# What kind of fuel would spaceships capable of faster-than-light travel use? [closed]

In my book series, faster-than-light travel is a thing, allowing the fastest spaceships to cross a Milky-Way-sized galaxy in a matter of days. The slower ships could manage that in about 2 weeks.

Anyway, the way this faster-than-light travel works is that pretty much all ships built for long-distance travel are equipped with a matrix ripper, a device that opens a portal to an alternate dimension called darkspace.

Unlike outer space, which is illuminated by stars, darkspace is in total darkness except for the lights of any ships that are in there. In darkspace, some laws and theories of physics do not apply (at least not in full), such as the theory of relativity. This allows spaceships to accelerate to a speed directly proportional to how deep into darkspace their matrix ripper allows them to go (matrix rippers do not offer full access to darkspace, but instead allows ships to skim its surface, which allows ships to move ridiculously fast but grounds any location they visit to a corresponding location in our dimension). When a ship reaches the point in darkspace corresponding to their destination, they use the matrix ripper to open another portal back to our dimension, where they emerge at their destination.

My question is, what kind of substance would work best as a fuel for faster-than-light travel devices such as matrix rippers?

• uhmmm... Nuclear? – Mr.J Oct 17 '18 at 2:01
• Without knowing more about what matrix rippers do in/to our volume, it's impossible to answer. – rek Oct 17 '18 at 2:18
• I would recommend any sciency material like dark matter, anti-matter, mycelium network or maybe even graviton or a particle of time (assuming you let time be a particle in your world). Higgs Bosons, Quarks. – Shadowzee Oct 17 '18 at 4:32
• Handwavium. You can't go wrong with handwavium. – The Square-Cube Law Oct 17 '18 at 5:10
• Since you handwaved your drive, you can easily handwave your fuel as well. A can of Schwartz did the trick for Lone Star back then. – Alexander von Wernherr Oct 17 '18 at 8:07

Your FTL drive is probably electrical.

I don't know what fuel you'd use for this kind of ship, but ultimately what you're trying to do (as opposed to what you're using to do it) is combine all the fundamental forces of the universe in a manner that allows you to operate in a super-dimensional construct of space-time, or hyperspace (or darkspace in the terms of your story).

If we focus on this, then the answer becomes more evident. We all know about the Maxwell equations from the 1860s, but what did they really do? Well, prior to those equations it was thought that there were 5 fundamental forces in the universe - Electricity, Magnetism, Weak Nuclear, Strong Nuclear, and Gravity.

After Maxwell, there were 4. They unified magnetism and electricity. This may not sound like much, but it has been single-handedly responsible for almost every advance in our society since. We can make things turn with electricity, and we can generate electricity by making things turn. As a result, we have radio, electric lights, home appliances, computers, and a myriad of other advances that were only possible by unifying these forces.

3 more to go.

The thing is, generating electricity is now amazingly easy, so when the other forces are unified, we'll probably manage them with electricity. Imagine (if you will) an electrical null-gravity field, or a field that can reduce the mass of an object by tweaking the nuclear forces somehow...

I say probably because we don't know yet how easy it might be to (say) convert all of our existing technologies to weak nuclear force once we find out how to integrate it. It might be even easier, but I doubt it. Electricity is incredibly versatile and it makes some sense from a perspective of speculation that we'd probably just manipulate the other fundamental forces with it once we know how.

So what fuel would you use? My guess is whatever most efficiently generates the massive amounts of electricity you'd need to manipulate all the fundamental forces sufficiently to get a portal to darkspace open.

• Is this a reference to "Back to the future" en.wikipedia.org/wiki/Back_to_the_Future? – Mr.J Oct 17 '18 at 2:59
• @Mr.J no it wasn't, but in point of fact the principle is the same. If you can get around the 2nd law of thermodynamics (entropy) and transport yourself to another point in time, then you'd need to manipulate all the fundamental forces of the universe in a very unique way. Time travel is trickier than FTL in this regard because you're not just 'cancelling out relativity', you're actually violating entropy which is more of a problem. But, ultimately you'd probably do so with electricity by applying it in a way that directly manipulates the other forces, like we already do with magnetism. – Tim B II Oct 17 '18 at 3:03
• I do get the Idea, its just they used electricity to time travel, which in your case, you used electricity for FTL drives. – Mr.J Oct 17 '18 at 3:09
• We might be down to 3 fundamental forces. I believe electroweak is a thing. – Michael Kutz Oct 17 '18 at 9:43

Choose a fuel that lets you move at the speed of plot

So, modern physics will wash their hands of this question. There is currently not only no known FTL device, but not even a reasonable theory on how to do it. So they wont be able to tell you anything you didn't already know. But we can explore what plot might do.

The big question you will need to ask yourself is how much this fuel is an energy source, versus something else. Energy is a fascinating concept in modern physics. It doesn't matter what form it's in, you can convert it from the form its in to the form you want. If you need 250kJ of electrical energy, and you have a cookie, you can convert its energy into 250kJ of electrical energy. If you need that 250kJ in the form of gravitational potential energy, you can convert it into that (perhaps via a motor that lifts an object).

If your fuel's primary purpose is to provide energy, the answer is that it doesn't matter what form it is in. We'll convert it to the right form and use it. As such, Mr J's comment is rather useful: Nuclear. Nuclear energy is currently the most dense form we know of, and energy density is a useful thing. If we have FTL, we likely have nuclear fusion power sources. We'll probably use them.

However, what we as laymen might call "fuel" has other purposes as well. It might be building blocks for some yet-undiscovered physics. 3d printers need energy to operate, but they need filaments of material too. You can connect your 3d printer to as much energy as it wants. It won't print unless it has a spool of plastic or what-not at it's disposal.

