I really, really wish that there was something to the emdrive/mach effect drive/etc, but alas, physical theories do not exist to make our lives better.
Many of those physical theories aren't all that old though. While I agree it's pretty unlikely, it's possible that they can be overthrown with more research.
The physical theories that prevent the EmDrive (conservation of momentum) are centuries old, and utterly fundamental to our university of reality on every scale from black holes merging to atoms radiating. A violation of this principle would involve radically altering the very foundations of modern physics, on a level more profound than anything that has ever happened in the history of the field.
i have a question about conservation of momentum. what about losses due to friction and/or heat?
I could imagine through some interesting device a way to have thrust in one direction with the "conservation" occurring as heat radiating in all of the other directions -- is this not compatible with conservation of momentum or am i a crackpot who doesnt understand the basics (the more likely case, i am sure)
Electromagnetic radiation has momentum - it's small, but not zero. If you're emitting a bunch of photons (e.g. infrared photons from blackbody radiation of a hot object) more to one side than the other, then the remainder of that device will have some thrust. But that does not violate conservation of momentum, as the momentum gained by the device will equal the momentum of these photons; and the total momentum of the whole system (the device plus all the photons radiated) will be constant.
Crackpot who doesn't understand the basics (not to be rude). Unlike energy, momentum is a vector quantity. A system can't disperse momentum "in all directions" because the net effect will cancel out. A bomb that has net momentum 0 still has net momentum 0 after it's been exploded.
What about the idea that parallel lines do not intersect and that there is exactly one line through a point parallel to another given line? These were thousands of years old and well accepted until pretty recently.
One of Euclid's axioms is that parallel lines do not intersect. This is true on a plane, so Euclidean's axioms describe planar geometry. In non-euclidian geometry you relax this requirement, giving rise to things like hyperbolic spaces and elliptical spaces.
Not sure what OP is going on about though, as this doesn't seem particularly on topic.
Our daily lives are not greatly impacted by this assumption not being true. Unless we look at the horizon or at a map, it is easy to forget that we live on a globe. And without atomic clocks it is very hard to measure the curvature of spacetime.
And slight flaws in the conservation of momentum wouldn't affect our current daily lives either.
But this would still be an extremely useful effect if it does exist, for devices designed to focus it. Look at how an electric field's influence on semiconductors has almost no relevance to anything except when harnessed just right.
> What about the idea that parallel lines do not intersect and that there is exactly one line through a point parallel to another given line? These were thousands of years old and well accepted until pretty recently.
Actually, that axiom made even the ancients uncomfortable. There were lots of attempts over the centuries to "prove" or "disprove" it.
The fact that violating it can still produce a self-consistent geometry was what was stunning.
Sure, but that’s true of ion propulsion too. It’s pretty common for you to use different motors at different stages of flight; even liquid motors usually have different bell designs for different altitudes. If the emdrive works (if!), then you’d just bolt one on top of a regular rocket.
If it works then we can just throw up a nuclear reactor into space and a small amount of nuclear fuel will create a continuous thrust which in space matters. Can lead to a spaceship that gets shuttled to which just ferries ships between planets.
If we could put a nuclear reactor in space large enough for this to be useful, we could use the reactor to boil water and get vastly more thrust. Or run an ion drive and get more thrust. Or just let the fission fragments out the back and get more thrust.
What this would be useful for is (by no coincidence) also the exact reason why it is considered crank science: you could use it to build a perpetual motion machine because it violates conservation of energy/momentum laws.
The trick is not requiring propellant. You can’t carry 90 years worth of water or gas. The Dawn spacecraft launched to Ceres in 2007 used up 425kg of Xenon for only eleven days of thrust for its ion engine.
You still need tons of fuel for that, in the order of tens of tons per year travelled - unrealistic for travel outside our solar system. Thrust doesn’t really matter at that time scale.
The fuel is the reactor fuel. Literally the fission products of the uranium/plutonium in your reactor, from where the power you want to use for the EmDrive comes from, would beat this.
If the EmDrive actually worked, the correct use is to violate conservation of energy and momentum, not as a straightforward substitute for the engines we have now.
EmDrive looks like an accounting error to me, not something that actually works. Any energy it expends turns into heat, radiating in a predictable but not necessarily isotropic way. This radiation carries momentum, but much less than the EmDrive claims to be capable of.
A rocket or ion drive? The energy goes into the kinetic and gravitational potential of the exhaust.
How long would it take a nuclear powered EmDrive to push a fully loaded semitrailer from 0m/s to the speed of the interntional space station?
The maximum mass for a semi-truck fully loaded is 36000kg. The EmDrive generates 12millinewtons per kw. 1n = 1kg*(1m/s^2). Leo ~=7.66km/s^. A nuclear reactor produces ~1gw. We would need 275760000N to accelerate a semi truck to leo speeds. A nuclear powered EmDrive would take ~265 days to push a semi truck to low earth orbit speeds.
The escape velocity of Earth's orbit is 11.19 km/s, and if you were going to take humans on the trip you'd need much more cargo than 36000kg. Granted, you wouldn't have to move the craft from 11.19km/s to 0km/s and then 0km/s to 11.19 km/s every time you entered and left orbit, but it would be a slow ride regardless.
I think we can't ignore the weight of the nuclear reactor though - we are not lifting just the truck, the reactor has to carry it's own weight. And a 1GW reactor will dwarf the 36t payload I think.
Ion thrusters already do this though. Even with conventional rockets once you're in space finding new fuel shouldn't be a big deal. It's just a matter of building the infrastructure. Right now leaving earth is still the biggest problem.
Yah that'll only require a few gigawatts. Or terrawatts? But if there is an unknown effect hopefully we can figure it out and refine it. Like with blackbody radiation it might be only incidentally overlapping a new effect.
Falcon 9’s engines combined produce ~7,500,000,000 millinewtons of force (at sea level) per SpaceX’s website (converted from their figure of 1.7M lb/foot of force).
So doing some napkin math with the article’s 12mN/kW, that’s close to a terawatt. For reference, I think worldwide electrical power generation capacity is around 10x that.
edit: made the math more explicit due to child comments and fixed spelling error
The missing value would be the 12mN/kW that the top post opened with. Getting 7.5 MN output thrust with that conversion ratio requires 625GW of input power.
The work achieved (lifting some tons of rocket) is orders of magnitude less work than the power extracted from falling water (hydro, thousands of tons per second).
