I would claim that the classical theory of particles is based entirely on interactions rather than entities.
The atom or molecule is a good object to think about. Following my view, atoms are not entities. But that seems nonsensical.
Well, we know from quantum mechanics that the inside of atoms is a blur of electron waves surrounding a nucleous that certainly seems to be particulate. But even the nucleous is a blur of quark waves that are highly confined, so we can define sharp boundaries for the nucleous.
The electron waves in the atomic shells are not so strongly confined, but still we can define fairly sharp boundaries of the atom as a whole. Its not like electromagnetic waves that are quit spread out and seemingly collapse to a point. The electron waves are all confined with in the boundaries of the atom.
The Pauli Exclusion principle is important here. Only one particle of matter or fermion can occupy any single state or set of properties. So even though the inside of an atom is a blur of electron waves, they are all separate energically.
It's the Pauli Principle that makes atoms bounce when they hit each other. So for thermodynamics or statistical mechanics or fluid flow, the atoms or molecules act just like particles.
The Pauli Exclusion principle does not apply to photons. As a result we cannot define the boundaries of a photon like we can an atom. So the EM wave structure becomes dominant, and it is even difficult to say that a photon exists.
The double slit experiment is crucial for distinguishing processes and entities. It works for both photons and electrons. Whether we send photons or electrons throuh the double slit (of differing size of course), an interference pattern is realized, even if the energy is so low that only one photon or electron passes through the slit at a time.
That, is the proof that electrons and photons do not exist- only EM waves and Electron waves really exist. If they were actually particles, an interference pattern could not exist. So using the words photon or electron is an approximation and is used to describe an interaction process. If there is no interaction, it is not correct to use that terminology.
In the case of the double slit, the interaction process happens when the waves hit the detector screen. So the electron waves can overlap in space, as they do in an atom. Yet they can interfere with each other. They add and subtract like EM waves. Of course to interfere, EM waves must have their polarization alligned and be coherent. So electron spins must line up and the waves must be coherent. I do not know how that is accomplished. Without quantum coherence from a laser, or classical coherence from a pin hole, there is no interference pattern.
The atom is an interaction process of electron waves with the radial electromagnetic field of the nucleous. The quantization occurs because of the interaction. So thinking in terms of quanta requires thinking about an interaction process.
So I think I have come around to my original thinking. Particles are processes and waves are entities. Waves exist and particles are approximations (like my understanding).