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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

#171

Post by XorNot »

pavlov wrote: post #169
XorNot wrote: post #159

Earlier quoted context omitted.

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 atmospher…

Yeah just saw that part. The abstract doesn't mention it, which is super-weird, and neither did the original Wired article.

But if they found the effect persisted when pumped down then that puts this way further into "interesting" territory.

EDIT: Ok I've just been through the paper, but it's buried at the end - "Vacuum compatible RF amplifiers with power ranges of up to 125 watts will allow testing at vacuum conditions which was not possible using our current RF amplifiers due to the presence of electrolytic capacitors"

There is a big description of the test rig, and how it can be pumped down to vacuum during tests, but they do not explicitly say that they pumped down to vacuum before running tests on the thruster. And the vacuum is never mentioned again until the very end, where we get this one ambiguous sentence. They might be referring to a new optimized thruster they couldn't test, or they might be saying they couldn't test in vacuum at all - it's never made clear and it's pretty damn important.

Re: Questions about Nasa's space drive answered

#172

Post by snowwrestler »

happyscrappy wrote: post #94
Luc wrote: post #71

Earlier quoted context omitted.

I'd really like the source for that quote, because it's dumb for obvious reasons, and I don't know Feynman to be dumb. In fact he said pretty much the opposite to the interviewer asking about magnets in this well known video: https://www.youtube.com/watch?v=MO0r930Sn_8

Hmm. The closest I can find is this: "Once I asked him to explain to me, so that I can understand it, why spin-1/2 particles obey Fermi-Dirac statistics. Gauging his audience perfectly, he said, "I'll prepare a freshman lecture on it." But a few days later he came to me and said: "You know, I couldn't do it. I couldn't reduce it to the freshman level. That means we really don't understand it." David L. Goodstein, "Ri…

I think Feynman is drawing a distinction between being able to calculate an accurate prediction, and "understanding" things intuitively enough to describe with plain English.

Re: Questions about Nasa's space drive answered

#173

Post by bane »

gone35 wrote: post #163
bane wrote: post #116

Earlier quoted context omitted.

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 sug…

Okay, yeah sure. Good point. If you want to get down into those kinds of philosophical details, I'm not sure I'm prepared to do that. Right now, I'm kind of like the Supreme Court on pornography, I recognize understanding when I see it.

I think Feynman handles the question incorrectly. The question is about his understanding of magnetism, but he places the burden on the receiver of the explanation. If they don't understand the explanation then it doesn't matter. I do get his point in this and I'm not entirely saying it's wrong. But I think also that it's a deflection.

Lets assume a "presently omniscient" listener asking the question, somebody who may not have the knowledge before it is presented to them, but will understand the explanation perfectly as it's provided.

Suppose a Feynman or some other physicist has such a listener and they go on a deep dive into all the myriad and intricate details, the sum of all human knowledge on the matter -- this kind of listener would be able to follow along entirely with every last detail.

This listener would still not have an answer to the question "how do magnets work?" Because science doesn't actually know the answer to this. We have excellent descriptions of what magnets do, and what produces magnetism. We can predict to some nth decimal point of precision the outcome of just about any given experiment such that we don't really bother much with experimental physics about most of the day-to-day magnetism.

But why do those things produce magnetism at all?

The answers to this is basically "it just does". And that's as good as all our knowledge is. That's all we've arrived at. For all we know, every time an electron starts circling something, invisible universe fairies produce "magnetism" magic that does what we observe.

We don't know why magnetism does what it does, only that it does it.

But imagine if we actually understood it, at a fundamental level, if we "groked" magnetism and were the masters of it...

https://news.ycombinator.com/item?id=8148377

Re: Questions about Nasa's space drive answered

#174

Post by FD3SA »

lmm wrote: post #38
madaxe_again wrote: post #26

Earlier quoted context omitted.

No, I've a masters degree in Physics, and did several research projects on turbulent/laminar flow. We have a detailed understanding of a variety of theories which correctly represent the lift effect experienced on a body moving through a flow, yet none of them do it perfectly or completely. We can implement the technology well, but not without the aid of wind-tunnels and brute-force computer simulations in order to v…

It doesn't imply a deterministic universe any more than vanilla many-worlds. Sure, the pilot wave is deterministic. But when you actually measure the position of the particle? You get one of many possible results, with probability determined by the pilot wave. Big whoop. We understand QM perfectly well in the only meaningful sense - we can predict the results of any experiment. There's plenty of arguing about "what i…

Exactly. I am constantly astounded by professional scientists who try to find a deeper meaning in mathematical models whose only purpose is to predict experimental results. Human brains work on intuition, but when dealing with imperfect models such as Quantum Mechanicns (QM), there is no intuition to be had. If Quantum Mechanics or General Relativity were perfect, we wouldn't actively be looking for a unifying theory to resolve their mutual inconsistencies.

Once we have a theory of everything, then we can begin trying to form an accurate intuition underlying the model. Until then, there is no point trying to intuit probabilistic models which are designed to predict experimental results, and nothing else.

Re: Questions about Nasa's space drive answered

#175

Post by cousin_it »

readerrrr wrote: post #64
cousin_it wrote: post #55

Earlier quoted context omitted.

