Essentially, by bending a few rules of physics and other sciences with as little handwavium and unobtainium used, could there be a way to travel several parsec and/or lightyears in a (relatively) short time?
Edit:
Time travel is fine, but there is a limit to how long you live. You might zip from Point A to Point B, to the observer, but you’ll still feel the journey’s length, no matter how quick or long it appears.
After all, why waste your time and fuel actually traveling through space? With only a half-dose of handwavium, you can just take that space between you and your destination and move it around behind you. It's the difference between clawing your way through a block of styrofoam vs. moving the styrofoam around behind you.
Required handwavium: Turns out we discovered mass doesn't distort space, it consumes it. That's why things fall together--they just consumed all the space between them. At the same time, balance is maintained by space appearing uniformly throughout the universe, which is seen as dark energy (since it only gets a chance to build up in the intergalactic void).
So we devised a system that simply sucks up space in front and expels it through the back. We haven't really moved, so it's not only transluminal but low power as well.
The only FTL system theorized with any real world evidence that it could actually be doable is the Alcubierre Drive. Using the Alcubierre metric, it has been mathematically demonstrated that the existence of negative energy might potentially lead to the existence of a faster than light engine via perpetual acceleration.
Last year, DARPA-funded research into Casimir cavities demonstrated that negative vacuum energies can be created. While the technology does not exist to do this in a way that we could make an FTL engine, the math and experimental data around Alcubierre metrics say that it is at least probably doable which is more than can be said for other FTL methods.
Wormholes. You don't actually travel faster than light yourself, you're just taking a shortcut. The problem is, that it would still break causality unless all wormholes in the universe existed in the same reference frame.
Simulation. If our universe is a simulation, and you either find a way to access an admin terminal or convince God (or however you call the ones who are running the simulation) to make an exception for you, you could just edit your coordinates and be wherever you want in an instant.
Soft Wormhole
Soft wormholes do not require us to invent any new physics. Soft wormholes break no known laws of physics.
The topology of spacetime is not flat. It has tunnels. Going from Earth to Alpha Centauri in a straight line takes over 4 years at lightspeed. Going a wavey-gravey path might take 10 years. Going through the tunnel gets you there in weeks without officially breaking the speed of light.
Your warp engine does not create such tunnels. It simply makes the visible.
Of course light and gravity also transmits through these tunnels. But that is no problem.
Going at the speed of light breaks physics as we know them (and maybe they're wrong, it's only our best collective understanding of how the universe works after all, not strictly how the universe works), and truth is light is effin' slow, and emphasis here is important because at the speed of light it would still take years to go anywhere outside the solar system and who wants that?
Enter the Mystery Engine™. It allows any ship to go at any speed, but of course that comes with an arbitrarily long or short list of downsides. It looks either super cool or very anticlimactic, it might have some weird effect felt by the people inside the ship.
How does it work? Well, that's the mystery. Engineers know how to make it run and maintain it, but not how it works. They might think they know, but they don't really. The fundamental knowledge of how it really actually works in details is something that only the very best scientists in the field have a grasp on and who, obviously, don't feature in the story.
The only thing we know of the Mystery Engine™ is that it works. And truly, what more do we need?
Why the Mystery Engine™ is the best engine for you
Two reasons really.
The first and foremost reason is it just works, and the less readers/viewers know about how it works, the less they'll be able to find this one weird trick that physicists hate to invalidate your explanation.
The second important reason is that it's rarely important. What's important to know for the reader/viewer is the capabilities, limitations, a visual identity or any other unique quirk.
Rather than wondering how to build an engine to be physically possible and then try to integrate it in your world and story, my suggestion is to engineer it to fit your world and story first and then solve the strictly necessary physics of it. You need to have clear bounds to what is and isn't possible. Ask yourself what's the role of FTL, both in and out of universe (i.e. in the world and in the story), how each aspect can serve or disserve the world and story. Ask yourself what kind of FTL you want, then wonder about the finer physics details to make these things happen.