And the heat output of burning hydrocarbons and nuclear reactions worldwide were concentrated into a few rocket nozzles, that would be rather mind boggling!
you seems to be conflating thrust(momentum) and energy a bit - linear on speed vs. quadratic on speed in classic case. It is very similar to photon drive - a lot of energy carried away by the photons while they generate too little thrust.
If there is a genuine effect, and as EmDrive generates more thrust than photon drive for the same energy, it would mean that EmDrive does eject some small mass at large speeds (kind of like super ion thruster) - whether it is some mass chipped from the EmDrive (i'd bet it is the case) and/or created using the spent energy (say some smaller mass boson interaction with some field which looks less probable to me) - that we don't know yet.
> whether it is some mass chipped from the EmDrive (i'd bet it is the case)
This would make sense of the standard design, but doesn't seem to make sense for the photon loop described in the article. The photon loop seems to be an entirely closed system.
That's easy. It mostly goes into heat. Eddy current heating of the copper tube should be the largest part. Wires, waveguides, a microwave generator aren't 100% efficient too. Small part of energy is lost as electromagnetic radiation.
What's mysterious is where the energy and the impulse are going if thrust is real. We can point the drive in such a way that it slows rotation of the earth, so the earth's rotational energy and angular impulse are decreasing. Where should they be going? I don't know.
First you shield your spacecraft with a gravity shielding device so it's not affected by earth gravity anymore. Then, even an emdrive's tiny propulsion output should be able to push your spacecraft all the way to space, powered with a clean cold fusion reactor. It's all imaginary though, but a man can dream...
Hmm, I'm not so sure. Once the gravity shield is invented, any reasonably strong human should be able to just throw the satellite into orbit. Why spend money installing an emdrive?
If nothing else, the EmDrive has been a great exercise in how hard it is to control all variables in a sensitive experiment where the measured effect is small.
It actually blows my mind how well the LIGO folks have accomplished this to be able to detect gravitational waves.
I really like the effort going into this, despite a positive result being impossible to our knowledge. Those are the high risk high reward experiments with the potential to discover new physics. I still expect it to be experimental error, but there's always that remote chance we'll learn something we didn't expect about the universe.
The problem with LIGO is that is not making the expected number of discoveries, it has, as far as I know, one signal that correlated to something visible with other means, and it is so expensive that there won't be independent confirmation soon.
Don't get me wrong, experiments like LIGO are massive achievements. But from an outsider point of view, that very scale and effort seems to be problematic when it comes to reproducing the results of experiments if there are no immediately useful predictions.
That is why they built two of them in two different locations, one in Washington and one in Louisiana. Only results that are measured by both are considered actual signals.
It would be really weird to build more than two because they are incredibly expensive and the incremental value of the third and fourth ones wouldn't be very high.
> that very scale and effort seems to be problematic when it comes to reproducing the results of experiments
First of all, LIGO is 2 observatories so every result out of LIGO was observed by at least two locations.
There is also an independent project called Virgo which is making gravitational wave observations, and the results are being correlated with LIGO. They have made a number of overlapping observations, which further moves us towards reproducibility.
Future observatories are also planned (like LISA), which will be another opportunity to further validate events.
I believe there have been visual/radio detections correlated with LIGO detections. I couldn't find a more authoritative source, but did find at least one reference in a Popular Mechanics[1] article.
This is in large part why we consider measurements probabilistically too.
LIGO could be wrong, sure, but that's why it's measured twice. The results fit numerical predictions by general relativity that we think the probability of it being wrong is very low. It might not be, but we could be inside a Boltzmann brain too.
It seems doing microscale gravity experiments face similar limitations. We can't get good atomic scale experiments to even test most quantum gravity experiments. It's fun to read what's required for even milli-Newton experiments.
Part of the problem with “cold fusion” was the claim that it was fusion, which it pretty clearly wasn’t. If the claim was merely that they’d observed apparently unexplained release of energy, or even that they believed they’d detected fission byproducts down near the limits of their instruments, it would have been more palatable. If they’d decided to release their ‘results’ in a peer-reviewed journal instead of in a press conference where they kept the details secret, they might have been treated better by the community. The problem with Cold Fusion wasn’t that it was bad science—-it was that it wasn’t science.
The Em Drive lacked the snake-oil showmanship of Cold Fusion, so it got treated better. It was also described well enough for the experiment to be replicated, and a few confirmations make it interesting enough to explore.
I think this is most likely to turn out to be experimental error, not a cause a revolution in electromagnetic theory, but it is worthy of the investigation, which Cold Fusion never was.
> I really like the effort going into this, despite a positive result being impossible to our knowledge.
Not despite, but rather, because of. The fact that it's impossible but we still keeping seeing a small positive signal is what is driving the effort. Nobody likes an unsolved paradox!
Even if it violates conservation of momentum, that doesn't really mean anything, since this is all happening on a quantum scale. It would definitely violate physics if you didn't need to apply a constant energy source for this to work, i.e. just one laser beam that spins in there virtually indefinitely while providing thrust. However, that is not the case.
This device presumably requires a reasonable amount of energy comparable to other existing drives. So what might happen here is a potentially unexplained quantum effect. Quantized Inertia seems like a really reasonable idea. Why wouldn't it be quantized? It doesn't even make sense for it not to be quantized.
It breaks the laws of physics as we know them. But we don't know everything, there is still a remote chance.
Conservation of momentum is so well established by this point, that's it's a very remote chance, and I'd expect it to still be conserved in that case, just through a mechanism we did not anticipate.
I'm just really rooting for new physics here, because I think is been about 70 years since we've had that.
Conservation of momentum is, via Noether's theorem, a mathematically proven consequence of translational symmetry in uniform space, i.e. that physics is not affected by linear movement through uniform space.
The bar for violating that is super high, unless you don't believe in mathematical proof.
Of course the space we occupy is not entirely uniform, due to general relativity, but GR addresses that, and the results are not consistent with em drive results, i.e. momentum is still conserved.
Physics is precise. The uncertainty is due to error-bars in measurements. Any measurement has error bars for systematic, random and absolute errors, then there is the combinative error as multiple types of measurement are combined together.
It’s more of a worry, tbh, if you don’t see an error estimate in a result...
I think the objection is that those are large error bars compared to the force measured. And that even a modest source of experimental error could put this at zero real output.
