I'm especially curious in the case of fantasy settings. I'm admittedly not super well read in the genre, I know about the Ways from the Wheel of Time series[^1] , and I'm sure D&D has its fair share of fast travel mechanics.
Anyway, in my case I use mass routers. Rather than a dry lore dump here's a slightly less dry lore dump in story form!
spoiler
He glanced nadirward through the observation window at the green and blue surface of the planet. A river, coruscating in Focus's rays, wound through the verdant jungle passing below. It was THE river, the measure to which all other rivers were compared. It was so old that it didn't even have a name. Every other river on Yih, and every watercourse wrought on other celestial bodies by pioneers in the intervening millennia, was, after peeling away one hundred thousand years of sound changes and semantic drift, named after this river.
But he had seen this sight countless times, and it failed to put his mind at ease. He spun the metal prayer ring on his writing claw, feeling each of the twelve teeth pass under the pad of his outer thumb. The ring had belonged to one of his sires, who had often handed the shiny trinket to him to amuse himself with when he was barely a pup. It had been years since he had prayed it, not until this morning just before being shriven. It had been years since he was last shriven, too. He'd be the first to say he wasn't the most pious Wayfarer, but there was a real possibility, however infinitesimal, that today his life would come to a messy end, and he wanted to have a clean conscience if it came to that.
He turned to face the cause of his anxiety. Attached to a bulkhead opposite the window was a cylindrical machine barely larger than a suspension capsule, with a bore just large enough to fit a single yinrih, and maybe a satchel if the yinrih in question was particularly svelte. He floated over and looked through the bore. It was like he was staring down the business end of a railgun.
«You're going to be fine, Hearthfire.» He tried to reassure himself. «Nothing's going to happen. We did gross upon gross of tests. Equator to pole, Low orbit to surface, surface to moon, even interplanetary hops, all the way from Hearthside to Moonlitter. Inert object tests, live tests, and all the tree-dwellers we sent came out perfect.»
«Except Moonbeam.» nagged a tiny voice in the back of his brain.
«Poor Moonbeam. I know you're not supposed to name them. Makes it harder when... That happens.» The little tree-dweller went in fine, but the impulse buffer on the egress router failed as she dropped back into realspace on the surface, retaining all the momentum from the ingress router in orbit. In the span of a temporal quantum she ceased to be biology and turned into physics, ending up impacting the opposite wall at 20 times the speed of sound. The barrier was built to take it, but her poor body wasn't. She ended up a maroon smear on the wall.
«Time to get strapped in.» said a sandy-furred engineer floating next to the mass router.
He took a deep breath and floated into the bore, slipping his forelegs into the harness, then his hind legs, then his tail, and finally his head.
A voice came through the earpiece around his left ear. «Hearthfire, this is Morningstar. Everything's up and up down here.» It was the same cleric that had given him absolution this morning. «Just for review, you're being routed through an intermediate router on the surface before egressing at the antipodes. The impulse buffer is good on both the intermediate and the egress, in case a packet gets dropped along the way.»
«Ingress and egress buffers are synced.» Said the sandy-furred engineer.
«Acolyte, begin the countdown. May The Light illuminate your way, Hearthfire.» Said Morningstar.
«Twelve...» The sandy-furred engineer began solemnly sounding off the numbers.
«Eleven...» In a matter of seconds, a thin sheath of realspace containing Hearthfire's body would be shunted into the Underlay.
«Ten...» This realspace bubble would be encapsulated into billions of discrete packets.
«Nine...» From the perspective of a hypothetical observer embedded in the Underlay, these packets would appear discontiguous, and could take separate paths to reach the same destination.
«Eight...» But from the perspective of an observer contained within one of these packets, the entire space would still be contiguous.
«Seven...» Blood would still flow, and nerve impulses would still travel uninterrupted.
«Six...» Or they would if the traversal through the Underlay weren't instantaneous.
«Five...» Hearthfire's stream of consciousness would not be broken.
«Four...» There would be no ontological question that what emerged from the egress router was the same Hearthfire that entered the ingress router.
«Three...» These packets would hop instantaneously through an intermediate router directly below at the surface.
«Two...» This router would, in mere nanoseconds, direct the flow of packets to an egress router at the antipodes.
«One...» The egress router would absorb all the momentum that Hearthfire had while in orbit before shunting him back into realspace. Should the intermediate router drop a single packet, the whole flow containing Hearthfire's mass would be shunted harmlessly back into realspace at that router, provided it, too, absorbed his momentum correctly.
«Zero.» Hearthfire felt a tingling sensation, as though his whole body had fallen asleep. The feeling lasted but a fraction of a second, then he felt the weight of his body pulling him down. He had made it. In less than the blink of an eye, he had gone from a space station in low orbit over Yih to a lab on the surface on the opposite side of the planet. Hearthfire was the first yinrih to traverse a mass router network, and he had done it without a hitch.
This was going to change everything.
[^1]: fun fact: the Ways inspired the Nether from Minecraft insofar as one step in one dimension is multiplied in the overworld
From the sci-fi setting, it's your pretty standard "bend space until both destination and departure points are actually nominally close to each other" kind of drive.
Time between jumps usually bottoms out at around 15-20 minutes for most drives, but increases exponentially as a function of distance traveled and desired accuracy of your destination point.
This is because the pre-calculation to compute a successful bend in space-time grows massively more complex the more gravity fields are involved. Extremely long-distance jumps can take hours or days to calculate, but inter-system jumps can be carried out rapidly.
Intersecting the event horizon of a fold in progress is bad. "You're reduced to a fine relativistic spray" bad. So far accidents have been "minor", as in they didn't kill thousands.
