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I'd like to have faster-than-light travel (and communications) be an late-game option for a video game I am working on. The extent of the playable universe is approximately 4 million light years in all directions, and this area will have at least 1 spiral galaxy in it, plus whatever other features I can contrive to make it look as realistic as possible. Probably a few dwarf galaxies and globular clusters as well, something that looks similar to the Milky Way and its immediate vicinity.

In-game, the passage of time will be 1 megasecond per 15 minutes of real-time, or about 3 years per real-day. I suspect that this rate will allow for significant exploration possibilities with advanced sublight propulsion (mmo, players might take real-weeks to send ships to destinations if need be).

I'd like to describe the FTL technology sufficiently so that players feel as if this is a real thing. I know that this can't be a science-based or hard-science question (FTL isn't those things at all), but I still want some suspension of disbelief.

There are quite a few science fiction tropes to choose from (or I could even choose multiple models I suppose), but many have issues that make them less than ideal.

Which FTL models could fit my requirements?

  1. It shouldn't allow instantaneous travel, even at the highest level of miniaturization/efficiency/whatever
  2. It should be compatible/consistent with an associated FTL communications concept, at the very least not ruling that out entirely
  3. Ideally, it also shouldn't directly imply FTL communications either, so that communications/propulsion might be independently discovered, in either order
  4. It should be ship-based, either requiring space vessels or that being the most practical way to utilize it
  5. Vessels shouldn't be easily interfered with while in transit, no photon-torpedoing the Borg while they're chasing you at warp speed, though technologies that prevent the FTL from functioning in a large area or make it less efficient aren't ruled out entirely
  6. Effective speed is still limited such that it might take several game-years (minimum) to cross the entire playable universe even in the very late game

Science fiction tropes, fringey pseudoscience, and any other concepts are all welcome. Answers that suggest more than one distinct concept to be available are also welcome. I'm modestly well-read on science fiction, but please include both author and title for those concepts I might be unfamiliar with so that I can google them if need be. Answers that suggest more than one concept also welcome.

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    $\begingroup$ about 3) FTL implies also FTL communication. Just attach the message to the thing traveling at FTL... $\endgroup$ – L.Dutch - Reinstate Monica Apr 14 '20 at 17:19
  • $\begingroup$ @L.Dutch-ReinstateMonica - I think that "FTL Comm" is generally interpreted to mean something like FTL "radio", vs. "Postal Service". $\endgroup$ – Jeff Zeitlin Apr 14 '20 at 17:25
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    $\begingroup$ If you allow for no FTL radio at all, the FTL model from the tabletop role-playing game Traveller seems to meet all of 1, 4, 5, and 6 (with 2 and 3 being irrelevant as there is no FTL comm at all, other than "put the message aboard a ship") $\endgroup$ – Jeff Zeitlin Apr 14 '20 at 17:27
  • $\begingroup$ On your reference of star trek, why not use matter/antimatter converters? It makes "sense" due to the amount of power theoretically released from such a thing. It'd be a nice fun reference to something your players most likely really love. Idk the copyright restrictions on something like that though. The only other thing I could think of it to somehow convert the entire ship and its content to tachyons and then convert them back at the destination. That'd be very pseudoscience but ftl travel IS pseudoscience $\endgroup$ – MingD14 Apr 14 '20 at 17:28
  • $\begingroup$ In the Odyssey One series it is suggested that non-instantaneous FTL travel can't happen without FTL communication, or at the very least is ridiculously dangerous with FTL sensors. The reason being that you literally can't see what's in front of you if you are travelling faster than the particles picked up by the sensory systems. As a result any stray debris or heavy particle could completely rip through the ship traveling at such speeds, and you would be unable to even see it coming, let alone adjust your course. To clarify, if you have FTL sensors, you have communications. $\endgroup$ – TitaniumTurtle Apr 14 '20 at 17:43
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Alcubierre drives for FTL Travel

Alcubierre Drives (similar to what you see in Star Trek) allow you to travel at superluminal speeds by displacing the false vacuum behind your ship to in front of it. This creates a negative mass behind you that pushed you forward, and a positive mass in front of you pulling you forward escentally making you fall forever in a single direction. Because the warp bubble is propertually part of your own reference frame, special relativity in regards to tachyon mechanics say that you should be able to exceed the speed of light like this.

