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.