Quantum tunneling is a well documented phenomenon. To explain a poorly understood incredibly complex problem in an answer here would be impossible, so lets do the basics.
A wave, like an electron, can meet a barrier. There is a possibility that it ignores the barrier, moving instantaneously to the other side of the barrier. Though it seems to have been proven it isn't instantaneous, it is so fast it puts light to shame. I think the researchers called the speed so fast it is practically instantaneous.
Now imagine we can apply this with a certain precision at a larger scale, like a whole ship. You convince the ship that everything between the ship and the destination is a barrier. Then you try to tunnel.
Even at a fraction of a percentage chance it works, it is still easier to try for a few decades and floating in space. When it works it costs no energy as far as I can tell, transporting everything at 'instantaneous' speeds to the destination. Voilà you have arrived at a low cost, 'only' bending the rules from existing quantum levels to a physics perspective.
Time travel is fine, but there is a limit to how long you live. You might zip from Point A to Point B, to the observer, but you’ll still feel the journey’s length, no matter how quick or long it appears.
No, relativity means you don't feel the journey's length.
If you have a drive that lets you accelerate at 2 Gs indefinitely (this, by the way, is insane super-tech, but not FTL), you could cross the galaxy from one side to the other (100,000 light years, give or take) in 616 years yourself.
Crossing 100 light years would only take 19.5 years as far as you could tell.
The time it takes to people not on the ship ends up being larger.
There are a lot of stars within 100 light years.
Now, the problem of a drive capable of 2 Gs of acceleration for centuries is an extremely hard one; it ends up using up multiple stellar masses of energy. So if we can pull this off, we can probably pull off uploading of consciousness, simulated consciousness and realities, and downloading.
So you could simply upload yourself, run yourself at 10000x slower than standard speed, cross the galaxy, and feel the trip only took about 2 days.
You could even go to an extreme. Upload yourself, send your self via radio waves to the destination, and print yourself out at the other end. This gets you speed of light travel without having to consume several stellar masses of energy. You could even imagine relay stations, so you don't have to make a broadcast tower capable of sending signals 100,000 light years (or whatever distance).
Come on people, sci-fi requires keeping up with the literature! The negative mass required for an Alcubierre drive is not needed, according to Erik Lentz (with agreement from Lavinia Heisenberg). Lentz' first paper was reputably published: E. W. Lentz, Breaking the warp barrier: hyper-fast solitons in Einstein–Maxwell plasma theory, Classical and Quantum Gravity 38, p. 075015 (Mar 2021). Here's the preprint of his first paper and here's the Scientific American article.
Yes, the drive requires absurdly large amounts of energy as currently described. However ... We've established what the universe is. Now we're just haggling over the price.
The issue with avoiding science handwaving is that you are asking for an answer which does not exist. Due to that, every answer is going to contain a bit of fantasy. Any method used should be safe enough to make it viable for people to use. A question I would ask is, does your story require a valid scientific method of FTL? There are many sci-fi fans which suspend their disbelief in order to enjoy a well written story. You could always come up with an method based on unanswered physics (FTL drive of the gap), but that introduces the risk of physics negating your method in the future.
Anyways, depending on what purpose FTL travel has in your universe, you likely need an answer which is flexible.
String-Drive: A drive which utilizes one dimensional string theory strings to achieve FTL travel.
Range: Constant (Each string is a set length requiring multiple "jumps" to reach the destination), Random (Depends on the string length, story driven), or Variable (Strings reach between nearby stars but do not exceed x-lightyears in length).
String Availability: Cyclical (Every x-hours/day/week/months like clockwork), Constant, or Variable (Ranges hours/days/weeks/years).
Risks: Being stranded in areas between stars with few strings. Long wait times between available strings. Encountering a closed string which might trap/destroy/vanish/stall a ship.
