"Eli Pariser made his mark on the Internet as the executive director of MoveOn.Org, the liberal group that was perhaps the first to turn the Web into a tool for massive political action.
Now he's worried the Internet is becoming too polarized, politically and otherwise, because of tools used by some of the technology and social-media world's biggest players.
His new book, "The Filter Bubble: What the Internet Is Hiding from You," details the ways Facebook, Google, Aol and numerous other online hubs quietly are personalizing the Internet for their users.
The stated goal is to make it easier for Web users to find the things online that they like. (And, of course, to make it easier for advertisers to hawk things to you that you're more likely to buy).
But the end result, Pariser says, is a silent, subtle bubble that isolates users from new discoveries and insights that may fall outside of their usual tastes and interests.
Pariser stepped down as chief of MoveOn in 2008 but is still president of the group's board. He spoke to CNN.com on Tuesday, the day his book was released.
On "the filter bubble" and how it works
One of the things that's really interesting about the filter bubble is that it's invisible. You can't see how your Internet, the websites you visit, are different than what other people see. They are sort of slipping further and further apart.
"A couple of years ago, when you Googled something, everyone would get the same result. Now, when I've done these experiments, you can really get these dramatically different results. One person Googles and sees a lot of news about protests and the other person gets travel agents talking about traveling to Egypt."