What we know about the EmDrive and Cannae Drive
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During the "Cold Fusion" era, when Pons & Fleishman had claimed to develop room temperature fusion, I worked for a major US lab doing superconductor research. (We invented the first superconductors that operated at liquid nitrogen temperatures-- Y1B2C3O)
While fusion isn't our area of investigation we, being physicists, were curious. We managed to get our hands on a pre-print of the Pons & Fleishman study and did our own experiments.
We kept this very hush hush. We didn't want it getting out that we were doing the experiments or people would claim that we replicated them.
So, I believe that SpaceX and other companies are experimenting with this, and if they found good results (as the eagle works tests imply they would) they would continue to do so, but in secret.)
We eventually published our paper because we constructed a novel experiment that disproved the P&F observation, from our perspective.
None-the-less, true to our fears, this was later reported by "Mondo 2000" (The "arse technica" crossed with WIRED of the day) that we had "confirmed cold fusion is real!!1!1". The letter to the editor I wrote and got our most eminent physicist to sign was never printed by the magazine (IIRC).
When you get to the fringes-- that's where the action is-- but it's also where you can have confusing or odd results.
And even 30 years ago the media was not trustworthy enough to reveal these results to. Our paper was published in a journal, and yet the media still mis represented the results.
I don't have access to the Mondo 2000 stuff today, but if any of that was to believed we'd have AI masterminded rockets to moon condos and eternal life by now. The big advances were actually missed as things like interchangable and standardized protocols, power saving SoCs, incremental battery improvements, touchscreens, and fast networks are "boring" compared to spacetravel and robots and such.
I feel I'm also seeing the same hype train today with VR, which has unsolved major issues like motion sickness and questionable applications in gaming, let alone anywhere else. To a lesser extent I see the same thing with electric cars that are always somehow 2-3 years from affordability and economic and range parity with ICE cars. These 2-3 years keep blowing past us, but there's no 200 mile range $20,000 car yet, if there will ever be.
Its a shame that practical and real advances are often "boring" to the typical sci-fi obsessed INTJ males who dominate science on the internet. I see so much spilled ink about SpaceX and very little about the upcoming SLS and its planned pioneering manned missions or NASA's robotic and science missions, which are all mindblowingly amazing to me. Sadly, this has all become politicized in the most asinine way possible with a dedicated libertarian group on the web voicing this private vs public rivalry to attack NASA, which is ironic as SpaceX is more or less a welfare program of NASA and the US taxpayers.
I hope this fad doesn't last long and good science, real breakthroughs, and the largely unpredictable and usually unsexy, in terms of whiz bang space operas, future continues to unfold before us in a wonderful way. The SLS will have us on an asteroid with just boring old chemical rockets, while the futurists continue to sell snake oil to the low information true believers and diminish the amazing and real accomplishments of the day.
"Everything's amazing and nobody's happy." - Louis CK.
eh-hem implying the Myers-Briggs Personality Type is based on rigorous science /sardony /irony.
BTW the reason SpaceX is more exciting than SLS is VTVL reusability.
I think this phrase sums it the best
I also usually remember that the Casimir effect, a tested and true effect, used to take a lab of experts some years to reproduce results
Heliocentric solar system.
Circulation of blood in the body.
Yes they're "a long time ago" (really, a few centuries isn't a long time), but they're the tip of the iceberg of contested knowledge.
Also the roundness of the earth was never as far as I know controversial among the learned. Heliocentricity was only controversial for religious reasons.
[1] http://www.wired.co.uk/news/archive/2013-02/06/emdrive-and-c...
You can't show something as simple as aspirine 'works' by setting up a lab experiment without test subjects. And as soon as you involve those, it becomes legally complex, expensive, time consuming and hard.
You simply can't compare medical experiments to physics experiments. A physics experiment can be set up to be extremely controlled. If you observe some effect, the number of things it could be due to is very small.
A medical experiment requires people with all their messiness and possibly confounding variables. If you observe some effect, there are zounds of possible explanations. Controlling for all of them requires many test subjects. That makes it expensive, time consuming and hard.
Even a medical experiment on human cells in a petri dish is infinitely more complex than a physics experiment, in terms of variables involved.
Homeopathy doesn't claim that "some substance heals people". It claims (according to Wikipedia [1]) "a substance that causes the symptoms of a disease in healthy people will cure similar symptoms in sick people".
It's fundamentally flawed, and despite revisionist practitioners, has not yet managed to raise it's head above "pseudoscience" status.
It shouldn't really be mentioned in the same sentence as research that is actually trying to determine if a substance has an effect, even if that research is flawed. Said research and homeopathy aren't really playing on the same field. It's like calling religion a science. It's based on a premise that can't be questioned without throwing out the entire idea.
This seems to be about "reaction-less drives" - I remember reading about how hard-headed SF editor J.W.Campbell had a weak spot for such devices, several decades ago. He entertained a few demos, if memory serves.
Didn't pan out then, probably won't now.
