Why should "our" big bang be the only one? Loop quantum gravity has made significant progress at exploring the classical big bang and black hole singularities. Both circumstances are non-singular when LQG is used to model them: what was formerly a singularity in the classical model is removed by quantizing, and the two regimes look rather similar see bojowald et al http://arxiv.org/abs/gr-qc/0503020 http://arxiv.org/abs/gr-qc/0503041 and references therein this carries the copernican revolution further by suggesting why should "our" bigbang be the only one?" Earlier astronomers looked at the stars and were able to ask "why should our sun be special? the sun resembles a star, so why shouldn't these other stars that we see have planets orbiting them too?" Now it becomes possible to look around and see a lot of black holes and ask "why should our bigbang be special? the big bang resembles a black hole (looked at in LQG from the other time direction), so why shouldnt these black holes that we see be big bangs starting other branches of time?" In my view this is a major thrust of Loop Quantum Gravity right now. Increasing numbers of LQG people are working on studying the big bang ex-singularity, and some key people have moved over to study the black hole ex-singularity (which is at a much earlier stage of understanding) Black hole ex-singularity research is now, in 2005, the way big bang ex-singularity research was in 2001, with the very first Bojowald paper that removed the singularity in the very simplest case. To me, this is at the guts of what is going on in LQG. And it is in this light that I see a very beautiful new Quantum Gravity paper by Rafael Sorkin (a senior QG guru at Smolin and Rovelli alma mater Syracuse, and also parttime at Smolin's Perimeter). This paper is a thoughtful one: deep and simple. It just came out 5 April05 http://arxiv.org/hep-th/0504037 [Broken] This paper, as I see it, goes a certain ways towards clearing up Roger Penrose thermodynamic objection to identifying black hole with big bang. Penrose thermodynamic objection is: "what happens to all the entropy?" As I read Sorkin, he says the entropy gets stuck on the screen door (the event horizon) and immediately inside, time starts flowing coherently in a new direction, which we, from our perspective, picture as down the hole. Time makes a fresh clean start, with huge negative entropy. All the old crud is there plastered on the windshield for us to look at as it gradually fades out of existence. Sorkin also has good things to say about unitarity and non-unitarity, and the "information paradox". For me this is an exciting paper, maybe it will be for some others.