melannen | Crossover backstories

I have written a lot of crossovers, but most of them I just put together for fun for a story. There are certain ones that get stuck for me, and make so much sense, and often make canon make so much more sense, that I 100% believe them to the extent you can assume anytime I'm playing in a world, that crossover is active, even if I never explictly mention it in the story. I've run into a few of them talking with people lately, so I thought I would make a list! (I have probably forgotten some that I'll have to come back and add later. And I've left out ones like "Ms. Frizzle is a Timelord" that everybody knows are true.)

There are no Young Wizards crossovers. Every universe is canonically part of the Young Wizards multiverse (though they may seem more or less so, depending on their own laws and the needs of their inhabitants) so every fic is a Young Wizards fic and none are crossovers.
Not every universe has Highlander immortals, but a lot of them do.
- Mad Max is an immortal whose memory gets super messed up every time he takes a Quickening. (Or, well, maybe more accurately: a Quickening that messes up its winner's memory whenever it gets taken.)
- The Old Guard is a Highlander movie; the people who invented the Game were just barely smart enough not to tell Andromache of Scythia about it.
- People with the Ancient gene are usually pre-Immortals (unless they're already Immortals) Also, the reason you don't mess around with quickenings on "Holy Ground" is that Quickening energy reacts really poorly with even trace amounts of Naquadah. In fact the whole Quickening thing was originally a defense against becoming Goa'uld hosts that was put in place by the last remnant Ancients on Earth during the first Goa'uld invasion, although that's almost entirely forgotten; descendants of Ancient people who left Earth before then don't have it. (This doesn't quite line up with all the lore but the Naquadah-Holy Ground part makes so much sense that I stick with it anyway.)
  - (Also, everyone on the Leverage team has the Ancient gene.)
Tolkien's Middle Earth is the universe from Diane Duane's Wounded Sky. Which makes K't'lk Ungoliant and assorted other powers the shadows of various Enterprise crew. (Someday I'll write the fic where they get a chance to visit.)
A Night in the Lonesome October gives the AU backstory of A Study in Emerald.
Sister Simplice from Les Miserables is the French vampire from They Who Hunt The Night. She is bleached-white with cool waxy skin and no detectable age, but she lived through the Great Plague, so it makes sense she'd go into nursing. (Honestly any time I mention vampires they're probably Hambly-style unless they explicitly aren't because they make so much more sense than any others I've read.)
The Earl of Red Gloria is friends with the Dukes of Denver.
Machineries of Empire and the Locked Tomb take place in the same universe, but quite far apart. Look the magic in Machineries isn't not necromancy-adjacent and a myriad is plenty long enough for a whole society to grow up that doesn't remember Earth.
The M25 is a demonic sigil in every universe where it exists. Not sure this counts as a crossover as opposed to a true fact that happened to be popularized by a book, but a lot of people assume it's a crossover when they notice it. Most bypass ring roads are demonic sigils actually; if they weren't before they were built they are after people have been driving them awhile. (The bit where CDs or cassettes left in a car turned into Best of Queen is also a thing that's just true that only happened to be popularized in a book.)
Good Omens is set in the same universe as Mark Twain's Adam and Eve Family Papers.
Indiana Jones and The X-Files take place in the same universe. They also share the same government storage warehouse. (I haven't seen the Indy movie that has aliens in it but also I don't care.)
San Fransokyo was built by refugees after the end of the Kaiju threat and disbanding of the PPDC. Apparently it's now canonically a post-1906 earthquake alternate history but I prefer my version.
Due South and Dresden Files are set in the same Chicago (it's just that the Due South characters understand the magic better.)
Every mysterious invisible island in Lake Michigan is the same island, connected interdimensionally (I've collected three so far, but I suspect a lot of worlds have them, it's just nobody's found them yet.)
All large libraries and small twisty bookstores are connected via L-space.
If you need a place where the air is sweet and everything's A-OK badly enough, then from any city in all the worlds, I can tell you how to get to Sesame Street.
The Minecraft "multiverse" is actually a very old Dyson swarm (or possibly a cluster of them.) Bedrock is scrith. You can fit about a quadrillion average-sized Minecraft worlds into a 1 AU full-sphere Dyson swarm, or 70000 max-sized ones, more if they're not completely flat. Yes I've done the math¹, if you assume scrith and artifical gravity this explains everything about Minecraft worlds. Of course there are many more than 70,000 Minecraft worlds but most of them are orders of magnitude smaller than the maximum. The respawn mechanic is that player characters are all cloned ancillaries. (I dare someone to either write Tisarwat and friends visiting that version of the Radch or your favorite Minecraft people making it outside the Radch for the first time.)

1.A standard minecraft "world" is a flat disk approximately 400 m thick, with 150m or so of rock, caves, lava and ocean capped by 250m of terrain and sky, bordered by an impassible forcefield at the circumference. The bottom five meters are made of "bedrock", a physics-breaking substance that cannot be moved, destroyed, or altered using any ordinary methods. The radius of the world is somewhere between 19m and 30,000,000m although very few are near either of those extremes - 30,000m is slightly beyond the largest radius in which End Portals generate in standard worlds, which is probably reasonable as an average size for a Minecraft world.

