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#1120 by spupeng7 on 31 Aug, 2017 05:58
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Bob012345,
If you read the paper I referenced, you will see it's not as simple as assuming the usual assumptions.
thankyou for not assuming the 'usual assumptions' but, when you continue to think for yourself you radically increase the chance of coming up with an explanation of your own. If you want it to fit the evidence then you are obliged to wade through as much of that evidence as you can. If, like me, this eventually leads you to make assumptions about what that evidence might be, you still have the problem of devising and successfully building the experiment which proves it
Good luck! -
#1121 by Bob012345 on 31 Aug, 2017 16:22
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In the paper they calculate the force as around 2 Newtons, not 2 micro Newtons which isn't consistent with being supported by the field momentum at the energy levels they give which are implied by the currents they use.
Power depends on voltage, not just current, so your claim still has no basis. They do not give energy levels.That implies they believe the fields can carry that large amount of momentum away. Perhaps a better argument would be to just claim that if Newton's Third Law is violated, the net force by definition is an external force and thus they don't need to discuss momentum conservation at all.
Newton's third law is not being violated. The balancing part of the force is felt by the fields (photons)QuoteIn this paper we make a detailed calculation and show that any momentum gained by the material part of the system is equal in magnitude and opposite in direction to the momentum gained by the electromagnetic field. Hence the total momentum of the system is conserved.
Will you please stop trying to twist these scientists' work to say the exact opposite of what they say?
The authors themselves state Netwon's Third Law is violated.QuoteWe have shown in this paper that in general Newton’s third law is not compatible with the principles of special relativity and the total force on a two current loop system is not zero.
From another related paper the same authors state;QuoteWe conclude that in general Newton’s third law is not satisfied
Feynman showed an electrodynamic case where the Third Law breaks down (Feynman Lectures on Physics Volume 2 26-5).QuoteThe forces between two moving charges are not always equal and opposite. It appears that “action” is not equal to “reaction.”
The Third Law and momentum conservation are not identical so when they argue momentum is conserved, they are not also claiming the Third Law is obeyed, which is against the thesis of their paper.
It's true they don't give energy levels per se but as an engineer, you should notice the currents, switching times, and the statement suggesting superconducting wires. Also note that if the force came purely from a photon rocket effect, then the force would have to be ~Power/c and the required power in the loops would be on the order of 2 Newtons times 3E8 or about 600 million watts. So ask yourself as an engineer, do you think they are really thinking about 600 megawatts when they discuss 100 amps in superconducting wires!
Another paper describes a device supposedly able to lift itself against Earth's gravity;QuoteFinally we would like to address the question of the possibility of the device to lift from the ground for this the force generated by the device should be larger or equal to the gravitational force
They compute a device with 5 Amps at 10 GHZ frequency. My point is that they seem to believe and suggest a practical device could even lift itself and it's unreasonable they would ignore power astronomical requirements but sure, I could be wrong. Perhaps I'll email the author and ask.
Having said all that, I'm not necessarily completely agreeing with the authors anyway. I'm just interested in the Lorentz force angle which may play a part in the EMDrive explanation. Thanks for the discussions.
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#1122 by Bob012345 on 31 Aug, 2017 16:34
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Bob012345,
If you read the paper I referenced, you will see it's not as simple as assuming the usual assumptions.
thankyou for not assuming the 'usual assumptions' but, when you continue to think for yourself you radically increase the chance of coming up with an explanation of your own. If you want it to fit the evidence then you are obliged to wade through as much of that evidence as you can. If, like me, this eventually leads you to make assumptions about what that evidence might be, you still have the problem of devising and successfully building the experiment which proves it
Good luck!
Thanks but let me assure you, I'm not looking to invent my own rules. In this case, when I mentioned the 'usual assumptions" I just meant all the usual textbook examples which assume forces act instantly. And under those assumptions everything written is correct. But only studying certain situations can make it harder to see other possibilities well within the known laws. Another example is Keith Wanser's paper I recently mentioned. It's completely within Newton's laws of motion yet shows very surprising results for center of mass motion if masses fluctuate by the Mach effect. New results from old established physics. I suspect the same for the Lorentz force but I don't have a dogmatic position and any new concepts must be tested. -
#1123 by meberbs on 31 Aug, 2017 16:49
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The authors themselves state Netwon's Third Law is violated.
