There were days on the internet when a car analogy was appreciated -- let me try here.
Suppose there was a rally driver who would claim that rally cars could go much faster if they were always driven in reverse. He did some rudimentary experiments and might have found a significant improvement. The general public and other racing drivers, who in my analogy can all be wonderful people but happen to know little about the mechanics of cars, are naturally enthusiastic: a potential breakthrough in driving! But clearly we need more experiments. So other rally drivers get to work: they set up an elaborate system with ropes and pulleys so they can reverse the driver's position in the car and run a car as fast as they can, but in reverse, on a test track. What do they find? Sadly, their answer is somewhat inconclusive, probably negative, but perhaps the test track had many bends. So they would like to repeat the experiment on a track with a few more straight segments: they write grant proposals, build a track, and plan other test runs... and all the time their progress is eagerly followed by the general public.
Now suppose you are a car mechanic in all this. What are you to do? This cannot work! It flies completely in the face of the way cars are set up, not to speak of the disadvantages in air flow. So you can loudly dismiss the claim as preposterous early on, but then you will be called a pessimist and the public point out that at least the rally drivers are trying something new - what the bleep have you been doing all this time? So you just wait the whole thing out, see it come... and go.
I guess I should at least be happy that I did not buy any shares in EnDrive Inc?
There is a difference here: cars are built by car mechanics; they know cars inside out --- cars are never designed to drive in reverse. Physicists, on the other hand, didn't invent physics, so they know their current understanding of physics could be wrong.
This idea that we are so sure of everything is pervasive. The kind of people who like science are often the kind of people who crave certainty. And so for them science becomes like a religion, it provides them with a sense of certainty. Consistency. So when they rally against stories like this what they are really doing is reaffirming their own faith in an orderly universe, reaffirming their own faith in their scientific religion. It serves an emotional need. Which is why, paradoxically, their arguments are not alterable through logic.
If you go read what the real experts in a field have to say about the state of knowledge, they are often incredibly humble. They state that there is so much that they do not know. That are so many things that could be wrong. That there are even bigger pictures just beyond their grasp.
Now these reactionless thruster concepts don't look to be doing too well. But I for one am not particularly convinced that mach 's principle is so stupid.
> they know their current understanding of physics could be wrong.
Sure, we do know!
And we know how to recognise when someone masters current literature (a.k.a. factual knowledge) and proposes a breaktrough in a yet uncovered field, and when someone is speaking out of his ... nothing!
If you prefer a non-car analogy: we all do know that a hundred consecutive heads is possible, still you are not going to bet your week pay on it, even if you were promised 2^100 weeks of pay in return.
> Physicists, on the other hand, didn't invent physics, so they know their current understanding of physics could be wrong.
They also know they have experimented extensively over the region this effect claims to exist, and have found nothing of the kind for well over a century, and that if the EmDrive did what some claimed, it would violate literally thousands to millions of experiments already conducted.
Claiming physicists don't know everything about possible physics does not imply they don't know a tremendous amount about the places they have extensive experimental and theoretical agreement. Those places are not likely to ever change.
This whole thing has been obviously dumb for a number of reasons not even related to physics. You could almost use it as a good litmus test for who should be running a company, or working at important positions in government.
> Physicists, on the other hand, didn't invent physics, so they know their current understanding of physics could be wrong.
Technically, yes. but not in the sense that the word "wrong" is generally used. Existing measurements confirm that the current theories are mostly correct to high degree of accuracy, and over a lot of measurements, in a wide range of circumstances.
Current understanding may be proven _incomplete_, but it won't be superseded by something completely different that contradicts those measurements. That would be a non-starter, but it's what people think of when they hear "x is wrong".
e.g. Newtonian mechanics is "wrong" or "incomplete", but it gives very good answers for everyday circumstances. Just not for very small or very fast.
The best essay on this subject is "The Relativity of Wrong", Asimov, 1989
I agree that on this point the analogy is weak. But it describes the ignorance of all those hyping it up well.
People are generally aware that if someone is presenting a perpetuum mobile they are wrong. Free energy doesn't exist. The fact that you can't have free momentum is just as strong (and has been known longer), yet less widely intuited.
Let me give you an analogy though:
Let's say someone proposes a water base perpetuum mobile like this:
It only works if you place the machine under a massive waterfall though. Now this would be very difficult to refute experimentally, because you have to account for all possible interactions in the waterfall.
That's what the EM Drive is. A perpetuual motion machine built in such a way that there's a lot of energy going around and it's hard to eliminate all spurious interactions.
It's tough to know absolutely everything about a complex dynamic system, even if it's built by humans. Take the economy, for instance. Invented by humans, made up of humans and human technologies and concepts, and yet people only have vague ideas about how to control it.
Or take computers for that matter. People designed and built them from scratch. Someone had to design and lay out the transistors on the CPU, and presumably they know everything about how to do that. And yet we are currently trying to figure whether there's an ordering to switching the transistors on and off that would imbue the CPU with human-level intelligence. There are plenty of people who know computers inside and out, yet there are still questions that need answers. We have a whole discipline called Computer Science that performs experiments on computers for the purpose of answering these questions.
I really don't think cars are designed by the same people who end up fixing them - ease of repair really doesn't seem to be a big factor in lots of designs.
The design of a car is obviously limited by fundamental aspects of physics which are outside of the control of car manufacturers. For example, car manufacturers didn't invent combustion, aerodynamics, etc.
