It is widely believed that in our quantum world physical facts about occurrences in space time must be grounded in the wave function. There are several long recognized and much discussed difficulties with this view.

Daniel Bedingham, Detlef Dürr, GianCarlo Ghirardi, Sheldon Goldstein, Roderich Tumulka, Nino Zanghì, "Matter Density and Relativistic Models of Wave Function Collapse", J Stat Phys (2014) 154:623–631