35 replies to this topic

[psudoname]

http://www.shelleys....uk/fdec02em.htm

This appears to be able to allow far more efficent space travel. Plus a future version that superconducts would allow hovercars and cheap space travel....

[JohnDoe1234]

Sent an email request for more information.

Looks kinda iffy.

[mikelorrey]

Sent an email request for more information.

Looks kinda iffy.

Not quite. While the reactionless concept, first promoted by Jerry Pournelle and the inventor of the Dean Drive, suffered setbacks, the Dean Drive concept uses mass operating at strictly conventional velocities. Prof John Cramer of UW has commented on this, and agreed that while such a device wouldn't work, this does not mean that the concept would not work if the working medium flowed at or near relativistic velocities, where mass and time dilation effects would, in fact, allow thrust to be produced with no reaction required. Both I and Sasha Chislenko had also independently arrived at the same conclusion.

It appears that the EM Drive, using microwaves through a varying cross section waveguide, may achieve this effect. I'm not sure how it works, but it might work via an electromagnetic equivalent of the effect one sees in the de Laval nozzle used in rocket engines. Keep in mind that electrostatic and electromagnetic phenomenon operate by Lorentz transformations and don't have mass to conserve.

Edited by mikelorrey, 12 September 2006 - 04:15 AM.

[JohnDoe1234]

It appears that the EM Drive, using microwaves through a varying cross section waveguide, may achieve this effect. I'm not sure how it works, but it might work via an electromagnetic equivalent of the effect one sees in the de Laval nozzle used in rocket engines.

Exactly why I said it was iffy, because I didn't see a nice little explanation of how it works, just vague claims, however that doesn't mean I'm saying it is impossible. [tung]

[mikelorrey]

Well, the inertial concept is that you have some working mass or medium that orbits in such a way that it generates more centrifugal force on one side of its orbit than the other. For example, take a vertical clothes washing machine, and load all the clothes on one side of the drum, wash, and spin, and you'll note that with more mass on one side of the drum, it wobbles as the center of mass travels around and around the center of rotation.

Now, imagine that you could keep that center of mass always on one side of the machine while the drum rotated, or changed the speed of the mass as it spun around the center of rotation. It would generate a force vector on the side the center of mass was on, or on the side where the mass travelled fastest, i.e. generating the most centrifugal force.

Dean accomplished this with his Dean Drive concept, by varying the speed of the masses as they rotated. The problem is that the velocity was so low that when you time averaged things, it didn't really work that well.

I designed several more sophisticated developments, which, rather than spinning one weight at a time, spun several weights, or in the hydraulic version, used a fluid as its working mass. While these devices worked in a gravity and friction environment, it is argued that they would not work in space (sadly, I did not have the funds to test either version there). However, Prof. Cramer, myself, and Sasha have advocated that, if you used mass or energy orbiting at a very high gamma (percent of c) or at c in the case of EM energy, the variations in velocity (or in the case of EM, variations in frequency/wavelength) as the medium orbited, would generate a force vector due to relativistic dilation.

[JohnDoe1234]

Yeah, I to have designed a simple 'Inertial Drive' which instead of using orbiting weights uses an array of conveyer belts which have weights attached that can be accelerated very quickly into one direction then retracted very slowly, and it does work, although the reason is simple, as you mentioned, the initial impulse forward overcomes friction, however the return stroke is slow enough that it won't reset the previous motion, so if I were to place it floating in a vacuum, it would only wobble back and forth because as the center weight moves to one end, it would push the device in the opposite direction.... useless in space. Which is why I am so skeptical about such claims that these types of devices can generate force without taking advantage of local friction

[mikelorrey]

Yeah, I to have designed a simple 'Inertial Drive' which instead of using orbiting weights uses an array of conveyer belts which have weights attached that can be accelerated very quickly into one direction then retracted very slowly, and it does work, although the reason is simple, as you mentioned, the initial impulse forward overcomes friction, however the return stroke is slow enough that it won't reset the previous motion, so if I were to place it floating in a vacuum, it would only wobble back and forth because as the center weight moves to one end, it would push the device in the opposite direction.... useless in space. Which is why I am so skeptical about such claims that these types of devices can generate force without taking advantage of local friction

That is where relativity comes in. When mass travels at high gamma (percent of light speed), its mass increases the closer it gets to c. Thus, if you have an inertial drive in which the masses travel the fast leg at high gamma, then the return leg at lower gamma, then you have a difference in mass between the two legs, and as a result get a free momentum kick: energy converted to momentum, but the net result is that in the grand scheme, the overall concept of conservation of mass/energy/momentum remains valid.

