I think you are misconstruing what Penrose is saying. All the laws of physics break down at a singularity, and anything can happen including a big bang or for that matter a gazillion big bangs. What Penrose is saying is that a universe similar to our own could not occur because of the Weyl curvature hypothesis. What this says is that a low entropy universe can be formed at an initial singularity but not a final singularity. For me to explain any further I would have to type for the next 3 weeks and I'm not going to do that. Read "The Emperor's New Mind" by Penrose chapter 7.