Only when they ignore the electrodynamic portions of the system. It's like saying cars violate conservation of momentum if your ignore the change of momentum of the Earth itself.Feynman showed an electrodynamic case where the Third Law breaks down (Feynman Lectures on Physics Volume 2 26-5).
Note the use of the word "appears". It is not true, it only appears to be true because you are ignoring the fields.QuoteThe forces between two moving charges are not always equal and opposite. It appears that “action” is not equal to “reaction.”
The Third Law and momentum conservation are not identical so when they argue momentum is conserved, they are not also claiming the Third Law is obeyed, which is against the thesis of their paper.[/quote]
Conservation of momentum and Newton's third law are equivalent, because force is defined as rate of change of momentum.It's true they don't give energy levels per se but as an engineer, you should notice the currents, switching times, and the statement suggesting superconducting wires. Also note that if the force came purely from a photon rocket effect, then the force would have to be ~Power/c and the required power in the loops would be on the order of 2 Newtons times 3E8 or about 600 million watts. So ask yourself as an engineer, do you think they are really thinking about 600 megawatts when they discuss 100 amps in superconducting wires!
Things don't become true just because you wish it. It would take enormous power to accelerate charges at the frequencies and current levels they are discussing. This is by nature of the properties of accelerating changes, so it does not matter if their is no resistance in the wires.Having said all that, I'm not necessarily completely agreeing with the authors anyway. I'm just interested in the Lorentz force angle which may play a part in the EMDrive explanation. Thanks for the discussions.
The Lorentz force is well understood and has been proven in general to never be able to do what you want it to.Thanks but let me assure you, I'm not looking to invent my own rules. In this case, when I mentioned the 'usual assumptions" I just meant all the usual textbook examples which assume forces act instantly.
You need to get a new textbook. A good EM textbook covers that forces are non-instantaneous. See Griffith's as an example. Non-instantaneous does not get around any of the limits that have been stated.It's completely within Newton's laws of motion yet shows very surprising results for center of mass motion if masses fluctuate by the Mach effect. New results from old established physics. I suspect the same for the Lorentz force but I don't have a dogmatic position and any new concepts must be tested.
"Mach effect" is not "old established physics." Your entire argument is "Maybe the Lorentz force operates different than any experiment or theory suggests." Unless you provide a new experiment or theory that shows this modified Lorentz force, this is simply a useless statement. -
#1124 by PotomacNeuron on 31 Aug, 2017 17:05
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The Third Law and momentum conservation are not identical so when they argue momentum is conserved, they are not also claiming the Third Law is obeyed, which is against the thesis of their paper.
It's true they don't give energy levels per se but as an engineer, you should notice the currents, switching times, and the statement suggesting superconducting wires. Also note that if the force came purely from a photon rocket effect, then the force would have to be ~Power/c and the required power in the loops would be on the order of 2 Newtons times 3E8 or about 600 million watts. So ask yourself as an engineer, do you think they are really thinking about 600 megawatts when they discuss 100 amps in superconducting wires!
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The interaction between the currents in the two wires are mutual. I think if we think one sends out large amount of (virtual?) photons, it also receives large amount of (virtual?) photons from the other party. So it is sending out 600 million watts but at the same time it receives 600 million watts so there is no net watts that we can observe if the two wires are fixed (no mutual movement). So the power of 600 million watts may be just a tool for thinking, to separate two virtual factors (the received force and the transmitted force) from on entity (the interaction itself). If we consider the entity as a whole, there is no 600 million watts. It may be like at any moment, air on one side of an imagined plane that separates a body of air into two parts sends large watts of kinetic power into the other side (by sending large amount of air molecules across the plane), but at the same time it also receives large amount of kinetic power from the other side. -
#1125 by Bob012345 on 31 Aug, 2017 17:19
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I never stated it was a violation. But if you read all their works you will see that the momentum of the field matches the momentum gained by the object under the Lorentz force, I.e. the forces are large and there is no mechanism which necessarily reduces the action of the force to the low level of the photon rocket.
Actually, I saw no calculation of the energy required, so this statement is baseless.So, the assumption it can be no better than a photon rocket may be challenged as the fields are not simple plane waves.
No, the energy/momentum relation is general, not strictly for plain waves. In addition to being something directly in electrodynamics, energy/momentum relations for massless particles are enforced by special relativity as well.But the issue really isn't their model of momentum conservation but their model of Lorentz force generation. They might be right about that and wrong about how the momentum is conserved.
Do you like countering your own points?
