what does the "collapse of the wave function" mean?

[gib65]

I have a question about how the wave function of particles collapses. I've heard that the wave function collapses when a particle interacts with another particle, but in the context of quantum mechanics, I'm not sure what "interact" or "collapsing of the wave function means". My understanding is as follows: The "wave function" is the perpetual propagation of the probability wave of a fundamental particle - a field of probability where the particle is most likely to be, and grows larger so long as no other particle interacts with it. Interaction in this case is kind of a fuzzy term since their positions are only probablistic. Is this understanding correct?

 

Also, what would happen if a particle just sat there in empty space with no other particle for light years to interact with it? Would the probability wave perpetually expand even becoming macroscopic?

[bloodhound]

hmm. i am not an expert on this, but from what i know ur almost rite. from what i have read, the wave function collapses on trying to observe the particle ( so i guess there is an interaction with EM photons.)

[swansont]

A particle can be in an indeterminate state (i.e. one of several possibilities), or what is called a superposition of states, and you won't know which one until you measure it. e.g. the electron can be spin up or down, Schroedinger's cat is alive or dead, the atom is in the upper or lower hyperfine state, etc. The act of "measuring" (really any interaction that requires the particle to be in one particular state) will "collapse the wave function" to reflect being in one state, with probability=1, rather than a probability of being in one of several.

[gib65]

So if a particle was sitting there alone in space, and all of its properties are in a state of superposition, then over time it's field of probability should grow. That is, say you had a particle in position (x, y, z) at time t. If it's properties are in a state of superposition, which includes its momentum (velocity and direction), then at time t + n (where n is an arbitrary positive number) its' position could be anywhere within a certain radius around (x, y, z). Then at time t + 2n, its' position could be anywhere within twice that radius, and at time t + 3n, 3 times that radius, and so on. So isn't it true that its' range of probability propagates outward over time?

 

Also, what does "interaction" mean in this case. Say you had a particle which you had more certainty as to its position and momentum, and you wanted to use it to measure the less certain particle. If the less certain particle is anywhere within a range of probability, what determines when and how your measuring particle will interact with it?