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I'm beginning to put together ideas for a science fiction story featuring interstellar travel. I want to put an emphasis on the "science" in science fiction for it though. In that I'd like to have few technological "leaps and bounds". I want the technology in this universe to be an extension of things we are currently working on and towards. The one big leap it will have is a FTL drive but I'd like that to stay inline with my former criteria.

To that end I've been reading about the Alcubierre drive and wormholes. They seem to be the most likely candidates for us actually achieving FTL travel at some point in the future barring current unknowns and issues. Is this accurate?

If so, which one is more plausible in the long run and what discoveries would we have to make to achieve it? What adjacent technologies would need to be developed as well? If they aren't though, what are more likely possibilities for FTL travel? Any insight would be appreciated.

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    $\begingroup$ Since FTL is impossible, according to the toil of whole battalions of physicists over the past century, the answer would seem to be "None of them." Plausibility, the suspension of disbelief, is a storyteller's task. A good storyteller teller can convince you that pink ponies are the key to FTL, and you will want to believe it. $\endgroup$ – user535733 Aug 30 at 2:21
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    $\begingroup$ @user535733 The Alcubierre drive does not exceed the speed of light within it's local reference frame, so yes it is within the laws of physics. Just not within the realm of practicality. $\endgroup$ – SurpriseDog Aug 30 at 3:29
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    $\begingroup$ If you want to make it a story about evolving science, it would be interesting to combine both, the Alcubierre and Wormholes, into your idea. There could be about two rivaling sides, one that is developing the Alcubierre Drive, and the other that is developing the Wormholes. It reminded me of the documentation "Stromkrieg" in which Edison (DC-Current) has had a rivalry with Westinghouse (AC-Current) youtube.com/watch?v=CWr79lpEY6o ( it is a german movie, though... ) I'm sure there is also plenty of things to read about it, it is pretty interesting! $\endgroup$ – rphii Aug 30 at 4:25
  • $\begingroup$ @user535733 Physics does not state that FTL travel is impossible. General relativity only states that you cannot accelerate to the speed of light using using conventional energy. That leaves quite a wide scope for science fiction writers (and innovative engineers). $\endgroup$ – DrMcCleod Aug 30 at 9:00
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To start with, the short version is that neither are actually plausible given our current understanding of physics. Faster than light travel or communications are entirely inconsistent with the scientific concepts of relativity and causality. If Einstein's theory of relativity is true, there is no difference between faster than light travel and a time machine. Both time machines and FTL can easily lead to situations that allow causality violations, which is the idea that if event a causes event b, event a must occur first.

While you could then say that Einstein's theory is incomplete, you would still need something that makes the same predictions, which includes calculations that let the GPS on your phone work and explain why the orbit of Mercury is stable. New theories can't simply say old ones are wrong, they have to explain the same phenomenon that the previous theory as able to explain in addition to the new one.

Having said this, I also understand how hard it is to make a space setting that doesn't cheat on this, which is why nearly everyone does it(bizarrely even those who don't have FTL travel often cheat on FTL comms, which are equally bad). Even settings like The Expanse that otherwise follow physics eventually wind up cheating to allow interstellar flight(and stealth, but that is a different issue). I guess this is my way of saying that the actual realism of either mechanism doesn't matter. What matters is which you'd rather have in terms of story options.

The big differences would come in how the technology is discovered and what we wind up doing with it. Wormholes are more likely to be discovered rather than created outright, though it could also be a possibility that they can be synthesized once they are discovered or that they can be controlled in different ways. The strategic situation revolving around wormholes is mostly what you see in Mass Effect with the mass relay network. The advantages here are that you have strategic choke points, which leads to interesting strategic questions about how to deploy fleets. There is also the potential dramatic advantage that travel outside of the network is extremely slow using conventional STL travel, which can lead to interesting questions about when things like backup will be there depending on where the heroes are relative to the network. Another effect here is that wormholes are an example of a technology that increases centralized power, as a government or large corporation with the resources to control it would be able to restrict access(if Star Wars had a wormhole network, it would have put a damper on both Han Solo and the entire Rebel Alliance). If the heroes are fighting against the system, they would have a hard time traveling between star systems given that some kind of wormhole port authority would inevitably be created.

Alcubierre style drives are likely going to be slower but much more flexible, in which they can allow much more controlled journeys to wherever your point your spaceship. The downside is that you now have another worldbuilding question that must be answered. If you have the energy abundance to sustain FTL travel and synthesize the negative mass required to make it work, how do you still have something to fight over? If you can synthesize negative mass in the quantities required, you can also synthesize any element on the periodic table just as easily. There would never be any real need for conflict given this level of energy abundance, which probably means you have either cheap fusion or a functioning Dyson swarm that takes in nearly all of the energy from the sun.

Of the two, I'd say that wormholes lead to less other story problems, but that Alcubierre drives lead to more flexibility in terms of how easily ships can travel to wherever they want. If your goal is a degree of realism, I'd probably go with wormholes because of the consequences implied by an Alcubierre drive.

