Are Reactionless Space Drives the Future of Propulsion?

[ubavontuba]

Lots of scientists have been researching inertial effects in an attempt to develop the "reactionless space drive" (sometimes called propellantless or self-contained space drives). Has anyone made any headway?

I sometimes find articles pertaining to this that will state things like, "Professor so and so of such and such university has devised a theoretical means of self-contained propulsion." These articles will often state that the results are extremely limited (less than the width of an atom in one case) or the concept is based on the highly theoretical reseach of so and so (meaning it's probably garbage to begin with, I suppose).

Are these concepts usually developed in an attempt to verify Newtonian Mechanics with the expectation of failure, or do scientists really sense that there must be a way around Newton's laws?

What's the latest news?

 

[mathlete]

There is a way around Newton's Laws... it's called Quantum Mechanics ;)

 

[ubavontuba]

Sure, but can you use it to drive a spaceship?

 

[Redhat]

There is a way around Newton's Laws... it's called Quantum Mechanics ;)

Another way would be Special and General Relativity.

Sure, but can you use it to drive a spaceship?

Yes. I'm not sure if QM could do it but relativity tells us that there is equivalence between mass and energy.

Mr. Newton taught us that Force = d/dt(mass x velocity) which becomes the familiar F = m x dv/dt when mass is constant but becomes F = (v x dm/dt) + (m x dv/dt) when mass changes. This, as I'm sure you know is the basic principle behind rocket propulsion.

Since a photon's energy is E = (h x freq.) and since E = mc^2, the effective mass of a photon is m = (h x freq.)/(c^2) .

So, if one blasts enough photons of extremely high frequency out of the back of a spaceship, the ship will move forward since this action transfers the photons' mass from the spaceship to the outside meaning that dm/dt is not zero and is directed in the backward direction. This creates a net force that would push the ship forward.

Whether this is a "propellant less" spaceship or not would depend on whether one considers the energy used to produce the photons as a propellant.

 

[vanesch]

I sometimes find articles pertaining to this that will state things like, "Professor so and so of such and such university has devised a theoretical means of self-contained propulsion." These articles will often state that the results are extremely limited (less than the width of an atom in one case) or the concept is based on the highly theoretical reseach of so and so (meaning it's probably garbage to begin with, I suppose).

Yes, that's probably it !
There isn't much stuff around that has technological applications and that isn't well described by "conventional" physics, you know. And to get away with non-conservation of momentum, you'd be in trouble with classical physics, with relativity, and with quantum mechanics...

 

[ubavontuba]

Redhat,

That's still a rocket. It's called a "photon rocket."

Vanesch,

Tell me more about the conservation of momentum in this regard. It's my understanding that in an isolated system any acceleration of the center of mass, off of its center of gravity, would break this conservation. Is this correct?

What about in the case where the position changes (like in quantum tunneling) but the relative momentum remains the same? Is this still a conservation violation?

 

[vanesch]

Vanesch,

Tell me more about the conservation of momentum in this regard. It's my understanding that in an isolated system any acceleration of the center of mass, off of its center of gravity, would break this conservation. Is this correct?

Yes. In Newtonian mechanics (point masses and forces and all that), the conservation of momentum is introduced by postulate, which is the action=reaction postulate. So in elementary Newtonian mechanics, it is put in by hand ; and what you put in by hand, you can take it away, too. You could formulate a force law violating this postulate (for instance, green balls exert a force of 3N on red balls according to the line connecting them, but red balls don't exert a force on green balls). However, the re-formulation of Newtonian physics in Lagrangian terms (the variational approach) includes this action=reaction part in its formalism, from the moment that there is spatial translation invariance (that means, that shifting the entire system over a translation vector T, doesn't change any of the internal physics). You cannot take it out "by hand" anymore once you use this formulation. And this variational principle is the building block of about all of modern physics ; so we understand now the conservation of momentum as a consequence of the translational invariance of physics.
Now, as with everything, this could, one day, turn out to be wrong. But then about all we know of physics today is wrong. I'd need to see SERIOUS indications for momentum not to be conserved for me to start to take such a drive seriously - and as far as I know, never ever such an indication has been found. Again, one day, this could prove to be wrong. Just as the following assertion could prove to be wrong one day: "when you step out of the window on the 25th floor, you fall down". Maybe one could postulate that this may be true on all days of the year, but not on the 8th of March...a day when you can safely step out of the window of the 25th floor and you'll be floating there, not falling... wouldn't it be great if this were true ? Why don't we look deeper in this possibility ?

