Author Topic: EM drive - predictive analysis  (Read 7436 times)

Offline cristian

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EM drive - predictive analysis
« on: 01/29/2017 07:37 PM »
I want to emphasize a few points related to this issue. I will assume that the thrust experimentally observed, as related to the EM drive, is a real phenomenon, and I will try to explain it. I will mention the following interconnected effects, the dynamical Casimir effect, Unruh radiation of accelerated mirrors, and the Schwinger effect.

First, the dynamical Casimir effect. There is an interesting reference here:

http://www.physik.uni-leipzig.de/~bordag/Talks/talks_on_QFEXT07/Ruoso.pdf

Basically, semiconductors under illumination can change their dielectric properties from completely transparent to completely reflective for selected wavelengths. A train of laser pulses will produce a frequency variable mirror and this will result in a dynamical Casimir effect.

Other similar experiments have been performed, with positive results.

https://www.technologyreview.com/s/424111/first-observation-of-the-dynamical-casimir-effect/

The problem with only photons being involved in the generation of thrust (related to the EM drive) is that the conversion of the battery energy (energy source in the experiment) into kinetic energy of the spacecraft is an inefficient process. Almost all the energy goes into photon energy. This inefficiency follows since the ratio of momentum to energy for the photon is 1/c.

You can find the proper reference about this here:

https://arxiv.org/pdf/physics/0303108v1.pdf

So we have a problem. The thrust observed in EM drive experiments is several orders of magnitude higher that what should be possible, if only photons (and the dynamical Casimir effect) are involved in the generation of this thrust. What is the solution then? Neutrinos cannot be seriously considered, because of their very small probability of interaction with matter and transfer the momentum. The only option left is electron-positron pairs.

Related to the Schwinger effect, a very interesting reference can be found here:

http://dunne.physics.uconn.edu/dunne-schwinger/

Professor Dunne discusses possible mechanisms through which virtual electron-positron dipole pairs can gain energy from an external field. If the field is sufficiently strong, these virtual particles can gain the threshold pair creation energy 2mc^2, and become real particles. The problem here is that the electric field required is very large, so unless the electromagnetic near field (around the mirror), and interference effects are considered, the energy level required is orders of magnitude higher than in the EM drive experiments.

We can also assume that the Coulomb fields of the nuclei of the atoms in the mirror might be involved in the process (but this would require gamma photons). This means that the presence of the nucleus facilitates the splitting of the virtual electron-positron pair, while the nucleus carries some of the momentum of the virtual electron away.

Conclusions. The energy - time uncertainty relations and the relativistic energy - momentum relation will help us estimate the energy range in which electron-positron pair creation becomes a possibility, and the magnitude of the transferred momentum. The Coulomb fields of the nuclei of the atoms in the mirror might be involved in the process. The dynamical Casimir effect and the Schwinger effect are probably the key to the problem. The momentum transfer is mediated not only by photons, but by virtual electron-positron pairs, which become real due to the effects mentioned above. Multiply layered mirrors, special cavity geometries, interference effects, near fields, specially designed metamaterials, might need to be considered, because the energy level in EM drive experiments is too low (in order to make the electron - positron pair creation relevant).

Predicted experimental result. If the thrust is real in EM drive experiments, positrons should be detected behind the system (in the opposite direction of thrust, if the dynamical Casimir effect and the Schwinger effect are involved). In this case, the momentum transfer is mediated by the electrons. If positrons are indeed detected in these experiments (or even electrons), then at least we are on the right track. In order to detect the positrons, the whole system must be isolated in a vacuum, and the presence of positrons should be simultaneous with the presence of thrust. There are two questions to be considered here:

Could the Schwinger effect come into play at lower energies?
Have any experiments been conducted, in order to detect the presence of positrons?


Any useful comments will be appreciated. Note that no new physics is required in this model, and all the laws of conservation (energy and momentum) are valid.



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Offline cristian

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Re: EM drive - predictive analysis
« Reply #1 on: 01/31/2017 03:47 PM »
In most experiments related to the dynamical Casimir effect  (Ruoso or Wilson), varying the electrical properties of the mirror is mathematically equivalent to physically moving the mirror through space. This means that for relativistic speeds of the mirror, the relativistic Doppler effect  might come into play, thus the frequency of an incoming photon will be elevated 3 or 4 orders of magnitude (as seen from the mirror ). That means that the conversion of the virtual electron - positron pairs into real electrons and positrons in the Coulomb field of the  nuclei of the atoms in the mirror,  becomes possible. For non relativistic speeds of the real electron  (which transfers the momentum to the nucleus),  the coefficient mentioned above  (momentum over energy ) is 2/v , where v is the velocity of the electron.  If we compare this with the same coefficient for the photon  (which is 1/c), we see that the efficiency of  converting the battery energy (energy needed in the experiment ) into momentum transfer could be improved 4 or 5 orders of magnitude.  This is what has been experimentally observed in EM drive experiments. This is a strong indication that the electron - positron pairs are involved in the process.
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Offline aero

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Re: EM drive - predictive analysis
« Reply #2 on: 01/31/2017 05:40 PM »
Ran across this yesterday and I wonder - can anyone explain why this works on astronomical scales, but doesn't seem to work at human scales? "The dipole repeller"

http://www.nature.com/articles/s41550-016-0036#f2

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Offline cristian

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Re: EM drive - predictive analysis
« Reply #3 on: 02/01/2017 03:44 PM »
Your question does not stay on the topic that I proposed,  but it's interesting and I will try to answer it. You can look at the discovery of the Dipole Repeller as a large scale Alcubierre drive, but this loose analogy is not perfect 

The Alcubierre drive stretches spacetime in a wave, causing the fabric of space ahead of a spacecraft to contract and the space behind to expand. The ship rides the wave to accelerate to high speeds.  Alcubierre first specifies a metric, and then finds the energy-momentum tensor associated with it, based on Einstein field equations. The solution can violate certain energy conditions,  and require negative energy or exotic matter.

Related to the Dipole Repeller,  in addition to being pulled towards  the known Shapley Concentration,  our galaxy is also being pushed away from the newly discovered Dipole Repeller.

This is a technology that might or might not become feasible in the far future. On the other hand,  the phenomena discussed in my post can lead to interstellar travel 'today'. In fact 'yesterday', some time ago the Chinese already tested the EM drive in space,  and they say that it works. If I am correct about what makes it work  (as I explained in my post ),  then it can be greatly improved.

One of the reasons why  there are major difficulties with building an Alcubierre drive at smaller scales is that it it not easy to collect a lot of negative energy in a small region of space.  Different story for astronomical scales.

