Steven Hawking's time traveller party
en.wikipedia.org
en.wikipedia.org
This is making a large assumption, of course, that time travelers had any interest in attending his party, or that they even would have heard about it.*
* I do not believe in time travel.
1.Time-travel will never become possible.
2.Time-travel becomes possible. Their time travel capabilities are inadequate to visit us.
3.Time-travel becomes possible. They do not wish to visit us.
4.Our archiving and preservation techniques are inadequate. Our message does not reach the future.
5.Time travel becomes possible. They are willing and able to travel to the past. Our archiving and preservation techniques are adequate. The message has not been accessed in its future database.
6. Time travel becomes possible. They are willing and able to travel to the past. Our archiving and preservation techniques are adequate. We are not able to perceive or become aware of their visitation.
Also, rebasing the future makes me think of time travel as git history.
Imagine the merge requests and the fights inside them
MR #1: went back in time and killed hitler.
That's what I thought about when I picked the word rebasing ;).
You can use it, but in doing so you remove the conditions for creating time travel. You can use it once and then you and your entire timeline cease to exist. In such conditions I might reserve the use of time travel for things like preventing an unlivable hellscape and not waste it on attending a party with balloons.
(Relevant Chris&Jack sketch:)
Then a bunch of other people arrived and they had a wild party.
Insanity would probably be an effective defense.
There's an analog to the film The Man From Earth where a similar claim tiptoes on the line of credibility and insanity, with the audience never truly knowing.
And this is effectively what Hawking did: the secret is just the location of the party.
(Obviously this isn't foolproof. If a reliable government agency prepares the envelope and makes sure nobody opens it, they could convince themselves you're legitimate. Which is why you need to do this as a fun, unserious joke.)
ETA: Also, if you wanted to make sure the government didn't torture the plausibly-deniable "time traveler" anyway, you'd swear everyone to silence and spread the rumor that "nobody showed up." How would we ever know? ;)