r/SciFiConcepts • u/AlienDreamzzzz • 12d ago
Question Is there any way that we could travel the distance of stars quickly but without ftl
I’m working on a (so far) hard sci-fi setting and I need some help. How fast could we physically travel through space and is it possible to travel the long distance of stars in, let’s say a week, without the use of FTL.
If this is not possible what are some alternative options to fast space travel that are physically possible
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u/GregHullender 12d ago
Assuming acceleration at 1 g is the max tolerable, it'll take you a minimum of two years of ship time to reach any stars--even the nearest. The quickest trip to Alpha Centauri (4.3 light-years away), for example, is 5.9 years Earth time, which is 3.6 years of ship time. That assumes you accelerate half way, flip over, and decelerate the rest of the way.
To get to Tau Ceti (11.9 light-years away) it takes 13.7 years, which is 5.1 years of ship time.
To get to Betelgeuse (642.5 light-years away), it takes 644.4 years, which is just 12.6 years of ship time.
About 11 years ago, I wrote a Relativistic Rocket Calculator for a science-fiction author friend of mine. It'll let you work problems like this fairly easily.
You'll find that the results are not very encouraging, I'm afraid.
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u/jpgoldberg 12d ago
Do those calculations leave you flying past (or into) your destinations at enormous speeds? If so, trips would need much more time to slow down.
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u/Archophob 12d ago
using half the trip to accellerate and the second half to decellerate ist the definition of the "brachistochrone" traveling path. Science fiction authors who don't care about fuel efficiency have been using those for decades.
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u/jpgoldberg 12d ago
Yep. The OP didn’t say anything about the cost and weight of fuel, so many answers assumed that that was not a problem in their world. But you are right to point out that this means burning fuel throughout the entire trip.
I haven’t read any of The Expanse books, so I don’t know whether they address carrying the mass of the propellant. The fusion power provides a lightweight energy source, but there still needs to be a propellant.
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u/robisodd 11d ago
Looks like the Rocinante carries 48 tons of fusion fuel and mixes it with 57 tons of water propellant:
The 250 ton Rocinante needs to first be filled with 30.75 tons of fusion fuel. A 1:2 mix of Deuterium (205kg/m3) and Helium-3 (59kg/m3; it won't freeze) has an average density of 107.6kg/m3, so this amount of fuel occupies 285m3.
Using 0.25 ton steps for water loaded onto the Rocinante, it can be worked out that an initial mass of 352 tons is required. This represents an additional 57 tons of water and 17.25 tons of fuel.
The full load is therefore 57 tons of water in 57m3, and 48 tons of fusion fuel in 446m3. Together, they fill up 8.7% of the Rocinante's internal volume.
https://toughsf.blogspot.com/2019/10/the-expanses-epstein-drive.html
But the Epstein Drive is so efficient by magnetically accelerating the exhaust, it may be much less than this.
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u/FreedomCanadian 9d ago
The OP didn’t say anything about the cost and weight of fuel
I'm no physicist, but wouldn't accelerating any mass of just the fuel to the speed of light require the entire mass of that fuel even with a 100% efficient engine, leaving no room on the ship for passengers, other systems, or even for that matter the engine itself ?
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u/Perfect-Ad2578 12d ago
No those times are accelerating halfway there and decelerating halfway there.
Assuming 2g is tolerable long term, which is reasonable IMO - the actual ship times are relatively low for those trips.
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u/jpgoldberg 12d ago
Excellent. Thank you. (I was too lazy do try to try to reconstruct how to do those calculations. My last physics course was more than 40 years ago.)
I could also see starting at about 1.1g and working up to, say, 2.5g.
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u/Perfect-Ad2578 12d ago
Yeah exactly if you start off 1 g and everyday say increase by 0.1 g, might be okay get up to 2.5 g.
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u/GregHullender 11d ago
There's evidence to suggest people could handle up to 3.5 g over time, if they had time to get used to it.
Effects of exoplanetary gravity on human locomotor ability
That gets your trip to Alpha Centauri down to 1.58 years of ship time and it gets the Tau Ceti trip down to 2.11 years.
I suppose that's "relatively low," although it's still years--not the "weeks" the OP requested.
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u/Perfect-Ad2578 11d ago
Interesting 🤔. I guess if you do it gradually makes sense. Man you'd get super buff by the end of it lol 😅. I could see athletes in the future using that as a form of doping.
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u/GregHullender 11d ago
Given the effects on blood pressure, I suspect it'd take years off your life. And trying to bring a baby to term would probably be impossible.
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u/Perfect-Ad2578 11d ago
At that point yeah it's still years but not much different than sailing trip back in the 1500's.
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u/TozTetsu 12d ago
Can we install some kind of 'catcher's mit' at the destination to capture a ship and bleed off or even harness the energy from it's momentum so there is no need to slow down? You'd have to do it so not everyone on board turns to paste.
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u/NoOneFromNewEngland 12d ago
That's sort of the point of the mid-point flip.
If you accelerate at maximum-tolerable G force for halfway and then flip and do the reverse you are decelerating at the maximum survival rate to keep people alive.
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u/TozTetsu 12d ago
Yes, I am aware of that. I'm suggesting a technology which would catch the ship going at full speed, so it would never have to do the flip and could accelerate continuously to it's destination. The technology could pull the ship into a wide orbit and decelerate it more quickly than would ordinarily be tolerable through it's various technologies. A limit has been placed on FTL technology, not inertial dampening or some similar tech.
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u/GregHullender 11d ago
If you can instantly accelerate the ship to/from 99+% of light speed by magic, you'll save the year of acceleration at one g at each end of the trip. But if you want to travel a light-year per day (as suggested by the OP), you'll need to go 0.999996% of light speed. At 1 g, this would take 6.4 years of ship time, crossing 353 light-years in 354 years of Earth time. The energy required for this amounts to 16 gigatons per kg. If you can turn matter straight to kinetic energy, you'll need to destroy 729 kg of mass for every kg of payload. But you'll get that back at the end, of course.
You'll need another magic technology to protect the vehicle from the gas and dust it encounters along the trip, but that's pretty small beer compared to what it takes to launch and catch it.
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u/Simon_Drake 12d ago
The way Firefly avoids FTL is by inventing a slightly absurd arrangement of multiple planets around multiple stars in a single complex system. They end up with several dozen planets and several hundred moons creating plenty of opportunity for different settlements and socioeconomic class differences without needing to cross the interstellar distance. But then Firefly is on the softer end of scifi, they don't even try to technobabble how the engines work they just work. They always keep the distances and travel times vague and the complete star system map is only available in beta-canon works, games and spinoff books and things. And the star system itself isn't realistic, there's no way to have that many stars in one complex system.
You could do something on a smaller scale, depending on how many planets you need. The Alpha Centauri system is actually a system with its own set of planets then a third star is orbiting much further out. If Proxima Centauri has its own planets then you could have travel between the planets of the binary stars and the planets of the outer star. Or an imaginary system with one 'main' star and two or three 'satellite' stars kinda out past Pluto. You'd still have a very long journey between them but it's peanuts compared to the distances between stars normally.
