When you step into a time machine, fax yourself through a "quantum foam wormhole" and step out in feudal France circa 1357, be very, very afraid. If you aren't strapped back in precisely 37 hours after your visit begins, you'll miss the quantum bus back to 1999 and be stranded in a civil war, caught between crafty abbots, mad lords and peasant bandits all eager to cut your throat. You'll also h...