For example with photons in a double slit, knowing the path of the photon leads to particle-like measurements and not knowing leads to interference (wave-like). In the interference case, is it fair to suppose the photon travels through more than one slit at the same time? Is this accepted thought or just completely naive? What could you argue against it? My understanding of the Copenhagen Interpretation (Griffiths) is that a particle has no position before it is measured, which according to common sense is just as implausible. Secondly, is there any evidence for the complementarity of wave-particle duality. Can we be sure that a photon doesn't behave like a wave and particle simultaneously? Then a measuring device could 'pick out' the appropriate state.