"As providing an insight into the nature of reality, and the nature of the physical universe, this whole area is really fascinating. I've thought a lot about it over the years, and I'm still undecided as to whether nature could never permit such a crazy thing, or whether yes, these entities, these wormholes, or some other type of gravitational system do at least in principle exist, and in principle one could visit the past, and we have to find some way of avoiding the paradox. Maybe the way is to give up free will. Maybe that's an illusion. Maybe we can't go back and change the past freely."