Extraordinary claims require extraordinary evidence. These drives would violate conservation of momentum.[0] Conservation of momentum is built in to the known laws of physics at an extraordinarily deep level. It is obviously not impossible that our known laws are wrong, but the alternative would be to somehow produce a radically different set of physical laws that nevertheless reproduce every test of existing theory to high precision (as much as 14 digits of accuracy in some cases). And you probably also need to explain why the existing theory worked so very well if its bedrock foundation doesn't describe our universe.
So really, don't get excited. And don't send these folks money that could do real good elsewhere until they give at least some small reason to expect that it's not a wild goose chase.
(Edit to add: I wish this were real, too. With all my heart. But it's not a realistic wish.) [Re-edited to cut some less-appropriate phrasing.]
[0] Yes, I know the EmDrive site FAQ (http://emdrive.com/faq.html) claims that it doesn't violate conservation of momentum. The explanation of why it doesn't actually indicates that it does: "The electromagnetic wave momentum is built up in the resonating cavity, and is transferred to the end walls upon reflection." But the wave's momentum has to come from somewhere, too. So either this is just equivalent to a photon drive (propelled by shooting light out the back), or their device is pulling momentum out of nowhere.
The NASASpaceflight.com group has given consideration to whether the experimental measurements of thrust force were the result of an artifact. Despite considerable effort within the NASASpaceflight.com forum to dismiss the reported thrust as an artifact, the EM Drive results have yet to be falsified.
After consistent reports of thrust measurements from EM Drive experiments in the US, UK, and China – at thrust levels several thousand times in excess of a photon rocket, and now under hard vacuum conditions – the question of where the thrust is coming from deserves serious inquiry.
And also, a quote from the paper he co-authored in mid-2014 (http://ntrs.nasa.gov/search.jsp?R=20140006052):
Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, 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. Future test plans include independent verification and validation at other test facilities.
i.e. "Something weird and exciting may be going on and let's all verify it and figure it out"
edit 2: io9 has a handy pop-sci summary of the EmDrive: http://io9.com/new-test-suggests-nasas-impossible-em-drive-w...
vvvv edit: Yes, it's very probably a minor phenomenon that's occurring (barring an outright error), and not new physics. But it's a somewhat consistent phenomenon (in separate China & US experiments) associated with this particular test setup, so hopefully we'll learn something of decent interest in the coming years. The skeptical crowd should do its important job and scrutinise the research, and in the meantime, we (and the admittedly enthusiastic Dr White) can hope :)
A few years ago, the enormously more respected folks at the OPERA experiment were willing to announce that they had seemingly detected neutrinos moving faster than light. Despite this coming from a large group of scientists with top-notch credentials, that was immediately doubted by almost the entire physics community, and sure enough, the observed effect turned out to have been caused by a bad cable connection.
If anything, conservation of momentum is more deeply embedded in the structure of known physical principles than the speed of light limit. And this little group within NASA doesn't have remotely the level of credibility that OPERA had. So it's even easier for me to believe that this measurement is due to some loose cable or improper calibration or failure to isolate the test environment, too.
I'm not saying anything about the experiment, but I think your statement that "conservation of momentum is more deeply embedded..." isn't quite so accurate.
[0] http://www.preposterousuniverse.com/blog/2010/02/22/energy-i... [1] http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_g...
It's important to note that these are separate questions. The inventors of these devices seem to have their own theories, but these may be wrong even if the devices do work.
At this point this is interesting but I won't get excited unless there are more replications. I would say that it seems to not be an "e-cat" situation. There are a minimum of two independent replications. So it would likely be error rather than fraud if it is mistaken.
Conservation of momentum is not more deeply embedded than c in that it isn't even a law (outside of classical mechanics) to begin with.
Edit: elsewhere in the thread you explain that yes, it must be local.
So if this isn't experimental error or some other minor effect, it seems safe to assume that however it works it is not violating conservation of momentum. Either that or the universe is much weirder than we thought.
Besides, classical mechanics is one of the assumptions of quantum mechanics.
All that being said I agree extreme skepticism is healthy here, though arrogance or dismissal doesn't seem quite appropriate as these results continue to be reproduced.
Local momentum conservation is foundational to all of physics: it is embedded in Newton's laws, and you can't get much more foundational than that. As such, if anything violates it the degree of "extraordinary" would be beyond anything ever seen. Far beyond superluminal nuetrinos.
So the previous posters are correct: momentum conservation, which is generally used to mean "local momentum conservation", is as deeply foundational to physics as Newton's laws, and the kind of observable-only-by-statistical-inference non-locality seen in QM is not known to have any impact on it.
As such, it would be earth-shaking at the deepest possible levels of physics if this result were correct. That does not mean it is wrong--although that is certainly my bet and that of virtually every other working physcist--but it's important not to understate what a big deal it would be, because understanding that opens up alternative ideas regarding how to test it.
This is neither arrogance nor dismissal, but an understanding that anything that violates local momentum conservation, via QM or anything else, and also lets the rest of physcis sail blithely on, manifesting no measureable effect of any kind on any of the millions of diverse and precise experiments that have been performed, is astonishingly implausible.
