Time travellers are welcome to attend Stephen Hawking’s memorial service next month. An online ballot to attend the service requires applicants give their date of birth, which can be any day up to December 31, 2038.

So far all applicants live in the present, according to the Stephen Hawking Foundation, but the door remains open to voyagers in a fourth dimension.

A spokesman said: “We cannot exclude the possibility of time travel as it has not been disproven to our satisfaction. "All things are possible until proven otherwise.

"But so far we have had applications from all round the world, and we do mean round - there are no flat-Earthers here."

The flexible policy suggests the professor undertook his own journey on the subject - over time.