Nice tough questions. The interpretation of quantum mechanics remains unsettled, but at least we can try to clear up some old ideas that donít reflect modern understanding.
Itís not necessary to say that a particle isnít there, or that it doesnít have properties, before itís measured. The properties of the pre-measurement quantum state are just usually different ones than of the post-measurement state. Often, for example, the pre-measurement state is spatially spread out, and the post-measurement state is more localized. Depending on the starting state and the type of measurement, however, the reverse can also occur.
Accelerating an electron through a field does not in itself collapse a wave function. We donít know if any
process actually collapses a wave function. We do know that different parts of a wave function at least ídecohereí, so they cease to be part of the same stream of experience, when there are interactions with lots of remote objects. Whether or not a collapse occurs, with all but one stream of experience disappearing, is unknown.
Scattering just follows a wave equation, similar to the classical scattering of water waves or sound waves off obstacles.
p.s. My colleague LeeH is away, so Iím taking the liberty of violating our rules and posting this myself.
(published on 10/22/2007)