For most of us, seeing an advertisement pop up while we’re scrolling on Instagram or reading an article or watching a video is the most banal experience possible. But in the background of those experiences is a $500 billion marketplace where our attention is being bought, packaged and sold at split-second speeds virtually every minute of every day. Online advertising is the economic engine of the internet, and that engine is fueled by our attention. Tim Hwang is the former global public policy lead for A.I. and machine learning at Google and the author of the book “Subprime Attention Crisis: Advertising and the Time Bomb at the Heart of the Internet.” Hwang’s central argument is that everything about the internet — from the emphasis data collection to the use of the “like” button to the fact that services like Google Search and Facebook are free — flows from its core business model. But that business model is also in crisis. The internet is degrading the very resource — our collective attention — on which its financial survival depends. The resulting “subprime attention crisis” threatens upend the internet as we know it. So this conversation is about the economic logic that undergirds our entire experience of the internet, and how that logic is constantly warping, manipulating and shaping the most important resource we have — our attention. But it’s also about whether a very different kind of internet — build on a very different economic logic — is possible.