ETA: and since “non-zero real output” implies that virtually all of our physics is incorrect, and needs to be rebuilt from the ground up, the bar for measurement error needs to be exceptionally small.
And it shouldn't die until the anomalous effect is adequately explained. That's how good experimental science works, regardless of current theories - if you see an effect you can't explain, you test it until you can explain it. There's a very high chance the tiny force is attributable to something mundane, but it's still worth finding out what that thing is.
i think we're wrong putting so much effort on understanding and proving it on Earth (where it can never practically be used anyway). Just put it into space and turn it on - whatever the nature of the effect if it is present - great, lets use it, and understand it with time, if there is no effect - well, we're done here.
It seems cheap relative to pretty much anything these days. People pay that much for rare cars, a rich person could snap their fingers and make it happen. I hate to tell people how to spend their money but I wish someone pitched it as an experiment to Elon Musk or Bezos. Just like you said - put it in space, switch it on. Either it works or it doesn't, should be obvious straight away, no?
Since nothing has been proven or disproven yet, we’re really in no different position that before all the experiments began. Might as well spend that money now to end it.
It fits so far out of our theoretical models that it's unfair to say it isn't proven or disproven. There are virtually infinite hypothesis that are neither proven nor disproven experimentally, but because theory states it's impossible we don't consider them worth testing.
We live in an attention economy. If you read a story, or watch a video, it doesn't matter if you agree or disagree with the content; you're still traffic.
Just viewing content on most of the internet boosts it's signal, and creates value for someone; much less engaging further by commenting, up/down voting, or sharing it. It's a pretty ugly system.
The most surefire way to acquire massive wealth in the 21st century is to get convince people to pay as much attention to your app's notifications as they would an incoming phone call.
Orbit is actually a very dynamic and variable place. The Earth’s gravitational fields varies due to asymmetric mass distribution of the continental shelves, mountain ranges and features below the crust. Our atmosphere has an affect on satellites at even thousands of km altitude. The magnetic field is constantly shifting and can affect the orbits of metallic satellites. Then there’s the solar wind. This is why a lot of satellites need station keeping thrusters. Decent thrust would be observable, but very small rates of thrust that are hard to measure at all in the lab could be swamped by these effects and just as hard to measure in orbit, if not more so.
To some extent yes, but at some point the amount of effort might not outweigh the benefits.
There are limits to how much time and effort it is worth to debunk a perpetual motion device (a term usually reserved for something that violates the conservation of energy but the conservation of momentum is close enough, or perhaps even equivalent under special relativity).
It claims to provide thrust without propellant, which is a violation of the conservation of momentum. Since momentum and energy are conserved in much the same way this is already bad enough, however in special relativity the 4-momentum mixes momentum and energy (or rest-mass) and I believe that a well chosen Lorentz boost could turn a violation of the conservation of momentum into a violation of the conservation of energy.
Seems like it violates conservation of energy just because kinetic energy is proportional to the square of velocity, and thrust has to be constant for a given input energy since there's no preferred reference frame. Thus the faster you go, the more kinetic energy you get for the same input energy.
Technically yes, but as I've been trying to get across; violating the conservation of momentum isn't just 'new physics' it shakes the whole foundation of modern physics. The very definition of momentum ensures it is conserved by the (classical) equations of motion, to be otherwise is patently absurd.
Your comment seems like it would rule out a photon rocket , which proves too much. I think the resolution is that the faster you go, the heavier you are and the more thrust you need to increase your dv.
So you can calculate, for a given thrust/energy ratio, what velocity you have to exceed to get more energy out than you put in. For relativistic effects to make enough difference to matter, that velocity would have to be pretty close to c. That translates to an extremely low thrust.
(I've been told that for a photon rocket, the threshold velocity is c, implying that a reactionless drive won't violate conservation of energy as long as it's no better than a photon rocket. I haven't done that math myself though.)
I agree with you in principle but the benefits here go beyond disproving one device. The engineering and experimental design required to disprove this design will no doubt have applications beyond the EM drive.
Right. Just like the pioneer anomaly it warrants investigation just in case if there is something going on we haven’t predicted. Even if it is eventually explained by a mundane process it’s still probably worth the refinement of techniques used to detect why it’s happening. If for no other reason there’s the risk of more film flam technologies making similar claims with no way to disprove them.
Imagine 10k years in the future. 2 aliens arrive on earth, and examine the rubble. "Hey, check it out. They were right on the cusp of developing stardrive". "Weird, what happened? Nuclear war? Climate change?" "Nah, looks like they just couldn't work the math out, so they gave up."
> The sticking point is the law of conservation of momentum, which says that inside a closed system momentum remains constant.
...wait...
> The current design is calculated to provide a thrust of about .012 Newtons (equal to the weight of a paperclip, or a raisin) for one kilowatt of power, similar to the drives used to maneuver satellites.
It requires power input. Doesn't that mean this isn't a closed system?
If you draw the boundary enclosing the power source, you still have a closed system for which conservation laws ought to work, so long as nothing travels through the boundary. It's not having no source that makes it closed, it's having a boundary that leads to all the sums having to add up.
So traditional thrusters, which also convert energy into momentum, shouldn't work either?
Conservation of momentum only applies to mechanical processes, such as force and collisions. Converting energy breaks out of those bounds, and so it no longer applies - and the emdrive breaks no physics.
If you include the ejected mass, then momentum is conserved in that system. The ejected mass goes one way, the rocket goes the other. The momentum of the rocket is equal and opposite to the momentum of the ejected fuel.
No, momentum is simply outright conserved in the same way that energy is conserved. There are the two simplest to derive conservation laws, stemming from spatial symmetry (momentum) and time symmetry (energy).
These relationships are derivable via Noether's theorem, one of the most foundational results in physics.
I have a similar question.
How can a system be truly closed ? It’s always interacting with the stars and galaxies through their gravitational fields.
Similarly, and closer to your question) the spent energy can only be Generated through a chemical or nuclear reaction (both of which should lead to a loss of mass, which will be impacted by the gravitational fields, making it a non-closed system), or by gathering energy from outside The system (solar panels or other technologies), thus making it a non-closed system
It can often be considered closed for the purposes of the phenomenon that we want to describe. To be specific, masses like galaxies, stars and planets accelerate all parts of our tiny rocket the same way. Yes, there are differences, but they are usually so small that they can be neglected. Our rocket works mostly the same no matter how it is oriented to these sources of gravity. Of course, as it gets closer to such masses, these forces (called tidal forces) start to matter and will eventually rip it apart, given that it doesn't burn up or collide first.
