Questions about Nasa's space drive answered
wired.co.uk
wired.co.uk
(1) News article! Prevailing view of physics overturned! Etc! Etc! Etc!
(2) Many excited comments!
(3) Much less excited comment, pointing to skeptical remarks by well-known professional physicists (e.g., John Baez, Sean Carroll).
(4) Much to-and-fro. People who once saw a Discovery Channel special on physics now appear to believe that they're in a better position to evaluate the new claims than the people from (3).
Now, points (1) and (2) do sometimes happen, without points (3) and (4).
For instance, the neutrino faster-than-light claims attracted very cautious comment from professionals. In other words, point (3) was absent or rather muted. That's because the people who'd done the experiments were known for being extremely careful, and were, in fact, very cautious in their announcement.
That kind of thing is genuinely exciting, and worth discussion.
Another nice example of an exception is the Alcubierre drive. It satisfied (1) and (2) (or the 1996 equivalent), but (3) was absent, except that professionals noted that the drive required the stress-energy tensor to have some unusual properties, not satisfied by any known substance. Indeed, Alcubierre pointed this out himself.
Again, genuinely exciting, and worth discussion.
But when the professionals are loudly deriding a result, it'd be nice for the amateurs to make a serious attempt to understand why, and not just airily dismiss it.
I'm interested to see what magnetic shielding was used and how well they characterized the magnetic field in the experimental volume. There was a mention of shielding against electromagnetic effects, but that could just mean a Faraday cage or Helmholtz coils, neither of which will reduce the B-field to zero.
Because the device is based upon microwaves in a conducting cavity, I would think that the first place to look for a theory of operation would be E&M, not quantum. The level of force involved is the kind that you can see when interacting with the Earth's magnetic field. Normally we ignore the force produced by the interaction of currents with the Earth's field, because they are so small. Was a mu-metal shield used, and if so, what was the remnant field? Was a stronger field induced to see if that increased the force? I hope that the experimenters try this if they have not already.
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 interesting (RF interaction with magnetostatic fields), but I don't think this has met the level of proof required of a claim of violation of momentum conservation.
God DAMN this is exciting.
As to the whole "we don't actually understand how it works" - we still can't make up our minds as to how wings work, so this isn't overly novel. Sure, we can explain the outcome, but whether it's Navier-Stokes or Bernoulli or something else, we can't make up our minds.
I suspect this will be similar for a long while - although puts physics hat on I think this is likely a relativistic temporal quantisation effect.
> ... we still can't make up our
> minds as to how wings work, ...
I've been convinced that the people who genuinely work with these things and study them properly, actually do know how wings work. You may not, I may not, the mythical "man on the street" may not, but there are people who really, really do.
Another example from Physics - quantum mechanics. We can describe the properties of a QM system, its outcomes based on inputs, the probabilities of states - yet we have not got the blindingest clue as to how it works. We have theories, but again, none are perfect - for instance see the Pilot Wave formulation of QM, which implies a deterministic universe, and isn't wrong, but isn't generally accepted - even though it describes QM systems well, for what little of it has been formulated in the last century.
Saying we can't decide how wings work is not at all in the same category as saying these guys don't know how Q works.
One "not knowing" is about not knowing exactly precisely how to model something perfectly because it has so much complexity.
The other not "not knowing" is about not having even a basic working theory that doesn't use mumbo jumbo and stands up to scrutiny.
Is the development of new programming languages evidence that we don't "understand" computers? In some very abstract sense, yes, but in a more practical sense - no.
Imagine if they permeate everything and are generally nonreactive, but still have pressure and viscosity (however small). Maybe the engine is working like an airfoil, displacing the gas locally and using entrainment to create a pressure imbalance with the surrounding virtual particles to cause a larger flow (like in the Bernoulli and Coanda effects). A broken analogy would be the lift to drag ratio of a wing. If it’s 10:1, then you can lift a 1000 pound glider by pushing on the tail with just 100 pounds of thrust.