The exotic matter required for drives is stupendously expensive. As a result, almost no ships have internal drives, but require a "drive barge" or "FTL barge" to exploit FTL. Despite this, barges are common enough that most families can afford to take an FTL trip if needed.
In UNHA operations, all drives are legally owned by the government and crewed by a detachment of naval personnel, with explicit orders to scuttle a drive rather than allow it to be misused.
In the fantasy setting, it's a little bit different. For one thing, no two fast travel castings work entirely alike. This is because it is a key tenet that magic is a deeply and intrinsically personal thing, and while casters than study concepts to gain inspiration, there's no such thing as a "standardized" casting which can be moved between casters.
For instance, some casters port you through an alternate dimension, and some bend space. Some open a gateway, some transmute you into photons then back, and some encapsulate you in a bubble which moves rapidly.
Even within a broad category, there are subsets: For instance, if they use an alternate dimension, is it one in which points are simply "closer together", or where time flows differently?
It's important to know these things, because different species or other casters being brought along can have... unexpected reactions to different methods.
Like a tugboat or tow plane with a glider. Unique.
What constitutes "misuse"?
Another thing about mass routers, really more about the Underlay, is that you need tailstone for FTL communication, which the mass routing protocol needs to form neighbor relationships with adjacent routers. Tailstone is manufactured by growing monocrystals and fractioning them into wafers. A tailstone wafer can only communicate with other wafers shaved from the same monocrystal, so Underlay tunnel interface cards are sold in sets (usually pairs) that are hard-linked to one another, containing matching wafers. The ansible links between nodes are therefor much more like hard wire runs in that they can't be easily changed to different endpoints.
This manufacturing process has a lot of cybersecurity implications. A bad actor planted within a tailstone fab could grow larger crystals than a downstream client ordered, then break the crystals up to form multiple normal sized ones, giving the client the expected quantity and keeping the other half. That bad actor could then perform MITM attacks on ansibles or routers using those crystals.
One such attack is route poisoning, which is where a malicious router injects false routes into the system, telling other routers that a particular endpoint is somewhere it isn't, redirecting travelers to a destination of the attacker's choosing.
Refreshing that the defining characteristic of your magic system seems to be that it isn't a system.
I love the trope of fast travel being inherently scary. One idea I had was an inversion of the typical hyperspace is hell concept whereby FTL shunted you through Heaven, the risk wasn't demonic possession but having your face melted off by overwhelming holiness Raiders of the Lost Ark style, meaning special precautions had to be taken to keep people from perceiving the environment outside the ship, even conceptually (via sensor readings, for example).
As for the Lonely Galaxy, there are rumors among the superstitious that the Underlay is in fact the Void (the Claravian version of hell), and that the reason why the Bright Way discourages even negative discussion of demons is that it would make them look bad if the network they invented was routed through the realm of the damned.
The big fears are trying to use one as a weapon is the big fear - slamming a barge at FTL into a colony-station or planet would ruin either - or theft by a foreign power. But since any misjump could be catastrophically deadly, any jump which does not match a planned and expected course is treated as potentially dangerous.
There have been attempts at using them for smuggling, quick business opportunities, petty theft, and - in one infamous incident - a crewmember attempting to evacuate his family.
Interesting. There's no way to "ping" the "network" and - by physics or other means - determine how many other cards are on that "network"?
Also, depending on how difficult it is to create Tallstone, this creates the possibility that there would be "certified secure" tallstone from well-regarded manufacturers, and riskier-but-cheaper options if you don't care. It also raises the possibility that beyond individual bad actors, governments or criminal groups could set up entire fabs producing batches with access for them.
Exactly. One of the themes I'm aiming for in this world is that magic is something intrinsically of the heart and soul; it's not something which can be objectively studied. You can still try and loosely categorize it and observe similarities, but magic can't be completely separated from the person.
Really, I just wanted to cut down on the 'easy fast travel' trope and make the world seem bigger... but it's also a cool idea to play with thematically! I like what you're doing with the social angle as well.
Not to be that guy, but it's tailstone. The word is a sort of fourth-wall-ish pun thing. (not sure what else to call it). The original Commonthroat is
sKGqrCg, which is a compound of the nounsKGqg(stone) and the verbrC(to flick with the tip of the tail). The in-universe etymology is that when asked how it worked, the inventor wordlessly flicked himself on the side with his tail (as though swatting an annoying inset). This gesture can mean "don't bother me", "go away", but also "don't concern yourself with that" or "never you mind". He didn't want to get into the technical weeds as he wasn't good at communicating complex scientific principles in an understandable way. But, since the gesture is a rough equivalent to a dismissive wave of the hand, the word can be translated "handwavium".Protocol-wise yes, there are ping equivalents in YAP (the link layer) and YIP (the network layer). Physics-wise no, you can't know who else is listening unless they speak up.
ding ding ding! The largest supplier of tailstone at the time of First Contact is Partisan Territory, which is on bad terms with pretty much every other polity at Focus. They only continue to exist because they've got their tentacles in almost every supply chain in the system. Partisan labor and raw materials are cheap, but there are accusations of spying on the part of the Partisan government in the manner you describe.
Sol may or may not be full to bursting with untapped sources of tailstone or tailstone precursors (haven't decided if it occurs naturally or must be synthesized). If so, First Contact may be seen by PT as an existential threat (rightly or wrongly). Since mass routers have comparatively tiny mass and volume limits, any tailstone manufactured at Sol would have to be drip-fed to Focus, making it scarce and thus more expensive. But since interspecies relations are a blank slate with no prior grudges to nurse or interests to secure, human-made tailstone would be seen by most yinrih buyers as more secure than PT-sourced tailstone.
Oooooh. Whoops. I totally misread that.
Hah! I do like that.