"WIRED understands that there are multiple labs around the world working on their own EmDrives, although Tajmar's is the only new one willing to go public so far."
I'm very curious about this bit. I wonder who is working on it?
I wonder how they rule out the effects of the Earth's magnetic field. I can see there being some small effect due to some kind of eddy currents pushing ions into one direction. Maybe they turn the apparatus at multiple angles and check the bias to north-south?
I seem to recall that they could not find any variance in the force by orienting the apparatus in different directions. Some good work has been put into finding the cause of this, and most of the easy and obvious errors have been tested and found to be unrelated to the effect.
"Roger Shawyer is encouraged by Tajmar's work, which he says validates his own theoretical predictions as well as his experimental results. Shawyer has often been dismissed because of his own lack of peer-reviewed scientific publications. That looks to be changing very soon; a paper Shawyer presented at the International Astronautical Conference in Toronto in 2014 is in the final stages for peer-review for publication. This describes an advanced EmDrive-powered spaceplane."
You're referring to an unpublished paper by the author, which appears to be a design for a space vehicle. I asked about independent tests of the claimed effect.
> 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.
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.
From the abstract: "We identified the magnetic interaction of the power feeding lines going to and from the liquid metal contacts as the most important possible side-effect that is not characterized yet. Our test campaign cannot confirm or refute the claims of the EMDrive..."
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.
The current theory of the EMDrive is complete, absolute bunk. Whatever an EMDrive is doing, can in no way be described by the incorrect relativistic reasoning used by Shawyer.
Smaller effect size as studies improve is the classic sign of a non-event. ESP and the like went through similar cycles - impressive early studies followed by a series of more rigorous studies with diminishing effects until people got bored and moved on to the next big thing.
In this case different tests have occurred at different power levels. Has anyone normalized the results? Of course with only a couple replications its early for a meta study.
In this case the tests weren't even normalized, this is one of the 1st tests that was conducted in vacuum under shielding, many of the earlier tests were not even thermally or electromagnetically shielded, considering the tiny amounts of thrust generated by both the "predictions" and the tests pressure difference due to thermal variance as well as magnetic forces could explain it just as well.
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.
Well yes, I don't expect a tiny fraction of a Newton of force to get them into orbit, but I meant more as a way to test whether the anomalous force is usable for spaceflight.
After all, it will either sit there and do nothing or it will move.
No one's ever claimed that the EmDrive could launch payloads to orbit, to my knowledge. That's not what it's for. Once you're already in space, a drive that can produce 0.001G indefinitely will get you going way faster than a rocket that can produce 10G for a few minutes before its fuel runs out.
Solar sails and (to an extent) ion thrusters work on the same principle.
At least $4000 per kilogram, based a quick google.
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.
Why the assumption that if it works it must violate a conservation law? That's the last thing I would suggest after exhausting every other possibility, even weird ones like space time distortion thst would still operate within known conservation laws.
The whole reason the EmDrive is supposedly so revolutionary is that it's claimed to produce thrust without requiring any propellant. If conservation of momentum isn't going to be violated, something with mass-energy has to be carrying that momentum away from the spacecraft, and if it's not matter, it has to be radiation. But the claimed efficiency is about 5 orders of magnitude higher than radiation pressure could possibly produce.
Explanations aside, if in the slight chance it's workably better than ion thrusters for certain applications, that's great. If it turns out to be snake oil or a hoax, that would not be a huge surprise either.
Ion thrusters still require expendable fuel as well as an electrical power supply, if you can cut out the need for expendable fuel that would mean allot for space travel especially to the outer solar system and beyond.
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.
There are independent replications, which IMO mostly rule out hoaxes -- or at least greatly reduce the likelihood to below other explanations. It's tough to create an independently reproducible hoax.
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.
I'm not suggesting it's explained by current physics. What I'm saying is that if it works, I'd consider new physical explanations that maximally preserve conservation laws first -- sort of for Ockham's Razor reasons.
"Every time this gets tested—presumably more and more carefully—the measured force gets smaller."
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.
No it is because the Chinese test dumped kilowatts of energy into the test item but the NASA test used only miniscule power. The guy you replied to presented the facts in a misleading way.
