The 'impossible' EmDrive could reach Pluto in 18 months?
wired.co.uk
wired.co.uk
Q. Does the Em drive produce thrust?
A. Undetermined. Several tests from multiple independent labs have reported thrust, including in a vacuum. However several of the labs that reported positive thrust come from a sketchy background.
Q. Does it violate conservation of momentum?
A. Undetermined. There are several competing theories trying to explain the phenomenon, but we lack raw data. I think the last thing anyone wants to see here is "new physics".
Q. Roger Shawyer seems like a scummy kook?
A. Yes. This is why more testing is really important.
Q. What about more tests?
A. A few dozen people have taken it upon themselves to hack together emDrives and test them. The first couple so far were plagued by poor construction, RF interference, and poor experimental design. However, the hacking community is slowly getting its shit together.
Q. Pluto in 18 months?
A. If it works. My intuition screams "its cold fusion all over again", but there is still a chance.
> I think the last thing anyone wants to see here is "new physics".
I really want to see new physics, because I want to see us get off this rock and far away. I think most people want to see new physics. I think that's why this topic is so popular.
That said, I can understand physicists not wanting to see new physics.
Wait. In a way, that sentence is crazy. In a way, physicists should want to see new physics more than anybody.
Where does the "not wanting to see new physics" sentiment come from? Just not wanting to be wrong?
But if you claim to violate the conversation of momentum, everyone is going to be skeptical and not believe it. We have hundreds of years of experiments and observations that support the law and have looked in many places from small to large and not seen violations. This is what makes people not believe it and thus physicists are going to assume you are wrong and not physics. It's not so much a negative concern, but more of a practical one. But should it be tested in a rigorous manner and reproduced, then physicists will believe it. It's just it hasn't and thus we are going to stick with the established very well understood and tested theory. Like are you sure you have properly counted all the initial momentum? Are you 100% you are not introducing energy to the system? The possible explanations is long and a good experiment will eliminate as many of these as possible.
As an example, look at the OPERA experiment which found to have superluminal signals. New physics? Nope, just a faulty piece of equipment. BICEP showing gravitational waves? Nope, just poor data interpretation and neglecting interstellar dust. So if you want to claim new physics, be damned sure you have ironclad proof.
If physicists don't want new physics, they should stop doing research!
I mean, wouldn't it be really frustrating to find out the law of conservation of momentum is not universal? Exciting, but also frustrating? Maybe even embarassing for physics? It would be like someone proving P=NP.
"Free Energy" is very appealing, so is "10x better batteries", "10x more flash storage", "momentum-defying space thruster", and so on. These modern-day fairy tales are gaining press simply because people want them to be true, not because they actually show a path for progress.
Similarly, a promise of a "miracle cure" is very appealing to the public, and so it may seem cynical to downplay any such claim right away, but it has absolutely nothing to do with actual advances in medicine.
The article's responds with the nonsensical "Some damage to our theories of physics is an acceptable payoff if we get a working space drive."
EDIT: Let me clarify why it's a nonsensical statement:
First, I think it meant to say "cost", not "payoff". Second, there would be no cost. None of the things we were able to do with our existing theories would be lost. We'd only be pushed to refine the theories (or in rare cases come up with an entirely new theories) that would be at least as accurate as the prior theories and cover phenomenon the old didn't. If anything, we'd be able to go back and do better at all the things to which we'd applied the old theories.
It's like saying "Some damage to Newtonian physics is an acceptable cost if we get a working understanding of relativity and gravity." Einstein did no "damage" to Newtonian physics. He made it better.
People seem to regard scientific progress as this kind of wave function, where some theory comes along and then some other theory or discovery disproves the previous one and so on and so forth.
But if you want to think of scientific progress that way, then you have to think of it as a dampened sine wave (https://en.wikipedia.org/wiki/Damped_sine_wave) -- that is, discoveries and theories tend to refine previous discoveries and theories, and scientific progress over the millenia has been rapidly zeroing in on the truths of our reality.
What is left at this point is mostly things at very large scales -- cosmological stuff like dark matter, dark energy -- and very small scales -- stuff like sub-subatomic particles and the Higgs boson and the nature of mass and so on -- and very complex things like biology and climate science.
What isn't left at this point is a revision of the laws of conservation. It is exceedingly unlikely that anything will be discovered at any point in the future which will do anything other than add perhaps the very smallest of exceptions to those laws, and even then, I doubt very much that will happen.
So, essentially, the age of physics discoveries in garages is mostly over. There will be many more discoveries in physics, but they now require the collective efforts of entire nations.