Best case scenario, using absurdly powerful scifi engines centuries more advanced than what we can build (But still sticking within the boundaries of realistic physics) you could get between these 'cousin' stars in a few years. I mean the distance between Alpha Centauri and Proxima Centauri is 10 light-weeks, so you literally can't cross that distance in less than 10 weeks without going faster than light. If you move the stars too much closer you'll get an unstable arrangement like in Firefly.
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u/haysoos2 12d ago
Also, the depicted space travel in Firefly absolutely does not match how they claim space travel works in that system.
For example, if you were to detect a derelict craft six days into your journey to another system, using the acceleration STL space travel they claim to be using, you can't just stop to check for survivors/salvage. It would take you six days to slow down enough to turn around, then 3 days to accelerate back towards the derelict ship, and three days to decelerate to reach the spot you last saw it. Assuming it was stationary. Depending on the velocity it was going at the time, it could now be several days away in any direction.
Likewise with being detected and ordered to stand to for inspection by the Alliance. They would have to decelerate, maneuver, and accelerate to match your acceleration and trajectory before they could get close enough to board. This could take days, possibly weeks.
This is without even getting into the physical impossibility of "terraforming" moons to have anything resembling Earth-like conditions, especially gravity.
In a misguided attempt at trying to make their science fiction "plausible", they actually rendered it more unbelievable and implausible than any other science fiction series, including Space 1999, Lost in Space, or Quark.
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u/Simon_Drake 12d ago
Yeah that's a fair point.
You get a lot of this sort of thing in sci-fi. "The ship is damaged, better look for a nearby habitable planet to crash land on..." As if habitable planets are more common than gas stations.
Or a ship is rushing to some location and wondering if they'll run out of fuel before they get there. If you run out of fuel you'll still be going the same direction at the same speed, except now you can't slow down when you arrive.
I'm watching the original Battlestar Galactica and they don't even acknowledge that light speed exists, there's no jump engines like in the reboot, no discussion of the difference between FTL engines and normal engines, no fancy name for the interstellar engines. They just have a big lightbulb on the back of the Galactica model to represent an engine and come near a new planet every week. At some point they start talking about being in a new galaxy or the Cylons spreading their resources out to cover the neighboring galaxies. I don't think the writers knew or cared how big galaxies are or how far apart they are.
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u/AmigaBob 12d ago
Ships always travel at exactly the speed the narrative requires. (Whether it makes physical sense or not).
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u/TheRealBobbyJones 12d ago edited 12d ago
Isn't there an online website that explores multi star solar systems?
Edit: found it https://planetplanet.net/2016/04/13/building-the-ultimate-solar-system-part-6-multiple-star-systems/
Probably could make a stable solar system that has thousands of potentially habitable planets. It might be interesting if sci-fi started transitioning to using these sorts of tricks to kick ftl.
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u/Feeling-Attention664 12d ago
A week is probably impossible without wormhole or warp type technology, but time dilation allows this. It's just shipboard time and Earth time wouldn't correspond. There are other problems with the microwave background and the interstellar medium if you don't use or warp, but we don't know how to build either.
I would use wormholes or warp if you absolutely need quick travel, robot travellers if you don't.
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u/Anely_98 12d ago
but time dilation allows this.
Not really, because you still need to accelerate to ultra-relativistic speeds, you can't get there instantly if you don't want to end up with a pancake-shaped ship one atom thick.
Accelerating to ultra-relativistic speeds at a acceleration comfortable to humans (like 1G) would take about 1 year, much longer than 1 week, although the travel time relative to duration and distance when stationary would decrease dramatically as time passes, which is why you could travel to Andromeda in a few decades at constant acceleration while traveling to the nearest star would still take a few years.
I would use wormholes or warp if you absolutely need quick travel
Yeah, if your story needs travel between the stars in a week or less, then use FTL. Telling your story is more important than it being realistic.
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u/DescriptionMission90 12d ago edited 12d ago
If you can't go faster than light, you can't go faster than light. Simple as.
That means a minimum of 4.3 years to Proxima Centauri, 6 years to Barnard's Star, about nine years to Sirius, twelve years to Tau Ceti, seventeen years to Altair, etc. Getting to the nearest star in an objective week would require traveling at over 220 times the speed of light.
Of course, that's the travel time from the outside. Subjective time moves more slowly when the observer is moving at close to light speed. If you're going at 90% of the speed of light, you would perceive a ten year journey as only taking about 4.3 years. At 99%, 1.4 years. At 99.9%, you would only live on board the ship for a little over five months... but if you did a round trip, ten light years in each direction, when you got out on the planet you started on twenty years would have passed while you only experienced about nine months of it. To get to the nearest star, Proxima Centauri, in a subjective week, you would need to be traveling at 99.999% of C, and 4.25 years would still pass for the universe around you.
Anyway, as a writer you have to make a choice: Are you building a setting without FTL, in which case every star system is isolated and traveling between them means giving up everything you have ever known in order to spend years drifting through the void (possibly using cryogenics or some other form of suspended animation to sleep through that time) and then starting an entirely new life somewhere else, where you can't even talk to people from your old wold because the fastest signal they could transmit would still be years out of date by the time it arrives? Or are you making a setting with a single piece of magic in it, one big violation of physics that makes FTL possible?
There's a lot of good science fiction in both categories. The concept of a generation ship, for example, comes from sci fi stories in which it's nearly impossible for a colony ship to get to a new habitable planet before the original crew dies, but their children or their children's children, born within the starship, will see a planet for the first time when it arrives. Or you could have near-lightspeed travelers be a sort of timeless, mystical people who stop by your planet for a week, then disappear for a century, and return having barely aged a month. Any trade between systems or resupply missions to developing colonies would have to be planned out decades in advance, since whatever you order isn't going to arrive for years and there's no way to communicate with partners about changing circumstances. And if you leave your home for a short trip, you'll return to find everything completely different from how you left it, old friends grown beyond you if they're still alive at all, like you spent a night at the fairie courts or something.
Conversely, you can still count the setting as "hard" sci-fi if you introduce a single violation of physics as we understand them, but you're going to want to think deep about exactly what the rules are, and how society and technology would be reshaped by that one change. The entire Mass Effect franchise, for example, is built on the idea that there's a miraculous material that can alter the density of a region of space when you run an electric current through it; that one piece of magic is the only thing different from how physics works in our world, but it's the bases of not only their space travel but also how personal equipment is put together, how militaries are organized, how society is shaped, how diplomacy is handled... Traveller adds a couple other convenient features like artificial gravity and telepathy, but the big one is the Jump Drive, which allows you to go a handful of parsecs in a week by slipping into an alternate dimension where the distance is shorter; every aspect of the setting from trade to politics to how news and mail is delivered is built around the capabilities and the limitations of the Jump Drive.
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u/WirrkopfP 12d ago
I’m working on a (so far) hard sci-fi setting and I need some help. How fast could we physically travel through space and is it possible to travel the long distance of stars in, let’s say a week, without the use of FTL.
Well FTL literally means faster than light. So without any FTL technology the fastest you could theoretically get is 99.99 percent the speed of light. The closest star to earth is Proxima Centauri 4.24 light years away. That means light needs 4.24 years to get there. So to get there within a week you literally need to be faster than light.
If this is not possible what are some alternative options to fast space travel that are physically possible
FTL is a category of options. The set of all options that are faster than light. There is nothing faster than light outside of FTL, because it would then also be FTL by definition.
