Is the EmDrive, or “Relativity Drive” possible?

Question

In 2006, New Scientist magazine published an article titled Relativity drive: The end of wings and wheels¹ [1] about the EmDrive [Wikipedia] which stirred up a fair degree of controversy and some claims that New Scientist was engaging in pseudo-science.

Since the original article the inventor claims that a "Technology Transfer contract with a major US aerospace company was successfully completed", and that papers have been published by Professor Yang Juan of The North Western Polytechnical University, Xi'an, China. ²

Furthermore, it was reported in Wired magazine that the Chinese were going to attempt to build the device.

Assuming that the inventor is operating in good faith and that the device actually works, is there another explanation of the claimed resulting propulsion?

Notes:
1. Direct links to the article may not work as it seems to have been archived.
2. The abstracts provided on the EmDrive website claim that they are Chinese language journals which makes them very difficult to chase down and verify.

Answer 1

It is impossible to generate momentum in a closed object without emitting something, so the drive is either not generating thrust, or throwing something backwards. There is no doubt about this.

Assuming that the thrust measurement is accurate, that something could be radiation. This explanation is exceedingly unlikely, since to get mN of radiation pressure you need an enormous amount of energy, since in 1s you get 1 gm/s of momentum, which in radiation can only be carried by 3*10^5 J (multiply by c), so you need 30,000 Watts of energy to push with mN force, or at least a million Watts for 80mN. So it's not radiation.

But a leaky microwave cavity can heat the water-vapor in the air around the object, and the heat can lead to a current of air away from the object. With a air current, you can produce mN thrusts from a relatively small amount of energy, and with a barely noticible breeze. To get mN force, you need to accelerate 300 cm^3 of air (1 gram) to 1 m/s every second, or to get 80mN, accelerate 1 m^3 of air (3000 g) to .2 m/s (barely perceptible) and this can be done with a hot-cold thermal gradient behind the device which is hard to notice. If the thrust measurements are not in error, this is the certain cause.

So at best, Shawyer has invented a very inefficient and expensive fan.

Answer 2

Shawyer's "analysis" is a mess, incoherent and deeply confused about fundamental aspects of relativity: he mixes up frames, assumes a universal rest frame, etc. The EmDrive supposedly works best when "stationary relative to the thrust", whatever that means, and Shawyer goes on to suggest using it for levitating vehicles with some kind of conventional propulsion for driving them forward: he apparently believes there is something special about gravitational acceleration.

According to his latest paper, the EmDrive supposedly acts as an electric motor, consuming energy when accelerating and producing it when decelerating. However, a deceleration is just an acceleration in a particular direction, so if it worked, the EmDrive could operate as an infinite energy machine just sitting on one end in a gravity field or while producing thrust for a spacecraft.

So to answer the question in the title: "No." As for other explanations of the observed propulsion, there aren't many details of the measurement procedures or results. There are videos of an EmDrive test on a rotating platform, but there's numerous pieces of equipment that may contain fans, thick power cables going to the equipment that may apply torques, and even a laptop with a hard drive that may be spinning up or down. (And on top of everything else, the whole thing's apparently rotating in the wrong direction.) If this rig is typical of his testing methodology, it's probably safe to chalk up the rest to bad measurements.

Answer 3

Well, the Wiki link you supplied also links to a paper:

Why Shawyer’s ‘electromagnetic relativity drive’ is a fraud

Dr. John P. Costella BE(ELEC)(HONS) BSC(HONS) PHD(RELATIVISTIC ELECTRODYNAMICS) GRADDIPED

Note the PhD in relativistic electrodynamics compared to Shawer's C.Eng MIEE.

Answer 4

In special relativity, 4 momentum is exactly conserved. The first component of 4 momentum is total mass/energy, but the next 3 are given by:

p = m*γ(v)*v

m is the invariant mass, how much inertia it has when you are moving at the same velocity of it.

This is Newton except now momentum is a non-linear function of velocity. Nonlinearity does not change anything. Mass and momentum still are constant (ignoring leaks), making γ(v)*v, and thus the center-of-mass velocity v, constant.

So how could we measure force? Possibly currents in the waveguide walls induce currents in the metal support structure which creates small magnetic forces between them.