"The uncertainty has deep implications. For example, it means that a quantum particle does not move along a well-defined path through space. ...The smearing of position and momentum leads to an inherent indeterminism in the behaviour of quantum systems. ...[T]he experimenter may fire an electron at a target and find that it scatters to the left, then, on repeating... the next electron scatters to the right. Quantum mechanics still enables the relative probabilities of the alternatives to be specified precisely. ...It can make definite predictions about ensembles of identical systems, but it can generally tell us nothing definite about an individual system."