Author Topic: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive  (Read 237213 times)

Offline Dmytry

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #300 on: 05/02/2015 07:38 PM »
In any case, whatever effect one can conjecture, the challenge is not only to prove the existence of the effect but just as important, to demonstrate conservation of momentum for a cavity accelerated under such an effect   :)

Alright, so the standing wave loses energy in an amount that offsets the kinetic energy gain associated with acceleration - and this is supposed to satisfy conservation of energy. And conservation of momentum is satisfied by using energy-mass equivalency?

I was just wondering what the mechanism is by which pumping up the standing wave then creates a net force on the cavity.

Here's a debunking by Greg Egan, showing why you can't have net force just because the cavity happens to be asymmetric:

Greg Egan is just showing the standing wave solution to Maxwell's equation for a truncated cone for mode shapes that have constant field in the transverse, azimuthal direction.   The solutions shown by Egan are known since the 1930's. 

That Maxwell's equations and special relativity satisfy conservation of momentum is known in general, for any problem, for any geometrical shape.  Thus, Egan is just "debunking" attempts (as done by Roger Shawyer for example or by Prof. Yang in China) trying to justify EM Drive space propulsion just using Maxwell's equations and special relativity.  Egan's paper does not and cannot debunk Dr. White's conjecture for example, or Prof. Woodward's conjecture.  Dr. White's conjecture can be objected on the grounds that it implies a mutable and degradable quantum vacuum, for example, but not solely on the grounds discussed by Egan.
Right. A lot of the handy-wavy "theoretical" justification isn't even falsifiable. Someone just makes up some other theoretical nonsense.

And the computer simulations are worse. They are based on Maxwell's Equations which literally don't allow something like the EM-drive as they conserve both momentum and energy perfectly. If you get a different result, it's either because you modified the equations that you're solving or you're just seeing an artifact of the computation.

So the theoretical work can be safely ignored.

I wouldn't use the words "non falsifiable"... most of so called "non-falsifiable" things start off pre-falsified by a very huge set of past experiments, but they may be sufficiently vague as to prevent concrete examples. Only a very good theory wouldn't trip up on some existing well verified data.

Let's say we have a theory where you got the force they measured on the cavity from EM waves exchanging their momentum with the cavity.

If it is claimed that this is all in accordance with Maxwell's equations, that's an algebraic error.

If it is claimed that microwaves exchange momentum with the quantum vacuum, you have a claimed deviation from Maxwell's equations which would have far reaching effects beyond some tiny forces on microwave cavities - namely the electromagnetic fields in the cavities would have to differ from those predicted by Maxwell's equations, by a huge % even when the force is very small. It is semi-plausible that nobody would notice a small force acting on enclosed resonant cavities, it is not plausible that nobody would notice the EM fields necessary to push the cavity with such force.

Any daily or seasonal variation (introduced for sake of conservation of energy given Earth's orbital motion) would be particularly bad.
« Last Edit: 05/02/2015 07:42 PM by Dmytry »

Offline Eye_one

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #301 on: 05/03/2015 12:02 AM »
I apologize in advance my understanding is likely no where near where it should be but, there are no stupid questions only stupid people so prove me stupid.

Is it possible this device is condensing spacetime at one side and expanding it at the other creating a gravitational flow to one side?

This could explain some things like why when more power is put in the force becomes more directional or why the force changes depending on its orientation to the Earth's gravitational field.

Maybe somebody should place an atomic clock in the force it is producing.

Offline LasJayhawk

So this made me think about the time I took a 3 port circulator apart. For those that are not familiar with circulators, the work like this:
Put power in port 1 and it comes out port 2, put it in 2 and it comes out 3, put it in 3 and it comes out 1. All with out much loss. But if you try to go backwards, say 3 to 2,  you loose 99% of the power.

Cool little device. So when I take it apart all it is is a flat triangle of copper, 2 triangle shaped pieces of ferrite, and a magnet.

If you don't know the math behind it, is looks at first blush as "silly" as the emdrive. No way could it do that. But it does. This thing may well work, we just don't know the math.

Offline Lourens

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #303 on: 05/03/2015 07:12 AM »
Interesting stuff. Either there's something odd with these experiments, or there's something odd with the laws of physics. Without a PhD in physics I can't judge, but it does seem like an extraordinary claim, and those require extraordinary evidence, so right now my money is on an experimental artifact. Exciting though, feels like reading a Greg Egan novel :).

On the other hand, I do think we can figure out just how extraordinary the claim is using basic high school physics. Does a propellantless drive necessarily violate conservation of energy? So I went and played around a bit, and came up with this high school-level thought experiment involving a bowling ball rocket. So, for everyone else who'd like a concrete example and some numbers that anyone can understand to go with Jason's explanation, read on :).

Bowling ball rocket
A bowling ball rocket is an ordinary rocket (a mass driver), with bowling balls for fuel. These are of course high-tech aerospace grade bowling balls: they mass only 4 kg each, and they have a spring attached that is coiled up and held in that position with a bit of string. The spring on each bowling ball stores 24 J of potential energy and has no mass.