Maybe a black body is on par with light pressure because the radiation is concentrated like in a rocket, but other geometries are able to interact more strongly with the quantum foam or whatever you want to call it, because they don’t radiate energy in one direction but instead excite the foam enough that it becomes opaque to radiation and can be interacted with (like what happens when an inert gas becomes a plasma). Say the thruster excited the foam so that it was moving faster on one side of the chamber than the other, then that would work like the top and bottom of a wing (where the air on the top side moves faster) and create a pressure differential. The chamber would move to the side with the highest velocity. This might sound far fetched but there’s some evidence that the wave particle duality can be simplified to particles traveling along waves:
https://www.youtube.com/watch?v=fnUBaBdl0Aw
Probably what we’re eventually going to find is that empty space is filled with these virtual particles, weighing much less than say electrons, and because of the uncertainty principle, they are spread over large volumes. So imagine the vertices being shed off of an airliner’s wing. Even though the wing is only a few feet wide, the vortices might be 100 feet wide, so maybe if you could put special glasses on, you’d see a big vortex being shed around the chamber, and if the foam weighs orders of magnitude less than air, the vortex could be really big. It’s probably even possible to tie the size of the vortex to the “lift to drag” ratio of the chamber. Now it doesn’t seem so far fetched that the engine could work when it’s pushing off such a large number of virtual particles.
By contrast, this "reactionless drive" posits both a completely unknown underlying physical mechanism and a major violation of physics-as-we-know-it (i.e. action without reaction).
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 it means" or "what's really happening", but that's not really physics in my book.
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.
Is argue that understanding the "basement" is very much physics - sure, it can err into the philosophical, but it's still definitely a "real" physical process which drives this.
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
"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, "Richard P. Feynman, Teacher," Physics Today, volume 42, number 2, February 1989, p. 70-75, at p. 75
[1] http://en.wikiquote.org/wiki/Talk:Richard_Feynman#Unsourced
[2] http://en.wikiquote.org/wiki/Talk:Richard_Feynman#Teaching_q...
I have frequently heard the quote without that section, that section seems flawed in that a layman would need to have all the underlying concepts explained to them also, indicating that application of the quote would not scale, as more underlying concepts were necessary to include.
Time to trot out my favorite quote about how airplanes fly, from Stick and Rudder by Wolfgang Langewiesche, page 9, published 1944:
»The main fact of all heavier-than-air flight is this: the wing keeps the airplane up by pushing the air down.
It shoves the air down with its bottom surface, and it pulls the air down with its top surface; the latter action is the more important. But the really important thing to understand is that the wing, in whatever fashion, makes the air go down. In exerting a downward force upon the air, the wing receives an upward counterforce--by the same principle, known as Newton's law of action and reaction, which makes a gun recoil as it shoves the bullet out forward; and which makes the nozzle of a fire hose press backward heavily against the fireman as it shoots out a stream of water forward. Air is heavy; sea-level air weights about 2 pounds per cubic yard; thus, as your wings give a downward push to a cubic yard after cubic yard of that heavy stuff, they get upward reactions that are equally hefty.
That's what keeps an airplane up. Newton's law says that, if the wing pushes the air down, the air must push the wing up. It also puts the same thing the other way 'round: if the wing is to hold the airplane up in the fluid, ever-yielding air, it can do so only by pushing the air down. All the fancy physics of Bernoulli's Theorem, all the highbrow math of the circulation theory, all the diagrams showing the airflow on a wing--all that is only an elaboration and more detailed description of just how Newton's law fulfills itself--for instance, the rather interesting but (for the pilot) really quite useless observation that the wing does most of its downwashing work by suction, with its top surface. ...
Thus, if you will forget some of this excessive erudition, a wing becomes much easier to understand; it is in the last analysis nothing but an air deflector. It is an inclined plane, cleverly curved, to be sure, and elaborately streamlined, but still essentially an inclined plane. That's, after all, why that whole fascinating contraption of ours is called an air-plane.«
So when schools teach this kind of BS, you can expect that the confusion will last a long time..
Edit: and of course it doesn't help at all that the silly and trivially disproven equal transit time theory continues to be the go-to explanation for how wings work for so many attempts to teach it.
Now consider a hovercraft. It sits on air. It does not push as much air downward as an airplane of equal weight would push. The amount of air it has to displace is probably proportional to the length of its perimeter (around the sides) multiplied by the height of the cushion of air it sits on multiplied by the air pressure underneath. Double the size of the hovercraft in both horizontal linear dimensions, and you've got double the perimeter, same air pressure (the machine's weight growing proportionally to area) and same cushion height, meaning you're holding four times the weight up with twice the air displacement.
Now consider a low-flying airplane. This is like an inefficient hovercraft, with the ground effect in play. Less air gets "pushed downward" than the same plane flying higher off the ground.
Consider a high-flying airplane. The ground effect is gone, but air's still got viscosity. Fly around the world forever and you'll notice that the amount of air beneath the plane is not actually increasing.
Hovering helicopters have to push more air downward than moving helicopters because they have to fight the stream of downward moving air that they've created for themselves.
