EmDrive study officially published (aiaa.org) 595 points by babak_ap on Nov 19, 2016 | hide | past | favorite | 427 comments

 Recent previous discussion:
 As the main hypothesis in this paper is that the momentum is transferred by pilot waves, it is worth to emphasize the (cited there) most known recent approaches - Couder's experiments which use classical object with wave-particle duality (droplet coupled with waves it creates), getting e.g. interference in double-slit, orbit quantization and many other quantum-like phenomena:https://en.wikipedia.org/wiki/Hydrodynamic_quantum_analogs
 This is pretty good news if only that we will get more research into this phenomenon.In 1933 von Neumann basically published a proof against the idea of any hidden-variable theory. It took 30 years but Bell then discredited it.My guess is that a lot of this will get revisited. The outcome of this in the next 10-20 years might be really cheap probes (via reusable launch vehicles like SpaceX is making) that need no propellent to continue onto their merry way for a long time. The current way of doing this would be using solar sails or something along those lines which is not exactly compact.Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed.
 Bell proved that there is no local hidden variable model that is consistent with quantum theory. He said the same thing as Von Neumann (quantum mechanics can't be understood merely in terms of hidden variables), only more robustly. No new physics was discovered.
 No, that's not the whole story. Bell pointed out that Bohm's theory, already known but ignored, is a counterexample to von Neumann's and others' claims on impossibility of hidden variables. He analyzed how that is possible and found out: 1) von Neumann made some unreasonable assumptions in his analysis; 2) the fixation on hidden variables is missing the point; the real surprise is that locality, not theory with hidden variables, is inconsistent with quantum theory. That's quite a discovery.http://www.ijqf.org/wps/wp-content/uploads/2014/11/Bricmont-...
 Wait a minute, my understanding of QM rejects both non-locality and hidden variables. Put it that way however, you kinda have to believe in macroscopic decoherence, that is, Everet's multiverse: there are 2 universes, one in which the cat is dead, and one in which the cat is alive, and observing one universe doesn't rule out the existence of the other. (Similarly, sending a photon (or settlers!) outside of the observable universe doesn't end its existence.)Non-locality sounds way, way weirder to me than macroscopic decoherence. Stuff like quantum collapse is really an additional, un-falsifiable claim: why the universe would zero-out precisely the stuff that the math says we can't observe?
 Er, are you familiar with the Bohmian mechanics [1] that was mentioned above? It has, basically, 'non-local hidden variables', and that works fine.
 This sounds really interesting but my physics are abysmal.Could someone kindly explain this thread in conceptually simple terms?
 These two Quanta Magazine articles are probably the most accessible-with-least-compromise articles about the subject, and also include a lot of the history behind it:https://www.quantamagazine.org/20140624-fluid-tests-hint-at-...
 It's pretty hard to say anything meaningful about quantum mechanics and above without being precise with the math (case in point, there are so many frustrating examples of people who don't have the math down making statements that aren't consistent with it).Here's a summary, cause talking about this stuff is fun, with the caveat that it won'tQuantum mechanics in its usual interpretations involves some randomness, where a measurement can give multiple results with different probabilities. The interpretations tell us that this is truly random; that the values are not known until you measure them, and then afterwards they are known and true everywhere.The obvious objection is "hey, maybe the values were there already, but until we measured them we just didn't know what they were". A theory with this property is called a 'hidden variable' theory.A 'local' hidden variable is one attached to a particle, such as its velocity. If you measured two entangled particles at the same time that are some difference apart, QM shows us that the results of one can be influenced by the results of the other - for example, if you measure one particle as having a positive spin on the Z-axis, the other would have to have a negative spin, in a certain experiment.Excluding superluminal communication (one particle did not send a message to the other), we might guess: well, one had spin up and the other had spin down to begin with, and we were just measuring them to find out which one was which.Bell's Theorem [1] proves (in an experimentally verifiable way) that this is not the case. There is no way that local hidden variables can reproduce the results of quantum mechanics. This is one of the most amazing discoveries of the 20th century, in my opinion.Nonlocal hidden variables still work, which is what Bohmian mechanics is. You're allowed to say "there is a variable accessible to every measurement that determines what the result of a measurement is. In Bohmian mechanics - which is mathematically equivalent to regular QM, just more complex - there is a 'pilot wave' that is computed from the whole configuration of the universe, and then is used to determine what the spin of a particule is.Basically you get to pick between nondeterminism (randomness) and a global function that influences everything that's much more complicated.The theory is appealing to many because it avoids non-determinism. It's unappealing because it's strictly more complicated than the interpretations that don't have this extra object, but predicts nothing beyond them. By Occam's razor it's not as good as the simpler interpretations.It is appealing to people who really don't want to accept the possibility of randomness in the universe, which I have no problem with. Not that it's not worth time investigating it, because it's interesting.(Some people think it's not worth splitting hairs over interpretations over QM, because they don't provide falsifiable predictions and so this stuff isn't science but philosophy. I disagree with this. Finding that one explanation is simpler than another is finding something, and constitutes, in my opinion, valid evidence for that explanation in a scientific sense.)
 Just to clarify, Bell's result implies that our universe is either lacking locality or counterfactual definiteness. Counterfactual definiteness means that for any measurement you could perform there is a definite fact of the matter of what the result is prior to or without taking the measurement. The Many-Worlds Interpretation is consistent with Bell's result because it lacks counterfactual definiteness -- there's not one result of measurement; there's several results, all real!
 Doesn't that mean that MWI has "global" counterfactual definiteness (across universe branches), but lacks it "locally" (within individual branches)?
 It lacks counterfactual definiteness globally, because there's multiple outcomes, not a single fact-of-the-matter. It lacks counterfactual definiteness locally from a subjective perspective due to the seemingly random outcomes.
 Isn't multiple correct outcomes still the same thing? Because you can say in advance that all the outcomes will happen, isn't it just another perspective? As a physical entity inside the universe you know that you'll have different copies of you experience a unique outcome each, rather than being able to say "I will experience outcome X".In other words, you can say what branches will exist but not with certainty say what you'll see as a result for yourself. By the dictionary definition, isn't that still counterfactual correctness? You'll know what happen in advance, because you can calculate the possibilities.Is the scientific definition strictly in the perspective of a physical observer?
 I think we're talking past each other, and there may be some confusion about terminology. I will do my best to try to describe what's going on to the best of my abilities and see whether that answers your questions.Bell's Theorem (also called Bell's Inequality) starts with assuming that the universe has locality and counterfactual definiteness and yields and inequality concerning correlations between certain measurements. Experiments later conclusively showed that these inequalities are violated in our universe. So, one of the assumptions of locality or counterfactual definiteness does not hold in the universe we live in. Historically, this result was used to discredit and eliminate a class of theories about quantum mechanics called hidden variable theories -- the idea that quantum mechanics is deterministic, and we just haven't delved deep enough to find out what's determining the behavior of particles.In my opinion it's most useful to think of Bell's result as a proof by contradiction: there are a bunch of assumptions (implicit and explicit) that go into it, and we're left with a prediction that reality violates. Therefore one of the assumptions is wrong, but we don't know which one, and different interpretations of QM will have different answers to this question. In the context of Bell's Theorem, counterfactual definiteness has a specific definition, and that's from the local perspective of an observer observing from within physics, because Bell's Theorem itself implicitly assumes a single universe and goes from there.Under the Many-Worlds Interpretation, the result of a measurement is that the observer is split, and different copies of the observer will experience all results. This is the global and deterministic view. The local view is that the observer will see one result or the other, and there is simply no fact of the matter as to why the observer sees this particular result instead of the other.The Many-Worlds Interpretation has some advantages over other interpretations in that it's local, deterministic, and mathematically the simplest. But it rubs a lot of people's intuitions the wrong way because it posits an unbelievable multitude of copies of what we know of as the universe.
 It's for comments like this that I bother reading the comments here on HN. Thanks for distilling a complex subject into understandable-to-a-layman terms.
 Agreed. I particularly valued this part, which helps me grasp some other content posted here:"Bohmian mechanics [describes] a 'pilot wave' that is computed from the whole configuration of the universe... a global function that influences everything".
 > The theory is appealing to many because it avoids non-determinism. It's unappealing because it's strictly more complicated than the interpretations that don't have this extra object, but predicts nothing beyond them. By Occam's razor it's not as good as the simpler interpretations.I'm not a physicist, but doesn't classical QM have the problem of the "collapse of the wave function", i.e. "suddenly" Schrödinger's equation does not hold anymore - a problem that the De Broglie-Bohm theory does not have? Shouldn't this be considered as a strong sign against "typical" QM formulations and for the De Broglie-Bohm theory?
 The wavefunction collapse is messy and awkward. It's taken as an axiom, basically, in the Copenhagen interpretation. It's not as awkward as introducing another equation and set of rules to skirt around it, as Bohmian mechanics does, in my opinion.Many-worlds - which starts with being a lot more rigorous about what 'measurement' is (entangled yourself with the system in question) is much simpler than either, I think.My general impression is that Many-Worlds is getting more popular as physicists make precise how entanglement, measurement, and decoherence exactly work. I think it'll supplant Copenhagen as what we teach in intro classes eventually. But this is just my impression from the physics blogs and papers I've read; I'm not a physicist myself.
 Classical QM (Copenhagen, if I'm not mistaken) does have that problem. The collapse is indeed an additional hypothesis done on the part of the wavefunction the math already says we cannot observe. As always, unfalsifiable additional hypotheses are bad.I can't speak for De Broglie-Bohm, but it would seem that theory also have a similar strike against it: the math is more complex than the equations QM physicists are familiar with. It's just not the simplest theory that fits the observation.The obvious alternative is to just stick to the math. Problem is, the simplest math that explains our observations implies a universe that forks all the time. For some reason, possibly the intuition of a unique universe, many people cannot accept that.
 >Basically you get to pick between nondeterminism (randomness) and a global function that influences everything that's much more complicated.That sounds as if the universe is passing everything through an RNG monad.
 edit for typo since I can't edit the post:* caveat that it's not enough information to let you make any concrete predictionsOther afterthought: The pilot wave model is definitely not directly compatible with relativity, since it purports to have a function 'defined everywhere' at once, and the concept of 'everywhere at a moment in time' doesn't work in relativity. There are apparently methods of working around this, and they're apparently very complicated.
 that's not entirely true. Non-einsteinian relativity allows for functions 'defined evewyhere' at once. An example is tangherlini relativity, which allows for anisotropy of the speed of light (and is not inconsistent with contemporary observations IIRC)....
 Preferred foliation is the term. Ctrl-F it here:
 Well, I was looking at that page too, but didn't bother to quote what it's called because the term doesn't say anything useful.
 in his book on QM David Bohm gives a relativistic version of the pilot-wave theory
 There was a philosophical disagreement at the turn of the century where a bunch of ho-hums (including Einstein) decided to speak for everyone by saying everything here in this reality is discrete and isn't affected by anything anywhere else. A lot of work went into proving this over the last 100 years, with mixed results that just led to more and more testing at higher energy levels. With the Higgs, we started thinking we were "stuck" with our current theories. With the EM Drive, we're seeing things that don't fit in that model.Going back to when the original disagreement started, there were a few physicists like Bohm and de Broglie who thought there was more than met the eye going on with discrete particles past a certain size limit. Their theories included a medium, or ether, in which all of this exists. To understand it a bit better, you might want to check out the "two slit experiment". There's one on Youtube that covers doing the experiment with photos, electrons, buckyballs and polarized lasers. Basically, when you understand the experimental results, you understand that matter acts like a wave sometimes and a particle others, even at large scales.Those waves in the two slit experiment are likely responsible for the forces we're seeing in the EM drive. Also, I'm sure I've left out important bits here, but that's the basic idea.To the moon!
