Of course I am entirely ignorant of physics

But the thrust can still be seen, and engineers still can’t explain what’s causing it.
If it becomes operatonal, the EMDrive propulsion system would permit travel at speeds until now only seen in science fiction.

But here’s my entirely ignorant prediction.

They need to weigh the drive. Accurately.

The thrust is coming from atoms (molecules? Protons, whatever) being knocked off the outside of the chamber by whatever is happening inside it. These are very few, but moving at relativistic speeds. Thus the thrust.

In effect this is a very inefficient ion drive. As such it won’t work for long distances as with long distances there won’t be a drive there.

Yep, I know nothing about this at all but as Ritchie would say, go on, prove me wrong! Thus I must be right, eh?

30 thoughts on “Of course I am entirely ignorant of physics”

  1. I do have a bit of professional background in theoretical physics and this is subject of more truly stupid reporting over the last year than anything else. Not sure if that is because the people behind it are snake oil salesmen or just all journalists idiots.

    A sample of idiocies on this matter offered here and in other publications:

    Propellant free travel is a revolutionary new idea based on novel physics!

    BS. Ever heard of a light sail? Based on the revolutionary mirror! No? A regular sail?

    It may violate conservation of momentum!

    Conservation of momentum is so deeply built into all physics for over 300 years, that if it was violated, there’d be nothing left of physics. Nothing is impossible, but … Unlikely.

    But quantum mechanics overthrew all these old certitudes and shows anything is possible!

    BS. QM preserved all of that and added some more constraints. It is today best understood as just the same as classical mechanics with an additional parameter to tweak. Set that to 0 and you have classical mechanics. Set it to very small and you get quantum mechanics. Otherwise same fundamental formulas.

    But NASA says so!

    No, NasaSpaceFlight, a dubious unaffiliated site says so.

    If anybody cares, I’ll add more as they occur.

  2. I imagine Professor Murphy could be prevailed upon to add some useful insight here – has anyone asked him?

    With his revolutionary PQE, he has already proved that orthodox neo-liberal economics is lying to us all and that, essentially, yes we really can have it all at no cost by simple money printing.

    Perhaps the “laws” of thermodynamics and conservation of momentum (who enacted these laws one wonders?) are similar attempts by the 1% to subjugate the masses. It would not surprise me if perpetual motion is possible and that this is being supressed by the 1% just to keep oil prices and their wealth high.

  3. It’s all relative, innit? It’s a quantum leap in this random, nonlinear world. The capitalist monopolists will want to squash it so that they can continue to exploit the finite resources of our
    …. blah, blah, effing blah.

  4. You could get a net thrust if some of the electromagnetic vibrations were differentially leaking out from one end. Such an effect would be tiny but, it not being my field, I don’t have a strong intuition for how it might compare with the reported thrust anomaly.

    > Conservation of momentum is so deeply built into all physics for over 300 years, that if it was violated, there’d be nothing left of physics. Nothing is impossible, but … Unlikely.

    Literally nothing. We’d lose conservation of energy at the same time, and, due to Noether’s theorem, at least one of the Lagrangian formalism and the homogeneity of physics in space and time would have to go. So we’d need a replacement theory that could account, without recourse to any of those things, for why the past few centuries’ physics was so phenomenally successful at explaining the structure and behaviour of the world around us. As you say, it’s certainly not impossible, but our prior probability for such an event has to be pretty low.

    > BS. QM preserved all of that and added some more constraints. It is today best understood as just the same as classical mechanics with an additional parameter to tweak. Set that to 0 and you have classical mechanics. Set it to very small and you get quantum mechanics. Otherwise same fundamental formulas.

    It’s perhaps more precise to say that we compare the size of the parameter with the energy- and time-scales of the physical scenario; the weirder parts of quantum mechanics become more dominant the larger the parameter gets in comparison with those scales. I would prefer to say that QM is always around, but because we are so large, the part of it we see in everyday life is what we call classical mechanics.

  5. I think the current theory is that thrust is generated by the movement of virtual particle pairs popping out of the quantum vacuum – which next disappear as they always do. These are the same virtual particles which cause (according to prof. Hawking) evaporation of black holes, thus causing another paradox which has stumped scientists by breaking the law of conservation of information. Look for “black hole firewall” to find more on this (without any relation to EM drive). Anyway, the point is that there are things which we do not yet understand and which seem to break the classical laws we know.

  6. @Philip Walker “It’s perhaps more precise to say that we compare the size of the parameter with the energy- and time-scales of the physical scenario; the weirder parts of quantum mechanics become more dominant the larger the parameter gets in comparison with those scales.”

    If I’d known that somebody else with a physics background was reading this, I would perhaps have said instead: The fundamental field equations are the same, regardless of whether you do classical or QM. Doing the QM, just requires you to do the math in a somewhat different, sometimes a little harder way.

