The problems of big bang theory. What are they?

Whilst the Big Bang Theory is the agreed mainstream of Cosmology, do Theoretical Physicists agree?I thought that the start of what we call our universe is postulated as something very different in M-Theory, the collision between two ten-dimensional 'universes' in the eleventh dimension which could have occurred over a considerable area rather at a single point.Coudl anybody explain or give references for the fate of that theory and how it has been expanded?

Thank you 'fearandloathing' for the reference.I also found the book Elegant Universe and its accompanying documentary by Brian Greene useful (http://youtu.be/ULlR_pkHjUQ). Both present this possibility of a collision of two objects in the 11th dimension which seems to contradict the Big Bang and perhaps explains anomalies such as the continued acceleration of the expansion of the universe to my tiny mind.I was wondering if there is a direct comparison to Big Bang.