All legal cases, Larsen points out, rest to some degree on facts, and, traditionally, the courts have relied upon what's called the "adversary system" to deal with them. Either side can introduce factual evidence into argument; if the other side thinks the facts are wrong, they can dispute them in court. Judges try to work with facts which have been vetted by both sides.
How the web has changed this:
Now, Supreme Court justices spend time Googling around, looking for facts to support their opinions. Around half of the facts cited in a typical Supreme Court brief now come, Larsen writes, "from sources that are not strictly 'legal.'"
And that means bias can creep in:
Liberal and conservative justices, like anyone else, tend to engage in "motivated reasoning," and will seek out information from sources which they know, in advance, will agree with them. Moreover, even the most objective justices can be biased unintentionally, since bias of some kind is the inevitable result of using search websites, which shape the results you find according to your preferences and tastes. Because of the way Google works, Larsen warns, searches "could produce different results for different chambers depending on, for example, the internet history (or Facebook profile!) of the users."