Similarly, if you are using electromagnetic energy (i.e. photons), and since E=mc^2, you can treat the frequency of a photon as a virtual form of mass. The higher the frequency, the more mass. Thus, an EM inertial drive would treat photons like the travelling masses, but vary their frequency during their trip around the device. The leg with the higher frequency generates momentum due to relativity, while conservation of energy remains valid.

[jaydfox]

Mike, pardon my ignorance (not of the physics, but of the specifics of these designs), but how can a reactionless drive result in a change in momentum (or even just position) without violating conservation of energy and/or momentum?

It's not that I don't understand the basic concepts you've discussed, such as having objects increase in mass on one leg of a journey, relative to the other leg, or having an object move faster on one side of a rotation, etc.

But as far as I can think of, any effort to produce these changes involves an imparting of additional energy/momentum, which counteracts the effect. Basic conservation laws would dictate that in order for a mass to move, another amount of mass would have to move as well. Assuming all masses are positive, for a given amount of mass to move to the left, another quantity of mass is going to have to move right.

Reactionless drives may be possible, but they would either:
A) Rely on forces to act on distant bodies, e.g. gravitational and/or electromagnetic forces
B) rely on an alternative form of propellant, e.g. photons, neutrinos, i.e., things we don't normally think of as propellant
C) break known laws of physics (which I suppose would imply that the known "laws", as far as we understand them, are wrong or imcomplete, just as Newton's physics were superceded by Einsteins).

I suppose a fourth possibility would be a warping of spacetime itself, but that's well outside the bounds of standard mechanical engineering (i.e., gears, springs, hydraulics).

So, my ignorance out of the way, how would any of these other specific plans actually work within the confines of the conservation laws?

[mikelorrey]

Mike, pardon my ignorance (not of the physics, but of the specifics of these designs), but how can a reactionless drive result in a change in momentum (or even just position) without violating conservation of energy and/or momentum?

Conservation laws are not violated because you can convert energy into momentum, momentum into energy (really, both are forms of energy, one is potential and the other kinetic). So long as the amount of energy you expend is equal or greater than the kinetic energy of the propelled objects momentum, no energy conservation law is violated.

It's not that I don't understand the basic concepts you've discussed, such as having objects increase in mass on one leg of a journey, relative to the other leg, or having an object move faster on one side of a rotation, etc.

But as far as I can think of, any effort to produce these changes involves an imparting of additional energy/momentum, which counteracts the effect. Basic conservation laws would dictate that in order for a mass to move, another amount of mass would have to move as well. Assuming all masses are positive, for a given amount of mass to move to the left, another quantity of mass is going to have to move right.

That depends. If your masses are moving around in an orbit or cycle, and are faster on one side than on the other, then all you need to do is have an identical unit in which the masses are rotating in the opposite direction, but in which the faster side is on the same side as the first unit. Thus, torque is cancelled out. Thus, the action/reaction is actually in torsion: masses travelling in opposite directions.

If the unit is an EM drive, I would expect that the microwaves are corkscrewing along a channel which has a biased cross-section, in which the photons are at a higher frequency on one side than the other, likely due to a denser EM field on one side of the channel than on the other. The Lorentz interactions would cause this velocity change to occur with every cycle of the corkscrew. You have two such devices, with opposite polarities so that the microwaves corkscrew in opposite directions in each, and your torque issue is neutralized.

Another possibility is that the microwaves are travelling out a channel and are somehow inducing some of their energy into the nozzle as they pass, and by lorentz transformation, it becomes an action/reaction of energy and momentum coupled together.

The thing you need to understand is that lorentz transformations are very different from the normal conservation laws we are used to.

[jaydfox]

Okay, let me try a similar line of questioning, but more fundamental. Consider your whole contraption, with its counter-rotating thingies with the torques cancelling and what-not, as a single mass. After all, just put it inside a closed shell (since it's reactionless), and consider everything inside the shell to be one mass. Its mass distribution can change, etc., but for all intents and purposes, it's a closed region of space. Any reaction with the outside world violates the principle of "reactionless".

Now, if it suddenly starts moving, then one or both of the following things must have happened, according to the conservation laws:
1) a mass external to this closed system moved as well
2) the center of gravity of the closed system shifted within the system, but did not move.

The center of gravity cannot move without violating a conservation law. It can shift within the closed object, but you can't get from here to Saturn if your center of gravity remains here, unless your ship is a billion kilometers long.