 Keep in mind there's no reason not to be hugely skeptical of the 'EM drive' right now.
 > conceptually simple terms?Physics does not seem to operate on conceptually simple terms. Three options, it is simple when approached from some way we have yet to think of. There is some inherent mistake we are making with a huge range of current experiments. Or, as seems most likely the universe operates very differently on different scales making it conceptually difficult to deal with.
 The Ptolemaic system was pretty complicated too...
 So that would be option one.
 I prefer to think of it as local variables over X amount of time. After that, they are non-local.
 What?
 Hmm, nope, sorry. I'll look that up.
 Regular QM has non-locality. Entanglement is non-local, at least any way that I've heard it to explain things like delayed choice erasers and the behavior of entangled anyons in confined electron gases. (Anyons (particularly fused anyons) themselves seem to have nonlocal quantum vales assocaited with them.)
 So we meet again, SomeStupidPoint. :) I still uphold my claim that regular QM is a local theory and just found time today to reply to your comment on non-locality that you posted a week ago:https://news.ycombinator.com/item?id=12936699Let me know what you think!
 The many-worlds interpretation doesn't need non-locality.
 Bell's Theorem states that there exists no local hidden variable theory for QM. AFAIK that implies that QM must be non-local because the other possibilities of a local theory can be reduced to a hidden variable theory or have no evidence for them.
 Not true. Bell's result precludes local realism. So physics is either not local or lacks realism (counterfactual definiteness). The Many Worlds Interpretation keeps the locality but lacks counterfactual definiteness. The fact that MWI is the only interpretation that manages to hold onto both determinism and locality is what makes it so aesthetically pleasing.
 Many-worlds still has nonlocal entanglement, IIRC, and all the weird phenomena therein.
 It does not require FTL signalling for the entanglement to work.
 Care to make rigorous how other interpretations require FTL signaling? For that matter, can you actually rigorously explain what it means for worlds to "branch", or why Born probabilities should be interpreted as though they are probabilities in MWI? Saying "all the possibilities actually happen!" doesn't really explain the correlations we actually observe in any interesting way.
 You make some good points. Regarding the Born probabilities, the extrapolation of Schroedinger equation to the whole universe seems to make the concept of probability superfluous and the Born rules lose their sense.
 > This is pretty good news if only that we will get more research into this phenomenon.Agreed.> Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed.I'm not sure that actually works. Most use cases are for exploring the outer solar system, or even outside of our solar system. As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration.
 > As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration.In space you move in elipses. It's possible to choose an elongated orbit that moves the probe closer and then further from the sun repeatedly and each time it is close to the sun it accelerates forward, moving the "far" side of orbit further away, until it gains enough speed to escape sun gravity.Or at least it's possible in Kerbal Space Program :)
 Yes, you move in ellipses; but you spend a lot of time far away and very little time close to the sun. I'm not sure that the average power is any higher than you would have for a circular orbit at the same energy...EDIT: Ok, let's think through the calculus here. Kepler's 2nd law says that the area swept by the line between a planet and the Sun is constant, i.e., r^2 dθ/dt = 2 π a b / P where a and b are the semi-major and semi-minor axes and P is the orbital period. Thus dt / r^2 = P dθ / (2 π a b); and the former is the instantaneous power absorbed. Integrating over an orbit, we get E = P / (a b); or the average power absorbed is proportional to 1 / (a b).Since the energy of an orbit is determined solely by the semi-major axis a, this means the power absorbed for any given orbital energy is maximized for b ≪ a; so you're right, that highly eccentric orbits are a better way to acquire energy for the purpose of orbital escape. (Subject of course to practical considerations of energy storage -- you'll absorb the most power at exactly the time you don't want to be changing your momentum.)
 > you'll absorb the most power at exactly the time you don't want to be changing your momentumThanks for doing the math. But I'm still confused, I thought you do want to accelerate when near the sun, as that makes the far end of the orbit go further? Again, no math behind, just how it worked in KSP :)
 Whoops, you're quite right. I was thinking that you wanted to add momentum when you were moving the slowest, but that's for when you want to get into a circular orbit (which is the opposite of what you're talking about).You should trust KSP more than you trust me. :-)
 It's Oberth effect, basically? :).http://www.askamathematician.com/2013/01/q-how-does-the-ober...By the way, I only know about it because I played KSP a lot ;).
 Does the Oberth effect really apply when your propellant mass is always zero?
 The simplest way (imo) to think about the Oberth effect is "you want to maximize the amount of time you're falling inwards (i.e. speeding up) and minimize the amount of time shooting outwards (i.e. slowing down.)"It doesn't just work with orbits and rockets and propellants, it works just as well with an oscillating weight on a spring that you flick with your fingers.
 It's about ∆v, so I'd say it does regardless of how you got that ∆v. I don't see a reason it couldn't work with solar sails, for example.
 If anything, it should increase your inertia, since you're not sacrificing mass for ∆v.
 my attempt at a thought experiment that seems to suggest elliptical orbits are better in this regard:if you have an efficient insulator, you could absorb an arbitrarily large amount of heat at the perigee, and retain it for the remainder of the orbit.if you were in a circular orbit, you'd only be able to absorb up to the ambient temp.
 Ambient temperature is a red herring; the sun is hotter than the ambient temperature so you can always win by absorbing energy from the sun and then emitting it to the rest of space.
 Nuclear/Batteries
 Wait, what? I thought Bell's Theorem made local hidden variables a no-go? Care to elaborate?
 > This is pretty good news if only that we will get more research into this phenomenon.Or maybe it's just a waste of time/money? (I'm not being facetious for the sake of it. See cjensen's comment[1])
 Nothing in that comment is news, but if we've reached a point where we're completely unwilling to accept that experiments could show us something new before theorists predict and explain it, then we should hang up our science hats and go home.Skepticism is warranted, but the team behind this study seems to be proceeding with a healthy dose of it, and AFAIK they have not made any inappropriate claims. The results so far are interesting, the experiments do not seem terribly expensive, and I see no reason why they shouldn't be followed to their conclusion (which will probably be the discovery of a mundane explanation for the phenomenon that's been observed).
 Are you actually worried that all of the world's scientists are completely unimaginative and incompetent? I don't understand why you'd escalate it this way just because this topic comes up. That certainly doesn't sound like a reliable frame of mind in which to be.
 You seem to be looking at my comment through a radically different lens than I was when I wrote it. You know it was in reply to another comment, right?
 > Nothing in that comment is news, but if we've reached a point where we're completely unwilling to accept that experiments could show us something new before theorists predict and explain it, then we should hang up our science hats and go home.Yes, but nobody's ACTUALLY saying that -- that's just the typical narrative of people-selling-perpetual-motion-machines. (Who, you'll note, have a slightly different agenda.).What's actually going on is that everybody's saying "this would require New Physics -- hold your horses!"... and the response seems to be "YEAH, BUT WHAT IF?!??!".Pithy answer to the "what if" challenge: Not good enough.
 But the question of how the scientific community should be reacting to this, and whether more time and money should be thrown at these experiments, seems wholly separate from the question of how the public should be reacting.You asked "Or maybe it's just a waste of time/money?", which is a question for the scientific community, but most of the "WHAT IF?!??!" reactions seem to be coming from the public.edit: I replied before you edited your post fairly heavily; I think what I said still applies, though.
 Apologies for the ninja edit! I tend to leave fairly heavy markers around, but didn't this time[1] -- just didn't expect that someone would respond so quickly!> You asked "Or maybe it's just a waste of time/money?", which is a question for the scientific community, but most of the "WHAT IF?!??!" reactions seem to be coming from the public.I really don't understand this. Is this some sort of PoMo response to my original challenge, or...?My contention is that the public interest may not necessarily have much to do with what the public is interested in. I don't think this a particularly controversial PoV...?(Though I do have reservations about it, but -- personally -- I've just about given up on even basic scientific literacy. You may be less jaded.)[1] Readability suffers, but DFW approves "from heaven". I must admit I'm quite DFW-like in that I cannot halt the loop before I write something, so here we are... with massive edits and such.
 > Apologies for the edit!No worries> I really don't understand this. Is this some sort of PoMo response to my original challenge, or...?What's PoMo?My interpretation of your first comment was that you were questioning whether this research is worth more time and money based on skepticism rooted in scientific knowledge i.e. these "new physics" needed to explain the EmDrive would conflict with a lot of what we currently think of as scientific "fact". Occam's razor, and so on.My interpretation of your second comment was that you think the "YEAH, BUT WHAT IF?!??!" reactions to this research (generally associated with internet comment sections) are inappropriate and rooted in ignorance of scientific principles (FWIW, I agree with you on that).I see those as separate concerns. The public is wholly ignorant, and their reaction to the results of this research to date (filtered as they are through awful clickbait articles) should have no bearing either way on whether the research continues. That's the point I was trying to make in my second comment.> My contention is that the public interest may not necessarily have much to do with what the public is interested in. I don't think this a particularly controversial PoV...?I don't think so either (and I agree).
 > What's PoMo?PoMo refers to Post Modernism , which is afaiu , "Literary/whatever Theory" that, I think, seems to embrace reletavism
 >Or maybe it's just a waste of time/money?We are currently shooting missiles that cost $800,000 each at people in caves on the other side of the world from boats that cost$4.4 billion dollars each. If anyone can justify that expenditure, I think we can find a small fraction of that money to investigate this further.
 Well, for one thing, that srticle describes a future warship and ammunition that is not yet in service, so it is incorrect to suggest anyone is 'currently shooting [...] at people in caves' with it.However, the justification (OK, a justification) for that action, as part of the war on terror (I believe this is your implication, based on the 'caves' reference) would be that the insured costs of 9/11 were around USD 40 billion [1] (ignoring the unknown intangible additional cost in human life) so spending USD 800000 to kill a terrorist who is planning to perform a similar event is something of a bargain.But, this sort of logic is flawed to begin with: We spend X on Y, which I disapprove of, therefore we should spend epsilon on Z instead.
 It not a "future" warship. Its an existing warship that keeps breaking down, despite the fact that its new and cost $4.4 billion to make. It just broke down again in the Panama Canal. That's a picture of the actual, existing-in-the-present ship.http://www.military.com/daily-news/2016/11/22/new-zumwalt-br...>However, the justification (OK, a justification) for that action, as part of the war on terror (I believe this is your implication, based on the 'caves' reference) would be that the insured costs of 9/11 were around USD 40 billion [1] (ignoring the unknown intangible additional cost in human life) so spending USD 800000 to kill a terrorist who is planning to perform a similar event is something of a bargain.Except for the fact that that justification is false. We've spent over$5 Trillion fighting the fictional "war on terror" in the 15 years since 9/11 and by every measurable metric there are more "terrorists" (people who would like to attack us) today then there were on 9/11.http://www.military.com/daily-news/2016/09/13/report-nearly-...This dwarfs by many orders of magnitudes the total science funding spent by the government since the government was formed. Its absurd to discuss "waste" or "inefficiency" in any context, let alone a tiny expenditure for investigating the EM drive, while ignoring the elephant in the room. The phrase "penny wise pound foolish" applies to that line of thought.
