In Understanding Quantum Mechanics, Ch.1, Sec. 5 Roland Omnes says: ".. hard x-rays can leave straight-line tracks in photographic emulsion and this is strongly reminiscent of a particle trajectory." How can we describe this in terms of the wavefunction / interaction / measurement paradigm? Is is a series of "position measurments" -- one measurement at each grain of the emulsion? And presumably, a grain of emulsion would have to absorb at most a tiny part of the photon's energy if we are to see many more absorptions further along the track. This seems to fly in the face of "all-or-nothing" annihilation of photons. And what of the expected "collapse" that should occur at each grain?