@maxdancona,
Well, that's not the cases that we did not talk about something pratical.
Though I'm not a physicist, my ability is only to encourage others to think and derive things.
I originally thought the wave-particle nature can be easily solved but I'm wrong.
The original solution is, the particles itself takes some kind of wave energy inside it(like a wavelet) other than its motion energy. Thus even if they were particles, they can still be observed as if they were waves. (and in this assumption, there are not only particles that would carry waves, there is also another kind of wave----field wave)
How did the observer interference with the particles? The observer used active readings, so that they cannot prevent from altering the wave inside the particles.(So that it's quite necessary to make clear that how did they 'observe')
However, there is a sole flaw in the explaination that some experiment let the single particles pass one by one and the interference can still be observed.
I must get to some more details on how these experiments carried out.