If planets, solar systems and galaxies are all moving at such remarkable speeds, is there anything in deep space that could be considered "still" relative to everything else? If not, what would be moving the slowest?
Well i was going to say the universe itself... but then i realized that it's probably moving to... and that i have no way of knowing that right now... well that ruins my answer. I don't think that we know of anything moving 'slowly' or not at all. Sorry.
