I got an email from someone who I knew in high school, and notwithstanding the whys and whynots, this person remembered me as "thin and dark". What nature, time and NY have done to me: I am no longer thin and I am and always was less handsome than "dark". The email, for a moment, pushed me to travel back in time, but I went past high school and hit the earlier boyhood of fun counting bananas (my introduction to arithmetic and eventually math). That is the problem with time travel, it is hard to get it right. Alan Lightman has a somewhat lightweight, marginally enjoyable fiction based on different hypotheses about time: what if the speed of time decreased with height over the ground, what if time gradually came to stop at a singular point on the Earth's surface, etc.