  7. Oh no worry! I wasn’t really being pedantic for the sake of signalling another physicist was in the thread: I was winding up to the final sentence of that paragraph. When teaching quantum theory I always try to emphasise to my students that it is not some kind of “bolt-on” to our everyday, classical-physics experience but rather a theory that encompasses both our everyday experience and the subatomic realm.

  8. @Philip Walker

    I agree completely. I find that bolt-on thinking particularly dangerous in teaching introductory special relativity: “Basically it is still all Newtonian, but when things move fast, masses increase, things shrink or elongate, clocks slow down, etc.” That may be comforting in the beginning, but in the long run makes thinking about relativistic speeds very hard and error prone. Much better to just take the leap and say that relativity is the real thinking. Newtonian thinking is just an approximation useful at low speeds.

  9. My understanding was that there were great gaping holes in our understanding of how QM scales up to relativistic scales, which is why there is no Quantum theory of gravity (yet) and no full unification of quantum mechanics and general relativity?

    But then it’s been a long long time since I studied Physics!

  10. @Andy H

    That’s true. One reason is that quantum effects only show up at extremely small time and space scales which corresponds to extremely high energies, while gravity is extremely weak and really only shows up at gigantic scales. So it is very hard to come up with experiments in which both show up measurably. Lacking any good experimental data, theorist have been playing freely with this for decades, but cannot choose between competing theories.

    But none of this is any reason to take that “EMDrive” seriously. Nothing connects it to that problem.

    For example, we still do not understand one of the other great puzzles of science: how the brain really works. Perhaps we cannot understand the brain, because if we could, we’d be too stupid to do it.

    But that is no reason to trust some snake oil salesman who promises that if you eat the berries he is selling, your IQ will go up by a 100 points!

  11. Bloke in Costa Rica

    It’s precisely because I do have a background in physics that I am not touching this with a ten foot pole. It looks fishy, but that’s as far as I’m willing to stick my neck out.

    Incidentally, someone once asked me what I thought was the most remarkable fact in the whole of physics and I unthinkingly replied “Noether’s theorem”. Of course then I had to provide a layman’s explanation, which is harder than it looks.

  12. @Bloke in Costa Rica

    Yeah, it has been two decades, but I recall the ninety minute grad school class in which Prof. Migdal first proved Noether’s Theorem and then started applying it was one of the most thrilling educational experiences I’ve ever had.

    What are the odds that there are (at least!) three blokes in a comment thread on the blog of a British bloke mostly devoted to harping on the idiocy of a particularly idiotic accountant would know Noether’s Theorem? The world must be much better educated than I ever thought.

  13. Bloke in Costa Rica

    @SSE: I guess there’s a selection effect, because this blog does tend to attract a lot of people with some fairly specialised knowledge, and it is a pretty well-known idea. Anyone who’s read Feynman III.17, for example, will have seen it applied to energy, momentum, angular momentum and parity, even if he doesn’t explicitly name what he’s doing. I’m sure I’ve seen it at least alluded to in a couple of pop-sci books by someone like Brian Greene or John Gribbin.

  14. @Bloke in Costa Rica: Are you trying to put me into nostalgia coma? I read the Feynman Lectures in my 17th summer which resulted in the choice of my first profession. Didn’t remember the Noether’s Theorem reference though.

  15. I’m another Noether fan! So that’s at least 4.

    The EMDrive thing is just another perpetual motion machine scam. The theory claimed to be behind it is nonsense, and the experimental results are on the edge of detectability and very likely to be some unaccounted for experimental error. (I think Tim’s ion drive idea is one of the theories other scientists have proposed.)

    Physicists nevertheless often investigate the more plausible-sounding claims, not because they think they’re likely to be correct, but because there’s often something to learn. Either some subtlety of theory that’s been misunderstood, or some subtle effect that does something interesting without breaking any of the rules.

    For example, consider the following scenario. A neutron and a proton are dropped down a well in a vacuum. They both fall at the same rate (as per Galileo), converting potential energy into kinetic energy. At the same time, the proton radiates electromagnetically (because it has an electrical charge and is being accelerated) while the neutron does not (because it is electrically neutral). Where does the energy for the radiation come from?

    Figuring out puzzles like this gives us a deeper understanding of the physics, or highlights gaps in our understanding that need to be filled. A lot of major advances arose that way.

  16. “(I think Tim’s ion drive idea is one of the theories other scientists have proposed”

    Hurrah!

    So I am just ignorant, not an idiot?

  17. “So I am just ignorant, not an idiot?”

    It’s a reasonable hypothesis. I’d have regarded it as a natural and perfectly respectable suggestion if it had come from a scientist – definitely not idiotic.

