Physics with Answers: 500 Problems and Solutions Book

This is a collection of six lectures given in celebration of Kip Thorne's 60th birthday (an academic tradition). The lecture topics aren't exceptionally cohesive because the lecturers were selected based on the fact that they are all (1) famous scientists and (2) connected to Thorne in some way. For instance, Stephen Hawking is Thorne's collaborator and rival, and he lectures about time travel, whereas Alan Lightman is Thorne's ex-grad-student and he lectures about being a scientist-novelist.

This is a great resource if you are curious about what the cutting edge minds currently think about the possibilities of time travel. Could time travel into the past be possible or not? And if it is possible, how do you resolve the paradoxes that might result? Both Hawking and Novikov weigh in on this topic at length. Thorne's lecture is more of an overview about the upcoming interesting steps in spacetime research and so he spends a good deal of time discussing gravitational waves, though he does briefly touch on time travel at the end. Novikov's lecture involves a series of fascinating thought experiments (originally calculated by Kip Thorne) concerning time-traveling billiard balls and whether any paradoxical results are possible (for instance, a version of the grandfather paradox: if the corner pocket is a time machine, can a billiard ball time travel into the past and collide with itself, thereby preventing itself from entering the corner pocket/time machine in the first place?).

On that note, the lectures by Lightman (on being a novelist) and Ferris (on science popularization) should be readable by all, but on the whole these lectures were given FOR physicists BY physicists and so it is not a light read. For instance, I'd recommend being pretty solid with spacetime physics before jumping into the lectures on time travel.