As for expenditure of energy, where does that energy go? If it's emitted in some form, as radiation, then perhaps that's the propellant? Otherwise, how is energy being used to convert to momentum? Energy converts to energy, or mass, and vice versa, but it doesn't convert to momentum. Energy and momentum each have their own conservation law, which work together, but neither is transformed into the other. Potential energy can convert to kinetic energy, and momentum can be generated in the process, but only with an equal and opposite impulse somewhere else to cancel it out.

I'm really not understanding how sustained motion can be achieve without applying force on the external world. Perhaps my mistake is approaching this from the direction of basic physics, instead of trying to understand something really complex.

[mikelorrey]

Your understanding of conservation laws conflicts with relativity.

Energy is converted to angular momentum. Angular momentum is converted centripetally/centrifugally to linear momentum by the relativistic difference in mass from one side of the cycle to the other. Linear momentum expressed as kinetic energy will always be less than energy expended in creating angular momentum. Ergo, no conservation laws are violated.

BTW: Is there a way to attach an image to these posts, one that isn't already online somewhere, like do an image upload? The IMG button only allows URLs

Edited by mikelorrey, 22 September 2006 - 10:52 PM.

[jaydfox]

Is there a website that explains the math? This is probably beyond what we can discuss in text alone, and I don't think I'm going to get it without examples.

[mikelorrey]

Is there a website that explains the math? This is probably beyond what we can discuss in text alone, and I don't think I'm going to get it without examples.

Actually, I made an animation for you to see that demonstrates it rather simply. Is there an image upload function here?

[jaydfox]

Hmm, basic members might not be able to upload, come to think of it. Well, you can give it a try, and if you can't do it, maybe I can help.

To upload a file, enter a brief message, then click "Go Advanced". On the next screen, you should see a "File Attachments" section, with a text box where you can enter the path of a file to upload (there's a "Browse" button to make this easier).

If that doesn't work, it's most likely because I restricted upload access to basic members at some point.

How big is it? If it's small enough, you can send it to my gmail account and I can upload it. (I only have about a 100kbit upstream, so size matters.) Otherwise, if you can post it somewhere else on the web, I can ftp it directly from the imminst server, which should have plenty of bandwidth for a large file.

[mikelorrey]

No separate file upload section. I went and uploaded the file to my website....

Okay, here it is. Each drum has two masses. When each is at the bottom, they are moving slowly, when they are at the top, they are moving fast. Color indicates relativistic mass dilation (blue = heavy, red=light, green=medium).

Now, if they were not travelling at high gamma, the mass wouldn't change, and there would be no thrust because time averaging (the amount of time each mass spends on either side of the drum) shows that time is inversely proportionate to centrifugal thrust, and thus cancels out. WITH relativistic mass dilation, time averaging doesn't work, and thrust is generated, with energy going into the system as angular momentum is drawn out as linear momentum, minus entropic losses.




http://lorrey.biz/im...eactionless.gif

[jaydfox]

This (or something like it) made it onto slashdot:
http://science.slash...2/2226258.shtml

[jaydfox]

By the way, I'm going to need an explanation of how relativity changes the principle of conservation of momentum. As far as I'm aware, conservation of momentum still applies in special relativity, using momentum four-vectors (I think that's what they're called). I still don't see how you can break the law of conservation of linear momentum.

It's not enough to cleverly say that energy is converted into angular momentum and then into linear momentum. The fact remains that under the principle of conservation of momentum, the center of gravity of any closed system has a fixed momentum (and position and energy, by extension under four-vectors). If the center of gravity is fixed, then the only way to move the center of gravity of a closed system is by also moving the center of gravity of another closed system with respect to the first (which, incidentally, would imply neither system was truly closed). Anything else is a violation of the conservation law.

So I'm not saying that energy can't be converted to angular momentum and then to linear momentum, because I haven't taken the time to work the math and prove or disprove it to myself. But it seems an obvious enough loophole that a person with basic math skills (basic in the sense of not having a PhD in math) could prove or disprove, and I'd expect the entire scientific establishment would be well aware by now that there's a loophole in the conservation laws if there actually were one. Yet this doesn't seem to be the case.

So I'm wondering what I'm missing here. How is there a loophole here that doesn't seem to be recognized by the math and science community at large?

[jaydfox]

BTW, if this were a loophole in general relativity, then I might see some merit. Most solutions to the equations of general relativity drop terms to simplify, and the equations tend to lend themselves to numerical analysis rather than ironclad mathematical proof, so perhaps the mistakes are simply unnoticed. But I really don't see this loophole as being a simple manipulation of special relativity. I could be wrong, as I said, because I haven't done the math myself, but simple logic implies that this loophole is most likely a miscalculation or misapplication of the appropriate math by those claiming the loophole.

