I think lasers are pretty wack when you think about them through this lens. A small, wand-like object in your hand can make light appear from seemingly nowhere. If it’s powerful enough it can set things on fire or blind people. Not to mention larger ones like laser cutters or the LLD, used to destroy missiles midflight. Thats sure to blow some feudal peasant minds
Smart phones. The caveat being you couldn’t take one back in time and impress them because the internet and cellular network wouldn’t be there.
I remember a great answer to this somewhere and they said a solar powered 4 function calculator is the simplest thing we have today that would blow people’s minds. You really don’t even need a scientific one to achieve the effect. Apart from the obvious (quick math, LCD display, and solar power) it also uses plastic.
You don’t need a network to make a smartphone black magic. Just taking pictures is enough, but also single player games, calculators, word processors, image editors, music players, really any non-networked application is still magic to pre-computer people.
Well, for like a day or two then the battery dies! But yeah, it would still be impressive, I’m not saying it wouldn’t. A time traveler must always ask themselves how long they intend on visiting!
You can bring a solar panel with you to keep it charged if you have a long visit of convincing people you’re magic planned.