Baez is right, there's no such thing as "virtual plasma". Just Google the phrase.

You missed the point. Someone probably used a different phrase trying to describe a physical phenomena, which exists, under a different description. You can take a look at some popular lectures of Dr.Krauss where he describes empty space in more detail, which is full of virtual particles.

Imagine you're reading a paper about programming, and suddenly it mentions "refactoring the abstract megabyte". A non-programmer might insist that replacing "megabyte" with "class" makes the phrase kinda sorta meaningful, so the paper is totally legit. But I don't think you'd buy it.

When you're unfamiliar with some field, and insiders to that field tell you that misuse of technical terms is a strong red flag, you'd better believe them. Their words come from painful experience.

Re: Questions about Nasa's space drive answered

#176

Post by [deleted] »

readerrrr wrote: post #64
cousin_it wrote: post #55

Earlier quoted context omitted.

Baez is right, there's no such thing as "virtual plasma". Just Google the phrase.

You missed the point. Someone probably used a different phrase trying to describe a physical phenomena, which exists, under a different description. You can take a look at some popular lectures of Dr.Krauss where he describes empty space in more detail, which is full of virtual particles.

[deleted]

Re: Questions about Nasa's space drive answered

#177

Post by gus_massa »

darkmighty wrote: post #165
gus_massa wrote: post #121

Earlier quoted context omitted.

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 (P Of 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 moment…

> For a very small energy cost (P c), you can generate a magnetic field to propel yourself forward. The opposing magnet won't move for D/c seconds, so you're transporting momentum at a much lower cost.*

The mechanical moment, i.e. the moment of the object you can see (for example magnets, electrons, ...), is not conserved. The total moment is conserved, i.e. the moment of the objects and the moment of the fields, in this case the electromagnetic field. The electromagnetic field is quantized, and the particles are the photons. So in this case the photons travel from the electromagnet to the static magnet, and they carry away some moment and energy, so the moment is conserved locally.

It's important to consider the moment of the fields, because some of the photons don't go to the other magnet, but go to other directions and are never absorbed, the thecnical name is "radiation". If you don't consider it, then the system will lost some moment and some energy.

> 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.

This is a solar sail. The solar sail is a real device. But I think that this experiment is not trying to build a complicated version of a solar sail. To test a solar sail, you should put the device in a strong light. I suppose that the test chamber is in the dark.

Re: Questions about Nasa's space drive answered

#178

Post by snowwrestler »

tobinfricke wrote: post #41

Here are two nice posts by physicist John Baez with some reasons to be skeptical about the "reactionless drive": https://plus.google.com/117663015413546257905/posts/WfFtJ8bY... https://plus.google.com/117663015413546257905/posts/C7vx2G85...

I think it's great to express detailed skepticism about experiments like these, but I find the high levels of attitude to be tiresome. It doesn't add anything of substance to the skepticism, and it seems like an anti-pattern for good science. Scientists need to maintain some level of humbleness about their certainty. Not be credulous, but not be sarcastically smug either.

NASA is not universally populated with geniuses, but they're not high school idiots. I don't think they should be ridiculed for reporting a best-effort attempt to test surprising or controversial results. Otherwise how would surprising results ever be found?

Re: Questions about Nasa's space drive answered

#179

Post by XorNot »

FiatLuxDave wrote: post #136
danbruc wrote: post #92

Earlier quoted context omitted.

http://www.libertariannews.org/wp-content/uploads/2014/07/An...

Thank you! It's always best to read the actual paper. I note that not only is there no shielding to reduce the Earth's magnetic field, but there are large NeFeB magnets in the torsion balance assembly. I strongly suspect that the "missing momentum" is going into the object producing the magnetostatic fields which lie in the RF cavity, whether that be the Earth or the damping magnets. Not to say that this wouldn't be…

Or the more obvious conclusion, which is Wired don't know how to read a paper, and nowhere in the actual experimental section do they say they pumped down the apparatus when they were actually testing.

Re: Questions about Nasa's space drive answered

#180

Post by snowwrestler »

crusso wrote: post #147
tensor wrote: post #131

Earlier quoted context omitted.

Not at all. Unlike the e-cat, the design here is clear and it sounds like it's independently verified from the ground up with good experimental conditions. The e-cat had "secrets" that they wouldn't divulge and it's tests were also questionable with the machine being plugged into a power source the whole time.

"verified from the ground up with good experimental conditions" No it hasn't. That's the hype. Read the Baez commentary referenced elsewhere. Research all the other physics breaking phenomenon that had experimental confirmation but were still shown to be wrong. It's not like this effect was just noticed yesterday. You'd think that for an effect that Shaw created a company for in 2000, we'd have solid experimental res…

The emdrive is being tested by NASA staff, who did not invent it. That alone is a very significant difference from the ecat, which was only ever demonstrated by its creator.

Now NASA is still probably wrong, but if so, they are innocently wrong. They wouldn't gain anything by faking an effect.

If anything, they are getting heaping abuse for reporting anything at all. Which I think is a problem for science. People should not be abused for honestly trying to test surprising things, even if they turn out to be wrong.

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