How does Google sell ad spaces and rank webpages? How does Netflix recommend movies, and Amazon rank products? How can you influence people on Facebook and Twitter, and can you really reach anyone in 6 steps? Why doesn’t the Internet collapse under congestion, and does it have an Achilles’ heel? Why are you charged per gigabyte for mobile data, and how can Skype and BitTorrent be free? How are cloud services so scalable, and why is WiFi slower at hotspots than at home?