Rockets, differently to balloons, do not depend on an interaction with a gravitic field for their operation. They work by ejecting reaction mass opposite to the flight direction and relying on Newton's third law of motion. Most of the time, the energy to eject the reaction mass is generated by combustion, but it doesn't really matter. Rockets can also be driven by the reaction mass's pressure inside its tank.
In general, any system can be turned into a closed system by including all sources of force in the description. Of course, the more forces are included in our model, the less useful it gets. Therefore, physicists and engineers must decide which forces can be ignored. Else, even experiments would become useless because without a model, the experience gained from experiments cannot be generalized.
As to your first question, distant gravitational fields can be ignored as per theory of relativity - if you're looking at an experiment in a black box (e.g. in an EmDrive) then an otherwise closed system in freefall in gravitational field is absolutely indistinguishable from a system at rest without that field, any experiment would give exactly the same results.
And for the second question, mass is energy and energy is mass (as per relativity). Adding or removing energy from a system makes it respectively heavier or lighter; if you heat up an object so that afterwards it has exactly the same atoms but just more internal energy, then it will be slightly heavier than when it was cold - the difference is very small (m=E/c^2, and c^2 is large) but nonzero.
If you're looking from outside at the behavior of an isolated black box, it's impossible to detect if inside it some mass is "lost" in a nuclear reaction i.e. converted to energy, as both the inertial and gravitational mass of a system is equivalent to the sum of both rest mass and energy, and that total is conserved. If that box pushes out energy/mass to outside or gains energy/mass from outside, then of course it is not a closed system. But converting rest mass to energy and vice versa in a chemical or nuclear reaction would not make it a non-closed system as long as all the inputs and outputs stay in the system, as the total gravitational effect of the system before and after the reaction would be exactly the same.
Conservation of energy and momentum are separate phenomenon and in this context, "closed" relates to the latter. You can have systems like particle collisions in a collider that receive energy from (are accelerated by) the electromagnets but the collision is a closed system because when the products scatter, they conserve the momentum of the colliding particles.
If you could produce a constant force (and therefore constant acceleration) for a constant power use, then both speed and the total energy spent would rise linearly with time. This is in conflict with the fact that kinetic energy goes up with the square of speed. In other words, if this works as described you can create energy out of nothing by sticking the drive on the outside of a rotating system and using it as a generator.
Please forgive my ignorance. If you are floating in a vacuum, how do you know what kinetic energy you have? isn't that all with respect to some other object?
I believe the trick here is that constant-acceleration with constant power use is due to the (puzzling) particulars that there's no ejection mass
Kinetic energy is relative to some inertial reference frame. You can pick any reference frame you want and each will give you different numbers, but conservation laws should still hold in each.
Addition of kinetic energy is pretty unintuitive in this regard, e.g. when throwing a ball, the "work" done by your muscles depends on the reference frame that you pick to analyze the event.
This seems, to me, to be the simplest explanation of why it almost certainly doesn't work, but that isn't mentioned frequently, am I missing something?
I'm not following you completely, but this particular argument seems to work equally well if you put a photon rocket in place of the EmDrive. Constant power, constant torque, but I don't see how it makes a perpetual motion machine.
When you do the math, in order to extract infinite free energy as per OP's argument, you have to get the drive up to a certain speed (think of a y=x line intersecting with a y=x^2 parabolic curve). The required speed depends on the performance of the drive (i.e. the N/kW figure), with a higher performance drive meaning a lower required speed before you can start extracting energy. For a photon drive, the speed you need to reach to extract infinite free energy is... the speed of light. Which you can't get to. So OP's argument only applies to drives which perform better than a photon drive, which naturally includes the EmDrive.
I thought that was implied by the description of the EM drive of "X kilowatt for Y newton". But I guess the effect could indeed depend on your speed relative to some special reference frame, like that of the microwave background.
If that's the case, then we can do something like the Michelson–Morley experiment, to check whether the effect is different depending on the direction the Earth is moving in its orbit.
I don't think it's implied anywhere that the force will remain constant. It's more a proxy to the ratio of the change in kinetic energy to the energy put in.
I suppose they used a very precise equivalent of a dynamometer that necessarily required some work to be done to give out a reading and this is what it showed.
The force cannot possibly depend on the drive's kinetic energy, because the kinetic energy is based on the velocity, which is relative to the frame of reference you use to measure it. If your frame of reference is the drive itself, then the kinetic energy is always zero, and conversely it's always possible to use a remote galaxy as a frame of reference, which makes the kinetic energy (and velocity) absurdly high.
Even if it did work I don't think the EmDrive would be revolutionary. A vehicle equipped with it still has to generate energy. It terms of how useful it is you've just moved the payload requirement from the fuel tank to the generator module. Going by these experiments the EmDrive doesn't have a hope of ever matching the mass efficiency of an ion drive.
That's the irony of it all. Power plants capable of powering an EmDrive that's practically useful for manned flight can be summed up with one word: nuclear. With the exception of the (lovely but insane) Project Orion, all of the nuclear propulsion designs like NERVA and the nuclear lightbulb generate a ridiculous amount of heat that we have trouble handling here on Earth, let alone in vacuum without convection - most nuclear plants are built with access to large natural or artificial bodies of water as a heat sink.
The future of manned space flight is almost certainly nuclear and it looks like tiny cabins attached to giant passive heatsinks or spacecraft that constantly have to accelerate just to dump all the waste heat and avoid cooking its inhabitants.
Here is some declassified test footage of Project Orion. I don't believe any of the test crafts used nuclear explosions, but you'll get the idea from this footage (on why it's a terrible idea that could only exist in the 40s or 50s)
Orion is an impractical idea but the risks do seem manageable.
In "peacetime" it could never launch from the ground, but assembled in space it could be fruitful. It's probably the only possible way to get a city of people off the planet.
>A vehicle equipped with it still has to generate energy.
Yes, with solar panels. No mass is expelled, which is why there's so many claims about it violating the law of Conservation of Moment.
> Going by these experiments the EmDrive doesn't have a hope of ever matching the mass efficiency of an ion drive.