Going back to my post,  I am a mathematician,  not a physicist.  I don't have a problem with the mathematical framework of QM, SR, or even GR, but the mathematics of QFT (the Schwinger effect ) is complex,  it would take me a few months  (at least ) to study it,  and I am not going to take that fight (posting here is fun, but I am not going into hard work with no motivation ).  I leave that for experts,  but I think that my intuition is correct. 
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Offline cristian

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Re: EM drive - predictive analysis - correction
« Reply #4 on: 02/02/2017 04:29 PM »
The detection of the positrons  (mentioned in my post ) might be impossible,  due to the rapid annihilation between the positron and an electron of an atom in the mirror.  The gamma photons created in the annihilation process will lead to the replication of the electron - positron pair production in the Coulomb field of the nucleus of another atom in the mirror (as long as the relativistic Doppler effect will elevate the frequency, so the  energy of the photon stays above the threshold value necessary for pair production), and so on. The electron will still transfer momentum to the nucleus, in each case, and the rest of the arguments remain valid.
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Offline cristian

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Re: EM drive - predictive analysis - correction
« Reply #5 on: 02/03/2017 07:23 AM »
When the mirror moves at 25% of the speed of light  (as in Wilson 's experiment ) in the direction of the incoming photon,  an observer on the mirror sees the frequency of the photon increased by only  about 30%. The observed frequency is elevated orders of magnitude only when the mirror moves at speeds very close to the speed of light. Still, this is sufficient to make the reasoning in my post valid. Also note that I am not talking about a 'quantum vacuum virtual plasma', a concept dismissed by well established physicists (I would just call it QED vacuum). I am talking about  a chain of events related to known phenomena of electron - positron annihilation,  and pair creation in the Coulomb field of nuclei of atoms in the mirror,  and the mediator of the momentum transfer is the electron.

I welcome any constructive comments,  pro and specially against my train of thought,  that would lead to progress in this matter. Note that in my model no laws of physics are broken  (the laws of conservation of energy and momentum are valid as always ).  Too much nonsense has been written about the EM drive  (and related designs, unfortunately including Shawyer's original explanation ), so that even if you get close to a forum of repected physicists, once you mention the EM drive you are classified as a dilettante. It's a pity, because I think that there is something interesting here, and many experiments proved that point.
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Online meberbs

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Re: EM drive - predictive analysis
« Reply #6 on: 02/03/2017 07:46 AM »
Any useful comments will be appreciated. Note that no new physics is required in this model, and all the laws of conservation (energy and momentum) are valid.
You should check your math again. If particles are being created, that is a lot of energy, and would make the result even worse performance than a photon rocket.

Saying no new physics means the emDrive does not produce useful force.

Offline cristian

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Re: EM drive - predictive analysis
« Reply #7 on: 02/03/2017 03:35 PM »
Thank you meberbs  for your comments. At the lower range,  a gamma photon can be  involved in the photoelectric effect. At higher energies, we have Compton scattering.  Around the threshold value of 2mc^2, the energy of the gamma photon is converted into an electron - positron pair. At much higher energies, we have photodisintegration and photofission.  We work around the threshold energy 2mc^2,  where m is the rest mass of the electron.An electron - positron pair is created. The electron is attracted by the Coulomb field of the nucleus, thus transferring momentum to the nucleus. The positron is repelled by the Coulomb field of the nucleus, and annihilates with the electron of another atom. Two gamma photons are produced,  at exactly the threshold energy. Now the  relativistic Doppler effect comes into play, and the frequency of the gamma photon is increased.  The Doppler shift must at least double the frequency of the  photon. Now, both  gamma photons have sufficient energy to participate in electron - positron pair creation in the Coulomb field of other nuclei,  and the process repeats. With each pair creation,  momentum is transferred to the nucleus. We have here some sort of chain reaction. The essential ingredient here is the relativistic Doppler shift, which makes it all possible. The process of momentum transfer with the electron as the mediator is much more efficient than the case when only photons are involved in momentum transfer.  What has been observed in the case of the EM drive  (in the microwave range energies ) is probably just a residual effect. The effect can probably be vastly amplified if we work in the right energy range.  If an X ray laser is considered, after the mirror has been put in motion  (using Wilson 's method,  for example ),  I suspect that interesting phenomena will come into play. Math checks out.
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Online meberbs

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Re: EM drive - predictive analysis
« Reply #8 on: 02/03/2017 03:40 PM »
So your claim is that the relativistic Doppler effect violates conservation of energy and momentum?

This is untrue, so I again suggest double checking your math. (There was almost no math in what you just posted.)

Offline cristian

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Re: EM drive - predictive analysis
« Reply #9 on: 02/03/2017 04:14 PM »
No, at no point do I claim anything like that.  People who attack the laws of conservation of energy and momentum are cranks. At every stage of the process,  energy and momentum are conserved. If you want some mathematics,  have a look here:

http://physics.stackexchange.com/questions /50106/pair-production-mathematically

There is a lot more mathematics involved in what I described,  and it all checks out. So much more that there is not enough space here for that.  Experts can retrace the steps of what I described. Photon drives are inefficient,  due to the very small coefficient,  momentum over energy,  for the photon, which is 1/c. The mechanism that I describe can transfer momentum to the mirror orders of magnitude more efficiently, and I emphasize,  the laws of conservation of energy and momentum are never violated .
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Online meberbs

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Re: EM drive - predictive analysis
« Reply #10 on: 02/03/2017 04:34 PM »
Energy and momentum conservation show that photons thrust is the best you can do if you start with pure energy. Generating particles to emit as reaction mass consumes energy and reduces the thrust per input power. I can just look at the initial and final conditions of your claimed setup and tell that you are violating energy or momentum conservation.

This means you are making a mistake in the middle somewhere. There is plenty of room for you to post your math here, and then someone (me if I have time) can help you find your mistake.

Offline cristian

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Re: EM drive - predictive analysis
« Reply #11 on: 02/03/2017 05:06 PM »
The ratio momentum over energy for a non relativistic electron is 2/v , where v is the velocity of the electron. This is orders of magnitude higher than 1/c, in the photon case. The chain reaction involving pair creation and annihilation,  facilitated by the relativistic Doppler shift, where momentum is trasferred by the electron for each pair creation step,  more than compensates for the energy required for the creation of the electron - positron pair. Your assumption that having the photon as the mediator of momentum transfer is the best you can do, is incorrect. Have you ever had a look at QFT mathematics? There are tomes of dense mathematics,  just to understand the basics, and this is what we are talking about. Any attempt to dive into that on these posts would be a joke.
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Online meberbs

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Re: EM drive - predictive analysis
« Reply #12 on: 02/03/2017 06:02 PM »
The ratio momentum over energy for a non relativistic electron is 2/v , where v is the velocity of the electron. This is orders of magnitude higher than 1/c, in the photon case. The chain reaction involving pair creation and annihilation,  facilitated by the relativistic Doppler shift, where momentum is trasferred by the electron for each pair creation step,  more than compensates for the energy required for the creation of the electron - positron pair. Your assumption that having the photon as the mediator of momentum transfer is the best you can do, is incorrect. Have you ever had a look at QFT mathematics? There are tomes of dense mathematics,  just to understand the basics, and this is what we are talking about. Any attempt to dive into that on these posts would be a joke.
If total energy and momentum at the end is not equal to total energy and momentum at the start, then energy and momentum are not conserved.

