one understands its true nature, hence multiple interpretations of collapse, and they are only interpretations. Much of physics is hopping on-board the Many Worlds interpretation. Sir Roger Penrose has a very unique take on it, a variation of the the Copenhagen interpretation, and it's part of the basis of Orch OR combined with Stuart Hameroff's work with microtubules.

Dean Radin's also carried out some interesting double slit experiments, but mainstream science considers his work and conclusions strictly woo. I can't comment on the validity of his work, but at the very least it shouldn't be dismissed outright.