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p.s. One of the authors, Yahalom, is affiliated with the Isaac Newton Institute at Cambridge so he might be considered somewhat of an expert on the Third Law and momentum conservationI believe they indirectly argue the field momentum is much larger than a photon rocket equivalent
I do not see them claiming this.
In the paper they calculate the force as around 2 Newtons, not 2 micro Newtons which isn't consistent with being supported by the field momentum at the energy levels they give which are implied by the currents they use. That implies they believe the fields can carry that large amount of momentum away. Perhaps a better argument would be to just claim that if Newton's Third Law is violated, the net force by definition is an external force and thus they don't need to discuss momentum conservation at all.
Yes, I did seem to counter my own point but I'm not trying to win an argument or debate but just to discuss this interesting topic.
I worked all this out for myself using MathCAD about 20 years ago. Based on this sheet, they are only considering the current in the pair of wires "I1I2". What is not shown is the voltage, capacitance, charge and electric field at the ends of those wires when the current goes to zero. The force due to charges and electric fields will oppose the force due to currents and magnetic fields. When both are included, the 2N of force is suddenly < 2uN and we are back to the thrust of a photon rocket. If the system is large, it could oscillate back and force at a relatively low frequency with much greater force, but the CM will not move except for the asymmetry in the EM radiation, (aka photon rocket).
I don't know your setup and your assumptions for that calculation but if you are trying to say anytime you switch it off it exactly must cancel out the well known Lorentz force, and under any conceivable configuration of times and currents and geometries, I'm very dubious and would have to see the details. I'm not saying your calculation didn't do that but were you specifically messing with conditions to make the events in each wire spacelike wrt each other?
Specifically, the Third Law can break down in specific circumstances precisely because the speed of light is finite and events can have a spacelike separation even while they are being independently controlled faster than light can mediate between the interaction between them. Pulses can be independently designed and arranged that compliment the net forces and counter unwanted forces. For example, the field from pulse in one wire might cause a force in a distant wire in such a way that there is no ability for a counter force to even exist on the first wire. That spacelike separation and control could include unwanted electrical effects through proper design. Though technically challenging, that breaks the symmetry and opens up new possibilities.
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#1126 by RERT on 31 Aug, 2017 17:41
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I agree with the above interpretation. The authors take some care to show that a time varying network of currents can experience a non-zero net force. They nod to momentum conservation, but don't calculate the field momentum, leaving the reader to scratch their head over the massive photon rocket implied...
FWIW, if you look at their power series expansion for the net force, it becomes somewhat singular where the dimension/ time delays are the same as the frequency of oscillation of the currents. -
#1127 by Bob012345 on 31 Aug, 2017 17:55
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The authors themselves state Netwon's Third Law is violated.
Only when they ignore the electrodynamic portions of the system. It's like saying cars violate conservation of momentum if your ignore the change of momentum of the Earth itself.Feynman showed an electrodynamic case where the Third Law breaks down (Feynman Lectures on Physics Volume 2 26-5).
Note the use of the word "appears". It is not true, it only appears to be true because you are ignoring the fields.QuoteThe forces between two moving charges are not always equal and opposite. It appears that “action” is not equal to “reaction.”
The Third Law and momentum conservation are not identical so when they argue momentum is conserved, they are not also claiming the Third Law is obeyed, which is against the thesis of their paper.
Conservation of momentum and Newton's third law are equivalent, because force is defined as rate of change of momentum.It's true they don't give energy levels per se but as an engineer, you should notice the currents, switching times, and the statement suggesting superconducting wires. Also note that if the force came purely from a photon rocket effect, then the force would have to be ~Power/c and the required power in the loops would be on the order of 2 Newtons times 3E8 or about 600 million watts. So ask yourself as an engineer, do you think they are really thinking about 600 megawatts when they discuss 100 amps in superconducting wires!
Things don't become true just because you wish it. It would take enormous power to accelerate charges at the frequencies and current levels they are discussing. This is by nature of the properties of accelerating changes, so it does not matter if their is no resistance in the wires.Having said all that, I'm not necessarily completely agreeing with the authors anyway. I'm just interested in the Lorentz force angle which may play a part in the EMDrive explanation. Thanks for the discussions.
The Lorentz force is well understood and has been proven in general to never be able to do what you want it to.Thanks but let me assure you, I'm not looking to invent my own rules. In this case, when I mentioned the 'usual assumptions" I just meant all the usual textbook examples which assume forces act instantly.
