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The first problem with that article is that it says it uses 'free energy', and that the inventors can't explain how it works.
No, it doesn't. I couldn't find mention of free energy anywhere in the article. It does mention that it violates conservation of momentum however, and that's a valid criticism.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Wolfram wrote ...
.
No, it doesn't. I couldn't find mention of free energy anywhere in the article. It does mention that it violates conservation of momentum however, and that's a valid criticism.
In the first paragraph it says "seemingly violating one of the most fundamental laws of physics,"
The second says " Newton’s third law, since you’re having an action (thrust) without a corresponding reaction, and the law of conservation of momentum. The claimants propose no viable mechanism, but merely contend that all of science is experimental, so if the experiment gives you this thrust, then it’s our understanding of physics that needs revision,"
Further on it says "we’ve broken the old laws of physics,"
Surely all these points refer to the 'apparent' claims of free energy?
No-one claims the EM drive uses 'free energy' except those who try to discredit it. It just harvests some of the existing EM radiation in the environment.
The first problem with that article is that it says it uses 'free energy', and that the inventors can't explain how it works.
This is not the case, it uses the background EM radiation in space to power it. It just isn't very efficient, but it will just keep accelerating forever without consuming fuel, assuming the measurements are correct.
What is to be resolved? Claims that the thrust violates the conservation of momentum, that you don't have to throw momentum overboard backwards to get a force forwards.
Why do people want to do this? Because at the moment, all space drives employ a tank of matter, and throw it out of the back somehow. Unfortunately any tank is finite, so the total change in momentum possible is finite. As it happens, there is already an alternative to carrying a tank of matter, and that's creating photons from energy and throwing those out of the back. Although they are massless, they carry momentum (don't ask me how, they just do). If you get the energy from solar panels, then you can generate thrust until the sun blows up. It works, but unfortunately it's very, very, inefficient.
What the proponents of the EM drive want to do is create more thrust than by throwing photons out the back. By having a cavity with a high Q, you can multiply the change in momentum (read radiation pressure) by the Q. Now, all you have to do is persuade your financial backers that the integrated internal pressure *doesn't* add up to zero, by shaping the cavity so that it looks like it shouldn't.
I liked the tone of that article (but then I would, wouldn't I?) The default position should be that any experiment showing differences from well accepted theory should be of good quality. Non peer-reviewed results of the order of experimental error do not count as good quality. I agree.
I saw the original Shawyer publications, and the key theory he rested on was the difference in area of the two ends of the truncated cone cavity (it's not a waveguide, it's a cavity, as nothing comes out). The problem with that is that the sloping walls also needed to be included in the integration for the total thrust, and he didn't. The thrust direction on a sloping wall due to radiation pressure is normal to the surface. He is a plot of magnetic field intensity for an example cone dimension and frequency.
While there is more hotspot area on the big end than the small, looking for all the world like 'of course the big end gets more reaction pressure than the small end', do you see all the stuff on the walls? When you do the surface integral normal to all the walls, then the net vector thrust for all surfaces sums to zero, if you believe Maxwell's equations, also relativity invariant like the momentum laws.
So it comes down to - if you believe either Maxwell or momentum, then the EM drive doesn't work. So if you want to overturn both these pillars of science, you need very good experimental results, reproduced in several different places in the world, by different teams, significantly different from the null hypothesis.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Ash Small wrote ...
Wolfram wrote ...
.
No, it doesn't. I couldn't find mention of free energy anywhere in the article. It does mention that it violates conservation of momentum however, and that's a valid criticism.
In the first paragraph it says "seemingly violating one of the most fundamental laws of physics,"
The second says " Newton’s third law, since you’re having an action (thrust) without a corresponding reaction, and the law of conservation of momentum. The claimants propose no viable mechanism, but merely contend that all of science is experimental, so if the experiment gives you this thrust, then it’s our understanding of physics that needs revision,"
Further on it says "we’ve broken the old laws of physics,"
Surely all these points refer to the 'apparent' claims of free energy?
No, all of them refer to the fact that it claims to break Newton's third law, conservation of momentum. Conservation of energy hasn't been mentioned until you brought it up just now.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
From Wikipedia: "Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body."
So it absorbs EM radiation, just like the metal in your induction furnace, heats up, and emits 'black body radiation', which is comprised of photons.
The only 'claim' made is that the 'waveguide' shape guides some of this EM radiation in one particular direction
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Ash Small wrote ...
From Wikipedia: "Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body."
So it absorbs EM radiation, just like the metal in your induction furnace, heats up, and emits 'black body radiation', which is comprised of photons.
The only 'claim' made is that the 'waveguide' shape guides some of this EM radiation in one particular direction
Where is the 'alleged' 'new physics'?
They are unable to make up a good explanation of how it works but the general idea is that the radiation bounces back and forth inside the cavity and shomehow bounces "more" against one end than the other. For each bounce you get additional force so giving a lot more fource than just radiating the same amount of energy conventionally at one end.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Bjørn wrote ...
.They are unable to make up a good explanation of how it works but the general idea is that the radiation bounces back and forth inside the cavity and shomehow bounces "more" against one end than the other. For each bounce you get additional force so giving a lot more fource than just radiating the same amount of energy conventionally at one end.
Yep, something like that. That's what waveguides do, pretty much. That 'bouncing against the ends' could possibly explain the results seen in atmospheric conditions, but does it not radiate photons in the form of black body radiation as well? Is it not this that's supposedly responsible for the 'results' obtained by NASA in a vacuum?
I agree there is some doubt as to the accuracy of the results, but the same results were obtained in several different orientations.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
Ash Small wrote ...
Bjørn wrote ...
.They are unable to make up a good explanation of how it works but the general idea is that the radiation bounces back and forth inside the cavity and shomehow bounces "more" against one end than the other. For each bounce you get additional force so giving a lot more fource than just radiating the same amount of energy conventionally at one end.
Yep, something like that. That's what waveguides do, pretty much. That 'bouncing against the ends' could possibly explain the results seen in atmospheric conditions, but does it not radiate photons in the form of black body radiation as well? Is it not this that's supposedly responsible for the 'results' obtained by NASA in a vacuum?
That is the 'new physics'. The force is too large to come from conventionally emitted radiation and the old physics is not able to explain how that is possible.
This is why Dr. Slack says "need very good experimental results, reproduced in several different places in the world, by different teams, significantly different from the null hypothesis."
So far we have seen very inconsistent and weak results that seems to support a flawed understanding of physics based on miscalculations. This sounds very much like a typical case of "you find what you look for if you look hard enough".
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Ash Small wrote ...
But there is some force from photons even under the 'old physics'.
There is a force from photons, but in any closed container that doesn't expel anything, this force cancels out.
The basic premise of this thing is that it produses thrust without expelling any mass, and that's where it violates Newton's third law. That's the extraordinary claim, now we're just waiting for the extraordinary evidence. Everything they've produced so far ticks several of the typical pseudoscience boxes.
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emDrive &NASA