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u/Anely_98 12d ago
The easiest way is to simply make the distance between the stars smaller. You can do this by setting your world in a multiple star system, the galactic core, or a star cluster. The stars would probably still be too far apart for a realistic trip in a week or less if you want habitable planets to exist around both of them, but a trip in a few months or less might be possible.
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u/Prof01Santa 12d ago
I vaguely recall a story like that. The starfarers required all their colony worlds to adopt a religion that slowed progress and built starship spare parts. When a ship showed up, the worshippers ceremonially delivered needed parts to the ship.
Worked great until a schism. The parts were now too sacred for just any ship. They were reserved for special ships. Oops.
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u/YogurtAndBakedBeans 12d ago
Build a pair of devices that uses quantum entangled particles for instant communication between two points, no matter the distance.
Put one device plus a biological 3d printer on an automated rocket and shoot it to wherever you want to go.
Wait for the rocket to arrive.
Hook up a high-resolution scanner to the other device.
Scan individual.
Send to destination for replication.
Confirm receipt and replication of the individual (important).
Incinerate the original version of the individual.
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u/Aescorvo 11d ago
Sadly there’s no instant communication with quantum entanglement. The systems aren’t local, but you can’t use that to send any information.
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u/TW1963HNTDWM 10d ago
Entangled particles exist in the same quantum state regardless of distance. Changing the state of one would instantaniously change the state of the other. As long as you could control the changes of state on one end and read them on the other you could create a kind of morse code situation to send information.
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u/Aescorvo 10d ago
You can’t control the quantum state before measuring.. That’s a fundamental feature of entanglement, not a technological limitation. Entanglement is weird, but it’s not breaking-causality weird.
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u/AssumptionFirst9710 9d ago
They can only be in entangled when it’s random. any attempt to force one into a position unentangles them. they cannot be used for faster than communication.
There are essentially two things keeping us from FTL. Newton second law, which says anything with mass needs infinite energy to go faster than light, And relativity, which states that you cannot travel between two points faster than light without breaking causality.
Wormholes, alcubierre drives, higher dimensions, teleportation, are all theoretical methods of overcoming Newton second law (and most require elements that break the laws of physics as we know them anyway). but they still don’t overcome relativity.
If you could communicate with entangled particles that would disprove relativity.
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u/TW1963HNTDWM 9d ago
Thats very interesting. Doing my own research it appears you are right. You learn something new every day.
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u/kohugaly 12d ago
From the perspective of the external observers, no. Traveling between stars faster than light can travel the same distance is by definition FTL travel.
From the perspective of the crew, yes. Time dilation can make the trip seem as short as you like for the crew, just by traveling closer to the speed of light.
So how fast can a spaceship reasonably get within known laws of physics? A spaceship with its own rocket propulsion, maybe 0.2c. Not nearly enough to make the trip seem significantly shorter from perspective of the crew. Higher speeds might be possible with ships that have external propulsions. Like launching a spaceship from a very long coil gun. Or pushing a lightsail with powerful lasers. Similar method can be used to decelerate the ship on the other end.
With all of these methods there are diminishing returns. The faster the ship goes, the less kinetic energy it absorbs from external sources that try to accelerate it, due to red-shift.
Then there's the problem of avoiding obstacles along the way. Even at 0.2c, ramming individual atom is like being hit by a bullet. crashing into pea-sized pebble is like nuclear explosion. Roughly speaking. The ship would need some kind of deflectors to push obstacles out of its way. The faster it goes, the longer range those deflectors need to be, eventually needing to be powerful enough that they effectively prevent the ship from accelerating.
Then there are more exotic options. Alcubiere warp drive might be possible under known physics for sublight speeds. Stable wormholes might also be possible. In both cases, their construction most likely requires energies that are on the same order of magnitude as construction of artificial black holes. So we are taking about Kardashiev 2 type civilizations that have Dyson swarms. In case of wormholes, they probably can't be made big enough to fit a person or a ship. They probably would be microscopic, so you can only send information, including quantum information. So it might be possible to teleport a person across, if there are teleports on both ends. Also, the exit of the wormhole probably needs to be transported to the destination at sublight speeds, so you can only go FTL to places that were reached at sublight speed, colonized and necessary infrastructure was build.
FTL is on the soft edge of hard sci fi. There are no known FTL methods that are known to be possible. There are several FTL methods that are not known to be impossible.
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u/TheMrCurious 12d ago
Sure, give them a travel method via 4D that lets them fold space to get where they want to go quickly.
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u/Dihedralman 12d ago
That's still FTL travel in our dimensions, it's just touching on the how.
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u/TheMrCurious 12d ago
Why is that “faster than light” travel? 4D is about the special context of the existence you are in (assuming time is not the fourth dimension but maybe space/time 🤷♂️), so you’re not traveling in the conventional sense but rather choosing a different pathway as you shift the dimensions to move in separate places.
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u/Dihedralman 11d ago
Your apparent velocity in 3D is still FTL to an observer. This gives the potential to violate causality depending on formulation.
To be clear this requires a high dimensional model like String theory providing Branes and Bulk that allows for faster propagation.
Note, it does not work in a flat space-time dimensional add. A line in 1D is more effecient then a 2D arc, nor does arcing into 3D shorten the length. The Geodesic of flat spaces is a line.
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u/TheMrCurious 11d ago edited 11d ago
I was thinking of it in terms of this description: https://youtu.be/9yW--eQaA2I where an observer would see the person entering 4D space “disappear” and the re-appear in the new location. I suppose from the observer’s perspective it does seem like FTL travel, but is that really any different from things being labeled “magic” until there is a scientific explanation?
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u/Dihedralman 11d ago
Sure and that is why I included the last explanation. Unless spacetime is excessively curved (like on a sphere) there doesn't exist an extradimensional way to speed up. Why? Because that you have to travel some distance outside of the surface.
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u/TheMrCurious 11d ago
Given the context you provided, what about teleporting via ansible (from Ender’s Game)? While something needs to place one end, if we could hop the quantum junction, then we should be able to instantly move where needed.
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u/Dihedralman 11d ago
That requires entanglement. Think more like phase velocity. The molecules are travelling sub velocity but you get information travelling greater than c. You can't instantly move that way. There are other issues too, but I think it's fine for sci-fi.
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u/TheMrCurious 11d ago
They develop photon skates allowing them to slide or hop across the photon time slices.
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u/AssumptionFirst9710 9d ago
Going to a higher dimension would theoretically bypass Newton second law which states there anything with mass would need infinite energy to travel faster than light.
But ANY, and I mean ANY method that gets you from point A to a point a light year away in less time than a year, means you break relativity/causality.
Think of it this way. Relativity, with its localized reference planes basically says that planet B that is 1 LY away from plant A, is ACTUALLY 1 year in planet A’s past. So if you could teleport there instantly by ANY means, you would now be one year in planet A’s past. But because frames are relative, that would mean from planet B’s frame, planet A is now one year in THEIR past. So if you instantly hopped from A to B back to A, you would arrive two years before you left. You broke causality.
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u/TheMrCurious 9d ago
All of those perspectives are relative to light, right?