So, apart from this reserve, all of current physics says that momentum has to be conserved, and we think we know the underlying reason for that, which is the symmetry that physics is invariant under space translations.

What about in the case where the position changes (like in quantum tunneling) but the relative momentum remains the same? Is this still a conservation violation?

In quantum theory, there's no violation of conservation of momentum. The reason is that the overall Hamiltonian is commuting with the momentum operator, which is nothing else but the generator for space translations: if a is a translation vector and P is the momentum operator, then the translation operator in quantum theory is given by T(a) = exp(i a P), where you see the explicit relationship of the symmetry mentioned before.

 

[ubavontuba]

"when you step out of the window on the 25th floor, you fall down". Maybe one could postulate that this may be true on all days of the year, but not on the 8th of March...a day when you can safely step out of the window of the 25th floor and you'll be floating there, not falling... wouldn't it be great if this were true ? Why don't we look deeper in this possibility ?

Isn't this the day that the window washer's scaffolding just happens to be positioned outside my 25th floor window for a scheduled washing?

So, apart from this reserve, all of current physics says that momentum has to be conserved, and we think we know the underlying reason for that, which is the symmetry that physics is invariant under space translations.

So you're basically stating that if anyone actually succeeds with the development of a device/experiment that can internally shift it's center of mass off of its center of gravity, then all the physics we think we know falls to pieces?

Does it seem then that physics (since Newton) might be founded on a single principle that may or may not be true? Other than by experiment, has anyone tried to verify this by trying to formulate physics in other terms? What happens?

 

[Redhat]

Hi ubavontuba,

From your original post, I was not aware of the requirement for a rocket-less propulsion system (Sorry, I've not read the articles you referenced. Are they available on the web? -- they sound interesting).

Regarding your recent post:

The "center of gravity" and center of mass of an object only coincide when the gravitational field is perfectly uniform. So, in the real universe where nothing is really perfect, such coincidence doesn’t actually exist.

To "shift" the center of gravity (even more) from the center of mass, all one needs to do is increase the non-uniformity of the gravitational field acting on the object of mass in question.

A dramatic example would be the “spaghettification” an object experiences as it falls into a black hole. As the object gets closer to the black hole, the gravitational field becomes less uniform. Simply put, the gravity at the “bottom” of the falling object is greater than the gravity at the “top” of the object. As such, the object experiences forces pulling it apart from top to bottom and squeezing it together from side to side.

Even though the object will eventually “fall to pieces”, the physics we know thankfully does not. ;)


Redhat

 

[ubavontuba]

Well, you can do a Google Scholar. Do one on "inertia" for starters. You can get more specific to propellantless space drive concepts if you use "propellantless propulsion" -tether -"solar sail." Also, substitute out "propellantless" for keywords: antigravity, reactionless-propulsion, reactionless-space-drive, self-contained-propuslsion and inertial-propulsion

There are a number of interesting papers to peruse.

Also, do a general Google of the same keywords and you'll find lots of articles and silliness. Adding the keyword "article" cuts out some of the clutter.

 

[vanesch]

So you're basically stating that if anyone actually succeeds with the development of a device/experiment that can internally shift it's center of mass off of its center of gravity, then all the physics we think we know falls to pieces?

yes. (if I rewrite your phrase simpler: that can accelerate its center of mass internally, in an inertial frame)

Simple as that.

 

[vanesch]

Does it seem then that physics (since Newton) might be founded on a single principle that may or may not be true? Other than by experiment, has anyone tried to verify this by trying to formulate physics in other terms? What happens?

"other than by experiment"

Of course. I can do it by the force of thought. I can clash together entire galaxies that way (but not by experiment, just in my phantasy...)

 

[ubavontuba]

Vanesch,

That's funny... not. I was referring to reformulating the basis for the standard model on different mathematical principles. Do all roads lead to the current paradigm?

In other words, if these researchers that are trying to develop asymmetry in isolated systems have any hope of success, musn't there be an alternative to our standard model that correctly predicts what is currently observed, plus predicts the effects they desire?

I know this is obviously too vague a notion (without observable experimental results) to do more than perform some cursory explorations. I'm just wondering if anyone has done this, and if so, what interesting (or not) results might they be finding (interesting as in "too bizarre to be true" would also be interesting). String theory approaches this level of exploration, doesn't it?