The bowling ball rocket itself has an empty mass of 8 kg, and it carries two bowling balls for fuel. It hovers in space somewhere conveniently far away from everything else, and next to it is us, wearing space suits and measuring things.

So, here's the initial situation:
m_b1 = m_b2 = 4 kg      mass of each bowling ball
m_r = 8 kg              mass of rocket
v_r = 0 m/s             velocity of rocket
v_b1 = 0 m/s            velocity of bowling ball 1
v_b2 = 0 m/s            velocity of bowling ball 2
And the energy balance looks like this

E_kin = 1/2 * m_r * v_r + 1/2 * m_b1 * v_b1 + 1/2 * m_b2 * v_b2 = 0 J
E_pot = 2 * 24 J = 48 J
E = 0 J + 48 J = 48 J

Notation note: I'm using primes in the following to denote instances of time, not derivatives.

First bowling ball
Now, the rocket uses its robot arm to place one bowling ball against the back side of its hull, with the spring touching the hull, and then it cuts the string. The spring uncoils, pushing away the bowling ball in the backward direction, and the rocket in the forward direction. All the potential energy in the spring is converted into kinetic energy.

Now, we want to know the new velocities (relative to our still stationary selves) of all the objects involved:
v_r' = ?                velocity of rocket after first bowling ball launched
v_b1' = ?               velocity of first bowling ball after launch
v_b2' = ?               velocity of second bowling ball after launch of first
Since the second ball is still on board the rocket, we know that v_b2' = v_r'. Also, this is an ordinary rocket, so energy is conserved, so the total kinetic energy of all the objects must equal the amount of energy stored in the spring. That gives us

1/2 * m_b * v_b1'^2 + 1/2 * (m_r + m_b) * v_r'^2 = 24 J

Secondly, momentum is conserved, so we have

m_b * v_b1' + (m_r + m_b) * v_r' = 0 kg*m/s

Solving these equations, we get

v_r' = 1 m/s
v_b1' = -3 m/s
v_b2' = 1 m/s

We can also calculate the kinetic energy (again relative to our stationary selves) of the various objects in the system:

E_kin_r' = 1/2 * m_r * v_r'^2 = 1/2 * 8 * 1 = 4 J
E_kin_b1' = 1/2 * m_b1 * v_b1'^2 = 1/2 * 4 * 9 = 18 J
E_kin_b2' = 1/2 * m_b2 * v_b2'^2 = 1/2 * 4 * 1 = 2 J

Also, we can calculate the momenta

p_r' = m_r * v_r' = 8 * 1 = 8 kg*m/s
p_b1' = m_b1 * v_b1' = 4 * -3 = -12 kg*m/s
p_b2 = m_b2 * v_b2' = 4 * 1 = 4 kg*m/s

Second bowling ball
Now, the rocket launches its second bowling ball. Rocket and second bowling ball together had 6J of kinetic energy, and 24J of kinetic energy is added by the spring, so the total kinetic energy of rocket and ball 2 must be 30J after the second launch:

E_kin_r'' + E_kin_b2'' = 30 J

1/2 * m_r * v_r''^2 + 1/2 * m_b2 * v_b2''^2 = 30 J

Momentum is again conserved:

m_r * v_r'' + m_b1 * v_b1'' + m_b2 * v_b2'' = 0 kg*m/s

Solving this (exercise for the reader :) ), with v_b1'' = v_b1', we get

v_r'' = 1 + sqrt(2) ~= 2.41 m/s
v_b1'' = -3 m/s
v_b2'' = 1 - 2 * sqrt(2) ~= -1.82 m/s

E_kin_r'' = 1/2 * m_r * v_r''^2 = 12 + 8 * sqrt(2) ~= 23.3 J
E_kin_b1'' = 1/2 * m_b1 * v_b1''^2 = 18 J
E_kin_b2'' = 1/2 * m_b2 * v_b2''^2 = 18 - 8*sqrt(2) ~= 6.7 J

p_r'' = m_r * v_r'' = 8 + 8*sqrt(2) ~= 19.3 kg*m/s
p_b1'' = m_b1 * v_b1'' = -12 kg*m/s
p_b2'' = m_b2 * v_b2'' = -7.3 kg*m/s

So that's an ordinary rocket, and everything works as expected.

Moving frame of reference
There's one more interesting property of this: it works from a moving frame of reference. If we had not been stationary in our space suits, but had done our measurements while moving along at 1 m/s relative to the starting speed of the rocket, then energy and momentum would still have been conserved.

