I’m sure that most physicists, given the opportunity, would jump at the chance to pick the prodigious brain of famed cosmological theorist Stephen Hawking. The man behind the bestselling “A Brief History of Time” not only has great insight into the workings of black holes but also knows how to have a good time, as evidenced by his zero-gravity exploits aboard a modified Boeing 727. It may seem surprising, then, that an open party hosted by Hawking at the University of Cambridge in 2009 was attended by exactly one guest: Hawking himself.
The size of the soiree may not be that great of a mystery, however, as Hawking waited to send out the invitations until after the party was over. The invites, now publicly available in a handsome print, offer a cordial invitation to “a reception for time travellers” to be held in the past, cheekily assuring possible attendees that no RSVP is (or late fore-when, in the formulation of Douglas Adams?) necessary. In a 2012 interview, Hawking claimed that the results of his ersatz experiment provide evidence that time travel is impossible. After all, he says, “I sat there a long time, but no one came.”
Other scientists have taken a slightly more rigorous approach to the search for travelers through time. Robert Nemiroff and Teresa Wilson of Michigan Technological University hypothesized that if future time travelers voyaged to the recent past, they would likely have spent time on the Internet. Perhaps some of these chrononauts were careless and made references to events that hadn’t yet occurred; if so, these mistakes could be found in search engine histories and social media postings. Nemiroff and Wilson focused on major historical and scientific happenings like the naming of Pope Francis and the discovery of the comet ISON. Even so, their queries turned up no evidence of visitors from the future.
The theory of time travel remains hotly debated: Hawking argues that Einstein’s general theory of relativity may allow trips into the past, while others hold that the absolute limit of the speed of light prevents this possibility. For now, physicists will just have to wait for the future… or work on hosting an even better party.