Relativistic dynamics is different from Newtonian dynamics in a lot of ways. Force isn't parallel to acceleration anymore. Acceleration gets harder the faster an object moves. You can mimic some of these changes by just pretending that you still have Newtonian dynamics but the mass can change with velocity, but we don't use this language in physics because it's misleading -- there are many effects this idea can't capture. (For example, the fact that force is not parallel to acceleration.) It is a very fragile analogy that causes a lot of conceptual mistakes.
It's easy to prove that Newtonian mechanics conserves momentum. It's also easy to prove that relativistic mechanics conserves momentum. A weird hybrid of Newtonian mechanics plus a magically changing "relativistic mass" does not conserve momentum, but nobody has ever thought this was a correct description of nature. It's the result of taking a helpful simplifying analogy too far. Any reactionless drive formulated using this Frankenstein theory doesn't work.
If you just bounce an object back and forth, in either Newtonian mechanics or relativistic mechanics, you won't get anywhere. If you change the rest mass of the object to be different going right than left, you will go somewhere, but it will cost momentum to do this, as explained in gus_massa's comments. So we haven't gotten thrust for free.
> For example, the fact that force is not parallel to acceleration.
This is the first I’ve heard of this and I would like to learn more, partly because of my own harebrained not-quite-reactionless engine idea that I know can’t possibly work really, but I can’t see why yet.
Conceptually it's because it gets much harder to speed something up, but not that much harder to change the direction of its velocity. So for a force with both radial (along velocity) and tangential (perpendicular to velocity) components, the acceleration points more tangentially than the force does.
A really excellent, conceptually clear exposition of relativity is given in chapters 11 and 12 of Morin's Mechanics. The modified version of F=ma is covered in section 12.5.
I would also say that I have been at least somewhat successful in teaching people about relativity by ttuncating the Lorentz transform to first order in β, as you can prove that you get the full results back from this as the matrix limit
N
lim [1 -φ/Ν]^
N→∞ [-φ/Ν 1]
... basically the physical content of Galileo’s transform is that as you accelerate forwards things start moving backwards. The physical content of Lorentz’s transform adds just one thing to first order: that as you are accelerating, clocks ahead of you appear to tick faster, and clocks behind you slower, proportional to their distance in the direction you are accelerating.
That key basic insight is not just the resolution to the twin paradox but the basis for event horizons near black holes and such. (There is a surface at coordinate -c²/a where time stands still.)
But note that the 4-force is parallel to the 4-acceleration. However, its spatial component only agrees with classical acceleration in the comoving frame. In general, there's an additional contribution that's however smaller by a factor of (v/c)^2.
"Oversimplified" is one way of putting it. I'd prefer to call it "simply incorrect". The manner in which the ring's rest mass is increased [decreased] is ignored[1]. If you don't ignore it, and apply conservation of (relativistic) angular momentum to the box-ring system, you'll see there's no reason to expect a net thrust at all.
Even things we think we know very well may be wrong, so having a certain budget for "fringe" subjects which may yield unexpected results is not a bad idea. At the same time it's probably a good idea to assume everything they report is a measurement/test setup error until further proof.
> Burns has worked on his design in private, without any sponsorship from NASA
Seems like they didn't, though as usual the article completely buries that information.
I kinda wish NASA had a policy like Disney, where you can't use your affiliation with them in association with personal projects (though for a different reason.)
It's always worth trying out new ideas. It's not like we're going to run out of paper or something.
My only complaint is that publicity is disproportionately allocated to the studies least likely to be right. While paper isn't limited, room in the newspaper is.
In a swing, the back-and-forth linear momentum comes from the tension in the wires, while the energy comes from your legs. No conservation laws are broken.
The vacuum part was an emphasis on requiring a counterpart to change momentum.
In an atmosphere you could flap your wings, or use electric fans, and argue what it means to ride a swing, but it would be besides the point, as in an atmosphere there is no need for propellant-less engines from the article.
A swing works by moving you back and forth relative to the Earth (and moving the Earth back and forth slightly as well, in the opposite direction, more or less.) The you + Earth system is not actually going anywhere. :-)
So you need to leave something behind in order to go somewhere? But it would only be relative to the thing I left behind? But then there is some "special" relativity that applies everywhere?
> So you need to leave something behind in order to go somewhere?
As a definition, no. But no one has been able to figure out reactionless propulsion; as far as anyone can tell, the only way to accelerate in space is to throw something in the opposite direction (matter or light).
If you tie a rope to a hammer, then spin it around as fast as you can like a hammer thrower, and drop it. Wouldn't the breaking force propel you in the same direction your let go of the hammer?
If you're in zero g and not on a surface with friction to push against, you're not going to be able to do what a hammer thrower can do standing on Earth.
But, if you provide some momentum to an object like a hammer and release it, you will move. That goes back to "you need to leave something behind in order to go somewhere."
The idea of the article is to use the change of mass in special relativity. Some particles go faster in one direction (and they have more mass), and then they return more slowly in the other direction (and has less mass).
In special relativity, when the charged particles accelerate and decelerate they emit electromagnetic radiation. The whole process conserve the energy and momentum. The momentum that the device provides is compensated by the momentum of the electromagnetic radiation, aka photons.
So this device should work. It doesn't break the laws of physics. It produce some photons in the intended direction and more photons in other random directions. So it is just a very inefficient photon thruster https://en.wikipedia.org/wiki/Photon_rocket. It's like attaching a laser to the back of your starship, and then adding some lamp to illuminate in every direction to make it more inefficient.
The claimed power to thrust ratio of 165 MW / N does check out as less efficient than a photonic rocket at 150 MW / N assuming the beam is reflected off the craft.
If you are bouncing the photos (like in a solar sail, aka a mirror attached to the back of the starship) then the minimal power is 150MW/N.
If you are generating the photons (like in a photon rocket, aka laser attached to the back of the starship) then the minimal power is 300MW/N (and you need a generator).
