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Questions about Nasa's space drive answered

wired.co.uk

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Re: Questions about Nasa's space drive answered

#161

Post by chton »

XorNot wrote: post #159
smellf wrote: post #149

Earlier quoted context omitted.

But there's three independent labs working on this concept, plus NASA. _Who_ is lying, the EmDrive folks? And if they are, then how are NASA, the Chinese and the other lab all replicating their results?

By not testing it in a vacuum, which would eliminate most of the immediate problems with thrust being produced by outgassing from heated wires (10kW is more power then your stove top) or coronal discharge. I don't know what's going on with whoever is doing this at NASA, but the joke of testing IN A VACUUM CHAMBER while not actually pumping it down is ridiculous. These people are scientists who have access to the devi…

This was not a huge experiment for NASA, most likely the budget wasn't there for vacuum-capable capacitors and the time to convert the equipment. It was either go with what they had, or don't go at all. I do hope that, with a tentatively positive result, they can now get a bit more budget to perform the test again with an improved setup.

Re: Questions about Nasa's space drive answered

#162

Post by [deleted] »

XorNot wrote: post #159
smellf wrote: post #149

Earlier quoted context omitted.

But there's three independent labs working on this concept, plus NASA. _Who_ is lying, the EmDrive folks? And if they are, then how are NASA, the Chinese and the other lab all replicating their results?

By not testing it in a vacuum, which would eliminate most of the immediate problems with thrust being produced by outgassing from heated wires (10kW is more power then your stove top) or coronal discharge. I don't know what's going on with whoever is doing this at NASA, but the joke of testing IN A VACUUM CHAMBER while not actually pumping it down is ridiculous. These people are scientists who have access to the devi…

[deleted]

Re: Questions about Nasa's space drive answered

#163

Post by gone35 »

bane wrote: post #116
tobinfricke wrote: post #45

Earlier quoted context omitted.

By "we", I mean humanity as a whole. Nobody would contest that there are a lot of widespread misconceptions about how an airplane - or, for that matter, anything - works. A nice blog post on the topic is Sean Carroll's article, "The Laws Underlying The Physics of Everyday Life Are Completely Understood" ( http://blogs.discovermagazine.com/cosmicvariance/2010/09/23/... ).

One of the problems with this idea, that we have the physics "perfectly understood", is that even that statement isn't accurate. What we actually have are unbelievably precise models for how things work and people who understand those models at extremely deep levels. But even something we experience literally every moment of every day, like gravity or magnets, we haven't the foggiest idea of how it actually works. We…

One of the problems with your argument is, as usual in these kinds of discussions, enthymematic: much lies in your particular notions of "explanation" and "understanding", which to you seem to self-evidently involve far from than their usual lexical sense --eg to many, Feynman's explanation of magnetism, with its remarkable succinctness, granularity and predictive power, is quite sound and satisfying!

So I would suggest you to begin by explicitly defining [1] what your particular notion of "understanding" is, so that you can then clarify what exactly is it that you find unsatisfying about modern physical law.

[1] http://www.philosophypages.com/lg/e05.htm

Re: Questions about Nasa's space drive answered

#164

Post by marcosdumay »

madaxe_again wrote: post #158
marcosdumay wrote: post #133

Earlier quoted context omitted.

Well, the relativity principle states that things don't "move from one frame of reference to the other". You choose a frame, and observe things on that frame; changing the frame of reference is your choice, and must not alter the results in any way. Accepting a flaw in conservation of momentum is already hard enough without you (and the original paper) imposing a flaw on the relativity principle to explain it.

Ah, the old "it's Einstein so it must be right" gambit. People used to say that about Newton - until experiment proved that he didn't have the full picture. It's highly improbable that relativity is any different. Yes, it gives demonstrably correct answers, but that doesn't mean that it holds in all cases. I mean, why would we be even talking about LQG if we thought relativity gave the full picture? You're right that…

You are proposing an experiment that shows that momentum does not always conserve. That's great, it's hard to accept the results (extraordinary evidence and everything), but if they hold, it's great.

Now, you do a huge amount of handwaving to try to explain the results, and in your handwaving you break another basic, unrelated principle. This time, no, I just won't accept your conclusions, you have no reason to break two principles when your experiments support only one.

By the way, the relativity priciple was first stated by Galileo, not Einstein.

Re: Questions about Nasa's space drive answered

#165

Post by darkmighty »

gus_massa wrote: post #121
lukev wrote: post #93

Earlier quoted context omitted.

> Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. I presume you're referring to the third law of motion, but if so, you've mischaracterized it. Nothing in the laws of motion state that engines must "emit" something. My car drives along quite efficiently without relying on any emission of mass. So does a sailboat. Of course, these are still third-law complia…

Actually, the conservation of momentum is local, so the car must emit some particles. The bottom of the tires emits (virtual) photons that are absorbed by the road. When you see it globally, the tires just push the road. (You can't go to the local mechanical shop and talk about virtual photons.) In the middle of the space, where there is only vacuum around, you can't use the "virtual particle that get absorbed almost…

I believe that the dp=dE/c requirement for thrust isn't valid with static fields: simply consider an electromagnet a large distance D away from a permanent magnet. For a very small energy cost (POf course, in free space magnetic field decays as 1/D^3, so eventually you will be better off spending F * c power to generate a force F. I do not disagree with "The device must emit something" though, since obviously momentum has to be carried by some particle, although I'm not a physicist to attest the specifics precisely.

