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Set in 2123AD, humanity created a time machine that can send people into the past as far back as 123AD. Currently the machine is able to send 2 persons and they must put on a special suit that protects the wearer against the spacetime turbulence which obliterates anything that comes into contact with it including the suit. Yes it means all time travelers would return completely naked! To make matter worst it has a side effect, all returning time travelers complaint of amnesia saying they had absolutely no recollection of any memory pertaining to the time travel. According to the users, they simply took a seat inside the cabin and then suddenly went blackout for a brief period of 5 seconds before regaining consciousness. How to proof the time travel works since they can't remember or bring back anything?

Operation manual translated by me: User must wear the suit provided and nothing else, machine will not work if the first rule is violated for safety measure. Please remain seated when the countdown starts and wait for the green lights before exiting the capsule. Be warned that you must return to the capsule within 7 days or you will be obliterated by the accumulated residual buildup of spacetime energy that not even the suit can save you.

Note: Whenever 2 events meet, a new timeline forks and this include returning to the original timeline. This residual buildup of spacetime energy applies to anything that traverse outside of their original timeline but can be offset by returning back to the original timeline.

user6760
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  • One imagines all the inevitable paradoxes (and non-paradox vandalism) would provide the needed proof. – user535733 Dec 07 '23 at 11:22
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    We have several questions, all asking how to prove time travel, with just different toppings. https://worldbuilding.stackexchange.com/questions/12348/how-do-you-prove-youre-from-the-future – L.Dutch Dec 07 '23 at 11:37
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    Scribble KILROY WAS HERE on the Colossi of Memnon? Hide a copy of Emperor Claudius's Etruscan and Carthaginian histories in a cave in Palestine, together with a copy of his Etruscan dictionary? Pay to have an inscription made giving the name of whoever was bishop of Rome in 123 CE, or else saying that there was no official bishop of Rome? Open a school in Rome teaching geometric perspective to painters? The point is that everything we know about the classical world in 123 CE came to us by other means than people remembering it; all they have to do is make sure they leave traces. – AlexP Dec 07 '23 at 12:50
  • Are the suits sealed? What do the wearers breathe and eat or drink? There are also obvious questions about what happens to the byproducts of those activities too. – Starfish Prime Dec 07 '23 at 14:40
  • Save yourself the mental effort, just decide to will have had left yourself a note informing yourself of how you will have previously convinced your interlocutor and then have gone back in time and have had done what it will have had said on the note. Then take a nap, you already have will previously will do it already yet. – g s Dec 07 '23 at 17:59

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Make a non memory message

Using cybernetic implants inside their bodies, while in the past they can make a record of what they saw. Since the suit only erases things outside their bodies, this allows them to keep a record of what they saw.

One easy way to do this would be to implant a keyboard or recording device under their skin and have it record what happens.

This could fail if there is intelligent interference e.g. if there is a time god who is wiping memories, but if there is a time god then they can't do much because the time god is all powerful.

Nepene Nep
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This is a Frame Challenge

How do you defeat a godlike character? You can't. You must introduce a weakness, an Achilles heel.

You've created a "godlike character" by developing rules of time travel that forbid proof of action. There's some problems with it...

  1. Apparently the suit is destroyed only after the round trip, which doesn't make sense. If it can be designed to survive traveling through time twice, it can be designed to travel through time thrice, thereby eliminating the "you're nekid!" restriction.

  2. Ignoring Arnold in The Terminator, the idea of everything "not you" not surviving the trip is ridiculous. Does hair survive? If so, then will anything made of Keratin survive? How does time travel know when something is "part of you" and not "part of you?" In other words, since you're inventing a non-science-based rule, who's to say they can't slip a piece of paper inside the suit and travel back with it, the suit disappearing and the paper, now unrecognized by the traveler, falling gently to the floor? No suit is actually "skin tight..." so how would your system even know if something not-the-traveler is inside the suit?

  3. Are you saying the amnesia only happens on the return trip? So the traveler is fully conscious of who they are and what they're doing in the past? What is it about the return trip that does this but doesn't do that after the first leg?

In short, you've created a godlike problem and it can only be solved in the usual "how do I defeat my godlike character?" way... you need to introduce a weakness.

So, in regard to my original answer, below, while it might be problematic to slip the Colossus of Rhodes inside your suit, I suggest that as a necessary component to solving your problem, travelers can slip things inside the suit... like a small Roman Fresco.

Air in their lungs

But, if that's not your cup of tea, the problem is automatically solved by analyzing the air inside the traveler's lungs. Unless you further perfect your godlike machine problem by stating the suits are hermetically sealed and the travelers can't leave their suits at any time.

This was my original answer before thinking about the "can't carry anything, can't remember anything" condition. It's here both for the Frame Challenge, above, and for entertainment purposes.

Take a piece of artwork believed to be missing

There are a fair number of pieces of art that have become lost to history.

Turns out at least one of them was lost to history because your time travellers boosted it.

The art can be proven to be from the past because it's missing all the chemical hallmarks of existing in the atmosphere during all those years. In fact, the further back you can go to (*ahem...*) borrow a painting the better due to the decreasing number of pollutants as you travel further into the past.

Who would have thought that polluting our atmosphere would prove useful?

While Roman frescoes would likely be the most practical choice, since you can travel a long, honking way into the past... long before modern hydrocarbon pollution came into play, and therefore prove you didn't just skip over to Italy and boost a piece while no one was looking... I should think you could get extra points for showing up with the Colossus of Rhodes.

Timmy... how'd you get that through the portal?

JBH
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eat something.

Or, store something in you mouth before you leave. say, some futuristic technology (futuristic in regard to the time you're travelling to) or an antique (if you're going to the past). along with a note and some pictures of people you know. that might help jog you memory. on the note, make sure you write when to return to the capsule.

hope this helps!

alkahest
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