Trip Length: None, Variable (based on the string length), Constant (it always takes x-time regardless of distance), Subjective (time is experienced differently between passengers and the rest of the universe but still based on a known rate).
Method: Sensors are used to detect strings and determine (with a plot driven margin of error) the viability of the string. A special particle accelerator locks onto the string which shifts the ship into a different dimension. The accelerator pushes the ship along the length of the string until it reaches the end, at which point the ship exits to normal space again.
Since string theory is also the theory of quantum gravity, you could work that into an explanation. "The energy from the ship's particle accelerator poured into the cosmic string, folding the ship, and everything contained within, into a multi-dimensional bubble. Quantum gravity, normally restricted to operating at the Planck scale, operated differently in this space/time. The ship fell towards the quantum gravity well as if it was approaching a blackhole, but the particle field was pulled along with the ship, shifting the singularity's location to always be just beyond reach. The ship would keep falling like this until it reached the end of the string, at which time the ship would be forced back into normal space. It was a rough, almost violent, way of achieving faster than light velocities, but it worked."
If FTL is going to play a major dramatic role in your world, it might be helpful to have a method which is less predictable/reliable.
Q: What would be the least physics breaking way to travel at light speed or faster?
Leaving a paradigm defining a reference frame is no small change.
I can't go into "or faster", because this question has a science based tag.. there's no "minimal change" when your model of space time is based on a light speed reference (or grid) of moving photons at zero mass and c.
It is like asking Euclides to leave his linear axes and apply an asymptote for grid distance somewhere on the X-axis. And then find an asymptote that is surpassing the previous one in gradient, until at some gradient, the asymptote breaks and starts to travel into the past (??) or back (??)
Propagating light speed c is like a reference to physics, not something you can "beat". Nearing c will enlarge the mass of your ship to infinity. There is no way to drive infinite weight ships, so cou can't ever reach actual c, let alone pass it.
For space colonization, you don't need to hurry.
Maintain 2G acceleration during about 11 years (299792458 m/s divided by a=20 (2G) divided by 3600*365.25) will bring you near c indeed, but for your passengers, 2G is very inconvenient and accelerating for 11 years requires a lot of energy. You'll need more and more energy, while approaching the actual c.. that will limit the effective mass of your ship and its usefulness for colonization purposes.
Excessive time travel into the future is impractical for colonists
It will depend on the ship's weight and and its purpose what to choose, when you approach c. For reconnaissance missions, involving solo, adventurous SF travelers with endless energy at their disposal, warping a few million years per month of travel won't be a problem, you could be underway for 63000 years per ship day.. time dilation..
https://www.fourmilab.ch/cship/timedial.html
..but if you do colonization, you'll need less time warping !
Traveling too near c could result in an unpredictable situations on arrival.
A colonization target exoplanet must be researched properly, on Earth, before you send a mission. You can't arrive on an exoplanet aeons later. When you'd arrive say 300.000 years in the future, you could find your target planet evaporated by a near supernova, or rendered inhabitable by a planetoid impact you never predicted. Colonization missions should be safe.
Easy go: generation ships
For colonization, time deviation should remain below 50% and bring you back to (about) the real world ! that is (about) current time, or say, twice current time. I think there will be discoveries of interesting planets in the 5-50 ly distance range in the coming centuries.. humanity will build generation ships to reach other places. Travel straight for say 20 years at 1G, to reach say 0.75 c. Time dilation will be about 1.5. Then, go straight and 0G for 0-40 years. Then, take 20 years to decelerate.. You can explore anything between 10 and 50 light years, within a century.. without the need for FTL. Or apparent (observer) FTL.
What year is the physics book that you are using to determine 'reality'?
Our physics textbook keeps getting thicker and thicker every year. Not only are the chapters expanded on, but entirely new chapters are written.
A form of near-instantaneous teleportation is now theoretically possible. However, it takes specific conditions. A near-empty environment, minimal heat (vibrations of particles), and devoid of gravity - exactly what inter-stellar space is.