You might be correct in saying that humans have characterized particles, objects, and phenomena that are closest to their scale and location, but we have done a poor job of understanding their fundamental nature. We also don't understand and have not even characterized things we've never observed (the 'black swan' problem).
> rapidly zeroing in on the truths of our reality
The truths? No, humans are as likely to arrive at the truths as ants an understanding of a microwave oven.
As a physicist I really can't imagine what answer would satisfy you and could be falsifiable the same time. It is what it is, all we can do is to characterize its behavior.
I'm not saying that asking what light is is not an important question. But there is a possibility that there is simply no answer and yet we can have fully working physics. At least nobody will question your theories just because you don't tell what exactly your elementary particles are. They are elementary, we just have them, maybe light is not one of them.
I would also like to be clear that I am not criticizing anyone for making insufficient progress; it is just that there is a lot out there left for us to understand, and not all of it is marginal stuff that's "very big or very small".
Finding the true nature and, whether it exists or not, is the domain of philosophy.
Science builds models. And we do have at this point extremely good models of electromagnetism which can correctly predict results of all experiments done so far.
Whether these models reveal some fundamental truth or not is a matter of opinion (or perhaps religion). It has nothing to do with refining the models or finding experiments that might prove them wrong.
I am not interested in whether these scientists reveal "some fundamental truth or not", but we cannot say that we understand all there is to know about electromagnetic phenomena because we can make a few simple predictions. It would be tantamount to saying that we understand the sun because we know where it is relative to us, and how bright it is, and can predict both of these parameters for a while. Understanding that it is a star, how it was formed, how it will cease to be, that it is made up of a number of elements, and converts large amounts of matter to energy are all very important discoveries, and we must continue to seek this kind of advance in the frontiers of our understanding in electromagnetic phenomena, matter, gravity, and many other areas.
So that leaves me a little bit stumped at what point you're trying to make here. Are you disagreeing with that view of science? Are you trying to say, "well, that's how it's been for hundreds of years, but at some point in the future I believe we'll all discover that physics is completely and utterly and embarrassingly wrong in every way"?
I've gone back and reread your reply to me at least half a dozen times. You seem to be disagreeing with me, but none of the examples you brought up really actually disagreed with me. At best, I chose some poor metaphors and that led you to misunderstand me, but then I still can't figure out what it is that you're actually trying to say.
Similarly, the current model of the sun is the simplest model that explains some observations (neutrino flux, the fact that some stars seem similar spectroscopically, our knowledge from other branches of science, etc.).
I see no fundamental difference between these two.
This is quite an understatement. QED, which is the underlying theory of EM, is the most accurate scientific theory ever. Full stop. It's theoretical predictions match experimentally measured observables out to ten decimal places. By your standards we don't really understand any physical phenomena. To bring up your analogy with the sun: our understanding of QED is like saying that we know the exact chemical composition of the sun to an accuracy of one part in ten billion. I think we would be justified in stating that we understand the sun in those circumstances.
On a related note, QED does provide a lot of context for what "light"(photons) is(are). It's the gauge boson (read: mediating particle) of the electromagnetic force. In my mind it doesn't get much more elegant than that.
http://chem.tufts.edu/answersinscience/relativityofwrong.htm
Asimov naturally describes it much better than I could.
Regardless, how is it relevant whether a large group of people made a mistake (by coming up with an incorrect theory) before an invention that had no basis in existing theory was made? I do not agree with the premise of the post I responded to, as a new drive does not necessarily contravene existing theories (since we do not understand its principle of operation).
I agree that contravening an existing theory is a bit of an odd course for an inventor to take, and may make it difficult to get angel funding, but that's about the only difference I can see.
http://arc.aiaa.org/doi/abs/10.2514/6.2015-4083
High levels of skepticism are still warranted, as much as I would love for this to pan out. Every time this gets tested—presumably more and more carefully—the measured force gets smaller. The original test at Chinese Northwestern Polytechnical University measured 720 mN; this latest test in a vacuum chamber, only 20 μN. This is so tiny that a test anomaly would seem a much more plausible explanation than a violation of the conservation of momentum.
Of course the ultimate test would be to put one of these in space and try accelerating something with it, in the same way that the ultimate test of a perpetual motion machine would be to make one perform macro-scale net work.
Given that this is a 700W microwave oven putting out a tiny amount of thrust, and that a positive finding would invalidate a basic conservation law, my money is on those wires.
I also have a strong gut feeling that this some none issue but it never hurts to test it the US, Russia, China and to lesser Extent the UK, France and other European powers have all conducted studies into ESP, the cost of such testing is ridiculously low compared to the potential discovery.
