Stephen Hawking once threw a party for time-travelers that he didn't announce until the day after the party
Stephen Hawking is a famous theoretical physicist and cosmologist. Known for his considerable intelligence, Hawking has contributed many scientific works and among other awards, received the Presidential Medal of Freedom (the highest civilian honor available in the United States).
So it was no joke when Hawking threw a party for time travelers. He held the party on June 28, 2009, but no one showed up. Was he just not popular enough? Nope.
Hawking didn't actually send out invitations or notify people about the party until the day after it took place. This was all part of an experiment about time travel.
Hawking does not believe it is possible, and says that his failed party proves this. No one retrospectively showed up despite his party announcements. In other words, no one traveled back in time to his party after they got the invitation.