If the craft runs out of ions to throw really fast behind it, how could it get more? Well, it can't. That's why the EmDrive is a paradigm shift; solar panels allow for the generation of electricity, which then powers a magnetron to create thrust.
And efficiency? Well, ion drives presumably have decades of head-start. Give it time.
I don't think human spaceflight will ever be a significant factor in our history. We evolved for this planet, and there is little reason to send humans through space when we can send robots. When we discover another earth-like planet, we will send robots there that can replicate human life, and the two civilizations will communicate with each other but it's unlikely any person will ever travel between the two. As to how robotic interstellar travel is fuelled, we'll probably use converted asteroids with thrusters built into them.
The best thing I can see to come out of this is some sort of standardized, more easily replicated test apparatus for precise measurements of very small thrust in vacuum chambers.
Such as for testing things that do actually produce thrust, built into low cost satellites, such as very small ion and hall effect thrusters.
Seems strange to not see a single mention of the "Quantum Vacuum" in an entire popularmechanics article about the EmDrive AKA Q-Thrusters.
Sonny White of the Eagleworks lab discusses this subject in a Breakthrough Discuss 2018 [0] talk. Has everything he says in that talk been since disproven or something?
"Yup, the Earthlings are still using warp drives to heat food. We will revisit this solar system in 25 of their planet's revolutions to check for further progress."
Can’t we just shoot one of these into space and see if it moves? We’d need only a few days to generate any appreciable thrust and prove or disprove the theory.
I cant find the numbers for the EmDrive research for the past 20 years but my guess is that it wasn’t cheap at all. Comparing that to sending a few pounds into orbit as a proof of concept is probably peanuts. I don’t have numbers and its all speculation on my part. If you do have numbers please share them
A small orbital rocket (like from Rocket Lab) costs 7-ish million. Then you have to actually design and build the payload/observation equipment to fit such a small rocket
For the people in this thread gleefully calculating the absurd energies required to achieve miniscule thrusts, please remember two things:
1) The version in the lab and the device that would actually be used for satellite production are very different. The lab version is not designed for efficiency. It's designed to be easy to manufacture and test, using simple, well-characterised technologies. For one, a production design would use a superconducting cavity for much better efficiencies, easily 100 to 10,000x better.
2) Miniscule propellentless thrusts are still useful with solar power. Satellite stationkeeping is largely limited by the finite propellent capacity onboard. Even Xenon plasma thrusters, the most efficient currently available, run out of fuel eventually.
Now, I'm not saying the EmDrive works, I'm just pointing out that it's a distraction talking about the efficiency or utility of a "benchtop experiment".
What is stopping us from producing a larger scale model with 10~100x the performance? Presumably the effect should scale in some fashion with the dimensions & power levels. I would expect a larger magnitude effect could make it easier to identify the cause(s).
Would require a military grade klystron to generate 10+kW of S-band energy, for starters. In a vacuum setting, I'm not sure how you'll sink all the resulting heat to avoid melting the thing.
I think even then it's very challenging to measure ~100mN thrust
Wrote an article on the EmDrive some years back and have a little more insight on it than the average bear.
Good to see the Dresden group is still plunking away after all these years. Other than Eagleworks and a group in China, they were early leaders on verifying the concept.
The law of conservation of momentum was created before quantum mechanics was discovered. Let's assume there's a base medium in which all energy (that is, mass) is embedded. Furthermore, let's assume there's a way to interface with this medium. The EmDrive works if one allows mass (that is, energy) to be transferred into this base medium. Momentum is conserved because the mass/energy is transferred to the all-encompassing medium. This medium is the same medium which enables quantum entanglement.
In theory, the quantum vacuum and surrounding phenomena provides that medium. Frankly, I feel the classical interpretation of CoM is insufficient to explain the workings of the EmDrive. The article uses the phrase "a physics violation," but a more accurate statement is "a high-school level physics violation."
How big of a deal is the EmDrive? It's an EM-wave-to-thrust device. Take a moment and consider the significance of such a device. Satellites could remain in space effectively forever, because solar panels continuously source the "propellant". Build one strong enough to counter Earth's gravity, and you get the hovercraft. As long as you have access to electricity, you can generate thrust.
The article also mentions Salvatore Pais and his patents. His story took off after one particular Hacker News post and a comment on that post. You can read the full comment at the link below, but here's the most important points:
"Whether or not the named inventor was a crank, and whether or not the invention was equally frivolous, this was a patent prosecuted by a Navy attorney, vouched for by the Navy CTO, and pushed through under atypical circumstances, in a public forum.
What's even more intriguing is that, if the Navy wanted, it could obtain the patent under a secrecy order that would keep it from the public's eyes until it was declassified.
Knowing all this, now ask yourself why this impossible sounding patent issued in a public forum with high-level brass support under tax payer dollars."
> if one allows mass (that is, energy) to be transferred into this base medium. Momentum is conserved because the mass/energy is transferred to the all-encompassing medium. This medium is the same medium which enables quantum entanglement.
What are you talking about? Entanglement is not mediated by a medium. If it was, it would have speed of light limitations.
This is like saying there's an unknown type of matter that enables statistical correlations to exist. It's mixing together incompatible concepts. Correlations just don't behave that way. Neither does entanglement.
>Entanglement is not mediated by a medium. If it was, it would have speed of light limitations.
This medium is that in which all energy is embedded. Two particles becoming entangled does mean they're highly correlated with each other. But what enables this correlation? I don't see this question as answered, because wave function collapse is actively disputed.
While my view of quantum entanglement is limited, I don't fully understand how entangled particles can be strongly correlated but can't transmit information FTL. Is it correct to say that two separate entangled particles are now one-and-the-same? I suppose you then get into a philosophical question of whether all parts of a system can ever observe the exact same thing at the exact same time. If this statement is false, then information must be transmitted, no?
>unknown type of matter that enables statistical correlations to exist
Matter and energy are one and the same. Why can't other types of energy exist which we don't fully understand? For example, how does dark "matter" work? We only have incomplete theories thus far, and I know of no paper that discusses physical manipulation of dark matter.
The ether as a concept existed because people didn't understand the vacuum of space. But perhaps the zero-point field is a more accurate rendition of what etherians were trying to communicate.
> Is it correct to say that two separate entangled particles are now one-and-the-same?
