Now, I just quoted from Google’s corporate website, and I used a hyperlink so you can see my source. Sourcing is the glue that holds humanity’s knowledge together. It’s what allows you to learn more about what’s only briefly mentioned in an article like this one, and for others to double-check the facts as I represent them to be. The link I used points to https://www.google.com/search/howsearchworks/crawling-indexing/. Suppose Google were to change what’s on that page, or reorganize its website anytime between when I’m writing this article and when you’re reading it, eliminating it entirely. Changing what’s there would be an example of content drift; eliminating it entirely is known as link rot. It turns out that link rot and content drift are endemic to the web, which is both unsurprising and shockingly risky for a library that has “billions of books and no central filing system.” Imagine if libraries didn’t exist and there was only a “sharing economy” for physical books: People could register what books they happened to have at home, and then others who wanted them could visit and peruse them. It’s no surprise that such a system could fall out of date, with books no longer where they were advertised to be—especially if someone reported a book being in someone else’s home in 2015, with an interested reader seeing that 2015 report in 2021 and trying to visit the original home mentioned as holding it. That’s what we have right now on the web... The problem isn’t just for academic articles and judicial opinions. With John Bowers and Clare Stanton, and the kind cooperation of The New York Times, I was able to analyze approximately 2 million externally facing links found in articles at nytimes.com since its inception in 1996. We found that 25 percent of deep links have rotted. (Deep links are links to specific content—think theatlantic.com/article, as opposed to just theatlantic.com.) The older the article, the less likely it is that the links work. If you go back to 1998, 72 percent of the links are dead. Overall, more than half of all articles in The New York Times that contain deep links have at least one rotted link.