If air had virtually no viscosity (suppose atoms were really tiny) then you'd have to fly by somehow forcing air to move downwards. If air had an extremely high amount of viscosity (relative to the mass and power of human-scale mechanical devices) then you wouldn't move it downwards at all -- planes would move around in the air like an amoeba or have a cylindrical conveyor belt surface. Our atmosphere is somewhere between these extremes.
Your final sentence is actually nonsense.
If you assume that time is quantisable (big assumption, I know), and that the planck time is lorenz invariant (not as much of an assumption), then an EM wave at a fixed frequency moving from one reference frame to another could experience quantisation due to the shifting time-base, resulting in an apparent net deceleration - resulting in a measurable acceleration of the system as a whole.
And now I'll take off my fringe hat and get back to the day job.
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.
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 I was wrong to say it moved from one reference frame to another, which is clearly bollocks - the EM undergoes an acceleration to relativistic mass, then a deceleration.
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.
What is it with Hacker News and anti-intellectualism?
http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
> There are many explanations for the generation of lift found in encyclopedias, in basic physics textbooks, and on Web sites. Unfortunately, many of the explanations are misleading and incorrect. Theories on the generation of lift have become a source of great controversy and a topic for heated arguments.
There are lots of bits of science where we have "useful lies" used to explain things to people, but when you get more in depth things get trickier.
Clifford Stoll uses the question "Why is the sky blue?" as an example. You keep asking "Why?" as a response and see how far someone goes. Most people will say "light scatters"; some might say "Rayleigh scattering".
Of course, there is a difference between "Science knows but the general population hasn't learnt it" and "science doesn't know" but for a surprising amount of stuff science doesn't know, yet.
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/...).
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 can describe in great depth anything we wish about our models for these things and experiments can reproduce our theories with exquisite precision.
But these models are merely complex rituals, we don't actually know, at a deep fundamental level, what happens.
The Feynman answer to magnetism, for example, is deeply unsatisfying because he describes all the rituals we've discovered with science about magnetism, but never really answers the question. His answer, in 7.5 minutes are "all the electronics spin in the same direction in iron and that produces a magnified magnetic field large enough we can feel". But why do spinning electrons produce a magnetic field at all? And why does that field work the way it does?
We have built beautiful mathematical tools to describe this force, down to elementary particles, but why it exists at all is a completely mystery.
But what is your point, really?
By "understand" in physics, we really mean that we can predict what will happen in a given experiment to any desired accuracy based on the established "laws of physics".
"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."
I think this does a deep disservice to how much we actually do know about how the universe works.
Feynman also addresses this, https://www.youtube.com/watch?v=05WS0WN7zMQ
The next Monday, when the fathers were all back at work, we kids were playing in a field. One kid says to me, “See that bird? What kind of bird is that?” I said, “I haven’t the slightest idea what kind of a bird it is.” He says, “It’s a brown-throated thrush. Your father doesn’t teach you anything!” But it was the opposite. He had already taught me: “See that bird?” he says. “It’s a Spencer’s warbler.” (I knew he didn’t know the real name.) “Well, in Italian, it’s a Chutto Lapittida. In Portuguese, it’s a Bom da Peida. In Chinese, it’s a Chung-long-tah, and in Japanese, it’s a Katano Tekeda. You can know the name of that bird in all the languages of the world, but when you’re finished, you’ll know absolutely nothing whatever about the bird. You’ll only know about humans in different places, and what they call the bird. So let’s look at the bird and see what it’s doing—that’s what counts.” (I learned very early the difference between knowing the name of something and knowing something.)
Models are just a complicated way of calling something, not a way of understanding it. Getting experimental results just means you've used the correct name, not that you understand anything in particular about it.
Calling a hot bright thing "fire" doesn't mean you understand it at all -- no matter how many complex tribal dances you do around an open flame. Knowing what fire actually is gave us modern civilization. For many fundamental everyday things like gravity or magnetism, on the scale from "calling an open flame 'fire'" to "rocket ship", we're charitably somewhere around "learning to cook meat".
No! It just means that we know vast amounts about the Universe, but we still have more to learn.
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.
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...
Feynman: "Magnets repel each other."
Interviewer: "What I want to know is what's going on ..."
Feynman: "Magnets repel each other."
Interviewer: "...between those two bits of metal."
Feynman: "Magnets repel each other."
Interviewer: "Well then, but what does that mean? Or why are they doing that? Or how are they doing it?"
Feynman: "Ah, [pause] uh you're asking ..."