I didn't notice before the 165MW/N in the slides, but their device is not bouncing the photons, so the theoretical minimum is 300MW/N, so it is impossible to use only 165MW/N. So they must have an error (numerical or conceptual) in the calculation.
In the slide, the energy is used to accelerate the particles, and then the energy is recovered when the particles return. So the article claim more efficiency, but let's ignore that part.
I think the main problem is that the particles will emit a lot of energy in the sharp turn at the top, something like the https://en.wikipedia.org/wiki/Cyclotron_radiation This radiation is what really push the device. In the sharp turn at the bottom the particles are going more slowly, so the radiation and push is smaller.
I don't understand why the calculation using a mix of classical and relativistic formulas give almost the correct result. The error is only in x2 (in the impossible direction), a x2 is not so off. I guess the main problem is assuming that the particles will have the same speed during all the turn???
Sun radiation is about 1.4KW/m2 at the Earth orbit and the pressure is 0.00001N/m2 - basically the same numbers as GP mentioned for the photonic drive - can be calculated as 1.5KJ (for roundness of numbers) of photons divided by c which gives 0.000005kg-m/s of momentum per second, double that for bounce and thus 0.00001N. As photons are usually the things being thrown for the thrust in the mass-less thrust schemas, then those photonic thrust numbers seems to be a theoretical limit .
If I understand correctly, these are different effects. The article uses Special Relativity. With Special Relativity you can't break the laws of conservation of energy and momentum.
The Woodward effect uses General Relativity. So the conservations laws are more complicated to define because the space-time is curved. Anyway, the curvature is so small that if it is real it would be very difficult to measure and even more difficult to use it in a thruster.
First, note that to fill the patent you don't need a working prototype. It's just a piece of paper.
The patent has the same idea, but it uses other device to move the particles. It looks more difficult to implement than the device in this article. (And the patent has a weird discussion about a maximal velocity.)
My previous comment applies without changes to the device in the patent too. It's just another very inefficient photon thruster.
If the author forgets to consider the momentum and energy carried away by the electromagnetic waves / photons, then the device appear to break the laws of physics, like the conservation of momentum or the conservation of energy. When all the effects are considered it's equivalent to using a laser as a thruster, or worse. (It's equivalent to use a normal flashlight, but a laser is more cool.)
Don't dismiss this article just because of the main image. It's a image of an EmDrive that is another impossible device that doesn't work but is totally unrelated to the device in this article.
The main part is:
> This mass changing isn’t prohibited by physics. Einstein’s theory of special relativity says that objects gain mass as they are driven towards the speed of light, an effect that must be accounted for in particle accelerators.
In special relativity, when the charged particles accelerate and decelerate they emit electromagnetic radiation. The whole process conserve the energy and momentum. The momentum that the device provides is compensated by the momentum of the electromagnetic radiation, aka photons.
So this device should work. It doesn't break the laws of physics. It produce some photons in the intended direction and more photons in other random directions. So it is just a very inefficient photon thruster https://en.wikipedia.org/wiki/Photon_rocket. It's like attaching a laser to the back of your starship, and then adding some lamp to illuminate in every direction to make it more inefficient. So you can dismiss this article after all.
EDIT: I copied most of this comment to other comment in https://news.ycombinator.com/item?id=21253796 , but the other comment was later moved here, so there is a lot of overlap. The other article at least don't use a big photo of an EmDrive.
> Don't dismiss this article just because of the main image. It's a image of an EmDrive that is another impossible device that doesn't work
Do you have a link for that? I haven't been following the EM Drive but a quick google now suggests that a team in Germany believe that they found the reason for the anomolous readings but I cannot find anything definitive.
The problem with EM drive testing in general is that you're looking for a signal (thrust) which should be zero, while pumping an enormous amount of energy into a system, and declaring any nonzero reading as success. Physicists know from experience that this is a recipe for fooling yourself. There are a million things that could imitate the purported signal.
In the last EM drive test I looked at, the "thrust" was pointing in the wrong direction, and moreover it perfectly matched the temperature curve of the apparatus, even though no theories of the EM drive say it should. That is a dead giveaway that the temperature is causing a fake signal, which e.g. could happen by thermal expansion messing up the meters. In general, the EM drive seems like a playground for sloppy experimentalists, because what anybody else would call a failure can be reported as a success.
The animation comparing the helical engine with same mass vs with relativistic masses was super helpful, I wish more articles that went into physics had these kinds of simple illustrations.
>“I know that it risks being right up there with the EM drive and cold fusion,” he says. “But you have to be prepared to be embarrassed. It is very difficult to invent something that is new under the sun and actually works.”
This was actually my favourite part of the article and a beautiful reminder that it's OK to fail.
The difference between this idea and the EM drive is that there's an at least somewhat plausible theory behind it, that's not entirely incompatible with known science.
EM drive proponents could make the same statement and it would be less credible in that context.
That's not to say that experimenting first and figuring out the theory later is a bad thing - that's often how science works - but generally, one follows strong evidence to reach a theory to explain it. EM drive proponents extrapolate wildly from extremely weak evidence. It's not good science.
The animations sure help, but I find the second one misleading because the ring bounces instantly and it has only 2 discrete sizes.
Instead of a discrete bounce, picture a slow motion elastic bounce where the ring gets heavier as it's being accelerated. It seems to me that when the box pushes the ring (left side), the ring would be gaining mass as it accelerates, thus cancelling the harvested movement, right?
I think the mass increase is not supposed to come from the forward/backward motion. Rather, the mass increase comes from rotating the ring.
Imagine the ring at the front of the ship spinning up to relativistic speed, then you push hard on it to get your ship moving a bit. Then you slow the ring down again before it hits the back, so it's much easier to bring back to the front.