On the other hand, this is the sort of attitude that would make an informed skeptic reject the theoretical possibility for nuclear power, two weeks before the first nuclear bombs were used in war.
It took a team of physicists four years to disprove this result. Did they do it just to prove a point, or because they didn't understand the car analogy? No, professional scientists are rarely that callous with their time.
There was a slim possibility that our understanding of physics was wrong, and now we know for sure that this was not an instance of that.
But everything that's really interesting happens at the edges. No groundbreaking scientific result, ever, has happened by rejecting out of hand unlikely observations that violate established theory.
These weren't rejected out of hand - from the very first results there were ripe questions being asked (i.e., why did it take so long to measure thrust, and how were they controlling for thermal expansion, see even here on HN, quoted elsewhere in this thread - https://news.ycombinator.com/item?id=12962579 )
You're absolutely correct that building better testing to disprove it completely is a good thing to do, just to remove the extreme unlikelihood that one of the most fundamental laws in thermodynamics are incorrect, but extreme skepticism is definitely warranted when the claim is so huge, and people are able to find realistic flaws (sufficiently realistic as to be proven to be correct) that would explain it entirely.
? A nuclear power plant was built before the bombs. It's main purpose was to generate bomb material, but they definitely showed the principle worked and powered a lightbulb with it.
Claim: banging your head against the wall makes you smarter.
Experimenters: that sounds amazing! So we tried. We can report that all test subjects reported a massive headache. Unfortunately none seemed to get significantly smarter.
You: a negative result, well done! Time to celebrate!
And now I hope you will accept my apologies for exaggerating to the point of being rude, all in reply to your entirely reasonable question.
I guess my point is this. There has to be a cutoff where a claim is too obviously incorrect and testing is simply not useful any more. But the natural cutoff point depends enormously on perspective. Are you a car mechanic, a rally driver, or a complete layman? And as the latter, who do you trust?
My original comment was written to highlight the frustrating perspective of the car mechanic. But an interested layperson (or a non-expert handing out grant money) might have the more difficult time.
hello, speaking as a diesel engine mechanic, this is exactly what modern emissions controls have sadly become.
professional drivers (truckers) want to cut out all the emissions control systems because "older trucks get better mileage!" On the face of the issue this seeems to be true, but even after cutting everything out and switching back to low-grade diesel all you've done is create a smoke and soot belching mess from the 1960's. Why is this?
Two reasons: older trucks got great mileage because there was less traffic congestion and fewer weigh station stops, and the national maximum speed limit law in 1973 made sure trucks drove a speed that got great mileage.
Interesting analogy, but the pessimistic view does not bring any progress. The optimistic view may often be wrong, but when it is actually right, it makes our civilization progress.
Not so long ago, the experts knew and said it was impossible to land and reuse a rocket.
What you call the "pessimistic view" might be very enthusiastic about projects that are orders of magnitude more likely to work. So in my opinion, the relevant axis is not optimistic vs. pessimistic, but informed vs. uninformed.
Can an outsider with no knowledge of the field make a chance discovery? It's theoretically possible, and we might want to support undirected experimentation for the one in a billion chance that something might work. But we should take those probabilities into account when allocating our collective resources.
Ironically, this serves as an excellent refutation of the above analogy’s goal (to scoff at EMDrive experiments):
* Imagine telling a mechanic that mounting a ski box on your car with the fat/blunt end pointed forward seems to improve fuel economy vs being mounted the other way.
* The mechanic believes it’s absurd to claim you can improve fuel economy from a change that increases wind drag, so therefore your experiment is wrong since it seems to contradict established theory — case closed.
* Imagine that you more carefully measure, and find that it still seems to work surprisingly well (though also mysteriously reducing braking and cornering performance)!
* The mechanic still denies the result (which is unfair), and questions your test methodology and demands replications of the experiment (which is fair).
* Imagine someone else tries to replicate the experiment with a differently shaped ski box (i.e. not an airfoil, or with the airfoil shape vertically inverted), and fails to reproduce your results.
* The mechanic community concludes that the original result was obviously just experimental error, since the latter failure to replicate aligns with current theoretical consensus of what should happen.
In a similar way, early pioneers experimenting with winged aircraft design were laughed/scoffed at endlessly by established scientists/engineers of the era, ridiculed and crackpots wasting valuable time and resources.
The aerodynamics of the airfoil (which also explains the above ski box phenomenon) is an extremely non-obvious emergent effect, and even to this day is not as fully understood as most people probably assume.
For a bit of context: a brand called DAF ("van Doornes Automobiel Fabriek") came up with a very clever drive system, called variomatic. It is still in use today under CVVT in Honda vehicles. DAF had an unfair reputation as a 'womans car' because you didn't have to shift gears at all, nor was there a finicky automatic gearbox to maintain, just two pulleys and a belt for each rear wheel. Which gave it insane acceleration as well because the torque convertor gave maximum torque at the lowest speeds ramping down the torque gradually and continuously as speed increased.
One peculiar aspect of this drive system is that it allows your car to go as fast in reverse as it does forward! Of course the Dutch could not let this go without setting up a race around that theme, which was wildly popular in the past.
Since dafjes have an 'unfair advantage' you also got a secondary class, with other car brands, this is a video of that race.
That video really hurts to look at by the way, the casual destruction of such a large number of what would be very special classics today is grating, especially that pretty 55 coupe is one that I'd love to keep around.
