I've watched some 2009 lectures by both Susskind and Krauss, and it sounds like they're telling different stories. Krauss seems to be saying that the origin of the universe is a plain-jane quantum fluctuation, but Susskind seems to be saying that at one point all matter in the universe was on top of everything else (meaning a singularity, right?). Also, Krauss says that using Type I supernovae as standard candles we now know the age of the universe to four places: 13.72B years. But then Susskind waffles and says that it's somewhere between 13B-14B years! Why do they seem to be telling different stories?