What is the Internet, really?

When a squirrel chewed through a cable and knocked him offline, journalist Andrew Blum started wondering what the Internet was really made of. So he set out to go see it -- the underwater cables, secret switches and other physical bits that make up the net.

For his new book, "Tubes," Andrew Blum visited the places where the internet exists in physical form: the cables and switches and servers that virtually connect us.