 > It not a "future" warship. Its an existing warship that keeps breaking down, despite the fact that its new and cost $4.4 billion to make. It just broke down again in the Panama Canal. That's a picture of the actual, existing-in-the-present ship.It's in the Panama Canal going from it shipyard to homeport. It isn't yet in service. Apparently the combat systems are not even installed yet. I believe that is what your parent poster means. [1]  Speaking as a experimental physicist:The research shown is relatively inexpensive, and can be pulled off with what many labs probably have lying around anyways.I'm sure it's more a work of love anyways and the guys doing this are probably facing serious headwind for trying 'crazy stuff'.  This paper that investigates how the EM propulsion drives might generate thrust, and as a side effect, the theory explains certain phenomena that we attribute to dark matter and dark energy. i only have undergrad physics degree, but it sounds interesting. anyone with more experience have any thoughts about this?http://arxiv.org/pdf/1604.03449v1.pdf >McCulloch (2007) has proposed a new model for inertia (MiHsC) that assumes that the inertia of an object is due to the Unruh radiation it sees when it accelerates, radiation which is also subject to a Hubble-scale Casimir effect. In this model only Unruh wavelengths that fit exactly into twice the Hubble diameter are allowed, so that a greater proportion of the waves are disallowed for low accelerations (which see longer Unruh waves) leading to a gradual new loss of inertia as accelerations become tiny. MiHsC modifies the standard inertial mass (m) to a modified one (m_i) as follows: m_i = m (1-(2c^2)/(|a|Θ)) = m (1 - λ/4Θ) (1) where c is the speed of light, Θ is twice the Hubble distance, ’|a|’ is the mag- nitude of the relative acceleration of the object relative to surrounding matter and λ is the peak wavelength of the Unruh radiation it sees. Eq. 1 predicts that for terrestrial accelerations (eg: 9.8m/s2) the second term in the bracket is tiny and standard inertia is recovered, but in low acceleration environments, for example at the edges of galaxies (when a is small and λ is large) the sec- ond term in the bracket becomes larger and the inertial mass decreases in a new way so that MiHsC can explain galaxy rotation without the need for dark matter (McCulloch, 2012) and cosmic acceleration without the need for dark energy (McCulloch, 2007, 2010).  McCulloch's papers have many, many problems[1]. No credible theory has been posited to date, and the experimental evidence fails to properly address systematic errors. If this device worked, one could use it to create an over-unity generator. It would also invalidate most of known physics. The chances of it working are nonzero, but that's the best that anyone can say about it. Most likely it will waste people's time and money for a few years before the public loses interest.  I mentioned this elsewhere in this thread. I'm really interested to hear some context around it from someone who knows what they're talking about; to me, it's a more appealing explanation than "conservation of momentum is wrong" or "we're using the quantum vacuum as a tractive medium which is supposed to be impossible but whatever".  IANAP, just someone with a lay understanding that's been following a lot of these topics for a while now.As I understand it McCulloch's requirement that wavelengths fit within the cosmic horizon is an assumption, not a proven logical implication.Additionally I think a lot of physicists are dismissive because they expect someone who desires to upend mainline theory to at least demonstrate fluency with the mathematics of mainline theory. McCulloch falls short of this.All that said, I think he's genuine in his pursuit and I've really enjoyed reading his blog over the years.  McCulloch's papers aren't very well-regarded because he was originally a biologist, not a physicist, and his theories (accompanied by blog posts) are very unconventional. I'm not trying to slime him or anything, just explain why he isn't cited often - I'm not well-educated enough to understand his work.  Shouldn't crazy stuff be exactly why we fund tenured positions?I would like to think tenure still produces crazy scientists  > Shouldn't crazy stuff be exactly why we fund tenured positions?Crazy stuff becomes an option after one is granted tenure, it doesn't necessarily make one more likely to achieve tenure. On the other hand, theoretical physicists aren't very expensive -- they only need a blackboard and an eraser. Compare that to a philosopher -- much the same but without the eraser.  Badah dum tish!  Classic, textbook example of lifeisgood-oceanswave syndrome.  I think you misunderstand. Tenure is usually granted to people with a (sometimes minor) track record of their ideas working out. Essentially it amounts to a bet on things to come, or IOW of "is person X a crank or not?". This, of course, is also tied to the field in which they are working, etc.(Sure, some good researchers turn into cranks later in life[1], but usually in a different -- often unrelated -- field.)[1] Nobel prize winners often succumb to this, sadly.  Seems like having the preeminent researchers in a field be the ones to do the weirdest research while teaching students on the foundations and established research is a pretty solid decision.  I guess you're referring to Brian Josephson, who went from superconductors (Nobel prize) to things like telepathy etc. but I'm interested if there are other examples. A quick search turns up Kary Mullis as a possible other example, but I don't know too much about him, and it's a difficult topic to research.  Linus Pauling (two Nobel prizes!) jumps to mind with his Vitamin C work  What similar research is the time and money better spent on?  Actually it's not as much useful as an engine as it may seem, at least at current parameters. Ion thrusters are pretty good as low-power engines. And it's not clear that emdrive is better than that even if it works. Maybe with powerful space-based nuclear reactors  The difference is that eventually you run out of ions to thrust.  Practically speaking though the power generation is the limiting factor. An emdrive requires way more power, which means way more generating capabilities, which ends up taking up way more mass on your spacecraft than the ion engine reaction mass.  If you have a nuclear reactor, the power vs mass loss could end up working in favor of the emdrive, especially for long range interstellar flights. None of this is, of course, practical anytime soon...  Nuclear reactors are incredibly massive though, especially with all of the required shielding. We've never launched anything even as close to as massive as a space-borne nuclear reactor would be. I agree with you that it won't be practical anytime soon (or at least not politically), so as long as we're positing some future level of tech, why not nuclear fusion?  Due to political and environmental concerns alone no modern terrestrial reactor design would be allowed to fly. That's usually not what nuclear propulsion proponents argue for.There are several other reactor designs that have been researched over the last half century that can operate in a closed loop with much smaller amounts of nuclear fuel and more manageable radiation emissions. Designs like the nuclear lightbulb, which was researched by United Aircraft Corporation and NASA for almost a decade before the plug on the Mars mission was pulled in the 70s, are much better suited and are what proponents of active nuclear propulsion most often have in mind. Once there is some political will, we have decades old research to start from to build a flight capable nuclear reactor.  The nuclear lightbulb doesn't generate power though -- it's a rocket engine, and "generates" reaction mass leaving at high velocities. So it's not suitable for use powering an emdrive, the whole point of which being indefinite flight without needing to use up any reaction mass, which a nuclear lightbulb can't do.  No, the nuclear lightbulb generates energy in the form of heat and electromagnetic radiation. How you use that energy output depends on the design of the reactor and propulsion system.You can seed expanding liquid hydrogen in the outer cavity with tungsten nanoparticles which absorb the UV radiation to heat the hydrogen for use as a propellant. You can pump the outer cavity with a UV transparent coolant and line the walls with parabolic photovoltaics (that convert UV instead of visible spectrum) for direct conversion of the black body radiation to electricity. You can theoretically even create a magnetohydrodynamic "turbine" in the outer cavity that is coupled to the spinning nuclear fuel (which can be charged plasma).You may be thinking of an earlier that was mistakenly called nuclear lightbulb or another design that was lumped into the concept. The variation I have in mind is just as general purpose as any other nuclear reactor, it just uses a lot less fuel and has to actively maintain temperature and pressure to keep the neutron cross section energy high enough to sustain power positive fision.  Do you have a link with more information to the specific concept that you're talking about? It looks like I was led astray by the Wikipedia article. I'm super interested.  Nuclear reactors have actually been launched into space multiple times [0][1]. Note, however, that their power output was on the order of a few kilowatts.  Wow, that's awesome. I hadn't realized. Unfortunately those systems were fraught with problems (that persist to this day in their orbital debris), but they flew and they worked. Looking at the power generation capacity of those reactors vs their mass, however, they weren't even that much better than plutonium RTGs! The TOPAZ generated 5 kW using a 320 kg reactor, and was only good for five years. That's 15.6 W/kg. Meanwhile, the standard RTG design we've been using in recent space probes, including New Horizons, generates 300 W at 57 kg, or 5.3 W/kg, but the half-life is a long 87.7 years and the system doesn't suffer the kind of wear problems that a nuclear reactor does, so the total lifetime energy output is substantially greater. This would matter for interstellar probes with near-present levels of technology, assuming a working emdrive but nothing else.  I don't really see a huge difference between a spaceborne reactor and the kind that have been in constant use for decades in submarines. We just need a new Admiral Hyman Rickover to make it happen safely and effectively.  Two big problems:1. Details on submarine nuclear reactors are classified, but five minutes' Googling shows that a reasonable guess for their total mass (including shielding) is 1,000 tons. Meanwhile, the entire payload to LEO of the largest rocket ever successfully launched, the Saturn V, is only 155 tons -- and that's for the entire top stage.2. Submarine nuclear reactors use water for cooling. Water that is not available in space. Cooling would be a huge problem.So, existing submarine designs are not practical. You'd need to design something from the ground up that is much lighter, and the cooling system would be entirely different and likely more massive, since you don't have all of that free water available to dump heat into. Instead you're talking massive radiators.  Good point re: the mass of the reactor, that's a hell of a lot more than I'd have guessed.But any mission involving humans is likely to carry a large amount of water beyond the crew's personal needs, because it makes such a good radiation shield. So presumably the same water would be used for cooling the reactor.  I am not convinced, if you can fly a reactor : https://en.wikipedia.org/wiki/Convair_NB-36H then I feel it unlikely that it weighs 1000 tons.  It all depends on the size and design of the reactor, though. A reactor that you put on a plane just for the hell of it (which is what that was) is going to be a lot smaller and lighter than a nuclear reactor that needs to power an entire submarine. The point to my reply was that submarine nuclear reactors were in no way suitable for space use because they aren't optimized for weight at all. Reactors optimized for plane use would be a closer fit. The reactor in that plane could be lifted to orbit on a Saturn V, so we're making progress, but, and this is a huge but, it was air-cooled.A 3 MW reactor puts out a hell of a lot of heat, and without the benefit of air-cooling in space, I'm not sure what exactly you would do with all of that waste heat. Consider how massive the space shuttle orbiter's radiators were (they are on the inside of the cargo bay here: http://i.stack.imgur.com/Flgzb.jpg ), and all of that is only capable of shedding waste heat in the amount of ~6 KW! We can put a much more capable reactor into space than we can possibly cool, so we haven't bothered. Cooling is the real problem. The total mass of the radiators and the structure required to support them ends up being way more than the reactor itself.So for good long distance transportation in space, not only do we need a working, efficient emdrive, but we also need better power generation that is much more efficient from a waste heat perspective. These are really hard problems.  You don't have to set off the equivalent of 500,000kg of TNT at the business end of a submarine to put it into the water.  did you not read the article? to mars in 70 days, i believe it says..  We can get to Mars in 90 days with chemical propulsion, today.  and this refutes how?  > Actually it's not as much useful as an engine as it may seem,It's worth more than any existing or previous theoretical engine. Put this rotating around a center point. Now put 1000s of them. Now we have power generation for outposts in space. The implications of a working EM drive are staggering.  The emdrive (at least the current version) requires way more power per Newton of force than even ion engines, which are themselves famously power hungry. You definitely could not get free energy out of an emdrive because the amount of power required to run it is way more than you'd get out.The advantage of the emdrive is that it does not require reaction mass, at the cost of incredibly high power consumption. Unfortunately that makes it not really viable for anything; ion drives are limited by power, not reaction mass, so the emdrive is actually worse because it uses way more in power than it saves in not needing reaction mass.  