Here's the actual paper [1]. The article was super confusing because it implied the box itself would need to be traveling near the speed of light for the theorized effect to work, which is pretty useless if you're at 0c to start with. I don't fully understand the paper, but it suggests using magnetically contained ions in a rotating ring arrangement. If nothing else, this will be a fun thought experiment for other physicists to break down.
> The article was super confusing because it implied the box itself would need to be traveling near the speed of light for the theorized effect to work, which is pretty useless if you're at 0c to start with
Even more useless when you consider that in your own frame of reference you're always at 0c.
If your starting point is a well understood theory that is known to conserve momentum (as a mathematical theorem), you design a complicated device using this theory and then within this specific design you find that momentum is not conservered then you should double check your calculations.
It first happened with classical electrodynamics (the EM drive) and now it happens with special relativity it seems.
To be fair, I am not arguing that conservation of momentum is 100% true. But starting from well established theories where conservation of momentum is a mathematical consequence seems to be a flawed approach.
I can't believe this is so far down. This is exactly why I don't need to pay attention to someone's weird magnet arrangement or marble track geometry to create a proportioal motion machine, I know they're playing with conservative fields and it isn't going to work.
However in this case, there is some significant acceleration which implies GR which is not in general conservative. I suspect it is though if you restrict yourself to the special case of accelerations with no significant gravity.
In general, however, this is still the correct approach to thinking about such problems. If you can find a no-go theorem, then you needn't concern yourself with the complex details. That said, if you can find a weird place where it looks like momentum isn't being conserved, it probably is because you are inadvertently predicting an effect of the theory that will take care of that problem.
You don't understand how the EM drive works, you just keep repeating a law, which is true, without any understanding how how the device actually works.
Mass is a Lorentz scalar and thus is invariant; the mass of relativistic particles does not increase as velocity increases. One can say the force necessary to keep a constant acceleration increases as velocity increase. This is a common misconception, and it appears even NASA engineers don't understand this. This is not science.
I used the word "inertia" to refer to the various inertia-related things that are used in mechanics. For example, the mass tensor that appears in curvilinear coordinate systems. This class of inertia-related things are usually given a name involving the word mass, and they are not usually Lorentz invariant.
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The problem is that you have a different "mass" when you try to accelerate the particle in the direction it is traveling and a different "mass" when you try to accelerate the mass in a perpendicular direction. (If the acceleration is not parallel or perpendicular, it's more complicated.)
Your formula is the correct one for the acceleration in the perpendicular direction, like in the magnetic field of a cyclotron, that is the typical example.
For an acceleration in the parallel direction you must add a ^3 to the correction.
m = m0/√(1 − v²/c²)³
Most modern books of advanced electromagnetism/relativity try to avoid the change in the "mass" an use only the rest mass m0. The other "mass" is sometimes handy and sometimes misleading.
"Lie" might be a bit strong, but the concept of relativistic mass is misleading and technically incorrect in various ways.
As a result, in the last few decades or so the concept of relativistic mass has gone out of favor in physics and its teaching.
The wikipedia section for relativistic mass[1] includes the following quote from the textbook "Spacetime Physics," by Taylor and Wheeler:
> "The concept of "relativistic mass" is subject to misunderstanding. That's why we don't use it. First, it applies the name mass – belonging to the magnitude of a 4-vector – to a very different concept, the time component of a 4-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of spacetime itself."
In short, relativistic mass is not a good way to understand what's actually happening in these scenarios.
Essentially, the relativistic kinetic energy of the object is being counted as mass, following E=mc^2. However, that only works because E=mc^2 is a special-case simplification that is designed to apply when momentum is zero, i.e. in an object's rest frame, to its rest mass.
If you look at the full mass-energy equivalence equation[2]:
E^2 = (pc)^2 + (m0 c^2)^2
...you can see the separate momentum component p. It's possibly to "cheat" and eliminate the (pc)^2 term and bundle it into a revised value for m, but this loses information and leads to various issues of the kind described by Taylor and Wheeler.
IANAP, but as far as I know it is true only if m is the relativistic mass which apparently is an obsolete and confusing concept which is not taught anymore (according to Wikipedia Einstein himself disliked it). Otherwise the formula only holds at rest.
Many times now, friends have introduced me to friends of their's that need help on some kind of engineering or are seeking investors for some new kind of technology. I heard about magnetic bubble memories, new logic gate designs for digital ICs, and improvements to starting batteries for internal combustion automotive applications. These seemed possible but quite risky.
However, some of the most interesting presentations were different. They seemed to be simply impossible inventions thought up by well-meaning, passionate people.
For example, two high schools kids swore that they had invented a video compression algorithm that worked better than existing ones such as H.264, while at the same time being lossless. They were trying to obtain investors and their parents had already contacted a public relations firm to promote their work. All they needed were some outside investors so that they could work out the kinks.
I was quite skeptical about their claim since: (1) they wouldn't reveal their methods nor any example of the algorithm in action, (2) they were completely unfamiliar with any literature on video compression, (3) didn't know how to program, and (4) couldn't understand the notation used for a mathematical discussion of the issues. Here's a quote: "What do the big E symbols all over the page mean?" (they were capital sigmas). The P.R. firm arranged for me to do a couple fo days of consulting with them to untangle what was going on. Unsurprisingly, the check I received for consulting with them later bounced.
Another time, a likable young guy claimed to have invented a purely mechanical, reactionless propulsion engine. It was a memorable experience. I listened and watched the "inventor" describe the weights, arms, and rotating parts. Forces were going in all kinds of directions and were quite dynamic. I explained that conservation of momentum meant that it wouldn't work and his reply was "Okay, but just explain why this part wouldn't push the whole thing forward when it swung around, [etc. etc.]" He simple didn't believe that conservation of momentum would keep his device from flying though space, on its own without expending any mass. Because I refused to calculate every force and integrate them over time as the parts revolved and slid back and forth he felt like I hadn't refuted his intuition about the mechanism. He had no understanding of vectors or calculus or physics. Every so often after our initial meeting I would hear from him again. He was a earnest, nice guy.