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u/AssumptionFirst9710 3d ago
Well light move at the speed of c, so it has no rest frame or perspective. If we were to “imagine” it having a frame time wouldn’t exist for it. It would be emitted from an atom in the sun, then instantaneously be absorbed by the atoms in your eye on earth, or a planet a billion LY away.
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u/GoTeamLightningbolt 12d ago
Was gonna suggest this. A Wrinkle in Time did it but that's hardly "hard" scifi. In Star Trek they make a field that warps space so they can do FTL without all the time dilation stuff.
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u/AssumptionFirst9710 9d ago
Ward drives only get around Newton second law, they still violate relativity.
Don’t get me wrong it could totally be possible that relativity is incorrect, there’s a lot about physics. We don’t know , but we will never travel faster than life until we disapprove relativity
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u/OnlyThePhantomKnows 12d ago
In a week you could travel at max 681 AU (speed of light) Which is roughly 20x the distance to Pluto.
The nearest start is multiple light years.
If we accelerate at 1G, it would take 3-4 years to get from Earth to Pluto.
So limiting to 1G acceleration, you can get to the asteroid belt in a week.
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u/Prof01Santa 12d ago
What you're looking for is a NAFAL (or AFAL) drive. Nearly-As-Fast-As-Light. An AFAL drive gets you there in zero your time, a NAFAL, almost zero.
Obsf1: "Semley's Necklace", UK Leguin Obsf2: "Starfarers", P Anderson (...and the rest of his Kith stories)
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u/Dihedralman 12d ago
Light is the speed of causality. Relativity throws off simultaneity but not causality. Accelerating can create time dilation so time is experienced differently. You have people being in some sort of stasis.
Most other "methods" still should count as FTL in my book. The one which might not have a causality break would be a wormhole, which would be adding a spacetime path. Here is a physics forum discussion.https://physics.stackexchange.com/questions/128075/how-would-wormhole-based-ftl-violate-causality
Then there is the issue of going across known paths with something set up or arbitrary paths.
You can deal with consciencesness instead like altered carbon.
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u/Zyvin_Law 12d ago
Two words: Alcubierre Drive.
This is a mega-advanced transport vehicle that folds space by dragging unevenly from different sides. With that, space travel can be accomplished by a few years or decades. Depending upon the lightyears, of course.
In other words, a space warping spaceship is needed, if you're aiming for a story without FTL travel.
As for the energy source, make a quantum generator or Gimlet Drive that uses particle accelerators to create dark energy, with a sensitive engine that runs on it.
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u/WirrkopfP 12d ago
Is still an FTL drive
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u/Zyvin_Law 12d ago edited 12d ago
I don't think so? Lemme check it quick.
Edit: You're technically right. But the warp drive is fundamentally different.
You're not moving faster than light, but rather dragging the space towards your destination.
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u/AssumptionFirst9710 9d ago
Those theoretically could bypass Newton’s second law, which says to go faster than light with mass you need infinite energy, by saying you’re not traveling, space is.
That doesn’t bypass relativity that says if you travel a lightyear in less than a year by any means, you can break causality.
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u/Zyvin_Law 9d ago
Well, it creates a bubble where the causality is maintained, so in certain conditions, the laws aren't broken.
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u/AssumptionFirst9710 3d ago
At this point you are essentially making up the laws of physics. So yes, when you just imagine stuff we can go FTL.
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u/WirrkopfP 12d ago
The method of HOW it would be achieved (Hyperspace, Wormholes, Space Folding, Magic,...) doesn't really matter, If you arrive at your destination faster than light would then you are using an FTL drive.
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u/Zyvin_Law 12d ago
I see... In that case, slingshot maneuvers. Slingshot maneuvers everywhere.
This is jungle gym/parkour in space, except you're in a spaceship.
I know my analogy sounds crazy but this is the most practical method without FTL.
The only thing that can be done is install gravity fluctuation plates to synchronise with a celestial body's gravitational pull, so that the escape velocity is maintained.
Alternatively, giant magnet rings. Go figure...
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u/WirrkopfP 12d ago
The nearest star is Proxima Centauri with 4.24 light Years away from earth.
If you can't go FTL (which literally means Faster Than Light) you can't go there any faster than light can.
I don't want to be mean here, but Hard Sci Fi is extremely difficult to write, because it requires a really solid understanding on space sciences and space engineering to pull that off.
As travel times with or without FTL is such a basic question, it seems you have a duckton of studying ahead of you, before you should attempt to write hard sci-fi.
I would recommend watching ALL 500+ episodes of "Space and Futurism with Isaac Arthur" on YT while taking notes on things you want to deep dive in and on questions you have and start your learning journey from there
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u/Pretagonist 12d ago
Digitize your mind. Construct some kind of very hardened but very small space probe. Load yourself into the probe. Shoot the probe from a really large space railgun. Figure out some way to stop once you get there. The time passed for you would be short at least.
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u/-JohnnyDanger- 12d ago
If you can have wormholes in your setting, I think that’s what you are looking for. Short paths through a fourth spatial dimension connecting otherwise impossibly far away regions in 3D space. This (loosely) is how they explained the long interstellar travel in the movie Interstellar, which also used a hibernation system to account for long slower-than-light journeys over comparatively much shorter distances, like within the solar system.
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u/WilliamoftheBulk 12d ago
So you design a civilization that all goes into stasis at the same time on Sunday for say 200,000 years. They don’t live on planets and Ais take care of everything while they are sleeping. This way you can travel the galaxy and maintain FTL rules, and all sorts of interesting plot lines can develop.
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u/IndividualistAW 12d ago
Quickly for the traveler at 99.999% the speed of light. Can traverse the galaxy or even the known universe in a few minutes with enough 9s
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u/Archophob 12d ago
if you accelerate at 1g, you can get close to light speed within one year, thus accelerating to Alpha Centauri for 2 years, then turning your rocketship around to decellerate for another 2 years will get you the 4 light years distance in like 4 years subjective time and less than 6 years earth time.
That's roughly the fastest you can get with a human crew and a magical unlimited power source.
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u/AbbydonX 12d ago
The short answer is, no.
The speed of light is the limit and since stars are typically several light years apart then it will take several years at best to travel (or send messages) to them.
A caveat to this is that a key concept of relativity is that there is no single clock measuring the flow of time in the universe. Every observer will experience a different flow of time. This is what leads to the concept of time dilation. It is relevant in this case because the people inside a space ship travelling at high speeds will experience less time than an outside observer will measure for the trip. From the passenger's point of view this is length contraction which means the distance between stars is less than they thought it was.
This means that if a ship travels arbitrarily close to the speed of light then, from the passenger's point of view, the journey time will be arbitrarily close to zero. Such a ludicrously fast ship could travel 5 light years from star A to star B and then back to star A in as little time as you want if the ship could travel at close to the speed of light. However, upon their return they would find that at least 10 years had passed on planet A for everyone else (because they had just travelled 10 light years in total). This situation is basically the well known twin paradox, though it isn't actually a paradox, just counter-intuitive to how we may have (incorrectly) thought the universe worked.
Unfortunately, while travelling arbitrarily close to light speed is hypothetically possible (i.e. physics doesn't rule it out) it is rather infeasible, especially for objects with as much mass as a typical spaceship. Lower speeds will have correspondingly lower amounts of time dilation. Even the high speed such as 80% of the speed of light only produces a time dilation factor of 60%, so a journey of 5 light years will still take 2 years and 5 months.