Interviewer: "I must say that's a perfectly reasonable question to ask"
Feynman: "Of course! It's a perfectly reasonable question."
See also his quote about quantum mechanics - "There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe there ever was such a time. There might have been a time when only one man did, because he was the only guy who caught on, before he wrote his paper. But after people read the paper a lot of people understood the theory of relativity in some way or other, certainly more than twelve. On the other hand, I think I can safely say that nobody understands quantum mechanics."
https://en.wikiquote.org/wiki/Talk:Richard_Feynman#.22If_you...
There's also that nice graph of measurements of the speed of light versus time, in which experiments tended to reproduce the results of (erroneous) previous measurements, due to confirmation bias.
Reproducing an experiment, even with reputable scientists at NASA or reputable universities is in no way a guarantee.
When the magnitude of the observed effect scales roughly with the margin of error of the experiment, one has very good reason to be skeptical ...
this doesn't mean that it sounds too good to be true.
edit: fixed units - dont have easy access to micro, thanks for pointing that out.
You can spell it out, like "91 micronewtons".
You can also use exponential notation like 91e-6 N or 91x10^(-6) N.
To be fancy you can copy-and-paste unicode characters and write 91×10⁻⁶ N.
(I follow the subject by browsing news now and then at http://talk-polywell.org/ which really is about the small fusion projects. That place should have more details then at Wired.)
Use 'μ' for micro, 'm' is for milli.
https://plus.google.com/117663015413546257905/posts/WfFtJ8bY...
https://plus.google.com/117663015413546257905/posts/C7vx2G85...
Baez is right, of course. I've been checking the (Word-generated) "papers" from this guy's group at NASA, they're extremely shoddy: There's another report with their unstable calibration for the torsion pendulum which shows their complete lack of undergraduate lab report skills. And a poster from them where they say: "Q-thruster test articles are going to be tested in a vacuum to reduce possibility of air currents polluting the thrust signal during testing, but electrolytic capacitors in signal amplifier are not vacuum compatible"... Awesome.
I've also checked the Chinese Physics B paper. Their device is completely different from this one. It's an open cavity and they only use classical EM. I don't understand very well how their thrust measurement set-up works so I hold my judgement on their claims, but at least they're trying to be legit.
Violation of momentum is an extremely serious claim (in words of D.J. Griffiths, "there is no principle in Physics more sacred than that"). The Universe would look nothing like this if that were true and all the Physics that we've discovered consistent with thousands of experiments would be gone. The way they use the quantum vacuum has nothing to do with the formalism that made it possible. Several detailed QED calculations backed up by experiments to astounding precision would be completely wrong and we know that's not the case.
BTW, the fundamental principle is conservation of momentum, Newton's 3rd law of motion is a consequence that sometimes doesn't hold, for instance forces between charged particles in electrodynamics don't follow the 3rd law (but approximately at low speeds). If you take into account momentum carried by the fields you get conservation of momentum back, quite nicely as well.
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?
What subfield of physics have you worked in?
In my experience, this is not remotely true. Almost paper I read in grad school (e.g., on arXiv/quant-ph) was written in LaTeX. The exceptions written in Word were indeed quite likely to be the work of crackpots...
Experimental condensed matter physics (free molecular beams). Never met anyone in my research group, or any other research group that anyone in my group collaborated with, who recently (in the past five years) composed a paper in LaTeX. I'm sure my thesis advisor did so when he was in grad school back in the dark ages, but even he uses Word.
> (e.g., on arXiv/quant-ph)
Yes, well, that is where the crackpots tend to like to hang out, isn't it?
EDIT: Oh, you mean research groups that don't do math.
I think he's slipping from skepticism to cynicism here.
Hoax phenomenon and devices always seem to fail in precisely the way that this one has. As you more carefully examine the test setups, suspicious conditions of the experiment persist (like the lack of using a vacuum in the vacuum chamber), and observed phenomenon continue to diminish as the accuracy of the test equipment improves.
And I use the word "fail" knowing full well that they claimed that they had positive results. If they couldn't use best practices in performance of the experiment like evacuating the vacuum chamber and they couldn't even show that their null device that wasn't designed to produce the same effect didn't work, then they have some serious problems.
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?
The original description might be clumsy, but the idea of empty space being full of virtual particles is not wrong.
Here is Dr. Laurence Krauss's description of empty space:
especially the idea that what we think of empty space is really not empty, correct?
