Space time is expanding, in other words non gravitationaly bound bodies get further apart. Ok, we can not detect this expansion if we limit our tests and observations to our own galaxy but, space time is still expanding within our galaxy, i think ST has been discribed as a super fluid or at least it must act like a super fluid, if we can not detect any effects in may have in our galaxy. So if ST is acting like a friction less medium, how does it carry non bound bodies apart?
If you had two rooms seperated by a door, in one room is normal atmospheric pressure and gas composition similar to the environment you are in now, the other room has been made a void empty space... a vacuum. When the door is opened, what happens? The answer is the rooms attempt to equalize pressure and the gas composition is dispersed against a greater volume. One theory for the universes expansion, is that to begin with there was just a infinite(or extremely close to infinite) vacuum to which one paradoxical instance caused energy to be injected. The energy or Spacetime attempts to equalize itself from it's emergence point with the volume of the universe... since the universes size is immense, it's going to take a long time to equalize, especially without boundaries.
Sorry, you do not ansewer the question at all, if i think of two bodies on a grid and the grid gets bigger (carrying the two bodies with it) i can say they are not bound by gavity. If the two bodies are not carried with it i can say they are bound by gravity. Gravity is a weak (force) but it can not be overcome by ST expansion, so ST must be all most frictionless, if so then why do non bound bodies travel with it?