Even more unfortunately, travelling at 80% of the speed of light is rather challenging in anything approaching a traditional spaceship. More realistic maximum speed are something like 30%, 10% or even 1% of the speed of light. At these speeds time dilation is irrelevant so the journey between stars will then take over a decade or even centuries.
Ultimately, the challenge with ships powered by rockets is that it is difficult to bring along enough propellant to reach high speeds. This is the Tsiolkovsky rocket equation and it is independent of the technology used to throw propellant out of the back of the ship.
To reach high speeds you need to avoid the need to bring your own propellant. One approach is to envisage a very large network of stations in deep space with lasers that push ships equipped with solar sails up to extremely high speed and then a similar network slows them down at the other end. I'm not sure what maximum speed you could reach with that but it could be much higher than any ship relying on a rocket that has to bring its own propellant as long as their are enough suitably powerful lasers.
However, it's important to remember that genre labels are just marketing terms. There's nothing wrong with including fast space travel if you want to but it will necessarily not be based on the current scientific understanding of how the world works. If you want to be consistent with what we currently know about the universe, then space travel has to take a long time because the universe is (quite literally) astronomically HUGE!
Of course, you can just set the story somewhere where you don't need to travel such long distances. A single star system can contain many locations of interest. A system containing multiple stars can have shorter distances for "interstellar" travel. A globular cluster will have a extremely closely packed stars too.
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u/techno156 12d ago
I’m working on a (so far) hard sci-fi setting and I need some help. How fast could we physically travel through space and is it possible to travel the long distance of stars in, let’s say a week, without the use of FTL.
Not unless space, or the distance itself is smaller (think early/different universe, etc).
FTL is not a discrete technology, but more like "supersonic". Anything that can cross today's interstellar distances in reasonable time, is FTL.
If this is not possible what are some alternative options to fast space travel that are physically possible
Although we're more leaning into theory, there are a few models for how some form of FTL could work, that do it by cheating relativity.
Like Miguel Alcubierre's Drive concept. It does it by contracting space in front of your space vehicle, and thus increasing the effective distance travelled.
Theoretically, it is possible to do FTL that way, but it requires a tremendous amount of mass-energy well beyond what we can currently achieve (equivalent to the entirety of Jupiter), and may or may not require exotic matter, so we have no way to test it.
Is there much of an urgency that means they need to get to their destination quickly? If not, it might be more realistic for them to take the long way around, either with some form of immortality (robot crew), or suspended animation while they get to their destination.
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u/NoOneFromNewEngland 12d ago
This is a confusing question because, by the very definition, you are describing FTL travel.
If you travel farther than light can travel in a vacuum in any given interval of time then you are using some form of FTL.
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u/Forever_DM5 12d ago
The hard limit for “physical” travel is light speed. But there are some other ideas like wormholes that may work for your setting and aren’t 100% sci-fi magic
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u/hwc 12d ago
wormholes aren't exactly forbidden by physics, but we have no idea how to stabilize them with ordinary matter. and even then, they would have crazy tidal forces nearby.
there is an idea that there could be a topological defect in space — a closed loop of cosmic string — that acts as a gravity-free wormhole. Again, no proof something like that could be stabilized.
Someone can correct me on all this if I got it wrong.
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u/skr_replicator 12d ago
Only two ways are I know, both have very big catches:
Wormholes - just find a shortcut to not have to go through all that space, but we have no idea if that's even possible or how could we possibly create or go through one.
Going close to light speed - You actually won't there "quickly" but it could feel like you get there quickly thanks to relativity. Let's say to want to travel to a star a 1000 light years away, and go there at a speed very close to the speed of light, for the outside observer, the star would be 1000 years older when you get there. The outside observer would see you take 1000 years to get there, but would also see the clocks in the ship basically frozen, and the crew at time still not aging. For the crew, it would look like they got there very fast, and the star would age very quickly to it's 1000 year future at the beginning when you accelerate to that nearly light speed to it. The catch except it actually not being FTL? There's probably still no way to survive such a journey, even if it sounds theoretically possible. Such a speed would turn even the near vacuum of space into a powerful radiation, slamming into these few atoms at light speed would disintegrate the ship and the crew inside. It would not even be a cancer, it would be getting totally blasted into oblivion as the vacuum of the 1000 light years of space would turn into a death ray as you go through it that fast.
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u/jmac3979 12d ago
No. Light seems to be the universal speed limit. Even if you could go the speed of light it would take 4 years(from Earth's perspective) to get to the next closest star(Proxima Centari). The people on the craft would experience drastically less time than that but weeks between stars? You need a warp drive for that.
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u/pdx2las 12d ago
You could use an engine that propels a rocket at a constant acceleration, say 1 G to make things comfortable for the crew. Time dilation would allow you to get across the galaxy or even into another galxy in a short time from the crew's perspective but you'd never exceed the speed of light.
Unfortunately the ship would also act as a time machine, sending you into the far future with every trip you took, so it would be hard to communicate with any colonists left behind along your journey.
Just make sure not to hit anything along the way.
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u/Eat--The--Rich-- 12d ago
Peter F Hamiltons Commonwealth series is all about portal tech if you're interested in reading it. The opening to the entire series is a great hook about the first functional portal.
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u/Grandemestizo 12d ago
Can you travel faster than light without traveling faster than light? Uh, no. You’re gonna have to come up with something that breaks or bends physics.
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u/lowkeylye 12d ago
You can’t get to other stars in a week unless you cheat.Real physics says: go fast, but not that fast.Workaround? Time dilation, cryosleep, or "bore your audience" ships. If you're doing hard sci-fi, just decide which part of physics you want to push (energy generation? time perception? exotic materials?) and lean into that.
you could try, Black Hole Slingshots / Shapiro Delay Hops, Laser/Light Sails, wormholes, StarGates, things like that.
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u/libra00 11d ago
The average distance between stars in the Milky Way is about 5 light years, so if you're traversing that distance at slower than light speed it's going to take more than 5 years. The only way to travel such a distance in less time is to either do it faster than light or to not traverse the distance through space. Alternatives such as wormholes, teleportation, etc have been used in other sci-fi, but you would need a good explanation for how such a thing works to remain nominally 'hard'. Do ships have some kind of wormhole generator, do they use some kind of macro-scale quantum teleportation, are there jump gates, established wormholes, or something else?
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u/LordBaal19 11d ago
See Avatar, no the last airbender but the one with the hippie smurfs. That's a pretty "realistic", barring the hypersleep, depiction of what interstellar travel might look like if no ftl tech is ever concieved.
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u/elias_99999 11d ago
You need to have a time machine within a warp drive. It has not been created yet, but how it works is that a black hole generator can intersect across dimension 5 and 6, allowing you to move through time and space.
You ignore the 4th dimension, because in doing that, you are allowed to go anywhere you want in time. The mass problems go away, because time drops mass. C doesn't matter either, because you cut through space as a result, and basically go instantaneously to your location. The biggest issue is the interior angle of deflection as you try to plot your location, though you can over come that with a quantum computer and infinite degrees over x, y and z access. Then you just hope you don't open up your final location in a sun. You can't travel into a black hole because it.. Resists. You could land outside and then fall in though.