KRAUSS: That's exactly right. Empty space is a boiling, bubbling brew of virtual particles that pop in and out of existence in a time scale so short that you can't even measure them. Now, that sounds of course like counting angels on the head of a pin; if you can't measure them, then it doesn't sound like it's science, but in fact you can't measure them directly.
But we can measure their effects indirectly. These particles that are popping in and out of existence actually affect the properties of atoms and nuclei and actually are responsible for most of the mass inside your body. And in fact, really one of the things that motivated this book was the most profound discovery in recent times, and you even alluded to it in the last segment, the discovery that most of the energy of the universe actually resides in empty space.
The faster-than-light neutrino experiment gave a result, too, but in these cases the onus is massively on the people making the wild claims, and rightly so.
http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-v...
>>In the paper by White et al, they also write that the Cannae Drive “is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma.” That last bit stopped me. What’s a quantum vacuum virtual plasma? I’d never heard the term, so I dropped a note to Sean Carroll, a Caltech physicist whose work dives deeply into speculative realms of cosmology and quantum theory.
Carroll wrote back immediately, with a pointed message: “There is no such thing as a ‘quantum vacuum virtual plasma,’ so that should be a tip-off right there. There is a quantum vacuum, but it is nothing like a plasma. In particular, it does not have a rest frame, so there is nothing to push against, so you can’t use it for propulsion. The whole thing is just nonsense. They claim to measure an incredibly tiny effect that could very easily be just noise.” There is no theory to support the result, and there is no verified result to begin with.<<
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.
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.
Are they just referring to how superconductors can float in an external magnetic field? That doesn't seem to give general purpose hover boards.
A superconducting version of the drive would be able to provide much higher Q, and thus much higher static thrust to power ratio.
It would also have much better performance at higher waveguide velocities.
I'm unqualified to comment on anything in this article, but this is really cool, and I didn't know Wired produced science journalism (or a highly technical Q/A) like this.
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.
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.
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.
Two magnetic objects can resist each other, but that is well understood already. And still, those reach equilibrium between gravity (from the levitator) and the strong force (from the support structure). From the way I understand superconductive magnetic levitation, the magnetic field collapses the superconductivity in the places they intersect. That would mean that over time, electrical resistance would drain the [mostly] superconductive material.
Right now, all examples of superconductive levitation involve supercooled superconductors, which means that any examples require massive amounts of energy to sustain.
This hoverboard idea would be like taking the magnetic base away and expecting the levitator to remain where it is with no extra energy supplied.
We've gone from "we can turn energy into motive force through unknown methods" to "we can prime this thing with energy once and have it exert force forever." If that were true, you could dump 1kw into the thing, rotate it 90 degrees and attach it to a rotor. Now you've got this thing that constantly pushes your rotor around and you've got free energy forever. See how I might think we're in crazy town now?
If we had this plus a reduction of cost-to-orbit by a couple orders of magnitude, say getting prices down to $10 per kilo? Space travel would actually become a thing -- something available to most people. And we could lower cost-to-orbit in a lot of proven ways, like using mass drivers for non-human orbital insertions.
This is firmly in the "too good to be true" category right now, but hell, I'm a believer. Even if we're wrong, even if there's some experimentation error, science still wins. People are being energized, lots of imaginative scenarios about space travel are playing out across the net, and so on.
This is a very good thing.
"9. Why isn't there a simple explanation of how it's supposed to work without violating the laws of physics?"
"If the new drive results continue to be replicated, then theory may have to catch up."
Reminds me of the quote: "In theory, there is no difference between theory and practice. But in practice, there is."
More interesting question: can I make one at home? I can do magnetic levitation, both pushing and pulling with high-frequency electromagnets; it would be cool if I could do this as well and having floating objects in my home 8-)
The reported thrust of the device is in the tens of micronewtons. Assuming it weighs 1 kg, you would need approximately a million times more thrust for the device to levitate (i.e. counteract its own weight) at the surface of the earth.
"EmDrive, produced 91 micronewtons of thrust for 17 watts of power"
http://www.wolframalpha.com/input/?i=91+micronewtons+*+1+yea...
428 miles per hour, after a year.
Am I doing the math wrong?
However this test rig apparently doesn't adhere to the same strict experimental setup used by NASA.
They think it works, but we don't know how. More tests will tell whether or not we have finally discovered the technology required to drive around easily in the solar system and propel skateboarding into the realm of Back to the Future.
Finally, the whole point of science is to discover things. Not make magic :|
What would make this phenomenon interesting if it actually works is not merely that it requires no reaction mass, but that it's much more powerful than a photon drive. If it turns out to just be a photon drive, then the magnitude of the effect has been greatly overstated, and this is a really complicated way to achieve the same effect as pointing a laser out the back of your spaceship.
Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. With this definition using a red LED Laser powered by a 1.5V battery in the back of the spacecraft is a "no reaction mass" thruster. The problem is that the momentum / energy ratio has theoretical limitations, and they are getting too much momentum.
Long version (based on a previous comment https://news.ycombinator.com/item?id=7162069):
I’ll try to explain what I had understood trying to find an explanations that don’t break the physics laws.
To move the spaceship you need momentum. You must use some particles to carry the opposite momentum away. It’s not clear, but the main candidates are photons (aka light). (The other possibility is gravitons, but that would be even more amazing)
The photons have no rest mass, but they have energy. So to produce them, you must "spend" some energy. The energy source can be carried in the ship (a nuclear reactor) or absorbed in place (solar panel).
If you are using a nuclear reactor, a small par of the mass of the atoms is transformed into energy and you put that energy in the photons. So the net effect is that some of the mass of the spaceship goes away, and it's no long a "no reaction mass" ship. (The same idea is valid to electric batteries, but the mass difference comes from the chemical bounds and not from the nucleus.)
If you use a solar panel, then when you absorb the photons the spaceship gains a little of mass. Unless you have a mechanism to dissipate the mass the spaceship would get heavier. Luckily, the photons that you are using for propulsion carry a little of mass (and the heat you are dissipating also helps). So this is essentially a solar sail, you get some photons, and send them in a different direction, and the change in the direction of the photons give some momentum to your ship. Perhaps a complex setup (solar panel + led) can be more directional that a simple setup (mirror). Perhaps you can gain a x3 or x6 efficiency. (But someone has to do the calculations, because this might break the second law, unless you get a laser light and also dissipate some heat without a specific direction, and the net result as good as a mirror.)
In the previous comment, throwaway_yy2Di noted that with photons "the ratio a photon's momentum to energy is fixed at 1/c, which is 3.3E-6 N/kW". The problem of photons is that to get some moment you need a proportional amount of energy to create them. Another possibility is to create particle-antiparticle pairs and accelerate them, but this is even more inefficient that using photon and you get less than 3.3E-6 N/kW.
The alternative solution is to accelerate other particles (for example the hydrogen atoms in the rocket fuel), you don't need energy to create them, because they are already there. So you can get more than 1/c=3.3E-6 N/kW, but it's not a "no reaction mass" ship.
They claim 40 microNewton/28W = 1.4E-3 N/kW ~= 400000/c. This is in the like 400000 times the theoretical limit, so they have a measurement problem (or they'll get a Nobel price).
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 compliant. My car exerts force against the earth (slowing it slightly), the sailboat takes energy from the wind.
To be third-law compliant, this alleged "reactionless" drive would need to apply force against something. But ejecting matter or energy to gain moment in the opposite direction is only one way to do that.
The biggest red flag about this is that there's no physical explanation. It's true that an explanation would imply some new physics. But it wouldn't be breaking the existing physical laws of motion, it would just be discovering some new thing to apply force against (virtual particles, or dark matter/energy, or whatever).
In the middle of the space, where there is only vacuum around, you can't use the "virtual particle that get absorbed almost immediately" trick. So you need to emit some real particles (like a photon).
To explain this experiment, you can't push against the virtual particles, because they collapse and create some real particle (like a photon) to carry the momentum away and then you get the momentum/energy upper bound. (It's more complicated, particles appear and disappear, but the net effect is the same.)
Most of the "explanations" use virtual particles, but as an alternative explanation it's possible that this is pushing "dark matter". Perhaps this is a neutrino fan. (I'm not sure if neutrinos are technically dark matter, but they are "dark" enough and very abundant). It catches some neutrinos from the sun, change their direction a little, and then the neutrinos exit the chamber unnoticed. The change in the neutrinos direction gives the momentum to the thruster. I think that this doesn't break any theoretical law in an obvious way. The problem is that the dark mater is "dark" because it's very difficult to measure and to interact in any way. It's very difficult to change the direction of neutrinos, but at least it's an engineers' problem, not a physicists' problem. (In particular, neutrinos can travel through the earth.) The easier explanation is a measurement error.
I'm just pointing out that there are a number of logically possible solutions that don't involve violating the conservation of momentum, which may or may not be physically possible.
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 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.
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.
The idea that the designs they tested (and EmDrive) would be reactionless is exactly why everybody is so baffled and excited by this. If they are, they must have some way to maintain those basic laws, through a process we don't know about yet. Aside from the practical uses, it could lead to a whole new physics to study.