 

[vanesch]

Vanesch,

That's funny... not. I was referring to reformulating the basis for the standard model on different mathematical principles. Do all roads lead to the current paradigm?

No, of course not. That was exactly my point. You can dream up all you want, you can postulate all you want. If you do not need to have agreement with experiment, there's a lot more "wiggle room" to think up new stuff of course. As I pointed out, in Newton's original formulation of mechanics (which is usually taught as introductory course to mechanics), you do not need action = reaction. It's postulated, but you can leave it out. Then you already have your theory which potentially works as you like, and in which there is no conservation of momentum.
As I said, you could have a toy universe consisting of red and green balls, red balls pulling on green balls, and green balls not pulling on red balls.
Define the force law:

F_green = G_greenred xM_red x M_green / r_green-red^2 x 1_green-red

(force excerted on a green ball, in presence of a red ball).

F_red = 0

(force excerted on a red ball)

We also define that red balls do not exert forces on red balls, and green balls do not exert forces on green balls.

All Newton's postulates (except for action = reaction) are respected this way.

It's a funny system to study. For instance, study what happens to a halter made of a red ball and a green ball, helt together by a strong steel bar of 1 meter length.Or study what happens if you have a dispersed set of green and red balls, and what happens to the center of gravity.

Question: it there conservation of angular momentum ? Is there conservation of energy ?

So here we have a theory, which is perfectly self-consistent, and in which there's no conservation of momentum. So clearly things do not HAVE to be that way. You can think up such theories, it is not difficult. The point is that they do not correspond to what's observed. I wouldn't know how to make it into a quantum theory, for instance. What's the point ?

 

[vanesch]

Hi ubavontuba,

From your original post, I was not aware of the requirement for a rocket-less propulsion system (Sorry, I've not read the articles you referenced. Are they available on the web? -- they sound interesting).

Regarding your recent post:

The "center of gravity" and center of mass of an object only coincide when the gravitational field is perfectly uniform. So, in the real universe where nothing is really perfect, such coincidence doesn’t actually exist.

To "shift" the center of gravity (even more) from the center of mass, all one needs to do is increase the non-uniformity of the gravitational field acting on the object of mass in question.

A dramatic example would be the “spaghettification” an object experiences as it falls into a black hole. As the object gets closer to the black hole, the gravitational field becomes less uniform. Simply put, the gravity at the “bottom” of the falling object is greater than the gravity at the “top” of the object. As such, the object experiences forces pulling it apart from top to bottom and squeezing it together from side to side.

Even though the object will eventually “fall to pieces”, the physics we know thankfully does not. ;)Redhat

I think one of us is mis-reading ubavontuba's post. I don't think he's talking about the difference between how gravity works upon an extended object, versus the centre of mass. He's more concerned with the possibility of a "propulsion-less" space drive or something, which would require non-conservation of momentum.
I'm trying to explain that conservation of momentum resides somewhere deeply in our understanding of physics, and that if momentum turned out not to be conserved, it would effectively shatter about all we know about physics to pieces. Now, I know that in GR, on large scales, things like "conservation of momentum and energy" become delicate issues, mainly because global quantities in GR are difficult to define (see for instance http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html). So I restrict myself here to conservation of momentum locally, in flat enough space (which is in any case the situation of a potential space drive).
Newton's theory, without action=reaction, is the last time we could accept violation of conservation of momentum. After that, we got Lagrangian and Hamiltonian formulations (which have it build into them if there is translation symmetry) of classical mechanics. And if you give up on that, you have no leg to stand on to do quantum theory. So most of 20th century physics would indeed fall to pieces if momentum were observed not to be conserved.

 

[Redhat]

vanesch,

I think I now understand his original post (thanks in large part to some of your explanations). It was this statement to which I was responding.

...

So you're basically stating that if anyone actually succeeds with the development of a device/experiment that can internally shift it's center of mass off of its center of gravity, then all the physics we think we know falls to pieces?

...

As an engineer, I take that as a challenge.

 

[ubavontuba]

Vanesch,

Thanks. Your letters cleared it up for me quite well. I now only have one question:

Why are these researchers so eagerly seeking asymmetry then? What's the point?

 

[ubavontuba]

As an engineer, I take that as a challenge.

I understand where you're coming from. I'm glad that you now understand what I was asking.

 

[vanesch]

Why are these researchers so eagerly seeking asymmetry then? What's the point?

Making fuzz ? Craving for attention ? Too much time on their hands ? I don't know.