It's not. If they were literally the same then swapping them should have no effect, and you shouldn't be able to distinguish whether you applied effects to one qubit or the other. But often this is not the case. For example, the state |00> + |01> - |10> + |11> is a maximally entangled state but applying the swap operation to it produces a different state. And if I give that state to you, and you secretly apply a bit flip to one of the qubits before giving it back to me, I can do measurements that determine which one you flipped over.
There are some entangled states where the swap operation has no effect, but there are no states where all possible operations on both qubits become identical. They're never literally the same.
> The law of conservation of momentum was created before quantum mechanics was discovered.
The law of conservation of momentum is a fundamental part of quantum field theory; without it, we don't have particle accelerators, nor any understanding of particle decay.
This is an interesting counterpoint to scientific discoveries that found utilization some time after the discovery happened. For each of those discoveries, there were always those standing on the sidelines going "Yeah, but what is it good for?" The world has been changed many times over by such discoveries that found later application.
The EmDrive sits on the other side of the fence. We know what it would be good for so there are critics who dismiss it precisely for that reason citing wishful thinking.
I do wonder if the curious force measurements would be much less contentious if people didn't know what it could be used for. The focus would be purely on "Why is it doing that?"
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[ 3.3 ms ] story [ 239 ms ] threadWhat’s that quote about sufficiently advanced science being indistinguishable from magic?
I could imagine through some interesting device a way to have thrust in one direction with the "conservation" occurring as heat radiating in all of the other directions -- is this not compatible with conservation of momentum or am i a crackpot who doesnt understand the basics (the more likely case, i am sure)
Electromagnetic radiation has momentum - it's small, but not zero. If you're emitting a bunch of photons (e.g. infrared photons from blackbody radiation of a hot object) more to one side than the other, then the remainder of that device will have some thrust. But that does not violate conservation of momentum, as the momentum gained by the device will equal the momentum of these photons; and the total momentum of the whole system (the device plus all the photons radiated) will be constant.
https://en.wikipedia.org/wiki/Non-Euclidean_geometry
But this would still be an extremely useful effect if it does exist, for devices designed to focus it. Look at how an electric field's influence on semiconductors has almost no relevance to anything except when harnessed just right.
Actually, that axiom made even the ancients uncomfortable. There were lots of attempts over the centuries to "prove" or "disprove" it.
The fact that violating it can still produce a self-consistent geometry was what was stunning.
Not with 12 millinewtons per kilowatt! In space, sure but not from launchpad.
What this would be useful for is (by no coincidence) also the exact reason why it is considered crank science: you could use it to build a perpetual motion machine because it violates conservation of energy/momentum laws.
If the EmDrive actually worked, the correct use is to violate conservation of energy and momentum, not as a straightforward substitute for the engines we have now.
EmDrive looks like an accounting error to me, not something that actually works. Any energy it expends turns into heat, radiating in a predictable but not necessarily isotropic way. This radiation carries momentum, but much less than the EmDrive claims to be capable of.
A rocket or ion drive? The energy goes into the kinetic and gravitational potential of the exhaust.
(Aside: kilowatts are power, not energy).
How long would it take a nuclear powered EmDrive to push a fully loaded semitrailer from 0m/s to the speed of the interntional space station?
The maximum mass for a semi-truck fully loaded is 36000kg. The EmDrive generates 12millinewtons per kw. 1n = 1kg*(1m/s^2). Leo ~=7.66km/s^. A nuclear reactor produces ~1gw. We would need 275760000N to accelerate a semi truck to leo speeds. A nuclear powered EmDrive would take ~265 days to push a semi truck to low earth orbit speeds.
The escape velocity of Earth's orbit is 11.19 km/s, and if you were going to take humans on the trip you'd need much more cargo than 36000kg. Granted, you wouldn't have to move the craft from 11.19km/s to 0km/s and then 0km/s to 11.19 km/s every time you entered and left orbit, but it would be a slow ride regardless.
But it is 99.9999% not going to work at all, the emDrive would just be a cheat at space travel.
Something that can transform energy into momentum without shooting stuff back is the Holy Grail of space travel -- after a warp drive.
So doing some napkin math with the article’s 12mN/kW, that’s close to a terawatt. For reference, I think worldwide electrical power generation capacity is around 10x that.
edit: made the math more explicit due to child comments and fixed spelling error
1 Watt = 1 Newton-meter/second
You're missing some values.
The work achieved (lifting some tons of rocket) is orders of magnitude less work than the power extracted from falling water (hydro, thousands of tons per second).
And the heat output of burning hydrocarbons and nuclear reactions worldwide were concentrated into a few rocket nozzles, that would be rather mind boggling!
https://www.adobe.com/products/coldfusion-family.html
Just out of curiosity, where is all the rest of the energy going?
If there is a genuine effect, and as EmDrive generates more thrust than photon drive for the same energy, it would mean that EmDrive does eject some small mass at large speeds (kind of like super ion thruster) - whether it is some mass chipped from the EmDrive (i'd bet it is the case) and/or created using the spent energy (say some smaller mass boson interaction with some field which looks less probable to me) - that we don't know yet.
This would make sense of the standard design, but doesn't seem to make sense for the photon loop described in the article. The photon loop seems to be an entirely closed system.
What's mysterious is where the energy and the impulse are going if thrust is real. We can point the drive in such a way that it slows rotation of the earth, so the earth's rotational energy and angular impulse are decreasing. Where should they be going? I don't know.
It actually blows my mind how well the LIGO folks have accomplished this to be able to detect gravitational waves.
I really like the effort going into this, despite a positive result being impossible to our knowledge. Those are the high risk high reward experiments with the potential to discover new physics. I still expect it to be experimental error, but there's always that remote chance we'll learn something we didn't expect about the universe.
The problem with LIGO is that is not making the expected number of discoveries, it has, as far as I know, one signal that correlated to something visible with other means, and it is so expensive that there won't be independent confirmation soon.
Don't get me wrong, experiments like LIGO are massive achievements. But from an outsider point of view, that very scale and effort seems to be problematic when it comes to reproducing the results of experiments if there are no immediately useful predictions.
That is why they built two of them in two different locations, one in Washington and one in Louisiana. Only results that are measured by both are considered actual signals.
https://en.wikipedia.org/wiki/LIGO
It would be really weird to build more than two because they are incredibly expensive and the incremental value of the third and fourth ones wouldn't be very high.
[1]: https://www.ligo.org/images/GW170817_images/GW170817-frontpg...
