Service de Physique de l'Etat Condensé

For over a century, the science fiction literature has offered ever more fanciful scenarios involving time travel in one's own past, while science has never seriously entertained their possibility. Even Gödel's discovery in 1949 of a general-relativistic spacetime with causal loops did not change that. For the last two decades, however, physicists and philosophers have ventured more boldly - and more seriously - into the business of time travel. I will show why time travel and time machines, understood in a technical sense to be defined, become serious business in modern spacetime theories and how they illuminate important foundational issues such as the cosmic censorship hypotheses and the quest for a quantum theory of gravity.