 

[Redhat]

How 'bout this?

I was thinking about this subject today while taking a shower and came up with this wild invention.

It seems to allow for space travel without relying on Newton's law of conservation of momentum. Instead it relies on special and general relativity and ironically is basically a "photon rocket" turned inside out. This ship also emits light but as “exhaust” and not as a “propellant”. As such, I'm unsure as to its overall efficiency compared to Newtonian propulsion systems.

I call it the Photon Sphere Drive. Though the technology does not now (nor may ever) exist, the principles are fairly elementary. Thus it’s not a matter of physics but a matter of engineering.

(I wish I could include a picture – is that possible on this forum?)


“Reaction-less Space Drive using a Photon Sphere”

The Engine: The Photon Sphere

The photon sphere is a device used to create primordial black holes for the purpose of space travel. Its radius (which relates to its power) might be on the order of thousands of meters if not more.

Its inner surface is technically quite amazing. It consists of an array of extremely high frequency lasers directed toward the sphere’s center. Each laser is capable of creating extremely high frequency gamma ray photons. Once firing the photons, the lasers shrink drastically in area so that the photon sphere becomes virtually transparent. After some period of time the lasers return to their normal size and fire again. The laser array almost completely covers the entire inner surface of the sphere and is extremely dense. In fact, each laser’s maximum diameter is only the wavelength of the gamma ray photons.

Each laser fires at a precise time (based on the speed of light, the sphere's speed and the laser's position) so that all photons reach the center of the sphere (in phase and at the same moment in time) which makes the energy density great enough at that point to curve space-time into a primordial black hole (which “absorbs” all consequent photons from the lasers). After some short period of time the primordial black hole evaporates and its Hawking radiation escapes into space through the holes in the photon sphere created when the photon sphere becomes transparent.


The Spaceship:

Attached to the part of the inner surface of the photon sphere not covered by the laser array is a long flexible and stretchable arm that at its end is a pod containing the control deck, crew’s quarters and power supply for the lasers. The vast majority of the mass of the ship is here and its location is slightly removed from the center of the photon sphere. Its’ position relative to the center of the photon sphere can be changed by the flexible arm connecting it to the sphere.

The principle of operation:

The mass of the primordial black hole (at the center of the sphere) and the center of mass of the ship (essentially the control pod) fall toward each other. But before the pod enters the primordial black hole’s event horizon and disaster ensues, the primordial black hole evaporates into space through the openings in the photon sphere when in it’s transparent mode. The cycle continues and the spaceship continues to accelerate for as long as the lasers can be powered.

The ship is steered, stopped and speeded up by moving the pod relative to the center of the photon sphere with the flexible arm.

Maybe to increase efficiency, the leading surface area (“front”) of the photon sphere would not turn transparent thereby utilizing the energy of the Hawking radiation to add to the ship’s kinetic energy. But this gets Newtonian so ...


Redhat

 

[vanesch]

How 'bout this?

I think you've made a complicated photon motor. The question is if the center of gravity of the entire system (including the Hawking radiation) is moving. I'd bet not. In fact, you've sent a lot of radiation to infinity to move your space ship, and you can consider this radiation as the "exhaust" of your spaceship...

 

[ubavontuba]

How 'bout this?

It seems to me that by the laws of thermodynamics this couldn't be nearly as efficient as simply aiming all of those lasers rearward, to create a simple photon rocket. This is becasue anytime you change energy froms you lose energy to radiant heat. Therefore you want to apply the energy to the task at hand in the fewest steps possible.

I think you might be thinking that a micro-blackhole (MBH) might somehow exert a large gravitational force on the mass of the ship. This isn't true. The gravitational field of the MBH is no greater than the gravity of all the photons it is made of. It's just that it has a very, very, ve-e-e-e-ry tiny event horizon. It won't pull the ship so much, but rather the ship will simply gravitationally attract it (it's mass would be virtually nothing, as oppsosed to the mass of the ship).

Also from a Mechanics point of view, the energy/photon mass you move from one part of the ship to the other to create the MBH will be exactly equal and opposite in force to any pull achieved by the MBH. There will be no net motion.

 

[soupbone]

Another way would be Special and General Relativity.



Yes. I'm not sure if QM could do it but relativity tells us that there is equivalence between mass and energy.