Tachyons mechanics say that you can move faster than light by following a downward curvature of spacetime, but you can only average the speed of light when traveling back and forth between two points because you have to then follow the curvature back up slowing you down by an equal proportion. Alcubierre Drives "hack" this trade off by bringing the curvature of spacetime with you instead of traveling along curvatures made by your environment.

These are also good in the since that a weaker drive may allow relativistic but not superluminal speeds giving you a smooth path of technological advancements to get from chemical rockets to really fast FTLs.

Quantum Entanglement for FTL Communication

Quantum entanglement takes advantage of particle pairs sharing quantum states. If you create a particle pair and trap both particles for observation, then you could keep 1 half at a communications hub, and the other on a ship. By stimulating the quantum state of one half using something like photon/atom phase switching, the changes would be instantly observed in the other half regardless of distances; so, a hub containing millions of halves could be used to relay messages across your entire fleet. Quantum Entanglement can not be used for FTL travel because particle pairs only share quantum states, not kinetic or positional states.

It shouldn't allow instantaneous travel, even at the highest level of miniaturization/efficiency/whatever

The Alcubierre Drive does not allow instant travel, the more power you put into it, the faster you can in theory accelerate, but engineering constraints such as inertia and spaghettification would at some point prevent you from accelerating faster than a certain speed before killing everyone on board.

It should be compatible/consistent with an associated FTL communications concept, at the very least not ruling that out entirely

Although the Theory of Relativity fails to explain quantum entanglement, Einstein himself accepted that it was a real thing he simply could not explain. That is to say, the observations and theories regarding the manipulation of the two phenomenons are not based on mutually exclusive theories.

Ideally, it also shouldn't directly imply FTL communications either, so that communications/propulsion might be independently discovered, in either order

These technologies rely on two separate scientific principles such that they would have to be discovered separately. In theory one could communicate with FTL courier ships, but once quantum entanglement communication is discovered, you can instantly communicate with anyone you come in contact with making such things obsolete. This is also better for game play since any system of communication that is not instant will just push players to communicate through other channels like Discord giving them an unfair advantage over those you rely on ingame methods to coordinate allied efforts.

It should be ship-based, either requiring space vessels or that being the most practical way to utilize it

Alcubierre Drives only work on ships because you need a movable reference frame for it to work.

Vessels shouldn't be easily interfered with while in transit, no photon-torpedoing the Borg while they're chasing you at warp speed, though technologies that prevent the FTL from functioning in a large area or make it less efficient aren't ruled out entirely

An Alcubierre Drive drive basically sandwiches your ship between a black hole and a white hole. Shots fired at the bow will be sucked into your artificial singularity, and those fired at the rear will be curved away from you at relativistic speeds making landing a hit on a warp ship only possible from the sides. However, anything that exits the warp gradient will suddenly be following the rules of normal space so trying to fly up along side another ship at warp to broadside it is going to be about as effective as trying to shoot down an F-22 by throwing a hand grenade out of your cockpit.

If you want to make an FTL inhibitor,it's both easy and impossible to explain. No one even has a theoretical concept of how one would go about manipulating the false vacuum of space like this; so, you can simply say they can be made because whatever hand wave explanation you give about how warp fields are made allows for it.

Effective speed is still limited such that it might take several game-years (minimum) to cross the entire playable universe even in the very late game

Along with the limits of inertia and spaghettification I previously discussed, maximum effective speed is also limited by the currently unknown "density" of the false vacuum of space. You can only create as steep of a curvature in space-time as there is scallar field mass/energy to draw from. Since this hard limit is known to probably exist, but no one knows what it is, you can just make it what you need it to be for purposes of your game giving warp drives a hard cap to thier maximum speed.

