Roger Penrose's New Theory: What happened before the BIG BANG This is a lecture by Sir Roger Penrose that I was lucky enough to attend. Here is the flash presentation of it: http://www.newton.cam.ac.uk/webseminars/pg+ws/2005/gmr/gmrw04/1107/penrose/ From what I can understand his theory is that the big bang happens after the end of the universe, starting a new one. The universe can end because eventually all matter falls into blackholes and blackholes evaporate into energy. So the universe ends up being nothing but energy at very high entropy. He says that when there is no longer mass in the universe time no longer applies. This is because there is only energy left and energy perceives infinite time as no time at all. So the end of universe is infinitely in the future but with only energy left that infinite time is reached. At that limit of infinity only energy and the gravitational waves left by the blackholes are left and the waves translate to density variations in the next big bang. In the beginning of the next Big Bang (which is also a limit that mass cant approach but energy can) only energy is there with density variations based on the gravitational waves from our current universe. What happened before the Big Bang is happening now! So that's what i got from the presentation. Its a very elegant theory because of its simplicity and seems intuitive to me. Only thin i don't completely understand is why is it that with only energy left you can approach infinite time where as with mass you cant. And how does the infinite limit of end of time translate to the beginning limit of time? ("limit" being a mathematical point at which you can approach but may never reach.