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Let's say I've been able to travel in time and I am back in the past (just by a few years or even centuries). I do not have any modern gadgets or even modern clothes, just me and my 21st century mind.

I do not have enough time to prove that I am from the future by predicting future events (like a future president or an environmental catastrophe), but I did prepare for a while using the answers to this question, so that any current scientific knowledge is actually usable.


How would I prove to other people that I am from the future?

Talking to a medieval person about Quantum Mechanics would just get me killed, since I could not prove anything.


What's the upper limit of time from which I will no longer be able to prove my identity?

For instance, if I just traveled back a year, I don't think I'd be able to prove that I'm from a more scientifically advances society.


Let me know whether I've been clear or not.

Thanks in advance.

I found this question but it is a little too specific. I would like a reference to the scientific knowledge of each "ancient" society. Furthermore, my question is not about surviving in the past, but about actively proving to other people that I come from the 21st century.

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    $\begingroup$ Hard science and science based are conflicting tag. Moreover, which sort of papers do you expect to quote on time travellers? $\endgroup$ – L.Dutch May 10 at 8:48
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  • $\begingroup$ @L.Dutch-ReinstateMonica the upper limit I was talking about $\endgroup$ – Simo Pelle May 10 at 8:58
  • $\begingroup$ I don't think that you would be able to talk about upper case S Science with anybody from a past beyond about 400 years ago, unless you possess very highly specialized knowledge. For example, suppose you want to prove to an ancient Greek astronomer, for example, Hipparchus, that planets move on ellipses according to Kepler's laws: you would need to know what instruments they used; how to use them; how to improve their accuracy and precision; how they wrote down their observations; how they did and notated math, including trigonometry; and so on, stuff which very few people study nowadays. $\endgroup$ – AlexP May 10 at 12:08
  • $\begingroup$ Talking to a medieval person about Quantum Mechanics would just get me killed Talking to them at all would be difficult given the language difficulties, but all quantum mechanics would sound like to them is drivel - they'd think you were crazy (at worst) or a story telling fool (at best). But they won't kill you. $\endgroup$ – StephenG May 10 at 12:16
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It depends on how long you have, and what resources you can apply, and who you're proving it to.

Low-credibility claims require high-credibility evidence.

Finding treasure is one way (be careful who you talk to, or they'll ask for more). Penicillin is another, and good as a miracle cure to some ailments.

You might also be able to get somewhere with railguns, or advanced mathematics, or a longitude-accurate clock. It depends on the priorities of your target civilisation and how many people you need to prove it to.

Go back far enough, and (assuming you can learn the language and aren't enslaved), metallurgy and chemistry could be sufficient.

The limiting factor is mostly in knowing where and when you are, so you know how to prepare.

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  • $\begingroup$ I think this might be the best answer... Even if I still have some doubts. Metallurgy and chemistry are quite difficult to apply without modern instruments. And yeah, I could talk to anyone about calculus or complex numbers, but I would just seem really smart, not a time traveller. $\endgroup$ – Simo Pelle May 11 at 20:57
  • $\begingroup$ I do really like the penicillin part, since it can be synthetized starting from natural ingredients. Could this mean that an upper bound to prove my identity is 1895? $\endgroup$ – Simo Pelle May 11 at 20:58
  • $\begingroup$ Metallurgy along the lines of "making bronze" works in older eras. For more modern times (with surviving records), pulling out knowledge of current events a few days or weeks before they happen is fairly convincing. If you're late enough for something to be more or less possible, you're at about the right time to make it convincing. Artificial dyes could also help - mauve was discovered in 1856. The use (or codebreaking) of electronic cipher machines could also get you taken seriously. $\endgroup$ – Anon May 13 at 3:55
  • $\begingroup$ Thank you very much! $\endgroup$ – Simo Pelle May 13 at 20:51
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I mean, just have future you start talking all about the inner workings of past you's past. If a person started telling me about my inner thoughts and whatnot, then I'd be pretty convinced.

A Q&A-based conversation between them would likely be enough.

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  • $\begingroup$ This is really interesting. However, my question was more based on how modern scientific knowledge could be applied using ancient technology or, in other words, if the actual limit for past people to discover today's knowledge was only the lack of instruments or even lack of "intelligence". $\endgroup$ – Simo Pelle May 11 at 21:20
  • $\begingroup$ @SimoPelle Your question is titled "Proving to the past that I am from the future". You made no specific statement about scientific knowledge, intelligence, or otherwise anything you just mentioned. You asked how to prove that you were from the future. The direct question in your explanation is: How would I prove to other people that I am from the future? $\endgroup$ – A Writer May 12 at 2:16

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