Comment Re:Could we be in a void? (Score 3, Informative) 157
No, and for two reasons.
Firstly, the universe is expanding symmetrically - all points are moving away from all other points. Any 'outside' force causing that would have to be symmetrical, but since gravity is an inverse square force, a spherically symmetrical amount of mass outside the sphere of the observable universe would have zero net gravitational effect on anything in that sphere. e.g., if the earth was a hollow sphere, you would feel no net gravitational force inside it because the gravity from one side would cancel the gravity from the other side.
Secondly, just as the light from outside the observable universe will never reach us because that region of space is expanding away from us faster than the speed of light, so will any gravity from outside never reach us, since gravity also moves at the speed of light. Everything outside the cosmic horizon is causally disconnected from our region of space. But the expansion of the universe is uniform everywhere, from regions far distant (and closer to the cosmic horizon), to regions closer to us that are causally disconnected from anything outside the observable universe.
Well, that's my understanding of it anyway..