[mikelorrey]

By the way, I'm going to need an explanation of how relativity changes the principle of conservation of momentum. As far as I'm aware, conservation of momentum still applies in special relativity, using momentum four-vectors (I think that's what they're called). I still don't see how you can break the law of conservation of linear momentum.

It's not enough to cleverly say that energy is converted into angular momentum and then into linear momentum. The fact remains that under the principle of conservation of momentum, the center of gravity of any closed system has a fixed momentum (and position and energy, by extension under four-vectors). If the center of gravity is fixed, then the only way to move the center of gravity of a closed system is by also moving the center of gravity of another closed system with respect to the first (which, incidentally, would imply neither system was truly closed). Anything else is a violation of the conservation law.

So I'm not saying that energy can't be converted to angular momentum and then to linear momentum, because I haven't taken the time to work the math and prove or disprove it to myself. But it seems an obvious enough loophole that a person with basic math skills (basic in the sense of not having a PhD in math) could prove or disprove, and I'd expect the entire scientific establishment would be well aware by now that there's a loophole in the conservation laws if there actually were one. Yet this doesn't seem to be the case.

So I'm wondering what I'm missing here. How is there a loophole here that doesn't seem to be recognized by the math and science community at large?

The conservation laws were written in the Newtonian Universe, not the Einsteinian Universe. Einstein basically had to rewrite them for relativity to work.

Look at it this way: In a normal centrufugal system, the center of gravity and the center of angular velocity are fixed in the same location by time averaging.

In a relativistic you accelerate an object to 0.9 c with x energy. You put x+n amount of energy in to accelerate it to 0.91 c, which increases the mass of the object. The fact that the mass of the object differs on one side of the drum versus the other side of the drum means that the center of gravity shifts away from the center of angular velocity. because of this shift separating these two points of force, a force vector is generated.

[jaydfox]

I'm just still not getting where the conservation law is bypassed. Like I said, I'm going to need a mathematical example, one that isn't so vague. I could try to make all kinds of assumptions about what you meant, but I'd be doing you a disservice.

When energy is added to the particle in its orbit, that energy left whatever accelerating device was used to add the energy. Roughly speaking, there's no instant shift in mass-energy. So that's my first concern. And now that the particle is travelling faster, there is a requirement for additional binding energy to hold it in its orbit. Binding energy is effectively negative energy. There are too many variables to keep track of in a simple explanation: the changes in mass and energy could be attributable to just about anything, conceptually. That's why I asked for a webpage or a manuscript or something that has the math worked out and shows what's going on. If we're talking exclusively about special relativity, then I really don't expect to see a conservation law violated. At best, I expect that someone made a mistake in their design.

On the other hand, if we're talking about an esoteric side effect of general relativity, then maybe I'd be willing to invest further energy into investigating this. But if we're talking about the rules of special relativity alone, then I really don't expect to find a nifty loophole around the law of conservation of four-momentum. The length/magnitude of four-momenta (a.k.a rest mass) are invariant under lorentz transformations, and it really doesn't matter what reference frame you do the calculations in, the answers should be the same, so relativistic velocities are beside the point.

General relativity is not so crystal clear: it involves terse mathematics, and equations with an infinite number of terms, of which physicists generally restrict their study to no more than the second or maybe third order terms. Here, I might be willing to buy the idea of a very complicated loophole. One which interested me in college, but which I never got the time to study further, was the "Woodward effect", if I recall the name correctly. It involved oscillating energy densities, taking advantage of the third order terms in the GR equations that are normally ignored. Even then, the effect doesn't seem to be "reactionless" per se, as the effect really involves using space-time warping effects to "move" the rest of the universe in the opposite direction to the propulsion, or something like that (it's been about seven years since I last read up on it, so forgive me if I botched the explanation).

[mikelorrey]

I'm trying to get across to you that the conservation law is NOT bypassed, you need to use the relativistic version, not the newtonian version, to understand what is going on.

I suppose you are trying to understand how EM or mass in an orbital path could transfer angular momentum to produce linear momentum in the device containing it.

First you need to understand that, without a gravity field holding that energy or matter in orbit around it, that containing that matter or energy in an orbital path is not natural, it take work, the matter or energy resists being bent to a curved path. The only reason matter follows an orbital path around, say, a planet, or sun, is because wrt space-times non-euclidean geometry, an orbit is actually a straight path, while a euclidean straight path is a curved path in a non-euclidean geometric space.

Conversely, since we don't have a gravitational field of any consequence in our engine, or spaceship, the engine containing that matter or energy has to do work to contain that matter or energy in a curved path. Generally this is done by either physical contact with the containment vessel, or by a field, such as an EM field, in which ions or electrons influence and are influenced by the EM field, exhibiting lorentz transformations, they induct a counter electromotive force upon the containment field coils, but at the same time they absorb kinetic energy from the energy or matter being forced into a curved path.