Mr. Newton taught us that Force = d/dt(mass x velocity) which becomes the familiar F = m x dv/dt when mass is constant but becomes F = (v x dm/dt) + (m x dv/dt) when mass changes. This, as I'm sure you know is the basic principle behind rocket propulsion.

Since a photon's energy is E = (h x freq.) and since E = mc^2, the effective mass of a photon is m = (h x freq.)/(c^2) .

So, if one blasts enough photons of extremely high frequency out of the back of a spaceship, the ship will move forward since this action transfers the photons' mass from the spaceship to the outside meaning that dm/dt is not zero and is directed in the backward direction. This creates a net force that would push the ship forward.

Whether this is a "propellant less" spaceship or not would depend on whether one considers the energy used to produce the photons as a propellant.

I thought photons had zero mass? Is this link incorrect?
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

 

[ubavontuba]

I thought photons had zero mass? Is this link incorrect?

That link you posted describes photons pretty well, defining the characteristic known as "relativistic mass." However, it's a pretty well accepted supposition that they have no rest mass. Technically, all we can really say is that any mass they might have can only be defined to the limits of our experiments. There is an active debate as to whether they are truly massless or not (similar to the old nuetrino mass debate). Some speculate that there may yet be a defined minimum mass.

 

[Redhat]

I think you've made a complicated photon motor. The question is if the center of gravity of the entire system (including the Hawking radiation) is moving. I'd bet not. In fact, you've sent a lot of radiation to infinity to move your space ship, and you can consider this radiation as the "exhaust" of your spaceship...

Well, I thought about that too and resolved it this way. The Hawking radiation is originating from the black hole’s event horizon and not from the ship itself so an overall change in momentum of the system would result from that difference.

An analogy:
In a "vast" region of space there exit two massive objects. One is a capsule containing a crew. The other is a small black hole radiating away.
The capsule and the black hole accelerate toward each other but before they meet, the black hole totally evaporates. It seems logical that after that event, the capsule will still have the momentum it gained from the encounter with the black hole.

The photon motor as you call it (not a bad name I must say) just cycles the above process only in a much smaller region of space.

It seems to me that by the laws of thermodynamics this couldn't be nearly as efficient as simply aiming all of those lasers rearward, to create a simple photon rocket. This is becasue anytime you change energy froms you lose energy to radiant heat. Therefore you want to apply the energy to the task at hand in the fewest steps possible. ...

You’re right here. This is not a very efficient means of propulsion compared to a photon rocket.
The whole concept depends on efficiencies in engineering the universe may never see, but from a purely physical standpoint it should be possible.

Just using basic physics, one can “construct” such a ship and calculate how much its momentum changes as a function of the forces acting on it over time. Now if I didn’t screw up the math or some constants I predict the following: (this makes the assumption on Hawking radiation previously mentioned and also that the ship is “transparent” enough so that the Hawking radiation imparts no momentum to it.)

A photon sphere having a radius of around 227m being able to produce gamma rays of 10e21Hz is connected to the ship such that its center of mass is 10m from the center of the of the primordial black hole (PBH) at the time of its creation. Such a photon sphere would create a PBH with a mass of 6.75e5 Kg. (not very big but as such, will evaporate in about 25.8s).

Assume the ship is 10 times this mass and so the ship and PBH will accelerate together. (BTW all free falling objects accelerate toward each other in a g field, not just the lightest one toward the heavier one – even the sun moves very slightly because of the earth’s gravitational effect on it).

Anyway, about 26 seconds after the PBH is created, the ship will have “consumed” the gravitational energy of the PBH (and after making a couple of simplifying assumptions as to rate of change of the distance between centers of mass and the rate at which the black hole evaporates) one might expect an incredible change in momentum of: 82e-3 Kg m/s. ! Okay so its not a reason to start looking for venture capital.


Having said all that, I think there is another reason that it wouldn’t work and that comes from the fact that the energy required to due this resides on the ship. To produce the above example’s result requires converting 10% of the ship’s mass into energy and then completely converting it back into mass. But that step transfers mass from the ship to a point in front of it which (according to Newton) should produce a force pushing the ship backwards. So perhaps the net effect is indeed zero just as vanesch says.



But the guys down at SciFi Engineering have been working on this problem and have come up with a modification to the outside of the photon sphere. If instead of powering the photon sphere from the ship, the sphere will absorb the required energy from the universe itself – a “solar, neutrino, cosmic ray, gravitational wave, etc..” collector of sorts having incredible efficiency. The ship would then convert radiant energy of the universe into mass which would attract the ship’s mass and provide it with power to move.

