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from the that-still-doesn't-mean-it-will-work dept.
After months of speculation and leaked documents, NASA's long-awaited EM Drive paper has finally been peer-reviewed and published [open, DOI: 10.2514/1.B36120] [DX]. And it shows that the 'impossible' propulsion system really does appear to work. The NASA Eagleworks Laboratory team even put forward a hypothesis for how the EM Drive could produce thrust – something that seems impossible according to our current understanding of the laws of physics.
In case you've missed the hype, the EM Drive, or Electromagnetic Drive, is a propulsion system first proposed by British inventor Roger Shawyer back in 1999. Instead of using heavy, inefficient rocket fuel, it bounces microwaves back and forth inside a cone-shaped metal cavity to generate thrust. According to Shawyer's calculations, the EM Drive could be so efficient that it could power us to Mars in just 70 days.
takyon: Some have previously dismissed EmDrive as a photon rocket. This is addressed in the paper along with other possible sources of error:
The eighth [error:] photon rocket force, RF leakage from test article generating a net force due to photon emission. The performance of a photon rocket is several orders of magnitude lower than the observed thrust. Further, as noted in the above discussion on RF interaction, all leaking fields are managed closely to result in a high quality RF resonance system. This is not a viable source of the observed thrust.
[...] The 1.2 mN/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 3.33–6.67 μN/kW (or 0.0033–0.0067 mN/kW) range.
Previously: NASA Validates "Impossible" Space Drive's Thrust
"Reactionless" Thruster Tested Again, This Time in a Vacuum
Explanation may be on the way for the "Impossible" EmDrive
Finnish Physicist Says EmDrive Device Does Have an Exhaust
EmDrive Peer-Reviewed Paper Coming in December; Theseus Planning a Cannae Thruster Cubesat
(Score: 2) by butthurt on Wednesday November 23 2016, @05:28PM
[...] photons by definition have no space-time existence [...]
I don't understand. There's evidence that they propagate through space. Are you saying that a resting photon can't exist?
To say the photon or field "has" or "carries" momentum is misleading, the action transfer occurs between the endpoints only.
I'm reading it as though you're suggesting that radiation pressure can only occur when there is something to absorb photos. For example, if a space traveller turns on a flashlight and points it at a nearby planet, the traveller's momentum will change, but if the traveller aims the flashlight into deep space, the traveller's momentum will be unaffected because there's no end point to receive the light. Am I misunderstanding?
(Score: 2) by dak664 on Wednesday November 23 2016, @06:12PM
Correct, the phase velocity of a massless particle is always C. The group velocity can be different through regions of varying potential.
Classically the fields do contain energy that propagates in 3 space, and your flashlight launches energy and momentum into the field whether or not it is ever absorbed by distant matter. If it *is* absorbed somewhere the event-separation of that light-like interaction is by definition zero and there can be no intervening events in the space-time manifold. If it is *not* absorbed then it seems there is nothing to enforce the quantized field. But relativistically there has to be some recipient for the action since the emission and absorption of the "photon" is the same event.
If the EM waves were propagating through some stationary ether, special relativity and quantum mechanics would probably both go away. Along with everything else, I suspect.