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"Realistic" FTL or near-FTL Travel

Witch0Winter

Witch0Winter

Witch ❄️f Winter
Location
Colorado
Pronouns
She/Her
Hi, SV! Lately I've been wanting to hop onboard the "hard sci-fi" train with my writing because, well, limits are a lot of fun. Art from adversity and all that. However, I admit, my knowledge of realistic sci-fi is rather small. It is growing, but so far mostly through reading older stuff like Dyson's "Interstellar Travel" paper from the 60s with Project ORION. So I was hoping that it'd be okay to ask (and I apologize if this is the wrong forum and will remove it immediately) if more knowledged people know of and/or can link to articles/papers on FTL or near-FTL travel ideas that at least broadly remain in the realm of realistic or hard science fiction. I'm not super strict on how hard it is, but just hope for something that's actually feasible and would fit in a hard sci-fi universe.
 
ToixStory said:
Hi, SV! Lately I've been wanting to hop onboard the "hard sci-fi" train with my writing because, well, limits are a lot of fun. Art from adversity and all that. However, I admit, my knowledge of realistic sci-fi is rather small. It is growing, but so far mostly through reading older stuff like Dyson's "Interstellar Travel" paper from the 60s with Project ORION. So I was hoping that it'd be okay to ask (and I apologize if this is the wrong forum and will remove it immediately) if more knowledged people know of and/or can link to articles/papers on FTL or near-FTL travel ideas that at least broadly remain in the realm of realistic or hard science fiction. I'm not super strict on how hard it is, but just hope for something that's actually feasible and would fit in a hard sci-fi universe.
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You'll probably want some sort of space-warping or wormhole system. The Alcubierre drive's one of your best bets, but a Slip-String Drive could also theoretically work. But, whatever you do, don't touch Heim Theory.
 
Are you willing to accept time travel as a result of your FTL? If not, you almost surely need a big rewrite of how physics work in your setting. Alternatives sound unconvincing so far.
 
I just write said:
You'll probably want some sort of space-warping or wormhole system. The Alcubierre drive's one of your best bets, but a Slip-String Drive could also theoretically work. But, whatever you do, don't touch Heim Theory.
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Why not Heim theory? And I'll check out slip-string drive. I've heard the Alcubierre drive isn't very feasible, though I of course could be wrong.
 
vicky_molokh said:
Are you willing to accept time travel as a result of your FTL? If not, you almost surely need a big rewrite of how physics work in your setting. Alternatives sound unconvincing so far.
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Time travel like The Forever War? Well, I'd prefer one that doesn't involve time travel (from what I recall doesn't the Alcubierre drive not involve it?) but if not I can work with it.
 
ToixStory said:
Why not Heim theory? And I'll check out slip-string drive. I've heard the Alcubierre drive isn't very feasible, though I of course could be wrong.
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Actually, with a lot of Shawn White's alterations the Alcubierre Drive is quite feasible. Admittedly it needs enough antimatter to fracture a continent to turn on, and some exotic matter to act as critical engine components, but it's quite possible the energy efficiency could be improved even further.
 
Hard-SF ? That's usually when I link Atomics Rockets.

ToixStory said:
Time travel like The Forever War? Well, I'd prefer one that doesn't involve time travel (from what I recall doesn't the Alcubierre drive not involve it?) but if not I can work with it.
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No, in The Forever War it's not time travel – and it's not even caused by the FTL system. It's just good old time dilatation caused by going at relativistic speeds.
What vicky_molokh meant is that you cannot have FTL travel, relativity and causality. The explanation is... complex, but it boils down to "sending information before its light means that you can have effects before causes".
 
Vyslanté said:
Hard-SF ? That's usually when I link Atomics Rockets.


No, in The Forever War it's not time travel – and it's not even caused by the FTL system. It's just good old time dilatation caused by going at relativistic speeds.
What vicky_molokh meant is that you cannot have FTL travel, relativity and causality. The explanation is... complex, but it boils down to "sending information before its light means that you can have effects before causes".
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I've been reading Atomics rockets a bit of course, haha. That's interesting, do you have any papers or articles to explain the details of it?
 
FTL is one of the thing that you kinda have to agree with to have in your setting or exclude it. Alcubierre so far is so theoretical it's abstract - AFAIK we only have math for it.
So either your hard-scifi does not have FTL at all, or it is already noty that hard anymore. And, admittedly, it is better not being completely thoroughfully solidified. You can settle in for centuries-long flights at relativistic speeds, though...
 
Darth_Biomech said:
FTL is one of the thing that you kinda have to agree with to have in your setting or exclude it. Alcubierre so far is so theoretical it's abstract - AFAIK we only have math for it.
So either your hard-scifi does not have FTL at all, or it is already noty that hard anymore. And, admittedly, it is better not being completely thoroughfully solidified. You can settle in for centuries-long flights at relativistic speeds, though...
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Well, the whole thing is murky enough at the moment that I could have FTL or I could not. Basically that part of the 'verse is set in the past where there absolutely isn't FTL and is set on massive generation ships. It's just in the "present" of the scenario I'm wondering whether FTL is feasible or not. And to be fair, I don't think FTL automatically disqualifies sci-fi as hard, just more theoretical in nature. I'm still looking to base a lot of my scenario on actual science, math, and physics rather than just making stuff up that seems cool.
 
'Hard' SF is often defined as that which explores stuff that doesn't contradict our knowledge about scientific fundamentals. As far as we know, FTL contradicts things we know if it is done without time travel or with causality.

