What kind of scientific effect is needed to have thrust less propulsion and levitation plausible and make floating and moving battleships/castles possible since anti-grav engines will disrupt local gravity and make things haywire.

Usable within earth-like atmosphere,

If you've watched Last Exile, you might know what kind of floating and thrust mechanism they were using since it is all reactionless drive from their flying fortress to capital ships.

I need a good explanation on how it would work.

All materials will be used can be found currently in earth, you can include radioactive materials as well... must not overly harmful to humans

Less technology more on physics/science theory is much more appreciated

I don't really care what technology it is but i need to know how will a thrustless propulsion and levitation work.

Please something that is theoretically possible with or w.o current technologies but plausible in physics.


"Capable of exerting mechanical force with no observable physical reaction(Propellers and Thrusters)"


Doesn't involve Gas filled ships!

Consider Steampunk level tech

My 1 idea for thrustless levitation is false gravity repulsion field, basically if gravity pulls you down, activating that technology should do opposite, instead it will counter the gravity and push you up in theory but then again theres no opposite "force" of gravity so i don't know if that is plausible with physics.

Theres negative mass for levitation as well, inducing negative mass to a matter.


closed as too broad by Xandar The Zenon, Hohmannfan, Frostfyre, Youstay Igo, fi12 Mar 19 '16 at 20:30

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  • $\begingroup$ using science and not wanting any thrust you're bound to make use of airship technology; if you don't want to use gas you could invent some phlebotium with negative mass :/ $\endgroup$ – dot_Sp0T Mar 19 '16 at 11:50
  • $\begingroup$ So negative mass can cause thrustless propulsion? $\endgroup$ – mico villena Mar 19 '16 at 11:53
  • $\begingroup$ Imagine it more like negative weight offsetting positive weight; e.g. you have a castle weighing some 2000 tons, now add something that weighs -2000 tons, you end up with 0 tons of weight $\endgroup$ – dot_Sp0T Mar 19 '16 at 11:54
  • $\begingroup$ Oh... so if i bring in -2010 tons mass to that castle what would happen? $\endgroup$ – mico villena Mar 19 '16 at 12:02
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    $\begingroup$ This is way too broad, you included magic and yet you did not include any specifics about that magic. Besides, we could make up any tech we want, like magnets which make your ship defy gravity, or materials that weigh less than nothing. $\endgroup$ – Xandar The Zenon Mar 19 '16 at 15:08

Reactionless is different from thrustless. You have used both terms and I think you are interchanging them when you shouldn't. Assuming what you really want is reactionless, then I can maybe give you a bit of an answer.

To keep it simple, thrust means movement because of Newton's third law (an action creates an equal and opposite reaction). Action: ejecting burned fuel out of your propeller. Reaction: the propeller moves in the opposite direction (aka thrust). If you are following Newton's laws, then making something levitate without thrust would require a lighter-than-air kind of thing. Then you're dealing with Archimedes instead of Newton which is another story.

Now that we're on the same page about thrust and reaction, what's the difference thrustless and reactionless? Thrustless means no thrust (something like no action and therefore no reaction). Reactionless means no reaction (i.e. action without reaction, or reaction without action from a certain point a view), which violates Newton's third law.

If I'm taking the same example as above, your propeller would move without ejecting burned fuel, which in Newtonian physics this is a big no-no. Yet... welp, things happened.

NASA reported a drive generated thrust in a way that is properly violating our laws of physics and should be impossible. Fair warning, as far as I know, the research hasn't been properly validated (or invalidated for that matter) yet and the jury is still trying to understand how and what happened really. It also generated thrust in the micronewton range, which is not a lot. An earlier Chinese experiment report several hundred millinewtons of thrust, though once again jury is still out.

The principle of the device however is fairly simple. Take a cavity, send microwaves in it, microwaves generate thrust by bouncing around. The details of how it works are A) above my understanding B) not clearly established as far as I know, so I'll direct you to wikipedia if you'd like to know more.

The bottom line is there might be such a thing as reactionless thrust after all. I have no idea if the principle is applicable in larger scale (i.e. to propel aircrafts or giant-floating cities), however with a little bit of magic or sci-fi it shouldn't be too much of an obstacle. The technology doesn't seem extremely advanced either, it pushes more our understanding of physics than it pushes our technical capabilities.

Assuming it works as advertised, your reactionless drive would appear as if floating in the air if fired in an upwards direction. But once again, there's still thrust even if it's reactionless. That would be the only way to make levitation plausible that I'm aware of.

  • $\begingroup$ Ah i see... Is there any answer for thrustless propulsion and levitation? $\endgroup$ – mico villena Mar 19 '16 at 17:28
  • $\begingroup$ As I said, if we are eliminating thrust then I can't think of anything other than making your structure lighter-than-air, either with gas balloons or with negative-mass-phlebotinium. However, I'll reiterate that the reactionless drive I mentioned should in fact be "exerting mechanical force" (here, thrust) "with no observable physical reaction" (here, no jet blast, no plummet of hot gas or anything). $\endgroup$ – AmiralPatate Mar 19 '16 at 17:36

No thrust, so that leaves out things like the EMDrive. Not wanting gas filled ships leaves out any sort of buoyancy based hovering. We're left with one choice, actual anti-gravity.

