Please, consider these attached pulbications about permanently removng momentum from a system. It is allowed by General Relativity.The emission of gravitational waves (from a quadrupole source) permanently moves the source. This has been proved by astrophysical observations. The Einstein therory allows gravitational waves to carry linear momentum away from the source, in a flat spacetime, no swimming in curved spacetime.More information in the concept of "linear frame dragging", another way of removing linear momentum from an isolated system...The effect is tiny, but can be increased with future technology. In the above references, it is estimated to be on the order of 1/c6. After a quick peek in the formulas, to be useful for a practical rocket, the effect that can be defined as a "quadrupole rotating engine" must have a big mass or rotate such fast that centripetal accelerations must be of 1024 m/s2A big technical challenge!
The simple answer is no. It is fundamentally disallowed by physics.The swimming through spacetime above is a real thing, but it relies on the curvature of spacetime, which would be caused by being in the gravitational field of another object, plus the motions themselves would be able to emit gravitational waves (tiny ones, but the motion itself is inconceivably small in a practical situation.) Therefore it can't be considered a closed system. It is comparable to how you can push off the Earth's magnetic field in LEO. Relatively easy to calculate how much force you get, but requires more careful work to show where the balancing force goes.
In what sense would this be better than a photon rocket?
There is no chance any kind of reactionless drive or warp drive or em drive or vacuum thruster ever to work if Newton's 3rd law holds always and everywhere in the direction of the expected acceleration.In a few words, from the moment the above aspect is not addressed by all those proposals, propellantless propulsion is nonsense except....
It’s worth noting this is wrong about, for example, the Alcubierre warp drive. Entirely.Not that we can make it work or anything like that, but it doesn’t violate Newton’s third law. Warp concepts in general would not.
You’re just repeating yourself.Alcubierre’s drive concept relies on warping space. That facet of it does not involve reactionless movement, because it doesn’t involve movement in that sense.
I have done a fast reading of Bonnor articles and seems that the gravitational wave rocket expels no energy other than the inherent of the gravitational wave itself. In this sense is better than the photon rocket, that expels only 1/c momentum unit for each energy unit expelled. According to Cooperstock (1967) Phys. Rev 165 1424 "Since this is the same orfer in c as the energy flux, it appears that the momentum flux can, in certain circumstances, play as significant a role as the energy flux".
... it would still need a power source such as a matter-antimatter reactor that could consume a significant fraction of the mass of the vehicle into raw energy to power the drive.
In various past posts here I've seen comments about so called "reactionless drives" and such, and I have a question (I'm a skeptic, but I enjoy these thought experiments). Is there any known example of a closed system that has the ability to relocate it's center of mass, even if only very briefly, and even if it swings thru some small trajectory, only to return to it's original position? That is to say, the system starts at rest in space (relative to some fixed point), has zero initial momentum, but moves it's internals or rearranges it's parts very quickly, such that the center of mass moves (relative to said point), before returning to it's original position and settling again at rest with no momentum. I understand that the system cannot gain net momentum, but could it do something like the above but where the net forces/momentum (after internal movement/rearrangement) are conserved?Thanks for your help.
Quote from: Josave on 09/10/2020 08:11 pmI have done a fast reading of Bonnor articles and seems that the gravitational wave rocket expels no energy other than the inherent of the gravitational wave itself. In this sense is better than the photon rocket, that expels only 1/c momentum unit for each energy unit expelled. According to Cooperstock (1967) Phys. Rev 165 1424 "Since this is the same orfer in c as the energy flux, it appears that the momentum flux can, in certain circumstances, play as significant a role as the energy flux".You seem to have missed that the statement "expels no energy other than the energy of the [] wave itself" applies equally well to both EM waves (photons) and gravitational waves. Both cases have the 1/c ratio of momentum to energy. (Your source seems to have made a serious mistake in calculation, as he says "This is larger than the momentum loss calculated by other researchers for different sources by a factor of c." Other researchers are right, he literally must be wrong, because he has the wrong units, a momentum/energy ratio must have units of inverse velocity, so his expression missing the factor of c would be unit-less and therefore wrong.)
