Pound-for-pound The Beginning of Infinity has to be the densest collection of batshit-crazy ideas I've ever come across. Never mind the bit about how there are trillions of copies of you constantly branching throughout the multiverse. Deutsch also claims there is nothing in principle stopping us from colonising the stars, transmuting matter like the alchemists of old, bringing an end to death, reversing global warming, and solving any other problem that arises. But that's not ambitious enough...