    Others are that it’s due to the instruments used to measure the force becoming less accurate when they get hot, air currents from convection when the device heats its surroundings unevenly pushing it, heating of air inside the drive causes lift, like a hot air balloon, heating of the drive causes expansion and a shifting of the centre of gravity, throwing the force-measuring balance off, etc. There are literally hundreds of possibilities.

    Apparently, it’s been observed that the ‘thrust’ continues even after the electrical power has been shut off, and fades slowly as the equipment cools. That suggests it’s a thermal effect.

  18. Bloke in Costa Rica

    Well, NIV, if the proton is emitting energy then it is not falling at the same rate as the neutron, is it? The work being done on it as it falls through the gravitational field would be partitioned between kinetic energy and EM radiation. But it isn’t radiating, by the equivalence principle (if they’re in free fall there’s no way of distinguishing the situation from that at rest in free space with no net gravitational field). The Unruh effect doesn’t rescue you either (if it exists) since it doesn’t have any charge dependency.

    In reality you couldn’t do this, of course, since the electric field of the proton would induce a polarisation in the wall of whatever container you were performing the experiment, which would dominate any effect you might see, and the actual energy being radiated would be too small to measure, even if the equivalence principle were wrong.

  19. @bicr
    by the equivalence principle (if they’re in free fall there’s no way of distinguishing the situation from that at rest in free space with no net gravitational field).

    I don’t know the answer to NiV’s conundrum, maybe you’re correct that the proton falls more slowly than the neutron, but afaik, its only the free falling proton that cannot know that it is free falling. Those who observe it from a ‘platform’ can see the gravity it falls under, and also the light it emits.

  20. Bloke in Costa Rica

    And I should add, Maxwell’s equations are Lorentz-invariant. In fact it’s precisely that invariance that was the primary driver of Special Relativity, not people throwing balls on trains or whathaveyou. If the proton’s not emitting EM radiation in its rest frame, then it’s not emitting in any other.

  21. “Well, NIV, if the proton is emitting energy then it is not falling at the same rate as the neutron, is it?”

    That’s one sensible way around the dilemma – that the ‘radiation reaction’ applies a resistive force opposite to the acceleration. Unfortunately, it doesn’t work because a freely falling particle doesn’t experience any acceleration in its own local rest frame. The 4-acceleration vector is zero, and so the Abraham force (the radiation reaction) is also zero.

    The other obvious way out of the dilemma is to say that a freely falling particle doesn’t radiate, because it’s locally not being accelerated. This falls prey to another problem – a charged body at rest on the Earth’s surface *is* being accelerated in it’s own freefall frame – but clearly doesn’t radiate. Where could the energy come from? The question of radiation of uniformly accelerated charges and the existence of so-called “runaway” solutions to the Lorentz-Dirac equation has been a long-standing question in electrodynamics.

    The actual physics is much more interesting. The conventional expositions of electrodynamics tend to make certain assumptions or approximations, and primarily concentrate on the “far field” at a large distance from the charge. But a more detailed consideration of how the field has to behave very very close to the charge shows some unexpected behaviours, that are invisible further out.

    It also depends on the true structure of particles. The approximation of particles as being pure points of zero size causes a huge number of horrible mathematical problems with the physics, most of which are glossed over when taught at a beginner level. For a start, the one-over-r-squared law implies that the potential is *infinite* at the particle’s location, and a charge located in an infinite potential has infinite energy. (It also means its mass is entirely within its Schwarzchild radius, turning it into a tiny black hole…) This is the source of all those infinities plaguing quantum field theory, and why we need ‘renormalisation’ to fudge them away.

    This problem isn’t a trivial one, but involves some of the deepest issues in physics.

    Anyway, the answer (assuming our current understanding of the theory is right…) turns out to be that freefalling protons *do* radiate, and *do* fall at the same rate as their uncharged brethren. The energy comes from the near-field very close to the particle – its so-called “Schott energy”. This energy can be negative, and so act as a ‘bottomless well’ of energy to reversibly supply radiation. Energy is conserved – we’re tapping the hyper-intense fields close to the particle ‘singularity’ to provide it.

    See here or Google “Schott energy” and “uniform acceleration radiation” for more technical detail.

    Anyway, my point was that physics can be subtle, and consideration of apparent paradoxical violations of the rules can lead to a deeper understanding of physics. That, I suspect, is why NASA spends money looking at these things. No serious physicists doubts conservation of momentum (or energy, which is essentially the same thing), and I highly doubt any of them think this EMDrive device can really be used for reactionless interstellar travel. But it’s still worth investigating, and if it gets people talking about physics, asking questions about physics, and inspires people to take up studying it, that’s all worthwhile.

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