Quantum Interpretation

Most recent answer: 10/22/2007

Q:
In quantum physics they drill home that until you measure it, a particle (say an electron) isn't really "there". How can it interact with stuff if it's not there? How does scattering happen? When you accelerate an electron through a high voltage, does that effectively collapse it's wave function? Thanks!
- June
Dallas, TX
A:
Nice tough questions. The interpretation of quantum mechanics remains unsettled, but at least we can try to clear up some old ideas that don’t reflect modern understanding.

It’s not necessary to say that a particle isn’t there, or that it doesn’t have properties, before it’s 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 don’t know if any process actually collapses a wave function. We do know that different parts of a wave function at least ’decohere’, 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.

Mike W.

p.s. My colleague LeeH is away, so I’m taking the liberty of violating our rules and posting this myself.

(published on 10/22/2007)