You are claiming that by some magic, you don't have to pay the E=m*c^2 cost for creating the electron. This violates energy conservation. If you included the energy to create mass, you would realize that 2/v is not the right answer. Try to explain where the energy that went into creating the electron came from (what is missing energy in the final state) this may help you see the issue.

Nothing you have described involves QFT math, at most it involves special relativity. Maybe in your head you have imagined some quantum way that quantum allows energy conservation to break, but it doesn't.

Offline as58

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Re: EM drive - predictive analysis
« Reply #13 on: 02/03/2017 10:42 PM »
The ratio momentum over energy for a non relativistic electron is 2/v , where v is the velocity of the electron. This is orders of magnitude higher than 1/c, in the photon case. The chain reaction involving pair creation and annihilation,  facilitated by the relativistic Doppler shift, where momentum is trasferred by the electron for each pair creation step,  more than compensates for the energy required for the creation of the electron - positron pair. Your assumption that having the photon as the mediator of momentum transfer is the best you can do, is incorrect. Have you ever had a look at QFT mathematics? There are tomes of dense mathematics,  just to understand the basics, and this is what we are talking about. Any attempt to dive into that on these posts would be a joke.

So where does the momentum go? What does the engine emit?

Offline sanman

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Re: EM drive - predictive analysis
« Reply #14 on: 02/04/2017 04:34 AM »
cristian,
So this Schwinger effect relates to gamma-gamma photon interaction, right? (ie. the high energies you mentioned)

Is it possible to achieve this with Squeezed Light? I realize Squeezed Light is just manipulating the overall distribution of the photon within the bounds of Heisenberg Uncertainty, but if a sufficiently high peak amplitude (dB) is achieved, then can't this result in a similar kind of interaction via the peak values?

If Squeezed Light can be produced at little/no energy cost via non-linear optical crystals, then couldn't it lower the burden on your power supply?


Offline cristian

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Re: EM drive - predictive analysis
« Reply #15 on: 02/04/2017 04:49 PM »
Answer for meberbs.

Thank you for your comments. Looks like I have to put my thinking cap on. First, and answer for meberbs. I attached a file (pairproduction.pdf), where everything related to this is nicely explained. We consider just a single event, pair production. Pair production cannot happen in empty space (the simultaneous validity of the laws of conservation of energy and momentum forbid it). We need a third body, we need the nucleus with its Coulomb field. In order to satisfy the conservation laws, the system that we study is the gamma photon + the nucleus (before pair creation), and the system electron-positron + nucleus (after pair creation). The law of conservation of energy says that the total Energy of the system before pair production is equal to the total energy of the system after pair production. Similar for the momentum. Everything is explained in the attached file (in relativistic notation). We agree up to this point, nothing funny up to this point. Momentum is transferred to the nucleus, with little energy transfer.

Where we disagree is related to whether momentum transfer with the electron as the mediator is more efficient than a photonic drive, where momentum is transferred directly, with the photon as the mediator.

For a single event, you are correct meberbs, the momentum transferred to the nucleus is smaller than the initial momentum of the photon.

Now we get into the hairy part, the chain reaction. We are on a reference frame tied to the mirror, in particular, to the nucleus. The electron - positron pair is created. The electron transfers momentum to the nucleus. The positron is repelled by the Coulomb field of the nucleus, and annihilates with the electron of another atom. Two gamma photons are created (at or slightly above the total threshold energy 2mc^2 , where m is the rest mass of the electron ). At about 60% of light speed, due to the relativistic Doppler effect, an observer on the mirror will see the frequency of the incoming gamma photon doubled (when moving straight towards the photon, all the possible geometrical configurations have to be considered, this is just a special case ). That means that each of the two gamma photons that were released after annihilation, now can trigger pair creation events in the Coulomb fields of the nuclei of other atoms (this is exponential increase!!!). The process repeats, and at each step, momentum is transferred to the nuclei of the atoms of the mirror. This is the chain reaction facilitated by the relativistic Doppler shift.

Problems with the chain reaction.

1. The direction of travel of each of the two gamma photons after each annihilation step is important, because the frequency increase as seen from the mirror depends on the particular geometrical configuration.

2. Energy and momentum conservation, before and after the chain reaction terminates. I don't know the answer to this one, you are correct meberbs , there is a problem here. I will think about this one. I hope you will too.

3. Is the chain reaction even possible, to start with?

4. I assume that the mirror is physically moving at 60% of light speed. The experiments described in my post (Ruoso or Wilson), do not qualify.

5. If this chain reaction is impossible, why is that the case? Can you prove that this chain reaction is not possible?

By the way, QFT (in particular QED) is need, in order to calculate the probability of these types of events, in order to see which are the dominating ones. There is no going around that, and the calculations are not pretty. This is actually the heart of the problem. Speculating based on the mathematics of relativity, and intuition, is not enough.


Answer for as58

The "engine" does not emit anything. For each pair production event, momentum is transferred to the mirror, due to the laws of conservation of energy and momentum. The problem is trying to prove that the total momentum transferred makes this "engine" more efficient that a straight photon drive. I tried it with my chain reaction model (described above), but surely I am missing something.

Answer for sanman

I don't know the answer to this one. We are still struggling with pair production (as you can see). I mentioned the Schwinger effect as an interesting venue of research related to all this, but as you can see from these discussions, we cannot handle even much simpler events.




 












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Offline aero

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Re: EM drive - predictive analysis
« Reply #16 on: 02/04/2017 05:23 PM »
Pair production - Seems to me that there is plenty of energy in the cavity. Production of one pair needs 1.022 MeV. Multiply by 1.60218 E-19 J/ev = 1.60218 E-13 J/Mev so energy required to produce a pair is 1.637E-13 J/pair. That is not very much considering that the frustum is driven by as much as kJ/second. The problem of course is frequency of the photons. That is, the energy of a single photon needed for pair production. Without getting around that we still have a problem.

But, once there are electrons and positrons inside the cavity, I'm led to believe that they will be accelerated along the energy gradient within the cavity as accel = grad * 2/3 * diameter of electron or positron. Here this is like a = grad * dx and the 2/3 comes from applying dx to a sphere instead of a cylinder of the diameter of the electron/positron.

Just some thoughts.
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Online MikeAtkinson

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Re: EM drive - predictive analysis
« Reply #17 on: 02/04/2017 05:32 PM »
If you draw a box around your device and its power supply, are any particles or fields crossing the boundary? If so what?

Some other ideas about how the EM drive works, have the box the size of the universe (because they act on the whole universe). These need not break conservation of mass/energy or momentum as the increase of the EM drive is balanced by reductions elsewhere in the universe.

