In the sci-fi comic Betelgeuse, the artist Leo presents a flying car with an unusual system for levitation and propulsion. The interesting point is that at the end of the comic, there is a page on which the "technical" behaviour of the system is described.

The principle is as follow:

  • A rotating axe in the center is powered by a motor, and is the main axis on which the vehicle is built
  • On this axe is linked a rope with a weight at its end, so the weight rotate around the central axe
  • A mechanism (not exactly explained) tracts the rope so that when the weight is at the bottom, it is the closest to the axe, and at the top of the axe, it is the farthest

The resulting forces of this move is that the centrifugal force is more important when the weight is at the top than when it is at the bottom, thus the resulting force is upward and the axe (and so the vehicle) is tracted upward.

Here is a picture:


Question: With minor modifications/ameliorations allowed if needed, and considering that enough electrical power is available (like a "super light and powerful battery") in order to rotate, is this system a viable one? I am especially not sure if the mechanism to put the weight close or far from the rotating axe is not creating a new force that nullifies the resulting upward force?

  • $\begingroup$ trying to imagine the device ... the device flings the weight upward and then pulls itself to it? ... that may work during the first cycle when the device is on the ground ... second cycle would force the device back to ground when the weight was flung upward $\endgroup$
    – jsotola
    Mar 29, 2023 at 23:03

2 Answers 2


This device is bogus. It cannot produce net thrust; it violates the law that forces come in pairs. It is strictly a science fiction device.

As a college freshman 53 years ago I tried to build a mechanical version of this without ropes and thereby invent a reactionless thruster. Then I learned sophomore level kinematics and dynamics of rotating machinery and realized that it was impossible, and furthermore, that the "thrust" I thought I had measured in my experiments was an instrumental artifact.

Variations on this general theme pop up every few years or so and show up in the popular press. For example, Dr. Eric Laithwaite, an electrical engineering professor in the UK, announced a machine identical to mine at about the same time and clung for decades to the false belief that it did indeed generate reactionless thrust.

  • $\begingroup$ Wasn't there something in the late 1950s called the 'Dean Drive' whose proposer managed to convince John W. Campbell, the editor of Astounding Science Fiction of its merit? I remember a cover of that magazine passed down by my uncle showing a Mars expedition consisting of a US Navy nuclear submarine adapted for space flight using the gizmo. $\endgroup$ Apr 4, 2023 at 12:47
  • $\begingroup$ Laithwaite also proposed that moths communicate electro-magnetically. In his proper field (heavy electrical engineering) he was very interesting, and strikingly like my own father, also an electrical engineer. $\endgroup$ Apr 4, 2023 at 12:54
  • $\begingroup$ @MichaelHarvey, yes indeed, and it is included in the wiki article on reactionless drives. And yes, Laithwaite was an interesting character, I corresponded with him in 1970-71 and tried to get him to form an international antigravity society! $\endgroup$ Apr 4, 2023 at 18:00
  • $\begingroup$ Someone should look through the papers of HG Wells and try to find the recipe for Cavorite. $\endgroup$ Apr 4, 2023 at 18:32

A system cannot act on itself to provide motion, levitation, or propulsion.

A complex object can be made to look like it moves by shifting its center of mass, but the center of mass will stay as is, and be affected by gravity just like a rock.

A system needs to push against something or eject mass from itself to move.

  • 1
    $\begingroup$ Interestingly, the last holdout mathematically, involving this device operating near a rotating black hole described by the Kerr metric, which seemed to indeed generate net thrust, has recently been debunked after about a century of trying. The key is that all materials have a non-zero elastic modulus. That effects density. That means the elastic modulus is subject to the laws of general relativity; and the minimum modulus is exactly that value that makes the machine not work! $\endgroup$
    – Phil Sweet
    Aug 27, 2023 at 12:27
  • $\begingroup$ "Objects between these two surfaces must co-rotate with the rotating black hole, as noted above; this feature can in principle be used to extract energy from a rotating black hole, up to its invariant mass energy, Mc2." Wiki hasn't caught up to this development, apparently. en.wikipedia.org/wiki/Kerr_metric $\endgroup$
    – Phil Sweet
    Aug 27, 2023 at 12:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.