QM doesn't mean the same thing to everybody. Many physicists think it includes both unitary evolution and (real or apparent) collapse during measurements, while

QM doesn't mean the same thing to everybody. Many physicists think it includes both unitary evolution and (real or apparent) collapse during measurements, while being valid for multiple observers and describing a single approximately classical world. That very common view is a paradox because different observers can have different notions of "measurement" and they are incompatible.