During times like these, who hasn't daydreamed about traveling forward or backward in time?In Time Travel: Ten Short Lessons, popular-science master Brian Clegg gives a grand tour of the essential lessons in this game-changing area of physics, from the imagination of novelists to current research.Einstein's special theory of relativity told us that time travel to the future was possible, and later his general theory of relativity showed us that loops in spacetime could exist,