So, let’s say I went back to 1909. I’m not even 100% sure when the Great War started, but I think it was 1914. I’d tell them that the moving pictures would become a big industry, and that they would have synchronised sound and even colour after a few decades. That the cars would become faster and faster, and that the sky would be filled by ever bigger planes. I’d try to explain aerodynamics, which might make my story more realistic (either that or they’d think I’m a complete nutter). I’d tell them about the Olympic games (which most people had not really heard of by 1909) and how big they’d be, and that soon more and more countries would take part in them, and even black people would be allowed to participate. And how women in my time are allowed to vote, and wear jeans, and even have jobs. I wouldn’t tell them they’re allowed to smoke and drive cars though, that would freak them out. I’d describe how in my time everybody has electricity, and that it’s used for all sorts of things: not just lights, but also television (which is a mini-cinema you can fit on a table), refrigerators (which can keep things cold without the ice ever melting), ovens that work without fire, electric heaters and air-condition units (or at least electric fans). And how we have telephones, even small ones that we can carry around and which work with batteries. The battery had already been invented, but it was too big. And maybe I’d try and explain computers to them, though I doubt they’d grasp the idea (even my dad had problems understanding what they were for until recently). And also how you can print anything you want in a few seconds, at home, with very cheap and small printers. And you don’t even have to pick the letters individually!
I have no idea who won any sports events back then. I don’t even know what teams existed, let alone who won the horserace. But maybe I could buy shares in Ford, and sell them before 1929, and buy booze when it was legal and sell it when it wasn’t, or warn people of a short Austrian madman with a moustache that was going to try and conquer the world in 1939. But then they’d just think I’m a prophet and burn me or something.