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Please note for this, assume technology is being used for their creation, not any kind of space major or anything.

Edit: Removed the ability to do so within systems without having generators on both ends.

Superluminal communications work using the same methods, by creating incredibly small wormholes and beaming the one way message to the recipient. Two way connections are possible, but less secure.

I've been fooling with wormholes for my setting. I implemented several restrictions:

  • The wormhole must go in a straight line from point A to point B.

  • Jumping between solar systems always exits you a good distance outside its outer regions, towards deep space.

  • The longer the distance, the longer you stay in the wormhole. The region is referred to as Aether, or Hyperspace. (I'm still struggling with naming the region.)

  • It takes time to open the entry and exit point, generally speaking around 5 minutes. Detection equipment will notice their distortions in real space allowing for reactions from local space.

  • Long jumps put strain on the ship due to the necessity of using negative energy to stabilize passage. Repeat jumps require delays between travel or risk damage to the craft.

  • While transitioning, a ships shielding array must be disabled as it interferes, leaving it vulnerable to attacks and possibly stellar phenomena.

  • Naturally as civilizations develop, certain solar systems become galactic "hubs" so to speak. Trade normally wants the shortest (ie, cheapest) path between them, thus arbitrary galactic highways form on well traveled routes. At least traffic jams aren't an issue!

  • It is possible to force exit of a ship via massive gravity generators, distorting the path taken. Automatic safety's drop the ship out a good distance away. (please note, I'm talking creating a gravitational field similar to a star, so it's not easy nor common)

  • The restrictions for keeping wormholes from being generated within gravity wells are removed when equipment is used on both ends. This allows for a wide variety of implementations.

  • Opening a wormhole in an enemy ship is nearly impossible while their (electromagnetic?) shields are up. Even if they weren't, without maintaining a constant distance between both, parts of the ship will get swept through the hole, damaging the ship but also your creation point and probably the equipment needed for making it.

That's all I've really got so far. I'm looking for complications or issues that I missed when creating these guidelines.

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    $\begingroup$ "Superliminal communications" — I suspect you meant superluminal, not superliminal. $\endgroup$ – celtschk Aug 23 '15 at 21:09
  • $\begingroup$ @celtschk He was using the second definition of superliminal. $\endgroup$ – PyRulez Aug 23 '15 at 21:46
  • $\begingroup$ You broke special-relativity by the way (in a way that also bracks general relativity.) $\endgroup$ – PyRulez Aug 23 '15 at 21:47
  • $\begingroup$ @pyrulez could you elaborate how? I would like to avoid those results. $\endgroup$ – Nonafel Aug 24 '15 at 14:56
  • $\begingroup$ @Nonafel physics.stackexchange.com/a/200653/40394 Describes exactly what kind of FTL isn't a time machine. $\endgroup$ – PyRulez Aug 24 '15 at 16:20
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It seems fairly reasonable, but I have a couple points to make. It's a bit long-winded, sorry.

First, there's no such thing as "outside" a solar system or planet's gravity well. For practical purposes, gravity wells are infinite, but decay exponentially with distance. Every point in space is under the influence of lots and lots of gravity from the billions of stars and planets around us. You could say the wormhole only works when the net gravity is less than some value.

But if you allow the wormhole to work between the "edge" of the solar system (e.g., Pluto's orbit) to the more civilized areas (e.g., Earth's orbit), there's really no reason you couldn't jump from anywhere in the galaxy straight to Mars' orbit. The difference between acceleration from the Milky Way in deep space and acceleration from the Sun near Mars (about 227 microgees) is considerably less than the difference between acceleration from the Sun near Pluto and near Earth (about 605 microgees). You'd still need to be away from the planet itself a little ways, but we're talking hundreds of thousands to a couple million km, which is a stone's throw in cosmic distances.

I would suggest (if we assume most habitable star systems are similar to ours) that you establish a baseline of something like the asteroid belt, and you just can't jump inside that range. It would still take hours to weeks at sub-light speeds (depending on how close to light-speed we can get) to reach the inner planets, while allowing jumps in the outer regions of the solar system which are huge. Also, this means you couldn't get closer than roughly the Moon to a planet, even if the planet is far from the local star, and big planets like gas giants would be farther.

The basic rule of thumb: take the farthest naturally-habitable planet from the local star, double the distance; you can't jump anywhere in that radius from the star. Take the farthest significant moon from a planet, double the distance; you can't jump closer to the planet than that, even if the planet is well outside the star's no-flight zone. Not quite scientific, but it's reasonably close without getting bogged down in math, and it means your defense forces always have some lead time to get prepared.

Second, the very idea of a wormhole is to bypass the straight line. You essentially create an entirely new tunnel through a higher dimension that is much shorter than the regular path. The wormhole intersects "real" space at its end points, but is totally outside real space at any other location.

However, I suppose you could say the wormhole tunnels parallel to realspace and is just extremely dilated spatially. Then huge gravity wells might reach out across extra dimensions and interfere. This would also allow longer realspace distances to correspond to longer wormhole distances.

This means you wouldn't be able to make a jump from one side of a black hole or other supermassive object to the opposite side, but the angular size of the object at the distances you're allowing jumps makes this a pedantic note. You could choose a random jump direction every 5 minutes for the rest of your life and the odds of accidentally trying to jump through a star or black hole are pretty much zero.

Third, there would be no feasible way to predict a ship's jump path, move your own ships to an intersecting line, then activate your super-gravity generator before the ship was long gone. The only time such a thing would reasonably work is if you were disrupting a well-established trade route, or knew ahead of time the exact path someone planned to use.