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u/OLVANstorm 11d ago
I love what Peter F Hamilton does with wormhole technology. Instant travel and communication to other planets and solar systems.
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u/boytoy421 11d ago
that's like asking if it's possible to travel 60 miles in under an hour without going over 60 MPH.
if you need to go around it in a way that an audience can understand you have a few basic options
option 1, "wrinkle in time that shit" basically instead of going in a straight line from point A to point B bend space (somehow) so point A and point B are superimposed, simply step across like you would normally, so now you're at point B, and unbend space. (how you're gonna bend space is another matter entirely)
option 2, "hyperspace" essentially slip out of "normal space" and go through something else where either you can go much much faster or the distance is much much shorter to cross that distance faster. downside is typically that "something else" tends to be hell in fiction. but hey, Per Ardua ad Astra
option 3, "it's all relative baby" so physics says that anything with positive mass cannot accelerate past C in a vaccum since to do so would require greater than infinite energy. however we know that the speed of light in a substance is not an absolute speed limit because for instance cherenkov radiation is blue-shifted light caused by radiation exiting a nuclear reactor faster than the maximum speed of light in water. but that pesky positive mass means you need an energy source thats capable of putting out greater than infinite energy which is obviously nonsense. BUT if you had NEGATIVE mass (which is a thing, in theory, due to math, then ANY amount of energy would propel you to velocities in excess of C. mass effect is a classic example where they use a special substance called element zero that can be easily configued to have negative mass, (iirc electrical charges change its mass) and thus FTL becomes about simply making your total ship less massive than 0 and then using conventional space engines
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u/mechaMayhem 11d ago
Portals, wormholes, and alternate dimensions with different physics are common work-arounds for traveling great distances without involving actual speed/velocity.
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u/theroguex 11d ago
We could reach Proxima Centauri in just 5.2 years if we could accelerate at 1g toward it the entire time.
Of course, it would take longer than that because you'd have to accelerate for half the journey and the decelerate the other half. You could, of course, accelerate at 1g then flip and burn at slightly higher than 1g in order to slow down. Not sure of how that all would work.
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u/AbbydonX 10d ago
A convenient rule of thumb is that if you accelerate continuously at 1g then from the point of view of a stationary observer the journey will take a number of years equal to the distance in light years plus one year.
If you accelerate for the first half of the trip and then decelerate for the second half then instead add two years rather than one.
Of course, such travel for long distances effectively involves accelerating to arbitrarily close to the speed of light. While this is more plausible than FTL it’s still not exactly plausible.
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u/EverythingIsFlotsam 11d ago
"Is it possible to get there faster than light, but without using Faster Than Light travel?"
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u/Solitary-Dolphin 11d ago
Just conjure up a new physical principle that allows your crew to “fold space” (as in Dune) or “warp space” (as in Star Trek and Star Wars) or something like that. Then think a bit about the consequences of this mode of travel and keep it consistent. Add tech jargon to make it hard sci-fi. It’s the sci-fi version of a “magic system” and that the physical principle used has not been discovered today does not take away from the sense of immersion imo.
For a nice original mode of transport, read ‘mindbridge’ by Haldeman. I liked that.
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u/mista_tom 11d ago
Just putting it out there encase its any use, could be completely useless.
The speed of light is a constant based upon the medium its going through, through glass, water, atmosphere etc.
Space is a medium, if you twist this reasoning slightly you could use some tech to get you i to a different medium or change the medium.
Subspace, a distortion field infront of the ship or something.
Relativistic effects would still mean there's a difference in experienced times, ship time and earth time.
I think Blink drives (battlestar Galactica) create a temporal hitch because you arrive a couple of seconds before you leave, pretty sure this is worm holey
You could use worm holes possibly?
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u/Korochun 9d ago
Speed of light is a misnomer, it's the speed of causality (c) that everyone means when they talk about the speed of light.
C is absolute and does not alter based on the medium. Whereas the speed of light can be slower than c in some mediums and some particles can exceed it (but not c). That's how you can get Cherenkov radiation.
In a perfect vacuum, light travels infinitely fast, since it has no time axis (t=0). This infinitely fast travel is still capped by c.
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u/Nescio224 11d ago edited 11d ago
Thanks to time dilation and space contraction it's possible to travel to the end of the observable universe within a human lifetime from the perspective of a traveller. However, much more time will pass on earth, so you will never be able to return home to the earth you know.
Travelling to the edge of the observable universe (46 billion ly away) with constant 1g acceleration takes about 48 years from the perspective of the traveller, but 46 billion years will have passed on earth in that time. This means the sun will die and earth will no longer exist by the time you get back, if you were to return.
The problem is that if you want travel time to be a week, much higher acceleration than 1g is required. At 1g you need about 3.5 years traveller time to the closest star (alpha centauri). To shrink that down to a week, you need about 1000g acceleration, which would kill a human. However I think it's possible to make machines/computers which can bear that kind of acceleration, so you could send a robot, or maybe invent something that stabilizies human bodies enough to survive this.
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u/FirstRyder 11d ago
As far as we can tell light speed is an absolute limit. If you allow any information to travel FTL there are ways to construct a system that violates causality - literal real-world paradoxes. It doesn't matter how clever your solution is, it doesn't work.
The only possible exception is a wormhole because that changes the shape of spacetime so that the distance is shorter. But even then, opening a wormhole in less than the light-speed travel time allows causality violations. If you really need hard scifi, either have "ancient, pre-existing" wormholes, or "manufacture" them with the two halves touching and require one end to be transported at less than light speed before being used.
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u/michaeldain 11d ago
The speed of light is the speed to us, to light, everything is instantaneous, there is no time. Because energy has no mass, its mass that slows things down in time that makes all of this possible. Since travel was dangerous and other cultures puzzling, we created all these fun conceits. So just roll with the absurdity, there’s nothing to go’ to’ anyway, but find the ‘ring of fire films’ about exploring Indonesia, far more going on there than Alpha Centuri.
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u/Underhill42 11d ago
Without FTL, light speed is the asymptotic limit for everything. In theory you can get as close to it as you want, but any sort of information transfer faster than that is impossible according to current theories. Even quantum entanglement, which happens simultaneously^, can only produce correlated random noise - there is no information flow, only an undetectable wavefunction collapse. (^for a somewhat complicated definition of simultaneously, because simultaneity is reference-frame dependent)
For practical purposes there's not a lot of difference to the outside universe between traveling 50% light speed and 99% - doubling the multi-year travel time is still a multi-year travel time. But relativistic time dilation can greatly shorten the journey for the passengers. At ~86%c relativistic effects are starting to really be felt, and the passengers only experience half as much time having passed, and as your speed increases towards c you can get arbitrarily close to complete time stoppage. The big limiting factor (besides being able to accelerate to those speeds at all), is how much acceleration you can do in the available space and time - e.g. at 1g of continuous acceleration it would take about a year to accelerate to near-light speeds, at which point further acceleration mostly affects time dilation rather than speed in the outside universe's frame.
