Knowing you would be more weirded out if you had more information, but you don't, so you are just baffled without all the information to be fully baffled by it, is a weird sensation.

"--It also shows performances?" Nailed it.

"Yeah! It's connected to the Internet which is-- a sort of way to send letters very fast, as fast as light? And also pictures and sounds? So you can find out anything you want there. People mostly use it for cat pictures, extremely stupid arguments, and porn."

He is an educated man from a sophisticated nation.

He is going to keep up with this conversation.

HE WILL DO GREAT TANG PROUD IN THE FACE OF WHATEVER THE HELL THE DIGITAL AGE IS.

"So like books, but faster-- and with more cats."

"Well, I don't know how many cat pictures there are in books in-- wherever you're from. China? Japan?"

"From Great Tang. We use the medium of woodblock printing to its full potential."

"Oh, I don't remember that one. Where is it on the map?"

Jing Yi traces the borders on the map with his finger. (The smartphone scrolls wildly, until his works out to hover his fingers over to do the tracing.)

He's definitely pointing at the area around China, but the borders are not where Lev would expect them.

"Oh! China! I wish I knew more Chinese history so I could know if you were in an alternate history--"

"Do 'Emperor Xuanzong' or 'Duke Chang' ring any bells?" (He means zero disrespect, but if anything was going to change in an alternate history, it'd be around that whole situation.)

(Also he's talking to someone who could, hypothetically, know his life as 'history' which is... a potential existential crisis he is going to ignore.)

"Uh, sorry, no, my ancestors are from here"-- he points to Russia-- "I have absolutely no idea about anything that happened in China at any point. Confucius something something Mao."

"I know very little about where your from, so I'd call that fair."

"My parents moved from here"-- he points to Russia-- "to here"-- he points to New York City on the North America map-- "for... various complicated reasons... but mostly that if you try to get all the peasants to own everything communally instead of individuals having property rights it doesn't work very well and makes your country very poor. So, uh, write that down somewhere I guess. Communal ownership of the means of production is a bad idea."

"Noted, communal production ownership is bad."

Look. Look. Sometimes to find out things you have to ask the really dumb questions. Even if you cringe as it comes out of your own mouth. He points in the general direction of the Americas. "Is making land masses a digital age thing, or has that-- always been there."

It turns out that when Lev is excited he bounces up and down in his chair.

"Actually we can make land masses! Uh, let me zoom in"-- he expands the map so it's only showing the place where he grew up-- "from there to there wasn't there originally, they just dumped a bunch of garbage and soil there and then it became new land. But that's not very cost-effective most places, they only did it in New York City because an acre of land in New York City costs-- uh, let me think-- about as much as ten thousand laborers make in a year? But of course we're much richer than you. Oh! Sorry. I got distracted. Yes, the Americas were there all along, at least in our timeline."

Okay, that is highly adorable. 10 out 10 enthusiasm for explaining things. Even if he did explain in the opposite order of usefulness. 

And if he can prove to himself and other people that this isn't some failing-at-entering-a-window head trauma induced dream, this is going to be so useful. Cartography! Extra secret landmasses. An inconvenient distance away, the logistics would be hell, but extra landmasses. "This place is excellent. Best window I've fallen through."

"It really is!!! I've been here for subjective weeks. Did you know that Bar will just sell you books from alternate universes." His tone of voice suggests that this is the most important imaginable fact.

That is not the most important imaginable fact, but it is up there. (So much information, and you can just purchase it.) "I'm guessing that's how you encountered the concept of black hole bombs."

"No, we theorized that those are physically possible-- um, I would explain what they are but I'm pretty sure your culture doesn't have the concept of black holes and possibly it's more important to share more practical science--"

"--oh no I wonder how Bar accounts for purchasing power parity."

Black holes: not 'practical', apparently.

"That's the 'much richer than you' thing? I wouldn't worry about that." Does he have access to arbitrary amounts of money? No. (Especially when Xiao Jinyu is not giving him his salary, the jerk.) Does he have access to relatively arbitrary amounts of money in the name of the family business? If he can convince his father this is real, yes.

"Right. In my culture a book costs-- about a half hour's wages for an ordinary laborer? And I think in a medieval society books cost. More. Than that. So I don't know if Bar is going to benchmark our books as costing a half hour's wages or as costing the same amount as a book does in your society."

The digital age has weirdly cheap books and land reclamation and smart phones, but weirdly cheap books at least makes some sort of sense. Woodblock printing is cheaper than writing everything by hand, ???? is cheaper than woodblocks.

"That's still affordable, considering how useful it could be. Though I wouldn't say no to being steered in the right direction." (Yes, person who has been here for subjective(?) weeks, tell me your secrets)

"Um. I think variolation was invented in China pretty early so I'm sorry if you already know this, but if you scratch someone's skin and put in a bit of powdered smallpox scab they'll get a milder form of smallpox and be less likely to die of it. That's very important. Our society has eradicated smallpox. --Also, check whether milkmaids don't get smallpox, if they don't then they have cowpox and you can do the same thing with cowpox and then no one will die."

"You don't have smallpox?" What is up with the digital age?

He can probably convince Leng Yue to try that. Or maybe Jinyu; he's more in favour of experiments but less medically inclined. It won't be easy, but he could. He'd just have to work out a saner explanation than 'a foreigner from the future who I found in my window told me to try it'

"We don't have smallpox! In my country we don't have malaria or hookworm or rubella. We used to not have measles but then people stopped getting vaccines for measles because they were worried it caused-- uh, 'autism' probably doesn't translate-- intellectual disability?"