You need to get a new textbook. A good EM textbook covers that forces are non-instantaneous. See Griffith's as an example. Non-instantaneous does not get around any of the limits that have been stated.It's completely within Newton's laws of motion yet shows very surprising results for center of mass motion if masses fluctuate by the Mach effect. New results from old established physics. I suspect the same for the Lorentz force but I don't have a dogmatic position and any new concepts must be tested.
"Mach effect" is not "old established physics." Your entire argument is "Maybe the Lorentz force operates different than any experiment or theory suggests." Unless you provide a new experiment or theory that shows this modified Lorentz force, this is simply a useless statement.
It's fine if you assert that the authors are flat wrong, I can then make a rational decision whether I trust your technical arguments or theirs. I keep saying, I just am interested in discussing it, not that my mind is made up. Thanks for your points. If it's impossible under any conceivable circumstances to take advantage the finite speed of light please point me to a proof or an experiment that tried independently to control events with spacelike separate faster that light could mediate between them since you say it's been forever proven to be impossible.
Also, I'm skeptical GHZ switching of amp level currents takes megawatts or gigawatts. Such switches are built in silicon. Please show me a calculation that it must be so.
BYW, I didn't say the Mach effect was old established physics, I specifically referred to the treatment of CM motion under the Second Law if the Mach effect mass fluctuations existed.
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#1128 by meberbs on 31 Aug, 2017 18:20
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It's fine if you assert that the authors are flat wrong, I can then make a rational decision whether I trust your technical arguments or theirs. I keep saying, I just am interested in discussing it, not that my mind is made up. Thanks for your points. If it's impossible under any conceivable circumstances to take advantage the finite speed of light please point me to a proof or an experiment that tried independently to control events with spacelike separate faster that light could mediate between them since you say it's been forever proven to be impossible.
I am not saying the authors are wrong, I am saying you don't understand their results, and are making unsupported claims about the required power levels. We control timing of spacelike separate antennas all the time. It is called a phased array antenna.Also, I'm skeptical GHZ switching of amp level currents takes megawatts or gigawatts. Such switches are built in silicon. Please show me a calculation that it must be so.
The easy way to do the calculation is to look at the radiated power. The momentum in electrodynamic fields is directly proportional to the pointing vector, which also defines the energy flux. Therefore, any electrodynamic fields with the momentum claimed here would require massive amounts of energy to produce. These are mathematical relationships found in any decent textbook. So far you have been trying to counter this with your intuition.BYW, I didn't say the Mach effect was old established physics, I specifically referred to the treatment of CM motion under the Second Law if the Mach effect mass fluctuations existed.
Yes, you gave an example using the Mach effect and then said "new results from old established physics." I can find no other way to interpret that than calling the Mach effect "old established physics." What you really gave an example of is new results from new physics. -
#1129 by Bob012345 on 31 Aug, 2017 18:41
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It's fine if you assert that the authors are flat wrong, I can then make a rational decision whether I trust your technical arguments or theirs. I keep saying, I just am interested in discussing it, not that my mind is made up. Thanks for your points. If it's impossible under any conceivable circumstances to take advantage the finite speed of light please point me to a proof or an experiment that tried independently to control events with spacelike separate faster that light could mediate between them since you say it's been forever proven to be impossible.
I am not saying the authors are wrong, I am saying you don't understand their results, and are making unsupported claims about the required power levels. We control timing of spacelike separate antennas all the time. It is called a phased array antenna.Also, I'm skeptical GHZ switching of amp level currents takes megawatts or gigawatts. Such switches are built in silicon. Please show me a calculation that it must be so.
The easy way to do the calculation is to look at the radiated power. The momentum in electrodynamic fields is directly proportional to the pointing vector, which also defines the energy flux. Therefore, any electrodynamic fields with the momentum claimed here would require massive amounts of energy to produce. These are mathematical relationships found in any decent textbook. So far you have been trying to counter this with your intuition.BYW, I didn't say the Mach effect was old established physics, I specifically referred to the treatment of CM motion under the Second Law if the Mach effect mass fluctuations existed.
Yes, you gave an example using the Mach effect and then said "new results from old established physics." I can find no other way to interpret that than calling the Mach effect "old established physics." What you really gave an example of is new results from new physics.