The drive being power hungry would not change the fact that kinetic energy goes up quadratically with speed (E=(m*v^2)/2) while this drive supposedly can keep accelerating with only constant power input. So kinetic energy would go up quadratically with time while expended energy only goes up linearly. You'd get free energy very soon.Since violation of conservation of energy is very unlikely, I'd say that this is a sign that the drive doesn't actually work. Or at least that there is some gotcha that we haven't understood yet.  Anything keeps accelerating with only constant power input. That's literally how all rockets in a vacuum work. Nothing special with an emdrive there. It doesn't mean that perpetual motion is possible, it just means that you're wrong about the ramifications of kinetic energy vis a vis power generation.  A rocket using chemical energy at a constant rate does not have this problem, because the excess energy it seems to gain from kinetic energy going up quadratically is balanced by a decrease in the kinetic energy that the expelled reaction mass is left with.  If you think of mass as the deformation of spacetime, mass reaction engines push off the wake from expelling mass rapidly in one direction to go in the other direction.The EM Drive is an energy reaction engine, rather than a mass reaction engine (if it works as described), so instead of pushing off wake, it uses energy itself to "deepen the fold", as it were, and increase speed (and mass, since the two are exchanged).That's interesting. I've never considered that the very act of increasing the velocity of the EM Drive would actually increase its mass. Hrm.  Not disagreeing with you there, but I don't see how that leads to free energy from an emdrive. How exactly do you get more energy out than you put in?And anyway, kinetic energy isn't a conserved quantity. It can be converted into potential energy in a gravity well, or lost entirely in inelastic collisions. Momentum is the quantity that is always conserved, and that is what the emdrive violates directly (though still not in a way that allows for perpetual motion or free power, near as I can tell).  As jack9 proposed higher up in this thread, you could put the EmDrive on the outside of a rotating system to provide constant torque, which accelerates the rotation. Then wait until the system has sped up to the point where the kinetic energy increases faster than the power you put in. Then use the whole thing to drive a generator.  I would think that once we determine the cause of the thrust, assuming it is real, the design of the 'drive' might be improved to increase efficiency. We currently don't even know what characteristics of the device are causing the generation of thrust.The first internal combustion engines were quite inefficient as well.  Here's hoping! It's so unbelievably inefficient right now though, it's hard to imagine it improving by orders of magnitude. The original internal combustion engines were comparatively way more efficient.  As I understand it, the version under test here was simply a proof-of-concept, not optimized for maximum efficiency. There are also plans for a version with a superconducting frustum, which should be even more efficient...  Naive questions from someone who does not understand a lot about physics (to put it mildly): Did you just invent the perpetuum mobile, or did I misunderstand what you said? Or do I just not understand how this thing is supposed to work?  Actually, yes!By special relativity you can't break the momentum conservation principle without breaking the energy conservation principle.Somehow most people feel more comfortable dismissing the momentum conservation principle, but they are intertwined.A carousel with Emdrives like the described in the previous comment should be a perpetual mobile and create energy if it's spinning in the right direction. (It will destroy energy in the reverse direction, so be careful.)[Anyway, I think that the emdrive doesn't work and the conservation of energy and momentum are safe.]  The Emdrive takes energy, though, doesn't it? It's not like you can plug it in and have it run, unless I misunderstand a lot of claims.  Yes.However, any true reactionless thrust is equivalent to a perpetual motion machine, because reactionless thrust drives produce the same acceleration regardless of speed, but the kinetic energy produced by the same acceleration goes up as the speed goes up.If you accelerate one kg from 0m/s to 1m/s, you impart 0.5joules of energy on it. If you accelerate it from 1m/s to 2m/s, you impart 1.5joules of energy on it. If you accelerate it from 2m/s to 3m/s, you impart 2.5 joules of energy on it, and so on and so on. Each added m/s costs more in energy.A reactionless drive working in a system with no preferred frame would add the same amount of acceleration for the same amount of cost, regardless of how much energy there already is. This would mean that eventually it would be going fast enough that the added kinetic energy would be more than however much energy it draws in. Then you can build a gigantic carousel that is spinned on the rim and takes energy from the middle and feeds some back in to move it, and now you have perpetual motion.This is why no real physicist actually thinks that this will be reactionless thrust. However, that does not necessarily mean it's useless. If it, for example, allows you to push against the earth's magnetic field more weight-efficiently than current magnetic propulsion systems, it would be a major win for satellite stationkeeping.  > reactionless thrust drives produce the same acceleration regardless of speedA) Where is that in the paper? Or am I missing something elementary to this?B) We don't even know if it produces the same level of thrust as speed increases. If it produces the same level of thrust across all speeds, then we have a problem, because as velocity increases, so does mass, and the same level of thrust would produce less acceleration over time, because of the increase in mass. Of course, that may only effect things at relativistic speeds.  Speed relative to what, exactly? There are no preferred reference frames. A true reactionless thruster could always treat itself as if it's initial speed was 0, and so it took 0.5J to accelerate by 1m/s.Rockets do that too, but they get away with it because they stored the necessary extra energy into the kinetic energy of the fuel.If there was a reactionless thruster that did, in fact, get less efficient at higher speeds, then that would also be world-shattering physics news, because then you could measure it's performance after accelerating in different directions and eventually get a true rest frame that is privileged over the rest of the reference frames out of it.  Put two emdrives on the ends of a rotating beam. Use the violation of conservation of energy/momentum to drive a generator. Infinite speed and energy are yours to command!  Driving the generator is going to rob the system of energy. That should be obvious, right? Nothing in the matter/energy equation is changing. This drive would just take electrical energy and convert it into kinetic energy.  He did, yeah. If it works as described, then you'd expect it to break conservation of energy along with conservation of momentum.That's another good reason to think it doesn't work.  He did not. The emdrive requires a very large amount of power to operate, way more per Newton than even an ion drive.  > Did you just invent the perpetuum mobile,That's the implication of the EM Drive. I didn't invent it, it's the very first thing that you think of once you violate the momentum conservation principle. This is why it's unlikely to be true, but at the same time an alchemists dream scenario.  This takes a huge amount of electricity to work.  What makes the power to power them?  easy: 1000000's of them rotating around a fixed point!  It's so frustrating. One micronewton per kilowatt. All that power going in, and so little force coming out. All it takes is some tiny noise effect to get that much force. The effect is so weak and they're so near the noise threshold.Quotes: "Components get warmer and the geometry changes slightly due to thermal expansion". "The thermal signal in the vacuum runs was slightly larger than the magnitude of the impulsive signal." "As the aluminum heat sink got warmer, its thermal expansion dominated the shifting center of gravity (CG) of the test article mounted on the torsion pendulum. This CG shift caused the balanced neutral point baseline of the torsion pendulum to shift with the same polarity as the impulsive signal when the test article was mounted in the forward or reverse thrust direction." "The seventh error is outgassing, which has the potential for a false positive from vaporization of surface molecules of the dielectric insert or other nonmetallic surfaces."  > It's so frustrating. One micronewton per kilowatt. All that power going in, and so little force coming out. All it takes is some tiny noise effect to get that much force. The effect is so weak and they're so near the noise threshold.Yep. Reminds me of psi. You can set up mechanical radiation-decay powered RNGs with pre-set runs of numbers in pre-registered double-blind experiments with remote audit logs analyzed carefully with permutation tests and randomness test suites, and all of the huge effects claimed by regular people and psychics go away... but you still get on net a slight excess of bit flips in the psi direction. Is psi real? Seems highly unlikely. But what could possibly be left - publication bias, fraud, or what? No one knows. At some point, effects become subtle enough that you just can't believe studies finding it on net - there's some sort of epistemological 'noise threshold' where stuff is happening but you don't know why or can come up with causal explanations.  > you still get on net a slight excess of bit flips in the psi direction.Is that "net" extracted from all published experiments, i.e. in some meta syntheses? And is statistically significance calculated in each individual experiment?> Is psi real? Seems highly unlikely. But what could possibly be left - publication bias, fraud, or what? No one knows.Publication bias toward positive results should be detectable via methods such as funnel plots.If you've looked into these aspects it would make interesting reading.  > Is that "net" extracted from all published experiments, i.e. in some meta syntheses? And is statistically significance calculated in each individual experiment?You can find excesses in both individual experiments and meta-analyses, IIRC.> Publication bias toward positive results should be detectable via methods such as funnel plots.Funnel plots have notoriously low statistical power, it would require only a little publication bias to produce excesses, and asymmetry in a funnel plot can be due to other reasons.  Thanks for these comments, will make for interesting investigations.  Dean Radin has published a lot on this topic. He has an interesting list of selected publications 1. A number of meta analysis are listed there. His book "The Conscious Universe" discusses many of the meta analysis in detail. Facinating stuff. He addresses the file drawer effect in depth.  The real mystery is why it always happens to people like White. Smart engineer who gets his PhD in physics at age 43.How can experimental physicists and research groups who have the decade of more experience avoid these traps?  I think they might be coming from a broader perspective: "If this is true then conservation of momentum and Noether's theorem are false, and we'd see that out in the wider universe: therefore this is a lab error and people who chase it obsessively are cranks."  I can't tell whether you're referencing a movie or talking about some interesting fringe science. If the latter, do you have any recommendations of papers I should check out?   No one knows  And no one needs to care. It shows that if psi exists, its practical value is zero, because it is weak and uncontrolled.  It's actually one millinewton per kilowatt, which I understand is only one order of magnitude off of current Hall thrusters. It's not great, but Hall thrusters are really useful for deep-space missions, so if this works, it could have use as a vehicle engine.  It seems it's their scaled-up estimate and that they actually measured micro Newtons, close to the margin of error of their setup? Specifically, the highest input power was 80 Watts, if I didn't miss some picture in the paper, which would give around 90 microNewtons actually produced per 80 Watts? So their summary seems to be misleading.I tend to believe that they measured "something" but that that something has some plain explanation.It seems that at the time the claims leaked (September) the figure was even "1.2N per MW", but still:http://www.forbes.com/sites/startswithabang/2016/09/02/nasas..."For the EMdrive, the device that was tested here, thrust was consistently observed on the device to be between 30-and-50 microNewtons, giving us that 1.2 N/MW figure. But the limits of the measuring device’s threshold was just 10-to-15 microNewtons! In other words, these results may be consistent and interesting, but this isn’t as robust as anyone wants it to be."  True but, according to some expert opinions I've read, if this thing pans out (and it's looking more and more like it will), that thrust is actually pretty damn good compared to other propellantless engines and not too damn bad compared to even conventional space probe engines.  [...] if this thing pans out (and it's looking more and more like it will) [...]Totally not, this is still with 99+ % a measurement error. We really understand theoretical physics pretty well, physicist have repeatedly predict measurement outcomes to a part in a million and less, have predicted particles decades ahead of the experiments discovering them. People really underestimate the power of theoretical physics and if there is a conflict between theory and experiment, it will almost always be the experiment that is wrong.  this thrust was not predicted by physicists. We have a repeatable non zero result where the prediction was zero.We also don't know how much it can be scaled or improved.  > We have a repeatable non zero result ...Yes, but they aren't sure what they're measuring. Remember that science (and Occam's razor) requires us to apply the most pedestrian explanations first, like some overlooked experimental error, not new physics. The "new physics" explanation should be the last possibility considered, not the first.This similar study comes to a much less encouraging conclusion (the abstract acurately summarizes the study):  the only reason HN is discussing this result is that it is unexpected. The point of the experiment is to zero out all pedestrian explanations.Occam's razor is a good guide, but it is not a rule the universe is obliged to follow.  > Occam's razor is a good guide, but it is not a rule the universe is obliged to follow.It seems to be, actually, because the rule follows straight from probability theory :).> The point of the experiment is to zero out all pedestrian explanations.Doesn't mean they did account for all of them. But that's why they're publishing. They've done all they could, they still get the unexpected effect, so it's time for other researchers to try it and at some point we will finally determine whether it's an error or new physics :).  No, we don't have a non-zero measurement where the prediction was a zero measurement. There are all kind of possible source of parasitic effects, especially because the measured signal is so close to the noise floor. The prediction for the ideal experiment is zero, actually it probably is not due to the impulse of the emitted photons, but for the real experiment the prediction is certainly not zero and the paper discuses and compensates for various parasitic effects.  i assume that this result is notable because they made all the needed corrections and took into account all known phenomena. Like serious scientists would.  They accounted for everything they could think of an that the experimental setup allowed to. It is still very much more likely that they missed at least one source of error than that our understanding of physics is wrong in such a serious way. Not that it is totally impossible that the effect is real, it just is still very, very unlikely.  Well that's why you publish research, isn't it? They accounted for everything they could think of, now they're giving everyone else a chance to spot mistakes.  Yes, of course. I never wanted to attack the paper in any way, I am just trying to say that this positive result will almost certainly turn out to be wrong and one should not draw the wrong conclusion that this is any kind of proof.  As did the OPERA guys, and yet a fiber optic cable attached improperly slipped through.  Experimental errors are very much predicted by physicists, though. https://en.wikipedia.org/wiki/Faster-than-light_neutrino_ano...  There seems to be a meme around the EmDrive where "it works" and "conservation of momentum is upheld" are mutually exclusive. Couldn't it be the case that there is some local phenomenon happening that we do not understand that still manages to maintain conservation of momentum? Isn't assuming that momentum conservation is violated a conjecture on the underlying physics of the device, which we don't know?  It's a little more complicated than conservation of momentum, which is just a subset of conservation of energy useful for intuition about the non quantum world. If you're converting energy into massive particles or photons for propulsion you can still have a "massless" drive while maintaining conservation of momentum because what you're really conserving is the total energy of the system. Research has previously shown that it is possible to create particles but it requires ungodly amounts of energy and a specially designed apparatus that separates the resulting particle and antiparticle using quantum effects before they can annihilate each other. There is even some research into using a vibrating "quantum mirror" that forces virtual photons to become real using only energy from quantum fluctuations but that's even more complicated and difficult to engineer.Either the EM drive has a unique combination of features that allows efficient creation and separation of particles using electricity, some other unknown quantum effects are present that can convert energy to momentum without an opposite reaction on another particle/field, or there is still a hidden error. Given the scientific knowledge we have today, it's extremely likely to be the latter but that doesn't preclude the possibility that we have discovered something novel.  If you use massless particles like a photon, the theoretical maximum trust/energy ratio is 0.0033 mN/KW. The problem is that they say they got x4000 the theoretical maximum.If you use a particle with mass, the trust/energy ratio is much lower. You have to split some of the energy to create the particles and convert a smaller part to momentum (you must multiply by c or c^2 to get the right units). So creating particles with mass is worse, not better.If you push a bunch of particles that you have stored, you can get much better result, but it's no more a fuelless drive.  Really annoying to see false expertise pop up again and again.> conservation of momentum, which is just a subset of conservation of energyThis is false. Momentum and energy are two different things, even with mass-energy equivalence. In particular, momentum is a vector while energy is a scalar, and their mass-energy equivalent units (impulse vs energy) are also different.Also: pair production doesn't necessarily require some amazing quantum device to keep the pair separate.> There is even some research into using a vibrating "quantum mirror" that forces virtual photons to become real using only energy from quantum fluctuations but that's even more complicated and difficult to engineer.This is true if you consider conservation of energy to be an engineering problem. Under no scientific theory can you pluck energy from the vacuum.  > Momentum and energy are two different things, even with mass-energy equivalence. In particular, momentum is a vector while energy is a scalar, and their mass-energy equivalent units (impulse vs energy) are also different.None of this is correct when you take relativity into account. In relativity, momentum and energy are both parts of a 4-vector, and that 4-vector is conserved. And in natural units, in which c = 1, energy and momentum have the same units. Particle physicists use these units all the time.  Yes, I know how the 4-dimensional momentum vector in relativity works.I'm not aware of a physical view for which energy and momentum are the same for the purposes of something like the EmDrive. In particular, you cannot completely turn one into the other by a choice of coordinates, and you cannot mix them by any physical process. And I could be wrong, but I'm 99% sure you need both energy and momentum conservation to get 4-momentum conservation.No matter your view, conserving the spacelike components of 4-momentum is not "a subset of the conservation of energy". And the truth/falsehood of this view has nothing to do with the "non quantum world". Relativity was an extension of classical electrodynamics before it was anything else.  > And I could be wrong, but I'm 99% sure you need both energy and momentum conservation to get 4-momentum conservation.I'm almost certain you're wrong. The most mathematically precise definition I remember for conservation of 4-momentum only requires that the interaction is invariant to spacetime translations. I don't see how that requires you to conserve both separately from the whole.> No matter your view, conserving the spacelike components of 4-momentum is not "a subset of the conservation of energy". And the truth/falsehood of this view has nothing to do with the "non quantum world". Relativity was an extension of classical electrodynamics before it was anything else.That was a poor choice of words on my part. I meant that an understanding of conservation of momentum based in classical mechanics is rather meaningless when talking about a drive that might use energy to create particles. What matters is that the total energy of the system is conserved and I stand by my choice of "subset" because momentum is not independently conserved. Calling conservation of momentum a subset of conservation of energy is not even close to calling energy the same thing as momentum and I have absolutely no clue where you got that idea.  > The most mathematically precise definition I remember for conservation of 4-momentum only requires that the interaction is invariant to spacetime translations. I don't see how that requires you to conserve both separately from the whole."Conservation" of a 4-vector means its components in a given inertial frame do not change. That entails that, from the viewpoint of a given inertial frame, the total energy and each individual component of the momentum are all conserved separately.  There's a confusion here which you still don't get. Momentum is not 4-momentum. Conservation of latter implies the former but the reverse is not necessarily true. And nothing in the above is a "subset of conservation of energy"--that's absurd.Actually, I'm not 99% sure, I'm 100% sure. It's very easy to imagine a relativistic system where momentum is conserved but energy isn't. Imagine if the universe was made of inelastic billiard balls, with no internal "heat", so every collision just lost energy. But momentum is still conserved.  > It's very easy to imagine a relativistic system where momentum is conserved but energy isn't. Imagine if the universe was made of inelastic billiard balls, with no internal "heat", so every collision just lost energy.This won't work. Let's suppose we have just two billiard balls, and that 3-momentum is conserved in the center of mass frame (in which it is by definition zero), but energy in this frame decreases at each collision. (Ignore the fact that this obviously implies that the 4-momentum of the system is not conserved, even though it is undergoing no external interactions.) Now transform into any other inertial frame. You will find that 3-momentum is not conserved either; it has a different nonzero value after a collision than before.  This is a bizarre comment. If we forget about energy, this is equivalent to saying 3-momentum is not conserved in inelastic collisions in real life. Which is false.  > this is equivalent to saying 3-momentum is not conserved in inelastic collisions in real life.No, it's not. In real life, energy is conserved, so the energy that is lost from kinetic energy in inelastic collisions needs to go somewhere. And whatever receives that energy will also have momentum (even if it doesn't in the center of mass frame, it will in other frames), so it has to be included in the accounting of momentum conservation as well as energy conservation. A relativistic theory that conserves energy as well as 3-momentum (i.e., standard relativity theory) will still conserve both energy and 3-momentum when you change frames, even in inelastic collisions. (In the simplest case, the lost kinetic energy goes into increasing the rest mass of the two billiard balls, by increasing their temperature.)What you hypothesized was something different: a hypothetical relativistic theory (which obviously does not match our actual world) in which energy is not conserved but 3-momentum is. In such a hypothetical theory, inelastic collisions could take place without the lost kinetic energy going anywhere: it simply disappears. I am simply explaining why such a relativistic theory is not possible: if energy is not conserved, 3-momentum cannot be conserved either (except in one particular frame, the center of mass frame, but that violates the principle of relativity so it is not allowed in a relativistic theory).  No, the 4-momentum is conserved as a vector given a reference frame, which means all 4 parts are conserved, which means 3-momentum is conserved. It doesn't "go somewhere".You seem to be obsessed about conservation of the magnitude of 4-momentum under Lorentz transformations. It's the whole vector I'm talking about, not the magnitude. and change-of-frame is not a necessary part of conservation laws.The claim that you can observe conversation in one frame but not another is absurd. The laws are affine; they hold in any frame or none.  > the 4-momentum is conservedIn standard relativity, yes. But not in your hypothetical "relativistic system where momentum is conserved but energy isn't". You said such a system was easy to imagine. I simply pointed out that, easy to imagine or not, such a system doesn't work. Nothing that I said about 3-momentum being conserved in one frame but not another applies to standard relativity where the 4-momentum is conserved. It only applies to the hypothetical system that you claimed was easy to imagine. I don't understand why you keep talking as though my comments about 3-momentum being conserved in one frame but not another referred to standard relativity.> It doesn't "go somewhere".By "go somewhere" I simply meant energy can get transferred from one part of the system to another. I didn't mean that total energy wasn't conserved (in standard relativity).> change-of-frame is not a necessary part of conservation laws.It is in a relativistic theory, since the principle of relativity requires that the laws of physics, including conservation laws, must hold in all frames.> The claim that you can observe conversation in one frame but not another is absurd.For standard relativity, of course it is. But not for your hypothetical system.> The laws are affine; they hold in any frame or none.This seems to contradict what you said earlier in the same post, that "change of frame is not a necessary part of conservation laws".  You seem confused by how conservation works, and intent on misunderstanding it.All I can say is that momentum conservation is Lorentz invariant in my system, and hence cannot depend on choice of reference frame. The conserved quantity is not invariant, and conserved quantities do not need to be Lorentz invariant, and fact almost always are not. If this confuses you, sorry, but I cannot follow your reasoning anymore.  > All I can say is that momentum conservation is Lorentz invariant in my systemIf by "my system" you mean your hypothetical theory where energy is not conserved but 3-momentum is, I strongly suspect you have not done the math. See below.