This attractive force
between branes would in fact be a special case of the kind of force that inflationary cosmologies posit to explain the early universe's blowup.
Space within the branes expands, and at first the distance
between the branes (in the bulk) grows too.
If the interaction
between branes was a collision, it would trigger a fantastically powerful reaction, Steinhardt guessed, given the immense amounts of matter and energy in each one.
When the brane worlds expand so much that their space is nearly empty, however, attractive forces
between the branes draw the world - sheets together again.
Not exact matches
So a crash
between two empty
branes would still be a collision of gigantic proportions.
If our
brane is folded over itself, then passing
between the folds could offer a shorter path
between two points.
So when the authors claim that our 3 - D universe is part of a 10 - dimensional «
brane» and that cycles of expansion and contraction result from collisions
between our cosmic
brane and a neighboring one, the best most readers can do is visualize two giant hands clapping the universe into existence over and over again.
Then later last year, the group discovered in collaboration with Nathan Seiberg of the Institute for Advanced Study that the singularity could be interpreted as a collision
between the two «end of the world»
branes, in which only the gap dimension separating them shrinks down to zero for an instant.