You say I don't understand them and am going off half (maybe all) cocked. Do you really think they would write all those papers if all they were saying is "Hey, here's an interesting way to make a propellent-less propulsion device that works far far less efficiently than a simple photon rocket and is entirely useless!!!!!"? Or maybe, "Hey, this would work but you need gigawatts of power!!!! Maybe that's the academic world but somehow, I doubt that. So, I'm going to paraphrase Feynman's question what do you think they are really trying to say with these papers?
Can you realistically imagine proposing gigawatt levels of power in meter sized coils carrying 100 amps of current? Wouldn't they just melt? As an engineer, what power do you think is in their device?
I think others here can reasonable understand my point about Wanser's CM motion paper. Thanks for the stimulating discussion.
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#1130 by meberbs on 31 Aug, 2017 18:59
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You say I don't understand them and am going off half (maybe all) cocked. Do you really think they would write all those papers if all they were saying is "Hey, here's an interesting way to make a propellent-less propulsion device that works far far less efficiently than a simple photon rocket and is entirely useless!!!!!"? Or maybe, "Hey, this would work but you need gigawatts of power!!!! Maybe that's the academic world but somehow, I doubt that. So, what do you think they are really trying to say with these papers?
I have no idea why they haven't calculated the power requirements, especially since there is an easy way to do so since the energy flux is equal to c times the momentum flux. Them not calculating it in no way changes the fact that this is a ton of power, and yes it probably would melt something if you tried to build such a device.
Can you realistically imagine proposing gigawatt levels of power in meter sized coils carrying 100 amps of current? Wouldn't they just melt?
It does not matter why they aren't discussing the power numbers, because the power numbers are what they are. Do you have anything to add that is actually based on math or physics? -
#1131 by kamill85 on 31 Aug, 2017 20:12
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Hello, I have a question. Excuse this layman example, but I'm new to EMdrive and the math behind it.
I understood there are issues with CoE and CoM. Lets imagine the following scenario:
1. "EMDrive" is enclosed in a box, blocking 100% of any energy from leaking out from inside of it.
2. There is a battery on board, 10kWh worth, enough for the engine to operate few minutes.
3. We have a race track, where the box can move freely, without any friction, from point A to B
4. At point B, we have a 100%-efficient kinetic energy recovery mechanism.
Now, assuming EMDrive somehow works, could it be that the 10kWh energy spent on the A-B travel, gets fully recovered (without any net) at point B, and the box arrives a little bit lighter at point B?
Yes, I'm saying there has been no exhaust at all, just a pure conversion of 10kWh from battery, into kinetic energy, does that break anything? Or is it the most plausible case (assuming it works)?
That being said, would that equal to a photon rocket? I mean, if we converted 10kWh energy into photons, shoot them out from the back of the box, would point B recover 10kWh?
Thank you. -
#1132 by PotomacNeuron on 31 Aug, 2017 20:53
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That being said, would that equal to a photon rocket? I mean, if we converted 10kWh energy into photons, shoot them out from the back of the box, would point B recover 10kWh?
Thank you.
There is no way you can recover 10 kWh at point B with a photon rocket. This is because photon rocket is very inefficient. Most energy is carried away by the photon. You can recover tiny-tiny-tiny portion of that 10 kWh. -
#1133 by wicoe on 31 Aug, 2017 21:11
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Yes, I'm saying there has been no exhaust at all, just a pure conversion of 10kWh from battery, into kinetic energy, does that break anything? Or is it the most plausible case (assuming it works)?
Conversion of potential (battery) energy into kinetic energy of a body without any exhaust (i.e. without giving the exact but opposite momentum to some other body/bodies) breaks both the CoM and CoE.
CoM: obvious in any inertial frame. Pick the ref frame in which the box is initially at rest, total momentum = 0. After switching it on and off, total momentum is non-zero. If the box is not interacting with the surroundings, CoM is broken.
CoE: pick two ref frames (inertial), moving relative to each other (with a constant velocity U). In the first frame (let's use one in which the box is initially at rest, and where its final velocity is V), the battery energy is converted into kinetic energy (m*V^2)/2. In the second reference frame, the same amount of battery energy is converted into kinetic energy [(m*(V+U)^2)/2 - (m*U^2)/2], which is larger than (M*V^2)/2. This is a general problem with converting potential energy into kinetic energy. Kinetic energy is frame-dependent, while potential energy is not. When you add an exhaust, this discrepancy goes away. You can't get rid of it without adding exhaust.