Could it happen? Sure. But it's really easy for laypeople to radically underestimate the implausibility of such claims, as was done all the time in the cold fusion community.
Nor does reproduction of the effect say anything very much about either the underlying theory (such as it is) or the actual cause. Lots of things can create forces of micronewtons, and given how utterly implausible the claim is, most physicists are starting with a prior barely above epsilon. As such, the amount of evidence required to update our belief to something close to unity is going to be huge. Laypeople, who start with an unreasonably large prior because they are ignorant of how fine-tuned such novel physics would have to be to never show up anywhere else, will require less evidence.
Almost all the entanglements and weird things of Quantum Mechanics are local. The electrons in a molecule have weird antisymmetric properties that mix different configurations (the easy picture is http://en.wikipedia.org/wiki/Resonance_(chemistry) the mathematics is more complicated).
You can entangle a few particles and move them at long distance, but if the particles hit another particle, the entanglement goes away. (You can transfer the entanglement, in very specific setups, but it's difficult, usually you get decoherence.)
I don't know a way to transfer a lot of momentum form one point to a very distant point using entanglement.
For example, you can put a box of particles in a rocket and each particle in that box in entangled with a particle that is in a box in Earth. When you measure the momentum of the particle in the rocket, it "changes" the momentum in the particle in Earth, so you can think that some momentum was "transferred". (This is not technically correct, but is a good enough approximation.)
The problem is that the momentum that you measure is in a random distribution, and half of the time you'll "transfer" momentum in one direction to make your rocket faster and the other half of the times the momentum will go in the other direction to make your rocket slower. It's impossible to transfer information using entanglement, and it's impossible to select the direction of the "transferred" momentum, in particular because that could be used to transfer information.
Local conservation of momentum is a fundamental property of any translation-invariant model in the framework of quantum field theory. All this means is that the (vector) momentum flowing into any point in space-time must equal the momentum flowing out plus any increase in "stored" momentum at that point (whatever that might mean).
Quantum mechanics is a "local" theory in the formal sense, at least in any halfway mainstream formulation (from Copenhagen to many-worlds). Even the "spooky action at a distance" that folks talk about in reference to quantum phenomena is never capable of transmitting information outside of the "cone of causality" in space-time (which is the "light cone" in most relativistic theories: information can't travel faster than light).
That's not what the pages you linked to are saying. They are saying that there are solutions in GR where there is not any well-defined notion of total energy, as in "total energy of the universe". But GR certainly does require local energy and momentum conservation, which is what EmDrive would violate if it worked.
The folks at the OPERA experiment stated that they found something that needed further testing. They even said that they doubted faster than light particles. They wanted their experiment audited and repeated and stated that they wanted help from the scientific community.
The media is who turned it into a circus.
We spent a great deal of time trying to figure out how the mechanism worked, and about half the team were theoreticians who would try and posit theories, or evaluate theories posited by other teams, and the the other half of the team spent time either testing the new theories, or experimenting to try and improve the results of previous experiments.
Y1B2C3O is not even a metal, but a ceramic crystal. This was kinda mind blowing at the time. It shouldn't even conduct.
IIRC the best theory at the time was that it was superconducting because of particular errors in the formation of the crystal due to the production process. But I left the lab in the early 1990s.
But maybe non-physicists don't have a sense of the range of meanings that "that isn't possible within current theory" can have. High-Tc might have been "impossible" under basic BCS superconductivity theory, but BCS theory itself taught us that it was possible to find novel theoretical mechanisms generating zero resistance, so needing a new one was surprising but not unprecedented. "Standard" low-Tc superconductivity appeared "impossible" under the usual models of materials' resistivity, but even that was merely a violation of a well-tested model when it was extended to a previously untested very-low-temperature regime. Resolving that apparent impossibility didn't require rewriting any fundamental principles, it just required very careful application of the existing theoretical framework.
These speculative new propulsion theories appear to violate the conservation laws underlying all of our existing models of physics, and in an experimental regime of size/temperature/etc. where (I believe) they have been very well-tested in the past. Any calculation within the framework of quantum field theory or general relativity will inevitably result in momentum being (locally) conserved: it's unavoidably built in to the formalism. So as I said to begin with, although it's obviously not truly impossible that some entirely different framework could turn out to be correct, that is an enormously bigger jump than any stage of the discovery and explanation of superconductivity.
A long time ago, people thought that the faster than sound planes were impossible, perhaps some wrote that formally. The materials didn't have enough strength, it would become too hot, the pressure at some point would be too high, ... To model a faster than sound plane you need to model a lot of complicated interactions between a lot of atoms, and then you need some simplifications, and with the simplifications used at that time it was impossible.
The conservation of momentum is a very low level result, so you don't need to put a lot of simplifications to prove it or measure it. For example you can measure the conservation of momentum when a photon hits an electron almost directly: http://en.wikipedia.org/wiki/Compton_scattering
I'm no physicist but this guy[1] is, and his paper — which is based off of research with evidence backing it up in the 1970's — suggests that the EmDrive creates propulsion from Unruh radiation[2].
[1]http://physicsfromtheedge.blogspot.co.uk/2015/04/light-in-bo...
(I'm not sure about Unruh radiation, but the nice thing about radiation is that when you see it far enough, it doesn't depend on the details of the source, it's simple a bunch of photons. (Well, the color of the photon depends on the details of the source, but they are undistinguishable from other photons.))
If this is consistent with special relativity, and the particles are mass less, then the Force/Power ratio is at most 1/c, that is 0.0033 uN/W = 0.0033 mN/KW.
If the particles are not mass less, and you just create them at the moment to emit them, the ratio is even smaller, much smaller.
If the particles are not mass less, and just accelerate them from a reservoir, the ratio can be much bigger, but now you have a standard rocket, not a fuel-less rocket.
Someone compiled here a list of experiments, with the Force/Power ratio: http://forum.nasaspaceflight.com/index.php?topic=36313.msg13...
They vary from 3x to 200000x the theoretical maximum if we assume that this doesn't break the conservation of momentum, special relativity and quantum mechanics.
(Perhaps it's not necessary to use quantum mechanics, because the classical electromagnetic waves have the same Force/Power ratio, because they are actually a good approximation of the quantum electromagnetic waves. But the photons picture makes all clearer.)
This would just be a standard photon rocket--the cavity would eject photons out one end and move in the other direction. AFAIK all the EmDrive experimenters are claiming that no radiation is coming out of the cavity.
You make it sound like the scientists reporting it didn't doubt it.
But on the other hand, they were willing to make that public announcement in the first place. If they'd really felt the same level of skepticism that most of the rest of the community did, they might have done the tests that eventually found that loose cable before they stuck their necks out. (But then, part of their intent was clearly to get help and suggestions in figuring out what the lingering errors might be, and to get broader input on how feasible superluminal neutrinos might be theoretically. I can't judge them too harshly, even if they did wind up looking a step or two more willing to believe than they should have been.)
See this paper: http://pus.sagepub.com/content/5/2/121.short (unfortunately behind a paywall)
After a few years, it was no longer socially acceptable for respected scientists to work on cold fusion. It didn't matter anymore how good your reputation was as a researcher, or how carefully designed your experiment was--if your research was in cold fusion, it would get largely ignored.
Unfortunately, this happened around the time a couple groups of respected researchers with good experiment design were getting interesting results pointing to real new phenomena, and perhaps explaining why prior results had been so erratic.
David Goodstein around this time wrote a great article [1] looking back at cold fusion, which included a discussion of these later results, and how socially science had reached a state where they could not be considered. Here are the last few paragraphs.
All of this was much less important than the fact
that Cold Fusion experiments, if they gave positive
results at all, gave them only sporadically and
unpredictably. When Bednorz and Mueller announced
the discovery of high-temperature superconductivity
in 1986, no one carped about control experiments,
because, once the recipe was known, any competent
scientist could make a sample and test it and it
would work immediately. If, at their press
conference, Pons and Fleischmann had given a
dependable recipe for producing excess heat, they
very likely would be Nobel Prizewinners now (as
Bednorz and Mueller are) rather than social outcasts
from the community of scientists. The essential key
to the return of Cold Fusion to scientific
respectability is to find the missing ingredient
that would make the recipe work every time.
Experiments done in the U.S. and in Japan, and
reported at the Maui meeting indicate that the
missing ingredient may have been found. In all the
various Cold Fusion experiments, the first step is
to load deuterium into the body of metallic
palladium. The issue is how much deuterium gets into
the metal. The ratio of the number of atoms of
deuterium in the metal to the number of atoms of
palladium is called x. It turns out, by means of
electrolysis, or by putting the metal in deuterium
gas, that it is rather easy to get x up to the range
of about 0.6 or 0.7. That is already a startlingly
high figure. If there are almost as many deuterium
atoms as palladium atoms in the material, the
density of deuterium (a form of hydrogen) is
essentially equal to that of liquid hydrogen rocket
fuel, which can ordinarily exist only at extreme low
temperatures. In other words, palladium (and certain
other metals including titanium) soak up almost
unbelievable amounts of hydrogen or deuterium if
given the chance. This is far from a new discovery.
However, according to the experiments reported at
Maui, x=0.6 or 0.7 is not enough to produce Cold
Fusion. Both the American and Japanese groups showed
data indicating there is a sharp threshold at
x=0.85. Below that value (which can only be reached
with great difficulty and under favorable
circumstances) excess heat is never observed. But,
once x gets above that value, excess heat is
essentially always observed, according to the
reports presented at Maui, and recounted by Franco
Scaramuzzi in his seminar at the University of Rome.
The audience at Rome, certainly the senior
professors who were present, listened politely, but
they did not hear what Franco was saying (that much
became clear from the questions that were asked at
the end of the seminar, and comments that were made
afterward). If they went away with any lasting
impression at all, it was just the sad realization
that a fine scientist like Franco had not yet given
up his obsession with Cold Fusion. They cannot be
blamed. Any other audience of mainstream scientists
would have reacted exactly the same way. If Cold
Fusion ever gains back the scientific respectability
that was squandered in March and April of 1989, it
will be the result of a long, difficult battle that
has barely begun.
