Thrust from Nothing

Really. It’s the controversial Em Drive, and it’s NASA science and peer-reviewed and everything. Formally it’s called “Measurement of Impulsive Thrust in a Closed Radio Frequency Cavity in Vacuum” by Harold White, Paul March, James Lawrence, Jerry Vera, Andre Sylvester, Davis Brady and Paul Bailey.

As Engaget explains it,

An EM Drive produces thrust without fuel, instead using microwaves that bounce around a conical, enclosed device. According to the theory, the momentum of those bouncing microwaves is higher at the wide end of the engine, which means the whole system should experience thrust.

I don’t pretend to understand the pilot-wave theory that the authors of the new paper propose as an explanation, but I gather it challenges the Copenhagen consensus that has dominated physics for a long time — and makes quantum behavior a tiny bit less weird in some ways (double slit experiments would have an explanation I could understand) but at a price of making large pieces of the universe more likely to be connected in some odd way. Or something.

But this part I think I get:

Although this test campaign was not focused on optimizing performance and was more an exercise in existence proof, it is still useful to put the observed thrust-to-power figure of 1.2mN/kW in context. The current state-of–the-art thrust to power for a Hall thruster is on the order of 60mN/kW. This is an order of magnitude higher than the test article evaluated during the course of this vacuum campaign; however, for missions with very large delta-v requirements, having a propellant consumption rate of zero could offset the higher power requirements. The 1.2mN/kW performance parameter is over two orders of magnitude higher than other forms of “zero-propellant” propulsion, such as light sails, laser propulsion, and photon rockets having thrust-to-power levels in the 3.33–6.67μN/kW (or 0.0033–0.0067mN/kW) range.

Yes, “for missions with very large delta-v requirements, having a propellant consumption rate of zero could offset the higher power requirements”.

Space! As long as you are not in a hurry to boost up to speed to get there.

I wonder if the Em Drive works equally well at relativistic velocities? Does thrust taper off if you are going faster relative to the pilot wave? (Does that question even make sense?)

UPDATE: Well, of course, it’s the Internet, so there’s an emdrive FAQ. And it seems you do lose thrust as you go faster:

Q. Why does the thrust decrease as the spacecraft velocity along the thrust vector increases?
A. As the spacecraft accelerates along the thrust vector, energy is lost by the engine and gained as additional kinetic energy by the spacecraft. This energy can be defined as the thrust multiplied by the distance through which the thrust acts. For a given acceleration period, the higher the mean velocity, the longer the distance travelled, hence the higher the energy lost by the engine.
This loss of stored energy from the resonant cavity leads to a reduction in Q and hence a reduction of thrust.

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One Response to Thrust from Nothing

  1. Dan Riley says:

    At least they pumped down their vacuum chamber this time, but their attempts to exclude systematic experimental confounders are still full of qualitative hand-waving.

    On their use of pilot-wave theory, I have to wonder if that section received any meaningful peer review, as it looks pretty far out of scope for the journal. If they are proposing an experimentally distinguishable result, that’s a distinct theory, not a different interpretation. However, on a quick read, it looks more like numerological technobabble to me (their supporting paper ref. 19 is in one of the world’s worst predatory journals, not likely any peer review there).

    wrt the “Copenhagen consensus”, among researchers interested in quantum foundations I think many worlds is actually dominant, followed perhaps by various relational interpretations. Copenhagen glues a classical measurement model onto a quantum system, which is fine for the “shut up and calculate” school where it doesn’t really matter if the wave function collapsed or diagonalized in a preferred basis, but not suitable for foundational work IMO. Bohmian pilot-wave remains unpopular at least in part because it is very awkward to formulate a consistent relativistically invariant field theory.

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