Note that CoM/CoE must hold in any inertial reference frame. -
#1134 by kamill85 on 31 Aug, 2017 23:26
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Yes, I'm saying there has been no exhaust at all, just a pure conversion of 10kWh from battery, into kinetic energy, does that break anything? Or is it the most plausible case (assuming it works)?
Conversion of potential (battery) energy into kinetic energy of a body without any exhaust (i.e. without giving the exact but opposite momentum to some other body/bodies) breaks both the CoM and CoE.
CoM: obvious in any inertial frame. Pick the ref frame in which the box is initially at rest, total momentum = 0. After switching it on and off, total momentum is non-zero. If the box is not interacting with the surroundings, CoM is broken.
CoE: pick two ref frames (inertial), moving relative to each other (with a constant velocity U). In the first frame (let's use one in which the box is initially at rest, and where its final velocity is V), the battery energy is converted into kinetic energy (m*V^2)/2. In the second reference frame, the same amount of battery energy is converted into kinetic energy [(m*(V+U)^2)/2 - (m*U^2)/2], which is larger than (M*V^2)/2. This is a general problem with converting potential energy into kinetic energy. Kinetic energy is frame-dependent, while potential energy is not. When you add an exhaust, this discrepancy goes away. You can't get rid of it without adding exhaust.
Note that CoM/CoE must hold in any inertial reference frame.
Thank you. Now, just to clear this a bit, I did say the box is a little bit lighter at B, to account for the tiny 10kWh missing. Shouldn't there be a way to convert mass directly into momentum? Cause this is what the box would be doing I think. If photon rocket is inefficient, and out of 10kWh, only tiny fraction is used to generate momentum, and rest is "lost" along with the missing photon, shouldn't there be a way to make a system where only momentum is generated, and the photon is recovered? On the bigger picture, 10kWh was lost in mass, turned into kinetic energy, where at B 100% was recovered and lets say turned back into missing mass. Object is at momentum=0 again, with equal mass & energy?
PS: I don't quite get your CoE example, could you elaborate via PM? (or here) Basically if here are 2 boxes and one has added relative velocity U to begin with, then of course at B the kinetic energy will be different for both boxes, or am I missing something? -
#1135 by wicoe on 01 Sep, 2017 00:10
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Thank you. Now, just to clear this a bit, I did say the box is a little bit lighter at B, to account for the tiny 10kWh missing. Shouldn't there be a way to convert mass directly into momentum? Cause this is what the box would be doing I think. If photon rocket is inefficient, and out of 10kWh, only tiny fraction is used to generate momentum, and rest is "lost" along with the missing photon, shouldn't there be a way to make a system where only momentum is generated, and the photon is recovered? On the bigger picture, 10kWh was lost in mass, turned into kinetic energy, where at B 100% was recovered and lets say turned back into missing mass. Object is at momentum=0 again, with equal mass & energy?
PS: I don't quite get your CoE example, could you elaborate via PM? (or here) Basically if here are 2 boxes and one has added relative velocity U to begin with, then of course at B the kinetic energy will be different for both boxes, or am I missing something?
A photon rocket is "inefficient" not because of energy losses. Even if you consider the most idealistic scenario where all the energy is converted into photons emitted in one direction, you get very small thrust because of the nature of photons. Specifically, even very high energy photons have very small momentum, compared to what you'd get using a different type of exhaust (mass). You spend a large amount of energy to generate them, but you get pushed back just a little (same momentum as the photons but in the opposite direction). Note that you convert energy into energy, not into momentum.
Regarding the CoE example, I was referring to the energy difference (before and after). It is obvious that the actual kinetic energy is different in different ref frames. What I'm saying is that if you convert some potential energy into kinetic energy, the amount of potential energy lost should equal the total gain in kinetic energy of participating objects (except for "non-directional" losses, such as thermal losses), and this equivalence should be observed in all inertial reference frames. If you consider a scenario where only one object gets kinetic energy, this equivalence breaks down (i.e. you get different KE gains in different ref frames while the amount of expended fuel energy is the same). -
#1136 by TheTraveller on 01 Sep, 2017 00:50
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Thank you. Now, just to clear this a bit, I did say the box is a little bit lighter at B, to account for the tiny 10kWh missing. Shouldn't there be a way to convert mass directly into momentum? Cause this is what the box would be doing I think. If photon rocket is inefficient, and out of 10kWh, only tiny fraction is used to generate momentum, and rest is "lost" along with the missing photon, shouldn't there be a way to make a system where only momentum is generated, and the photon is recovered? On the bigger picture, 10kWh was lost in mass, turned into kinetic energy, where at B 100% was recovered and lets say turned back into missing mass. Object is at momentum=0 again, with equal mass & energy?