I'm slightly more skeptical about EmDrive than optimistic, however, you are right: if someone has to distort the truth in order to make a point it might be time that they question their standpoint on a matter. This looks like a lot of opinions about science. Which is a logical contradiction. An opinion has absolutely no sway in determining whether or not the device works. Opinions have nothing to do with science.
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.
The new test was at slightly lower power but within an order of magnitude of the original test: 700 W versus 2.5 kW. The measured effect, on the other hand, has decreased by more than four orders of magnitude.
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.
The difference in measure thrust is due to different test articles and testing done in different labs. The 720 mN result was from China and they dumped a ton of energy into it. The smaller 20 μN result was from NASA's testing which used far less power, so the resulting thrust measure was also smaller.
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.
One derivation starts with E = mc^2, which is a special case of E^2 = m^2c^4 + p^2c^2 but with velocity set to zero. In the second equation if you instead set the mass to zero you get p = E/c (momentum equals energy divided by the speed of light) for massless particles.
Because photons travel at the speed of light, we need to consider relativistic effects. Under special relativity, classical momentum (mass * velocity) is not actually conserved. To achieve conservation of mass, we consider the "inertial mass" of an object instead of the classical mass, where the intertial mass is given by:
m'=ym
y=1/sqrt(1-(v/c)^2)
As you can see, y>1 and y approaches infinity as you speed approaches the speed of light. This is why we say that the mass of an object increases with its velocity, and that any object with mass traveling at the speed of light will have infinite mass.
Now consider the momentum, p, of a photon. We have:
p=m*y*v
m=0
y=infinity
v=c
this gives us p=0*infinity, which is indeterminate, so we cannot use this equation to determine the momentum of a photon.
Instead, we can use the engery-momentum relationship, which states:
E^2 = (mc^2)^2 + (pc)^2
(This is a generalization of the famous E=mc^2 equation to also consider the momentum). In this equation m refers to the rest mass, not inertial mass. Because we are dealing with a photon, we have m=0, which gives us:
E^2=(pc)^2
p=E/c
Indicating that the momentum of a massless object is proportional to its energy.
Yes (but also no). The initial form of this equation is
(mc^2)^2 = E^2 - (pc^2)^2
The Pythagorean theorem tells you the length of a 2D vector when you know x and y lengths. Here mc^2 is the length of the 4-momentum vector [E, pc^2] (where p is a standard 3D vector). However since our 4D spacetime is not Euclidian but Minkowskian the sign in the generalised Pythagoras theorem is a minus and not a plus.
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)
ds is an "invariant proper time" which has the same value in all frames of reference. Check any special relativity textbook for the details.
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
which is the frame-invariant length of the energy-momentum 4-vector.
(I think that m is better written as m_0, the rest mass, since the "m" notation sometimes means relativistic mass, which is different.)
No, it is not a coincidence [0]. It is a direct result of the fact that in relativity temporal and spatial information has to be unified into a single vector (a four-vector [1]). Since (in the Noether theorem sense [2]) energy is the conserved quantity related to symmetry of displacements in time and momentum is the conserved quantity related to symmetry under displacements in space, it is quite natural to unite them into one four vector, related to symmetry of displacements in spacetime.
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.
"Relativistic Inertial mass" (m' = ym) is a bogus term invented so as to make the equations look the same as the classical ones in some limited circumstances - namely, when a force is acting in the same direction as the relative velocity. If a force is acting in a different direction, to obtain a relation of the form F=mdp/dt, you need a different* so-called relativistic inertial mass.
I know of no one doing modern research in relativity using this obsolete concept.
While your comment doesn't add much to this discussion, I won't turn down a chance to educate.
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.
That's got to be the first one I've ever heard of that can do that. I don't imagine it'll make much difference in most cooking but for things like softening butter that you only do for 10-15 seconds I could see it making a big difference.
If you pay careful attention to a typical microwave, you can easily tell when the magnetron is on and when it's off. E.g. when on the light will dim slightly, and if you're heating some food it might visibly bubble.
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.
I have a Panasonic and it makes a difference. (or maybe it's just confirmation bias?)
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.
I would expect it to make a bigger difference at low power settings, so I don't think it's confirmation bias at all. 10 seconds of almost-high output compared to 9 seconds of high output won't see much difference. However, 10 seconds of low output vs 2 seconds of high will see a big difference. Same amount of energy, but delivered over a 5x longer time period.
