One of the strongest arguments against time travel is that we are not overrun with curious tourists from the future. A university student in Boston plans to change that, by inviting budding Doctor Whos to the world's first time traveller convention this weekend.
The organiser, Amal Dorai - a masters student in electrical engineering and computer science at the Massachusetts Institute of Technology - aims to test the theory of time travel by inviting people from the future to the event.
"We are doing this as a very low-risk, low-cost way to investigate the possibility of time travel," he said. "I think the probability they will come is very low, but if it does happen it will one of the biggest events in human history.
"Of course, no time travellers doesn't rule out the possibility of time travel, they could have just decided not to come to our convention."
Physicists believe some kind of time travel is theoretically possible, but it will take hundreds or even thousands of years to work out the technical details.
Concerned that people will have forgotten his convention by then, Mr Dorai is urging volunteers to publicise the event to future generations by carving the details into clay tablets and burying notices in time capsules. He has slipped invitations on long-lasting paper inside dozens of obscure books in the MIT and Harvard University libraries.
"If we put them inside books that are only touched every 50 years or so then they'll stay there and people in the future might learn of the convention. The big danger is that it's forgotten. Once that happens then it doesn't matter if someone invents time travel, we won't be able to see it."
The invitations ask visitors to turn up on the MIT campus at 8pm on Saturday and include precise latitude and longitude coordinates. "Time travel is a hard problem and may not be invented until long after MIT has faded into oblivion," they note.
Visitors from the future are advised to bring proof of advanced technology, such as a cure for cancer or a working nuclear fusion reactor. Sonic screwdrivers are optional.
"Because of the small chance of time travel I think people will be sceptical," Mr Dorai admits. "But I hope time travellers won't take that as an insult. If what they bring as proof doesn't satisfy us then they could always go back into their future and grab something else."
Professor Neil Johnson, a physicist at the University of Oxford, said Mr Dorai may not be wasting his time. The weird world of quantum mechanics suggests time travel could one day be possible through tiny holes, loops and channels in the fabric of spacetime.
"We're talking a long, long time in the future to be able to do this but it's not impossible," Prof Johnson said. "It would be very hard to send through something that weighed anything, like machines and people, but you could conceivably send messages through light and radiowaves. The chances of somebody from the future turning up on Saturday night are pretty remote, but they could get a phone call."
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