Every time I see an article like this I think briefly that I should send him a link to it, but it's probably better that I don't.
"""It would also need to be big – some 200 metres long and
12 metres in diameter – and powerful, requiring 165
megawatts of power to generate just 1 newton of thrust,
which is about the same force you use to type on a
keyboard. For that reason, the engine would only be
able to reach meaningful speeds in the frictionless
environment of space. “The engine itself would be able
to get to 99 per cent the speed of light if you had
enough time and power,” says Burns."""
So it falls into the same "impractical except at very high speeds for long, long, long journeys" category with "we can explode nuclear bombs on one end of the ship and use the explosion against a giant shield, to speed us up".
With ion engines, you need fuel to be ionized - usually xenon. The faster you want to go, the more of your energy just goes toward accelerating the fuel in your tank. The upper limit for speeds you can reach approaches the speed of the exhaust - which tops out around 50 km/s for current ion drives, about .0002C.
> The upper limit for speeds you can reach approaches the speed of the exhaust - which tops out around 50 km/s for current ion drives, about .0002C.
That is not correct. The delta-v of a rocket (i.e., the maximum speed it can reach) depends on the effective exhaust velocity and on the mass fraction of its propellant; see [1]. For example, a rocket which is initially 90% propellant, can reach a velocity ~2.3 times its effective exhaust velocity.
They seem so at first glance, but you have to build a couple of sheilds -- one for nuclear debris and the other for interstellar debris. There are also other problems with emission, fuel, etc. Issac Arthur has a good video on it (https://www.youtube.com/watch?v=3aBOhC1c6m8). All of Issac Arthur's stuff is, quite frankly, amazing. He has a clear understanding of the material and manages to convey it in a way to laymen, like no one else.
Re: the Sun article on the helical NASA engine, there is a correction on why this will not work.
Please see:
https://www.universetoday.com/143741/nasa-engineer-has-a-gre...
But relativity still obeys Newton’s third law, so the idea doesn’t work in the real world. Burns is right that there’s an error in his paper, but it’s a subtle one.
His design only accelerates the circular motion of the particles, so he assumes their speed forward and backward along the axis of the rocket should remain constant. But in relativity, as the mass of the particles increase, their speed along the axis would slow down. This is due to the relativistic effects of time dilation and length contraction. As a result, the particles give the rocket an equal push at both ends. Einstein’s theories don’t let you get around Newton.
In fairness, Burns knew his idea was a long shot, which is why he put it out there for others to review. That’s what science is all about. That’s also why it’s worth getting just a little excited when ideas like this are put forward. Most of them will fail, but someday one just might work. We could get to the stars after all, but only if we’re willing to keep testing new ideas.
Koberlein's explanation is okay but I read Burns's "Keep velocity constant on z-axis" as an instruction rather than an assumption. In that light the error doesn't appear so subtle (it manifests as a simple error of "conservation arithmetic").
The laws of physics can't be violated. The human definition of "the laws of physics" is what has been violated, and this will continue for as long as human's exist and evolve our understanding of reality.
> But, Burns asks, what if the ring’s mass is much greater when it slides in one direction than the other? ... In fact, a simplistic implementation of Burns’s concept would be to replace the ring with a circular particle accelerator, in which ions are swiftly accelerated to relativistic speed during one stroke, and decelerated during the other.
OK... that's great, but how do you plan to quickly accelerate particles without expending lots of energy (and without receiving a 'reaction')?
I think the guy has the diagram backwards. As the ring moves counter to the boxes motion, it has higher relative velocity (in terms of the box frame), and therefore higher mass. As it moves in the direction of motion of the box, it will be moving more slowly (almost sitting still), so it will have less mass / momentum in that direction. The result is that after a few iterations, it will balance out.
He's drawn the diagram relative to the outside observer (where the ring seems to go more slowly on the backstroke), but not relative to the box (where the ring has much higher relative velocity on the backstroke, and lower relative velocity on the forward stroke).
Another issue here is that the ring uses the box itself to pull itself forward with the spring, and if the mass is increasing, then its pulling ever more on the spring as it "gets faster", thereby slowing the box down by that much on the way back.
I was thinking about the propellant problem a couple of days ago. Is there a reason we can't use electrons? It's relatively easy to accelerate them to high percentages of the speed of light, and it's almost a certainty that your ship would start collecting stray electrons to replace the ones you lost.
It's better to accelerate the nuclei, because you get more momentum for the same energy. You need to send the electron in the same general direction. From the Wikipedia page:
> Ion thrusters emit a beam of positively charged xenon ions. To keep the spacecraft from accumulating a charge, another cathode is placed near the engine to emit electrons into the ion beam, leaving the propellant electrically neutral. This prevents the beam of ions from being attracted (and returning) to the spacecraft, which would cancel the thrust.
Most device use Xenon, but other devices use Hydrogen instead. Perhaps you can try to collect the Hydrogen from the almost vacuum (there are a few Hydrogen atoms per cubic feet), but I don't know if it will work in real life.
1) the more reaction mass you conserve, the more energy you need, so relativistic exhaust (electrons or anything else) asymptotically approaches an overly complicated photon drive.
2) using only electrons puts a large cloud of negative charge behind you while giving you a positive charge, which will act as drag slowing you down. Ion drives spray out equal + and - currents of ions and electrons (or equivalently a neutral plasma) to avoid that.
This comment just seems pedantic, like when people complain that a 'free [thing]' is never actually free because taxes or some other product paid for it. Everyone knows that free in that context actually means 'no charge for the user at the time of transaction' but some people feign being obtuse so that they can nitpick.
Obviously it means that it violates the laws as we currently understand them. I know it means that, you know it means that, so what's the actual problem?
Then the headline should read something like "Breakthrough points to new physics". This is just a clickbait title. When you read the article it becomes clear that there's a lot of wishful thinking involved. Others have pointed out that this is not likely to work.
