I know that Hawking and Penrose proposed that a singularity existed at the beginning of the big bang (and that they apparently changed their minds later). They extrapolated GR back and according to the mathematics, the density and gravitational field becomes infinite. But doesn't quantum mechanics, as currently formulated, say that GR must break down at times less than the Planck time? Does this mean that GR cannot be used to imply that a singularity occurred prior to the Planck time because the theory breaks down? My question is essentially if the singularity proposed by the earlier mathematics means that it actually was infinitely dense etc. or that these infinites is the models way of saying that it has broken down?