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).
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).