Time Travel: A History

James Gleick

The Universe Next Door: A Journey Through 55 Alternative Realities, Parallel Worlds and Possible Futures

New Scientist

Frequently Asked Questions about the Universe

Jorge Cham

What If? 2: Additional Serious Scientific Answers to Absurd Hypothetical Questions (What If?, #2)

Randall Munroe

We Have No Idea: A Guide to the Unknown Universe

Jorge Cham

What If? Serious Scientific Answers to Absurd Hypothetical Questions

Randall Munroe