Stephen Hawking, pictured above left, was considered one of the world’s smartest people during his lifetime. The author of “A Brief History of Time”, Hawking was an expert in theoretical physics — and he had a lot of theories about the way the universe worked well beyond his core area of study. He famously did not believe in any sort of higher power, was sure that the chance of an alien encounter over the foreseeable future was nil, and dispensed with the idea that time travel could be real. All of these takes were firmly grounded in science, of course, but they also often sparked debate, both in the scientific community and among lay people.

In June of 2012, Hawking attempted to put one such debate to rest — the one around time travel. To see if it was real, he threw himself a big party, “complete with balloons, hors d’oeuvres, and iced champagne,” per Scientific American. And on the invitee list was everyone. Here’s a copy of the invitation, below:

You’ll immediately note two things about the invitation: one, it’s intended to be a welcome party for time travelers, and two, it took place in June of 2009, about three years before Hawking told anyone about the party — assuming time is linear, that is. But for a time traveler, that shouldn’t be an issue. If time travel were possible, Hawking half-jokingly observed, at least one of the time travelers out there would have at least made an appearance. After all, who wouldn’t want to hang out with Steven Hawking? And if you’re a time traveler, it’s not like you’re too busy.

And yet, no one showed up. Professor Hawking and his team were left alone in the room, a banner reading “Welcome Time Travelers” hanging from the wall waiting to greet the guests that never arrived. He was disappointed — per Altas Obscura, Hawking stated that he “was hoping a future Ms. Universe was going to step through the door” — but not surprised. In an interview in 2012, Hawking (per History Channel) cited the party as “experimental evidence that time travel is not possible.”

Of course, there are plenty of other explanations as to why no time travelers showed up at Hawking’s party. Perhaps non-interference with former events is the law of the time-traveling future, as doing so would have implications on future timelines that we can’t appreciate. Maybe time travelers were there but were invisible, on some sort of other planes of existence. Or maybe Stephen Hawking’s parties are known, throughout timelines, to be really boring and best avoided.

Regardless, Hawking and his proteges almost certainly saw this “experimental evidence” as more joke than science. After he passed away in March of 2018, he was interred in Westminster Abbey as thousands gathered to pay their final respects. The Stephen Hawking Foundation gave out 1,000 tickets to the event, issuing them via a lottery hosted on the organization’s website. Anyone who wished to get a ticket could register for the drawing by filling out a form that, among other things, asked for the person’s birthdate. And as one London travel blogger noticed, the Foundation made some efforts to accommodate time travelers. Despite the fact that Hawking was interred in 2018, the Foundation’s website accepted well-wishers extending to 2038 — just in case any future-born time travelers wished to attend Hawking’s funeral.

(As far as we know, none did.)