* - I believe in this case the energy cost is so low because you're "storing" energy in the field, energy you're spending acts more like a trigger. As a thought experiment consider a stream of photons carrying a large amount of power P through a cross section. Now suppose your "device" is a mirror aligned parallel to the stream. Now for an arbitrarily small energy cost, you can align the mirror to the stream and cause the photons to produce a force P/c, "triggering" the system to relocate energy.

Re: Questions about Nasa's space drive answered

#166

Post by [deleted] »

ep103 wrote: post #72
Mandelbug wrote: post #18

Earlier quoted context omitted.

What? Of course the apparent affect matters. If the underlying physical principles can be understood, there is a possibility of increasing its efficiency for larger throughput. And if the underlying process isn't understood, there is no way to rule out something that isn't actually producing thrust or some other fluke. Finally, the whole point of science is to discover things. Not make magic :|

I think what he means is even if it turned out to just be thermal energy, then that means this device has the capability of directing thermal energy as a viable proportion source, so its still pretty great : )

[deleted]

Re: Questions about Nasa's space drive answered

#167

Post by FiatLuxDave »

MiguelHudnandez wrote: post #150
JulianMorrison wrote: post #102

A superconducting version of the EmDrive, would, in principle, generate thousands of times more thrust. And because it does not require energy just to hold things up (just as a chair does not require power to keep you off the ground), in theory you could have a hoverboard which does not require energy to float in the air. If they have just solved flying cars and hoverboards, I think we can officially declare this to…

> And because it does not require energy just to hold things up (just as a chair does not require power to keep you off the ground), in theory you could have a hoverboard which does not require energy to float in the air. An item where you could dump electricity into it once, cut power, and have it resist gravity -- forever, and for free! -- is absolute horse shit.

>An item where you could dump electricity into it once, cut power, and have it resist gravity -- forever, and for free! -- is absolute horse shit.

Um, you are completely wrong. There is a difference between force and energy. It is certainly possible to expend a small amount of energy to create a force which lasts in perpetuity. Energy = Force x Distance, and if there is no displacement in distance, then no energy is spent by the exertion of a force.

Not to say that making hoverboards and flying cars is an easy engineering proposition, but that is due to the parameters of the problem, not due to any intrinsic issue with the physics of providing a force against gravity. If people weighed a nanogram, or the Earth's magnetic field were 1 Tesla, or the electrostatic potential between the stratosphere and the Earth was 100,000 times stronger... any one of these and we'd have had hoverboards a long time ago. But that's just numbers. There is no problem with spending a finite amount of energy to create a perpetual force.

Re: Questions about Nasa's space drive answered

#168

Post by chopin »

MiguelHudnandez wrote: post #150
JulianMorrison wrote: post #102

A superconducting version of the EmDrive, would, in principle, generate thousands of times more thrust. And because it does not require energy just to hold things up (just as a chair does not require power to keep you off the ground), in theory you could have a hoverboard which does not require energy to float in the air. If they have just solved flying cars and hoverboards, I think we can officially declare this to…

> And because it does not require energy just to hold things up (just as a chair does not require power to keep you off the ground), in theory you could have a hoverboard which does not require energy to float in the air. An item where you could dump electricity into it once, cut power, and have it resist gravity -- forever, and for free! -- is absolute horse shit.

Any superconductor levitating on a magnet does exactly this. Afaik there is no law in physics we know of which forbids this.

To put it even further: every stone lying on the ground does exactly this. It doesn't change its position relative to the gavitational field. And without expending any energy for that (or increasing the systems entropy ot hold its position). And this comes ultimately down to electromagnetic forces (between valence electrons) holding it at its position. So, no horse shit here.

Re: Questions about Nasa's space drive answered

#169

Post by pavlov »

XorNot wrote: post #159
smellf wrote: post #149

Earlier quoted context omitted.

But there's three independent labs working on this concept, plus NASA. _Who_ is lying, the EmDrive folks? And if they are, then how are NASA, the Chinese and the other lab all replicating their results?

By not testing it in a vacuum, which would eliminate most of the immediate problems with thrust being produced by outgassing from heated wires (10kW is more power then your stove top) or coronal discharge. I don't know what's going on with whoever is doing this at NASA, but the joke of testing IN A VACUUM CHAMBER while not actually pumping it down is ridiculous. These people are scientists who have access to the devi…

The OP (Wired article) says that the vacuum chamber was indeed pumped down:

While the original abstract says that tests were run "within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure", the full report describes tests in which turbo vacuum pumps were used to evacuate the test chamber to a pressure of five millionths of a Torr, or about a hundred-millionth of normal atmospheric pressure.

Re: Questions about Nasa's space drive answered

#170

Post by [deleted] »

forgotketchup wrote: post #160
mnl wrote: post #120

Earlier quoted context omitted.

I'd never understand how intelligent and educated people lose it completely when it comes to Physics. They've been exposed to some PopSci tales not meant to be accurate at all and then feel entitled to be right when they figure out some nonsensical consequences by themselves -no proper maths involved ever-. It's depressing. Baez is right, of course. I've been checking the (Word-generated) "papers" from this guy's gro…

> I've been checking the (Word-generated) "papers" from this guy's group at NASA, they're extremely shoddy. Not defending this particular paper, but I'm curious why you highlighted the fact that it's written in Word. Just about everybody in physics these days uses Word to compose papers (Word + Mendeley is a dream, by the way). Maybe you think he's not a 'real man' because he doesn't sling raw LaTeX?

[deleted]
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