"Severe bruising and cold damage," Cam tells Flitwick, and "Do you want one that's like what they've got now or a futuristic one, I was going to do the latter for comfort and ease of motion but if you're not gonna put it on...?"

"I want to see the kind the first humans on the Moon had!"

"One exact replica of Neil Armstrong's suit coming right up." Bam.

It was so many parts! And a zipper! Burbage will entertain herself with the space suit the whole way there, while the others talk about the upcoming term. Does Cam want to get brought up to speed on his new workplace's office gossip? Because that's what's going to happen.

Office gossip includes:

- These two seventh years got engaged over the summer, good for them

- Snape is mad that Burbage got the Defense job instead of him, also isn't he sooooo annoying 

- Probable Quidditch lineups for all the house teams, featuring friendly ribbing between McGonagall and Flitwick 

- Granger is going to be time travelling intermittently to make it to all her classes, that girl is either going to burn out by sixteen or end up in the history books 

- They're redesigning the Arithmancy OWL exam again and Vector doesn't approve of some of the changes 

- Those two sixth years broke up over the summer 

- Hagrid is excited about becoming Care of Magical Creatures professor and Kettleburn is excited about not being Care of Magical Creatures professor anymore 

"...you guys have time travel??"

"Yes, but it's very limited, both practically and legally. Time-turners can only go back in time in one-hour increments, no time-turner can occupy the same point in time more than twice or experience more than thirty-two hours in any twenty-four hour period, it is both dangerous and highly illegal to interact with one's past self, and a great deal of documentary parchmentwork is required for any use. Nonetheless several past students have been able to use them responsibly and effectively to fit two or three extra class periods into a week."

"...that is. An interesting application for time travel. Why is it dangerous to interact with one's past self, is it too tempting to destabilize your time loop and stuff explodes or what? Wouldn't that risk apply to existing in the same general area at all?"

"Entirely too many wizards, upon observing their past selves, attempt to interact with them in ways inconsistent with their own memories of the other perspective. Since a single consistent timeline must always result, their attempts to create contradictions necessarily fail. If someone on the scene is sufficiently quick-witted, consistency can be preserved with memory modification; however, in many cases events turn out to be consistent by preventing the interaction at all, often injuriously to the time traveller or nearby people and scenery. Are you familiar with Muggle accounts of the 'Tunguska Event'?"

"Well, yes, though on my Earth it was in fact just a meteor. I suppose something like that has to be going on to keep the timelines recognizably similar though it beats me how..."

"Yes, though I'm puzzled why the timelines would be similar at all. It is admittedly convenient."

Vector chimes in: "Maybe there are loads of timelines and whatever caused Swan to end up in the wrong one can only go between similar ones. So it's like asking why the lottery's numbers and the winner's numbers happen to be similar."

Flitwick: "What's a lottery?"

Vector: "Muggle way of robbing each other, don't worry about it."

"Oh, come on, I'm not interested in defending the lottery but it's gambling, not robbery, haven't you lot got gambling?"

Vector: "Only bets between individuals, not massive things like the muggles have, but fair enough, I was being glib."

Flitwick: "The Daily Prophet had a big drawing sort of thing this summer."

Vector: "Oh, did they? Alright. Anyway, when you're an arithmancer all 'games of chance' look like complicated ways of robbing each other no matter who's doing them."

"In terms of expected monetary value, absolutely, and some people get dangerously in deep to any form of gambling, but it's usually the done thing to construe it as people paying for the experience of having a chance, small but not in a way that's easily legible to the average person, of winning big. A lottery ticket is a fantasy-construction aid, as it were - in its most responsibly played form, which of course is not the overwhelming use case."

"Huh. You learn something new every day. Say, I've always wondered how much Arithmancy it's possible to do without magic, I mean my kind of magic. How about I give you some lessons this year, whenever we're both free, just to see how it goes?"

"Sounds great! I don't sleep unless I'm super bored or something so I hope to have plenty of time. Is arithmancy importantly different from just... math? Arithmetic, algebra, calculus, all that jazz?"

"A lot of it is just math! Probability, algebra, tensor calculus when things get really interesting. And then some of it's magic. It's a bit like how potions is just cooking, but also magic, but the boundaries are even harder to define."

"I was assuming that the ingredients were magic, or that magic was done to them? I'm definitely confused about how you do magic to math, though."

"The ingredients are often magic, but a muggle with the right ingredients following the right recipe wouldn't get the right results. I suspect a similar phenomenon is at work in arithmancy: many divinatory processes call for a random number or a gut estimate or a measurement taken with an enchanted device. But spell development in particular, to the best of my ability to determine, is purely nonmagical though rather complicated math applied to magical subject matter, such that the only difficulty to be expected would be in testing one's hypotheses. Which is also the hardest step for wizards, albeit for different reasons."

"Huh, so I could do spell development if I wanted?"

"Unless there turns out to be a magic step I don't know about, yes! Except for the part where you find out if what you've made is a spell to blow yourself up."

"I'd have to outsource that, which is a real shame, I'd cope better than most."

"Ironic, that." Vector joins in the Quidditch chatter for the rest of the way to the Moon.

It's a dumb game but Cam feels that way about most sports and doesn't feel the need to weigh in.

Moon!