Posted: May 16, 2017 2:43 pm
Randall and Sundrum's theory is the brane-world idea, that universes start in a manner akin to a bumper-to-bumper collision on a packed motorway (which is where they were when they came up with their model). It doesn't seem very natural to me! I much prefer the Lee Smolin idea that universes are black holes as seen from within their own space.