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  • $\begingroup$ I have always wanted to use entanglement for communication but when you force an action to one of the pair you break the entanglement, that aside as we are talking about pseudo-science, what tech or explanation would you suggest as to how you stimulate one of the pair? $\endgroup$ – user69935 Apr 15 '20 at 15:54
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    $\begingroup$ @Nosajimiki-ReinstateMonica You are grossly misinformed. In real life, quantum entanglement cannot be used for communication, and stimulation of one entangled particle has no effect on the other. $\endgroup$ – Logan R. Kearsley Apr 15 '20 at 18:15
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    $\begingroup$ @ZeissIkon No, it's not. It's based on the mathematics of quantum mechanics (and supported by the more complicated mathematics of quantum field theory). Yes, you can entangle particles that have never been in contact in with each directly, but you still can't use them to communicate faster-than-light, and it still true that poking one entangled particle will have no effect on another. Maybe there is some undiscovered physics that will permit FTL signalling between fundamental particles, but if so, it won't be called "entanglement". $\endgroup$ – Logan R. Kearsley Apr 15 '20 at 18:28
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    $\begingroup$ @Nosajimiki-ReinstateMonica "quantum teleport says qubits can be transferred FTL." No. It absolutely does not. $\endgroup$ – Larry OBrien Apr 15 '20 at 21:03
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    $\begingroup$ @Nosajimiki-ReinstateMonica Quantum teleportation requires a classical STL channel to transfer qubits. And while yes, "quantum woo" may be good enough for a video game, I find it morally irresponsible to perpetuate a pseudo-scientific explanation that has already been used in so much media that many people assume it to be fact. When everybody knows that your sci-fi is, in fact, sci-fi, continuing to use the trope is fine; but when a trope consistently interferes with actual science education, it's time to dump it. $\endgroup$ – Logan R. Kearsley Apr 15 '20 at 21:37
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Hyperspace

Or fourth dimensional space travel, or tesserring, or whatever term you want to use to travel in the space between spaces, across the fourth spacial dimension. Hyperspace neatly solves all of your problems. Oh, and just to clarify - despite the fact that they claim to use hyperspace, Star Wars does not use hyperspace properly. Go read A Wrinkle in Time, it does a fantastic job explaining the concept.

  1. Hyperspace doesn't allow for instantaneous travel, as you're still traveling distance, just not the direct distance. In other words, instead of using Path A which is five lightyears, you use Path Q which travels between dimensions. Path Q can still require time to clear, as it still is composed of a distance, just not the five lightyears of Path A
  2. Check. Messages can go through hyperspace just as easily as real ships.
  3. Nope. But this condition contradicts the previous one. You shouldn't have two different systems of lightspeed travel, one for information and one for people. The readers will wonder why they don't just use the better one. I'm sure you can technobabble up an explanation, but it'll be pushing the envelope of suspension of disbelief.
  4. Check. Hyperspace is usually ship-based, the hand-waved explanation is that it can only be done in the vacuum of space because planet's gravity makes it too hard to activate the hyperspace tunneler.
  5. Check. You're not traveling through normal space, you're traveling the space between spaces. Normal weapons like torpedoes or lasers are useless. And, as mentioned previously, you can use gravity wells to stop jumping into hyperspace.
  6. Check. Effective speed is limited because you still have to travel distances in hyperspace.
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  • $\begingroup$ Is #5 truly fitting? What if two ships enter hyperspace at the same time, are they then not close in hyperspace as well? And what would cause lasers to fail to work there, or missiles for that matter? Radio waves still work in it though? $\endgroup$ – John O Apr 14 '20 at 19:28
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    $\begingroup$ @JohnO I don't think that's the idea. The idea is that things in the outside 3D universe can't shoot at you. Something in the 4d space at rest with respect to you can be be thought of as being the same part of you, and you can certainly shoot at yourself. But, many sci-fi stories use this extra dimension idea. Maybe the extra dimension is littered with radiation and particles that diffuses or hinders conventional weapons. $\endgroup$ – BMF Apr 14 '20 at 19:38
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    $\begingroup$ @JohnO At that point it's really just fine to have the scientist say 'It doesn't work, and you need three degrees to understand why'. $\endgroup$ – Halfthawed Apr 14 '20 at 19:39
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For communication: Wormholes. Tiny wormholes. You figure out how to make wormholes that are big enough to send pulses of high-frequency light through, and remain stable indefinitely... but trying to scale them up to where you can send even a single atom through intact is just not feasible. Like, it'd require more {limiting resource} than is available in an entire galaxy. It doesn't work like radio, though--more like a landline phone system. Wormhole mouths are created in local pairs, and each mouth has to be carried through other means across whatever distance you want to communicate. You could have individual pairs of ships meet up to exchange wormhole mouths and establish direct communication from then on (like building a dedicated phone line), but it would be more efficient to establish a network of communication hubs, where a ship just has to visit any hub to generate a connection to the network and can then have its messages routed wherever they need to go.