Cool. This is still unusual for a consumer microwave, at least for the current moment. But I'm glad to see some manufacturers including it. Hopefully my post will be antiquated in the near future!
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.
Seriously, it isn't that expensive to get a shot on a possibly blowing up test rocket that is going into orbit, launch something and fly it out to mars and back. We'll believe you then.
Making projections like "this drive could get a probe to Pluto in 18 months" seems kind of premature, given that scientists still aren't certain that the drive works at all, let alone how efficient it actually is.
I've been following this story pretty closing for several months now. So here's the opinion of an actual research scientist.
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?
Laymen tend to underestimate the very vast body of research which supports current physical models. "New physics" would imply that something has been fundamentally wrong with physics for a long time, and that is unlikely.
I'd love to see new physics! Every physicist I know loves new physics.
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.
That makes sense, but that's not how I interpret "nobody wants to see new physics" in the ancestor comment. (But who knows.)
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.
99.99% of the time when "new physics" is invoked, it amounts to crookery or kookery. Nobody wants to see that, because it takes energy to disprove even the obviously flawed claims, and the energy is taken away from more promising endeavors, that are usually less appealing to the public.
"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.
> I think the last thing anyone wants to see here is "new physics".
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.
Well, it’s improbable, not nonsensical. If someone goes and implements a technology that trounces our working theories, we certainly need to update those theories. It’s just that that’s exceedingly unlikely to happen.
Photoelectric cells were invented before we understood the photoelectric effect, alcohol and preserves were used to store drinks and foodstuffs before we understood microbes, forging and annealing used before anyone had a theory on metallic crystal formation, and incandescence was used before anyone understood electromagnetic radiation; to name but a few examples. Why would it be surprising that someone invented a device which functions in a manner which is not understood?
Oh! This is one of my favorite questions about scientific progress.
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.
I'm sorry, but your reasoning completely escapes me. The only things that are left are very big, and very small? In addition to this being an incredibly vague catchall (which misses all the possible discoveries of 'black swans', that is phenomena and occurrences we have never seen), your statement more importantly misses the fact that humans don't even understand what something as common and important as light (or electromagnetic radiation in general) is. Is light really big or really small? We've certainly characterized light's behavior (to some degree), though we still have basically no understanding of what it actually is (though I may be the only one who finds the circular definitions of electromagnetic fields unsatisfying). The same is true of things like matter and gravity. Once we have better understandings of what these are, I may grant that further fundamental insights will be difficult to come by; but we're not there yet.
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).
I think it was implied that "truths" meant scientific truths, which are well defined as anything that can be verified beyond statistical doubt with experimental evidence.
> We've certainly characterized light's behavior (to some degree), though we still have basically no understanding of what it actually is.
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.
One could say the same of a stone, a plant, a planet, or a star, yet we do not simply characterize any of these, we endeavor to understand its origins and constituent parts. In the case of the star, we could have analysed its spectrum, size, trajectory (through space), and surface characteristics, then called it a day; yet we continually try to understand the elements which make up the star, what their state of matter is, how they are reacting, and many other aspects of the star. I disagree with you when you say (of light) that "all we can do is to characterize its behavior".
Well maybe that's not all we can do. Maybe the abstraction of treating light and the rest of the Universe somewhat separately will break (of course we describe the coupling too). Maybe the abstraction of treating light as a non-dividable entity in the Universe will break. It would only create other axioms and/or other non-dividable entities, at what point would you be satisfied? It could very well be that you can't divide light any further and I would be satisfied with it if we can describe its behavior fully. If one says that light is a broken abstraction and you can describe the Universe using only "string" then you would ask "Yeah, but what strings are?".
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 think that your last point gets to the heart of the question, and you are right that we may never achieve a deeper understanding of light, matter, or gravity; but that does not mean that a deeper understanding is not desirable, or that we should stop asking the questions. Further, we will never know for certain when we have reached the bounds of our capacity to understand, so I will continue to ask "Yeah, but what strings are?". I always like to keep in mind that 'atom' means 'indivisible' in Greek, and yet we found that bound of knowledge to be surmountable (with debatable consequences).
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".
> we still have basically no understanding of what [light] actually is.