Fourth, some additions to the trade routes idea. I would expect that most ships would have no wormhole capabilities, and would instead rely on fixed jump gates. Star systems would likely have massive wormhole nodes, much like airports, and people would simply fly to the node, pay the appropriate fees, then fly through the wormhole when it's their turn. It could even be like a traffic light, where the wormhole is opened to one destination for some period, dozens of ships fly through, that portal is closed, then another is opened to a second destination. Repeat for each of the local star systems.

For large, wealthy systems, the wormholes would be open almost constantly, and you'd have very little delay before traveling. For smaller systems, you might have to wait several weeks before the next scheduled departure.

Also, the wormhole network would likely have a sort of hierarchy. So you'd travel from the less-populated star systems to a regional hub, then from the hub to a different local star system. Then you'd have super-wormholes between regional hubs. The super-hubs would likely be spatially separate from the regional hubs for security but don't have to be.

All hubs on the wormhole network would undoubtedly have very intense security sweeps and so forth. All ships would be checked for illegal / dangerous cargo, dangerous cargo would require licenses and permits, all passengers would require the appropriate passports, etc. Military and/or security ships would be everywhere, and the entire hub would have some type of shielding to prevent unauthorized wormholes in the vicinity. Perhaps the shielding has some kind of "signature" so you can bypass them with the correct key (probably just some physical property, like the frequency distribution of the shielding or something). Then the station operators can tunnel into and out of the shielded areas, but others can't. This caveat would allow scenarios where terrorists or mercenaries could bypass shielding, but they'd have to gain access to the shield key first. The difficulty of doing so would determine how rare such events are.

Under this setup, only very wealthy people and governmental agencies would have their own wormhole drives. More advanced cultures and star systems would have a higher proportion, but cost efficiency would likely mean the only reason to use your own drives is if you're going somewhere far off the beaten path.

Also, individual planets could have local wormhole facilities for interplanetary travel within a star system without leaving the surface. You'd probably still need to be in a spaceship of sorts to launch through the void, and the wormhole ends might need to be created in a near-vacuum. This would prevent people from just teleporting around. Also, the ability to create the wormholes so close to the planet could be very expensive and complex, so only a few planetary wormholes would exist.

Finally, with communication nodes: I would suggest that even small wormholes are fairly expensive, so most people wouldn't have personal superluminal communications. However, interplanetary networks would exist, so you could talk to people on other planets in nearly realtime as long as you're connected to the local sub-light internet. Many to all spaceships would be equipped with superluminal communication, but the ranges could vary. Most ships could at least communicate within the star system, but only sophisticated and powerful communications arrays would work in deep space.

Alternately, there could be repeaters near major planets, moons, and space stations. In this case, most ships would communicate at sublight with the repeater, which would relay the information to different nearby hubs. Communications this way would have delays of seconds to minutes unless both ships were very close to the repeater. Again, expensive ships could still communicate via superluminal connections at much greater ranges with minimal delay.

Any kind of convoy (a military fleet or cargo operation) would likely have one or two flagships with superluminal connections, then all the small ships would communicate at sublight with the flagships. For recon missions, a communications ship might accompany the scout ships to keep in low-latency contact with the flagship.

Also, there could be superluminal communications equipment as a movable package, so you just buy a couple packages then put them in whichever ship makes sense for the current context. They could be transported to the ground for landing parties. If they're big and bulky, it would make sense to leave them at some kind of base camp, or in a ship left in geosynchronous orbit.

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Re Wormholes cannot be used for time travel

How does all the other stuff you listed work with this? The finite transit time would be the normal light speed. Saying it is a straight line between the points, as well, does not sound like a wormhole which doesn't have any relationship with the real-space path. It sounds more like a teleporter, as used in some Niven stories. In that idea, though, the occupents don't experience the time.

You might not be aware of the general principle that getting someplace faster than light, even if it's not done via travelling through space, and the existence of more than one such path, allows time travel.

Ah, I remember now my favorite solution: have the FTL system use a constant reference frame for all uses. This doesn't describe wormholes, but can be imposed on a "subspace" approach. It also can naturally provide interesting usage restrictions for the story, including not being accessible close to a gravity well, and the requirement of matching velocity with the subspace frame of reference before entering.

This matches up with some of your other ideas: if the subspace has a correspondence with points in real space and you fly through subspace (with its own physical speed limit being much greater than light in our space) the ship is "under" the points in a straight line path and can be ejected or detected as you note.

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How do you make sure two ships don't land on top of each other?

If there are 'busier' systems, isn't there a chance that two ships will jump too close to each other and crash?

To solve this, you probably need some sort of FTL communication so you reserve a spot for your wormhole to come out on.

Otherwise, Michael's idea of jump gates could help with this problem too. (Have synced departure/arrival times for both sides).

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  • $\begingroup$ I inferred that since gravity has an effect on the exit point, you wouldn't bump into anything. Furthermore since a wormhole is connecting one point to another, this ship inside isn't actually moving all that fast. The exit area would likely require enough area to accept the incoming mass from one location to another. Avoidance rather than forced impact, similar to repelling magnetic fields? I didn't give it much thought. $\endgroup$ – Nonafel Aug 24 '15 at 21:30
  • $\begingroup$ @Nonafel The gravity thing makes sense for things planet-sized, but what about another ship moving through real-space quickly toward the wormhole exit? A ship could exit the wormhole and collide with someone shortly after, without significant gravity being around the exit. $\endgroup$ – Martin_xs6 Aug 24 '15 at 22:03
  • $\begingroup$ Hence the need to open them on the fringes of a solar region. exit points wouldn't collide since the mass would generally repulse each away from one another. It's possible to run a craft or something into the exit point, however I always envisioned the exiting ship moving very slowly through the end of the wormhole. $\endgroup$ – Nonafel Aug 25 '15 at 1:19

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