Just a note, the 11 dimensional theory is reduced to a
theory of 10 dimensional branes connected over a
complex circle, this connection is the dimension along which the branes travel.
The travelling branes are now 10 dimensional objects. Of these 10 dimensions 6
contain all of the majic of some modern
particle physics
(
supersymmetric physics and the like). The visible
brane (our brane)
and the hidden brane live at opposite ends in a backgroud
gravity.
They live at the same potential and between them there is a potential
drop. The Colliding brane falls down the potential and as it moves
it gains extra energy from the background. When this brane
collides with our brane the extra
energy that it absorbed from the
background is release as the "
big bang" event in our universe.
An important point is that the brane has long enough to move to
allow quantum fluctuations to equilibrate across the brane,
these are then imprinted on our univese, given the appearerence
of superluminal correlations on our sky. The Brane
definitly moves across the gap at subluminal velocities and may move at
substatially subluminal velocities. This is a large departure in
method from inflation.
M-theory is an 11 dimesional theory.
You need to get rid of 7 of these dimensions.
The method for doing this is called compactification.
The choice for compactification that the ekpyrotic universe
makes is arbitrary and is chosen to agree with
cosmological observations.
At a talk on the ekpyrotic universe that I attended reecently
given by one of the theories inventors, Brian Greene
made the comment that for a long time cosmologists
said that boundry condtions for their theories would be justified
from improved particle physics models, now it seems that the reverse is
happeneing. There is not yet an ab initio criteria for these theories
other than the antropomorphic one.