Colliding brane cosmology is actually a ‘cyclic model’, i.e., it does not require a beginning of time, because the two (or more) branes must have existed before our current cosmic expansion started. In fact the ekpyrotic model says that it could be an ‘eternal’ process of collisions and ‘heat death’ due to expansion, because the two branes would move only a short distance apart before approaching again for another collision. The ‘short distance’ could however take billions of years to accomplish, by which time each brane has expanded a significant amount.