LONDON (Reuters) - Stephen Hawking’s family have invited time travelers to his memorial service, seeking to tackle one of the curiosities that eluded the British physicist during his extraordinary life. . . . The option to have a date of birth in the future was spotted by London blogger ianvisits who wrote on his site: “Professor Hawking once threw a party for time travelers, to see if any would turn up if he posted the invite after the party. “None did, but it seems perfect that the memorial website allows people born in the future to attend the service. Look...