In my last few questions, I found out that space is, in fact, hard. Making a realistic sci-fi spaceship that does the things I want it to do (throwing around multi-ton kinetic projectiles at dozens of kilometers per second, having hundreds of kilometers of delta-v and several gees of acceleration on a ship that won't melt from the waste heat) stretches the bounds of what might be considered 'realistic'. Mass Effect justifies the things that it wants to do by allowing for one fantastical element (literally, Element Zero) that enables incredible technologies by bypassing the typical laws of physics. So I figured that I could do something similar.

Enter, the Aether. It turns out that space is, in fact, filled by a normally invisible, intangible substance that doesn't typically interact with the rest of the universe or itself, even gravitationally. However, technology has been developed that enables normal matter and energy to briefly interact with it. You can take advantage of this by creating engines that push against Aether in order to generate thrust, in the same way that jet or propeller engines on Earth push against air. Additionally, waste heat can be disposed of more efficiently than radiators would allow by venting it into the Aether. This neatly bypasses the cruel bonds of both the rocket equation and waste heat on spaceship design. BUT...

What would the implications of this be on other facets of spaceship design, and human civilization in general? Is this concept of Aether simply too far into the fantastical to be found in hard-ish science fiction? How can the idea be fleshed out and improved?

EDIT: If you can find a way to use the existence of Aether to create a perpetual-motion machine, the idea of the Aether is an automatic fail.

  • $\begingroup$ Either you based your proposal on this and this will give other people some background info or you'll find this interesting. The idea of some spacefilling Aether is nothing new and the article gives a very basic overview of its history. Many of these proposals are meant as additions to normal physics and should thus not interfere with them in any universe breaking way. $\endgroup$ Sep 7, 2019 at 2:53
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    $\begingroup$ This explains why so many of our spaceships keep getting lost and crashing upon on the Planet of The Apes. $\endgroup$
    – user535733
    Sep 7, 2019 at 2:59
  • $\begingroup$ That magical RF resonant cavity thruster from NASA. Have a look at that. $\endgroup$ Sep 7, 2019 at 2:59
  • $\begingroup$ @Renan That got disproved fairly recently, if I'm not mistaken. Nice to fantasize about, but if it worked it would have opened an enormous can of worms for physics as we understand it. $\endgroup$ Sep 7, 2019 at 3:04
  • $\begingroup$ (1) Jet engines do not push against air. Hint: reaction engines work in space. (2) If your Aether can be used as a heat sink then it immediately becomes possible to build a perpetual motion machine of the second kind... Just saying. $\endgroup$
    – AlexP
    Sep 7, 2019 at 7:52

1 Answer 1


The idea sounds faintly troubling, in that the aether has become some magical place where you can just send unwanted energy and everything will be ok, but so long as it doesn't allow FTL or form a privileged reference frame then you might just about be ok, from the point of view of not annihilating physics as we know it.

(also, make sure you have a read of Project Rho's entry on reactionless drives, because this does apply to you here even if they seem reactionless, because the knock-on effects will be similar. Note Burnside's Advice: Friends Don't Let Friends Use Reactionless Drives In Their Universes.)

Big problem number one, then, is not so much "physics goes foom", but "no planet in your universe is ever safe ever again", because you're allowing super-efficient high-thrust low-power propulsion and enhanced heat sinking, and that means that anyone with access to aether drive technology can make stealth relativistic kinetic kill vehicles on a whim and hit anything with enough energy to totally smoosh it, and you might not even be able to see the projectil being accelerated in the first place so it will be a total surprise (unlike laser-driven or antimatter-driven projectiles, which are deeply unsubtle for years ahead of time). You might have to handwave maximum velocities, but they'll have to be fast enough for convenient space travel which implies that kinetic weapons with tens or hundred of km/s muzzle velocity could be commonplace and straightfoward. That's hazardous.

