There is speculation that time travel may be real due to footage from the premier of Charlie Chaplin's "The Circus" silent movie in 1928. An old woman walks by doing what looks like talking on a cell phone. The phone even looks like an iphone...
While this could be some sort of prank that people have done (and added to the DVD set when it was released) there is the question: is this a time traveler caught on tape? And, if so, how close are we to that possibility? If it is a prank, it was very ingeniously done as it is hard to argue that the woman that walks by is not part of the original film.
It's a long shot, but I guess you can't rule it out. The title link goes to an article and the video. You can decide for yourself: elaborate prank? Alien technology? Undisclosed small portable object from 1928? TIME TRAVEL?
For sure a Sci Fi mystery. Enjoy!