  Experiments that look for nonlinear quantum dynamics test the fundamental
premise of physics that one of two separate systems can influence the physical
behavior of the other only if there is a force between them, an interaction
that involves momentum and energy. The premise is tested because it is the
assumption of a proof that quantum dynamics must be linear. Here variations of
a familiar example are used to show how results of nonlinear dynamics in one
system can depend on correlations with the other. Effects of one system on the
other, influence without interaction between separate systems, not previously
considered possible, would be expected with nonlinear quantum dynamics. Whether
it is possible or not is subject to experimental tests together with the
linearity of quantum dynamics. Concluding comments and questions consider
directions our thinking might take in response to this surprising unprecedented
situation.
