Reflections on Brane Cosmology
Of course, a multi-dimensional universe is restricted to a brane inside a higher-dimensional space, called the "bulk" with additional compact dimensions contained in the extra dimensions. In this context it is well known that no reference to the bulk is appropriate nor desired. In the bulk model, however, other branes may be moving through the bulk and thus interactions with the bulk, and possibly with other branes as they proliferate and spread across the universe, can influence our very own brane and introduce effects not seen in more standard cosmological models.
-- with apologies to Wikipedia
ZHID BOW SKIS
(As the facts unravel I've found this to be true)