This is not clickbait. This is just a catchy title. Clickbait is when you write a title, to infer something, and that something is not part of the content.
a "law of physics" is a human construction. There's no guarantee the physical universe matches these equations exactly or that there are even exact laws the universe follows. So a violation of a physics law is just physical evidence that disagrees with these constructions.
Of the options proposed the most promising propellantless thrust mechanism for space travel? As of now, which one has been tested the most and is most likely to become our first choice. Could it enable interstellar travel?
Unless I've missed anything, the only known, proven to actually work, propellantless thrust system are solar sails (and various beam-powered equivalents). Even nuclear photonic rockets slowly use up reaction mass.
However, ion drives are already fairly mature and perfectly viable for interstellar travel, if you're willing to wait.
Sails aren't yet feasible outside the solar system (and are still in their infancy even within), but with enough power production they might be another option in the future.
None of them have been proven to actually generate anomalous thrust. The prior probability of such a thing working is so small that without dramatic evidence to the contrary, they're all nearly indistinguishably equally unlikely.
That said, "EM drive" prototypes have actually been built, as have Mach-effect thrusters, etc. None of them have convincingly been shown to work, mind you.
This thing just exists on paper. It's not that hard to come up with a derivation on paper that's actually subtly wrong- much easier, sometimes, than actually finding where they went wrong.
surely this is pretty easy to debunk?
So it gains mass while you accelerate it.
But the reaction force required to accelerate it as it gains mass increases at exactly the same time in the opposite direction.
f=ma holds just the same if you change the mass as when you change the force.
Things absolutely can violate the laws of physics, in which case the laws of physics have to be rewritten. In fact, that's the holy grail in physics, is to find an experiment which reliably breaks the currently existing laws of physics. That is how progress is made. If it were like you say, then there would be no need for physics research, everything would already be known.
Errors in the laws of physics can be found in two ways:
1) new experimental data which conflicts with the currently accepted laws of physics
2) inconsistencies within the current laws of physics
or
3) The "error" in physics is not there and there is an error in the derivation of the inconsistency.
What happens here is that an engineer attempts to use the accepted laws of physics without measuring new experimental data in hopes of violating the accepted laws of physics, but without formulating an explicit contradiction. This is why gus_massa's BS alarm got triggered: using only accepted laws in physics it should be impossible to derive a contradiction, and any seeming contradiction is either a complicated form of already understood propulsion mechanisms (photon rockets) which consume rocket rest mass, or else the seeming contradiction is an actual contradiction, in which case the derivation should be simplified to the extreme to point out the inconsistency in physics. The latter was not illustrated so it entails either an error in derivation, or an inefficient photon rocket.
Considering that "the laws of physics" means by definition "the things that are observed to happen in the natural world" I don't think observable phenomenon can break the laws of physics. They can change our understanding of the laws of physics, but the laws themselves remain the same. It's a bit of a definitional issue though.
I think that they actually mean "our description of how reality works". As in, the laws are part of the map, not the territory. "Breaking" those laws just means finding out they're an inaccurate description.
what you say is true, but in this case there is no voyaging the territory going on at all. what the engineer proposes is like looking at a map and correcting the map without exploring the real world. it is possible to guess corrections to the map without actually exploring the world, but it means detecting inconsistencies. Correcting the map without travelling or referencing neglected observations would entail a realization. For example suppose our map of the world looked like 3 copies of the world, and we somehow believed there are 3 New Yorks, 3 Paris'es etc, that seem to develop in parallel, ... then the person proposing that the first repetition is actually a return to the same point would be making a point to the rest of the world using the triple copy earth. Here there is no pointing out a misconception of the laws of physics, and there is no referencing of anomalous observations, so you can not fix the map using nothing but the old map unless you also point out what is wrong with the map.
> Why is a magazine like New Scientist pushing magic?
New Scientist is not a high brow journal despite it's name. It's sold in supermarkets and newsagents (corner shops).
I used to subscribe to it for a very long time, until they started dumbing-down the articles and also pre-selling the main story to other online news sites who published them online, BEFORE my subscriber issue hit my doormat.
I was annoyed as this title as well; it is as clickbaity as it can get.
Obviously nothing can break the law of physics, by definition! It can certainly break our current knowledge of them (we were mistaken).
The charitable interpretation of the title is that it would be "breaking" the law of newtonian mechanics - which we know are a good approximation only in certain conditions, ie. when the speed of the body is not approaching the speed of light, that are not met there (that's the whole point of this design!)
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Re: the Sun article on the helical NASA engine, there is a correction on why this will not work.
Please see:
https://www.universetoday.com/143741/nasa-engineer-has-a-gre...
But relativity still obeys Newton’s third law, so the idea doesn’t work in the real world. Burns is right that there’s an error in his paper, but it’s a subtle one.
His design only accelerates the circular motion of the particles, so he assumes their speed forward and backward along the axis of the rocket should remain constant. But in relativity, as the mass of the particles increase, their speed along the axis would slow down. This is due to the relativistic effects of time dilation and length contraction. As a result, the particles give the rocket an equal push at both ends. Einstein’s theories don’t let you get around Newton.
In fairness, Burns knew his idea was a long shot, which is why he put it out there for others to review. That’s what science is all about. That’s also why it’s worth getting just a little excited when ideas like this are put forward. Most of them will fail, but someday one just might work. We could get to the stars after all, but only if we’re willing to keep testing new ideas.
Relativistic dynamics is different from Newtonian dynamics in a lot of ways. Force isn't parallel to acceleration anymore. Acceleration gets harder the faster an object moves. You can mimic some of these changes by just pretending that you still have Newtonian dynamics but the mass can change with velocity, but we don't use this language in physics because it's misleading -- there are many effects this idea can't capture. (For example, the fact that force is not parallel to acceleration.) It is a very fragile analogy that causes a lot of conceptual mistakes.