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  • $\begingroup$ While this is a good answer, I do have a quibble. FTL and time machines do not inevitably lead to causality violation (CV). There are circumstances where they both violate causality. For example, there are time travel models where CVs don't & can't happen. Also, not every FTL trip leads to CVs. Certainly it's conceptually possible to arrange for CVs. Even so, a universe with CVs would be conceptually difficult, but nature isn't a slave to our wishes. $\endgroup$ – a4android Aug 30 at 8:51
  • $\begingroup$ This answer is physically inaccurate, FTL travel is not forbidden by General Relativity, only acceleration up to the speed of light using conventional energy. $\endgroup$ – DrMcCleod Aug 30 at 9:03
  • $\begingroup$ For wormholes specifically, it is theorized that even if they do exist (which they almost certainly don't), they'll automatically self-destruct at the moment they would have allowed time travel (closed timelike curves, to be exact) because quantum fluctuations that would normally be limited by the conservation laws are now unconstrained... and presumably the collapse would also sterilize anything on the straight path between the wormhole's mouths. $\endgroup$ – John Dvorak Aug 30 at 9:04
  • $\begingroup$ The Alcubierre drive has a different problem, in that it would most likely require an infrastructure along the route to maintain the warp bubble and catch it at its destination, and this infrastructure then establishes a preferred reference frame. Although I'm not sure what prevents a loop of pylons that could carry warp bubbles in a closed timelike fashion (except for the aforementioned fluctuations, which would presumably still apply). Another problem is that warp bubbles inevitably sweep up the dust on its route and release it as a massive blast that sterilizes everything at the destination $\endgroup$ – John Dvorak Aug 30 at 9:16
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If FTL proves to be possible at some point in the future, 2020 science will say it's impossible, just as Newtonian physics says quantum tunnelling is impossible. I'd suggest its better to not attempt to explain it and leave it beyond the knowledge of your characters.

However, there is a low tech way to get FTL travel using proven technology currently available to us, and some quirks with special relativity, allowing one to travel at up to 5,000ly / year. The kicker is its one way.

You just accelerate at 1g (in your own frame of reference). As you approach the speed of light, time dilation occurs. You age a year, but thousands of years may have elapsed from the perspective of Earth:

At a constant acceleration of 1 g, a rocket could travel the diameter of our galaxy in about 12 years ship time, and about 113,000 years planetary time. If the last half of the trip involves deceleration at 1 g, the trip would take about 24 years. If the trip is merely to the nearest star, with deceleration the last half of the way, it would take 3.6 years. https://en.wikipedia.org/wiki/Space_travel_using_constant_acceleration

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The long and short of it is that there is no FTL. And there will never be.

If by FTL you mean faster than actual light. That is impossible. Wormholes and this strange drive are not FTL. At no point is the ship faster than light. It might appear as such from some POV´s but that is not important. When you point a Laser at Mars and move it 1 Degree, the Point of Mars will have moved several times faster than light. Same goes for Shadows or other "Looks faster then light" stuff.

The moment you bring FTL into the story, it aint realistic anymore.

The only thing you can do is travel very fast and let Relatavistic Effects play into your hand. But that has the downside of you "travling" in time. So you might reach a destination extremly fast. But for everyone else, a Million years have gone by.

So you might want to go with Wormholes. Only one problem, they are about as realistic as FTL itself. To this day, there is not a single proof of that concept. Only Equations that tell us it can be done. But that is meaningless because you can make an Equation tell you everything.

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  • $\begingroup$ You're right that we need empirical evidence, but equations tell us what's possible, even probable. Often new evidence leads to new theories and new equations, but also-often old math will guide the search for evidence supporting that math ('cause math doesn't lie; it it is only wrong sometimes). Think of how general relativity was inspired by the weirdness of Mercury's orbit, but then predicted gravitational waves decades before they were discovered. Science fiction isn't about what is, it's about what is possible. And math tells us what's possible. $\endgroup$ – Palbitt Aug 30 at 18:40
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Following our current level of science of space travelling and the mechanics of our Univer it's not possible travel faster than ligh, also reaching the speed of light for us is now impossible. Regarding the two type of traveling:

  1. The Alcubierre drive, need a exotic matter and a large amount of energy to genererate a negative mass to open a Warp Bubble the warp is like a tunnel but the border region of the warp are a large space curvature, the working of this drive is to contract the space in front of the ships and dilatating the space behind the ships, this could produce a damaging effect on destination releasing an energetic outburst. The working is similar to Start Wars hyperspace jump, i think this is an expensive device to install in a ship and the it need exotic matter to function.

  2. Wormhole, you need to collapse the space time to link the start and destination, to create a gravitational tunnel, omitting the possibility of time traveling, in a wormhole you travel in subluminal speed, regarding the improbability of FTL travel also apply locally. For this tech you need a large amount of energy and i think it isn't possible install this device on a ship, so there're an Organization that develope and mantaine the wormholes in the Universe.

At the end both of them are interesting regarding a story of interstellar travel, there are multiple plot that you can do to achieving the tech regarding the type of the story, Alcubierre drive "permits" to have more freedom of movement, the character can travel in autonomy. The Wormhole are exotic and more shrouded of mystery but more controlled by a huge Organization.

I think it is possible have both of them, when some "rebels" reaching the tech of Alcubierre to break the ruling of an Organization that control a space travels.

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