When you open things up to this wider class, which I'd choose to call "resources" because that helps open up the brainstorming options more than "fuel" does, it gets interesting. Now you can look at the plot elements you need, and pick resources accordingly.

For example, one obvious plot requirement is that nobody invented FTL before it's time. If matrix ripping was accomplished by a pair of magnets and a coil of wire, someone would have figured it out rather quickly. So you want one of the resources to be hard enough to acquire to limit your access to the technology until your plot is ready for it.

What civilizations do you want to have access to this resource? Do you want one society to have a monopoly on it? If so, you want a fuel which is easily cornered. If you want everyone to have FTL, it should be something that is uniformly distributed across the universe.

Do you want this to be a continuous capability or a discrete one? Consider an example where you need to crush a monolithic crystal to accomplish your goal. Think Khaydarin crystals and the death star. If you have to destroy a precious discrete thing, you'll treat FTL very differently than if you merely ablate the crystal or suck a liquid fuel down. Indeed, many fantasy systems rely on a very small number of teleportation objects (or other spell objects) which must be destroyed to complete the spell. Black Flame Candles from the movie Hocus Pocus is an excelent example of going down this path.

Personally, my opinion would be to work in octonions into the mix. But that's only because I'm rooting for it as one of the underdog Theory of Everything options that's in the mix. Octonions are just confusing enough that you can handwave whatever functionality you need, and nobody is ever going to do the math to prove you're wrong.

Hmm, so every point of darkspace is congruent to a point in regular space, except that it has an extra dimension, depth, which regulates maximum speed. This congruence can't be accidental (says the physicist in me), so our space is merely the topmost layer of darkspace, the depth=0 layer. Ha, we live on top of darkspace!

So, we are all bobbing like corks on the surface of an (infinitely deep?) ocean and matrix ripper is the thing that lets us dive down. What might such a device be powered by? Well, it can't be a "material" available at the surface, since anything that sinks would have sunk already. Dark matter, exotic matter, all of that just went out of the window. What could be left?

Well, perhaps there is a field that couples to matter (but not to photons!) and gives it "buoyancy". It permeates everything, so we don't notice it. In fact, it's a lot like the Higgs field, so call it the hyper-Higgs. If we can reduce the coupling between matter in your spaceship and the hyper-Higgs, it should sink right smartly. Shouldn't be too hard, everything interacts with the hyper-Higgs, so we just have to pump energy locally into the hyper-Higgs field to get it out of the ground state and relax its hold. The thing is, we ned a lot of energy. A serious amount.

We're talking mass-energy of a small planet here.

But you can't drag whole planets around, so let's just use a miniature black hole which you happen to carry around. In fact, use two. Merge them, extract the mass-energy (in the form of gravitational waves) and pump it into the hyper-Higgs. Make your trip, then pump the energy out of the hyper-Higgs and use that to re-create the original black hole pair. Um, you'll need a bit of handwavium to do that, thanks Renan.

In summary, except for system inefficiency, you can do it almost for free, provided you have a couple of black holes in your back pocket.

Antimatter, manipulated by magnetic fields, thus (as Tim B II notes), electricity.

Except instead of using antimatter to combine with matter and produce energy, we discover that antimatter in quantity produces anti-gravity, and beyond that we find new physics of antimatter. When iron atoms have their magnetic poles aligned they are all reinforced (not canceling each other) and create a useful magnetic field.

So once we have enough antimatter atoms of various elements, we discover something similar about one of them, a field that allows normal matter to "sink" into dark-space.

As Tumbislav notes, our space is continuous with and floats on darkspace. This approach can also explain the (IRL) dilemma of the missing antimatter in the universe; it is basically all in darkspace as antimatter. Like oil and water, they have separated, and although they can be mixed and were thoroughly mixed at creation, they naturally tend to separate into light-space and dark-space. As a result, the collective anti-gravity of anti-matter (anti-gravitons) in dark-space will repel photons, which is why it is dark.

Photons are their own anti-particle (maybe) but (hand-wavy) the anti-gravity keeps them out of dark-space, and if photons are emitted IN dark-space, they don't travel in a precisely straight line, they have a half-life: after a few light minutes they will "decay", vanishing from dark-space and emerging spontaneously in light-space. That's what the expanded quantum theory says, anyway, and to us in light space, this happens naturally so seldom we never observed it, or attributed it to experimental error or spontaneously formed photons from the quantum foam.

However, now that we can access dark-space and emit photons in it, we have verified that component of expanded quantum physics.

The matrix ripper field, like magnetism, can be controlled in power by physically manipulating the antimatter (say it is a specific element, like anti-Hassium). We can do that with strong magnetic fields. Just like we can use magnetic fields to levitate, spin, and move magnetic objects around. So I'd make this matrix-ripper field something we get by spinning anti-hassium at relativistic speeds (near light speed) using magnets (in a vacuum of course), and we can physically move spinning spheres of anti-hassium around to give shape to the matrix ripper field, and spin it faster or slower to control the depth in dark-space.

If our engines fail (they can be anti-matter engines too) then the anti-hassium sheds energy into the matrix ripper field, slows down, and the ship emerges from dark-space into light-space. Perhaps catastrophically if this is uncontrolled, into a planet, sun or black hole.

Hassium (HS, the normal version) is a silvery metal in the same column of the periodic table as Iron, Ruthenium and Osmium, all of which are metals with magnetic properties. Only about 100 atoms of Hassium have been formed in super colliders; and it has a half-life of about 10 seconds; but I'd hand-wave something that "stabilizes" it, or hand-wave a machine that produces a constant supply.

It will likely be centuries (to never) before we can perform actual chemistry on anti-matter and produce anti-atoms of anything but the lightest materials, so all of this is "can't prove me wrong" science.