At this juncture in time, humanity does not know how to travel into the past, or even if such a concept has any meaning. So if you are an astrophysicist who wants to uncover evidence of time travel, what do you do? If you're Michigan Technological University astrophysics professor Robert Nemeroff and his PhD student Teresa Wilson, you look for time travelers on Twitter.
Time travel into the future is a fact – we do it every day. Accelerated time travel into the future can be measured using atomic clocks in fast airplanes. However, time travel into the past is a dicier proposition. While it appears that this is not forbidden by any current physics, we also don't know how to accomplish the task.
There is a (rather short) tradition of attempts to contact people who have arrived here from the future. In 2005, an MIT graduate student held a convention for time travelers. Despite considerable pre-convention publicity, no time travelers owned up at the convention. In 2012, Stephen Hawking held a party for time travelers, sending out the invitations after the party was held. Again, no one came to his party.
Surely one of the main ways to vet someone who claims to be a time traveler is their knowledge of something that has not yet occurred. This concept inspired Nemeroff (co-creator and editor of the Astronomy Picture Of the Day website) and Wilson to search the internet for signs of anachronistic factoids. For example, a post from 2006 containing the phrase "President Obama" would hardly be anachronistic, as his potential candidacy was already being discussed.
It seems there are very few events that can be uniquely identified by a couple of words. Such events have to be surprises to the extent that the descriptive words have likely never previously been combined. The Michigan Tech astrophysicists came up with "Comet ISON", which was discovered on September 21, 2012, and "Pope Francis", a name first appearing on March 16, 2013.
No comet had previously been called Comet ISON, and no previous pope was named Francis, so these phrases are unlikely to have been used previously. Even if they appeared in some context ("there may someday be a Pope Francis"), it would be easy to eliminate these as possibilities. What they were looking for was a text from one person to another in 2009 accidentally referring to Pope Benedict XVI as "Pope Francis."
Most search engines have a great deal of difficulty searching for items posted within a given slice of time. After studying the capabilities of a number of search engines and social media, our intrepid investigators chose Twitter as their hunting ground. With one exception deemed overly speculative (as described above), they came up empty. No evidence of precogniscience appeared in roughly a trillion tweets. They further performed a number of related searches, which came up empty.
Although this may seem a silly bit of research (IgNoble Prize material?), it is actually a reasonable attempt to see if time travelers have left traces of their anachronistic presence in the blogosphere. However, now that the concept of such searches has surfaced, it seems unlikely that any more will be carried out. Fake evidence of time travel would be too easy to retrofit into the collective memories of our history. While time may be out of joint, it appears that no one sent from the future to set it right has left obvious traces, at least on Twitter.