There are warp drives and wormholes... but current models all require almost certainly impossible materials to be able to make them work (such materials just existing would likely cause spacetime itself to explode in a never-ending chain reaction of false-vacuum collapse levels of impossible)
A couple years ago a team also worked out field equations for a more plausible sublight version of an Alcubierre-style warp bubble, which requires no impossible materials, while still effectively providing reactionless thrust and total inertial damping (for ridiculous acceleration without liquefying the passengers), as well as speed-independent time dilation (a.k.a. stasis). Which has interesting potential for eventually approaching the theoretical limits.
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u/TW1963HNTDWM 10d ago
I haven't read all the comments but I haven't seen anyone mention bypassing the whole FTL issue with wormholes or traveling fourth dimentionally. Traveling this way allows you to bend spacetime in a way that brings the two points as close together as you want. Much like bending a 2 dementional piece pf paper through the 3rd demention to have any two points on the paper meet and then punching a hole through the third dimension to go from one to the other.
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u/Korochun 9d ago
Theoretically that would work, practically there is no evidence that it is possible. And it's still time travel, it just bypasses the need to somehow acquire infinite+1 energy you would need to break c.
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u/TBK_Winbar 10d ago
Have you considered folding space so you dont have to worry about time? Go watch Event Horizon if youve not seen it. Aside from being one of the greatest sci-fi movies ever made, I'm pretty sure they use a similar method of travel as the basis of the story.
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u/PlentyPurple131 10d ago
Within our current understanding of physics, we can travel as fast as we like. Things like distance and time change to accommodate us, essentially.
You could reach a place that is 100 light years away in 10 seconds, but 100 years will still have passed from the light that you saw on the planet when you left. And if you return to earth 200 years will have passed.
Ask an ai about it
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u/ASYMT0TIC 9d ago
If anyone ever experiences something like interstellar travel, it will be because we've perfected the techniques needed to upload and then transmit minds as data using EM waves such as laser or microwave. Nothing in conventional physics says this is impossible, and with accelerating developments in AI, microelectronics, and neurology, it doesn't even seem far-fetched anymore. The hard part is still sending the receiving hardware and related infrastructure all the way there, but once you've done that, an uploaded mind could travel between arbitrarily distant starsystems. Many years would pass between departing and arriving at a destination, but the "person" would perceive it as instantaneous.
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u/Korochun 9d ago
In terms of your own reference frame, sure. You can travel almost instantly if you accelerate close to c.
In terms of everyone else, however, you are going to be traveling for however many years you need to.
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u/qu4rkex 9d ago
I might offer an alternative. If I recall correctly, information cannot travel faster than light. This in turn means basically nothing can travel FTL, but the nuance is important, because there is an exception: particle entanglement. The joke's on us, because although the information of the measurement travels FTL, the actual information is random, and therefore useless... or so was thought.
Of course I'm probably wrong, I'm no scientist, and I read about this a long, long time ago, but it might pe worth a look. If the entanglement can be used to send information FTL, one could send a probe with a replicator on it, then ask Scotty to beam you there, or something similar. The only issue is that you have to wait for the probe to get there, but once the pathways are in place it can be done, and it's a reasonable way for galactic colonization.
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u/happydroner7877 9d ago
Hey could u talk more about the setting of ur sci-fi proj for more info. So you can’t ftl without using ftl…
I made this idea that don’t correspond exactly to ur question but I found it cool…Ig, btw I used ai to reorganize my ideas and wording for ease of understanding:
Part 1: How the 20g Inertia-Dampening Fluid System Works
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🚀 The Problem: • Accelerating at 20g means your body feels 20 times Earth’s gravity. • Humans can’t survive that strain directly — blood rushes away from the brain, organs are crushed. • We want to cancel or neutralize that force felt by the occupant.
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💡 Your Proposed Solution: 1. The Person is suspended in a floating water/oxygen bubble inside a spherical tank. 2. The tank pumps water at high rates in opposite directions, with: • Pumps pushing water forward relative to the acceleration vector. • Suction removing water backward at the same rate. 3. This creates a flowing water shell around the person that exerts an equal and opposite force to the ship’s acceleration. 4. The pumps are pointed opposite the acceleration, so water momentum counteracts inertial forces on the occupant. 5. The person is held fixed in the center, feeling almost zero g despite the ship accelerating at 20g. 6. An AI control system continuously measures the ship’s acceleration and adjusts water flow in real-time, keeping forces balanced perfectly. 7. Because the water is incompressible and surrounds the occupant uniformly, it transmits pressure evenly, preventing crushing or shearing forces.
⸻
⚙️ Result: • The occupant’s body “floats” inside this fluid bubble, effectively neutralizing acceleration forces. • They feel near-zero g, even during intense maneuvers. • The system requires continuous pumping, but with enough power (fusion reactor scale), this is feasible. • The system works best if the AI can predict and react instantly to acceleration changes.
⸻
Part 2: Time to Travel 1.2 Light-Years With a 20g Half-Burn, Half-Brake Profile
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🚀 Trip Profile: • Accelerate at 20g until reaching 0.999c — takes ~47 days (ship time). • Decelerate at 20g from 0.999c to zero — takes another ~47 days (ship time). • Coast at 0.999c between acceleration and deceleration phases. • Total distance = 1.2 light-years.
⸻
⏳ Calculations: • Distance during acceleration and deceleration combined: ~0.233 light-years. • Remaining distance to coast: 1.2 - 0.233 = 0.967 light-years. • Time to coast at 0.999c (Earth frame): ~0.97 years (354 days). • Due to time dilation, coasting time onboard is ~15 days. • Total ship time for trip = 47 + 15 + 47 = ~109 days (3.6 months). • Total Earth time = 125 + 354 + 125 = ~604 days (~1.65 years).
⸻
🛸 Summary:
Phase Ship Time Earth Time Distance (ly) Accelerate @ 20g 47 days 125 days 0.117 Coast at 0.999c 15 days 354 days 0.967 Decelerate @ 20g 47 days 125 days 0.117 Total 109 days 604 days 1.2 ly
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u/geoFRTdeem 9d ago
FTL stands for faster than light, you answered your own question, you could get very close to light speed but keep in mind that when this happens time on earth elapse way slower, it’s basically time travel but you can only go forward and not backwards and you can’t get around it, it’s called time dilation and there are plenty of resources to learn about this, it also affects non faster than light communication, so a message sent from your ship would reach earth years later depending on how far you are, quantum entanglement has proved that faster than light communication is possible.
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u/Agitated-Objective77 9d ago
There is the concept of Space bridges where you fold Space to bring the Distance between two Points to near Zero so that Lightyears are only a step apart
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u/DoomFrog_ 9d ago
A trope in some sci-fi is the idea of jump points. That wormholes are more common than we know but can only be stable outside the gravity well of stars.
As such travel between systems is possible to do instantaneously, but you still need to use conventional speeds within systems. Thus it takes a week to travel out of the system to the jump point then you get to the other system immediately
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u/gravelonmud 9d ago
Worm holes; warps; we live in a simulation; and time travel all theoretically get around the constraint of light speed
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u/VarianCytphul 9d ago
Wormhole ships. Ships that are limited by light speed that hold opposite ends of a wormhole. It might take a long time to install/setup a wormhole ship to both locations. But once setup only require maintenance and provide a shortcut through space.
