Time travel is an extraordinarily popular pastime. Or at least it would be if it were possible. Evidently it isn’t, though; as Stephen Hawking once observed, we never encounter any tourists from the future.
To make his point, Hawking once held a party for time travelers from the future, but nobody came. Of course, he didn’t post the invitation until after the date of the event, in order that only people from the future would know about it.
So for the time being, time travel remains fictional. But it has been fictional for a long time. Decades before Doctor Who, H.G. Wells wrote his famous book The Time Machine (1895). More than a century and a half before that, an Irish writer named Samuel Madden published (anonymously) Memoirs of the Twentieth Century (1733). Madden declared that he had the “honor and misfortune” to be the first historian to depart from writing “the accounts of past Actions and Times” and “dar’d to enter by the help of an infallible Guide, into the dark Caverns of Futurity, and discover the Secrets of Ages yet to come.” Those secrets had been revealed to Madden by a time traveler who had appeared one night like an angel, leaving him a series of volumes containing state papers from the reign of George VI.
A little over a century later, Edgar Allan Poe, in a prose poem titled Eureka, mentioned a letter, found in a bottle, dated 2848. Its writer complained about ancient scientists’ devotion to deductive and inductive reasoning, when in fact, science “makes its most important advances … by seemingly intuitive leaps.”
So maybe there’s a flaw in Hawking’s experiment, based as it was on deductive logic. After all, it’s easy to come up with explanations for why his invitation went unnoticed. Maybe by the time that time travel is invented, everybody has forgotten about Hawking, or YouTube has gone out of business.
On the other hand, perhaps time travelers just want to keep their existence a secret. But even highly trained supersecret time travel agents might slip up occasionally and accidentally reveal their future origins. Like for instance, by typing Comet ISON into Google before that comet had even been discovered. But even if they did, who would ever know?
Well, Robert Nemiroff and Teresa Wilson of the Michigan Technological University physics department might. Comet ISON was discovered in 2012, so it is very unlikely that anyone from the present would have searched online for it, or tweeted about it, before then. Nemiroff and Wilson reasoned that searching the Internet for pre-2012 mentions of Comet ISON might turn up evidence of a time traveler.
It’s not easy to conduct such searches, and the results can be misleading. Old web pages often contain new ads, for instance. And while it’s possible to search a site that records Google search queries, that site only reports on terms with a high search volume, so a single request for Comet ISON info would not have been recorded.
Twitter, though, can be searched comprehensively. But Nemiroff and Wilson found no evidence for any tweeting about Comet ISON before it was discovered. They tried various other searches of other databases, also without success. They also tried searching for any mention of Pope Francis before he became pope, just in case time travelers aren’t interested in astronomy. Still no luck.
But unlike Hawking, Nemiroff and Wilson do not conclude that time travelers therefore do not exist.
“Although the negative results reported here may indicate that time travelers from the future are not among us and cannot communicate with us over the modern day Internet, they are by no means proof,” Nemiroff and Wilson write in their paper.
After all, deductions about time travel are vulnerable to the flaws afflicting all deductions — such as relying on premises that might not be true. Poe’s letter writer from 2848 commented on this point. He observed that ancient logical reasoning based on deduction from “self-evident” truths, or axioms, is bogus, as there is no such thing as a self-evident truth. Even 19th century scientists should have realized that, the letter writer pointed out, as some supposedly self-evident truths (such as, “a thing cannot act where it is not”) had already been shown to be wrong.
Poe’s letter writer then commented that perhaps one “palpable truism” had in fact been identified, by a 19th century logician named Mill: “‘Ability or inability to conceive … is in no case to be received as a criterion of axiomatic truth.”
Surely, many false things have been conceived (unicorns), and many inconceivable things have turned out to be true (USA beats Soviets in ice hockey, 1980). So the ability of many writers and even scientists to conceive of time travel does not prove that it is true. But the inability of many others to conceive of time travel does not mean it is false.
Next up: Tom's top 10 time travel movies
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