And if that is the case, why does our reference frame feel the motion, if acceleration is relative? I hope I'm explaining this the right way. I'm not saying that its being relative acceleration should shelve the notion of feeling (physical awareness of motion). But it doesn't make entire sense. My golden retriever and I are on a train. The conductor applies the brakes. The pup and I jerk forward. However--and Einstein explains this in his book--this could also be seen as my pup and I were at rest and the backwards speed of the earth passing by was slowed down. So, if that's the case, and regardless of reference frame, how did I really feel anything? Or is this feeling of motion not being defined the right way? Or am I just a dodo bird? Also, what role does space play in our feeling of this motion (if we really do)? Space seems to have an unexplained role in this physical feeling of (encounter with) motion.