Yes, but where does inertia come from? It seems to oppose the products of the fundamental forces.
Ah! Not sure I can help you there. The mechanism by which inertia is predicted to arise by the standard model of particle physics is via an interaction with something called the Higgs field. I know little about it and have little interest in it until they find the Higgs boson at the LHC, but the often used analogy is that particles that couple to the Higgs field are akin to people walking through treacle.
Inertia (i.e. rest mass) is essentially the energy that a particle has in its rest frame (i.e. the reference frame in which it is not moving). Relativity and quantum theory already provide mechanisms for changing the rest mass of something, but people who know a lot insist we require an entirely new mechanism to create it in the first place. Relativity, as you know, finds that E=mc^2 for a particle at rest, and charged particles that radiate away energy when binding to other charged particles have lower mass than before (more strictly, the bound system has lower mass than its individual components). This to me suggests that mass emerges from excitation from the vacuum state, in other words massive particles are simply those for which a given value of momentum p corresponds to something other than p*c as a value of energy in an energy-momentum graph.
Imagine two massless particles with opposite charges, spins and energies in the same location: that gives no net mass, no net charge, no net spin, no net energy... it isn't there! If you apply an electric field across this nothing pair, the opposite charges will be accelerated in different directions. Within a certain critical electric field, the charges are still bound to each other and, further, they have a imaginary momenta (this sounds bizarre, but it applies in solid state theory too and the fact that your PC and mobile phone work suggests solid state theory is on to something). These are 'virtual' particles. However, above the critical electric field, the momenta become real and the charges are essentially becoming ionised from each other. This gives a non-zero energy corresponding to a zero momentum: rest energy, or 'mass', or 'inertia'.
That is NOT accepted theory, although I have yet to read anything that explains why such ideas based on well-understood phenomena are not tolerated. That's how I think about mass - I like it, but I can't condone it!
But this seems like one-way interaction. The light interacts with the charge of the mass/bound energy/particle, simply because the charge is indifferent to momentum; and I suppose the charge changes the wave properties of the particle. But the particle does nothing to the photon?
It eats the photon. And if it doesn't like it, it spits it out again. :bigsmile: