This is not worth getting excited about. Really.
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.
According to physicist Harold White, leader of the NASA Eagleworks team, it can't simply be a "photon rocket":
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.</i>
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 :)
Realize that this is the exact same level of verification as superliminal neutrinos, except at a vastly decreased level of rigor. At this point the overwhelmingly likely explanation is that there is some phenomenon at work which we don't understand or haven't properly accounted for, not that there is new physics afoot.
Really what's the difference. Either we can fit it in to our models or we have to change the models. It always bothers me that so many people in the scientific community speak of our scientific models of the physical world as if they were truth itself.
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.
> 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.
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.
> 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
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.
Don't you think thinkers have always thought this at every point of time in history? The answer is yes they have. There have been large innaccuracies discovered in our models before. So what makes you think that it's so different this century? I'm not saying the these drives work, just that appearing to fundamentally violate our models makes it unlikely to be a real effect. But it isn't impossible, lets not be too self assured here. Pride makes you feel good, and bringing emotion into your reasoning is rarely a good thing where science is concerned.
From a Bayesian perspective, it isn't. One experiment that is difficult to disprove does not carry the same weight as 5 different ones giving similar results.
I think that the most likely explanation is experimental error.
Yes, sure, they've measured something surprising. I have no reason to doubt that.
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.
This reminds me of the story behind the "discovery" of cold fusion in the 80s. Sure, Pons & Fleischman may have thought they measured something, but in the end the whole effect could be attributed to careless experimental design and procedure.
See this paper: http://pus.sagepub.com/content/5/2/121.short (unfortunately behind a paywall)
That was taken very seriously at the time. I went to a well-attended talk at Stanford by a Stanford physicist who was trying to replicate the Pons/Fleischman experiment. When they first set up the apparatus, they had radiation detectors with alarms, in case it started generating a dangerous level of neutrons. After some initial tests where not much happened, they moved the radiation alarm gear back a bit.
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.
Cold fusion is a bit more complicated than that. The early experiments were certainly flawed, and there were way to many people announcing results for publicity before they had checked their work.
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.
[1] http://www.its.caltech.edu/~dg/fusion_art.html
That was one experimental setup, that was not replicated by other experiments though. It is a bit different when you get multiple experiments by lots of different teams.
So, it is worth bringing up: GR doesn't require global conservation of momentum or energy.[0,1]
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...
Yes, it would be more precise if I had prepended "local" every time I said "conservation of momentum" above. With that clarification, I'm happy to stand by what I've said.
"local" seems like a fairly large assumption for something hypothesized by at least some to work through quantum mechanics, of which a central tenant is non-locality. In fact, given the consistency of qm experimental results over the past 50 or so years, it seems entirely plausible to think that it would be a field of study which could upend classical physics.
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.
I may have been using a technical term too glibly there.
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).
Except the non-locality of QM is irrelevant to a device that is apparently a closed cavity. Simply because the same word is used does not mean the underlying concept is sufficiently similar in both contexts to be relevant.
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.
Quantum Mechanics is weird but it's not magic. One of the most unintuitive effects is entanglement.
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.
Furthermore momentum is only conserved in classical mechanics. It is actually information that is preserved. E.g. In a particle accelerator momentum is converted into energy, but information is not lost.
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.
Conservation of momentum can be derived as a necessary result in any theory whose basic laws are translation invariant (that is, if the defining equations are unchanged if you move everything in the universe 6.2 cubits to the left). This is true in classical physics, relativistic dynamics, quantum mechanics, quantum field theory, or even string theory). You can prove it in various ways depending on which formalism you're working in, but the most elegant proofs I know are based on Noether's Theorem (http://math.ucr.edu/home/baez/noether.html). It's beautifully general, and it applies equally strongly to classical or quantum systems.
Must it be local conservation? In other words can we rule out systems that push against something nonlocal or against everything in the universe at once?
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.
Translation invariance has been a core assumption of every physics theory because we've observe it to be true. That's what a law is: that which you've observed.
Besides, classical mechanics is one of the assumptions of quantum mechanics.
Hmm. So there's some indication that this device warps space. If that's true does that mean it could violate those conservation laws?
Nope! :) That's the point of the "locally conserved" clarification I made in a sibling comment: these conservation laws hold at every individual point in space, regardless of whether the point is part of a curved manifold or a flat one. (Curvature can definitely interfere with attempts to define a global conservation law, like "total momentum in the universe is constant". But the essential feature of a manifold is that near any given point it is locally equivalent to simple flat space.)
I would not even go so far. Assuming this isn't a mirage, we don't know what it's doing. It could be conserving momentum but in some weird non-obvious way, or even doing something weirder. First question is whether it "works" at all, then how... and I would look for ways it might work while conserving momentum before challenging a conservation law.
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.
> GR doesn't require global conservation of momentum or energy
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.
Happens the other way too. In the 80s high-temperature superconductors were discovered, which were 'impossible' by previous understanding. The theory is still catching up to that.
I worked for the Texas Center for Superconductivity, where Paul Chu discovered superconductors that operated at liquid nitrogen temperatures, in the 1980s a year or so after his discovery.
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.
And even low-Tc superconductors looked "impossible" under the physics of their day. No question about it! Science thrives on surprises: it's the very best part of what we do.
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.
I agree completely. I´ll try to explain this with a simpler example.
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
For the longest time, everyone thought that the earth was flat as well until this heretic said, nope it is flat.
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.
Which "heretic" would you be referring to? Pythagoras? He was persecuted, but not for believing in a spherical earth.
The heretic, Galileo Galilei, claimed that the earth revolved around the sun instead of the sun revolving around the earth. That the earth is (almost) spherical was known since antiquity.
I thought his name was Copernicus.
Copernicus came up with the theory. Galileo became a heretic for how he popularized it.
Interesting side note, it wasn't thought to be flat for as long as most people think. The roundness of earth is a pretty ancient piece of knowledge.
https://en.wikipedia.org/wiki/Myth_of_the_Flat_Earth
Go read up on Eratosthenes. http://en.wikipedia.org/wiki/Eratosthenes
The neutrino phenomenon was caused by a calculation error regarding GR and was miniscule magnitudes of error. I'm genuinely curious how a measurable force is a calculation error. Notwithstanding that whether or not it can be explained it works. The measured forces are so substantial that even a high school student with high school apparatus would notice them, it's hardly caused by a wobbly cable in precision equipment.
This doesn't have to violate conservation of momentum to work. We don't understand how it works yet, which precludes us from saying that it violates our current understanding of physics.
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...
[2]http://www.ptep-online.com/index_files/2015/PP-40-15.PDF
If this is consistent with quantum mechanics, this must emit some kind of particles, the main candidates are photons (and far less probable gravitons, but some alternatives / variations claim to use gravity).
(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.)
> the EmDrive creates propulsion from Unruh radiation
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.
>Despite this coming from a large group of scientists with top-notch credentials, that was immediately doubted by almost the entire physics community
You make it sound like the scientists reporting it didn't doubt it.
Well, that's a funny question, right? On the one hand, they really were careful in their announcement to indicate "we're not sure about this". They were clearly making a real attempt to exercise proper scientific skepticism of such a remarkable result.
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.)
At the time I saw it as a big request for help in finding the experimental oversight. They had tried pretty hard to rule everything out, and they wanted fresh eyes.
This statement is extremely dishonest and inaccurate.
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.
Why isn't it worth getting excited about? I get excited about lunch. It costs me nothing to follow the progress on low-probability, high impact technological advancements (see: space elevators, commercial fusion power, etc)
I guess this is really the point: space elevators and commercial fusion are many, many orders of magnitude more likely to pan out than this is. Both of those are engineering challenges, and materials science challenges. They may be insurmountable ones, or they may not. But neither one would unconditionally require changes to the bedrock principles of physics.
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.
Well here's the thing. We could put a fully-functioning fast food restaurant on the moon by 2020. It's an engineering challenge and 100% surmountable. But we won't. It's more likely that we've fundamentally misunderstood physics than we would actually put in the effort to do that.
But the economic consequences of, say, commercial fusion would be enormous. Whoever mastered it would stand to become the wealthiest nation/corporation/person on the planet. Can't say the same for a Jack-in-a-box on the Sea of Tranquility.
I can't begin to tell you how much more likely I would consider a lunar McDonald's publicity stunt than a demonstration that "momentum isn't conserved after all". The first is so implausible as to be laughable. But the second makes the first look mundane. The future behavior of large groups of people is enormously more complicated and less understood than quantum field theory and the standard model.
I'm not really talking about this specific thing. (Though are you sure it even requires momentum to not be conserved?)
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.)
I get really tired of these ignorant psuedo sceptic responses. It's so obviously a straw man attack it makes me cringe. Why are you so set on assuming that it is violating conservation of momentum? No one of import is claiming this. My god, authority must always be right! All who move beyond appeals to authority when constructing arguments must be decried as beyond the fringe! Heathens! Infidels! Traitors! Expell them from within the walls of science, from the walls of Freedom. Yeah muh Science/freedom/nationalism/whatever makes me feel safe by allowing me to feel like I belong and satisfies a psychological need to construct a them and us world. Ffs. Grow up. Seriously hacker news. Grow up. Please, please humanity, grow up. Arrrrgggghhhh. I cant even. - Edited to remove swear words
I got the same response when I informed /r/science that "No, no one in the OPERA Experiment actually believes that neutrinos are actually going faster than light and breaking special relativity, they're asking for input on what went wrong with their observations"
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.
I honestly don't even know where to begin in responding to this. You've called me (or my words) "ignorant" and "pseudo-skeptic", you've suggested that I have relied on appeal to authority in making my arguments, and you've implied that I'm motivated by an ignorant "us vs. them" mentality. You've told me to "grow up". All of that seems like pure personal attack, rather than any sort of robust engagement with ideas.
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 was angry at a great deal of posts like yours over a range of topics. Perhaps in this instance the anger was missplaced. In a previous post I have worked out how to articulate my concerns: A lot of the time posts with an overtly negative tone that claim to come from a place of rationality, are in fact reactionary. They claim to be defending a core of rationality from encroaching confusion, when in fact they are a symptom of irrationality, a result of the innapropriate application of emotional reasoning to areas of life where it has no explicative power. I believe that the rigidity of the models to be found within the minds of certain kinds of folks has less to do with the defense of rationality and more to do with the defense of identity. I find it extremely irritating to deal with people who are irrationally certain in an uncertain world - especially when they justify themselves by claiming they are just being more reasoned than the next man. Having said that I can hardly claim my post was anything but an emotional outburst.
> Why are you so set on assuming that it is violating conservation of momentum?
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.
'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.' What you are doing here is saying - I will take my model of the world and check that their observations are consistent with what it predicts are physically possible. Then saying I found their observations to be inconsistent with how I expect the world to behave given my model. A natural follow on step from this is to conclude that they have missunderstood how their experiment is constructed - there is something about the way they are performing their experiment which is not accurately reflected in the model of their experiment. For instance there might in fact be conventional exhaust escaping from the device in a manner they had not anticipated. This is fine, this is also my interpretation. But where we differ is that I am very able to imagine a world where my model is innacurate and I appreciate that sometimes things that appear to require radically different models can in fact be produced by relatively minor ammendments. And that many people I meet seem to be very unwilling to question their own models and ammend them where necessary, upsets me. It upsets me because I believe in many instances it is born of the same kinds of irrationality that the whole enterprise of rational thought was designed to fix in the first place. At times, to me, it feels like it has become just another church for people to cling to. The rigid models I percieve within public discourse on these topics are a symptom of the very same creeping irrationality that they are purportedly defending against.
> What you are doing here is saying - I will take my model of the world and check that their observations are consistent with what it predicts are physically possible.
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.
'it's not just a feature of my or anyone's "model" of the world.'
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?
> it is still just a model, it is not actual reality.
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.
I give up. I think you're wrong, you think I'm wrong. I dont have time to iron out all the mistakes you are making and Im sure you feel the same way.
> 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.
Is it even possible to give them money? I wasn't aware that NASA accepts earmarked donations, or contributions from private individuals in general.
In the back of my mind, I suppose I'm hoping that some administrator involved with the NASA budget is reading my comment. (Just for instance, I would say that the possibility that we could find life on Europa or the other outer moons is many, many orders of magnitude higher than the possibility that these drives turn out to be even a little bit worthwhile.)
Are you serious? If you had the power, you would actively prevent NASA from doing these experiments and trying to falsify the claims?
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.
Yes, actually. Every dollar that NASA spends has the potential to accomplish something for humanity. To my eye, even the vast potential benefits of this technology are more than washed out by the tremendously low probability that it will turn out to be real.
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.
Given the small amounts involved, it's worth the money just to figure out the source of experimental error. NASA isn't giving money to random kooks off the street, these are actual physicists in labs doing the work.
Not only is it not random kooks off the street, it's the Advanced Propulsion Physics Laboratory, a group NASA set up for the express purpose of exploring exotic and unlikely propulsion concepts.
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.
Steuard is too polite to point this out himself, so I will do it for him: he is a physics professor. That the amount of money is small is a measure of how incredibly unlikely he thinks any useful result would come from the experiments.
Thank you for the pointer, I have a bad habit of not noticing usernames anyway. That said I still think my argument is valid, if you are seeing an incorrect result in a simple experiment it's still worth lab time figuring out which of your instruments or equipment is introducing it, even if you have 0.00% confidence that it's anything special or interesting.
Steuard himself would hopefully point out that although being a physics professor grants his opinion a greater weight than those of us who are less informed, to claim that he is automatically correct would be fallacious.
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.
I am not saying he is automatically correct. I am saying that one should consider his profession, expertise, his level of skepticism, and then reconsider priors.
You're entitled to your opinion, of course, but I think NASA has struck an appropriate balance between skepticism and curiosity. After results claiming thrust from the EM drive were given by paid lab testing and a Chinese study, NASA threw a miniscule amount of effort at this, expecting it to fail. It generated positive results, so they threw in a hair more. This will continue until either very rigorous, well-funded studies duplicate these results, or they are invalidated at a lower- or mid-tier levels of rigor.
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 don't accept earmarked donations, but they do accept unsolicited and unconditional private contributions. http://nodis3.gsfc.nasa.gov/displayDir.cfm?Internal_ID=N_PD_...
I suppose "unsolicited" is why I've never heard of this. Thanks, learned something new today.
Compared to making a feature film, the budget required to check this out very carefully isn't much.
Worth it, even if it has 1 in 10000 odds (my guess).
"But I also wish that I could cure cancer with a single magical kiss, and that I had my very own pet dragon"
This kind of condescending response doesn't do science or scientists any good. It's actually actively harmful. Don't do it.
Nonsense. These devices are on the far extreme end of the "requires extraordinary evidence" spectrum. Until this extraordinary evidence is provided, they are well within the prior probability category of providing pet dragons.
If the evidence is out of the ordinary, no one will believe it anyway. /s
Fair point, and thanks for calling me on it. In retrospect, accurate or not, that sentence grew out of feelings of frustration more than a desire to teach, which is always a bad sign. I've rephrased it.
(I really do have much the same feeling about the magical cancer-curing kiss, though. Oh, how I wish...)
Also conservation of energy. Thrust can't vary by velocity because there's no such thing as absolute velocity. So your velocity (relative to whatever) keeps increasing linearly, while kinetic energy increases quadratically. At some point you start getting more energy out than you put in.
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.
I'm not understanding this argument. Wouldn't the same amount of thrust get you less and less delta velocity as your velocity increases?
Velocity compared to what? You have an infinite number of velocities, depending on what you compare to. But you can only have one acceleration at any given time. So how can your acceleration depend on your velocity?
Not unless you're experiencing friction.
You'd never get more change in kinetic energy than the energy you put into it, right?
Well that's the point: you would, so that's an argument why the device doesn't likely work.
> Also conservation of energy. Thrust can't vary by velocity because there's no such thing as absolute velocity. So your velocity (relative to whatever) keeps increasing linearly, while kinetic energy increases quadratically. At some point you start getting more energy out than you put in.
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).
Because a photon rocket is throwing stuff out the back like any other rocket. It doesn't really matter that it's just photons due to mass-energy equivalence.
Also, as everybody knows, it is impossible that the earth could be orbiting the sun rather than vice versa - all books on the subject confirm it, and this would totally defy the theological principle, which is certainly impossible.
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.
Even if something disproves the functionality of these things it's still likely to be quite interesting. I think there's room to be excited either way.
The FTL neutrino was a fiber-optic cable from a frequency generator that was slightly loose. So no, it could still be something really stupid, and not exciting. Beyond the fact I wish someone from that team had sent a video into FailArmy on YouTube.
Please do explain dark energy, given that all of physics is known and in the can?
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.
> 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.
What about this well known, tested and well accepted effect:
http://en.wikipedia.org/wiki/Casimir_effect
I'm not sure this working implies what you think it does.
I'm not sure what you're getting at, either. The Casimir effect is real, absolutely. I think it was an exercise in one of my quantum field theory classes. In particular, the Casimir effect is something that you can compute entirely within the structure of existing physics, and it doesn't violate any conservation laws.
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).
...and if you did, then you'd be on shaky ground.
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.
> Extracting energy from the zero-point energy all around us
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.
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".
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.
> 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.
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.
When you say, "If you run the numbers", what you mean is, "If you do the calculation for the operation that we know how to do then..."
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.
A quantum field theory class isn't enough to actually understand and explain a Casimir experiment if you want to go beyond the 'shut up and calculate' approach. Being able to compute the Casimir force is insufficient for understanding and explaining the entire experiment.
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.
> Extraordinary claims require extraordinary evidence
So what do you call a second, replicated experimental setup conducted in vacuum, if not extraordinary?
I want to be pithy and say "N=2", but it's not even that. As the experimental controls get stricter, the effect becomes more negligible. That hurts the likelihood, not helps it.