So then all our parts are "falling" together constantly through this expanding space? I say falling, but I understand it is other local forces besides gravity.

So then all our parts are "falling" together constantly through this expanding space? I say falling, but I understand it is other local forces besides gravity. I struggle to wrap my mind around what that means for concepts I learned long ago in college physics... what is an inertial frame of reference then? What about the speed of light and relativistic effects? I suppose the answer is back to the original statement that the effect is really only noticable at cosmological scales. Locally, it's well below any margin of error?