I don't think that works - if it were the case that bubble of denser material should be collapsing in, due to its own gravity. We would see that at blue-shifted light in the CMB. Instead we see red-shifted light.
Bryan
The idea is that our visible universe is a bubble of lower density, not higher density, hence it being evacuated into the surrounding invisible universe. It's rather like the formation of galaxy superclusters and the voids between them.
That is exactly what I meant in my last post.
The denser, "outside" universe should collapse into our smaller, less-dense "inside" universe - the net gravitational pull the "outside" universe would feel would be towards the centre of the low-density bubble - i.e. our universe (i.e. sucks to be us).
And it also wouldn't account for the acceleration we see (making some assumptions on my part). If you have an "empty" space surrounded by a roughly spherically-distributed material on the outside, the net gravitational pull inside of that sphere is zero - i.e. the gravity from one direction cancels out the gravity from the other. This is why there is no gravity on the inner surface of theoretical constructs such as Dyson spheres, and thus they need rotation to provide centripetal force. Ergo, on the galactic scale there shouldn't be a net accelerative force*
*assuming a lot - i.e. roughly spherical and even distribution of the "outside" universe, no delay effects due to travel-time of gravity (which I think occurs at 'c'), etc.
This model would also suggest that we occupy a rather special space in the "inner" universe; one relatively close to the centre. Otherwise, we should see uneven degrees of spreading depending on the direction we look - we do not.
Bryan
