When it comes to groundbreaking technology, few things can match the pure “gee-whiz” factor of holograms. Ever since Princess Leia’s flickering form appeared imploring Obi-Wan Kenobi for help in Star Wars, people have been fascinated by the technology. More recently, supergroup ABBA has produced ABBA Voyage, a “live” concert with digital avatars of the band’s members singing and dancing for fans’ delight.