Although the efficiency of that compared to a simple solar sail is even questionable.

Bottom line: “inertial” drives (at least using gravity) seem inherently much less efficient than drives based on momentum conservation. However, they do not seem to violate physical laws.

 

[vanesch]

Well, I thought about that too and resolved it this way. The Hawking radiation is originating from the black hole’s event horizon and not from the ship itself so an overall change in momentum of the system would result from that difference.

An analogy:
In a "vast" region of space there exit two massive objects. One is a capsule containing a crew. The other is a small black hole radiating away.
The capsule and the black hole accelerate toward each other but before they meet, the black hole totally evaporates. It seems logical that after that event, the capsule will still have the momentum it gained from the encounter with the black hole.

The photon motor as you call it (not a bad name I must say) just cycles the above process only in a much smaller region of space.

We work in an asymptotically flat spacetime (otherwise, concepts such as global energy and momentum are badly defined), meaning that we have an essentially flat Minkowski space, but locally, we have our spaceship and our black hole. Now, the spaceship is accelerating towards the black hole (Newtonian vision) and the black hole is radiating (and also accelerating towards the spaceship, right ?). As such, you will have a blue-shift of photons that are irradiated from the black hole in the direction of the spaceship (because the BH is accelerating), and a redshift of the photons sent out in the opposite direction (away from the spaceship).
So after a while, the BH is evaporated, and our spaceship is having a constant speed ; while the emitted photons behind the ship are "bluer" and the photons in front of the ship are "redder". This means that the EM field is now carrying a global momentum opposite to the one of the ship.

So essentially, the structure has served to impart momentum to the EM field, and to give opposite momentum to the space ship. The blue-shifted photons are the "exhaust" of the entire system.

 

[Redhat]

We work in an asymptotically flat spacetime (otherwise, concepts such as global energy and momentum are badly defined), meaning that we have an essentially flat Minkowski space, but locally, we have our spaceship and our black hole. Now, the spaceship is accelerating towards the black hole (Newtonian vision) and the black hole is radiating (and also accelerating towards the spaceship, right ?). As such, you will have a blue-shift of photons that are irradiated from the black hole in the direction of the spaceship (because the BH is accelerating), and a redshift of the photons sent out in the opposite direction (away from the spaceship).
So after a while, the BH is evaporated, and our spaceship is having a constant speed ; while the emitted photons behind the ship are "bluer" and the photons in front of the ship are "redder". This means that the EM field is now carrying a global momentum opposite to the one of the ship.

So essentially, the structure has served to impart momentum to the EM field, and to give opposite momentum to the space ship. The blue-shifted photons are the "exhaust" of the entire system.

Yes! Although I would say that all the Hawking radiation should be considered “exhaust”. Maybe SciFi Engineering could get the photon sphere (or ellipsoid) to re-capture that energy and increase the efficiency. Kind of an inertial drive “turbo-charger” ...

BTW: In case anybody’s interested. I redid my calculations, eliminated a simplification and found a bonehead algebra error so I now predict the spaceship (with mass = 10x the black hole’s initial mass of 6.65e5 Kg) will experience a change in momentum from an encounter with the black hole (when the center of mass of the spaceship is 10m from the center of mass of the black hole at its creation) of: 114 Kg m/s. This comes at the cost of “burning” 6.65e5 Kg, resulting in an efficiency of (a "whopping" ) 1.6e-24 %.

Redhat

 

[Maybenot]

Vanesch,

Thanks. Your letters cleared it up for me quite well. I now only have one question:

Why are these researchers so eagerly seeking asymmetry then? What's the point?

That's a very good question, actually. If conservation of momentum is a fundamental law, then it means that action and reaction are always perfectly symmetrical, regardless of the number of bodies involved.
This goes back to Newton's Principia, where Corollary 3 of the Axioms or Laws of Motion states:
"The quantity of motion, which is determined by adding the motions made in one direction and substracting the motions made in the opposite direction, is not changed by the action of the bodies on one another."
Saying it is one thing, but proving it is a different story. Newton could obviously not try every trick in the book, so his conclusion was that:
"…it would be too tedious to demonstrate every particular that relates to this subject."
Fair enough but the problem is, the 3rd corollary is not always right.

