Hi, I'm slightly confused with the Aguirre-gratton model, and was wondering if someone could explain using simpler terms? I have read from : http://www.preposterousuniverse.com/blog/2007/04/27/how-did-the-universe-start/ " Aguirre and Gratton have presented a proof by construction that such a universe is conceivable; essentially, they demonstrate how to take an inflating spacetime, cut it near the beginning, and glue it to an identical spacetime that is expanding the opposite direction of time. This can either be thought of as a universe in which the arrow of time reverses at some special midpoint, or (by identifying events on opposite sides of the cut) as a one-way spacetime with no beginning boundary. In a similar spirit, Gott and Li suggest that the universe could “create itself,” springing to life out of an endless loop of closed timelike curves. More colorfully, “an inflationary universe gives rise to baby universes, one of which turns out to be itself.” 1. what does it mean by "cutting the space time near the beginning and glueing it to an identical spacetime that is expanding the opposite direction of time? " Doesn't time only go in one direction too? 2. What does "space-time with no beginning boundary" mean? Could someone please give an explanation of the aguirre-gratton and how it creates the no-boundary state? thanks so much! (and if you have time, a brief explanation of the Gott-Li model) Thanks!