Stephen Hawking came up with a rather novel way of testing if time travel is possible—he held a party for time travellers.
The late theoretical physicist held the party then sent out invitations after the event took place. That way, he thought, only time travellers could possibly have shown up.
Sadly for him, nobody did turn up from the future for a glass of Champagne and a few canapés with the author of A Brief History of Time.
“I have experimental evidence that time travel is not possible,” Hawking told the Seattle Science Festival in 2012. “I gave a party for time travellers, but I didn’t send out the invitations until after the party. I sat there a long time, but no one came.”
His invitation gave the exact GPS coordinates of the party’s secret location in the University of Cambridge, where he was a professor.
“You are cordially invited to a reception for Time Travellers,” the invitation said. “I am hoping copies of it, in one form or another, will survive for many thousands of years. Maybe one day someone living in the future will find the information and use a wormhole time machine to come back to my party, proving that time travel will one day be possible.”
In a lecture on the possibility of time travel on Hawking’s website, he keeps an open mind.
Hawking concludes that “rapid space-travel, or travel back in time, can’t be ruled out, according to our present understanding. They would cause great logical problems, so let’s hope there’s a Chronology Protection Law, to prevent people going back, and killing our parents.”
Sharp-eyed readers will note that Hawking only references time travel backwards. That’s because the same logical problem—those travelling to the past could alter the future, disrupting the present—doesn’t exist.
So time travel to the future is more plausible. Which doesn’t really help if you want to win the lottery by knowing the numbers in advance. But it’s still pretty cool.
Hawking died aged 76 on March 14, 2018.