Comments on: The Theoretical Dream Of The EmDrive

By: Brian Koberlein

Brian Koberlein — Sat, 26 Aug 2017 14:25:10 +0000

There’s a difference between phase velocity and bulk velocity when it comes to waves. Phase velocity is an apparent motion due to syncopated disturbances. Bulk velocity is the actual motion of the wave. Photons move at the bulk velocity, which is always the speed of light, even in a cavity. Shawyer’s argument confuses the two, which is part of the problem. Put simply, the argument is that if you can violate the laws of physics (assume a varying speed of light in a vacuum) then you can explain a device that violates the laws of physics. That isn’t an explanation, it’s special pleading. The fact that advocates keep making these weird theory arguments is not doing them any favors. It makes it look like they don’t understand basic physics.

By: Victor Zubkov

Victor Zubkov — Sat, 26 Aug 2017 13:32:32 +0000

Simple and understandable explanation of the Emdrive engine work principle (if it works).
I think that explanation EMdrive engine work (if it works) principle ( Roger Shawyer Explaining The Basic Science behind #EmDrive, https://www.youtube.com/watch?v=wBtk6xWDrwY ) can be considerably simplified and made more understandable.
It is well known that
1. According to second postulate for the special relativity theory the speed of light (and other electromagnetic waves or microwaves) in vacuum is the same for all observers ( https://en.wikipedia.org/wiki/Theory_of_relativity ). Observers should not be accelerated.
2. The speed of the electromagnetic waves or microwave in the waveguide depends on cross-section or diameter of the waveguide likewise the speed of the light in the glass depends on the refractive index of the glass.
3. Light and other electromagnetic waves or microwaves can carry energy, have some virtual mass as energy equivalent, can carry some momentum and create some pressure.
4. Power and energy of the light and other electromagnetic waves are defined by their frequency. Light and electromagnetic waves do not change considerably their frequency during reflection from relatively massive reflecting body, save their energy and cannot give energy to the massive reflecting body during reflection. Thus microwave reflection cannot create real force for acceleration of the massive reflecting body during reflection. Obviously microwaves cannot decelerate relatively massive reflecting body during reflection as even massive reflecting body cannot considerably change frequency of the electromagnetic waves during reflecting.

Work of the Emdrive engine in a great measure is based on the independence of the microwaves velocities of the cavity velocity ( Roger Shawyer Explaining The Basic Science behind #EmDrive, https://www.youtube.com/watch?v=wBtk6xWDrwY , pic. “Independence of velocities” at the time moment 3.13 of the video, approximately ). These microwaves travel and are gained within the cavity. Independence of the microwaves velocities of the cavity velocity is very similar to the second postulate for special relativity theory. The microwaves velocities can depend on the cavity diameter but should not depend on the cavity velocity. It is always true. Independence of the microwaves velocities on the cavity velocity means that microwaves can push the cavity in principle in spite of that microwaves travel within the cavity, but cavity should be designed properly for it. I think it can be imagined for simplicity that microwaves in the cavity are entirely independent and move on themselves like they move in the open space, but velocity of the microwave that travels from the wide side (butt) of the cavity to its narrow side (butt) decreases, and velocity of the microwave that travels from narrow side (butt) of the cavity to its wide side (butt) increases ( Roger Shawyer Explaining The Basic Science behind #EmDrive, https://www.youtube.com/watch?v=wBtk6xWDrwY , pic. “Tapered cavity” at the time moment 5.45 of the video, approximately. ) Then microwave that travels from wide side (butt) of the cavity to its narrow side (butt) loses momentum and should give lost part of the momentum to the cavity. Cavity should get this part of the momentum and should be accelerated in the direction from its wide side (butt) to narrow side (butt). Microwave that travels from narrow side (butt) of the cavity to its wide side (butt) get momentum for account of the cavity momentum and the cavity should be additionally accelerated in the direction from its wide side to narrow side. Cavity gets total momentum that is twice each microwave momentum change due to microwaves velocities changing. As mentioned above microwaves save their frequency, power and energy during reflection from the ends (butts) of the cavity, real force due to such reflections cannot be created because microwaves cannot give energy to the cavity, cavity cannot give energy to the microwaves.
Thus cavity can be accelerated due to microwave velocity changing during propagation within the cavity.

By: Ken vogt

Ken vogt — Fri, 25 Nov 2016 12:42:19 +0000

how could such device take us to the stars if it reqites solar panels?

By: genialityofevil

genialityofevil — Thu, 28 Apr 2016 11:37:27 +0000

Well, I’m not saying it’s pushing air around (or using radiation as a propellant, that was just an alternate example). I’m just saying that we can’t account for what it might be while there are external factors.

By: XCman

XCman — Thu, 28 Apr 2016 01:09:17 +0000

I agree. If none of these tests have been done in a Vacuum. It’s pointless. As far as I’m concerned the propellant is air and the microwaves are pushing air around.

By: Aldaer

Aldaer — Wed, 27 Apr 2016 20:17:50 +0000

A device using radiation (own, not external) as a propellant is called a photon rocket (a staple of SciFi of the 50s). That’s not what the EM drive claims to be.

By: Emmet Ford

Emmet Ford — Wed, 27 Apr 2016 17:26:54 +0000

The answer to this conundrum is to scale the device up such that the force produced is a blunt fact that cannot be dismissed. Do that, and theoretical physicists will start expending intellectual capital to address it. Do that, and engineers will stick an EMdrive on a satellite and employ it to delta the V.

Yet here we are 15 years into this thing, and no one has scaled it up to the point where the effect is unambiguously real. One is tempted to infer from this that they don’t know how to scale it up, that bench top attempts to double or quadruple the effect have so far failed, and lacking a theory that passes the sniff test, they don’t know how to proceed.

Is that where this thing is at? Does anyone know? Yeah, someone knows. Probably all the people on those separate teams of experimenters knows. But we are not reading about that in any of the coverage. Instead, we get “it’s controversial.” “Newton’s Third Law!” “Here’s a new paper that no one believes.” Well, all that is true, I guess. And it must be a good too, because no news is good news, right?

By: genialityofevil

genialityofevil — Wed, 27 Apr 2016 16:20:38 +0000

Doesn’t it depend on what you consider a propellant? I mean, solar sails (not to mention Kepler) use radiation pressure to achieve thrust. The real problem with the EmDrive is that it claims able to “amplify” microwave resonance without any corresponding directional reaction. It’s like trying to sweat in space. The only thing I can think of is if highly resonant microwaves produce some heretofore unknown decay of… something.
The only way to test it effectively would be in a true vacuum (i.e. space).

By: Brian Koberlein

Brian Koberlein — Wed, 27 Apr 2016 15:57:09 +0000

It’s closed, but it does need to be powered. The controversial aspect of this device is that it doesn’t have a propellent. No plasma or photons or hot gas racing out the back end to give it thrust.

By: Quine Atal

Quine Atal — Wed, 27 Apr 2016 15:51:45 +0000

Something I don’t see in the description of the device. Is the “business end” closed or open? If closed I get the mystery.