At Hawking's home at Cambridge University, his party had already begun.
A lavish spread of food and drinks had been prepared, with dozens of balloons decorating the place. Hawking sat in his wheelchair, quietly waiting for possible "time travelers" to arrive from the future.
His caregiver walked over and asked, "Professor, where should I hang the banner you wanted?"
Sitting in his wheelchair, Hawking took a long while before replying through his speech synthesizer, "Hang it in the living room, then take a picture of me."
His caregiver was named Irene. She had worked for him for ten years, and with a smile, she hung a banner reading "Welcome, Time Travelers" in the brightly lit living room.
Looking at the words on the banner, Irene laughed. "Wow, so our doctor is going to discuss matters of the universe with people from the future. As a mere muggle, shouldn't I stay out of this?"
"Of course. So don't sneak any salad. Whatever you do, people from the future will know," Hawking said in his distinctive electronic voice, his head tilted to one side.
Irene laughed even harder. She took a picture of Hawking with her phone, then snapped several more of the party table, the balloons, and the banner.
Finally, she picked up a plate and ate some fruit salad. "Really, Professor? If I sneak a bite, people from the future will know too? Mm, there isn't enough salad dressing."
"Of course they'll know, because to them, it has already happened," Hawking said.
After eating a few bites, Irene said, "Don't you think time travel doesn't exist? I remember it was called some kind of protection..."
"The Chronology Protection Conjecture. So this is a test, and also a joke. The future me knows, but I can't come back to the present