# When does a wavefunction get re-created after a collapse? [closed]

Maybe another way of asking this would be, "When is decoherence un-done for a particle?"

Example: Consider that we shoot an electron from a gun. Whilst in transit the electron is just a probability wave. At some point along it's path we make a measurement which collapses its wavefunction (decoherence). When does that electron ever become a probability wave again? Surely its wavefunction doesn't stay collapsed forever, or else everything in the universe would be collapsed at this point. So the question is, at what point in time, and what event/action, causes the electron to ever become probabilistic again, returning it to a state which is equivalent to when it was in transit before we made our measurement?

Another way of looking at the question would be: In the electron gun, the electron is bound to a proton, and collapsed. When, and what, makes it uncollapse when it is ejected from the proton and out of the gun, turning it back into pure probability?

• The wave function is a formula on paper that describes the ensemble, it's not a physical thing that somehow wobbles trough space. It's a man made construct to describe what we see, and so is the collapse, except that the collapse is a nonsensical and utterly useless construct, while the wave function is useful. The only thing that is "real" is the physical vacuum, which has excitations that can be described by quantum fields. These quantum fields can only interact by exchanging quantized units of angular momentum, energy etc.. That's what an electron is: one of these units. Jul 11, 2016 at 20:43
• The state evolves according to the Schrodinger equation after the measurement, just as it did before. Jul 11, 2016 at 20:45