Londenio, a loyal MR reader, asks:I am reassured to discover that I am not the only person in the world who has considered this question. Actually, my version of this fantasy usually puts me in Elizabethan England, so that with a little acclimation I'd be able to speak the language.I wanted to ask for survival tips in case I am unexpectedly transported to a random location in Europe (say for instance current France/Benelux/Germany) in the year 1000 AD (plus or minus 200 years). I assume that such transportation would leave me with what I am wearing, what I know, and nothing else. Any advice would help.I hope you have an expensive gold wedding band but otherwise start off by keeping your mouth shut. Find someone who will take care of you for a few days or weeks and then look for employment in the local church. Your marginal product is quite low, even once you have learned the local language. You might think that knowing economics, or perhaps quantum mechanics, will do you some good but in reality people won't even think your jokes are funny. Even if you can prove Euler's Theorem from memory no one will understand your notation. I hope you have a strong back and an up to date smallpox vaccination.
Even in that variation, Cowan is right that most of my modern knowledge is pretty useless. The first little while, it may be a struggle just to survive, though by virtue of being a well-nourished modern it would take me weeks to starve. But if I could find my feet, I'd try to sell my services as a physician: just knowing to wash my hands and boil water makes me the greatest physician in Europe.
Plus, you'd think that a cellphone is a useless brick in the Dark Ages, but you'd be wrong. Mine has a calculator function, which means that I'd be able to create the only accurate table of logarithms, roots, and trig functions in the world before the battery runs down, the dream that enabled Babbage to get funding for his failed difference engine.
There's lots of interesting discussion of the question in Mr Cowan's comments thread, if you like that sort of thing.