  This paper gives a thorough critique of the foundations of quantum physics in
its mainstream interpretation (i.e., treating pure states as primitives,
without reference to hidden variables, and without modifications of the quantum
laws). This is achieved by cleanly separating a concise version of the
(universally accepted) formal core of quantum physics from the (controversial)
interpretation issues. The latter are primarily related to measurement, but
also to questions of existence and of the meaning of basic concepts like
'state' and 'particle'. The requirements for good foundations of quantum
physics are discussed. Main results:
  * Born's rule cannot be valid universally, and must be considered as a
scientific law with a restricted domain of validity.
  * If the state of every composite quantum system contains all information
that can be known about this system, it cannot be a pure state in general.