When you say "reactionless" you mean that the device doesn't emit anything and it breaks the momentum conservation law? The previous experiments tried to give some theoretical explanations, but usually they were equivalent to emitting photons or gravitons. The conservation of momentum is a very fundamental law. It's possible to change the physics laws, but you need to have very good experimental evidence. (Hey! I believe in the Higgs boson!) This is like the faster than light neutrinos. It's very exiting if it were true, but the easier explanation is an experimental error.
"Although several people are drawing that comparison, they're really not in the same class. OPERA did an extremely thorough analysis of the faster than light neutrino result before they published. In the end it turned out to be a very subtle experimental error that cause the problems.
In contrast, this is just junk science from start to finish. The initial claim was likely an outright lie to lure investors."
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 device - how did they not turn it on? For lack of a suitable capacitor? That's a nothing part for such a massive potential breakthrough.
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.
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.
I was just comparing that there was also a lot of excitement.
According to the experiments, the drive seems reactionless so far. It's possible that it does emit something that we can not measure, it's also possible that it transfers momentum to something else, or that it works on something else entirely. We simply don't know yet. There is potential here, if there does turn out to be experimental evidence for it being truly reactionless, for that to require an addition to physics. Even if the evidence turns up something else, it'll at least be interesting.
I agree that there are a lot of ifs, ors and buts. That's why everybody is calling for independent confirmation. Just like the neutrino case, that's how science is supposed to work. But any potential for expanding our understanding should be given proper attention and enthusiasm.
I understand this thread was about the theory, but from an engineering perspective that's a substantial distinction.
The problem here is where are they getting the thrust from and what mechanism is causing virtual particles to become real? And where in the energy for that coming from? Because you're paying not just KE but also the rest energy cost to make them real with Hawking radiation.
> If you are using a nuclear reactor, a small par of the mass of the atoms is transformed into energy and you put that energy in the photons
This applies equally to nuclear reactors and to AA batteries (like you mention earlier). All forms of energy have mass.
(Photons can carry differing amounts of energy, and therefore momentum. This is exhibited as differing wavelengths. Specifically, light being emitted from a moving object is blue/redshifted depending on the relative motion of the observer.)
Attach the thruster to a wheel.
When the thruster is firing, it consumes constant power and the wheel accelerates, spinning ever faster.
The wheel can be attached to a generator that produces power which is thrust times the rim velocity.
Thus, after a certain speed, the wheel produces more power than the thruster consumes.
This was discussed on a rocketry list.
Power of the wheel = thrust * rim velocity. That's just basic physics you should learn in high school.
P_1 = F * v
The claimed thruster produces a constant thrust for a certain power, let's use a factor k for that:
P_2 = k * F
F * v = k * F
v = k
We can also have some friction, let's say the wheel generator is 50% efficient. We then need to run the wheel twice as fast to get the same effect.
There actually exists a trivial "reactionless" thruster if we use a flashlight and the light pressure. But it turns out the velocity is the speed of light then.
In special relativity, momentum and energy are much related, so if you break the conservation of one of them, you break also the conservation of the other. (It's not very clear if the authors say that this device break the momentum conservation, all the information is very confusing.)
But the example is nice. Just get two of these devices and put them in the opposite sides of a carrousel or a spinning space station so you don't have to worry about friction.
1. If this works, forget spacecraft. Free energy for everyone! 2. I think it's a measurement error.
There are other reasons to think so as well, a person said that the "out there" advanced space propulsion research community traditionally gives a lot more leeway than some other research disciplines where this might have come up.
The part I don't understand is why you think this "Wheel Generator" would impart any significant thrust to the wheel.
That is, let's say (for the sake of argument), that you needed 1 watt to generate 1 newton of thrust. And, that one newton of thrust could get a wheel spinning at 10 m/s. Now, we hook that wheel up to a generator, and it's capable of generating 1/10th of a watt of energy, but in doing so, obviously comes to a halt without external energy being imparted (because obviously the generator uses up its momentum to generate energy) - but, the energy being created by the spinning wheel (1/10th of a watt), only can get the wheel spinning at 1 m/s.
The entire system comes to a halt quickly.
I'm not suggesting that the entire idea of a reactionless thruster doesn't have huge holes in it - but it certainly doesn't seem to (at least) suggest that you have a perpetual motion machine.
Most of the limitations describing solid state materials come from that we can't solve the Schrodinger-equation directly (even with simulation). So we have to make assumptions and reasonable approximations of the resulting wave functions of electrons. For many solid state materials there are standard approximations that are working really well but they are not working for all materials.
