Einstein for Everyone 
From the "Completeness of Quantum Theory" chapter (on one theory of the determinability of quantum systems):  "If an atom has a probability of one half of radioactive decay over an hour, then all that really means is that its wave function describes an ensemble of many different atomic systems, half of which decay in an hour. Whether one particular atom in the ensemble will decay in one hour is definitely determinable. However we will not be able to discern it if all we know is the quantum wave associated with it. Whether it decays or not depends upon properties of that system that have been smoothed away by the quantum wave and thus are unknown to us. It is our ignorance of these smoothed away properties that makes a probabilistic assertion the best we can do."<p>HN, what does "Whether it decays or not depends upon properties of that system that have been smoothed away by the quantum wave" mean?!  What properties exactly, and smoothed away how?  Just by the fact that observing the system causes a change within the system and therefore changes the quantum waves?