The problem with any sort of science-based anti-gravity device is to produce it we need negative mass to produce negative gravity. More precisely, we need to curve space-time in the opposite direction of gravity... we need an energy density lower than that of a vacuum. Fortunately for you, gravity is not well integrated into other physical theories (the famous lack of a theory of quantum gravity) leaving you some wiggle room.

Traditionally negative mass is impossible, but work on the Alcubierre Warp Drive has shown it might be possible and consistent with some theories. Again, it's not so much negative mass as an energy density lower than that of vacuum which produces a negative pressure, like in air. The Casimir effect is one candidate and various unconfirmed forms of exotic matter are another.

If you think of gravity as a curved slope heading down towards the Earth, negative mass would allow you to make a little ledge for your ship to sit on. This counteracts not just the ship's own attraction to the Earth, but the far larger Earth's attraction to the ship. This would require a lot of energy. Unfortunately that is beyond my abilities to exactly calculate, but we can get an idea by looking at the gravitational force. Take HMS Dreadnought at 18,000 tonnes (go big or go home). The gravitational force alone is 1.8 x 108 N which is about 14 Space Shuttle boosters.

So you're going to need a massive energy source to power your negative energy pressure field.

The other option is something something something DARK ENERGY!!!

Currently, Dark Energy is an unknown force which is accelerating the expansion of the universe. It does this by providing a negative energy pressure to all of space-time... our anti-gravity!

Since we don't know what Dark Energy is, the exotic matter mentioned above is one candidate, and because it's everywhere it's within the realm of sci-fi to propose somebody figured out how to harvest, store and manipulate it.

The good news is it's probably everywhere. The bad news is it's probably evenly spread out over the whole universe so there's not a lot of it anywhere. Current theory puts it at 7x10−30 g/cm3 equivalent mass-energy. That means in the whole volume of the Earth there's the equivalent of 7.5 mg of Dark Energy. To float a person we'd need 100 kg or about 15,000,000 times more. To float a battleship we need 18,000,000 kg.

In your story you'd need a plausible reason why there's suddenly a lot of dark energy available to a Victorian society.

Finally, I would be remiss not to mention the fictional Element Zero from the video game Mass Effect. This is a substance produced by a star going supernova. When you pass electricity through it, it produces Dark Energy which is manipulated into the titular "mass effect field" which can raise and lower the mass of objects.

Element Zero is used to explain all the apparently magical effects in this science-fantasy game. FTL travel, armor, weapons, levitation, and even psionic abilities are all explained in terms of raising or lowering an object's mass.

I would recommend playing the first Mass Effect to get ideas, and it's a very good game.

  • $\begingroup$ I don't see how even negative mass would help--as I mentioned in this post on physics stack exchange, negative mass does have a repulsive gravitational effect on other bodies, but it is itself attracted by the gravity of positive masses, so it would still fall downward in the Earth's gravitational field. $\endgroup$ – Hypnosifl Mar 19 '16 at 21:38
  • $\begingroup$ @Hypnosifl I hadn't thought about that, and I'm not sure what to think about it. Though that would appear to assume "negative mass" is a particle. I was very careful to make it clear we need a negative-energy pressure field, negative mass is just one of the ways to achieve this. $\endgroup$ – Schwern Mar 19 '16 at 22:04
  • $\begingroup$ I think the General Relativity derivation wouldn't really distinguish between particles and fields, since GR usually idealizes matter as distributed continuously rather than concentrated into particles anyway. Also, as I pointed out in that answer, anything that falls "up" in a gravitational field presumably wouldn't seem to fall "up" inside an accelerating box in deep space far from any significant gravity fields, and that means it would violate the equivalence principle which is a fundamental part of GR. $\endgroup$ – Hypnosifl Mar 19 '16 at 22:08
  • $\begingroup$ @Hypnosifl I think the elevator analogy doesn't apply here because it doesn't account for something inside the elevator itself significantly altering spacetime, the "anti-gravity" device. The mass of the person in the elevator, being insignificant compared to the mass of the Earth, is ignored. As a counter example, the Cavendish experiment could be done in the elevator. A better analogy would be an observer cannot distinguish between the "anti-gravity" device accelerating away from them vs being repelled away from the device. $\endgroup$ – Schwern Mar 19 '16 at 22:37
  • $\begingroup$ I suppose it depends on whether you're thinking of the device as one that's specifically moving the way it does because it's interacting with an external source of gravity, being repelled by it, or if you're just thinking of it as a sort of thrustless gravitational 'propulsion' system that could be pointed in any direction you want, just as easily making it accelerate towards the Earth at a greater rate than something in free fall as making it hover or accelerate away. The former shouldn't work in a zero-gravity elevator, the latter could. $\endgroup$ – Hypnosifl Mar 19 '16 at 22:41

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