Democracy in America
AS WELL as being a staple of science-fiction, time travel is also the inspiration for serious (or at least semi-serious) speculation by theorists. Some have devoted themselves to working out how it might be possible in theory, if difficult in practice, to build a time machine using exotic configurations of black holes, wormholes or cosmic strings. Others have considered whether a “self-consistency principle” operates to ensure that time travellers cannot cause paradoxical situations by, for example, going back in time and murdering their own ancestors. Then there are those who have taken an experimental approach, and searched for time travellers directly. How do they do it?
One idea, tried by Amal Dorai, a graduate student at the Massachusetts Institute of Technology (MIT), is to hold a convention for time travellers and see if any show up. He held such an event in May 2005, invitations for which were slipped into obscure library books or added to time capsules, in the hope that they would be found in the far future when time travel had become possible. Visitors from the future were asked to land their time machines on the MIT volleyball court, which was reserved for the occasion. But of the 450 people who attended the event, none claimed to be time travellers. In 2009 Stephen Hawking, a British physicist, performed a variation of this experiment, holding a party for time travellers but sending out the invitations after the event had taken place, so that only visitors from the future could possibly attend. But nobody came. Dr Hawking said this constituted “experimental evidence that time travel is not possible”.
The latest twist in this unusual field is to use the internet to search for evidence of time travel, an approach proposed by Robert Nemiroff and Teresa Wilson of Michigan Technological University, who presented their findings at an astronomical conference this month. They scoured the internet for “prescient” information—in other words, online posts suggesting knowledge of the future. In particular, they looked for two distinctive phrases that emerged at specific times: “Comet Ison” (the name of a comet discovered in September 2012) and “Pope Francis” (the name taken by Jorge Mario Bergoglio when he became pope in March 2013). Any mention of these terms before the dates in question might be the work of time travellers. But analysis of Google, Facebook and Twitter usage, and examination of the search logs of a popular astronomical website, did not produce any evidence of time travel.
Of course, this does not prove that time travel is impossible. It may be that time travellers are not interested in comets or the pope, or prefer to keep a low profile. Some theorists reckon that if a time machine is ever invented, it will not be possible to travel further back in time than the day of its invention. (If that is the case, the inventor of the first time machine may therefore suddenly be surrounded by time tourists when switching it on.) But this latest experiment is an interesting proof of concept that uses a technology that does exist (the internet) to search for one whose existence is uncertain. The researchers suggest that it is “the most sensitive and comprehensive search for time-travellers yet conducted”. They are only half joking.