Offline sanman

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Re: EM drive - predictive analysis
« Reply #18 on: 02/05/2017 12:11 PM »
Answer for sanman

I don't know the answer to this one. We are still struggling with pair production (as you can see). I mentioned the Schwinger effect as an interesting venue of research related to all this, but as you can see from these discussions, we cannot handle even much simpler events.

cristian,
regarding your thoughts on Dynamical Casimir Effect - isn't it really the small-end of the frustum that you'd mainly focus on to observe Dynamical Casimir Effect? If an EMdrive were moving in a linear relativistic velocity, it would be the trailing small-end that would be expected to accumulate those pair-escaped particles, right?

But because the frustum is asymmetrically tapering, those pairs may not be able to produce in the first place, since the space is too narrow to support their wavelength. So your Static Casimir Effect would suppress the Dynamical Casimir Effect, would it not?

And maybe that's even what helps to allow the internal "bump-dip" inside the frustum cavity to facilitate motion in the first place (the "Warp-in-a-Bottle"), even for regular slow non-relativistic velocity frames.
« Last Edit: 02/05/2017 12:13 PM by sanman »

Offline cristian

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Re: EM drive - predictive analysis
« Reply #19 on: 02/05/2017 04:39 PM »
I think that aero  solved all our problems gentlemen (with his last remark above ), but maybe not exactly the way he described it .  We could consider positron channeling in crystals..  So we have an experimental setup where after the pair production event,  the electron transfers some momentum to the nucleus,  and the positron will channel through the crystal,  thus increasing its momentum. No pair production  - annihilation chain reaction, all laws of conservation of energy and momentum are valid, and it explains the enhanced momentum transfer.  Bingo. I think that we are on the right track here.
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Offline sanman

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Re: EM drive - predictive analysis
« Reply #20 on: 02/05/2017 08:07 PM »
I think that aero  solved all our problems gentlemen (with his last remark above ), but maybe not exactly the way he described it .  We could consider positron channeling in crystals..  So we have an experimental setup where after the pair production event,  the electron transfers some momentum to the nucleus,  and the positron will channel through the crystal,  thus increasing its momentum. No pair production  - annihilation chain reaction, all laws of conservation of energy and momentum are valid, and it explains the enhanced momentum transfer.  Bingo. I think that we are on the right track here.

So based on what you've said - what is the way to optimize the effect of "enhanced momentum transfer"? Is there some kind of "mean free path" metric that needs to be increased? Is it the case that the longer a produced pair persists before anihilation, then the more momentum transfer happens? Is there some travel requirement that has to be maximized for a produced pair?

Online meberbs

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Re: EM drive - predictive analysis
« Reply #21 on: 02/05/2017 08:36 PM »
Where we disagree is related to whether momentum transfer with the electron as the mediator is more efficient than a photonic drive, where momentum is transferred directly, with the photon as the mediator.

For a single event, you are correct meberbs, the momentum transferred to the nucleus is smaller than the initial momentum of the photon.

Now we get into the hairy part, the chain reaction.
Which is just the same process again, the conclusion won't change if you don't make a mistake

We are on a reference frame tied to the mirror, in particular, to the nucleus.
To be clear, we are in the initial rest frame of the surface, we are not tied to it as it accelerates, because conservation of momentum and energy need to be calculated in an inertial frame.

The electron - positron pair is created. The electron transfers momentum to the nucleus. The positron is repelled by the Coulomb field of the nucleus, and annihilates with the electron of another atom. Two gamma photons are created (at or slightly above the total threshold energy 2mc^2 , where m is the rest mass of the electron ). At about 60% of light speed, due to the relativistic Doppler effect, an observer on the mirror will see the frequency of the incoming gamma photon doubled (when moving straight towards the photon, all the possible geometrical configurations have to be considered, this is just a special case ).
You just jumped to a completely different frame, so your calculations are invalid. Why are you suddenly moving at 0.6 c anyway?

5. If this chain reaction is impossible, why is that the case? Can you prove that this chain reaction is not possible?
It isn't possible, because the energy doesn't balance, at each step, you are expecting the mirror to have gained a relative 0.6 c in speed compared to its original. This magic acceleration is where all of the bonus energy is coming from enabling the chain reaction.

By the way, QFT (in particular QED) is need, in order to calculate the probability of these types of events, in order to see which are the dominating ones. There is no going around that, and the calculations are not pretty. This is actually the heart of the problem. Speculating based on the mathematics of relativity, and intuition, is not enough.
When the energy/momentum doesn't balance, the chance of the event is 0 (QFT requires calculation of virtual particles and such, but only within a near-instantaneous event, when the smoke clears, the final answer must conserve energy/momentum). It is a useful shortcut for cases like this.

Offline as58

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Re: EM drive - predictive analysis
« Reply #22 on: 02/06/2017 12:08 AM »
The "engine" does not emit anything. For each pair production event, momentum is transferred to the mirror, due to the laws of conservation of energy and momentum. The problem is trying to prove that the total momentum transferred makes this "engine" more efficient that a straight photon drive. I tried it with my chain reaction model (described above), but surely I am missing something.

If it doesn't emit anything, it's not even a photon rocket. It just doesn't move.

If the device starts at rest, operates for a while and moves a distance, what has moved the other way to balance the centre of mass? 

Offline aero

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Re: EM drive - predictive analysis
« Reply #23 on: 02/06/2017 02:18 AM »
I think that aero  solved all our problems gentlemen (with his last remark above ), but maybe not exactly the way he described it .  We could consider positron channeling in crystals..  So we have an experimental setup where after the pair production event,  the electron transfers some momentum to the nucleus,  and the positron will channel through the crystal,  thus increasing its momentum. No pair production  - annihilation chain reaction, all laws of conservation of energy and momentum are valid, and it explains the enhanced momentum transfer.  Bingo. I think that we are on the right track here.

So based on what you've said - what is the way to optimize the effect of "enhanced momentum transfer"? Is there some kind of "mean free path" metric that needs to be increased? Is it the case that the longer a produced pair persists before anihilation, then the more momentum transfer happens? Is there some travel requirement that has to be maximized for a produced pair?

Someone with more em physics may consider how the Lorentz forces might affect the electron and positron pairs. It's fine if the x and y force components are equal and opposite, but if all 3 force directions are equal and opposite then we're back to only the radiation pressure providing a differential acceleration on the particles. That might or might not be enough. The energy gradient in the cavity is quite large relative to the particle mass after all.
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Offline cristian

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Re: EM drive - predictive analysis
« Reply #24 on: 02/06/2017 02:03 PM »
Channeling accelerators, this is the core idea. Conduction electrons in a metal form a uniform high density plasma with longitudinal plasma oscillations. Charged particles are accelerated along atomic crystal channels by plasma waves in metal. Positively charged particles are guided by the average electric fields produced by atomic rows or planes in the crystal. The particles make a series of glancing collisions with many atoms and execute classical oscillatory motion along the interatomic channels.

For reference, read the attached file, "Channeled particle acceleration by plasma waves in metals" .