It's easy to prove that Newtonian mechanics conserves momentum. It's also easy to prove that relativistic mechanics conserves momentum. A weird hybrid of Newtonian mechanics plus a magically changing "relativistic mass" does not conserve momentum, but nobody has ever thought this was a correct description of nature. It's the result of taking a helpful simplifying analogy too far. Any reactionless drive formulated using this Frankenstein theory doesn't work.
If you just bounce an object back and forth, in either Newtonian mechanics or relativistic mechanics, you won't get anywhere. If you change the rest mass of the object to be different going right than left, you will go somewhere, but it will cost momentum to do this, as explained in gus_massa's comments. So we haven't gotten thrust for free.
This is the first I’ve heard of this and I would like to learn more, partly because of my own harebrained not-quite-reactionless engine idea that I know can’t possibly work really, but I can’t see why yet.
Where should I look?
A really excellent, conceptually clear exposition of relativity is given in chapters 11 and 12 of Morin's Mechanics. The modified version of F=ma is covered in section 12.5.
That key basic insight is not just the resolution to the twin paradox but the basis for event horizons near black holes and such. (There is a surface at coordinate -c²/a where time stands still.)
This includes the relativistic version of Newton's second law, which shows that F is generally not parallel to a.
[1] https://iopscience.iop.org/article/10.1088/1742-6596/1141/1/...
It's a complicated way if saying almost everything is possible so don't believe old dogs who have given up on optimism. https://www.brainyquote.com/quotes/arthur_c_clarke_100793
> Burns has worked on his design in private, without any sponsorship from NASA
Seems like they didn't, though as usual the article completely buries that information.
I kinda wish NASA had a policy like Disney, where you can't use your affiliation with them in association with personal projects (though for a different reason.)
My only complaint is that publicity is disproportionately allocated to the studies least likely to be right. While paper isn't limited, room in the newspaper is.
The vacuum part was an emphasis on requiring a counterpart to change momentum.
In an atmosphere you could flap your wings, or use electric fans, and argue what it means to ride a swing, but it would be besides the point, as in an atmosphere there is no need for propellant-less engines from the article.
As a definition, no. But no one has been able to figure out reactionless propulsion; as far as anyone can tell, the only way to accelerate in space is to throw something in the opposite direction (matter or light).
But, if you provide some momentum to an object like a hammer and release it, you will move. That goes back to "you need to leave something behind in order to go somewhere."
In special relativity, when the charged particles accelerate and decelerate they emit electromagnetic radiation. The whole process conserve the energy and momentum. The momentum that the device provides is compensated by the momentum of the electromagnetic radiation, aka photons.
So this device should work. It doesn't break the laws of physics. It produce some photons in the intended direction and more photons in other random directions. So it is just a very inefficient photon thruster https://en.wikipedia.org/wiki/Photon_rocket. It's like attaching a laser to the back of your starship, and then adding some lamp to illuminate in every direction to make it more inefficient.
If you are generating the photons (like in a photon rocket, aka laser attached to the back of the starship) then the minimal power is 300MW/N (and you need a generator).
I didn't notice before the 165MW/N in the slides, but their device is not bouncing the photons, so the theoretical minimum is 300MW/N, so it is impossible to use only 165MW/N. So they must have an error (numerical or conceptual) in the calculation.
In the slide, the energy is used to accelerate the particles, and then the energy is recovered when the particles return. So the article claim more efficiency, but let's ignore that part.
I think the main problem is that the particles will emit a lot of energy in the sharp turn at the top, something like the https://en.wikipedia.org/wiki/Cyclotron_radiation This radiation is what really push the device. In the sharp turn at the bottom the particles are going more slowly, so the radiation and push is smaller.
I don't understand why the calculation using a mix of classical and relativistic formulas give almost the correct result. The error is only in x2 (in the impossible direction), a x2 is not so off. I guess the main problem is assuming that the particles will have the same speed during all the turn???
https://en.m.wikipedia.org/wiki/Woodward_effect
The Woodward effect uses General Relativity. So the conservations laws are more complicated to define because the space-time is curved. Anyway, the curvature is so small that if it is real it would be very difficult to measure and even more difficult to use it in a thruster.
First, note that to fill the patent you don't need a working prototype. It's just a piece of paper.
The patent has the same idea, but it uses other device to move the particles. It looks more difficult to implement than the device in this article. (And the patent has a weird discussion about a maximal velocity.)
My previous comment applies without changes to the device in the patent too. It's just another very inefficient photon thruster.
If the author forgets to consider the momentum and energy carried away by the electromagnetic waves / photons, then the device appear to break the laws of physics, like the conservation of momentum or the conservation of energy. When all the effects are considered it's equivalent to using a laser as a thruster, or worse. (It's equivalent to use a normal flashlight, but a laser is more cool.)
The main part is:
> This mass changing isn’t prohibited by physics. Einstein’s theory of special relativity says that objects gain mass as they are driven towards the speed of light, an effect that must be accounted for in particle accelerators.
In special relativity, when the charged particles accelerate and decelerate they emit electromagnetic radiation. The whole process conserve the energy and momentum. The momentum that the device provides is compensated by the momentum of the electromagnetic radiation, aka photons.
So this device should work. It doesn't break the laws of physics. It produce some photons in the intended direction and more photons in other random directions. So it is just a very inefficient photon thruster https://en.wikipedia.org/wiki/Photon_rocket. It's like attaching a laser to the back of your starship, and then adding some lamp to illuminate in every direction to make it more inefficient. So you can dismiss this article after all.
EDIT: I copied most of this comment to other comment in https://news.ycombinator.com/item?id=21253796 , but the other comment was later moved here, so there is a lot of overlap. The other article at least don't use a big photo of an EmDrive.
Do you have a link for that? I haven't been following the EM Drive but a quick google now suggests that a team in Germany believe that they found the reason for the anomolous readings but I cannot find anything definitive.