> The conserved quantity is not invariant, and conserved quantities do not need to buslye Lorentz invariant, and fact almost always are not. If this confuses you, sorry, but I cannot follow your reasoning anymore.I understand what you are saying here, but it does not refute what I was saying. You are saying that, for example, in standard relativity, energy is conserved--in a given frame, it stays the same through any series of events--but it is not frame invariant; changing frames changes the energy. I agree with that.What I am saying is something different: in your hypothetical relativistic theory in which energy is not conserved, then 3-momentum cannot be conserved in any frame other than one particular one (which in my example was the center of mass frame). I am not saying the numerical value of the 3-momentum has to be the same in all frames. I am saying that in all frames but one, the numerical value of the 3-momentum, as evaluated in that frame, is different after an inelastic collision than before, i.e., 3-momentum is not conserved in that frame.Here is the math backing up that assertion. Suppose 3-momentum is conserved in the center of mass frame. In that frame the 3-momentum is zero. We assume that our system consists of just two billiard balls, each with the same rest mass m. Before the collision, one ball has speed v and the other has speed -v (we can restrict ourselves to one spatial direction). After the collision, one ball has speed w and the other has speed -w, where w < v (because the collision is inelastic). So 3-momentum is zero before and after the collision in this frame, and energy is not conserved--it is smaller after the collision.Now transform to any other frame. Call the relative velocity of the Lorentz transformation u. Then, in this frame, the speeds of the two balls before the collision are (I am using units where c = 1)v+' = (u + v)/(1 + uv)v-' = (u - v)/(1 - uv)and the speeds after the collision arew+' = (u + w)/(1 + uw)w-' = (u - w)/(1 - uw)Now we evaluate the 3-momentum in this frame. Before the collision, it ism ( v+'/sqrt(1 - (v+')^2) + v-'/sqrt(1 - (v-')^2) )After the collision, it ism ( w+'/sqrt(1 - (w+')^2) + w-'/sqrt(1 - (w-')^2) )Substituting and straightforward algebra simplifies these tobefore = 2mu/sqrt[(1-u^2)(1-v^2)]after = 2mu/sqrt[(1-u^2)(1-w^2)]These are obviously not equal, hence 3-momentum is not conserved in this frame. (In standard relativity, where energy is conserved, 3-momentum would be conserved as well; as I mentioned before, the simplest way for that to happen would be for the two billiard balls to heat up, increasing their rest mass. More complicated ways would involve other particles, or the billiard balls emitting radiation, or something like that.)  Just to clean up one item: I did assume in the above that the rest mass of the billiard balls was unchanged in the inelastic collision. But we can drop that assumption and still prove that, if energy is not conserved in the center of mass frame, 3-momentum cannot be conserved in any frame other than the center of mass frame. Suppose the rest mass of the balls after the collision is M (instead of m). Then we have for the 3-momentum before (P0') and after (P1') the collision, in a frame with velocity u relative to the center of mass frame:P0' = 2mu/sqrt[(1-u^2)(1-v^2)]P1' = 2Mu/sqrt[(1-u^2)(1-w^2)]But we can simplify this by writing down the total energy before (E0) and after (E1) the collision, in the center of mass frame:E0 = 2m/sqrt(1-v^2)E1 = 2M/sqrt(1-w^2)So we can see thatP0' = E0 (u/sqrt(1-u^2))P1' = E1 (u/sqrt(1-u^2))Hence, if E0 > E1, we must also have P0' > P1. In other words, the only reason we happen to have P0 = P1 in the center of mass frame is that being in that frame is equivalent to having u = 0 in the above formulas.(It is also straightforward to show that if energy is not conserved in the center of mass frame, it is not conserved in any frame. So the Lorentz invariance of the two conservation laws, energy and momentum, cannot be separated--they are inseparably linked.)  Right, most people think of mass energy equivalence which is E=mc^2 but this only describes energy for a mass at rest, with a momentum of zero. The full equation relating energy to intrinsic mass and momentum is E^2=(pc)^2+(mc^2)^2 which is why smashing particles in a collider works. The momentum of two particles colliding at relativistic speeds is "conserved" in the classical sense but it is really converted to photons and massive particles, among other things.What I meant in my original post was that intuition regarding conservation of momentum in classical mechanics may not apply here because as long as the total energy of the system is conserved, the EM drive is free to convert energy to particles and motion because momentum will still be conserved between the drive and the new particles (which is how regular chemical propulsion works). The system experiences a net change in momentum of zero but what matters is that the total energy of the EM drive slowly falls as energy is converted to particles that provide propulsion.  > the EM drive is free to convert energy to particles and motion because momentum will still be conserved between the drive and the new particlesI agree that this would conserve momentum if if were what was happening in the EmDrive. But all of the papers I have read insist that it is not what is happening; no particles are being ejected from the test device; there is no "rocket exhaust".  How do they measure the exhaust? With the EM field in the cavity I would imagine precisely measuring the photon emissions would be very difficult and the SNR might not be high enough to draw a conclusion. If the force is generated by new massive particles it would be headline news in experimental physics as the most efficient energy-mass converter ever made but if it's somehow generated by high energy photons, what are the chances they have adequate imaging to measure UV, X, and gamma rays, especially if the emissions have some sort of complex interference pattern? (although the theoretical maximum for force/power input is much lower with photon pressure than the results in this paper so it's still unlikely)  > How do they measure the exhaust?I don't know that they are specifically looking for any exhaust other than RF emissions (which they say are not observed). If there were in fact an exhaust at some other frequency I don't know that it would be detected. (If such were present it would still be rather unexpected, in my view; there is nowhere near enough energy being pumped into the apparatus to start creating particle-antiparticle pairs, or to trigger any kind of process that would produce UV or X or gamma rays.)  "Under no scientific theory can you pluck energy from the vacuum."You can if you're very patient, have a lot of material, and lucky aim, thanks to the metric expansion of space.From within a galaxy cluster shoot one end a very very long wire into the central black hole of a galaxy in a distant galaxy to anchor the far parts of the wire, and wind some near part of the wire around the pole of an electrical generator in your galactic cluster.You won't get much power for a long time by human standards, but you'll get an awful lot of energy (and eventually substantial power give or take divergence in the stress-strain tangent modulus and related quantities) even after the gravitationally anchored far end has receded outside your generator's Hubble volume.Mining \Lambda dark energy for fun and profit, brought to you by$nabla_\mu T^{\mu\nu} = 0$, where$nabla_mu$is the covariant derivative. It only takes a large up-front investment that you'll wish you had made billions of years ago.  Did you see my response to the parent, where I give a sketch of how conservation of momentum follows directly from conservation of energy in all frames of reference? What is your objection to that argument?  Remove either conservation law and work out the equations for an elastic collision, and you'll see a new degree of freedom pop up. In classical mechanics they are logically independent, and since the space is affine, frames of reference don't help you.Your sketch takes as a premise, something that is actually a consequence of conservation laws: the way quantities change under frame-of-reference changes.You can get both by looking at the least action principle under frame of reference changes and using Noether's theorem, but that's not what your sketch is about.  You've got it backwards: in an elastic collision, kinetic energy is conserved by definition. Removing one conservation law makes the whole exercise physically meaningless because elastic collisions require as a given that kinetic energy will not be converted to other forms of energy. This premise guarantees that the momentum is treated as a quantity separate from the total energy of the system (which, as a reply to your first post pointed out, when expressed in relativistic units, includes not just the energy-mass equivalency but energy-momentum as well).In reality, momentum in almost every collision will be converted into other forms of energy such as when intramolecular bonds are broken and materials are deformed in a car accident or when momentum is converted into mass in particle colliders. The elastic collision equations are only useful as a rough approximation precisely because they go out of their way to simplify the energy-momentum equivalence to conservation of kinetic energy just like Newtonian mechanics is a simpler but useful rough approximation of relativity at low energies.You can't use elastic collisions to reason about energy-momentum equivalence because their most basic assumption is that there is no energy-momentum equivalence.  Is there some objective sense in which conservation of momentum is more fundamental than conservation of energy in a different reference frame? Since either can be derived from the other, how do you determine which is "actually a consequence" of which? (I ask out of genuine curiosity)  Well, what is fundamental isn't the point. If you imagine a world where different quantities are conserved, there would no doubt be different change-of-frame equations describing how they are. The point is you can imagine a world where energy is conserved but momentum is not. Actually it's possible to imagine physical systems, with affine frames of reference, where nothing is conserved at all.Fundementality is a different thing, but it's more natural to assume conservation laws and take frame-of-reference equations are a consequence. You can do it the other way (I'm pretty sure, but not 100% sure because my physics math is rusty) but you're still making assumptions, and you still don't have one conservation law following from the other.  Excuse my almost complete lack of knowledge of physics but when you say it is possible to create matter from energy but you must separate the particle/antiparticle pair is this not similar to what happened after the big bang and did that not result in an asymmetry of particle/antiparticles, at least as far as we can tell? Could it be that there is some other way to either separate the particle pairs or create particles sans antiparticles that does not require a complicated apparatus? Perhaps the EmDrive somehow approximates the conditions of the early universe in some miniscule manner.Honestly, I'm clutching at straws but I can't believe that the only way to create matter from energy is with some complicated device since the existence of the universe seems to say otherwise. As an example, compare our attempts at creating fusion with the 'solutions' that nature has come up with.  The open question abut the universe here is where did all that missing antimatter go? Because we can't find it so far. EmDrive could hint at an answer, but on the other hand it also could not. We need to figure out what's going on with the drive (and whether it really isn't an error) to be sure.> compare our attempts at creating fusion with the 'solutions' that nature has come up withWell, if you just want to have a nature-like fusion, we've figured that out in the 40s and made it work in the 50s ;).https://en.wikipedia.org/wiki/Thermonuclear_weapon#HistoryOur attempts at fusion are now focused on getting useful energy out of it without incinerating everything around the reactor.  I had never realized that conservation of momentum is just a special case of conservation of energy, thank you for sharing this interesting observation! (I see now that, since the change in energy when changing the frame of reference is determined by the dot product of the momentum with the velocity of the new frame of reference, conservation of momentum follows from conservation of energy in _all_ frames of reference)  Coming from complete ignorance here, but wouldn't conservation of momentum be upheld if there is some medium that the emdrive is reacting against? For instance, a propeller driven motorboat doesn't need propellant to move, as it displaces water. Could there be some new force at work displacing (regular or dark) matter in the vicinity?  It's only exciting if it violates the conservation of momentum. If it doesn't, it's not useful as a space thuster or a flying car, and whatever is causing the miniscule force is just some leaky edge case that's difficult to measure.It's boring if it doesn't violate momentum conservation.  I dunno. Accidentally discovering a way to, say, shove dark matter around with microwaves and do useful work with it would not necessarily violate momentum conservation, and wouldn't really be that boring.(Not that I think this is what the EM drive is doing, or that I'd bet on it with anything other than very long odds, but I'm glad someone is looking into it).  Is it really true said "leaky edge case" is applicable throughout our entire local space? e.g. the solar system? or even the vicinity of Earth?  In high school my physics teacher taught us about induction and eddy currents. My group got to build a variation on a Gauss gun using a circular projectile that sat over a magnetic coil which an alternating current passed through. With the right frequency and voltage you could launch the ring across the room.My armchair crackpot theory is that's not what's going on here, but some other similar principle is at play. Some other physical law is behaving in a way similar to eddy currents, and the force comes from the field working against itself at a small delta-t  What if it's moving dark matter or some other kind of unknown substrate?  Not if it works by momentum being transferred through the power cable.  > Couldn't it be the case that there is some local phenomenon happening that we do not understand that still manages to maintain conservation of momentum?Ever hear of the Luminiferous Aether? From what I can tell, it could explain this phenomenon. Most people consider it an outdated crackpot theory largely because it's at odds with the entirety of quantum theory and the theory of relativity. But, this is the sort of thing that makes you go back to square one and re-consider everything you thought you knew.  L.A. isn't only problematic because it's inconsistent with theory, but also because it's inconsistent with experimental evidence. Michelson & Morley debunked it pretty thoroughly without having to invoke quantum or relativity IMHO.  