Recently, I told this story in a Philosophy course
we teach at Caltech called "Ethics of Research." The
first question, when I finished my tale, was, do I
believe in Cold Fusion? The answer is, no.
Certainly, I believe quite firmly the theoretical
arguments that say Cold Fusion is impossible. On the
other hand, however, I believe equally firmly in the
integrity and competence of Franco Scaramuzzi and
his group of co-workers at Frascati. I was disturbed
when I saw that Franco had gotten caught in the web
of science-by-news conference in April 1989
(although I was truly pleased that he finally got
the long overdue recognition his agency ENEA owed
him), and I was even more distressed when I learned
that Franco and his group had observed excess heat
(the "bad kind" of Cold Fusion). However, I have
looked at their cells, and looked at their data, and
it's all pretty impressive. The Japanese experiment
showing that heat nearly always results when x is
greater than 0.85 looks even more impressive on
paper. It seems a particularly elegant, well
designed experiment, at least to the untutored eye
of a physicist (what do I know about
electrochemistry?) What all these experiments really
need is critical examination by accomplished rivals
intent on proving them wrong. That is part of the
normal functioning of science. Unfortunately, in
this area, science is not functioning normally.
There is nobody out there listening.
I suppose that, if nuclear fusion really does take
place whenever x is greater than 0.85 in palladium,
the world of conventional science will eventually be
forced to take notice. If not, then the whole story
I have told you is nothing but a curious footnote to
a bizarre and ugly episode in the history of
science. Either way, I think the story illuminates
the inner dynamics of the scientific enterprise in a
way that few other stories have done. For that
reason alone, it may be worth telling.
Total measured neutron output, best case, appeared to be twice background. That's small enough that people moving around (people are mostly water) was enough to cause such variation. So they moved the experiment to a "neutron cube", a big box built of lead bricks where few background neutrons penetrated. Then there was no significant difference in neutron levels between "off" and "on".
They also tried heat generation measurement. Because you have to put power into the Pons/Fleischman apparatus to get anything to happen (it's not self-sustaining) it's a difficult experiment to do accurately. It requires water jackets, insulation, and lots of measurements. They were unable to detect any heat output above measurement noise.
Challenging group think and being skeptical is part of being a proper scientist. Perhaps they end up learning something entirely new from all of this.
All models are flawed and only imitate reality by definition. We must accept that our models are only a glimpse of the real thing. We barely manage to grok our own planet let alone galaxies unfathomably beyond our reach yet we are consistently surprised when our models turn out to yet again be wrong. We know for a fact that our currently accepted physical models are flawed. To start with, we cannot fully reconcile gravity or "spooky action at a distance." The only reason our current models are useful, like any useful model, is that they are somewhat good at predicting a very limited set of future outcomes given measurable parameters.
Why can't we admit that what we currently know only seems impressive to a few moderately advanced apes but in reality it is likely only tiny drop in the bucket compared to the knowledge our universe holds.
All that said I'm very pro skepticism. Just because science is dumb does not mean every other random idea is valid. It's the common arogance of the scientific community that grates on my nerves.
End rant.
Because that would be to deny without any reason but empty speculation that what a small group of scientists have done in the past 300 years is a singularly impressive achievement, adding more to human understanding of the universe than far large groups have done over far longer spans of time.
People don't know very much aren't impressed by what the discipline of publicly testing ideas by systematic observation, controlled experiment, and Bayesian inference has taught us about the world, and they radically under-estimate how much we know, instead comparing the vast and wonderous extent of our actual knowlege with their own fantasies of what might be known one day.
I look back at the science of the 1800's and I'm impressed by how much they knew, how much they did. I expect scientists a century or two from now will look back and think the same of us, while the ignorant people of their day will dismiss the thoughts and judgements of scientists of that time as nothing much compared to the fantasies of the ignorant.
I believe there are many who don't know very much who are easily impressed. I consider myself pretty well informed about science.
All you can say is that compared to humans of the past (and to other species that we know of) we know a lot and that our acquisition of knowledge is accelerating. To me, this is expected rather than awe inspiring. It's mainly impressive to us because our own minds are working at capacity and we were fairly recently huddling in caves in fear for our lives. Don't get me wrong, I'm rooting for team human, but we are very arrogant.
Human beings are not good at distinguishing between levels of "very low probability". Getting excited about space elevators is awesome, even though we're awfully unlikely to see them in our lifetimes and they might never pan out. But these drive theories are pretty literally too good to be true.
I'm just trying to say that our knowledge is incomplete enough that I would very solidly bet on certain "impossible" things being more likely than certain "possible" things. So sure people are bad at judging highly unlikely things, but even possible/impossible is not a reliable criterion. (As long as you don't cheat with hindsight.)