So ultimately, the energy stored in the Coulomb fields of the nuclei of the atoms in metals is the energy that will accelerate the positrons to high velocities.

Also, have a look at a comparison between the classical and relativistic momentum:

http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Relativity/relativistic_momentum.html

This is what makes the difference, the relativistic mass increase of the positrons.

From a practical perspective, how do we actually build the system? Here is how I would do it, but keep in mind that there may be other ways. The central idea is always channeled acceleration.

Stage 1. Generation of an electron beam. For reference, see the following:

http://ozradonc.wikidot.com/generation-of-electron-beams

Stage 2. Creation of a source of positrons. For reference, see the following:

http://cerncourier.com/cws/article/cern/28542

Note that channeling is also used at stage 2.

Stage 3. Channeled positron acceleration by plasma waves in metal.

The attached article is the required reference for stage 3.

Due to the relativistic momentum increase of the positrons , this will assure the enhanced thrust for the system.

Note that the "battery" energy (the energy required to set up the system), is only used at stage 1 and stage 2. Stage 3 is all about the energy stored in the Coulomb fields of the nuclei of the atoms in the metal (the crystal lattice that will accelerate the positrons generated at stage 2). This is what makes the difference, and what makes this superior to a pure photonic drive.

I must give credit to aero for the following remark:

.......But, once there are electrons and positrons inside the cavity, I'm led to believe that they will be accelerated along the energy gradient within the cavity ......

Just some thoughts.

Of course, aero was thinking about the acceleration within the cavity, but in my mind, this remark made the difference between my dilettante talk about pair production - annihilation chain reaction, and other dead ends, and the real deal, the interesting idea of using the Coulomb fields of the nuclei of the atoms in metals, in order to increase the momentum of the positrons. Thank you aero, surely two minds are better than one.

So that's it. The system will eject high velocity positrons, and will gain an enhanced thrust, as compared to a purely photonic drive or anything else. All laws of conservation of energy and momentum are valid, and no weird physics necessary. This is so far from the original design of the EM drive that I will not even try a comparison, or ask why the original design works the way it does. This is a completely different system, and no fuel necessary. Pair production is essential.

Alpha Centauri, here we come!












 

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Offline cristian

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Re: EM drive - predictive analysis
« Reply #25 on: 02/06/2017 03:45 PM »
And if you think that electron - positron annihilation will dominate (and positron channeling won't happen for a sufficiently long time , which I don't think is the case, if you read the references  ), then you can skip step 2, and channel the electrons directly. The results will be similar.
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Re: EM drive - predictive analysis
« Reply #26 on: 02/06/2017 05:14 PM »
Note that the "battery" energy (the energy required to set up the system), is only used at stage 1 and stage 2. Stage 3 is all about the energy stored in the Coulomb fields of the nuclei of the atoms in the metal (the crystal lattice that will accelerate the positrons generated at stage 2). This is what makes the difference, and what makes this superior to a pure photonic drive.

False. Read the article again, you need a high energy source to generate the waves in the plasma, and even the authors of that reference you attached weren't sure how to do it. Read from the middle of page 5.

Offline cristian

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Re: EM drive - predictive analysis
« Reply #27 on: 02/06/2017 05:32 PM »
Compared to the way relativistic momentum increases with velocity,  that is a small price to pay (you can do the math ). The efficiency will still be higher than anything currently possible, including the photonic drive. I am glad that you are paying attention. The energy stored in the Coulomb fields of the nuclei of the atoms of  the crystal lattice that channels the particles is quite large.
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Offline as58

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Re: EM drive - predictive analysis
« Reply #28 on: 02/06/2017 06:38 PM »

So that's it. The system will eject high velocity positrons, and will gain an enhanced thrust, as compared to a purely photonic drive or anything else. All laws of conservation of energy and momentum are valid, and no weird physics necessary. This is so far from the original design of the EM drive that I will not even try a comparison, or ask why the original design works the way it does. This is a completely different system, and no fuel necessary. Pair production is essential.

Alpha Centauri, here we come!

Ok, it will emit positrons. So it's not propellentless at all, more like a normal electric propulsion system such as ion thruster.

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Re: EM drive - predictive analysis
« Reply #29 on: 02/06/2017 07:00 PM »
The energy stored in the Coulomb fields of the nuclei of the atoms of  the crystal lattice that channels the particles is quite large.
You can't just magically access this energy. The energy to accelerate the particles  comes from the waves you generate, which come from your power supply. Read the article more carefully, the waves don't spontaneously exist.

Compared to the way relativistic momentum increases with velocity,  that is a small price to pay (you can do the math ). The efficiency will still be higher than anything currently possible, including the photonic drive. I am glad that you are paying attention.

Yes, lets do the math. Since all of the energy to create and accelerate the particles is coming from your power supply, (and ignoring that you would probably have a bunch of wasted power due to inefficiencies) this means the energy required is a minimum of E = sqrt(m^2*c^4 + p^2*c^2), where p Is momentum. For a given E, it is clear that p will be smaller than for the photon rocket case E=p*c.

You are moving towards the idea of an ion engine. These are efficient because you don't have to pay the energy cost to create the matter. This comes at the cost of carrying limited propellant with you. If you had antimatter available to turn the propellant into raw energy, then you would be better off doing so and emitting the energy as photons rather than sending matter out the back.

Offline cristian

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Re: EM drive - predictive analysis
« Reply #30 on: 02/07/2017 04:03 PM »
Thank you meberbs for keeping me on my toes.  I have to put my thinking cap back on. The relativistic energy - momentum relation is perfectly valid, but you omit the phenomenon of self-oscillation,  when the energy losses in the oscillating system are small.  In this case,  in order to sustain self-oscillations,  the quantity of energy entering the system is very small in comparison with the total energy within the oscillating system.

I will make a naive, imperfect analogy,  dealing with a simple classical situation.  We consider a sinusoidal train track, hill,  valley,  hill, valley,  and so on. A levitating train starts at the top of the first hill, we have to put it there, so we spend some potential energy. We release it. The levitating train will go up, down, up, down, and so on. Potential energy (at the top of one hill) is constantly converted to kinetic energy (in the valkey), but there are some small energy losses due to air resistance. From time to time, when it approaches the top of the hill, we have to give it a small push, in order to continue its travel. Now,  let's  imagine that every time the train is in a valley  (maximum kinetic energy), we release a small ball through the window.  In principle, we can release as many balls as we want,  at a very small expense of energy. Clearly, the analogy is far from perfect,  but you get the idea.

The electron plasma waves take advantage of the ''landscape", the distribution of the nuclei (with their Coulomb fields) of the atoms  in the crystal lattice that channels the particles. We have to spend some energy to excite the plasma, but then the energy required to maintain the self -oscillatory system is minimal (regardless of how many particles are channeled through the lattice ). This is where we take advantage of the energy stored in the  Coulomb fields of the nuclei of the atoms of the crystal lattice.