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 think you misunderstand my point. Model-building is only one aspect of science, and happens to be the most prevalent in some (though not all) of today's mathematical and statistical based studies of physics (which are often criticized as an exercise in curve-fitting). One example is how string theorists are making a valiant (though perhaps errant) effort to understand matter; they are not simply modelling well characterized behaviors. There are many physicists and other scientists who are continually trying to understand their subject matter (pun intentional) at a deeper level, such as those who discovered and described DNA.
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, I originally argued the point that progress in the physical sciences generally doesn't involve utterly canceling out previous discoveries. The link to Asimov's article elsethread illustrates this better than I could hope to. Relativity for instance did not find that Newtonian mechanics was wrong, it simply revised it under pathological cases. The Bohr model of the atom isn't completely wrong, and it's still useful in chemistry, it's just that as physicists have learned more they've found details where it's not completely right either. This kind of constant revision is a theme throughout the history of scientific progress.
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.
I guess you can say that ariving at Maxwell equations or QED is an exercise in curve-fitting in some sense. In the end, it is the simplest set of rules that matches a set of observations.
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.
"we cannot say that we understand all there is to know about electromagnetic phenomena because we can make a few simple predictions"
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.
Thank you! I had read this in the past, and it was one of two major influences on my thinking about scientific progress, but I couldn't remember exactly what it was I had read.
Asimov naturally describes it much better than I could.
Yeah, that specific article was on my mind when I wrote my comment. But I didn't say there were no more discoveries left to be made; I said they weren't happening in people's garages anymore, which is true in the majority.
Inventing a device which is not well understood and inventing a device which contradicts things that are thought to be well understood are two different things. The photoelectric effect was pretty big news though and it did break existing laws that time so it doesn't really fit here.
I could argue that all the inventions I mentioned violated one existing theory or another at the time of their creation, though the level of scientific reasoning behind each is different. Remember that at one time, many believed that heat was an element released from logs by fire, which is a theory clearly violated by the incandescent light bulb, and other earlier examples of incandescence (such as that of other heated metals).
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.
Not sure what is to fear from new physics. Sounds like something new and exciting to work on. Aren't physicists tired of perpetually iterating over string theory and making no new discoveries?
EmDrive and Cold Fusion are the perfect complementary technologies. Next someone should claim to invent a cooling system that doesn't reject heat, and we can start building Stargate Puddle Jumpers.
I've been following this story pretty closly for several months now. So here's the opinion of an actual research scientist.
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 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 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.
Conversation of momentum is strongly tied to the conservation of energy through relativity theory. If it actually works (I doubt it) it has really strong implications.
Conservation of momentum is a much bigger deal than conservation of energy. We already know of situations in which energy isn't conserved (like the energy of a photon decreasing when there is metric expansion where it is.)
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.
Much like conservation of energy is a consequence of time translation symmetry. If you mix spatial and time coordinates through relativity theory you can see that these are strongly coupled.
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.
Question: why did someone build this drive if theory predicts it won't work? Were they just tinkering or did they have an alternative theory from which they could deduce it might work?
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[ 2.9 ms ] story [ 235 ms ] threadI'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.
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.
[http://emdrive.com/faq.html]
So, the momentum simply "builds up". That's an exceptionally weak explanation.
The deeper reasons are above my pay-grade.
Now consider the momentum, p, of a photon. We have:
this gives us p=0*infinity, which is indeterminate, so we cannot use this equation to determine the momentum of a photon.Instead, we can use the engery-momentum relationship, which states:
(This is a generalization of the famous E=mc^2 equation to also consider the momentum). In this equation m refers to the rest mass, not inertial mass. Because we are dealing with a photon, we have m=0, which gives us: Indicating that the momentum of a massless object is proportional to its energy.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 is an "invariant proper time" which has the same value in all frames of reference. Check any special relativity textbook for the details.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
which is the frame-invariant length of the energy-momentum 4-vector. (I think that m is better written as m_0, the rest mass, since the "m" notation sometimes means relativistic mass, which is different.)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
[3] https://en.wikipedia.org/wiki/Lorentz_transformation
[4] https://en.wikipedia.org/wiki/Invariant_mass
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.
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.
https://www.reddit.com/r/EmDrive/
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.
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 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 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.
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."