The only actual point of science that I can find here is your claim that "No one of import is claiming" that these drives violate conservation of momentum. In my original comment, I explicitly addressed this: the EmDrive FAQ's own attempt to explain how their drive doesn't violate momentum conservation seems to imply a violation of momentum conservation. Maybe I'm mistaken about that somehow: if so, I'd very much appreciate knowing how! (At the very least, I find it perhaps telling that the site's authors don't understand that their attempted answer is no answer at all.)
As for the personal attacks, I'll just give one piece of context for the "ignorant" bit. I'm a tenured professor with a Ph.D. in theoretical high energy physics from the University of Chicago. That doesn't give me any special magical authority to declare truth about the universe, but it does mean that I've got a pretty solid base of knowledge for my statements and (I hope) decent judgement about how confident to be in my beliefs about questions in my area of expertise. I work on crazy theories that might or might not wind up describing our world at all, so I'm very aware of both the vastness of our ignorance and the importance of pushing at its boundaries in bold and unconventional ways. And with all that background, I think these drive ideas sound entirely unreasonable. If you've got equally solid reasons to believe otherwise, more power to you, and I'd love to hear them.
I got a tirade of responses just like yours informing me that I'm a biggot, childish, close minded, backwards thinking, co-dependent on authority, cretin who will be the responsible for the downfall of humanity. ect. ect. ect.
I believe I got down to -45 karma on that post, my lowest score ever, and I wasn't being aggressive or hauty or anything. I was just saying "they're just looking for explanations on their observations, there's no way it's actually happening."
I never got an apology for that, strangely enough.
Because the EmDrive experimenters themselves are saying that thrust is being produced without any exhaust--i.e., momentum is being added to the cavity in one direction, without any compensating momentum being ejected in the other direction. That violates conservation of momentum.
> No one of import is claiming this.
Not directly, perhaps, but that is the clear implication of the results they are claiming. No exhaust, no momentum conservation. If they were saying "oh, we did see some radiation being ejected in the other direction", that would make a huge difference. But they're not.
> All who move beyond appeals to authority when constructing arguments must be decried as beyond the fringe!
It's you who are appealing to authority: you are saying there can't be violation of conservation of momentum, simply because the experimenters said there wasn't any. That's not how science works. You're supposed to question what they're saying; you're supposed to look at logical implications to see if what they're saying is all consistent. You're not supposed to just take them at their word.
Conservation of momentum has been confirmed by many, many experiments; it's not just a feature of my or anyone's "model" of the world.
> there might in fact be conventional exhaust escaping from the device in a manner they had not anticipated.
Yes, that's quite possible. But as far as I can tell, the experimenters are not even considering that possibility, or checking for it.
> I am very able to imagine a world where my model is innacurate
Sure, imagining a world in which momentum is not conserved is easy. But, as I said above, experiments have shown us that we do not live in such a world.
Of course it is logically possible that momentum is conserved almost all the time, instead of absolutely all the time, and these experiments just happened to be the first ones anyone ever ran that poked reality in a place where momentum was not quite conserved. But in Bayesian terms, my prior for that being the case is much, much lower than my prior for the experimenters having made a mistake somewhere. Experimenters make mistakes all the time; but nobody has yet discovered any violation of a conservation law.
This may just be semantics, but I dont see how you could argue that it isnt a feature of a model of the world. A neural representation of the world shared amongst a group of humans. Tested against reality in the best ways we can imagine. But it is still just a model, it is not actual reality. Are you really so sure about those priors? You are also have a very influential prior there which supposes that that if the device functions, it does so because it violates conservation of momentum. Surely you cant know this? Are there really no other explanations which fit more neatly with our current models?
We have a model that includes conservation of momentum. But experiments have shown that reality also includes conservation of momentum--that that feature of the model is an accurate representation of reality.
> Are you really so sure about those priors?
Yes.
> You are also have a very influential prior there which supposes that that if the device functions, it does so because it violates conservation of momentum.
That isn't a prior; it's a hypothesis--the one the EmDrive proponents are claiming.
> Are there really no other explanations which fit more neatly with our current models?
"The experimenters have made a mistake somewhere" is another explanation which fits in more neatly with our current models. Their mistake could be that the device isn't actually producing thrust, or it could be that it's producing thrust because it's ejecting radiation out the back end which they aren't detecting. Either one of those invalidates the EmDrive proponents' claims.
Is it even possible to give them money? I wasn't aware that NASA accepts earmarked donations, or contributions from private individuals in general.
I could somehow understand that if the experiments cost a billion dollars. But they don't. Any Europa mission is in no way related to nor threatened by these drive tests.
I absolutely do not want NASA to give money to every person who comes to their door claiming to have a recipe for a warp drive. There has to be some threshold of viability, or else all of the folks with home-brewed theories of everything who spam my inbox (I'm a theoretical physicist) could secure their own grants. I honestly have no idea what about this project put it over that threshold, but it seems to imply that the threshold is too low. I want NASA to spend some money on speculative ideas! But surely there are speculative ideas out there that don't require us to rewrite all the laws of physics. Let's fund those.