We simply didn't find any working approximation for high-temperature superconductors (but I think there are some not well tested theories out there).
How big is a two megawatt nuclear power source anyway? A quick search showed nuclear power plants are in the hundreds to low thousands of megawatt range, and RTGs are in the tens to hundreds of watt range. I have no idea what something that lies between those two would be.
Toshiba 4S gives 10 MW.
"a 50 MW version [will be] available in the future"
For an example, when I worked on the Hubble, a thermal short was discovered that would severely limit the life of one of the cameras, which have to be very cold to operate. In order to counteract that, a pretty complex cooling system was built to counteract the effect. It consisted of a couple of large metal boxes (a couple hundred pounds each, if I recall) attached to a couple of huge radiator panels. (About 3'x10' each, if memory serves). The whole thing took over a year to build and took a lot of care to launch and install.
And extremely hot (100C + in near-earth orbit) in the sun, and -273 in the shade - with nothing to conduct heat away - meaning that you can only emit heat as EM radiation (photons).
Cooling is always a problem in space.
One example is the small nuclear reactors that have been used in orbit already: http://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor
It sound too good to be true. My bet is on experimental error.
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.
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 results by now that addressed every single problem.
It mostly reminds me of the E-Cat in that there are people who want it to be true so badly that they cherry pick the results and statements that they want to believe while disregarding contraindications.
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.
When they had a chance to look critically at their own experiments in their report, they spent effort and text hyping theoretical applications or something like that. They deserve some "go back and do it right this time, junior" criticism.
I'd rather they not waste our tax dollars on this kind of nonsense.
When a person "invents" something that is obvious bullshit, and uses that as a means to milk money out of investors or consumers, that is fraudulent. Over the past 30 years a style of communication has been developed that uses sarcasm and outright mockery to attack these people. James Randi practically invented this style of communication, or at least greatly popularized it, and now it has been adopted by a number of science bloggers.
Why, though? Because fraudsters are good at attracting attention, so to counter it, critics have to generate controversy. And there's no better way to generate controversy than to make things personal. In other words, it's done with a purpose.
But over time that communications strategy has been warped by people who don't understand it. They think the idea is to personally attack and mock ANYONE who reports a surprising result. We saw it with the FTL neutrino results, we saw it with BICEP2, we see it all the time.
It's a major problem. For one thing it trains non-scientists to auto-reject any scientific result that seems weird to them. For another thing it gives greater license to people who are not critiqueing science in good faith (like, say, Rush Limbaugh or Ken Cuccinelli) to attack scientists personally. It reduces its utility as a means of countering fraud, because people come to think that that is just how science communication is done. And it makes it harder to obtain sufficient funding to investigate areas of science that are not as well-known to the public.
What's happening here is not attempted fraud. A team at NASA [1] that is specifically employed and funded to test out crazy ideas, tested out a crazy idea, and published their results. That's it.
So, critique their methods and results? Yes. Critique the press coverage? Absolutely. Attack and mock the researchers? NO. Doing so is a fundamental mistake in communications strategy.
And some of the critiques are even self-contradictory. For example you suggest that they should go back and do it right, but you also don't want them to spend tax dollars on it. Well, the quality of an investigation is directly affected by its level of funding. The NASA crazy ideas lab is minimally funded, so of course not every detail can be worked out. The researchers explicitly state this in their paper.
[1] And yes, they are employees of NASA...saying "this is barely 'NASA'" is a nonsensical statement.
Which is not a criticism. Not all science fiction has to be hard. But none of the technology is a product of scientists sitting down and thinking about how the technology of the future might work. It's a product of writers thinking about what technology would make for good stories, and any explanation you come up with (e.g. impulse drives are reaction drives with warp fields that let them have an exhaust velocity higher than the speed of light) is a retrofit made up to appease fans and sell more books.
The paper is $25 .... mmm http://arc.aiaa.org/doi/abs/10.2514/6.2014-4029
This post has some more info https://plus.google.com/117663015413546257905/posts/WfFtJ8bY...
OK, so, there's microwaves producing forces on either end of the cavity, and one end is bigger and…
wouldn't the forces be proportional to the area normal to either direction? i.e. one end may be smaller, it may even be a point (making the cavity a cone), but microwaves bounce off of the tapered neck of the cavity too.
But you're right that there are no actual dimensions in it.
Space Scientists Don't Want Obama To Know These 10 Secrets About Warp Drive