If you like all the Quantum Theory/String Theory type stuff then you should read The Elegant Universe. It makes your brain hurt but it's worth it. If you can't be bothered to read the book, just watch the TV series:
http://www.pbs.org/wgbh/nova/elegant/program.html
If I could go back in time and kill anybody I'd sort out Stalin first. Most estimates for the death toll are between 8 and 20 million people. This seems to have gone largely unnoticed.
Dave