When it costs near to nothing to explore a phenomenon that can change how we understand physics it's worth exploring no matter how ridiculous it is.
I think that the best metric is to compare this with the maximal Force/Power ratio that is consistent with a "massless" thruster and special relativity, (i.e. a laser beam, photon thruster, ...). In this case the Force/Power ratio is at most 1/c, that is 0.0033 uN/W = 0.0033 mN/KW.
The results in the table vary from 3x to 200000x the theoretical maximum if we assume that this doesn't break the conservation of momentum, special relativity and quantum mechanics.
After all, it will either sit there and do nothing or it will move.
Solar sails and (to an extent) ion thrusters work on the same principle.
I'm sure someone will put the cash together eventually if the dirtside experiments look promising, but there's no sense in risking the money until we're pretty sure.
http://www.you-tech.it/index.php/content/download/12369/1124...
On the other hand, the decrease in effect size is closer to a factor of 40,000.
You're forgetting mass-energy equivalence. <x> energy / <y> thrust is a specific impulse, once you work in the factor of c^2 (that being the minimum amount of mass you need to burn to get the energy to produce the thrust.)
In this case, for instance, they are saying they think it produced 20 uN with an input of 700w. That works out to an effective specific impulse of 2.5x10^9m/s as an upper limit (yes, this is tachyonic. One of the problems with this drive is that it throws conservation of energy and momentum out the window...), assuming we could convert mass to energy directly. (If you're using D-T fusion, it's a specific impulse of ~9.7x10^6m/s instead as an upper limit, assuming 339.72 TJ/kg. Other reactions are lower.)
If you're assuming solar panels or some other external power source, then the only real difference between this and a laser is that this produces a constant factor more thrust per energy input. Sure, it's reactionless - but, effectively, so is a neutrino source, for instance. All that means is that you don't need to be as careful as to which direction you burn in.
Right now my guess is either measurement artifact or some form of obscure but conventional effect like EM interaction with the surround environment. That's most likely.
If those can be ruled out, then we're in new physics territory.
Uh oh. That's a classic sign of a bogus effect. It's like physicists at Stanford trying to replicate the Pons-Fleischmann cold fusion experiment. At first, they were enthusiastic, and expected big results. They started out with the apparatus surrounded with radiation alarms in case it generated dangerous amounts of neutrons. After a while, they discovered that the effect was at most twice background radiation. Since humans have water in them and water is a neutron reflector, just moving around the equipment could produce effects at that level. Then they moved the equipment to the inside of a cube of lead bricks, to eliminate external neutrons. No more neutrons, background or otherwise.
The device will either be shown to work or not to work with additional experiments and nothing anyone says regarding how it can or can't work will change that.
I haven't studied the theory behind the device, but it's hardly a distortion to characterize such a disproportionate drop as a declining effect size in the face of additional testing.
Like you, I don't claim to have any idea whether this ultimately pans out. As I said, the ultimate test is to put one in space and see what it does. Until that (or at least a more promising lab test) happens, all we have is speculation. But my point is that more skepticism is warranted than was implied by the Wired headline and by some of the comments in this thread.
5. Q. Why does the EmDrive not contravene the conservation of momentum when it operates in free space?
A. The EmDrive cannot violate the conservation of momentum. The electromagnetic wave momentum is built up in the resonating cavity, and is transferred to the end walls upon reflection. The momentum gained by the EmDrive plus the momentum lost by the electromagnetic wave equals zero. The direction and acceleration that is measured, when the EmDrive is tested on a dynamic test rig, comply with Newtons laws and confirm that the law of conservation of momentum is satisfied.
So, the momentum simply "builds up". That's an exceptionally weak explanation.
The deeper reasons are above my pay-grade.
m'=ym
y=1/sqrt(1-(v/c)^2)
Now consider the momentum, p, of a photon. We have:
p=m*y*v
m=0
y=infinity
v=c
Instead, we can use the engery-momentum relationship, which states:
E^2 = (mc^2)^2 + (pc)^2
E^2=(pc)^2
p=E/c
E^2 = (mc^2)^2 + (pc)^2
(mc^2)^2 = E^2 - (pc^2)^2
Four dimensional space-time has a metric analogous to but not quite the same as euclidean space: the time part has the opposite sign from the space parts.
ds^2 = (c dt)^2 - (dx^2 + dy^2 + dz^2)
Just as you can start with distance and then build up to momentum and energy in classical physics, in relativistic mechanics you can start with this metric and build up vectors in 4-space for velocity and energy/momentum. (Turns out that the time part is an energy while the space parts are momentum.) The upshot is that
(m_0 c^2)^2 = E^2 - (p c)^2
What's peculiar is that the temporal entry of the four vector gets the "opposite sign" for the Pythagorean theorem. That is, if you have a vector (t, x, y, z), then the "hypotenuse" (called an invariant) is t^2 - x^2 - y^2 - z^2 (up to a conventional choice of overall sign). What's surprising is that the hypotenuse is the thing that's the same for different observers. So, if you do a Lorentz transformation [3], t and the spatial entries will change, but the invariant combination won't.
