  Delayed choice and quantum eraser experiments have attracted much interest
recently, both theoretically and experimentally. In particular, they have
prompted suggestions that quantum mechanics involves acausal effects. Using a
recently developed approach which takes apparatus into account, we present a
detailed analysis of various double-slit experiments to show that this is never
the case. Instead, quantum experiments can be described in terms of a novel
concept of time called stages. These can cut across the conventional linear
time parameter as experienced in the laboratory and appear to violate
causality.