Minecraft worlds have a constant, equal length day/night cycle marked by the sun moving across the sky at a constant speed from east to west at zenith and then rising again in the east. At night the stars move in the same direction as the sun. The minecraft world also has an 8-day lunar cycle in which a moon remains at full opposition from the sun while going through full-waning-new-waxing-full phases, one per day.

"Gravity" acts differently on different substances and not according the rules of the wider universe.

Things we will not worry about:

The structural viability of the Minecraft world. It's made of scrith, it maintains its shape regardless of any ordinary physical forces.
Gravity. "Gravity" on a Minecraft world does not work the same as Earth gravity and we must assume that large-scale gravity is basically negligible and the gravity effects that are observed are due to a technical artificial gravity system we will not be attempting to invent at this time. The artificial gravity system presumably also compensates for centripetal and Coriolis forces and maintaining an atmosphere and so on.
Absolute time. Time on a Minecraft world is hard to gauge; in theory a day-length is 20 minutes, but things happen in that day that are unlikely to be able to happen in only 20 minutes on any known planet, so we're going to assume that while relative times are accurate (eight days per lunar cycle) there may be some unknown time dilation effects relative to our source of information, and so we're not going to worry about that.
The End and the Nether. That's extradimensional necromancy stuff and outside our ambit.

OK. So, with those postulates, I propose:

Minecraft worlds are individual artificial satellites in a Dyson swarm. This by itself describes nearly all remaining characteristics of a Minecraft world, and a nearly complete Dyson swarm at 1 AU could contain approximately one quadrillion individual Minecraft worlds of 30,000m radius, or one trillion at 300,000m radius. (The best estimate is that far fewer than a billion have ever been visited by a player at all.) And you can, of course, have a larger orbit than one AU or more than one shell, and most generated Minecraft worlds are much smaller than 300,000 blocks.
In order to get the day/night cycle, you have to spin the worlds. While there are ways to fudge a sunrise and sunset on a non-rotating world, in order to have the stars also spin you're basically going to have to spin the world (or else have them be projected on some kind of nearby sphere, but at that point you might as well propose they're some kind of computer-simulated virtual world or something silly like that.). Because we've already postulated artificial gravity and scrith, we can probably ignore any other issues that would result from this. As a bonus, spinning a satellite uses gyroscopic forces to increase its orbital stability, which is extremely tricky and important in a Dyson swarm, so it probably makes some sense to add a spin anyway. (does it make sense to have your swarm components be flat disks with biosphere on only one side? shhh we're not asking that question.)
While the stars would be outside the sphere and therefore might be eclipsed by other worldlets, most of the times when that would be possible would be at dawn and dusk (as the habitable surface of the worldlet is facing away from the interior of the sphere during its night) and depending on how the rotations of different worldlets are synced, the nearest ones might be edge-on during that time. (However, for low-tech empirical proof of this theory, carefully looking for eclipsed stars in the band of sky that's at zenith right at dusk and dawn is probably the best method. ETA: having spent a few nights stargazing, atmospheric twinkling gives the effect of frequent eclipsed stars through the whole sky - so without very precise measurements it would be impossible to tell either way.)
The stars don't, as far as my observations go, move at all relative to the sun, which is a problem because the Sun should move through the Zodiacal ring as the worldlet orbits over the course of the year. However, the orbits of worldlets in a Dyson swarm are an extremely complicated math problem that I don't understand at all. One possibility is that they have a millennia+ long year, so in the ten-ish years of observations we have they just haven't moved noticeably yet. That would actually imply that the Dyson swarm is in a very large orbit circling a very bright sun - maybe closer to Kuiper belt range that Earth orbit range - which would greatly increase the spacing possible for a trillion+ worldlets and reduce the chance of observable occultations of stars.
This leaves the question of the moon. For it to remain constantly in opposition to the sun, each Minecraft worldlet needs to have its own moon, which orbits the sun just outside the world's orbit but at the same rotational speed, remaining stationary relative to the line connecting the worldlet and the sun. In theory this would be the L2 point (the James Webb space telescope is in the equivalent point relative to Earth) but, as the L2 point isn't stable anyway, the "moon" is going to need some orbital stabilization. In fact for any Dyson swarm even close to complete, there would need to be quite a bit of active orbital stabilization, so the "moons" may also provide some kind of external stabilization to the main worldlets as well (if they're in some kind of artificial gravitational relationship with their worldlet, they may be closer than L2.) Some Minecraft worlds have noticeably different moons than others - for example, Hermitcraft Season 8 or SMPEarth - so an individual moon in stationary orbit makes sense in those terms as well.
Because the moon does not move relative to the sun and worldlet, the phases must have a different source than the phases of Earth's moon. One is that the moon is a regular solid body that is simply colored half dark and half light and rotates once every eight days relative to the worldlet. There is also a possibility that the moon phases are caused by periodic eclipses of the moon by the worldlet (maybe as part of an orbital correction cycle?) - the annular appearance of the new moon implies this - but it's half-black, half-reflective and rotates in eight days requires much less math to prove plausibility.

Crossover backstories

Re: Thoughts