Maybe you should reread my post. I didn’t, in any sense, say the particle had a definite position prior to measurement. I said:
Whenever a measurement is made on a quantum particle it presents itself, amazingly, as a particle. When an electron transits from a higher energy state to a lower energy state it emits a photon which is a point particle. When an eye absorbs this photon a measurement has been made.
The wavefunction of an electron that is in the process of making a transition from an excited state to the ground state has a probability density that is an oscillatory function of time.
Since its charge distribution is proportional to its probability density this creates an oscillating electric dipole of frequency (E2-E1)/h.
Schrodinger, who despised Bohr’s quantum jumps said, “It is hardly necessary to point out how much more gratifying it would be to conceive of a quantum transition as an energy change from one vibrational mode to another than regard it as a jumping of electrons.”
How can an oscillating electric dipole, that persists for some period of time, create a discrete photon of the above frequency?
Despite the similarity, it’s not an electric dipole; it’s an electron. The mechanism of photon emission doesn’t derive from the fact that the setup resembles a classical electric dipole, but from the fact that electrons emit photons. As for that mechanism, it’s part of QED (and quantum mechanics doesn’t really cover creation and annihilation of particles).
So, we’re pretty much back where we started. A stationary electron can only emit virtual photons, and in order for it to emit a real photon it must obtain the energy from somewhere to do so.
In spontaneous emission from an atom, triggered by virtual photons from the zero point energy of the EM field, the electron derives this energy from the increased binding energy of the atom. And this occurs because the electron transitions from a higher energy state to a lower one.
Now we don’t know from where the electron began this transition or where it ended up, but by consulting the radial probability density function we can make an educated guess that, if we make a measurement, its distance from the nucleus has probably decreased.