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Reactionless drive?


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35 replies to this topic

#31 jaydfox

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Posted 03 October 2006 - 06:37 PM

Well, yeah. I meant in layman's terms. And even then, the distinction is by point of view. On earth, an example of a propellantless propulsion system is a standard automobile. The reaction is the friction-based force where the tires meet the pavement. But no propellant is used in acceleration. Of course, fuel is burned and expelled, but the expulsion of propellant itself does not provide propulsion (if the car had a tank, it could store waste gases; or you could even aim the exhaust pipes forward, ensuring that if anything, the exhaust was slowing you down).

On the other hand, a "rocket car" would use a propellant for acceleration, not friction.

In the sky, one doesn't use the air the same way we use the ground, but it's similar. In the case of a prop-plane, the air becomes the propellant (again, the exhaust could be stored or redirected to be removed from consideration).

In space, there isn't a corresponding body one could push against. You can't use "space" itself as a propellant, because it has no mass-energy associated with it. In deep intergalactic space, you would need to carry propellant of some sort, even if it's merely energy that gets converted to photons or gravity waves or some other means of radiating energy (which has an equivalence to mass). In deep space, all drive systems would essentially be propellant-based (as opposed to the automobile or the airplane, which can use the external world as "propellant", as something to "react" with).

In our solar system, one could use the solar wind or even the radiation pressure of the sun. So even within our solar system, one could have a propellantless system. But I assume we were talking about something relying solely on its own internal properties, something that could function in deep intergalactic space, in an effective vacuum. In which case, propellantless and reactionless would equate fairly well. (Not exactly, but fairly well. I realize that even in deep intergalactic space, space isn't a complete vacuum...)

#32 knite

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Posted 03 October 2006 - 08:24 PM

This is actually bringing up very interesting side questions, such as Does space really have no mass or energy in its structure? Are there really no detectable emissions from this drive that could affect another body? It seems to me that gravity is the most obvious reaction the drive could be having with other bodies, but I think its a good idea to wait for a test, because I have a feeling that if it works we will find something surprising that no-one had thought of before.

#33 jaydfox

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Posted 03 October 2006 - 08:37 PM

This is actually bringing up very interesting side questions, such as Does space really have no mass or energy in its structure?

Well, this one is tricky. There is plenty of stuff in space that has mass/energy. Even the gravitational field from distant massive objects causes space to be permeated with energy. But it's not the space itself that has this mass/energy. Space is like a massless bottle: it can contain stuff that has mass, but doesn't itself have mass. (I suppose under certain theories space might have mass, but not under any mainstream theories I'm aware of.)

Are there really no detectable emissions from this drive that could affect another body? It seems to me that gravity is the most obvious reaction the drive could be having with other bodies

My guess, should any such "reactionless drive" ever be created, is that gravitational waves/energy will be involved somehow, if not something more mundane like EM waves. I don't foresee anything coming along that uses physics so radically different from what we know now that it would seem "reactionless" based on currently known physics.

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#34 mikelorrey

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Posted 09 October 2006 - 08:22 PM

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.


Jaydfox, your idea of "pushing against" is hopelessly mired in a newtonian conception of the universe. Its the same sort of gobbldegook that led the New York Times in the 1920's to denigrate Robert Goddard for ignoring "what every schoolchild knows" about newtons laws, when he proposed that rockets could fly men to the moon. NYT assumed that rocket exhaust had to "push against" an ambient atmosphere to generate thrust... Similarly, by a strictly Newtonian understanding of gasses, a de Laval rocket nozzle should not produce supersonic exhaust gasses, but if you use the Navier-Stokes equations, all is explained.

Newton is dead, and so are his laws.

Photons are not solid, they are binary energy packets, and only exhibit pseudo-mass as a function of their frequency or wavelength as relativity predicts. The sort of device I am describing also has an action and reaction: quanta are added to photons following a circular wave guide, the photons interact by Lorentz transformation with the ambient magnetic field, dumping those quanta into the coil as momentum via EMF/CEMF reactance. This device is not 'reactionless', but it is 'fuelless' other than consuming energy. No conservation laws are violated, as kinetic energy of the momentum gained will always be less than the energy put into the system.

#35 jaydfox

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Posted 09 October 2006 - 09:08 PM

"Hopelessly mired"? I might not have a PhD in physics, but I'm no idiot when it comes to physics.

A car "pushes against" the ground.
A propellor "pushes against" the air.
A rocket doesn't push against space. It does get pushed by gas pressure, the net result of which is that it "pushes against" the exhaust gases. A light sail pushes against the bombarding photons and/or solar wind.

I'm well versed in special relativity. I understand the concepts of mass shells and binding energy, and that all forces that act over non-zero distances must be mediated by an exchange of energy (with consequent momentum) at the speed of light (or less, but then the exchange is just a simple inelastic particle system).

Under special relativity alone, what you describe is so obviously mathematically flawed that there's no argument, and I can sit back and let you dig yourself deeper and make a fool of yourself. Don't tell me Newton's dead. Tell me special relativity is dead, and then please explain to me why. Otherwise, I will continue to sit back and enjoy this.

I've already conceded that this, if it works at all, must be using a quirk of general relativity. Such quirks might in theory exist, though the experimental evidence is equivocal and the concept itself generally mocked, but I like to keep an open mind. But if this works via general relativity, then please explain how, and explain where the specific departure is from special relativity. You mention relativity and lorentz transformations and relativistic mass, but under special relativity, four-momentum is still conserved, so it's impossible for there to be a net momentum change without a "reaction" taking place outside the closed system, and/or an emission of some sort that imparts thrust.

#36 jaydfox

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Posted 09 October 2006 - 09:23 PM

BTW, don't get the wrong impression. I generaly respect you, and I enjoy reading a lot of things you write. In the fields of politics, history, etc., I would consider myself inferior in terms of knowledge and perhaps even critical thinking (which isn't to say that we can't both learn from each other).

However, since I was a child, math and physics and been my forte. While my IQ overall is not terribly high (tested at 147 prior to turning 8), my IQ within the domain of math and physics is probably in excess of 160. It's hard to say for sure, other than to use milestones as a measure (e.g., qualifying for the USA Mathematics Olympiad, one of about 140 in the U.S. that year).

Whatever I lack in knowledge, I can quickly gain. If there is a theoretical framework I'm missing, point me the way and I will study it and apply it as necessary.

I have only ever studied relativity as a hobby, so I don't have a "deep and profound" understanding of it. But I understand the basis of the conservation laws well enough to know that they can't be violated by creativity alone: a phenomenon which violates the basic laws of physics is the only way to violate these laws.

But like I said, general relativity is very complex and interconnected, so perhaps an exception exists? I'd like to know how.




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