The terminus of such a transportation system would have to be far from any gravitational source, and could not be 'built in' to the spaceship, rather the spaceship is 'launched' from this special facility and is thereafter 'on its own'. That is, the spaceship would have to be encapsulated in a special containment vessel, and forced into a quantum state. Then, probability takes over its actual location - it becomes a quantum wave. Just like entering the StarTrek transporter. All the action takes place in the transporter room, not in the space between origin and destination. Unfortunately, currently there is no real way to 'aim' it at a particular location.
Holding a nanoparticle this tightly in a single spot is just the start. The goal is to put these objects into a so-called quantum superposition — where it becomes impossible to say, before measuring them, just where they are. A particle in a superposition could be found in one of two or more places, and you just don’t know which of them it will be until you look. It is perhaps the most startling example of how quantum mechanics seems to insist that our familiar world of objects with definite properties and positions comes into being only through the act of looking at it.
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All the same, researchers have been steadily increasing the size at which superpositions and related quantum effects can still be observed — from particles to small molecules, then bigger molecules, and now, they hope, nanoscale lumps of matter. No one knows how far in principle this expansion of quantumness can continue. Is there — as some think — a size limit at which it simply vanishes, perhaps because quantum behavior is incompatible with gravity (which is negligible for atoms and molecules)? Or is there no fundamental limit to how big quantumness can be?
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Aquantum particle in a superposition, contrary to common belief, is not really in two (or more) states at once. Rather, a superposition means that there is more than one possible outcome of a measurement. For an object at everyday scales, described by classical physics, that makes no sense — it is either here or there, red or blue. If we can’t say which it is, that’s just because of our ignorance: We haven’t looked. But for quantum superpositions, there simply is no definite answer — the property of “position” is ill-defined.
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Interactions between a quantum particle and neighboring particles, such as gas molecules or photons, entangle both objects into a kind of joint quantum state. In this way, a superposition of the original particle gets spread into the environment.
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Rather like an ink droplet diffusing and spreading in a glass of water, this spreading superposition makes it ever harder to see the original one unless you look at every spot it has spread to and reconstruct it from that information. As entanglement mixes the wave function of the initial superposed particle with those of its surrounding particles, the wave function seems to lose coherence and become just a mass of incoherent little waves. This process is called decoherence, and it makes the superposition undetectable in the original object: Its quantum nature seems to disappear.
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Decoherence of a quantum superposition happens extremely fast unless the interactions of the particle with its environment can be minimized — for example, by cooling it to extremely low temperatures to reduce the disruptive effect of heat, and keeping the object in a vacuum to eliminate molecular collisions. The bigger the object is, the more interactions it is likely to have, and the faster decoherence happens. For a dust grain about 10 micrometers across floating in the air, a superposition state of two positions in space separated by about the same width as the grain itself is estimated to decohere in about 10−31 seconds — less than the time it takes for a beam of light to travel the width of a proton.
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Arndt says his goal is to increase the mass of the particles by a factor of 10 every year or two. That would soon take them well into the size and mass range of biological objects such as viruses. Meanwhile, in 2009 Romero-Isart, then at the Max Planck Institute for Quantum Optics in Garching, Germany, and his co-workers sketched out an idea to levitate viruses in an optical trap — where tiny objects are held fast by the forces induced by intense, focused light beams — and then coax them into a superposition of two vibration states and look for interference between them.
Why stop there? The researchers even speculated about doing the same to unambiguously living organisms, such as the phenomenally robust little animals called tardigrades, which are about a millimeter wide and have been found to survive several days of exposure to outer space. The researchers wrote that the plan would allow them to create “quantum superposition states in very much the same spirit as the original Schrödinger’s cat” — the famous thought experiment intended to highlight the apparent absurdity of quantum superpositions for large (and especially living) entities.