PS: I don't quite get your CoE example, could you elaborate via PM? (or here) Basically if here are 2 boxes and one has added relative velocity U to begin with, then of course at B the kinetic energy will be different for both boxes, or am I missing something?
A photon rocket is "inefficient" not because of energy losses. Even if you consider the most idealistic scenario where all the energy is converted into photons emitted in one direction, you get very small thrust because of the nature of photons. Specifically, even very high energy photons have very small momentum, compared to what you'd get using a different type of exhaust (mass). You spend a large amount of energy to generate them, but you get pushed back just a little (same momentum as the photons but in the opposite direction). Note that you convert energy into energy, not into momentum.
Regarding the CoE example, I was referring to the energy difference (before and after). It is obvious that the actual kinetic energy is different in different ref frames. What I'm saying is that if you convert some potential energy into kinetic energy, the amount of potential energy lost should equal the total gain in kinetic energy of participating objects (except for "non-directional" losses, such as thermal losses), and this equivalence should be observed in all inertial reference frames. If you consider a scenario where only one object gets kinetic energy, this equivalence breaks down (i.e. you get different KE gains in different ref frames while the amount of expended fuel energy is the same).
Hi Wicoe,
The example of a photon rocket, while inefficient, carries no propellant as such to exhaust but instead on demand converts electrical energy into photons with both energy and momentum due to the mass equivalence of the photon energy and when emitted always travel at c.
For a 1 second, 1kW burst of photons from a laser on a 1,000kg spacecraft we have
t = 1 second
Kg = 1,000
E = 1kW
Force = E / c = 3.3x10-6 N,
Work = (N^2 * t^2) / 2 * kg, assuming zero initial velocity from last rest frame of the 1t mass before acceleration starts = 5.45x10-15 j, so not a lot of energy lost from the 1,000 j in the 1 sec laser burst.
Which also shows virtually all the initial photon energy and momentum is still there because the force was so small, the energy used to do work, moving the mass was also so very tiny.
However both CofM and CofE are conserved because the momentum and KE gained by the ship's 1t mass are lost from the emitted photon stream.
That same 1kW by 1 sec long pulse of photon energy could next hit a totally reflective solar sail, which would experience a 6.6uN momentum transfer and 1.1x10-14 j KE gain, one 3.3uN photon absorb event, followed rapidly by another 3.3uN photon emit event, at the expense of reduced photon energy and momentum. Here again the solar sails gained momentum and KE is sourced from lost photon energy and momentum. No propellant is exhausted, but instead energy and momentum are transferred from photon created from electrical energy to mass.
Of course as the 1 sec long photon stream losses energy and momentum, at each absord or emit event, the wavelength of all the photons increases at each inelastic emit event. -
#1137 by dustinthewind on 01 Sep, 2017 01:25
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Any force (including Lorentz forces) acts in two opposing directions between the source(s) of the field(s) and the object (action and reaction), so the resulting momentum will be equally distributed between the source and the target and will cancel out due to opposing directions. If the source of the field and the object you're looking at are co-moving, the center of mass will get zero momentum change.
Under the usual assumptions, yes, but the Third Law can break down in specific circumstances precisely because the speed of light is finite as the paper I referenced showed. Then you can have a net force on the system.
No you don't have a net force on the (closed) system. Even though force can not propagate faster than light, people are smart enough to figure out that the force carrying messenger (light in the case of electric or magnetic forces) itself carries momentum. So momentum is still conserved. If your system is closed, that light later on is interacted with other parts of your system to create the counter force. So you merely moved the mass center of your system. If your system is open, you have a light rocket.
It is not usually thought that the Third Law applies instantaneously at the point of interaction between field and object rather than at the two parts of the system interacting. But if you do, you have to admit that the photon momentum change must be capable of providing the large internal forces since you are saying its conserved instantaneously. That makes the authors point that large forces are possible and it's not limited to a photon rocket.
In the case of two current carrying wires interacting in space, you are conserving momentum both at each wire immediately and at the delayed response with the other wire. Both sets cancel. But both are equal so that would show the field carries much more momentum that E/c if it's true. So if two wires are spacelike events, and if momentum is conserved immediately while the forces are significant, the field must be carrying more momentum than we think, of the forces must be smaller than the texts say.