 

[ubavontuba]

That's a very good question, actually. If conservation of momentum is a fundamental law, then it means that action and reaction are always perfectly symmetrical, regardless of the number of bodies involved.
This goes back to Newton's Principia, where Corollary 3 of the Axioms or Laws of Motion states:
"The quantity of motion, which is determined by adding the motions made in one direction and substracting the motions made in the opposite direction, is not changed by the action of the bodies on one another."
Saying it is one thing, but proving it is a different story. Newton could obviously not try every trick in the book, so his conclusion was that:
"…it would be too tedious to demonstrate every particular that relates to this subject."
Fair enough but the problem is, the 3rd corollary is not always right.

Really? Can you be more specific?

 

[Maybenot]

Simpler than you think...

OK ! (Would be a good idea to have pen and paper on hand…)

First we have a system of three bodies. One is a pivot to which the other two are linked by two arms. The mass of the pivot is equal to the combined mass of the two bodies, the bodies themselves are of identical mass to each other and the mass of the arms is negligeable. The system is positioned like an upside down V, the pivot pointing upward. The arms form a 45 degrees angle pointing down on each side of a vertical axis passing through the pivot. And last but not least, no gravity.
Get it ?
Case A : An external force F (whatever) propels the 2 bodies away from the central axis at right angle to the arms, or if you prefer at a 45 degrees angle pointing up.
The bodies and the pivot pull on each other, but for the sake of the demonstration we will say that the bodies are « pushing » on the pivot, and that that the pivot is « pulling » on the bodies. Our system is symmetrical with respect to the central axis and the force exerted by the two bodies on the pivot is equal to FcosTeta, or the angle between the arms and that axis.
Total momentum is constant. Any change to the pivot’s momentum in one direction is equal to an opposite change in the momentum of the two bodies, right ? Since mass of pivot = mass of 2 bodies, then the pivot accelerates as much in one direction as the bodies acelerate in the opposite direction, along the same axis.
So far so good.
Case B : Let’s reset the counter to zero and repeat the experiment, this time in the opposite direction. The force propels our two bodies toward the central axis, at a 45 degrees angle pointing down.
Same thing happens and we will say that the bodies are « pulling » on the pivot, and vice-versa, with a force equal to FcosTeta in the axis of displacement.
Any minus in momentum of the bodies is balanced by a plus to the momentum of the pivot. In other words, the pivot accelerates while the bodies are slowed down.
Now the force exerted on the pivot by the bodies in case B is superior to the force exerted in case A. Why ? The angle in case B gets smaller, then FcosTeta gets higher. In case A, the angle gets wider and the force smaller. Conclusion : the acceleration of the pivot in case B is higher than in case A.
So what ?
Well what happens if we have four bodies (and four arms) tied to the same pivot, instead of two ? Still our inverted V shape with two arms pointing down on one side and two on the other.
Case C : This is case A and B together. This time the force is between the bodies on each side, internal to the system and we have two bodies going up and away from the center (case A) and two going down and toward it (case B).
We know that the acceleration of the pivot in case B is higher than in case A. The question is : now that they are together, how can the pair going up « push » on the pivot if the pair going down « pulls » on it faster than the first pair can push ?
Simple : it can’t. But the bodies will nevertheless be accelerated. Two accelerations in one direction and only one in the other. The center of mass is now moving.
What more can I say ?

 

[ubavontuba]

Maybenot,

I suppose you can start by defining the the force acting on the system. Where does it come from? What are its characteristics? What is its source?

See? It's too easy to mentally introduce an imaginary force that doesn't have to answer to the conditions of the system.

In a real space environment, this force must come from something, somewhere. Whether it be rockets, ion beams, meteor showers, or whatever, it introduces added mass and energy to the system that must be accounted for if we are to consider the system in full isolation. You can't just "(whatever)" it into irrelevance.

Think about it like this. If your pivot was motorized such that all the energy of opening and closing the "V" came from an internal source, what would happen?

In your last example, whether you realize it or not, the center of gravity will not move. "Raising" two arms does throw the apparent center of mass (the pivot) "downward" in relation to the system's boundaries more than closing the two lower masses together "raises" it, but the compensation will be that the pivot will apparently move "downward" and, in fact, the boundaries move in perfect sync to the center of mass which while only apparently moving "downward" is compensated for by the redistribution of weight around the center of mass. Therefore what is really happening is that the center of mass for the system is changing in relation to the mass distribution, but not in relation to the center of gravity. Your mistake is probably in viewing the pivot as representing the center of mass irrespective of the mass distribution around it.