This seems a lost battle. Every EM Drive discussion I have seen has been dominated by non-scientists pontificating about how we don't know anything, and our theories might be wrong, and we should keep an open mind ...
Re the airflow point, many cars are indeed MORE aerodynamic than normal in reverse, particularly hatchbacks.
It's best to have a smooth, progressive tail to minimise flow separation at the rear of the car (think of an airfoil shape - quite blunt at the front, thin at the back).
Hatchbacks often have very flat rear ends compared to the front which usually has a more progressive slope. A famous example is the Austin Allegro, but it's actually quite common.
also for all the knowledgeable people hurt by naive enthusiasm.. I guess a healthy dose of cynicism is to find a way to benefit from this and then reuse them for your better thought out projects
How exactly could this be done reliably? With shorts you have to commit to a timeframe for not only finding evidence to reject the claim but also for the news to break and convince other investors.
Meanwhile you can be targetted by financial actors that play your positions on the stock market, at times even disregarding the atual company behind it. Further you have to mind monetary policy. If faith in the stock suffers compared to other stock but the overall market just goes up and up, your shorts have a problem again.
Personally, I have no informed opinion on EmDrive, but I have been very pesimistic about companies in the past and I am about some right now. Still, I do not think that shorts are anything appropirate for me. I'd much rather buy competitior's stock than burn myself with shorts or waste hundreds of hours getting into the financial market that I could also use to create value in my actual job/profession
Short the individual researchers? Research projects? Short private funding?
Scams like EmDrive (but there are countless others – "save the planet with X") may be amusing, as long as it's on someone else's dime. Live and let live.
But the minute they manage to convince enough people, whether by virtue or shady marketing, it becomes a political problem. And then it's your problem too, through taxation and "too big to fail", no matter your position. Shorting on the stock market gets you only so far, and only for entities that actually exist on the stock market.
I would point out that cars have gears, but then someone would say that in the US they do not, and I would have to explain that that is not the case, actually, and it would all get very tiring very quickly.
> Who are the experts on emDrive tech, and what principle does the emDrive violate?
A physicist would point out that momentum is conserved, so nothing can start moving without something else moving in the opposite direction, but then someone would point out that cars seem to be able to do just that, and then I would point out this big round thing underneath a car, and it would all get very tiring very quickly.
It is purported to generate thrust by reflecting microwaves internally in the device, in violation of the law of conservation of momentum and other laws of physics.
For everyone that’s expressing a view like “what a waste of time”, consider this. This hypothesis was by a respected scientist. The experiments have been done by lots of labs. There has been a reasonable position the skeptics have taken throughout. It still has taken a very long time of a bunch of smart people on how to build an experiment to rule these kinds of things out. That means theories have tighter bounds. Technology has been improved in the area which can have knock on beneficial educational and technological effects, etc. Being able to quickly and efficiently rule out hypotheses is a hallmark of the area that science shines in. Being able to say “no, definitely not” with very good certainty is a useful thing to this disciplines toolbelt. From that perspective it’s a pure win and worth any distraction on the scale of all human investment globally.
Yeah this is great - they have made an advance in how they can make measurements. There will be many more reaction-less thruster concepts to analyse in the future. Now we have a much better idea how to test them effectively.
These measurement techniques are useful in other areas, too. Less error means more confidence in results for experimental physicists and potentially one less source of error to care about.
Or maybe finally learn mechanics 101 - what the conservation of momentum is. The kind of stuff we expect to understand from smart 16 year olds.
This is the physics equivalent of someone writing a brute-force recursive SAT solver and wondering why it takes so long. Perhaps we don't measure time correctly? What if mirrors are an illusion? We mustn't stop advancing the field!
So far I think it has been handled well. Let's just hope this doesn't end up like cold fusion where no amount of proof that it doesn't work can't make it go away and conspiracy theories keep growing.
Just to be clear, for most anyone with low-thrust measurement experience, thermal drift had been suspect nr 1 from the moment Eagleworks published their work. Here is a comment I made back at that time:
Lol at the lone reply you received. You called it and that's what you got. I hope we can learn to look at all points from more perspectives in the future.
It is what is mentioned in this fragment of the article:
"When power flows into the EmDrive, the engine warms up. This also causes the fastening elements on the scale to warp, causing the scale to move to a new zero point"
Basically, thermal expansion of the thruster and the measurement device causes the rest position of the thrust balance to drift with time, which is hard to differentiate from the actual thrust generated. This is most critical when the thrust-to-weight ratio is low, as is the case here.
For everyone that's disappointed, remember that thrust without reaction mass is still possible with enough electrical power and lasers, and doesn't appear to violate any known laws of physics.
It's also possible without any energy transmission using lasers etc. as long as you are in some non-flat spacetime (i.e. there is some mass in your vincinity). It's called "swimming in spacetime" [1]
[edit] You can find a less scientific / more illustrative introduction to the concept here [2].
> as long as you are in some non-flat spacetime (i.e. there is some mass in your vincinity)
I'm not an expert, but isn't that definitionally everywhere? Or is it that it works better when your vicinity is more curved? The paper is a bit beyond my ability to get anything from, and the summary on Wikipedia isn't much better, and also doesn't seem to match what you're implying it is.