First of all, LIGO is 2 observatories so every result out of LIGO was observed by at least two locations.
There is also an independent project called Virgo which is making gravitational wave observations, and the results are being correlated with LIGO. They have made a number of overlapping observations, which further moves us towards reproducibility.
Future observatories are also planned (like LISA), which will be another opportunity to further validate events.
[1]: https://www.as.arizona.edu/discovery-optical-counterpart-gra...
[1]: https://www.popularmechanics.com/space/deep-space/a28631/neu...
LIGO could be wrong, sure, but that's why it's measured twice. The results fit numerical predictions by general relativity that we think the probability of it being wrong is very low. It might not be, but we could be inside a Boltzmann brain too.
The Em Drive lacked the snake-oil showmanship of Cold Fusion, so it got treated better. It was also described well enough for the experiment to be replicated, and a few confirmations make it interesting enough to explore.
I think this is most likely to turn out to be experimental error, not a cause a revolution in electromagnetic theory, but it is worthy of the investigation, which Cold Fusion never was.
We might even learn something valuable just by figuring out what the cause of the experimental error is, no?
Not despite, but rather, because of. The fact that it's impossible but we still keeping seeing a small positive signal is what is driving the effort. Nobody likes an unsolved paradox!
This device presumably requires a reasonable amount of energy comparable to other existing drives. So what might happen here is a potentially unexplained quantum effect. Quantized Inertia seems like a really reasonable idea. Why wouldn't it be quantized? It doesn't even make sense for it not to be quantized.
Anyway, I hope this thing works.
Conservation of momentum is so well established by this point, that's it's a very remote chance, and I'd expect it to still be conserved in that case, just through a mechanism we did not anticipate.
I'm just really rooting for new physics here, because I think is been about 70 years since we've had that.
The bar for violating that is super high, unless you don't believe in mathematical proof.
Of course the space we occupy is not entirely uniform, due to general relativity, but GR addresses that, and the results are not consistent with em drive results, i.e. momentum is still conserved.
Somehow I thought physics was meant to be a little more precise than this
It’s more of a worry, tbh, if you don’t see an error estimate in a result...
ETA: and since “non-zero real output” implies that virtually all of our physics is incorrect, and needs to be rebuilt from the ground up, the bar for measurement error needs to be exceptionally small.
We live in an attention economy. If you read a story, or watch a video, it doesn't matter if you agree or disagree with the content; you're still traffic.
Just viewing content on most of the internet boosts it's signal, and creates value for someone; much less engaging further by commenting, up/down voting, or sharing it. It's a pretty ugly system.
There are limits to how much time and effort it is worth to debunk a perpetual motion device (a term usually reserved for something that violates the conservation of energy but the conservation of momentum is close enough, or perhaps even equivalent under special relativity).
But investigating this might uncover what is causing the confusion. Some other external force unknown to us might be at play.
Don't forget that photons still have momentum, even if they don't have mass.
(I've been told that for a photon rocket, the threshold velocity is c, implying that a reactionless drive won't violate conservation of energy as long as it's no better than a photon rocket. I haven't done that math myself though.)
The use of "fake" here really bugs me. Fake implies lies and I don't think that's at all present here.
https://en.wikipedia.org/wiki/Pathological_science
...wait...
> The current design is calculated to provide a thrust of about .012 Newtons (equal to the weight of a paperclip, or a raisin) for one kilowatt of power, similar to the drives used to maneuver satellites.
It requires power input. Doesn't that mean this isn't a closed system?
Conservation of momentum only applies to mechanical processes, such as force and collisions. Converting energy breaks out of those bounds, and so it no longer applies - and the emdrive breaks no physics.
At least, that's how I've always understood it.
Not true for the EmDrive.
These relationships are derivable via Noether's theorem, one of the most foundational results in physics.
https://en.wikipedia.org/wiki/Noether%27s_theorem
What am I missing here ?
Rockets, differently to balloons, do not depend on an interaction with a gravitic field for their operation. They work by ejecting reaction mass opposite to the flight direction and relying on Newton's third law of motion. Most of the time, the energy to eject the reaction mass is generated by combustion, but it doesn't really matter. Rockets can also be driven by the reaction mass's pressure inside its tank.
In general, any system can be turned into a closed system by including all sources of force in the description. Of course, the more forces are included in our model, the less useful it gets. Therefore, physicists and engineers must decide which forces can be ignored. Else, even experiments would become useless because without a model, the experience gained from experiments cannot be generalized.
And for the second question, mass is energy and energy is mass (as per relativity). Adding or removing energy from a system makes it respectively heavier or lighter; if you heat up an object so that afterwards it has exactly the same atoms but just more internal energy, then it will be slightly heavier than when it was cold - the difference is very small (m=E/c^2, and c^2 is large) but nonzero.
If you're looking from outside at the behavior of an isolated black box, it's impossible to detect if inside it some mass is "lost" in a nuclear reaction i.e. converted to energy, as both the inertial and gravitational mass of a system is equivalent to the sum of both rest mass and energy, and that total is conserved. If that box pushes out energy/mass to outside or gains energy/mass from outside, then of course it is not a closed system. But converting rest mass to energy and vice versa in a chemical or nuclear reaction would not make it a non-closed system as long as all the inputs and outputs stay in the system, as the total gravitational effect of the system before and after the reaction would be exactly the same.
https://en.m.wikipedia.org/wiki/Space_tether
https://www.popularmechanics.com/science/energy/a22678/em-dr...
https://www.sciencealert.com/the-impossible-em-drive-is-abou...
I believe the trick here is that constant-acceleration with constant power use is due to the (puzzling) particulars that there's no ejection mass
If you are in orbit you can measure your speed relative to something else, the only that doesn't work is a privileged frame.
Addition of kinetic energy is pretty unintuitive in this regard, e.g. when throwing a ball, the "work" done by your muscles depends on the reference frame that you pick to analyze the event.
This seems, to me, to be the simplest explanation of why it almost certainly doesn't work, but that isn't mentioned frequently, am I missing something?
If that's the case, then we can do something like the Michelson–Morley experiment, to check whether the effect is different depending on the direction the Earth is moving in its orbit.
I suppose they used a very precise equivalent of a dynamometer that necessarily required some work to be done to give out a reading and this is what it showed.