All you've done there is defined a closed system incorrectly. If it is interreacting with something 'outside' the system (and observation is itself an interaction, both in the quantum sense and in the classical shooting-photons-at-an-object-and-watching-where-they-bounce sense) then you no longer have a closed system. To take the 'phone in airplane mode' example: the phone is emitting EM radiation due to being hot. The phone is in contact with ambient air and driving air circulation (convection). If the screen is on then it will be emitting further higher frequency EM. If it is on a table, it is heating the table through conduction. The phone has mass, so is attracting the Earth upwards slightly (as well as slightly attracting all objects nearby towards it ever so very slightly), and is also being attracted by the Earth. A truly closed system must include ALL these interactions.
Quote from: meberbs on 10/29/2020 12:01 amQuote from: Josave on 09/10/2020 08:11 pmI have done a fast reading of Bonnor articles and seems that the gravitational wave rocket expels no energy other than the inherent of the gravitational wave itself. In this sense is better than the photon rocket, that expels only 1/c momentum unit for each energy unit expelled. According to Cooperstock (1967) Phys. Rev 165 1424 "Since this is the same orfer in c as the energy flux, it appears that the momentum flux can, in certain circumstances, play as significant a role as the energy flux".You seem to have missed that the statement "expels no energy other than the energy of the [] wave itself" applies equally well to both EM waves (photons) and gravitational waves. Both cases have the 1/c ratio of momentum to energy. (Your source seems to have made a serious mistake in calculation, as he says "This is larger than the momentum loss calculated by other researchers for different sources by a factor of c." Other researchers are right, he literally must be wrong, because he has the wrong units, a momentum/energy ratio must have units of inverse velocity, so his expression missing the factor of c would be unit-less and therefore wrong.)They are using Planck unitshttps://en.wikipedia.org/wiki/Planck_units
In particle physics and physical cosmology, Planck units are a set of units of measurement defined exclusively in terms of four universal physical constants, in such a manner that these physical constants take on the numerical value of 1 when expressed in terms of these units.The four universal constants that, by definition, have a numeric value 1 when expressed in these units are:the speed of light in a vacuum, c,the gravitational constant, G,the reduced Planck constant, ħ,the Boltzmann constant, kB.
A system that 'jiggles' is performing zero shifting of it's CoM and has zero momentum. It will only gain any momentum if one of it's jiggles hits another object, and now... you need to include that object in your closed system, and have simply created a crude reation drive. And if you want to start positing mysterious reactionless drives then you need to be VERY careful about ensuring you have gone down sufficiently 'in the weeds' before declaring you've discovered an effect!
Even so... your above statement is wrong, when you assert that the center of mass does not change. It is the changing center of mass that causes the “jiggle”, or vibration.
This began just as a response to the following sentence from the OP, “ Is there any known example of a closed system that has the ability to relocate it's center of mass, even if only very briefly, and even if it swings thru some small trajectory, only to return to it's original position? ”
Quote from: OnlyMe on 12/04/2020 11:36 pmEven so... your above statement is wrong, when you assert that the center of mass does not change. It is the changing center of mass that causes the “jiggle”, or vibration. No. Wikipedia says 'unbalanced mass', not center of mass. No one else is saying center of mass. Those are only your words. In the vibrator, a shift in internal mass is countered by an opposite shift in external mass. Were you to drop one out the airlock in space, you'd actually find that the outer casing enclosing the motor would begin to rotate in the opposite direction of the drive shaft. The center of mass, of all components, remains unchanged. Back here on Earth, the vibrator attempts to spin as well; but is prevented from doing so by the person or test bench holding it in place. This actually transmits the torque from the spinup of the motor to the ground; and ultimately the Earth itself must be considered part of your system. This forum (and others) are very much flooded with ideas from people who have neglected that. edzeiba is correct. You've not gone sufficiently deep into the weeds. Quote from: OnlyMe on 12/04/2020 11:36 pmThis began just as a response to the following sentence from the OP, “ Is there any known example of a closed system that has the ability to relocate it's center of mass, even if only very briefly, and even if it swings thru some small trajectory, only to return to it's original position? ”This was correctly answered by meberbs as 'no' with a ', but...' .
I also don’t see anywhere he added any ‘, but...” to his statement. Point it out more clearly if I missed something.
There was and is no COM issue, as far as I can tell in the workings of a vibrator and whether in its simplest form, the internal mechanics could be considered a closed systemWhen you spin an unbalanced mass, the center of mass moves with the imbalance. Stop the spinning unbalanced mass at several different points and the center of mass of the system as a whole will have changed. And while it spins there is momentum involved, both in the spin and the out of balance vibrations.This really should not have been so complicated and is not worth further energy.