> “Swimming in spacetime” is a geometrical motive principle that exploits the curved spacetime metric of the gravitational field to permit an extended body undergoing specific deformations in shape, to change position. In weak gravitational fields, like that of Earth, the change in position per deformation cycle would be far too small to detect, but the concept remains of interest as the only unambiguous example of reactionless motion in mainstream physics.
Photon drive is not "thrust without reaction mass", because photons do have mass (they have zero rest mass, but are never at rest). Mass of a photon is, unsurprisingly, E/c^2, where
E=h\omega. If photons had zero mass, they would not have been influenced by gravity, and bending of light by the solar mass has been measured in the beginning of 20th century.
You're using outdated terminology. Modern physicists use "mass" to refer to what was called "rest mass" shortly after relativity was developed in order to distinguish it from the new concepts they at the time called "relativistic mass" and "inertial mass". The term "relativistic mass" was motivated in part by the desire to still think of all gravitation as being sourced by some sort of mass, but the modern terminology is to say that gravity is sourced by the stress-energy tensor, of which (rest) mass is just one component.
Modern physicists unequivocally say "a photon has zero mass, but has non-zero momentum and energy".
That terminology is outdated. Today, mass generally means invariant mass, corresponding to rest mass in case of 'massive' particles. The invariant mass of photons is 0, hence it's 'massless'.
The gamma factors hidden by the relativistic mass definition of course still occur, but they get folded into the 4-vector quantities instead, which happens naturally if you use proper time for your derivatives.
This way, we avoid having to introduce things like transverse and longitudinal mass, which was the explanation within the variable-mass picture as to why the spatial part of 4-acceleration generally isn't parallel to 3-acceleration.
The photon paths bend due to the curvature of space-time caused by gravity. This does not mean that they have non-zero mass. iirc, it has been proved that photons have non-zero _momentum_ but I am not sure about mass.
Scott Manly did an overview of potential ways of propulsion in space including some very wacky setups. The most promising ones seem to be using nuclear or fusion reactions to accelerate tiny amounts of mass to very high speeds. The engineering issues are substantial of course. But definitely goes a bit beyond the limitations of chemical processes (i.e. burning fuels). https://www.youtube.com/watch?v=QEZv_OXA_NI
I'd say beamed energy propulsion is more promising for high speeds. That's because the main problem becomes keeping the vehicle from destroying itself with waste heat, and beamed propulsion keeps the waste heat back at the beam souce. You can even actively cool an object with laser light (via anti-Stokes scattering and the like.)
In the end it's all about a very simple equation: E(kin) = ½mv² so it's all about exhaust velocity. The closer you can get that to its theoretical maximum (e.g. c), the less reaction mass is required.
But the question still remains: is there a practical non-Newtonian way? We already know of rather impractical ones, such has deforming spacetime.
I mean, sure, ultimately mass==energy. It broadens your options but doesn't change the problem that you have to take it with you, it gets used up, and the more you take the more you have to use.
The difference is quantitative, but multiple magnitudes big: The ratio of impulse to mass is given by the exhaust velocity, and velocities for massive propellants barely reach 0.01% of the speed of light. Thus the thrust can be more than 10 000 times higher for the same propellant mass.
On the flip side, the exhaust velocity also determines the ratio of (kinetic) energy to impulse, so energy beam propulsion needs over 10 000 times more stored energy.
Energy beam propulsion is only viable if you have compact high-capacity energy storage available (antimatter?).
The thing is we know how to harvest solar energy while in space. Harvesting matter has been proposed with ram scoops but contrary to solar cells, these are just theoretical propositions.
Being able to use energy directly instead of propulsion mass would make a lot of travels more sustainable and with potentially lighter vehicles.
Note that in contemporary usage, the term 'mass' without qualifier is normally understood as a reference to invariant mass (aka rest mass). Photons have energy, but no mass. They can be used for propulsion due to having nonzero momentum.
I mean I would just load couple of metric tons of antimatter in the ship and then just use up picked up interstellar space mass (1 atom per cubic meter is not much, but you will be moving trough shitload of them) along the way to annihilate. the faster you move the faster you will go up to a couple of limits. BUT deceleration may be a bit of a problem.
In 2003 a scientist published a paper about cyclic changes in the shape of a quasi-rigid body on a curved manifold. He shown that it can lead to net translation and/or rotation of the body in the manifold, so in simple words "swimming in space". I guess this is only possible on very large structures.
Kudos for spending four hard years to publish a negative result! It will hardly make any of them famous, while it still is a very important result. Hopefully this means that we can leave the whole EmDrive debacle behind us once for all.
And to those that says that the outcome was given, and that they wasted their time, I'd say that we do have to sometimes try for the really long shots. In addition, it is important to show that we don't sweep any controversial results under the carpet just because they don't align with current "dogma".
> Kudos for spending four hard years to publish a negative result!
All scientific results are positive, but I have the feeling people end up skewing their research just to show what they want to see. Yesterday I read a study [1] by the most renown Brazilian university claiming that the control of Covid on Brazilian football is bad because 11% of the players got it while in Germany only 0.5% were sick. Then I looked the data up and the Bundesliga has the exact same 11% [2], but the researchers chose a very specific time frame in which they didn't have many cases, just to "prove" their point.
This was easy to verify, but I wonder how many long term researches find gibberish results and no one will ever know.
Considering how much waste heat can be thrown off by high powered microwave stuff (as in the original resonating cavity waveguide horn setup of the emdrive, which people thought to be producing thrust), I am not surprised at all that the apparent thrust was thermal expansion and contractions.
