Would I know I had gone back in time? It's a very dangerous thing to go back in time, the tiniest of changes to the past make the most monumental differences in today. (sorry, I just finished Steven King's 11-22-63, about going back in time to stop the assassination of Pres. Kennedy)(great book, btw) I can't think of a particular century but I would dearly love to relive the birth of my two children, and watch them grow up again.