Depends how much time you want to spend on it. I first learned about this topic in Brian Green's book The Elegant Universe back in 2005 or so. At the time there

Depends how much time you want to spend on it. I first learned about this topic in Brian Green's book The Elegant Universe back in 2005 or so. At the time there was a glut of popular science books on the topic (Lee Smolin had an excellent book titled The Trouble with Physics which made an excellent counter argument to Green's string theory-heavy title). If you want to go much deeper, Roger Penrose wrote The Road to Reality which is a much much harder read (I was never able to complete it after 3 separate attempts).