Klystrons and TWTAs are not exactly known for being low wattage pieces of equipment, in terms of their TDP (thermal dissipated power). Ask anyone that's ever worked on a 1000W+ uplink power amplifier for two way geostationary satellite stuff... It's a lot of heat to get rid of.
So these guys are trying to duplicate results of like 1 millinewton per kilowatt, meaning you'll need a microwave source of at least 3-4kW, of course it's going to throw off a lot of heat.
I do wonder if any of the scientists trying to duplicate this effect have thought to bring in some commercial industry manufacturers of big C, X, Ku band TWTAs and get their advice on building a test rig.
Or to try modern small but high power GaaN SSPAa vs TWTAs...
Even very low powered terrestrial microwave radios are a lot of waste heat compared to what they output in rf. The radio head on a ptp microwave dish setup that is a 35W load on -48vdc might be outputting around +18 into the waveguide, equivalent to around 200 milliwatts. The rest is all radiated into the atmosphere and what it's mounted on. This why you'll see ridges of heatsink fins on the body of a full outdoor modern 18 or 23GHz radio. This is considered to be totally normal (a 35W 1024qam dual linear polarity radio with a capacity close to gigabit Ethernet line rate is sure a big improvement over a full 42RU rack size Harris Megastar 64QAM radio consuming 1800W from 25 years ago)
Counterfactual: Assume it worked, let's say it's producing a millinewton per kilowatt.
That would mean one could put it on a spinning arm with a generator in the center and make overunity power.
If you ran it at 1 m/s, it would only produce 1 milliwatt (1 mN * 1 m/s). Underunity. If you ran it at a million metres per second, it would produce its own power, 1 kilowatt. And if you ran it at 2 million metres per second, it would produce twice the energy that it consumed.
2 million metres per second is 2000 km/s and less than 1% of light speed. Relativity can be ignored. Would it be possible to build such a system? In vacuum with UHMWPE wire, one could build a spinning system 2000 kilometers in diameter that would spin 3 times per second. The centripetal acceleration would be 200,000 gees. Wikipedia tells me this is in current ultracentrifuge acceleration range. https://en.wikipedia.org/wiki/Ultracentrifuge
Depending how far down the rabbit hole they go in weird microwave resonating cavities and power amplifiers, maybe something of practical use for radar systems or other uses of multi-kilowatt microwave band power amplifiers will come out of it.
The outcome was known for 4 years already, but then he needed 4 years to confirm the first results with fool proof measurements. Nobody else should need to wait years for test results, but the pressure and expected flashback was enourmous.
I just had a look at Tajmar's other publications[0]. They read like science fiction (well, that's of course because in a way they are):
> Tajmar, M., and Assis, A.K.T., "Particles with Negative Mass: Production, Properties and Applications for Nuclear Fusion and Self-Acceleration", Journal of Advanced Physics 4, 77-82 (2015)
> Tajmar, M., and Bertolami, O., "Hypothetical Gravity Control and Possible Influence on Space Propulsion", Journal of Propulsion and Power 21(4), 692-696 (2005)
> Lörincz, I. and Tajmar, M., "Null-Results of a Superconducting Gravity-Impulse-Generator", 52nd AIAA Joint Propulsion Conference, AIAA-2016-4988, Salt Lake City, July 25-27 (2016)
I think his job ranks among the coolest positions in physics that I've come across: He does fundamental physics (something almost every physics undergrad dreams of doing), both theory and experiment and both quantum mechanics and General Relativity, and he literally does rocket science. Unreal. I didn't think such a position could exist.
He's had some controversy in the past and had a bit of a quack reputation. It's nice to see this research done. When I saw the name associated with this I assumed the opposite result.
> He's had some controversy in the past and had a bit of a quack reputation.
Can you provide more details or, possibly, sources? Was it just because he dared considering (and testing) "crazy claims" like the EmDrive in the first place?
Readit News
Suppose there was a rally driver who would claim that rally cars could go much faster if they were always driven in reverse. He did some rudimentary experiments and might have found a significant improvement. The general public and other racing drivers, who in my analogy can all be wonderful people but happen to know little about the mechanics of cars, are naturally enthusiastic: a potential breakthrough in driving! But clearly we need more experiments. So other rally drivers get to work: they set up an elaborate system with ropes and pulleys so they can reverse the driver's position in the car and run a car as fast as they can, but in reverse, on a test track. What do they find? Sadly, their answer is somewhat inconclusive, probably negative, but perhaps the test track had many bends. So they would like to repeat the experiment on a track with a few more straight segments: they write grant proposals, build a track, and plan other test runs... and all the time their progress is eagerly followed by the general public.
Now suppose you are a car mechanic in all this. What are you to do? This cannot work! It flies completely in the face of the way cars are set up, not to speak of the disadvantages in air flow. So you can loudly dismiss the claim as preposterous early on, but then you will be called a pessimist and the public point out that at least the rally drivers are trying something new - what the bleep have you been doing all this time? So you just wait the whole thing out, see it come... and go.
I guess I should at least be happy that I did not buy any shares in EnDrive Inc?
If you go read what the real experts in a field have to say about the state of knowledge, they are often incredibly humble. They state that there is so much that they do not know. That are so many things that could be wrong. That there are even bigger pictures just beyond their grasp.
Now these reactionless thruster concepts don't look to be doing too well. But I for one am not particularly convinced that mach 's principle is so stupid.