The future of manned space flight is almost certainly nuclear and it looks like tiny cabins attached to giant passive heatsinks or spacecraft that constantly have to accelerate just to dump all the waste heat and avoid cooking its inhabitants.
Here is some declassified test footage of Project Orion. I don't believe any of the test crafts used nuclear explosions, but you'll get the idea from this footage (on why it's a terrible idea that could only exist in the 40s or 50s)
https://www.youtube.com/watch?v=Q8Sv5y6iHUM
In "peacetime" it could never launch from the ground, but assembled in space it could be fruitful. It's probably the only possible way to get a city of people off the planet.
Yes, with solar panels. No mass is expelled, which is why there's so many claims about it violating the law of Conservation of Moment.
> Going by these experiments the EmDrive doesn't have a hope of ever matching the mass efficiency of an ion drive.
If the craft runs out of ions to throw really fast behind it, how could it get more? Well, it can't. That's why the EmDrive is a paradigm shift; solar panels allow for the generation of electricity, which then powers a magnetron to create thrust.
And efficiency? Well, ion drives presumably have decades of head-start. Give it time.
Such as for testing things that do actually produce thrust, built into low cost satellites, such as very small ion and hall effect thrusters.
Sonny White of the Eagleworks lab discusses this subject in a Breakthrough Discuss 2018 [0] talk. Has everything he says in that talk been since disproven or something?
[0] https://www.youtube.com/watch?v=o-hjS7pdXGU
1) The version in the lab and the device that would actually be used for satellite production are very different. The lab version is not designed for efficiency. It's designed to be easy to manufacture and test, using simple, well-characterised technologies. For one, a production design would use a superconducting cavity for much better efficiencies, easily 100 to 10,000x better.
2) Miniscule propellentless thrusts are still useful with solar power. Satellite stationkeeping is largely limited by the finite propellent capacity onboard. Even Xenon plasma thrusters, the most efficient currently available, run out of fuel eventually.
Now, I'm not saying the EmDrive works, I'm just pointing out that it's a distraction talking about the efficiency or utility of a "benchtop experiment".
I think even then it's very challenging to measure ~100mN thrust
Good to see the Dresden group is still plunking away after all these years. Other than Eagleworks and a group in China, they were early leaders on verifying the concept.
The law of conservation of momentum was created before quantum mechanics was discovered. Let's assume there's a base medium in which all energy (that is, mass) is embedded. Furthermore, let's assume there's a way to interface with this medium. The EmDrive works if one allows mass (that is, energy) to be transferred into this base medium. Momentum is conserved because the mass/energy is transferred to the all-encompassing medium. This medium is the same medium which enables quantum entanglement.
In theory, the quantum vacuum and surrounding phenomena provides that medium. Frankly, I feel the classical interpretation of CoM is insufficient to explain the workings of the EmDrive. The article uses the phrase "a physics violation," but a more accurate statement is "a high-school level physics violation."
How big of a deal is the EmDrive? It's an EM-wave-to-thrust device. Take a moment and consider the significance of such a device. Satellites could remain in space effectively forever, because solar panels continuously source the "propellant". Build one strong enough to counter Earth's gravity, and you get the hovercraft. As long as you have access to electricity, you can generate thrust.
The article also mentions Salvatore Pais and his patents. His story took off after one particular Hacker News post and a comment on that post. You can read the full comment at the link below, but here's the most important points:
"Whether or not the named inventor was a crank, and whether or not the invention was equally frivolous, this was a patent prosecuted by a Navy attorney, vouched for by the Navy CTO, and pushed through under atypical circumstances, in a public forum.
What's even more intriguing is that, if the Navy wanted, it could obtain the patent under a secrecy order that would keep it from the public's eyes until it was declassified.
Knowing all this, now ask yourself why this impossible sounding patent issued in a public forum with high-level brass support under tax payer dollars."
https://news.ycombinator.com/item?id=19763445
My gut tells me the EmDrive works. Time will tell, of course.
What are you talking about? Entanglement is not mediated by a medium. If it was, it would have speed of light limitations.
This is like saying there's an unknown type of matter that enables statistical correlations to exist. It's mixing together incompatible concepts. Correlations just don't behave that way. Neither does entanglement.
This medium is that in which all energy is embedded. Two particles becoming entangled does mean they're highly correlated with each other. But what enables this correlation? I don't see this question as answered, because wave function collapse is actively disputed.
While my view of quantum entanglement is limited, I don't fully understand how entangled particles can be strongly correlated but can't transmit information FTL. Is it correct to say that two separate entangled particles are now one-and-the-same? I suppose you then get into a philosophical question of whether all parts of a system can ever observe the exact same thing at the exact same time. If this statement is false, then information must be transmitted, no?
>unknown type of matter that enables statistical correlations to exist
Matter and energy are one and the same. Why can't other types of energy exist which we don't fully understand? For example, how does dark "matter" work? We only have incomplete theories thus far, and I know of no paper that discusses physical manipulation of dark matter.
The ether as a concept existed because people didn't understand the vacuum of space. But perhaps the zero-point field is a more accurate rendition of what etherians were trying to communicate.
It's not. If they were literally the same then swapping them should have no effect, and you shouldn't be able to distinguish whether you applied effects to one qubit or the other. But often this is not the case. For example, the state |00> + |01> - |10> + |11> is a maximally entangled state but applying the swap operation to it produces a different state. And if I give that state to you, and you secretly apply a bit flip to one of the qubits before giving it back to me, I can do measurements that determine which one you flipped over.
There are some entangled states where the swap operation has no effect, but there are no states where all possible operations on both qubits become identical. They're never literally the same.
Am I correct in reading that the broader scientific community doesn't fully understand the mechanism which enables this correlation?
The law of conservation of momentum is a fundamental part of quantum field theory; without it, we don't have particle accelerators, nor any understanding of particle decay.
I strongly suggest, well, everything on this site, but in particular, https://profmattstrassler.com/articles-and-posts/particle-ph... and https://profmattstrassler.com/articles-and-posts/particle-ph... . It's the best review of modern physics I've seen anywhere that is both accessible to a lay-but-interested reader, and aligns correctly with the actual math.
The EmDrive sits on the other side of the fence. We know what it would be good for so there are critics who dismiss it precisely for that reason citing wishful thinking.
I do wonder if the curious force measurements would be much less contentious if people didn't know what it could be used for. The focus would be purely on "Why is it doing that?"