Stephen Hawking - one of the most famous theoretical physicists, cosmologists and brightest people of our time. Hawking has written numerous scientific papers and received numerous awards, among which are the Presidential Medal of Freedom - the highest civilian award in the United States.
So when scientists announced his party to travel in time, it was not entirely a joke. The event was scheduled for the 28th of June of 2009. But no one came to him, and not because Hawking was not popular enough. He just sent out invitations and the party officially announced the next day, the 29th. It was part of his experiment on time travel.
Hawking does not believe that this is possible, and says that his "party" once again proves it - in other words, if someone could travel in time, you would have done it to get to his house.