Sure, we do know!
And we know how to recognise when someone masters current literature (a.k.a. factual knowledge) and proposes a breaktrough in a yet uncovered field, and when someone is speaking out of his ... nothing!
If you prefer a non-car analogy: we all do know that a hundred consecutive heads is possible, still you are not going to bet your week pay on it, even if you were promised 2^100 weeks of pay in return.
They also know they have experimented extensively over the region this effect claims to exist, and have found nothing of the kind for well over a century, and that if the EmDrive did what some claimed, it would violate literally thousands to millions of experiments already conducted.
Claiming physicists don't know everything about possible physics does not imply they don't know a tremendous amount about the places they have extensive experimental and theoretical agreement. Those places are not likely to ever change.
Technically, yes. but not in the sense that the word "wrong" is generally used. Existing measurements confirm that the current theories are mostly correct to high degree of accuracy, and over a lot of measurements, in a wide range of circumstances.
Current understanding may be proven _incomplete_, but it won't be superseded by something completely different that contradicts those measurements. That would be a non-starter, but it's what people think of when they hear "x is wrong".
e.g. Newtonian mechanics is "wrong" or "incomplete", but it gives very good answers for everyday circumstances. Just not for very small or very fast.
The best essay on this subject is "The Relativity of Wrong", Asimov, 1989
https://chem.tufts.edu/answersinscience/relativityofwrong.ht...
People are generally aware that if someone is presenting a perpetuum mobile they are wrong. Free energy doesn't exist. The fact that you can't have free momentum is just as strong (and has been known longer), yet less widely intuited.
Let me give you an analogy though:
Let's say someone proposes a water base perpetuum mobile like this:
https://en.wikipedia.org/wiki/Perpetual_motion#/media/File:W...
It only works if you place the machine under a massive waterfall though. Now this would be very difficult to refute experimentally, because you have to account for all possible interactions in the waterfall.
That's what the EM Drive is. A perpetuual motion machine built in such a way that there's a lot of energy going around and it's hard to eliminate all spurious interactions.
Or take computers for that matter. People designed and built them from scratch. Someone had to design and lay out the transistors on the CPU, and presumably they know everything about how to do that. And yet we are currently trying to figure whether there's an ordering to switching the transistors on and off that would imbue the CPU with human-level intelligence. There are plenty of people who know computers inside and out, yet there are still questions that need answers. We have a whole discipline called Computer Science that performs experiments on computers for the purpose of answering these questions.
Dead Comment
that's just plain wrong, friend.
It took a team of physicists four years to disprove this result. Did they do it just to prove a point, or because they didn't understand the car analogy? No, professional scientists are rarely that callous with their time.
There was a slim possibility that our understanding of physics was wrong, and now we know for sure that this was not an instance of that.
But everything that's really interesting happens at the edges. No groundbreaking scientific result, ever, has happened by rejecting out of hand unlikely observations that violate established theory.
You're absolutely correct that building better testing to disprove it completely is a good thing to do, just to remove the extreme unlikelihood that one of the most fundamental laws in thermodynamics are incorrect, but extreme skepticism is definitely warranted when the claim is so huge, and people are able to find realistic flaws (sufficiently realistic as to be proven to be correct) that would explain it entirely.
If it wasn't considered theoretically possible, what do you make of Einstein's famous letter?
Why not celebrate it?
Experimenters: that sounds amazing! So we tried. We can report that all test subjects reported a massive headache. Unfortunately none seemed to get significantly smarter.
You: a negative result, well done! Time to celebrate!
And now I hope you will accept my apologies for exaggerating to the point of being rude, all in reply to your entirely reasonable question.
I guess my point is this. There has to be a cutoff where a claim is too obviously incorrect and testing is simply not useful any more. But the natural cutoff point depends enormously on perspective. Are you a car mechanic, a rally driver, or a complete layman? And as the latter, who do you trust?
My original comment was written to highlight the frustrating perspective of the car mechanic. But an interested layperson (or a non-expert handing out grant money) might have the more difficult time.
professional drivers (truckers) want to cut out all the emissions control systems because "older trucks get better mileage!" On the face of the issue this seeems to be true, but even after cutting everything out and switching back to low-grade diesel all you've done is create a smoke and soot belching mess from the 1960's. Why is this?
Two reasons: older trucks got great mileage because there was less traffic congestion and fewer weigh station stops, and the national maximum speed limit law in 1973 made sure trucks drove a speed that got great mileage.
Not so long ago, the experts knew and said it was impossible to land and reuse a rocket.
Can an outsider with no knowledge of the field make a chance discovery? It's theoretically possible, and we might want to support undirected experimentation for the one in a billion chance that something might work. But we should take those probabilities into account when allocating our collective resources.
Who said it was impossible to combine them? And "impractically expensive and counterproductive" doesn't count.
* Imagine telling a mechanic that mounting a ski box on your car with the fat/blunt end pointed forward seems to improve fuel economy vs being mounted the other way.
* The mechanic believes it’s absurd to claim you can improve fuel economy from a change that increases wind drag, so therefore your experiment is wrong since it seems to contradict established theory — case closed.
* Imagine that you more carefully measure, and find that it still seems to work surprisingly well (though also mysteriously reducing braking and cornering performance)!
* The mechanic still denies the result (which is unfair), and questions your test methodology and demands replications of the experiment (which is fair).