So, really, no worm hole or handwaving required, and based on current theory. It is technically not 'moving' anything, except the informtion in the waveform.. 'Superposition' an entire spaceship into a quantum state. But where she lands, no one knows. It is all about probability, the spin of the wheel.
Oh, and no guarantees that life could survive the process. Something about that 'quantum state - low energy' thing. Room temperature quantumness, anyone? We are aiming for room temperature superconductivity, after all.
Create a method to decouple from the Higgs field, thus negating mass )and presumably inertia). This would still presumably stop at c rather than allowing infinite velocity.
'Newer physics text book' next chapter
Most of the proposed solutions involve the mechanism for travel be inherent in the spaceship. The ship itself carries the delta-V. Okay, that gives tremendous flexibility, steering, and choice of destination, and 'travel on demand'. However, there is an alternative. It is like the difference between a rocket-powered projectile and a gun-shot projectile.
For the background concept, one proposed solution to interplanetary travel that is going the rounds is a 'laser sail' that propels the tiny ship through a laser beam sent from some platform. Thus, the tiny ships do not need to carry the delta-V with them, the delta-V is provided by the beam of light generated at some energy-rich source, and projected at the spaceship.
Let's carry this further. For travel between two specific destinations, there is no real need for in-flight course corrections. 'Ballistics' methods are good enough.
One potential solution is suggested by 'solitons'
In mathematics and physics, a soliton or solitary wave is a self-reinforcing wave packet that maintains its shape while it propagates at a constant velocity. Solitons are caused by a cancellation of nonlinear and dispersive effects in the medium. (Dispersive effects are a property of certain systems where the speed of a wave depends on its frequency.) Solitons are the solutions of a widespread class of weakly nonlinear dispersive partial differential equations describing physical systems.
The soliton phenomenon was first described in 1834 by John Scott Russell (1808–1882) who observed a solitary wave in the Union Canal in Scotland. He reproduced the phenomenon in a wave tank and named it the "Wave of Translation".
The disadvantage of most EMF waveforms is the 'Inverse Square Law' - because they propagate in a concentric circle radiating out, the energy dissipates by the square of the distance. But suppose, somewhat like a laser. a 'beam' could be shot out that does not dissipate, but maintains its shape. It is constrained on all sides, essentially traveling down a tube. That is in essence what a soliton is.
Consider, as an example, the vortex air cannon, shooting an air donut out. This air donut is essentially a soliton, a body of air moving through space at a constant velocity and maintaining its shape.
Instead of shooting air, suppose this cannon shoots out a warp bubble that ravels through space, towards a pre-determined destination, at a constant velocity and coherent contiguous shape.
Now, put a 'spaceship' in front of, or in the middle of, this soliton, so that the spaceship travels with the soliton like a surfer on a wave. No need for the spaceship to carry any delta-v, it is all supplied by the original source that created the soliton in the first place, like a gun instead of a rocket.
If one's physics text book is as new as just a few years old, this solution becomes imminently reasonable.
Consider this idea, from "Breaking the Warp Barrier for Faster-Than-Light Travel: New Theoretical Hyper-Fast Solitons Discovered"
If sufficient energy could be generated, the equations used in this research would allow space travel to Proxima Centauri, our nearest star, and back to Earth in years instead of decades or millennia. That means an individual could travel there and back within their lifetime. In comparison, the current rocket technology would take more than 50,000 years for a one-way journey. In addition, the solitons (warp bubbles) were configured to contain a region with minimal tidal forces such that the passing of time inside the soliton matches the time outside: an ideal environment for a spacecraft. This means there would not be the complications of the so-called “twin paradox” whereby one twin traveling near the speed of light would age much more slowly than the other twin who stayed on Earth: in fact, according to the recent equations both twins would be the same age when reunited.
If these solitons could be generated at the origin, and then shot out towards their destination like the vortex air cannon all energies are supplied at the origin, not on the spaceship itself.