Big problem number two: is the aether "at rest"? If so, what it is "rest" relative to? If the aether is at "rest" relative to the sun, what will happen as the sun progresses in its orbit? We're moving at about 230km/s around the centre of the galaxy. If the aether rotates with the galaxy, that might be ok, but if it doesn't gravitationally interact, there's a problem there (like how that even happened in the first place). What happens in half a galactic year's time? Will turning on an aether drive suddenly fire you out of the solar system at 460km/s? If you're not willing to wait that long, what about if you fly to Barnard's Star, will activating your drive give you a big 90km/s boost? If the aether is at rest relative to something else, turning on your drive wil subject you to massive accelerations, suitable for interstellar travel but not interplanetary work so much. Also, it risks becoming a massive special frame of reference, and that has some Potentially Bad knock-on effects vis-a-vis relativity (alternatively, it might form the basis of a non-time-travelling FTL mechanism, depending on which way you wish to wave your hands). Given this, you might consider some other kind of reactionless drive that doesn't accidentally create a privileged reference frame, like an Alcubierre warp or perhaps something more like a tachyon rocket (with the latter perhaps being modified into a less physics-destructive aether drive, with a bit of thought? would certainly make a change from the usual warp drives people often have)

With that out of the way, here's something else to think about: with an aether drive, I'm imparting some momentum to whatever it is the aether is made up of. Presumably it has its own equivalent of mass, or you have other problems (like, what speed does an aetheric particle have after you've interacted with it?). These particles don't interact with each other or the rest of the universe, so they'll never shed any energy, and you probably won't get any equivalent of thermal blooming. These potentially high energy particles can only interact with other aether drives. Suddenly I can interact with stuff at a distance without all that tedious mucking about with gravity or electromagnetism!

On an object with significant mass of its own (like a moon or planet) I can create a drive beam that can impart momentum to any active aether drive it can hit. This can be used to accelerate objects away from the planet, decelerate incoming objects and, interestingly, repel anyone in range with an active aether drive. Ergo, you may need permission from local traffic control if you want to be able to fly in a straight line. It also means you might not be able to use aether drives to do terminal guidance of missiles or manoevering of space fighters (because point defense can push you away).

You could therefore also presumably use it to beam energy and information through any solid object (including neutron stars and the like) and provide remote power and communications. Point-to-point communications without line of sight or the need for satellites seems useful. I'm not quite sure how power generation would work, but you could presumably make something as dumb as an aetheric turbine (shoot an aether beam at one side of a wheel covered in aether drives) so I'm sure something much more sensible could be made. This potentially allows spacecraft to be remotely powered and propelled and have a limited heat signature. Maybe not enough to be a sort of submarine in space, but hey: they're your hands to wave.

Finally (for now) this is probably a better way of driving a starship than any other. Use an aether beam to push em, and a magnetic sail to brake em. All you need to worry about then is shielding, but you have the semi-realistic prospect of relativistic spaceflight ahead of you.

  • $\begingroup$ Hmmm. Good points with the relativistic drives and effects on other drives at range. Maybe I should have the aether interact with itself, though I was hesitant to do that because if it can react gravitationally, all that mass would probably create a black hole. What would an aether black hole look like? Anyway, if aether reacts more like an atmosphere, then I would expect it to induce drag on matter coming into contact with it, which may force a 'top speed' on ships using it. It may even have currents which effect which direction that top speed is in. $\endgroup$ Sep 7, 2019 at 17:24
  • $\begingroup$ @FlyingLemmingSoup I've just made an edit that might require a bit more of a complicated re-think, eg. is the aether in motion? if not, you have a relativity problem. If it is, your ability to use the drive is seriously constrained by the local motion of the aether. $\endgroup$ Sep 7, 2019 at 18:26
  • $\begingroup$ @FlyingLemmingSoup also, whilst I remember... there appears to be quite a lot of dark matter in the universe, but it doesn't appear to have all just clumped up into black holes despite being capable of gravitational interaction. You might want to look into that. $\endgroup$ Sep 7, 2019 at 19:11
  • $\begingroup$ I thought about that. The difference is that in order for Aether to do what I want it to do, it would have to outmass all other matter in the universe by a factor with a extremely long number of zeros after it. I can't imagine that much matter not creating black holes. Also, if it interacted with the rest of the universe gravitationally, that much matter should be trivial to detect... would it be possible for it to be effected by normal gravity without impacting it? If you think of gravity as point-masses pulling each other, no. If you think of gravity as bending space, maybe yes? $\endgroup$ Sep 7, 2019 at 19:26
  • $\begingroup$ @FlyingLemmingSoup honestly, I've no idea. You could try asking a separate question about that, but I don't know how useful the answers would be... and ultimately as the author, you can just simply wave your hands and declare it to be so, as a last resort. $\endgroup$ Sep 7, 2019 at 19:38

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