* Imagine someone else tries to replicate the experiment with a differently shaped ski box (i.e. not an airfoil, or with the airfoil shape vertically inverted), and fails to reproduce your results.
* The mechanic community concludes that the original result was obviously just experimental error, since the latter failure to replicate aligns with current theoretical consensus of what should happen.
In a similar way, early pioneers experimenting with winged aircraft design were laughed/scoffed at endlessly by established scientists/engineers of the era, ridiculed and crackpots wasting valuable time and resources.
The aerodynamics of the airfoil (which also explains the above ski box phenomenon) is an extremely non-obvious emergent effect, and even to this day is not as fully understood as most people probably assume.
https://youtu.be/a59KyXhk74w?t=177
One peculiar aspect of this drive system is that it allows your car to go as fast in reverse as it does forward! Of course the Dutch could not let this go without setting up a race around that theme, which was wildly popular in the past.
Since dafjes have an 'unfair advantage' you also got a secondary class, with other car brands, this is a video of that race.
Here are the DAFs:
https://www.youtube.com/watch?v=zoh8i0jfpTo
That video really hurts to look at by the way, the casual destruction of such a large number of what would be very special classics today is grating, especially that pretty 55 coupe is one that I'd love to keep around.
=> so it may be faster indeed... :-)
https://tubedubber.com/?q=a59KyXhk74w:MK6TXMsvgQg:0:100:174:...
It's best to have a smooth, progressive tail to minimise flow separation at the rear of the car (think of an airfoil shape - quite blunt at the front, thin at the back).
Hatchbacks often have very flat rear ends compared to the front which usually has a more progressive slope. A famous example is the Austin Allegro, but it's actually quite common.
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also for all the knowledgeable people hurt by naive enthusiasm.. I guess a healthy dose of cynicism is to find a way to benefit from this and then reuse them for your better thought out projects
Dead Comment
Meanwhile you can be targetted by financial actors that play your positions on the stock market, at times even disregarding the atual company behind it. Further you have to mind monetary policy. If faith in the stock suffers compared to other stock but the overall market just goes up and up, your shorts have a problem again.
Personally, I have no informed opinion on EmDrive, but I have been very pesimistic about companies in the past and I am about some right now. Still, I do not think that shorts are anything appropirate for me. I'd much rather buy competitior's stock than burn myself with shorts or waste hundreds of hours getting into the financial market that I could also use to create value in my actual job/profession
Short the individual researchers? Research projects? Short private funding?
Scams like EmDrive (but there are countless others – "save the planet with X") may be amusing, as long as it's on someone else's dime. Live and let live.
But the minute they manage to convince enough people, whether by virtue or shady marketing, it becomes a political problem. And then it's your problem too, through taxation and "too big to fail", no matter your position. Shorting on the stock market gets you only so far, and only for entities that actually exist on the stock market.
When the facts change, opinions can change.
The objection to the EmDrive is that is that it makes no sense, which is much less likely to change.
Not sure a mechanic is better than anyone with understanding of car dynamics, but the "air flow" argument is the key to this.
Who are the experts on emDrive tech, and what principle does the emDrive violate? If you can't say, then you are indeed a pessimist.
I would point out that cars have gears, but then someone would say that in the US they do not, and I would have to explain that that is not the case, actually, and it would all get very tiring very quickly.
> Who are the experts on emDrive tech, and what principle does the emDrive violate?
A physicist would point out that momentum is conserved, so nothing can start moving without something else moving in the opposite direction, but then someone would point out that cars seem to be able to do just that, and then I would point out this big round thing underneath a car, and it would all get very tiring very quickly.
It is purported to generate thrust by reflecting microwaves internally in the device, in violation of the law of conservation of momentum and other laws of physics.
https://en.wikipedia.org/wiki/EmDrive
Extraordinary evidence is required for extraordinary claims. Any hint of evidence at all is required for idiot claims before waisting people's time.
This is the physics equivalent of someone writing a brute-force recursive SAT solver and wondering why it takes so long. Perhaps we don't measure time correctly? What if mirrors are an illusion? We mustn't stop advancing the field!
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https://news.ycombinator.com/item?id=12962579
But then, nobody had Tajmar's perseverance; kudos to his team!
It is what is mentioned in this fragment of the article:
"When power flows into the EmDrive, the engine warms up. This also causes the fastening elements on the scale to warp, causing the scale to move to a new zero point"
Basically, thermal expansion of the thruster and the measurement device causes the rest position of the thrust balance to drift with time, which is hard to differentiate from the actual thrust generated. This is most critical when the thrust-to-weight ratio is low, as is the case here.
https://en.wikipedia.org/wiki/Photon_rocket
https://en.wikipedia.org/wiki/Nuclear_photonic_rocket
https://en.wikipedia.org/wiki/Laser_propulsion
[edit] You can find a less scientific / more illustrative introduction to the concept here [2].
[1] http://groups.csail.mit.edu/mac/users/wisdom/swimming.pdf
[2] http://www.brophy.net/Downloads/AIL%20Class%20on%20Reality%2...
I'm not an expert, but isn't that definitionally everywhere? Or is it that it works better when your vicinity is more curved? The paper is a bit beyond my ability to get anything from, and the summary on Wikipedia isn't much better, and also doesn't seem to match what you're implying it is.
