"At its core, Google ranks web pages based on the number of incoming links they receive. The assumption is that the more links a page has, the more important it must be on the web. The algorithm has been adjusted and modified hundreds or thousands of times over the years, of course, but incoming links are still a huge part of what determines any site's ranking in a search. Google's engineers adjust the algorithm periodically in hopes of making sure it returns the highest quality searches, not simply the most popular sites.
To weed out popular lies, Google has devised a method/model that measures the "truthfulness" of a web page instead of its online reach. A post on a blog might have a big reputation, but that doesn't always mean it's factual. As NS explains, instead of counting incoming links (a measure of its reach) Google's new system could count the number of "facts" in the page. Each source is then analysed for how many lies it has and scored on that using something called a "Knowledge-Based Trust" score.