  I argue that the marquis characteristics of the quantum-mechanical
double-slit experiment (point detection, random distribution, Born rule) can be
explained using Schroedinger's equation alone, if one takes into account that,
for any atom in a detector, there is a small but nonzero gap between its
excitation energy and the excitation energies of all other relevant atoms in
the detector (isolated-levels assumption). To illustrate the point I introduce
a toy model of a detector. The form of the model follows common practice in
quantum optics and cavity QED. Each detector atom can be resonantly excited by
the incoming particle, and then emit a detection signature (e.g. bright flash
of light) or dissipate its energy thermally. Different atoms have slightly
different resonant energies per the isolated-levels assumption, and the
projectile preferentially excites the atom with the closest energy match. The
toy model permits one easily to estimate the probability that any atom is
resonantly excited, and also that a detection signature is produced before
being overtaken by thermal dissipation. The end-to-end detection probability is
the product of these two probabilities, and is proportional to the absolute
square of the incoming wavefunction at the atom in question, i.e. the Born
rule. I consider how closely a published neutron-interference experiment
conforms to the picture developed here; I show how this paper's analysis steers
clear of creating a scenario with local hidden variables; I show how the
analysis steers clear of the irreversibility implicit in the projection
postulate; and I discuss possible experimental tests of this paper's ideas.
Hopefully, this is a significant step toward realizing the program of solving
the measurement problem within unitary quantum mechanics envisioned by
Landsman, among others.