Interesting what are the fundamental reasons for the thrust. It's certainly not throwing photons. Hypotheses:* Flawed study. It actually throws something (like, cavity material slowly ablating) or repels of Eddy currents in surroundings;* It repels of Earth (and the force has either gravitational or magnetic nature); then it's not suitable for deep space propulsion* A sort of ether actually exists, and it throws that. Though, then there would be some anisotropy showing ether wind; in this case it is suitable to be used in deep space  If you read through their conclusions, they suggest that there may be a quantum vacuum capable of transmitting oscillations and this vacuum is what this this device pushes off of leaving a wake behind.  [Disclaimer: I think it's a measurement error.]Just ignore the theoretical explanations. Just imagine that it's something they wrote to avoid the crackpot tag. That explanation doesn't make any sense. Also avoid all the other theoretical explanations, they are also very sloppy.Just concentrate in the experiments, that is the less sloppy part of these reports.If they discovered something new, then they can make a working prototype and improve it until it's clear that they are measuring something really new and it's not an experimental error or a misattributed force. They can make foolproof instructions so anyone can make a version in a good enough lab and reproduce the experiment, or sell an experimental setup in Ebay. Then it will "confirmed".There has been a many famous experiments that were later debunked, like:* cold fussion https://en.wikipedia.org/wiki/Cold_fusion , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment.* arsenic in DNA https://en.wikipedia.org/wiki/GFAJ-1 , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment.If you want success cases, my favorites are:* the asymmetric disintegration of cobalt in a magnetic field https://en.wikipedia.org/wiki/Wu_experiment , I guess they had some wrong explanation, but the correct explanation was discovered like 20 years later* high temperature superconductivity https://en.wikipedia.org/wiki/High-temperature_superconducti... IIRC they have some explanation or practical rules, but the correct explanation was discovered like 20 years laterJust concentrate in the experiments, and wait 20 years for a good explanation.  > They can make foolproof instructions so anyone can make a version in a good enough lab and reproduce the experiment,Is that not what this is? Roger Shawyer invented it, but NASA, NWPU and the Dresden University of Technology have all built and verified their own versions to work.  The TU Dresden people did not "verify" that the device works --- instead, they identified many spurious error sources, and recognized that the final results were essentially null on the level of measurement accuracy, and unable to say whether there's thrust or not.  Oops, you're right. Thanks for the correction!  AFAIK we still don't really have an explanation for high-temperature superconductivity. The state-of-the-art is several competing ones.  A few years ago I talked with someone that make and test high temperature superconductors in a lab (at very high pressure), and my impression was that the research community had a good understanding of what was happening, something related to flux pinning.I just read the Wikipedia article about this, and it's clear that the explanation is still not clear :(, so you are right.  pilot wave theory, the force is able to push upon itself despite lack of medium to otherwise push upon.  Ya, I was wondering the same thing. It seems like uneven ablating on the outside surface is the most obvious reason for the thrust.Why didn't they do a careful analysis of the cavity mass before and afterwards? Or electron microscope analyses of a few points of the outer surface before and afterwards to see if the microscopic topology changed?Did they rule these out some other way?  * It exploits some kind of bug in our matrix-like simulation that is supposed to have conservation of energy and momentum by design  This is the most terrifying. If we're part of an experiment then being aware of the experiment might cause it to be shutdown, like patients discovering if they're taking the placebo or not.  Placebo "works" even if the patient knows it's a placebo :).  If it repels of Earth, then it can be used to keep orbit.If there is an anisotropy in the ether, Sagnac interferometer should catch it.  I think regardless of if this ends up working or not, it makes some serious changes to how science perceives the universe.  There is an elaborate analysis of potential error sources, which I appreciate highly. However, I would have preferred a more rigorous quantitative analysis.The offered explanation model is highly fascinating. I'd appreciate if somebody would chime in with a more understandable version or resources thereto.  A while back I read an interesting but possibly also batshit crazy article that proposed an explanation possibly involving something like quantization of inertia, and/or generation of extremely long-wavelength photons, wavelengths on the order of the size of the universe.Does anyone know what I'm talking about? IIRC it was based on some theoretical work that was done before EmDrive was a thing, and it seemed less hand-wavey to me than simply "conservation of momentum is wrong" or "we're using the quantum vacuum as a tractive medium which is supposed to be impossible but whatever" explanations.I'm not saying this explanation is right (or wrong, or that the thrust observed in these experiments is or isn't caused by "new physics"); I'm just curious whether anyone knows what I'm talking about and can provide some more context.Any thoughts?  I think you're talking about McCulloch's quantisation of inertia theory. http://www.ptep-online.com/index_files/2015/PP-40-15.PDF which I believe was originally inspired by the rotation of galaxies.  Yup, that's it. I found the article I read, edited my post to include it.  If anyone's lazy, I highly suggest at least reading parts 9 and 10. One of the interesting takeaways here is that Q * -thrust is 2 orders of magnitude stronger than Photon-thrusters, and about 1-2 orders of magnitude lower than Ion-thrusters.* A Q-thruster is a thruster which pushes off of the zero point fluctuations in vacuum, which is still not understood.  But if you will try to discuss pilot-wave and walking droplets here (they are mentioned in part 10), you will receive lot of downvotes here.Quote:Although the idea of a pilot wave or realist interpretation of quantum mechanics is not the dominant view of physics today (which favors the Copenhagen interpretation), it has seen a strong resurgence of interest over the last decade based on some experimental work pioneered by Couder and Fort [13]. Couder and Fort discovered that bouncing a millimeter-sized droplet on a vibrating shallow fluid bath at just the right resonance frequency created a scenario where the bouncing droplet created a wave pattern on the shallow bath that also seemed to guide the droplet along its way. To Couder and Fort, this seemed very similar to the pilot-wave concept just discussed and, in subsequent testing by Couder and others, this macroscopic classical system was able to exhibit characteristics thought to be restricted to the quantum realm. To date, this hydrodynamic pilot-wave analog system has been able to duplicate the double slit experiment findings, tunneling, quantized orbits, and numerous other quantum phenomena. Bush put together two thorough review papers chronicling the experimental work being done in this domain by numerous universities [14,15].  > But if you will try to discuss pilot-wave and walking droplets here (they are mentioned in part 10), you will receive lot of downvotes here.If you try to claim, without evidence, that pilot waves predict different behavior than standard quantum mechanics, you might deserve that downvote.Pilot waves are a mathematical framework, they may be useful mathematical tricks in some cases, but they don't predict new behavior AFAIK.I've been to talks about Couder et al's work, and the authors don't argue that pilot waves are validated as descriptions of the universe by their work. They do demonstrate a novel macroscopic system that observes the laws of classical mechanics, and under certain circumstances, behavior emerges that is nicely described by the pilot wave equations. This does not mean that pilot waves are somehow a more fundamentally correct description of what's really going on.  This is actually incorrect. Pilot wave theory gives a deterministic explanation of phenomenon that the standard model treats as frequentist random events. Only if you assume no knowledge of the underlying hidden variables does the model reduce to the same as the frequentist standard model.This is exactly analogous to statistical mechanics (e.g. the ideal gas law) arising from classical Newtonian mechanics when you assume no specific knowledge about gas particles (individual positions or velocities), just aggregate mass and energy.An experiment that "proves" an extension of pilot wave theory might be, e.g., observing that decay rates of radioactive isotopes are affected by being in a quantum corral or something like that. An experiment that shows there is a more fundamental, and influenceable process underlying phenomenon that the standard interpretation treats as frequentist.For this reason it could be easily argued that theoretical physicists should be spending more time on pilot wave theory since it is this sort of theory from which future advances would come, vs the standard interpretation which puts up a semantic stop sign and says "proceed no further".  > This is actually incorrect. Pilot wave theory gives a deterministic explanation of phenomenon that the standard model treats as frequentist random events.That's a remarkably incorrect statement. Let's see:* The "standard model" is a quantum field theory and has essentially nothing to do with this discussion.* Standard quantum mechanism says nothing about frequentist vs Bayesian interpretations of anything.* Standard quantum mechanism is a deterministic theory, too. Take a look at the Schrödinger equation: it's deterministic.Determinism is tricky. Suppose you have a particle doing its thing (going through double slits or whatever) and then you measure its position. In standard QM, you have two choices: you use the Born rule (or a fancier version -- I like the POVM formalism) and get a distribution of outcomes and a new post-measurement wavefunction, or you can include the measurement apparatus in your system and you end up with many worlds. In PWT, I think you have two similar choices. You can start with a distribution of your (hidden) initial condition and get an resulting distribution over the outcomes (which will be the same as the Born rule distribution if you calculate it correctly). If you do this, you still need to model decoherence, and I believe it looks at least as artificial as the standard QM case. Alternatively, you could presumably add degrees of freedom and more hidden variables to describe the measurement apparatus and you end up with an IMO extremely messy version of many worlds.  No, I don't claim that PWT predicts different behavior. PWT is reinterpretation of physic facts we already have.However, walking droplets shows that relativistic and quantum effects can be explained in terms of Newtonian physics. For example, just by looking at walking droplet experiment with two slits, I can say that speed of sound in water is constant and it isotropic regardless of speed of particle, because waves around particle are propagating, so water is not moving at all (unless wave is really big, so path to travel will be longer). It is easy to understand. It also explains why Michelson-Morley experiment failed.  > I can say that speed of sound in water is constantIt's not constant. It varies by temperature.This is why you're getting down voted. You're asserting a very minority view in physics as a certainty, while making sweeping statements that contradict a high school physics education.You are placing way too much weight on youtube videos of excited oil droplet propagation. Your lay understanding of these videos is not equivalent to the consensus of people who dedicate their entire lives to these topics.  >> I can say that speed of sound in water is constant> It's not constant. It varies by temperature.It's worse than that. The relevant speed is (I think) the speed of surface waves, and surface waves in water are really quite complicated.Also, pilot waves get interesting when more than one particle is involved. Two dancing droples do not act like two noninteracting quantum particles.[edit: formatting]  > It's not constant. It varies by temperature.Yeah, so when we will have vacuum cooled below 0K, it will confirm existence of ether.Yes, I asserting very minority view in physics, but I'm able to back it with video of real experiment. It is not a hand waving.Let be honest. The quick way to check understanding of something is to ask "why?" few times. People, who dedicates their entire lives to relativistic and/or quantum physics, are not able to answer even to single "why?". It's because of orthodox education.However, they can downvote.  > Yes, I asserting very minority view in physics, but I'm able to back it with video of real experiment. It is not a hand waving.I think you may be rather confused about that video. I've watched what I think is the same video along with many other videos by the same experimenters (presented by the experimenters themselves!).The waves in the water are not pilot waves. They kind-of-sort-of look like them. With one droplet, you get approximately the behavior that the pilot wave equation would predict, but the interesting bits are missing. If you observe the droplet twice (which you do in the video -- each frame is quite literally an observation), you get behavior that is completely inconsistent with an actual double-slit-experiment particle. If you add a second particle, the whole analogy breaks down: the pilot wave for two 2D particles is a function of five variables (time, x1, y1, x2, and y2), but the water wave is still just a function of three variables (time, x, and y).But much more importantly, that video is a video of a bouncing water droplet and some surface waves. The droplet is a macroscopic droplet of water, and the waves are waves in a puddle of water. They obey the laws of fluid mechanics. If you grab the droplet while it's bouncing, it'll be gone and the water will still have waves. If you heat it up, it'll boil. If you turn the experiment upside down, everything will fall out and get things wet. Saying that the video proves that pilot waves exist is like saying that the experiments that play with "acoustic black holes" prove that black holes exist.  > Yeah, so when we will have vacuum cooled below 0K, it will confirm existence of ether.I think you will face great difficulties in convincing anyone that works in the topic area of this.> Yes, I asserting very minority view in physics, but I'm able to back it with video of real experiment. It is not a hand waving.It's clear you do not understand the propagation of acoustically excited droplets are a limited analogy, not a perfect model of QM/QFT. The people doing those experiments would not agree with your statements or characterizations.> Let be honest. The quick way to check understanding of something is to ask "why?" few times. People, who dedicates their entire lives to relativistic and/or quantum physics, are not able to answer even to single "why?". It's because of orthodox education.This is willful arrogant ignorance and a gross mischaracterization of the world of physicists. They absolutely address more than "a single why?". You have not put forth the effort necessary to understand the broadly accepted answer, let alone invalidate it.  i.e. at best, it provides no new information at the expense of learning an entirely new framework.  IMHO, if we will know better the physics of quantum and relativistic effects, we will be able to model them at macro level, so it will be much easier to understand and study these effects.Mathematics will not change, calculation results will not change, but understanding of processes will rise significantly, which may lead to new advances in physics.  That would have to be worth the increased confusion in communication between experts using these different languages. Furthermore, given that the physics of the "pilot wave" are not significantly different from that of the wave function it seems unlikely that it will lead to any new intuition.  The same could have been said about heliocentrism.  Heliocentrism makes different predictions, it's a totally different comparison.  I'm not a physicist, so my understanding of this is shaky. Can you explain to me how the ESSW paper could possibly have been seen to "disprove" PWT if it doesn't make any different predictions? Isn't the assertion that particles take deterministic paths a prediction?  I am a physicist, and you are not misunderstanding anything. ESSW defeated a strawman mis-generalization of PWT.  I think, you can't simply push off zero-point fluctuations in vacuum w/o creating particles occasionally.And if you admit you do, you're at level of photon thrusters at best.  I'm not sure what you mean. The way I understand it, the vacuum is capable of creating arbitrary particles as long as the quantum numbers are conserved and ΔEΔt >= ħ/2. With e- being the lightest (apart from neutrinos, which are negligible), the vacuum is producing virtual e-/e+ pairs, which are long lived enough to interact with real particles. As an approximation, the vacuum is exclusively an e-/e+ soup, since the other quarks and leptons require much too large of a ΔE to instantiate. The way I understand γ-thrusters is that they make use of the very tiny amount of momentum in a single photon, p = ħk, along with the large N of them bombarding the object. I haven't seen any calculations for γ-thrusters that take into account vacuum fluctuations, though.  http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-v...About the previous tests of the same team:"The testing was done by five NASA employees in a lab devoted to exploring unorthodox propulsion ideas. The team leader is a researcher named Harold “Sonny” White, himself a proponent of ideas about faster-than-light warp drives that most of his colleagues have classified as physically impossible. The lead author is one of White’s Eagleworks teammates, David A. Brady. Calling this group “NASA”—as almost every popular news story has done—is a gross oversimplification."  They fund it, no?  Would it be better if NASA wouldn't have less then 10 people, out of their 18,000 employees (0.05%), working on testing nevertheless such claims which almost surely don't work?Maybe, if that 0.05% is used against NASA by claiming it doesn't do its job how it should.  Interestingly, NASA used to have a group working on such projects.https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physic...And I believe they actually did a serious job, which is probably why they never found any warp-drive ;-)  It's my understanding that they are working with this project on their free time.NASA pays small amount of money ($50,000 or so) and gives them a room to do experiments. Or at least did in 2011. Eagleworks and their team are not official NASA research. They just have facebook page. Contact attempts trough NASA don't work.Glenn Research Center offered to replicate the experiment in a hard vacuum if Eagleworks manages to reach 100 µN of thrust.
 If you pressurize a sealed cavity with a gas, it's not going to move due to the internal pressure regardless of what shape you make it. If you sum all of the collisions of the gas atoms along with the container, the sum momentum will be zero. Momentum is mass x velocity.Contrast this with pressure created via light. Velocities with light don't add that way. Instead there is a red/blue shift in the frequency.I can't put my finger on how this could work, but it seems there is a discontinuity here between the speed of light being constant in all reference frames and summing velocities to calculate momentum.Maybe with light, only energy conservation matters and momentum can be changed via redshift/blueshift relative to the container.
 No, light is not different. If you want to adjust for "red/blue shift", you may use special relativity, and in special relativity you have the conservation of 4-momentum, which will give you the same result.
 Ah, if my understanding is correct then this makes sense.In my initial argument I bring in relativity and the invariant speed of light. What I neglected is everything else in relativity, like lorentz transformations.I mentioned a discontinuity between invariant speed of light and summing velocities to calculate momentum. The discontinuity is distance. Velocity is distance x time, but under lorentz transformations distance is relative. The discontinuity is resolved if you include length contraction (and time dilation).
 You know that everything around us is both matter and wave at same time (wave-particle duality). Right? I.e. small bit of matter surrounded with wave. (See any of walking droplets videos to develop intuition).Unlike regular matter, waves are propagating through space, by contraction and expanding of a field. Because of particle-wave duality, when matter is moving, EM field around matter expands and contracts at high frequency. Right?EM radiation in form of radio-waves can interact with these surrounding waves because of interference. Right?IMHO, interference between radio-waves and surrounding waves may cause effect similar to used in acoustic levitation.
 I think "particle-wave duality" is a bit of an old-fashioned idea that needs to go away. It is true in the sense that we can choose to describe the behavior of elementary particles from both a quantum view point and a Newtonian viewpoint, but that doesn't mean that things (e.g., electrons) are literally particles and waves at the same time or depending on the situation. It's waves all the way down--waves with momentum and kinetic energy and attractive and repulsive forces, just like what we think of as "particles."
 > You know that everything around us is both matter and wave at same time (wave-particle duality). Right? I.e. small bit of matter surrounded with wave.It's not quite like that. Imagine a particle whose location we don't know, so we're obliged to make an educated guess about where it is. That's the wave interpretation. Later on we actually observe the particle at a specific location. That's the particle interpretation. My point is the wave/particle duality idea doesn't mean there are particles riding waves like miniature surfers -- it's more like making a statement about where a particle is likely to be in advance of observing it, given certain statistical rules.> Unlike regular matter, waves are propagating through space, by contraction and expanding of a field.Not necessarily contracting and expanding -- that would be true of a longitudinal wave like sound waves in air, but not an electromagnetic wave in space, which is transverse.http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/tralon.html> Because of particle-wave duality, when matter is moving, EM field around matter expands and contracts at high frequency. Right?No. See the transverse/longitudinal link's explanation.
 But electron and other particles are actually demonstrating interference patterns, so it is not just interpretation. They are particles and waves. Waves are propagating.Walking droplets demonstration of quantum-like behavior is also done with transverse waves (waves, which are perpendicular to plane of motion of droplet). OK, they are no expanding and contracting, they are rising and falling, thank you for correction.
 >>> Because of particle-wave duality, when matter is moving, EM field around matter expands and contracts at high frequency. Right?>> No. See the transverse/longitudinal link's explanation.> But electron and other particles are actually demonstrating interference patterns, so it is not just interpretation.Your comment addresses my objection to the idea that matter expands and contracts, not that there are wave phenomena, which is certainly true -- but that wasn't what I commented on.
 These anonymous downvotes are frustrating. I cannot guess what caused them, so I cannot learn on my mistakes.
 I downvoted for basically the same reason as 'danbruc -- the comment contains inaccuracies (as far as I understand physics, IANAP) that don't become accurate just by appending "Right?" to them. I don't really read that "Right?" as condescension like 'humbledrone but more as a verbal tick. I hear it from others and even suffer from it myself sometimes, the idea is that a "Right?" pause offers the other party in the conversation a chance to interrupt and correct you, because you're not entirely certain of your own assertions. But that doesn't work so well in written communication except maybe with instant messaging.I gave you an upvote for persisting in getting corrections/tips from people like 'danbruc and 'lutusp though. Since you were interested in simulation you might enjoy this article (or others on his site) from an actual physicist: http://oyhus.no/QuantumMechanicsForProgrammers.html
 I'm guessing that you were downvoted because your post doesn't make very much sense.
 Let me quote paper:«Although the idea of a pilot wave or realist interpretation of quantum mechanics is not the dominant view of physics today (which favors the Copenhagen interpretation), it has seen a strong resurgence of interest over the last decade based on some experimental work pioneered by Couder and Fort [13]. Couder and Fort discovered that bouncing a millimeter-sized droplet on a vibrating shallow fluid bath at just the right resonance frequency created a scenario where the bouncing droplet created a wave pattern on the shallow bath that also seemed to guide the droplet along its way. To Couder and Fort, this seemed very similar to the pilot-wave concept just discussed and, in subsequent testing by Couder and others, this macroscopic classical system was able to exhibit characteristics thought to be restricted to the quantum realm. To date, this hydrodynamic pilot-wave analog system has been able to duplicate the double slit experiment findings, tunneling, quantized orbits, and numerous other quantum phenomena. Bush put together two thorough review papers chronicling the experimental work being done in this domain by numerous universities [14,15].»So it makes sense in paper, but does not makes sense at HN?
 I can't speak for anybody else who downvoted you, but I did it because your post comes across as being quite condescending. Take this pattern, for example:> You know that X. Right?> Y. Right?> Z. Right?The "You know that" part makes your argument unnecessarily personal, when your comment could just as easily be stated without any reference to the person behind the comment you were responding to.The "Right?" ending each line is also very patronizing. This sounds like how an adult might talk to a child, walking them through a line of reasoning.Maybe you did not intend to sound condescending, but you did, and this is no place for that.(Also, your post is worded as if the pilot wave theory is a fact, when it is actually not even particularly widely accepted. It is one of many interesting views of QM, but certainly not the only one.)
 Oh, sorry. I forget about that effect. After lot of endless battles in newsgroups, I learned that text contains no emotions, so all emotions, which I may draw on my opponent, are in my head only.How I should rewrite that text so it will not cause unwanted emotions, but will not look like a dictionary article? Can you help me, please? My level of English is not strong enough to be sure.PS.Even when (if) Pilot-Wave theory will be widely accepted, it will be theory, not a fact. :-)Actually, PWT explains some effects much better than GTR. Moreover, walking droplets shows that relativistic and quantum effects can be described in terms of Newtonian physics, which is much easier to imagine and argue, which may cause significant advance in physics, after almost 100 years of "shut up and calculate".
 > How I should rewrite that text so it will not cause unwanted emotions, but will not look like a dictionary article?That's easy to answer. A "good" post, one likely to generate light, has many topical references and almost no, or no, first-person ("I") or second-person ("you") pronouns.A less desirable post, one more likely to generate heat instead of light, has fewer topical references and more first-person and second-person pronouns.So when composing a forum post, a post to be read by strangers, it's desirable to either remove or edit all constructions that might be taken to describe a distinction between oneself and others.One could go so far as to write it as an equation:Forum post Q factor = (topical references) / (1+sum of first-person and second-person pronouns)The advantage of the equation is that it could hypothetically be automated and added to a forum post editor, so one's score could be seen to rise and fall as the post is typed. The drawback is that it's a classic case of reductionism -- the possibly misguided idea that everything can be reduced to (for example) mathematics.There's obviously more to quality forum posting than this, but it's at least easy to explain and apply.