In the last EM drive test I looked at, the "thrust" was pointing in the wrong direction, and moreover it perfectly matched the temperature curve of the apparatus, even though no theories of the EM drive say it should. That is a dead giveaway that the temperature is causing a fake signal, which e.g. could happen by thermal expansion messing up the meters. In general, the EM drive seems like a playground for sloppy experimentalists, because what anybody else would call a failure can be reported as a success.
And as anyone who's worked with sensors should know, if your sensor is reading exactly zero, that means your sensor is broken.
https://rationalwiki.org/wiki/Woo
>“I know that it risks being right up there with the EM drive and cold fusion,” he says. “But you have to be prepared to be embarrassed. It is very difficult to invent something that is new under the sun and actually works.”
This was actually my favourite part of the article and a beautiful reminder that it's OK to fail.
EM drive proponents could make the same statement and it would be less credible in that context.
That's not to say that experimenting first and figuring out the theory later is a bad thing - that's often how science works - but generally, one follows strong evidence to reach a theory to explain it. EM drive proponents extrapolate wildly from extremely weak evidence. It's not good science.
Instead of a discrete bounce, picture a slow motion elastic bounce where the ring gets heavier as it's being accelerated. It seems to me that when the box pushes the ring (left side), the ring would be gaining mass as it accelerates, thus cancelling the harvested movement, right?
Imagine the ring at the front of the ship spinning up to relativistic speed, then you push hard on it to get your ship moving a bit. Then you slow the ring down again before it hits the back, so it's much easier to bring back to the front.
I appreciate the courage of this.
[1] https://ntrs.nasa.gov/search.jsp?R=20190029657
Even more useless when you consider that in your own frame of reference you're always at 0c.
It first happened with classical electrodynamics (the EM drive) and now it happens with special relativity it seems.
To be fair, I am not arguing that conservation of momentum is 100% true. But starting from well established theories where conservation of momentum is a mathematical consequence seems to be a flawed approach.
However in this case, there is some significant acceleration which implies GR which is not in general conservative. I suspect it is though if you restrict yourself to the special case of accelerations with no significant gravity.
In general, however, this is still the correct approach to thinking about such problems. If you can find a no-go theorem, then you needn't concern yourself with the complex details. That said, if you can find a weird place where it looks like momentum isn't being conserved, it probably is because you are inadvertently predicting an effect of the theory that will take care of that problem.
https://news.ycombinator.com/newsguidelines.html
What are you talking about? This stuff was taught in high school to me:
The problem is that you have a different "mass" when you try to accelerate the particle in the direction it is traveling and a different "mass" when you try to accelerate the mass in a perpendicular direction. (If the acceleration is not parallel or perpendicular, it's more complicated.)
Your formula is the correct one for the acceleration in the perpendicular direction, like in the magnetic field of a cyclotron, that is the typical example.
For an acceleration in the parallel direction you must add a ^3 to the correction.
Most modern books of advanced electromagnetism/relativity try to avoid the change in the "mass" an use only the rest mass m0. The other "mass" is sometimes handy and sometimes misleading.As a result, in the last few decades or so the concept of relativistic mass has gone out of favor in physics and its teaching.
The wikipedia section for relativistic mass[1] includes the following quote from the textbook "Spacetime Physics," by Taylor and Wheeler:
> "The concept of "relativistic mass" is subject to misunderstanding. That's why we don't use it. First, it applies the name mass – belonging to the magnitude of a 4-vector – to a very different concept, the time component of a 4-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of spacetime itself."
In short, relativistic mass is not a good way to understand what's actually happening in these scenarios.
Essentially, the relativistic kinetic energy of the object is being counted as mass, following E=mc^2. However, that only works because E=mc^2 is a special-case simplification that is designed to apply when momentum is zero, i.e. in an object's rest frame, to its rest mass.
If you look at the full mass-energy equivalence equation[2]:
E^2 = (pc)^2 + (m0 c^2)^2
...you can see the separate momentum component p. It's possibly to "cheat" and eliminate the (pc)^2 term and bundle it into a revised value for m, but this loses information and leads to various issues of the kind described by Taylor and Wheeler.
[1] https://en.wikipedia.org/wiki/Mass_in_special_relativity#Rel...
[2] https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalenc...
AFAIK, most physicists these days will only use the invariant mass, or at least be explicit about it if they talk about the relativistic mass.
https://en.wikipedia.org/wiki/Invariant_mass
The full equation[1] is:
...where p is momentum, and m0 is rest mass (mass in the rest frame of the object.)[1] https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalenc...
However, some of the most interesting presentations were different. They seemed to be simply impossible inventions thought up by well-meaning, passionate people.
For example, two high schools kids swore that they had invented a video compression algorithm that worked better than existing ones such as H.264, while at the same time being lossless. They were trying to obtain investors and their parents had already contacted a public relations firm to promote their work. All they needed were some outside investors so that they could work out the kinks.
I was quite skeptical about their claim since: (1) they wouldn't reveal their methods nor any example of the algorithm in action, (2) they were completely unfamiliar with any literature on video compression, (3) didn't know how to program, and (4) couldn't understand the notation used for a mathematical discussion of the issues. Here's a quote: "What do the big E symbols all over the page mean?" (they were capital sigmas). The P.R. firm arranged for me to do a couple fo days of consulting with them to untangle what was going on. Unsurprisingly, the check I received for consulting with them later bounced.
Another time, a likable young guy claimed to have invented a purely mechanical, reactionless propulsion engine. It was a memorable experience. I listened and watched the "inventor" describe the weights, arms, and rotating parts. Forces were going in all kinds of directions and were quite dynamic. I explained that conservation of momentum meant that it wouldn't work and his reply was "Okay, but just explain why this part wouldn't push the whole thing forward when it swung around, [etc. etc.]" He simple didn't believe that conservation of momentum would keep his device from flying though space, on its own without expending any mass. Because I refused to calculate every force and integrate them over time as the parts revolved and slid back and forth he felt like I hadn't refuted his intuition about the mechanism. He had no understanding of vectors or calculus or physics. Every so often after our initial meeting I would hear from him again. He was a earnest, nice guy.
