Physicists Searched The Internet For Evidence Of Time Travelers

On June 28, 2009, theoretical physicist Stephen Hawking sat alone in a college at the University of Cambridge and waited patiently for party guests to arrive. Then he sent out invites.

Hawking was doing a (presumably, quite tongue-in-cheek) experiment to see if time travel is possible. The idea was that if he sent the invites out after the event took place, only time travelers would know to arrive.

Of course, nobody showed up . You could conclude from that that time travel to the past does not get invented by humans, or that they have a better use for it than partying hard with Stephen Hawking. Maybe there are more interesting times to visit, or paradoxes to be avoided.

But there have been other attempts to look for signs of time travelers visiting our timeframe, including one team of physicists who searched the Internet for evidence of knowledge nobody could have had unless they had traveled back in time. Of course, time travelers might want us to know they are here, might want to keep themselves hidden, or not really care either way.

"Even time travelers who want to advertise their presence may do so ineffectively," the team writes in their paper, "those who want to hide their presence might make a revealing mistake, and those indifferent might or might not leave traceable Internet content."

The team focused on searching for time travelers from the future rather than the past, figuring that the technology to create a time machine has not existed in the past, and any knowledge they had would relate to events in our past , making it pretty difficult to distinguish from people who have studied history.

The team attempted to find unique events that could not be referenced by anyone without a time machine, but would hopefully be recorded for a significant amount of time into the future. They eventually settled on the discovery of Comet ISON (C/2012 S1) in 2012, and Jorge Mario Bergoglio choosing the name " Pope Francis " upon his selection as the head of the Catholic church.

"Histories of bright comets like Comet ISON are generally well kept by societies and journals around the world, indicating that Comet ISON might remain memorable well into the future," the team explained. "Conversely, there is little reason for anyone without prescient information to be referring to something as 'Comet ISON' before 2012 September. Therefore, discussions or even mentions of 'Comet ISON' before 2012 September were searched for as potentially prescient evidence of time travelers from the future."

The team searched through Facebook posts, tweets, and Google Trends, which shows when people are searching for particular terms (once a particular threshold has been met). Though disappointing – who wouldn't want to know there are time travelers vacationing in the 21st century? – the team found no evidence of these terms being used on the Internet before the events took place, as detailed in their paper, which has not been peer-reviewed.

To widen the net and catch any time travelers who wanted to make themselves known, the team also performed a similar test to Stephen Hawking. They asked time travelers on the Internet to email them, and then later revealed the email address. To get the attention of time travelers, they created a hashtag to make it visible on X (then Twitter).

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The team also created a hashtag for time travelers who are worried about changing the past.

"Alternatively, time travelers who believe that they cannot change the past were requested to tweet '#ICannotChangeThePast2' on or before 2013 August, or include that hashtag at the end of an email sent to "home.nemiroff@yahoo.com" between 2008 November and 2013 August," the team explained. "For this part of the experiment, we were careful NOT to search Twitter or email until after the hashtag was publicly advertised in 2013 September. Therefore, by not pursuing a pre-advertisement search, the past might not have had to be changed in order for this tweet to have been discovered in 2013 September."

Unfortunately, no prescient tweets or emails were received from time travelers, sent before knowledge became available to all non-time travelers. While disappointing, and indicating that time travelers are not hanging around in the early days of the Internet, the team suggested a number of other reasons why.

"First, it may be physically impossible for time travelers to leave any lasting remnants of their stay in the past, including even non-corporeal informational remnants on the Internet," the team explained. "Next, it may be physically impossible for us to find such information as that would violate some yet-unknown law of physics, possibly similar to the Chronology Protection Conjecture. Furthermore, time travelers may not want to be found, and may be good at covering their tracks."

The study is posted to preprint server arXiv .