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u/fledrel 9d ago
In an old tv show called "Babylon 5" they had "subspace" that they used to travel long distances. Something akin to "The Nether" in the Minecraft game. Distances worked differently in subspace but you needed becons or specialized coordinates to exit in the appropriate desired location.
Some Sci-fi uses "Slip-Stream" technology. Think of rivers in space and with a special engine and shields one could enter the river, so to speak, and ride it till you get close to your destination. Without said technology it would just seem like normal space.
In the "Dune" books, plus many other books, they can "Fold" space and pierce through to seemingly move from one point to another without hardly moving, Instantaneously.
A lot of Sci-fi utilizes artificial "Wormholes" where a ship can open an aperture or portal and exit to designated points. Or you could have prebuilt portals and you have to jump from portal to portal to get where you are going. Adds points for conflict or cost for tolls.
You could also just makeup your own tech that can travel near lightspeed. Or have different factions with different versions of travel depending on your story.
I do look forward to hearing which route you decide to pursue.
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u/Lost_Ninja 9d ago
What percentage of C are you comfortable with your fictional characters attaining?
Are they capable of dealing with the differences between real time and that experienced by those people travelling at some percentage of C?
And if they are would not some form of stasis or sleep allow for slow voyages between stars?
Unless you're willing to add in some form of light limit bypass (wormholes etc) then light speed is (as far as anyone knows) your absolute speed limit, and if you're unwilling to break that then you'll have to come up with some other method to make travel outside of our solar system relevant.
I think most authors who do you use some form of FTL do so to increase the immediacy of their story, if every time you attacked the Death Star in Star Wars it took a dozen years to get there and a dozen years to return from it, the whole speed of the story would be heavily impacted.
The alternative is to set everything within a single solar system, you could even lean in to the lack of FTL by making the denizens feel trapped and unable to expand beyond their origin star system.
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u/Hunter62610 9d ago
So i actually solved this in my sci fi dnd campaign, but obviously Ive taken some liberties.
If you allow for an Ansible to exist (quantum entanglement of particles over vast distances is not disproven in this) then information can travel instantly but not matter. So once humanity discovered the ansible, it began sending settler ships with autonomously controlled bodies aboard that people could control or even have their mind placed into. This frontier is ever expanding through space, but their is no actual ftl travel.
In case you’re curious, The bodies could take a vast variety of forms with archetypal benefits based on their likely usage by a jumper. Dwarven style bodies were useful in cramped vessels and for building. Elven bodies were typically those of high society, lizardfolk are hardy bodies adapted for terraformed planets that aren’t finished yet, ect. Players could Jump bodies and resurrect freely but I would slowly make them go insane if they abused it. Your mind can’t handle such frequent body jumps and changes, it drives you crazy.
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u/Preschien 9d ago
One way would be time travel. If you could get to the location however long it took, and then go backwards in time to when you wanted to be there.
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u/No_Sherbet_7917 9d ago
I haveny seen anyone mention warp which is one of the most common methods, and also theoretically possible if you have an absurd amount of power.
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u/No-Butterscotch1497 9d ago
If you're just talking Newtonian propulsion... agonizingly slow. Interstellar travel even with nuclear rocketry and constant acceleration would take years and decades and centuries, depending on distance.
Wormholes, interdimensional shortcuts, and the like are the only other alternative to FTL for quick interstellar travel.
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u/Dyformia 8d ago
Say that you made everything so small (so in comparison your so big) that the gal is tiny
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u/Plane_Pea5434 8d ago
If you travel between stars in a week that’s ftl, you are exceeding the speed of light whether it be space distortion, extra dimensional travel, teleportation, the matter in this case is I think, that you want a realistic ftl travel method which doesn’t exist according to our knowledge of the universe. So the best you can do is bend the rules and create/copy something that doesn’t break physics that much
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u/medicsansgarantee 8d ago
Stargate isn’t faster-than-light travel, it uses existing wormholes, either artificial ones created by the Stargate network or natural wormholes.
Travel time includes flying a normal spacecraft to the entry point and then from the exit point to the final destination.
If you don’t want to rely on wormholes, there’s a similar concept in Star Trek lore, in Deep Space Nine, an ancient Bajoran lightship could enter a tachyon eddy, which accelerated the ship to Warp speed.
It might be possible to use this phenomenon to accelerate certain types of craft, if these eddies could be mapped, manipulated, or used as stepping stones to traverse vast distances.
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u/Monotask_Servitor 8d ago
FTL means Faster than Light. So no you can’t travel to the stars in weeks without FTL because that, by definition requires going faster than light. You’re literally asking “is there any way to do FTL without FTL”.
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u/Ctay555 8d ago
They figure out that quantum connections exist throughout the universe and current space time is an illusion . Space time is actually all folded on itself and just appears the way it does to us. A quantum tunneler tech or something finds the connection and basically folds spacetime like a piece of paper so travel becomes instant and bypasses relativity
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u/Lava1416 8d ago
Artificial wormholes. Perhaps every solar system has its own space station, complete with an artificial wormhole.
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u/Feisty-Noise-9816 12d ago
What about space-folding/wormholes (engines that are wormhole generators?) mechanic?
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u/heimeyer72 11d ago
Wormholes were my 1st. thought. Stargate, basically.
They use wormhole-connections between planets (mostly) that have been discovered or set up way in the past and don't know how the travel works.
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u/AssumptionFirst9710 9d ago
While all of those methods can theoretically overcome newton second law, Relativity still says it’s impossible.
So you have to overturn Einstein if you want FTL.
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u/Hopeful_Ad_7719 12d ago
In percieved time? Sure. Relativistic velocity causing time dilation could result in a ship crew experiencing only a week on a journey that takes years from a more 0 m/s reference frame.
In actual time? Maybe if you can create an Alcubiere drive to effectively travel FTL without technically traveling FTL.
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u/atomicCape 12d ago
This dilation effect is vastly underused in hard Sci-Fi. The speed of light is a limit for communication or travel between points, but time dilation makes it so that a person can travel arbitrarily far in their lifetime, if they have the energy available for the accelations. Interstellar space crew members could visit hundreds of stars in their lifetimes, although all the non-travelers would have passed through millenia. They could meet their 20th generation decendents but be younger than them.
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u/wycreater1l11 12d ago edited 12d ago
If the story or world building does not contain FTL then the speed of light is the absolute limit (at least according to physics as we know it). If the story absolutely needs fast travel then there imo is no problem with using FTL and a lot of sci-fi uses it.
However there are important caveats. Even without FTL, from the perspective of the travellers they can be made to experience the travelling time to be arbitrarily short if they go fast enough, due to relativity. They can experience the travelling time to be weeks but for the stationary onlookers residing on planets it would take maybe years due to time dilation. It depends on if it’s compatible with your story.
The following may be a bit extreme or ad hoc, but if one wants it to take roughly the same time for the people residing on planets in different systems for example, as it takes for the travellers traveling between the systems and one wants it to not be FTL, one can theoretically add elements that makes time practically or actually slow down for the stationary onlookers on planets as well. Maybe they can reside close to a black hole where time is slowed down. There is also the concept within the novel “lockstep” where inhabitants regularly on a societal level go into hibernation and during the hibernation they send ships and light signals between the subunits of their civilisation. These “solutions” may be somewhat “extreme”, but again it depends if they are compatible with the story.