Everybody knows E = mc^2 is the relationship between a particle's mass and its energy. But what is its energy if it's moving? Certainly the particle gains energy the faster it moves, right? Yes. E = mc^2 is the 0-momentum version of a relativistic expression. Since E is temporal and momentum p is spatial, the four vector can be written (E, pc), which has an invariant E^2 - (pc)^2. We call this invariant the rest mass[4], up to some factors of c. Algebraically moving things around gives us the "Pythagorean" form.
[0] https://en.wikipedia.org/wiki/Energy%E2%80%93momentum_relati...
[1] https://en.wikipedia.org/wiki/Four-vector
[2] https://en.wikipedia.org/wiki/Noether%27s_theorem
I know of no one doing modern research in relativity using this obsolete concept.
I'm glad they're testing this until it's proven one way or the other but if it somehow works I doubt that'll be the explanation.
I'm very curious about this bit. I wonder who is working on it?
The Northwestern Polytechnical University in China is testing a version of the EmDrive: https://dx.doi.org/10.1088%2F1674-1056%2F22%2F5%2F050301
Finally, a number of amateurs are interested as well: http://emdrive.wiki/Building
http://ntrs.nasa.gov/search.jsp?R=20140006052
Turning 17 watts of microwave power into 40-91 micronewtons of thrust isn't exactly stunning, though.
> Ion thrusters have an input power spanning 1–7 kilowatts, exhaust velocity 20–50 kilometers per second, thrust 20–250 millinewtons and efficiency 60–80%.[1][2]
3 orders of magnitude less thrust than for not needing to accelerate any fuel all the way into orbit? i'll tell you space companies will send trucks full of money to anyone who can make a reliable one.
Conservation of momentum is a consequence of the translational symmetry of physics via Noether's theorem, so that's what we'd need to give up to hope to see it broken.
Your photon example works because there is no time translational symmetry in the case of metric expansion and it's a general relativity model. In general relativity there is no conservation of momentum either. It would be hard to even define since coordinate systems change from point to point. We can only say that the energy-momentum vector is going through parallel transport, which is like conservation in the local coordinate system.
But they also laughed at Bozo the Clown."
Conventional microwave ovens only have two states: on and off. (I won't rule out the possibility of some exotic build having multiple powers, but the ones you interact with on a normal basis don't.) So, power levels cannot change the output level of the magnetron. Instead, the power levels control what percentage of time the magnetron is on. A power level of 50% means the magnetron is on for roughly 50% of the indicated time. These off periods will typically result in more even heating at the cost of time. The off periods give the heat a chance to conduct through the food and balance, reducing the lava-and-ice problems seen when heating frozen things in microwaves.
HIGH just means 100% power level.
Mine does, and it cost $120.
http://www.amazon.com/Panasonic-Countertop-Microwave-Technol...
(I don't find that it actually makes a difference when using it, though.)
Like: http://www.amazon.de/gp/product/B0076ZQQ14?keywords=mikrowel...
Or: http://www.amazon.de/gp/product/B00T8138J2?keywords=mikrowel...
Set a typical microwave oven to 90% and you will see the magnetron 100% on for perhaps 15 seconds and 0% on for 2 seconds.
The Panasonic claims to operate differently. It actually adjusts the power to the magnetron. So the magnetron itself is continuously operating at 90% power.
A quick google turned up this article, which pretty much says the same thing. http://www.techlicious.com/review/microwave-ovens-with-inver...
If you want to investigate further, the key is to include the keyword "inverter", which is how Panasonic advertises it.
Where the Panasonic shines is at lower power settings. E.g. if you defrost at 30% power for 3 minutes you get much more pleasant results than using the typical microwave. In a typical microwave the thinner areas actually start cooking rather than simply defrosting when operating at 30% power.
And, as mentioned by others, you really won't see a difference on the higher power settings, because there really isn't much of a difference. 10 seconds of almost-high output or 9 seconds of high output... On lower power, you should notice much bigger differences though.