Time travellers, if they really exist, seem to be keeping their adventures to themselves.
Researchers with perhaps a bit too much time on their hands conducted an extensive internet and social media search for evidence of time travellers going back in history and then bragging about it online.
And they came up empty. No real life Dr Who or Marty McFly from the movie "Back to the Future" tweeting secrets a bit early.
Spurred by idle chat during Thursday poker games, an astrophysicist and his students at Michigan Technological University in Houghton, Michigan, searched for mentions of Pope Francis and Comet ISON - before they popped into reality. Francis was elected pope last March and ISON was first detected in September 2012.
The idea: If someone mentions a Pope Francis in a 2011 tweet, Facebook post or blog item, then they must have come back from the future with special knowledge.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
But no one posted anything prescient.
And last September, the researchers asked people to tweet "#Icanchangethepast2" - but do it before August, a month earlier. Again, no one did.
The disappointing results, rejected by three physics journals, will be presented on Tuesday at the American Astronomical Society conference in Washington.
If someone went back in time and said something to hint about the future, it would prove the concept of time travel, said astrophysicist Robert Nemiroff.
He said this was merely summer fun that cost nothing to do.
"This wasn't a major research push," Nemiroff said on Monday at the astronomy meeting.
"This was typing things into search engines. Billions of dollars are spent on time travel movies and books and stuff like that. This probably costs less than a dollar to check on it."