The Woodward Effect is related. I'm not a trained physicist, so forgive me if I'm not communicating it effectively. Professor John Cramer can explain it much better.

The essential issue is that when you are dealing with masses, or energy, at relativistic velocities, the difference between gravitational and inertial mass become distinct.

Here is Cramer's article:
http://mist.npl.wash...AV/altvw83.html

[bgwowk]

Hang on a second. Suppose I have a rock accelerating at a classical velocity due to a reactionless drive buried inside it. To any outside observer, that rock will disobey Newton's Third Law. It doesn't matter what relativistic weirdness is going on inside it, the net classical effect on the whole rock will be an observed violation of momentum conservation. Right? That would seem to be a violation of the Correspondence Principle, which although usually applied to quantum mechanics, is also valid for relativistic physics. It states that in the classical limit, effects to due non-classical physics must still reduce to classical laws of physics.

As you probably know, every symmetry has an associated conservation law. The symmetry associated with conservation of momentum is the homogeneity of space, or the invariance of laws of physics with position. That seems pretty fundamental and hard to break.

[Mind]

Here is a PDF with equations and more in depth discussions

If I understand/read this correctly, the drive is powered by a (microwave) magnetron. Thus the theoretical spacecraft "engine" will be powered by electricity instead of liquid hydrocarbons, correct?

[JohnDoe1234]

Correct, there are no combustion reactions taking place.

[bgwowk]

Here's a Wikipedia article on the same idea.

http://en.wikipedia.org/wiki/EmDrive

I skimmed the PDF, and I'm not buying it. It has the flavor a physics paradox, which is a problem formulated to apparently give a result that violates laws of physics, but that is actually ignoring something that upon deeper analysis resolves the paradox. These kind of paradoxes are fascinating intellectual puzzles to figure out, but there is very unlikely to be new physics in them. I suspect the measured thrust is almost certainly an experimental artifact of some sort.

Bear in mind that microwave leakage could produce thrust by carrying away momentum as photons. That's an old and perfectly valid means of converting electricity to thrust without expending fuel or conventional reaction mass. Only if a device radiates no microwave leakage and still produces thrust is there experimental verification of something weird going on. Even then, all possible extraneous factors (air convection off hot parts?) must be ruled out. Extraordinary claims require extraordinary evidence.

[Mind]

Well, we will find out soon enough if it works. The company trying to produce the drive has a research grant and has been working on it for about four years.

[jaydfox]

I'm trying to get across to you that the conservation law is NOT bypassed, you need to use the relativistic version, not the newtonian version, to understand what is going on.

Well, let's be clear here: are we talking your basic run-of-the-mill special relativity, or general relativity. The laws of physics under special relativity are based on ironclad mathematics: you can't violate the law of conservation of four-momentum. If you can make an apparently closed system (a ship and "reactionless" drive) accelerate, then something is being radiated from that closed system that is carrying away momentum in the opposite direction (in which case it isn't really closed, nor is the drive "reactionless"). The Newtonian laws of conservation of energy and conservation of momentum are encapsulated in the law of conservation of four-momentum: this law cannot be bent by clever apparatus design.

Now, if we're talking about general relativity, then maybe things are a little different, because I don't understand GR that well (few people do). Even then, I suspect a "reactionless" drive would be radiating something detectable or predictable, be it gravitational waves or EM waves or whatnot.

[knite]

i think a better term would be "propellantless" jayd.

[jaydfox]

Reactionless, propellantless, it's the same concept. Pushing against nothing. For every "action", there's an equal and opposite "reaction", etc. "Reactionless" implies one violated this basic law of physics, which is probably where the term came from.

Propellant usually implies something solid, such as chemical exhaust, maybe even photons. Using (anti-)gravity to move an object wouldn't involve something people normally think of as "propellant", but it still involves an action and "reaction", so I think reactionless is the more appropriate term. Reactionless conveys the principle that there's an action without a reaction somewhere else.

[bgwowk]

Reactionless, propellantless, it's the same concept.

No, it's not. Reactionless means Newton's Third Law is being violated. Propellantless means that no mass is expended during propulsion (except for E/c**2 if internal energy is used). Whether this drive is truly reactionless or merely propellantless (if it works at all) is not just a terminological preference, but a key physics issue. There are lots of ideas for propellantless drives (e.g. photon sail, magnetic field interaction drive), that are consistent with known laws of physics. A reactionless drive is another animal that is hard to reconcile with known physics.