On June 28, 2009, Stephen Hawking sat alone in a college at the University of Cambridge and waited for party guests to arrive. He waited patiently for his guests, but not one of them showed up. 

Then he sent out invites.

Sending out invites after a party is a pretty surefire way to make sure your guests don't show up (little pro-tip for all you introverts out there, looking for a quiet night in). However, Hawking wasn't just looking for guests, he was looking for time travelers. 

"Here is the invitation giving you the exact co-ordinates of time and space," he said, talking about the party in the documentary Into the Universe with Stephen Hawking.

"Copies of it will survive in one form or another 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."

No one did. There are a number of reasons why time travelers didn't show up. For example, the invites may not have lasted until time travel was invented, the time travelers might have shown up but Hawking kept it secret to protect the space-time continuum, or perhaps you can only travel back to the point where time travel was invented.

However, Hawking was publicly unoptimistic about what his one-man party meant.

"I have experimental evidence that time travel is not possible," Hawking told Arstechnica. "I sat there a long time, but no one came."

In Into the Universe with Stephen Hawking, he added, "What a shame. I was hoping a future Miss Universe was going to step through the door."

Well, time-traveling Miss Universe contestants, you missed the party but you still have a chance to pay your respects to Hawking.

Stephen Hawking's family are releasing tickets to his memorial service to members of the public. If you want to attend, you can apply for one of the 1,000 available tickets via a public ballot on the Stephen Hawking Foundation's website.

In a move we're sure Stephen Hawking would approve of, the ballot is not just open to members of the public from our own time, but to people from the future as well.

The ballot allows you to enter your birthdate, but you won't be stopped from getting tickets just because you haven't been born yet. In fact, you can select any date up until December 31, 2038.

Time travelers, if you missed the party and want to show us that time travel is not impossible, here is your chance.