This is of course not the only definition - another one I keep encountering is that Hard SF focuses on exploring hard sciences and Soft SF focuses on exploring soft ones. But that's usually not the definition used when asking whether a given invention is hard enough to fit into a Hard SF setting.
 
vicky_molokh said:
'Hard' SF is often defined as that which explores stuff that doesn't contradict our knowledge about scientific fundamentals. As far as we know, FTL contradicts things we know if it is done without time travel or with causality.

This is of course not the only definition - another one I keep encountering is that Hard SF focuses on exploring hard sciences and Soft SF focuses on exploring soft ones. But that's usually not the definition used when asking whether a given invention is hard enough to fit into a Hard SF setting.
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I knew about time dilation but didn't know about the FTL time travel stuff. But to be fair, now that I do, any FTL I have will involve the time travel aspect. So I think technically it could still be classified as "hard". Not that it really matters, I suppose. I just really like the idea of making sci-fi that could feasibly happen at some point. Which I think makes it fun. So I guess I dunno if it's "hard" or not but I am definitely going for "this could feasibly happen in actual real life".

Thanks for entertaining my questions, too. :)
 
vicky_molokh said:
'Hard' SF is often defined as that which explores stuff that doesn't contradict our knowledge about scientific fundamentals.
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That's the definition I use, yeah. Hence why pure handwavium like 'magic' artificial gravity or forcefields, in my opinion, automatically disqualifies something as "hard SF".
FTL, on the other hand... I know it's just pure magic, but the author wants it, I want it, everyone wants it, so I can let it slip.
 
I handwaved stuff away by saying that the entire mass/energy cannot be created or destroyed applied to a multiverse, not a single universe. And then I bypassed causality and relativity by going through wormholes to different universes that operated under the same laws of physics in our universe. So since matter could be transferred between universes without violating physics, you could move between solar systems fairly quickly, just ones on different planes of existence, thereby creating the illusion of faster-than-light travel. And causailty wan't violated since it's between universes, so your light is never going to allow you to have time travel.

Now, this probably fails under scrutiny, but its good enough for me right now.
 
ToixStory said:
And to be fair, I don't think FTL automatically disqualifies sci-fi as hard, just more theoretical in nature.
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Hardness of scifi is integer, not boolean value, anyway. You having FTL just excludes the work from hardest of them all sci-fi, and you wouldn't get there anyway, because there always will be some bore who will criticize you on the fact that you, say, incorrectly calculated trajectories and Δv​ of the spaceships in your work (or if you didn't at all, and he did, and found out that it should be impossible). For some people this will be enough to put you in the "Fantasy-not-scifi" ghetto. So I would not bother with it at all - if you NEED FTL in your work in order for the plot to happen - then keep it. Exact principles are not important, well, as long as it is not working via literal fairies.
 
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Darth_Biomech said:
Hardness of scifi is integer, not boolean value, anyway. You having FTL just excludes the work from hardest of them all sci-fi, and you wouldn't get there anyway, because there always will be some bore who will criticize you on the fact that you, say, incorrectly calculated trajectories and Δv​ of the spaceships in your work (or if you didn't at all, and he did, and found out that it should be impossible). For some people this will be enough to put you in the "Fantasy-not-scifi" ghetto. So I would not bother with it at all - if you NEED FTL in your work in order for the plot to happen - then keep it. Exact principles are not important, well, as long as it is not working via literal fairies.
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  1. Integer? I'd expect a float.
  2. Always calculate your ΔV! I once decided to do it just on a whim in a sci-fi campaign. As a result, I managed to find that the NPC under scrutiny never managed to escape a decaying orbit (of a gas giant), and that we were speaking to a digital copy only even when we first met. Fun times, not sarcasm.
 
Darth_Biomech said:
Even if it is completely irrelevant to the story?
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How do you know that it's irrelevant before you check it? I certainly didn't know that it's an important clue until I calculated how much delta the ship had and what the escape velocity of the GG in question was.

ToixStory said:
I was going to pretend I know what ΔV is, but that doesn't help anyone, so...would you mind explaining? Yes, I'm new to this, I'm sorry. I'm an English major, sadly.
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It's always OK to ask a question.
ΔV, Δv, delta V, delta-vee or however you prefer to write it down. Literally means 'change of velocity', but in context of spaceship performance, it means either (a) how much velocity a ship can achieve relative to whatever starbase/planet/carrier/etc. on its fuel tank or (b) the amount of change in velocity required for some manoeuvre. In a simplified calculation of fuel expenditure, you should just treat it as an amount of use you can get out of a fuel tank. The other important bit is that you need X worth of ΔV if you want to achieve orbit around a planet[oid] with an X stable-orbit velocity (first space speed, whatever you call it in your school). Likewise, you need as much ΔV to escape orbit as the escape velocity (second space speed yadda yadda) of a planet.

It's the most expensive thing a ship has in a hard-sci setting, usually. (In soft-sci and/or fantasy settings like Star Wars, Star Trek, Rebel Galaxy etc. it's indeed irrelevant, because their drives are essentially perpetual motion engines.)
 
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vicky_molokh said:
How do you know that it's irrelevant before you check it?
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Law of Conservation of Detail. If you didn't write down in the story that heroes having trouble because they miscalculated their maneuver and ended up on a decaying orbit without fuel, then it is not important to the story and you should not waste your time on it (And even then, was it really important what exactly were Δv​ of a ship? Simple statement is enough too). In the same sense that people don't waste time calculating exactly which streets, roads and bus stops main character traveled to get from point A to point B and exact speed he was walking with. Or calculating when and where main character had dinner or took a dump. It is assumed that character took care of it by himself and that situation allowed it to happen, because it happened.
 
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The easy solution is just to give everyone massively extended lifespans so travelling for hundreds of years isn't a big deal.
 
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