There should be a reasonable threshold at which we are willing to test ideas that would upset traditional scientific knowledge, or we risk displaying the mental rigidity which we mock in the religious and scientific orthodoxy of ages past. Obviously the perfect candidate idea for such testing would be one in which a sound theory was already present, but there have been examples of profound changes in theory that came about due to strange observations - consider the motion of Mercury and higher-temperature superconductors.
I too am excited about the possibility of life in our solar system, and I hope NASA gets probes to Europa, Titan and Enceladus as soon as possible, but these projects don't have to compete. The small amount of funding this has received so far is unlikely to be the difference between go and no-go for life-seeking probes.
They've done a small experiment on this particular concept and gotten interesting results. It would be utterly baffling if a group set up to explore such things explored them and then quit when they got interesting results.
Politeness in this regard is preventing appeals to authority.
I personally disagree. The money has been allocated to a section of NASA designed to research exactly this sort of theory. Pulling funding from these people would be like telling Ernest Solvay to put away his wallet.
Worth it, even if it has 1 in 10000 odds (my guess).
This kind of condescending response doesn't do science or scientists any good. It's actually actively harmful. Don't do it.
(I really do have much the same feeling about the magical cancer-curing kiss, though. Oh, how I wish...)
For some reason, this disturbs a lot of people more than violating conservation of momentum.
The alternative is that there really is absolute velocity, so the basic assumption of relativity is false. But that makes it a pretty big coincidence that atomic bombs work.
Still can't say I mind them checking just to be sure.
Can you explain why photonic rockets are not breaking conservation of energy using this reasoning? They have the same property you describe, but are considered feasible as far as I understand (if unpractical to implement).
Only hereticks waste their time thinking of such stupid ideas as a heliocentric solar system. They should spend their time productively, and cut up some cats for their humours.
Nothing is ever cut and dry, or proved - just commonly accepted and proved within our current paradigm - there's plenty to suggest that we've got the nature of reality fundamentally wrong.
How does dark energy show that? It's either a cosmological constant, or a quantum field with a particular equation of state. Both possibilities are covered by our current theories. Also, both possibilities obey local energy and momentum conservation, so even when we discover exactly what kind of stuff dark energy is and why its density is what it is, those conservation laws won't change.
We certainly don't know everything, but we do know some things.
http://en.wikipedia.org/wiki/Casimir_effect
I'm not sure this working implies what you think it does.
Now, if you suggest that I can somehow extract the Casimir energy without having put the same energy into the system first, I'll start arguing about violations of the laws of physics (in much the same way that I have above).
Extracting energy from the zero-point energy all around us no more violates conservation of energy than extracting energy from E=mc^2 does. And we can no more figure out how to do so than Einstein could figure out how to do so a century ago.
Heck, simply finding an efficient way to store lots of energy that way would be a nice trick as well! We know of no reason why you can't beat any existing battery technology by many orders of magnitude!
The trick is that we cannot think of any plausible way to do these things. And once you open up the window of, "This would be amazing if we could, and we can't prove you can't," then you've got something of great interest to cranks who convince themselves that they have done so. So you'd be on safe grounds promptly excusing yourself from any conversation where someone is trying to convince you that it has been done.
But dismissing them with a general wave of the hand and appeal to conservation laws makes you as wrong as they are.
Which can't be done because it's the zero point energy--i.e., it's the state with the lowest possible energy. If there were a lower energy state possible, we would be calling that the "zero-point".
> We know of no reason why you can't beat any existing battery technology by many orders of magnitude!
We know more than that: we know how to store orders of magnitude more energy than existing battery technology. Just use rest mass to store it: equal quantities of matter and antimatter. The problem, of course, is how to do that safely.
The Casimir force demonstrates that the zero point of vacuum can be ABOVE the zero point of the same space with a different arrangement of stuff in it. In other words the zero point energy is not necessarily the minimal configuration that can be achieved.
Thus the apparently trivial answer isn't necessarily correct.
Yes, that's because if you arrange stuff in a "vacuum" it's no longer a vacuum. In the case of the Casimir effect, you now have a pair of uncharged plates in what used to be vacuum.
The question is, how do you propose to extract net energy using this effect? It takes energy to arrange the stuff in the first place (for example, to put the uncharged plates in place)--in other words, it takes energy to perturb the "vacuum". If you run the numbers, you'll see that there's no way to get back more energy from something like the Casimir effect than it took to arrange the stuff the right way in the first place. Which is just another way of saying that the "zero point" of an actual vacuum--no stuff present at all--is still effectively the lowest energy you can achieve.
And I agree. We do not know how to perform an operation that extracts net energy from the zero point energy. We have no idea how to go about it. And we have good reason to suspect that this is impossible.
We just have no proof of it.
For an analogy to a past situation like this, it is like the situation for many decades when it was known that Maxwell's demon could break the laws of entropy, but we were pretty sure it couldn't be built. And there was a century long back and forth on the topic before that was demonstrated.
In a Casimir experiment, which closed system can you define in which you require conservation of energy? How do you calculate the total energy in the system in the 'before' and 'after' configurations?
