Re:Feeling the acceleration (Score 1)

You "feel the acceleration" only relative to the rest of the universe. The rest of the universe "feels the acceleration" relative to you.

No. An astronaut feels the acceleration of his rocket much more than the rest of the universe. That is because the universe has a "little bit" more mass than his rocket, while the total energy that both experience stays the same.

Simple movement without acceleration is a different thing, because in this case there is no change in energy levels.

If the universe consisted only of the twins, then you would be right, of course...