"Does Hogwarts have like...history books. Of the last century. And a bit. And/or dead people."

"We have an excellent library. And several ghosts. Including our history professor." 

"What a serendipitous coincidence! Where's the history professor?"

"Almost certainly in his office. It's on the fourth floor; I can write you a set of directions." He takes a piece of parchment and a flamingo feather quill out of a desk drawer.

She watches him write out the directions, then accepts them and thanks him and heads off to start following the directions. She would think they were weird if she hadn't already seen how damn Parabolan this place's architecture was. 

She knocks on the office door. 

The architecture is very Parabolan, and also occasionally hyperbolic. Her knock is answered with a soft, surprised "Come in?".

She opens the door. 

"Hi! I'm from another timeline where it's a hundred years ago and London was taken underground and I was hoping to catch up on the local history, and also find out if you will stop being dead if I glow at you, because I have glowing-at-people-and-making-them-not-be-dead powers."

"Hello. I don't think I've seen you in any of my classes," says the transparent elderly man. "You say you want to learn history? We can start in 1066 . . ." he appears to be winding up for a lecture.

"--Uh, I'm definitely not in any of your classes, and I was wondering if we could start a bit later than that, also, the resurrection thing, I mean if you'd rather be a ghost that's fine but."

Lucy can almost see the gears turning in Binns' head as he tries to think an original thought.

"Not being a ghost, you say? Well, it was certainly more convenient being alive and able to hold papers . . ."

"Excellent!" she says brightly. 

She glows. 

And suddenly there is a youngish man, solid and alive and made of meat, dropping into his desk chair from where he had been hovering above it. It creaks unnervingly. 

"My goodness! Everything is so much clearer now, I clearly wasn't thinking straight before. Thank you, miss . . . oh dear, if you said your name I failed to retain it."

"Lucy Whitman. Pleased to meet you. What was wrong?"

"Professor Cuthbert Binns, and very much likewise. What was wrong? Well, it appears that in addition to being dead, I was rather old and barmy. Anyway, did you mention you wanted to learn some history?"

"Yes, I'm from an alternate timeline where it's a hundred years ago and I'd like to catch up."

"An alternate timeline? I'll definitely want to hear more about that later. But you want the last hundred years, eh? They've been very eventful ones . . ." he winds up for an exposition dump again, this one much more animated (you might even say reanimated) and on topic. The muggle Industrial Revolution and attendant faster population growth got some wizards worried (wizards have always had a harder time having children than muggles, but were for most of history better at keeping those children alive), and this escalating tension plus the disruption of the first world war gave the dark wizard Grindelwald an opening to attempt to unify the muggle world under a puppet muggle conqueror and then conquer the result. He was eventually stopped by the combined efforts of Albus Dumbledore, several wizarding governments, and all the muggles who didn't want to get conquered. 

Professor Binns now has to breathe occasionally; does Lucy have any questions so far?

"Why do wizards have a harder time having children?"

"Nobody's sure! It's been like that for all of recorded history. It gets worse in cultures that marry their cousins a lot, but even without that wizards just end up with smaller families than muggles."

"That happens with royalty too. The cousins thing." 

"Yes, hemophilia and so forth. While it's certainly better than interbreeding with muggles, there are plenty of wizards who aren't one's cousin around."

"--Wait, why is it better?"

"Because then you'd be married to a muggle and have half-blood children?"

"Are half-blood children in any way materially disadvantaged compared to non-half-blood children, because for your edification, if my blood wasn't half-and-quarter-and-quarter you would still be dead."

Blink blink. "I'm sorry? Half and quarter and quarter what, exactly?"

"Half human, quarter giant space crab, quarter star."