> “Swimming in spacetime” is a geometrical motive principle that exploits the curved spacetime metric of the gravitational field to permit an extended body undergoing specific deformations in shape, to change position. In weak gravitational fields, like that of Earth, the change in position per deformation cycle would be far too small to detect, but the concept remains of interest as the only unambiguous example of reactionless motion in mainstream physics.
Modern physicists unequivocally say "a photon has zero mass, but has non-zero momentum and energy".
The gamma factors hidden by the relativistic mass definition of course still occur, but they get folded into the 4-vector quantities instead, which happens naturally if you use proper time for your derivatives.
This way, we avoid having to introduce things like transverse and longitudinal mass, which was the explanation within the variable-mass picture as to why the spatial part of 4-acceleration generally isn't parallel to 3-acceleration.
edit: s/velocity/acceleration/ where appropriate
But the question still remains: is there a practical non-Newtonian way? We already know of rather impractical ones, such has deforming spacetime.
On the flip side, the exhaust velocity also determines the ratio of (kinetic) energy to impulse, so energy beam propulsion needs over 10 000 times more stored energy.
Energy beam propulsion is only viable if you have compact high-capacity energy storage available (antimatter?).
Being able to use energy directly instead of propulsion mass would make a lot of travels more sustainable and with potentially lighter vehicles.
https://dspace.mit.edu/handle/1721.1/6706
And to those that says that the outcome was given, and that they wasted their time, I'd say that we do have to sometimes try for the really long shots. In addition, it is important to show that we don't sweep any controversial results under the carpet just because they don't align with current "dogma".
All scientific results are positive, but I have the feeling people end up skewing their research just to show what they want to see. Yesterday I read a study [1] by the most renown Brazilian university claiming that the control of Covid on Brazilian football is bad because 11% of the players got it while in Germany only 0.5% were sick. Then I looked the data up and the Bundesliga has the exact same 11% [2], but the researchers chose a very specific time frame in which they didn't have many cases, just to "prove" their point.
This was easy to verify, but I wonder how many long term researches find gibberish results and no one will ever know.
[1] https://globoesporte.globo.com/sp/futebol/campeonato-paulist...
[2] https://www.sport1.de/fussball/bundesliga/2021/02/bundesliga...
Klystrons and TWTAs are not exactly known for being low wattage pieces of equipment, in terms of their TDP (thermal dissipated power). Ask anyone that's ever worked on a 1000W+ uplink power amplifier for two way geostationary satellite stuff... It's a lot of heat to get rid of.
So these guys are trying to duplicate results of like 1 millinewton per kilowatt, meaning you'll need a microwave source of at least 3-4kW, of course it's going to throw off a lot of heat.
I do wonder if any of the scientists trying to duplicate this effect have thought to bring in some commercial industry manufacturers of big C, X, Ku band TWTAs and get their advice on building a test rig.
Or to try modern small but high power GaaN SSPAa vs TWTAs...
https://www.cpii.com/docs/datasheets/17/t22ci_mkt326.pdf
https://www.cpii.com/products.cfm/153
Even very low powered terrestrial microwave radios are a lot of waste heat compared to what they output in rf. The radio head on a ptp microwave dish setup that is a 35W load on -48vdc might be outputting around +18 into the waveguide, equivalent to around 200 milliwatts. The rest is all radiated into the atmosphere and what it's mounted on. This why you'll see ridges of heatsink fins on the body of a full outdoor modern 18 or 23GHz radio. This is considered to be totally normal (a 35W 1024qam dual linear polarity radio with a capacity close to gigabit Ethernet line rate is sure a big improvement over a full 42RU rack size Harris Megastar 64QAM radio consuming 1800W from 25 years ago)
That would mean one could put it on a spinning arm with a generator in the center and make overunity power.
If you ran it at 1 m/s, it would only produce 1 milliwatt (1 mN * 1 m/s). Underunity. If you ran it at a million metres per second, it would produce its own power, 1 kilowatt. And if you ran it at 2 million metres per second, it would produce twice the energy that it consumed.
2 million metres per second is 2000 km/s and less than 1% of light speed. Relativity can be ignored. Would it be possible to build such a system? In vacuum with UHMWPE wire, one could build a spinning system 2000 kilometers in diameter that would spin 3 times per second. The centripetal acceleration would be 200,000 gees. Wikipedia tells me this is in current ultracentrifuge acceleration range. https://en.wikipedia.org/wiki/Ultracentrifuge
"We were able to greatly improve our measurement technology as a result"
> Tajmar, M., and Assis, A.K.T., "Particles with Negative Mass: Production, Properties and Applications for Nuclear Fusion and Self-Acceleration", Journal of Advanced Physics 4, 77-82 (2015)
> Tajmar, M., and Bertolami, O., "Hypothetical Gravity Control and Possible Influence on Space Propulsion", Journal of Propulsion and Power 21(4), 692-696 (2005)
> Lörincz, I. and Tajmar, M., "Null-Results of a Superconducting Gravity-Impulse-Generator", 52nd AIAA Joint Propulsion Conference, AIAA-2016-4988, Salt Lake City, July 25-27 (2016)
I think his job ranks among the coolest positions in physics that I've come across: He does fundamental physics (something almost every physics undergrad dreams of doing), both theory and experiment and both quantum mechanics and General Relativity, and he literally does rocket science. Unreal. I didn't think such a position could exist.
[0]: https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/forschung/f...
Can you provide more details or, possibly, sources? Was it just because he dared considering (and testing) "crazy claims" like the EmDrive in the first place?