The Mammoth Book of Extreme Science Fiction is a new collection that features 25 hard sci-fi stories that really push the boundaries, from names like Charles Stross, Robert Reed, Peter Hamilton, and Neal Asher. Highlights feature a perpetual war fought within a cosmic string; a machine that detects alternate worlds and creates a choice of Christs; murder in virtual reality; and a spaceship so large that there's an entire planetary system within it.