The public—and time travellers—are being offered free tickets to attend the memorial service of iconic cosmologist Professor Stephen Hawking at London's Westminster Abbey

The public ballot for tickets to Professor Stephen Hawking's thanksgiving service opened Saturday—with visitors from the future welcome to apply.

The theoretical physicist who captured the imagination of millions around the world died on March 14 at the age of 76.

His ashes are being interred on June 15 at London's Westminster Abbey, by the graves of fellow scientific giants Isaac Newton and Charles Darwin.

The world-renowned cosmologist's three children Robert, Lucy and Tim are offering up to 1,000 free tickets to the public through a ballot system, run by the Stephen Hawking Foundation.

Applicants need to give their birth date—but eagle-eyed fans of the man who dedicated his life's work to unravelling the mysteries of the universe spotted that it can be any day up to December 31, 2038.

London travel blogger IanVisits was among those who noticed the quirk that allows people born more than 20 years into the future to apply.

"Professor Hawking once threw a party for time travellers, to see if any would turn up if he posted the invite after the party," he wrote.

"None did, but it seems perfect that the memorial website allows people born in the future to attend the service.

"Look out for time travellers at the abbey."

Potential applicants—from the future or otherwise—are forewarned not to apply if they cannot arrange their own transport and any necessary visas.

The service is set to be attended by Hawking's family, friends and colleagues.

"We are so grateful to Westminster Abbey for offering us the privilege of a service of thanksgiving for the extraordinary life of our father and for giving him such a distinguished final resting place," said Lucy Hawking.

Propelled to stardom by his 1988 book "A Brief History of Time", an unlikely worldwide bestseller, Hawking's genius and wit won over fans from far beyond the rarefied world of astrophysics.

Westminster Abbey will also be open to the public free of charge after the service so people can pay their respects at his grave.

John Hall, the Dean of Westminster, said: "The service of thanksgiving for the life and work of Stephen Hawking will celebrate not only his remarkable achievements as a scientist, but also his character and endurance through his years living with a devastating illness."

Hawking's death triggered a flood of tributes from Queen Elizabeth II to NASA, reflecting his impact both as a scientist and for his refusal to give up in the face of crippling motor neurone disease.

© 2018 AFP