Logically, gravity in our Universe comes from the energy of the Big Bang, which will have imparted enough "oomph" into all the matter and energy to bring it back to a single point.
I couldn't say what's logical regarding Big Crunch v Big Freeze. It seems we don't know nearly enough, but...
If gravity is weaker than one would expect, because it is leaking into other dimensions, does that mean that there will not be enough to bring everything back together? No big crunch? No bouncing universe?
Quite possibly, it seems.
Leaking Gravity May Explain Cosmic Puzzle:
http://www.freerepublic.com/focus/news/1353071/posts"[New York University physiscist Georgi Dvali] borrows from string theory, which states that there are extra, hidden dimensions beyond the four we are familiar with: three directions and time. String theory suggests that gravitons -- hypothetical elementary particles transmitting gravitational forces -- can escape to other dimensions. Dvali says this would cause "leaks" in gravity over cosmic proportions, reducing gravitational pull at larger distances more than expected"
Actually this is something on the LHC agenda - to look for gravitons, and see if they can be witnessed sneaking off into other dimensions - which would be taken as support for String Theory.
But the question I'd like to ask Dr. Dvali is: what's to stop gravitons from dimension X re-entering our 4D spacetime?