How does separating two plates put energy into that system in such a way that it can subsequently manifest itself as the Casimir force? Does separating the plates increase the zero point energy and is that subsequently decreased by the Casimir force? Is it known to be possible to change the zero point energy like that?
Arguing violations of the laws of physics is not very interesting if we can't microscopically pinpoint what happens in the first place. Which can be surprisingly hard: it took decades to properly explain Laplace's demon.
So what do you call a second, replicated experimental setup conducted in vacuum, if not extraordinary?
Best case, we get a new awesome thrusters.
Worst case, we get the learn new things. So far these drives have pass tests and stumped experts and researchers. So even if it doesn't violate the current laws of physic, it'll paint a better picture of the current laws of physic and better testing method in the future.
You're correct, but I'd rather a few million dollars going to this research than a few million dollars going to some magnetic-healing-band toting pseudo-guru.
The "first world" wastes ridiculous amounts of money every second. Can we divert at least some of it to disproving crack-pot scientific ideas? It'd at least be entertaining (like Mythbusters on steroids!).
Or even cell phones. We were using radio signals in hand held devices for nearly 50 years before a vast majority of consumers were walking around with phones in their pockets in the mid to late 90s. Sure, there were early adopters in the late 80s and early 90s, but the technology was still expensive. And the technology (like walkie talkies) had existed for decades before...
This would very quickly move from "let's wait for NASA to do more tests" to "let's beat NASA to the test."
That's all assuming it's real, of course. I'd bet against it.
The most thrust anyone was getting was 750mN at 2.5KW. At that efficiency you need to have something that produces >32.7W/g just to hold itself up. That's rocket engine territory: http://en.wikipedia.org/wiki/Power-to-weight_ratio
We barely have supercapacitors that'll deliver that sort of power output. For a few seconds, maybe. Not accounting for the mass of the device itself.
Hopefully if this ever turns out to be something the efficiency will improve. But I'm not holding my breath.
(Number taken from here: https://news.ycombinator.com/item?id=9474610 )
The only thing that's amazing about the EM Drive, if true, is that it doesn't require a propellant. It's extremely energy intensive, but since energy can be derived from a reactor or solar panels, this is often easy to overcome.
In an atmosphere solar panels are drag, and a reactor is completely insane.
But yeah, it's more likely there's some confusion in there.
What is the ratio of wattage to thrust, that's what I'd be curious about? And how efficient is it?
I guess change in kinetic energy can never be greater than energy inputted to the device, correct?
http://www.wired.com/2010/11/1110mars-climate-observer-repor...
Even if it's not the start of a Star Trek-eseque future, this is some pretty neat stuff and I'm really anxious to hear more about what new gates of knowledge this unlocks. The plot line is right out of sci-fi and it's what makes me love technology so much: we truly never know what we will find.
The proper Bayesian approach to these tests is to downgrade your prior of "drives require reaction mass" from 99.99999999% to 99.999999%
I think they need to precisely measure the mass of the whole device before and after the experiment, to make sure the thrust isn't coming from ionization or some decay.
There's a whole lot of power being thrown around inside those boxes.
Units cancel out to give m/s.
This is just specific impulse. Though Isp is generally measured in seconds (implied gravitational field of the Earth gives s * m/s/s = m/s.)
As for the accuracy of the 750 millinewton figure, that's the only one I've seen for the Chinese results but again, that has to be an error, even if the EmDrive did pan out in the end that's just an unbelievably high amount of thrust. I would assume it's supposed to be micronewtons and that was lost in translation.
The Casmir effect and the Casmir-Polder Force is considered by many scientists to be a result of asymmetrical forces being generated by and or from the quantum vacuum based on the materials and geometries being used.
It did take decades to verify to the level people don't consider it experiment error, and we're sill arguing over if it's really a quantum mechanical effect. Some people do not like the whole quantum field theory thing and their efforts to disprove things related to it is important for science.
Personally QFT makes a lot of sense to me so I look at the work being done at Eagleworks and wish there was a way to help accelerate the pace of research because this thing isn't the LHC its not trillion dollar stuff, a few million is probably the total bill to do all the work and the subsequent re verification by JPL, NASA and Johns Hopkins that they want to do. This could be "done" in a year if we stop going slowly. It's 2015 and I would like my hover car next year thanks.
2500W is 50x 50W of power. 0.05mN x 50 = 2.5mN, not 750mN.
That's a hell of a ramp up in thrust. Does it keep ramping the more power you put into the cavity? If so, how much power is required to say get a fighter jet to fly which is around 100,000N of thrust?
Or is my math WAYYY off?
Also would it make the hoverboard feasible, or does it require way too much energy?
This inefficiency would still be great in space because you don't have to carry reaction mass with you. (and hovering on earth would mean sustained 1g acceleration in space, which is fantastic.) But if you're swimming through reaction mass anyway, then just push it as efficiently as possible.
The classic quote from the time "We know they have WMDs because we have the receipts!"
WMDs = pretext, real reason: Oil and GeoPolitical