For travel An Alcubierre-style warp drive is as good as any, and dovetails with wormhole communication pretty well. They both require exotic matter, and modern treatments of the Alcubierre metric indicate that the quantity of exotic matter required can be driven arbitrarily low with appropriate modulation, so the idea that you can only generate very small amounts of it to make tiny wormholes still fits. And developing either technology first would logically give you a leg up on developing the other one, since they both require figuring out how to do engineering with exotic matter.

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Alderson points.

These are places associated with gravitational bodies where FTL is possible. Probably the FTL is possible only to a finite set of points, not to every point. You could structure them like a subway system. From point G I can reach F and H and B; I need to go to B first if I want to go to A. It is a number of jumps to Q.

http://www.technovelgy.com/ct/content.asp?Bnum=448

Also known at the "Crazy Eddie" point. The idea presented here is that there are pairs of points widely distant in space that are connected outside of normal space. A vessel equipped with the Alderson Drive can take advantage of this pair of points, moving from one to another without traversing the space in between.

I've been on trips where it was faster to drive over to another Alderson point, make a Jump, move around in the new system, Jump somewhere else, keep doing that until you come back to the original system at a different place - do all that and it would still be faster than merely to sail across the original system in normal space. From The Mote in God's Eye, by Larry Niven (w/J. Pournelle). Published by Simon & Schuster in 1974

A fair amount on this concept in this idea: Can this version of the Alderson Drive be used to violate causality?

In "Mote in God's Eye" I recall that the Alderson Point in question (the accessed the alien system) was inaccessible somehow - possibly within the heliosphere of the star, and so these aliens were cut off from the rest of the universe.

You could have these points be natural phenomena accessible with correct tech, as in Mote. Or you could make them be built things of ancient and unknown provenance, more like Stargates.

If you have them just constantly open spots where our space connects in 4d then you could send radio transmissions thru; maybe you could have repeaters (built in?) to enable messages that would go thru more than one point.

So you can't just slip into warp to escape your troubles. You have to get to the nearest Alderson Point. Your enemies might be in the way.

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Slower-than-light acceleration up to near light speed, then a "jump" to a speed just higher than light speed. Another "jump" goes back to under light speed. Each "jump" is very taxing on fuel, so must be used sparingly.

The twist is: while over light speed, the ship runs backwards in time, as seen from the outside. Moreover, the quicker it flies, the quicker it goes to the past.

Communication is done using small messenger drone ships, also able to "jump".

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  • $\begingroup$ Baryonic to tachyonic? Huh. Why the discrete jump though, and how does it address the OP's requirements? $\endgroup$ – BMF Apr 15 '20 at 0:10

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