"Are there beings in some sense like you, elsewhere in the universe, or are we the only ones around? It's one of the most basic questions there is." Carl SaganCarl Sagan, when asked his assessment of the importance of the search for extraterrestrial intelligence (SETI), replied, "You find out who you are. It's a basic question. Are there beings in some sense like you, elsewhere in the universe, or are we the only ones around? It touches deeply into myth, folklore, religion, mythology; and every human culture in some way or another has wondered about that kind of question. It's one of the most...