Overtime, I've seen a lot of ideas like this come and go. They don't work. There is a fun way to experiment with these concepts though. I recommend that you download this free http://Newton.delphigl.de/Newtonplayground.html. Although it's designed to be a game driver, it can be used to conduct quite accurate physics simulations. For zero-g space, set the gravity to zero, delete the floor and make sure all of your objects aren't dampened (by default). You can then design, build, and test your ideas in a zero-g environment. If they propel themselves in this program (without pushing on anything), that would be very interesting... indeed.

P.S. Before you go there, having the masses on the ends be gyros has been investigated. No resultant propulsive properties were noted.

 

[Maybenot]

More than meets the eye

Your observations are general and don't adress the specificity of this case. The nature of the force is irrelevant. It could be a spring, it could be electromagnetic, etc since what we study are the interaction and the velocities after impulsion.
The question is this: After impulsion, at T+∆t, what are the linear accelerations (y axis) of the bodies going up, the bodies going down and finally of the pivot? (mass of pivot = mass of 2 bodies)
For the momentum to be conserved, the acceleration of the pivot has to be twice the opposite acceleration of either pair of bodies. How can the pair going "up" accelerate the pivot more than its own acceleration? THAT is the question
It's nice of you to say that the center of mass (or gravity) will not move anyway, but can you answer the question? Just give me the ratios of the acceleration of the bodies vs the acceleration of the pivot at a given time after impulsion.
That shouldn't be so difficult.

 

[Maybenot]

And by the way, we had it modelised with I-DEAS, an industrial digital modelling tool, by an independant company. The software is used to design racing cars, machines, etc.

 

[ubavontuba]

No, I quite directly addressed the specifity of your case. The nature of the external force acting on your system is entirely relevant. If you think you can just pretend that any part of the system is irrelevant, then so can I. Therefore I declare the mass to be irrelevant. What now?

The relative velocities of the bodies going up and down is truly irrelevant though. You are making the mistake of thinking of your bodies as individual entities. They are not. They are all part of an interconnected, single mass that can change shape and change it's internal mass distribution... and that's it. The assembly as a whole cannot accelerate without expelling mass/energy. All it can do is wobble all about.

As far as your computer simulation is concerned; garbage in = garbage out. Simply the fact that you regard the force acting on the device to be irrelevant tells me that it's garbage. If you paid for the service, you were ripped off.

Use that free download to model it and send me a copy of the file. Someone else did this with a very similar concept. I had fun watching it wobble all about.

I think the real issue for you is that it seems naturally intuitive that systems like this should work. This is probably because our intuition is based on earthbound systems. That is to say that our intuition fails us in an isolated space environment. It's common to think that swimming motions can propel you in space like they do in water. This is not true... and your concept functions very much like a swimmer in water. You have a central mass (torso), two lower extremities that are close together (legs), and two upper extremities with a greater range of motion (arms)... much like a person! Do you see how your intuition misled you straight to an example of your own body propelling itself through a liquid medium (the closest earthbound analogy to a zero-g environment)?

Anyway, I understand that you probably feel that I'm being obstinate and am blinded to the fact that you're the guy that beat Newton. Whatever. I've been there myself too. If you're smart you'll see the futility of it in a year or so and move on to other things (I have). Otherwise you'll doom yourself to a life of frustration... and perhaps madness. As an example, check out this http://www.forceborne.com/FBW/principle.htm" ".

Don't feel too bad though. Many quite ingenius people have been caught up in these mind traps. Newton himself spent the latter part of his life in futile pursuits. The list of engineers and scientists that have pursued these concepts is quite extensive. In fact I'm considering the notion of writing a book on it.

Lastly; the moderators here don't much like me and your ideas go beyond speculative (they're just plain wrong), so I suspect they may soon lock this thread. If this happens feel free to send me personal messages and we can continue discussing this privately.

 

[Maybenot]

Thanks for the advice, I'll send you something in the next few days. Actually, I don't feel like the guy who beat Newton because this no about wether Newton or anybody else is right or wrong. This is about one thing and one thing only: What are the accelerations of the bodies and the forces those bodies exert on each other. The rest is just feelings. No need to lecture, just sit down with a pen and a piece of paper.
Anyway, no need to end the thread, I am out of here.

Talk to you later.

 

[ubavontuba]

Maybenot,

Without intending to lecture: You might as well examine how much acceleration force you can apply to yourself by pulling on your socks.

Have you conducted any research to determine if any similar concepts have been proposed?