I don't think I'm going to get a chance any time soon to test this idea out, though I would like to, so I'll just share it with you here. This is what I would like to test some time in the future. It is a hybrid of the patent I cited on the link I shared https://forum.nasaspaceflight.com/index.php?topic=36911.0 . I substituted iron in the center of the coil. The capacitors make it an LC circuit. Resistors can be introduced if needed. Power is fed in through a side inductor. The pure magnetic signal must travel through a dielectric slab that slows the signal such that the wavelength of the signal through the dielectric slab and space between the coils is exactly 1/4 lambda. The current in the top coil is out of phase with the bottom coil by 90 degrees or pi/2.
There should be no charge separation interaction as long as the charge nodes remain at the capacitors. There will be magnetic interaction between the coils. This way there is no static electric force opposing the magnetic.
I was pondering if this could be happening in the EM drive. If you continuously advance a phase of a signal injected you pretty much just change the frequency. Resonance in a cavity can be off the main frequency by a small amount so its possible to have resonance at a bit too high of a frequency. Because the signal frequency is too high light should keep penetrating a bit deeper into the metal till it meets electrons that are free to move out of phase with the light and reflect the light but more light keeps being fed in that is too high of a frequency. This might suggest a phase problem. For a waveguide the light is fed in from one side. If fed in through the bottom or top could feeding a frequency slightly too high suggest inducing a semi traveling wave? Also feeding in a slightly off signal reduces Q. I don't think we necessarily want a high Q anyways so this is intriguing to me. No charge separation happens in a cavity with a Transverse Electric mode. This suggest feeding in too low of a frequency signal might reverse the effect.
attached below is my suggestion to test for magnetic propulsion "Pure magnetic phased propulsion.png"
An illustration of a reverse magnetic phased array. "Reverse magnetic phased array.png"
The last file is the patent I was talking about here:
, ---->> "Phased array propulsion US20140345251A1.pdf "<<---- see file below or click this link - please check this out if you want to know the details.
the patent really already has it all except they don't use ferrous material in the center. Possibly on purpose. The patent drawings are the best. They really illustrate some of the concepts
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#1138 by mwvp on 01 Sep, 2017 06:11
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During continual acceleration, as KE increases, the energy to support increasing Work and KE is sourced from cavity energy, increasing energy loss per cycle, dropping Q and dropping N.
Because it makes no sense, it implies that an emdrive that has been accelerating for 10 minutes will produce less force than one that has been accelerating for 10 seconds, when there is nothing physically different between them. There is no mechanism by which it can tell the difference, the RF is from a co-moving source, so there will not be Doppler problems, and you have claimed that simply turning it back off and then back on will reset the magic tracking how long it was running for by some additional magic.
Why is this so hard to accept?
There is a physical difference between the drives accelerating for different times. You can tell the difference between them from the RF spectra. There is a Doppler "problem" in an accelerating drive with a co-moving source (frustrum injector antenna) though not in a constant velocity frustrum.
If this were not so, we'd have no Sagnac fiber-optic gyros.
There is a finite propogation delay in the frustrum, between the antenna, the sidewalls, and the end reflectors. If the frustrum accelerates, the frequency is Doppler shifted. Also the dissipation of the frustrum loss phase shifts and attenuates, and does so frequency-selectively according to tuning.
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#1139 by mwvp on 01 Sep, 2017 06:21
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...
Also, I can accept that there would be a relationship between the force and acceleration but that could result from loss mechanisms due to Doppler shifts or other phenomenon and not from imparting kinetic energy to the device. If static tests show all the input Rf becomes heat, I suspect dynamic tests would show that too but that will eventually be testable. In fact, if the Rf energy is the source of the kinetic energy, then the cavity should be self-cooling under greater acceleration becoming even more efficient. There would be measurable less heat dissipated if the EMdrive is undergoing a constant acceleration than in a static test.
That's exactly what I expect to find from an opto-mechanical, / laser heating-cooling perspective analysis. If the frustrum preferentially dissipates the lower sideband, and the cavity/system is designed for lower-sideband excitation, it accelerates. If mounted on a spring, it would oscillate.
Unless you've damped the livin h*ll out of your test setup. But that doesn't matter so much with a non-superconducting cavity because the the oscillations of Q's around 10^4 are going to be around kilohertz. Perhaps you could make a glass or ceramic frustrum sing.
