Could you travel to the past and visit Julius Caesar? Could you travel to the year 4000 and see what the future is like? Find out about the possibilities and paradoxes of time travel. Time marches on except in astrophysics. Einstein taught us that time is a coordinate in space, and it's all relative. Learn about the weird physics of our universe that could make time travel possible. Standing in for Lynne Koplitz this week is J. Richard Gott, author of Time Travel in Einstein's Universe. Guest: J. Richard Gott III, Professor of astrophysics at Princeton University, and author of Time Travel in Einstein's Universe.