One more observation that might make you think. Just as an example,  heavily doped silicon has its plasma frequency in the infrared region,  close to microwave (so some materials have their plasma frequency close to microwave ). In some designs of the EM drive,  a dielectric resonator is added in front of the narrower end. That is interesting, isn't it? The microwave field in the cavity excites the electron plasma in the resonator,  and we could have here some sort of electron channeling, that generates the thrust. If the EM drive works,  channeling has something to do with it. The relativistic momentum increase of the channeled particles is what generates the thrust.  Could be much more efficient than a photon drive. I hope you agree. 

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Offline sanman

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Re: EM drive - predictive analysis
« Reply #31 on: 02/08/2017 12:58 AM »
The relativistic momentum increase of the channeled particles is what generates the thrust.  Could be much more efficient than a photon drive. I hope you agree.

See, that's what makes me wonder about Laser Wakefield acceleration - because it provides such a high accelerative gradient to achieve relativistic velocities for electrons, that you can get extra action-reaction from that via relativistic momentum increase. Of course, the duty cycle on a Laser Wakefield accelerator is low, but it's still something to think about.

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Re: EM drive - predictive analysis
« Reply #32 on: 02/08/2017 02:08 AM »
The relativistic momentum increase of the channeled particles is what generates the thrust.  Could be much more efficient than a photon drive. I hope you agree.

See, that's what makes me wonder about Laser Wakefield acceleration - because it provides such a high accelerative gradient to achieve relativistic velocities for electrons, that you can get extra action-reaction from that via relativistic momentum increase. Of course, the duty cycle on a Laser Wakefield accelerator is low, but it's still something to think about.

While the SCSC was to big to put into any foreseeable spacecraft, it did accelerate protons (much more massive than electrons) to approximately 99% the speed of light in the first 20 feet of travel from the start. At least that was the design if I understand Seashells right. (she worked on the SCSC).
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Offline cristian

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Re: EM drive - predictive analysis
« Reply #33 on: 02/08/2017 03:42 PM »
Well,  together we reached an interesting conclusion.  The principle of operation of the EM  drive has something to do with  electron channeling in a crystal lattice.  The thrust is connected to the relativistic momentum increase of the channeled particle. An interesting article to read is "Interpretation of electron channeling by the dynamical theory of electron diffraction ",  written by Kambe,  Lehmpfuhl, and Fujimoto (can be easily found for free on the net). Nonlinear dynamics, self oscillations,  and other phenomena are essential. Based on these principles,  the design of the EM drive  (with the right materials,  at the correct operational parameters,  in terms of energy and geometry)  can be vastly improved.  Compared to the tomes of nonsense that have been written about this issue,  I think that we reached a down to earth, interesting conclusion, in a relatively short period of time (and I am not aware of anybody else who followed this trail ) . I hope that experts will follow this direction of research. Thank you aero, meberbs, sanman,  as58, and everybody else who participated in this discussion.
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Re: EM drive - predictive analysis
« Reply #34 on: 02/09/2017 02:56 AM »
Thank you meberbs for keeping me on my toes.  I have to put my thinking cap back on. The relativistic energy - momentum relation is perfectly valid, but you omit the phenomenon of self-oscillation,  when the energy losses in the oscillating system are small.  In this case,  in order to sustain self-oscillations,  the quantity of energy entering the system is very small in comparison with the total energy within the oscillating system.
...

I am not sure how you think I am omitting something. All the the energy that got the oscillations started had to come from somewhere (your battery) and if you want to keep them going, you will need to add in just as much energy as you extracted by accelerating a particle.

To use a planetary flyby as an example: it appears to violate conservation of energy, only because you neglect the change in the planet's velocity.  You really are stealing energy from the planet, and if the planet didn't have so much energy to start with, you would have to have a giant rocket move the planet back to its proper orbit.

Well,  together we reached an interesting conclusion.  The principle of operation of the EM  drive has something to do with  electron channeling in a crystal lattice.  The thrust is connected to the relativistic momentum increase of the channeled particle.
I am not sure how you reached this conclusion. You have neither shown how your proposed mechanism could be happening in an emDrive (typical emDrives are not single crystal to start with), nor shown that any better than a photon rocket worth of thrust can be produced. You keep handwaving steps saying "relativistic momentum gives a boost" when this does not happen. If you actually did math and calculated the energy and momentum you would see this.

Also, you phrase this as an absolute statement as if this must be the mechanism of operation. The most likely explanation of emDrive force measurements remains experimental error (thermal expansion, etc.)

Offline cristian

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Re: EM drive - predictive analysis
« Reply #35 on: 02/09/2017 06:47 AM »
You are correct in what you are saying, but I will clarify what I mean. We write E_b for the energy of the battery. We write E_e  for the energy of the electron,  E_p for the energy of the photon. We also write a for the energy conversion coefficient for the photon (the fraction of the battery energy transferred to the photon ) , and b for the energy conversion coefficient for the electron. We write c for the speed of light.  Clearly we have a < 1 and b < 1.

The photonic drive.  In this case we have  E_p = a * E_b  = c * p.  The efficiency coefficient,  the ratio between the momentum  of the photon and the energy spent  (battery energy) to put it in that state is
 efficiency_photon = a/c , where c is the speed of light.

Electron channeling.  I  this case we have E_e = b * E_b = sqrt (m^2 * c^4 + p^2* c^2). In this case, the efficiency coefficient is  efficiency_electron = b * p/sqrt (m^2 * c^4 + p^2 * c^2).

If b is larger than a, and we assume that we do not have to spend energy to create the electrons, then we have efficiency_electron > efficuency_photon. We work with the electrons already existent in the crystal lattice  (the material ) that performs the channeled acceleration.  The operational life span of such a crystal could be many years (until structural defects in the lattice appear, or other problems).

In electron channeling,  we are dealing with nonlinear dynamics, self oscillations,  and other complex phenomena.  A good reference to start is "Interpretation of electron channeling by the dynamical theory of electron diffraction",  that I mentioned in my previous post.  It is perfectly conceivable that b > a. That is the point that I am trying to make, but the proof requires expert level solid physics,  and I do not have the required background.  Neither can you prove that my speculation is incorrect,  but the burden of proof rests with me indeed,  because I make the speculative statement (with the help of the people that participated in this discussion ). The relativistic momentum increase of the accelerated electrons (leaving the channeling crystal ) is what gives the required thrust (conservation of momentum ). The fact that the design of the EM drive includes a dielectric resonator with plasma frequency not far from the microwave region, and the fact that unexplained thrust has been observed in experiments all over the world mean something. They could not all have neglected thermal effects.

Compared to baloney theories like "relativistic pressure imbalance ",  or "virtual quantum plasma", or theories that attack the laws of conservation of energy and momentum  (and there are many other ), this model is down to earth and decent. I think that there is something interesting here that is worth further investigation.  A few decades  of operational life span of the channeling crystals are enough for a trip to Proxima Centauri.

