I remember Richard Feynman stating on a few occasions (like here, in lecture 1, around 21:10) that physics has no explanation of what causes inertia, that it seems to be some sort of deeply mysterious first principle.

I am wondering: have there been made any advances at all towards an explanation in recent decades/years - maybe more recent developments in particle/quantum physics, string theory, ... have shed some light on the matter (pun definitely intended)? Or does Feynman's statement still stand and is this phenomenon as mysterious as ever nowadays?

Edit, since this question is seen as a possible duplicate: my question is subtly different I think. I would like to know whether inertia is still seen as a first principle, or if there have been recent discoveries that reveal it to emerge from underlying principles or ideas, interactions of this or that type of particle with this or that field, ...

  • $\begingroup$ Forgive me, but you do know about the mass equation connected with gravity and the mass equation connected with inertia? Equivalence Principle. I ask because you don't mention it in your post, but the correspondence between the two definitions of mass remains something we need to explain. $\endgroup$ – user140606 Jan 16 '17 at 23:51