On June 28th 2009, Stephen Hawking threw a party, but no one came.
He’d set the table, threw up some balloons, popped open a bottle of champagne. And then he waited. And waited. And, well, waited.
Perhaps no one arrived because Hawking didn’t send the invitations until the party was over. Yeah, you’d think that’s the biggest reason he spent the night alone. But this wasn’t an ordinary party (is there such a thing when the host is a theoretical physicist?). Actually, come to think of it, his guests weren’t altogether ordinary, either.
He’d only invited time travelers.
Possibly taking a cue from Enrico Fermi (you know, the Fermi Paradox*), Hawking was trying to prove that time travel isn’t possible. If he held a party and sent the invitations afterwards, published for any time travelers in the future to discover, if time travel were real he could expect his party to be filled with guests from the future.
“You are cordially invited to a reception for Time Travellers…”
Obviously, that didn’t happen. No one came.
There are a number of reasons why time travelers may have given Hawking the cold shoulder. Perhaps, of course, time travel just isn’t possible. Or, maybe, none of the time travelers could be bothered with a dinner party in the year 2009.
Maybe time travel only works with a closed time-like curve, and you can only travel back to the point at which the time machine was turned on. If that’s the case, we’re destined to be without visitors from the future until we create one.
Or, just maybe, Hawking was partying it out with all those time travelers in an alternate universe.
It could happen, and as interesting as this party experiment was, it’s not definitive proof that time travel is impossible.
For now, we’re left with the rather depressing image of Stephen Hawking sitting alone at an otherwise empty table, waiting for visitors from the future who will never arrive.
Or will they?
* The Fermi Paradox is the strange contradiction between the probability of the existence of extraterrestrial civilizations (which, as large as the universe is, is fairly high) and the distinct lack of evidence we have for them. In the case of time travelers, Hawking seems to be asking, “If time travel becomes possible in the future, why aren’t we seeing any time travelers today?”