Professor Stephen Hawking's memorial service may see a few time-travelling guests who are yet to be born – if you believe such a thing could be possible.
The public ballot form for tickets lets people scroll from 1918 to 2038 when choosing their date of birth.
While it is unclear if the choice of years is deliberate, a spokesman for the Stephen Hawking Foundation said time travel had not yet been proven impossible.
It would also chime with a cheeky "experiment" once staged by the famous A Brief History of Time author.
Prof Hawking, who died in March this year aged 76, held a party for time travellers in 2009.
Balloons, canapes and champagne were laid on at the event, however no one showed up to meet the world famous physicist.
The invitation read: "You are cordially invited to a reception for time travellers to be hosted by Professor Stephen Hawking.
"To be held in the past, at the University of Cambridge Gonville & Caius College, Trinity Street, Cambridge."
It also included precise co-ordinates for any wandering space-time travellers.
Crucially, the invitations were not sent until the date had passed, so only those who had figured out how to go back in time could attend.
"I sat there a long time, but no one came," Prof Hawking told reporters in 2012.
He said he hoped copies of the invitation would last for thousands of years so that one day somebody might figure it out and eventually show up in their time machine.
More from Stephen Hawking
A memorial service for Prof Hawking will take place on 15 June – his children are offering 1,000 free tickets to the public for the Westminster Abbey event.
The ashes of the physicist will be interred between the graves of Sir Isaac Newton and Charles Darwin.