Every time I see an article like this I think briefly that I should send him a link to it, but it's probably better that I don't.
In other words, it's no Alcubierre drive.
Not my field, but with that power, wouldn't an old-fashioned ion drive give you a lot more thrust than that??
[after some searching]
With 165MW is looks like you could run hundreds of existing ion engines to get you to about 1/2C speed with a thrust measured in 1000's of newton's.
https://en.wikipedia.org/wiki/Ion_thruster
That is not correct. The delta-v of a rocket (i.e., the maximum speed it can reach) depends on the effective exhaust velocity and on the mass fraction of its propellant; see [1]. For example, a rocket which is initially 90% propellant, can reach a velocity ~2.3 times its effective exhaust velocity.
[1] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
His design only accelerates the circular motion of the particles, so he assumes their speed forward and backward along the axis of the rocket should remain constant. But in relativity, as the mass of the particles increase, their speed along the axis would slow down. This is due to the relativistic effects of time dilation and length contraction. As a result, the particles give the rocket an equal push at both ends. Einstein’s theories don’t let you get around Newton.
In fairness, Burns knew his idea was a long shot, which is why he put it out there for others to review. That’s what science is all about. That’s also why it’s worth getting just a little excited when ideas like this are put forward. Most of them will fail, but someday one just might work. We could get to the stars after all, but only if we’re willing to keep testing new ideas.
OK... that's great, but how do you plan to quickly accelerate particles without expending lots of energy (and without receiving a 'reaction')?
He's drawn the diagram relative to the outside observer (where the ring seems to go more slowly on the backstroke), but not relative to the box (where the ring has much higher relative velocity on the backstroke, and lower relative velocity on the forward stroke).
Another issue here is that the ring uses the box itself to pull itself forward with the spring, and if the mass is increasing, then its pulling ever more on the spring as it "gets faster", thereby slowing the box down by that much on the way back.
It's better to accelerate the nuclei, because you get more momentum for the same energy. You need to send the electron in the same general direction. From the Wikipedia page:
> Ion thrusters emit a beam of positively charged xenon ions. To keep the spacecraft from accumulating a charge, another cathode is placed near the engine to emit electrons into the ion beam, leaving the propellant electrically neutral. This prevents the beam of ions from being attracted (and returning) to the spacecraft, which would cancel the thrust.
Most device use Xenon, but other devices use Hydrogen instead. Perhaps you can try to collect the Hydrogen from the almost vacuum (there are a few Hydrogen atoms per cubic feet), but I don't know if it will work in real life.
1) the more reaction mass you conserve, the more energy you need, so relativistic exhaust (electrons or anything else) asymptotically approaches an overly complicated photon drive.
2) using only electrons puts a large cloud of negative charge behind you while giving you a positive charge, which will act as drag slowing you down. Ion drives spray out equal + and - currents of ions and electrons (or equivalently a neutral plasma) to avoid that.
Obviously it means that it violates the laws as we currently understand them. I know it means that, you know it means that, so what's the actual problem?
However, ion drives are already fairly mature and perfectly viable for interstellar travel, if you're willing to wait.
Sails aren't yet feasible outside the solar system (and are still in their infancy even within), but with enough power production they might be another option in the future.
That said, "EM drive" prototypes have actually been built, as have Mach-effect thrusters, etc. None of them have convincingly been shown to work, mind you. This thing just exists on paper. It's not that hard to come up with a derivation on paper that's actually subtly wrong- much easier, sometimes, than actually finding where they went wrong.
I imagine ducks and rabbits would be the best spacestock.
So it's magic?
Except as the article says there absolutely nothing that violates the laws of physics.
Especially given it's theoretical so I'm not sure how using a simulation it may violate even the current laws of physics.
Why is a magazine like New Scientist pushing magic?
1) new experimental data which conflicts with the currently accepted laws of physics
2) inconsistencies within the current laws of physics
or
3) The "error" in physics is not there and there is an error in the derivation of the inconsistency.
What happens here is that an engineer attempts to use the accepted laws of physics without measuring new experimental data in hopes of violating the accepted laws of physics, but without formulating an explicit contradiction. This is why gus_massa's BS alarm got triggered: using only accepted laws in physics it should be impossible to derive a contradiction, and any seeming contradiction is either a complicated form of already understood propulsion mechanisms (photon rockets) which consume rocket rest mass, or else the seeming contradiction is an actual contradiction, in which case the derivation should be simplified to the extreme to point out the inconsistency in physics. The latter was not illustrated so it entails either an error in derivation, or an inefficient photon rocket.
New Scientist is not a high brow journal despite it's name. It's sold in supermarkets and newsagents (corner shops).
I used to subscribe to it for a very long time, until they started dumbing-down the articles and also pre-selling the main story to other online news sites who published them online, BEFORE my subscriber issue hit my doormat.
Obviously nothing can break the law of physics, by definition! It can certainly break our current knowledge of them (we were mistaken). The charitable interpretation of the title is that it would be "breaking" the law of newtonian mechanics - which we know are a good approximation only in certain conditions, ie. when the speed of the body is not approaching the speed of light, that are not met there (that's the whole point of this design!)
His design only accelerates the circular motion of the particles, so he assumes their speed forward and backward along the axis of the rocket should remain constant. But in relativity, as the mass of the particles increase, their speed along the axis would slow down. This is due to the relativistic effects of time dilation and length contraction. As a result, the particles give the rocket an equal push at both ends. Einstein’s theories don’t let you get around Newton.
In fairness, Burns knew his idea was a long shot, which is why he put it out there for others to review. That’s what science is all about. That’s also why it’s worth getting just a little excited when ideas like this are put forward. Most of them will fail, but someday one just might work. We could get to the stars after all, but only if we’re willing to keep testing new ideas.