Only in this sense,  and for a finite period of time, the efficiency of the electronic channeling drive is superior to the photonic drive.
 
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Offline cristian

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Re: EM drive - predictive analysis
« Reply #36 on: 02/09/2017 07:31 AM »
One more short note meberbs.  Even if we spend energy creating the electrons on board (pair production ),  the relation efficiency _electron > efficiency_photon can still be satisfied if b is much larger than a, but this is less likely.  Please feel free to poke many more holes in my theoretical speculations,  I like it, and it is constructive.
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Offline as58

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Re: EM drive - predictive analysis
« Reply #37 on: 02/09/2017 12:08 PM »
It is not strange (and definitely not new) that with the same power you get more thrust by ejecting massive particles instead of photons. But that is obviously not propellantless propulsion. I'm not seeing what is new in your proposed scheme.

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Re: EM drive - predictive analysis
« Reply #38 on: 02/09/2017 03:59 PM »
There is no free lunch in science,  that's what I think. It's a matter of efficiency,  as defined in the discussions above. You can carry a lot of propellant on the ship,  and eject it at relatively low velocities,  for short periods of generated thrust,  or you can carry less propellant and eject it at high velocities  (taking advantage of relativistic momentum increase ),  for long time of  generated thrust. If the efficiency is high enough  (compared to a photon drive ),  you can even create electrons on board  (through pair production ),  in order to continue the journey. This is what would be needed for interstellar travel.

Related to the Woodward effect (and many related issues ),  I have no opinion whatsoever,  since I did not study the issue.  Related to particle channeling propulsion,  the principles are not new,  of course,  but the efficiency could be far superior to anything else achievable with current technology. The devil is in the details,  though.
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Offline cristian

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Re: EM drive - predictive analysis
« Reply #39 on: 02/09/2017 05:10 PM »
Since we are in the predictive analysis section,  let's not forget the first step in all this. Related to the EM drive, when thrust is detected , electrons should be detected behind the dielectric resonator  (should look for positrons too, but less likely), in the oposite direction of thrust. Their velocity distribution should be studied. Various materials  (with plasma frequency close to the frequency of the radiation) should be tested. Experimental physicist know how to approach this problem, so that any possible sources of "noise " would be eliminated .  My bet is that high velocity electrons will be detected.
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Online dustinthewind

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Re: EM drive - predictive analysis
« Reply #40 on: 02/15/2017 03:12 AM »
Energy and momentum conservation show that photons thrust is the best you can do if you start with pure energy. Generating particles to emit as reaction mass consumes energy and reduces the thrust per input power. I can just look at the initial and final conditions of your claimed setup and tell that you are violating energy or momentum conservation.

This means you are making a mistake in the middle somewhere. There is plenty of room for you to post your math here, and then someone (me if I have time) can help you find your mistake.

The photon recycling thruster immediately disproves the assumption that the best thrust you can get is that of collimated light.  The thrust achievable with photon recycling thrusters is larger.
« Last Edit: 02/15/2017 03:40 AM by dustinthewind »

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Re: EM drive - predictive analysis
« Reply #41 on: 02/15/2017 03:37 AM »
It appears to me your on a similar subject to what I was looking into earlier.  Here is a paper I wrote on the subject.  It is underdeveloped as I haven't had a lot of time to work on it. 

Here is one quote from the paper,

Quote
III. THEORY OF ACCELERATED LIGHT AND OTHER SOURCES
If one searches for the term “waveguide” in the book, “Theory of Photon Acceleration” by J T Mendonca2 it discussed how the effective mass of a photon can change in a waveguide that approaches cutoff wavelength, as well as a plasma. Another source was found discussing a change in the effective mass of light in a waveguide approaching cutoff wavelength titled, “Alternative perspective on photonic tunneling” by Zhi-Yong Wang1, Cai-Dong Xiong, Bing He5. It appears they show how a photon in a narrow waveguide may appear to change in mass and how it relates to evanescent waves. The author suspects how photons in the vacuum can excite electron positron (ep) pairs and those pairs when they annihilate can create photon pairs suggest that photons may them selves be low level excitations of overlapping ep pairs. If our quantum vacuum is made up of hidden ep pairs, then an acceleration of light may directly be a form of accelerating the quantum vacuum. This may parallel to locally accelerating a frame as happens when light enters a gravitational field.

The document is attached below and I will give you the research gate link here: https://www.researchgate.net/project/Is-the-frustum-EM-Drive4-decelerating-light-for-propellantless-propulsion

It might be possible that anti-matter is negative matter running backwards in time.  That is a positron is a negative energy electron running in reverse time such that it appears to have a positive charge and appears to be positive matter.  When a position overlaps with a positive energy electron that runs forward in time, the time should cancel and the appearance of the positron overlapping with the electron should be that of negative energy canceling with positive energy and they should vanish into the vacuum. 

However, the vacuum not being empty is full of other such pairs which never truly disappear and osculate at minimum energy (the minimum temperature of the vacuum).  Upon experiencing the electric field of the two pairs annihilating these other pairs are disturbed and so a light wave is excited upon the annihilation of a positron-electron pair. 

If we reverse time all that light converging on one point will excite again the formation of this e-p pair.   As we can see energy is conserved upon the annihilation of the pair. 

If we can accelerate light and its local frame we may be accelerating the local pairs in which most matter may be in an intricate dance with, called the vacuum.   

I suspect the stretching of the wavelength of the light in the cone tip of the frustum may be changing the effective mass of the pairs, which are not fully separated (very small separation) such that they transfer different ratio's of energy to a certain side of the cavity as opposed to the other side due to differences in effective mass.  This would explain why the Q of the cavity is important or with each photon reflection cycle a bit more energy is transferred to the cavity and the light should lose energy.  The change in frequency of the light would represent a change in the local frame of the e-p pairs or an acceleration of them and in doing so influence the cavity. 

Hopefully that isn't too confusing of an explanation. 

I have been very busy unfortunately as of late, however message me if you have any specific questions. 

Offline as58

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Re: EM drive - predictive analysis
« Reply #42 on: 02/15/2017 06:35 AM »
Energy and momentum conservation show that photons thrust is the best you can do if you start with pure energy. Generating particles to emit as reaction mass consumes energy and reduces the thrust per input power. I can just look at the initial and final conditions of your claimed setup and tell that you are violating energy or momentum conservation.

This means you are making a mistake in the middle somewhere. There is plenty of room for you to post your math here, and then someone (me if I have time) can help you find your mistake.

The photon recycling thruster immediately disproves the assumption that the best thrust you can get is that of collimated light.  The thrust achievable with photon recycling thrusters is larger.

Yes, and the reason for this has been explained many times. It has nothing at all to do with propellantless thrust.

Offline sanman

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Re: EM drive - predictive analysis
« Reply #43 on: 02/15/2017 05:07 PM »
The photon recycling thruster immediately disproves the assumption that the best thrust you can get is that of collimated light.  The thrust achievable with photon recycling thrusters is larger.

