Image credit: Seth Lloyd, et al.

All theories of time travel have been faced with the challenge of the “grandfather paradox:” say, a traveler going back in time could kill his grandfather and thus prevent his own existence, which would also prevent the murder taking place. In the early 1990s, David Deutsch came up with a  model which  allowed the time traveler  remember killing his grandfather without having actually done it -- an improvement which however retains inherent inconsistencies between the past remembered and the past experienced, remarks Seth Lloyd, director of the MIT center for extreme quantum information theory (xQIT),  who has been testing quantum time travel theories with a team of researchers including the Italians Vittorio Giovannetti and Lorenzo Maccone.

Lloyd's group put forth a "post selected model" of time travel, an experimental simulation which censors "paradoxical situations" by "going back and outlawing" any event that would prove paradoxical in the future. The xQIT theorists' model  beat the  "Grandfather Paradox" -- or, as they put it, "no matter how hard the time-traveler tries, she finds her grandfather a tough guy to kill."

Read more...

• Taming time travel, Science News
• Gödel e il paradosso di uccidere la nonna, by G. Giorello, Corriere Sera
• Si avvicina il sogno più antico «Possibile viaggiare nel tempo», by G. Caprara, Corriere Sera