Brewster Kahle is no stranger to ambitious projects, but this one may be his biggest: he's trying to collect a physical copy of every single book ever published. The 50 year old MIT-trained computer scientist has gathered 500,000 books so far in a California warehouse.

The emphasis on physical copies didn't come about because he's digital-phobic: Kahle founded the nonprofit Internet Archive in 1996 to save a copy of every web page ever posted, and he's scanning every book he collects so that people can access them online. Still, he sees saving physical copies as a way of hedging against the uncertainty of future technological changes, and he hates to see books being thrown away.

Brewster knows it's unlikely he'll grab a copy of every single book out there - Google estimates 130 million books have been published worldwide - but he's determined to do as much as he can to preserve physical evidence of the written word.