Yes, and the reason for this has been explained many times. It has nothing at all to do with propellantless thrust.

You're right that the Recycling Thruster has nothing to do with the Quantum Vacuum and Propellantless Propulsion. However, it does demonstrate that Resonance can milk more juice out of photons to obtain more momentum transfer than is possible from an ordinary Photon Rocket like a flashlight-in-space.

Unlike Prof Bae's Recycling Thruster, the EMdrive concept seeks to do the Propellantless Propulsion, but it seeks to exploit the Resonance to help it do so in a meaningful way - ie. achieve a more meaningful amount of thrust than would otherwise be possible without the resonance.


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Re: EM drive - predictive analysis
« Reply #44 on: 02/16/2017 12:23 AM »
The photon recycling thruster immediately disproves the assumption that the best thrust you can get is that of collimated light.  The thrust achievable with photon recycling thrusters is larger.

Yes, and the reason for this has been explained many times. It has nothing at all to do with propellantless thrust.

You're right that the Recycling Thruster has nothing to do with the Quantum Vacuum and Propellantless Propulsion. However, it does demonstrate that Resonance can milk more juice out of photons to obtain more momentum transfer than is possible from an ordinary Photon Rocket like a flashlight-in-space.

Unlike Prof Bae's Recycling Thruster, the EMdrive concept seeks to do the Propellantless Propulsion, but it seeks to exploit the Resonance to help it do so in a meaningful way - ie. achieve a more meaningful amount of thrust than would otherwise be possible without the resonance.

I think you got the point.  It is about effectively siphoning the energy from a photon if possible.  A large object firing off a very weak in mass projectile is a recipe for transferring very little kinetic energy to the large object.  A laser firing into space would observe very little energy received as kinetic energy from such an act. 

However, if the mass of a photon can change with its electric field.  That is if changing its wavelength in free space changes the effective impulse of a photon.  Or in other words, a photon is actually a phantom e-p pair that can change effective mass depending on separation.  (non-fully formed e-p pair out of the vacuum) then by effectively changing mass maybe its possible to change effective impulse or ratio of energy transferred to one side of the cavity. 

After many reflections it may be possible to more effectively drain energy from light, similar to the way a recycling photon thrust works, but where as a recycling photon thruster pushes on its other half.  An object pushing off light (a closed cavity) might be accelerating the local frame of light (e-p pairs in the vacuum) inducing Doppler shifts that effectively drain energy from light to kinetic energy of the large object.

Indeed some experiments have already shown detection of changes in the impulse of light when it changes in wavelength and reflects off a mirror.  Particularly in water.  This seems to imply an effective change in mass of the photon, changing its ratio of energy exchanged with the mirror.
« Last Edit: 02/16/2017 12:36 AM by dustinthewind »

Offline sanman

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Re: EM drive - predictive analysis
« Reply #45 on: 02/18/2017 02:27 AM »
Could the Rocket Bell in conventional chemical rockets provide a useful analogy?

Whether or not you have the Rocket Bell there, you are still spewing the same hot gas out of your combustion chamber.

But having the Rocket Bell there allows you to extract more useful energy from the exhaust gas than would otherwise be possible.

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Re: EM drive - predictive analysis
« Reply #46 on: 02/18/2017 02:49 AM »
Could the Rocket Bell in conventional chemical rockets provide a useful analogy?

Whether or not you have the Rocket Bell there, you are still spewing the same hot gas out of your combustion chamber.

But having the Rocket Bell there allows you to extract more useful energy from the exhaust gas than would otherwise be possible.

My guess is just an educated guess because I haven't studied much in rocket physics.  I would guess the bell shape is more to direct the propellant in a certain direction.  Probably as it exits with out it the particles may scatter in all direction.  What you want is collimation of the propellant, so it all travels in the opposite direction of the desired thrust. 

Propellant scattering degrades the thrust.  I would guess the bell helps focus this.  It is similar with laser light as the light is highly collimated but laser light provides so very little thrust because of its extremely small "effective" mass compared to the mass of the ship exhausting it.  With propellant the particles are much more massive with respect to the ship compared to photons.  Be careful not to tell people that photons have mass.  They only have "effective" mass because of the energy they possess. 

Often to get more thrust, more energy is given to the exhaust so it has higher velocity, but the ratio of energy exchanged between each particle of propellant expelled and the ship remains the same, depending on their respective masses. 
« Last Edit: 02/18/2017 02:52 AM by dustinthewind »

Offline sanman

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Re: EM drive - predictive analysis
« Reply #47 on: 02/18/2017 03:31 AM »
Meh - in the end, even a Rocket Bell seems to be about extracting more energy or momentum for better performance.

The question is - do the photons bouncing around in EMdrive get used up? And if they do, then where do the skeptics think that energy goes?

Offline aero

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Re: EM drive - predictive analysis
« Reply #48 on: 02/18/2017 07:01 AM »
The de-Laval nozzle or convergent-divergent nozzle (bell nozzle) is designed to provide a uniform increase in cross-sectional area as a distance from the nozzle throat, and based on the throat radius. Making the area increase linearly avoids shock waves forming in the nozzle flow. That is, internal to the nozzle, once the flow exits, well we've seen the videos showing shocks in rocket exhaust.
Retired, working interesting problems

Re: EM drive - predictive analysis
« Reply #49 on: 03/14/2017 09:17 AM »
I want to emphasize a few points related to this issue. I will assume that the thrust experimentally observed, as related to the EM drive, is a real phenomenon, and I will try to explain it. I will mention the following interconnected effects, the dynamical Casimir effect, Unruh radiation of accelerated mirrors, and the Schwinger effect.


Law of conservation of momentum: The geometric sum of the momenta of the bodies making up the closed system remains constant for any motions and interactions of the bodies of the system. This is one of the fundamental laws of physics. If  EM Drive has uncompensated force in an experiment, then is not closed system (have is interaction with the external environment). I repeat, effects are secondary and are the result of interaction with the external environment. F(EM) = 0
« Last Edit: 03/15/2017 08:35 PM by iRoman »

Offline ppnl

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Re: EM drive - predictive analysis
« Reply #50 on: 03/18/2017 01:51 AM »

Note that the "battery" energy (the energy required to set up the system), is only used at stage 1 and stage 2. Stage 3 is all about the energy stored in the Coulomb fields of the nuclei of the atoms in the metal (the crystal lattice that will accelerate the positrons generated at stage 2). This is what makes the difference, and what makes this superior to a pure photonic drive.



There is energy in fields but you cannot use that energy without destroying the field. Like all energy if you use it it must go away.

In the case of an atom you may extract energy by splitting or fusing the atom. With electrons you can get energy by annihilating them with anti-electrons. In all cases you will vastly alter the particle that furnishes the energy.

There is no free lunch. If there is a source of energy and you use it then you use that source up. It is just another battery.