In that case, we start with an initial kinetic energy of 1/2 * 16 kg * 1 m^2/s^2 = 8 J and momentum of 16 kg * -1 m/s = -16 kg*m/s (we're moving at 1 m/s relative to the rocket, so we measure the rocket moving at -1 m/s relative to us). After the first bowling ball is released, we measure velocities

v_r' = 0 m/s
v_b1' = -4 m/s
v_b2' = 0 m/s

which gives a kinetic energies

E_kin_r' = 1/2 * m_r * v_r'^2 = 1/2 * 8 * 0 = 0 J
E_kin_b1' = 1/2 * m_b1 * v_b1'^2 = 1/2 * 4 * 16 = 32 J
E_kin_b2' = 1/2 * m_b2 * v_b2'^2 = 1/2 * 4 * 0 = 0 J

The total kinetic energy is now 32 J, which equals the initial 8 J plus the 24 J contributed by the spring. Energy is conserved. For momentum we get

p_r' = m_r * v_r' = 8 * 0 = 0 kg*m/s
p_b1' = m_b1 * v_b1' = 4 * -4 = -16 kg*m/s
p_b2 = m_b2 * v_b2' = 4 * 0 = 0 kg*m/s

So the total is -16 kg*m/s, which equals what we had initially as well. Momentum is also conserved in this moving frame of reference. I'll leave the situation after the second bowling ball is launched for the reader.

Magic spring rocket
So, now let's try a propellantless rocket. We replace our aerospace grade bowling balls with magic springs. Those are just the springs from the bowling balls, still storing 24 J of energy, but now without the bowling balls attached. They have no mass whatsoever, but when they uncoil, they still push the rocket ahead.

First magic spring
So, we go back to our unmoving reference frame, reset the rocket to 0 m/s, and have it trigger its first magic spring. Assuming that the magic springs conserve energy, this converts 24 J of potential energy into 24 J of kinetic energy, which is added to the rocket. Its kinetic energy relative to us space suited observers will become

1/2 * m_r * v_r'^2 = 24 J

from which we get velocity and momentum

v_r' = sqrt(6) ~= 2.45 m/s
p_r' = m_r * v_r' = 8 * sqrt(6) ~= 19.6 kg*m/s

Now here's something odd, because momentum has not been conserved. Apparently our magic spring has transferred 19.6 kg*m/s of momentum somewhere else. If I understand the reasoning a bit, this is supposed to be taken care of by mass-energy equivalence, which requires the extended concept of momentum from Special Relativity, and is beyond the simple Newtonian physics we're using here.

Second magic spring
Now, the rocket triggers the second magic spring. This adds another 24 J of kinetic energy, for a total of 48 J, giving velocity and momentum

v_r'' = sqrt(12) ~= 3.46 m/s
p_r'' = m_r * v_r'' = 27.7 kg*m/s

There are two interesting observations here: the delta-v we got from the second magic spring is less than what we got from the first magic spring (1.01 m/s vs. 2.45 m/s). Also, the momentum change is less, 8.1 kg*m/s vs. 19.6 kg*m/s. But energy is conserved. This is one type of propellantless rocket.

Constant thrust magic spring rocket
TheTraveller claimed that the EMDrive gives constant thrust at a constant power input. For the magic coil rocket, that would mean that each coil gives the same delta v. Let's see what happens with the total energy of the system if we assume that the second coil gives as much of a velocity change as the first:

v_r = 0 m/s
v_r' = sqrt(6) ~= 2.45 m/s
v_r'' = 2 * sqrt(6) ~= 4.90 m/s

E_kin = 1/2 * m_r * v_r^2 = 0 J
E_kin' = 1/2 * m_r * v_r'^2 = 24 J
E_kin'' = 1/2 * m_r * v_r''^2 = 96 J

So, here we have a situation where we put in two coils of potential energy, for a total of 48 J, but we're getting 96 J of kinetic energy back for it, at least relative to an unmoving observer. Constant acceleration, but no conservation of energy. That's a second type of propellantless rocket, and this is what ppnl is describing when (s)he says you can't have constant acceleration without violating conservation of energy.

So, which of the two types of propellantless drive is the EMDrive? According to the whitepaper linked by TheTraveller:

Thus as the velocity of the waveguide increases in the direction of thrust, the thrust will decrease until a limiting velocity is reached when T=0.

So, apparently it's the first type. Which means that it doesn't necessarily violate conservation of energy, at least, based on Newtonian physics.

There's one more issue though. According to AdrianW (in Reply #216), while the first propellantless rocket type doesn't violate conservation of energy, it implies that it now matters from which reference frame you are measuring. So let's reset the type 1 rocket one more time, fire our suit thrusters to get us up to 1 m/s relative to the rocket, and measure the initial situation:

v_r = -1 m/s
E_kin = 1/2 * m_r * v_r^2 = 4 J
p_r = m_r * v_r = -8 kg*m/s

After the first spring, we get

v_r' = sqrt(6) - 1 ~= 1.45 m/s
E_kin' = 1/2 * m_r * v_r'^2 = 4 * (sqrt(6) - 1)^2 = 28 - 8 * sqrt(6) ~= 8.40 J
p_r' = m_r * v_r' = 8 * (sqrt(6) - 1) ~= 11.6 kg*m/s

So, from this perspective, we again lost 19.6 kg*m/s of momentum by uncoiling the first spring, but now energy isn't conserved! We get different results when measuring from different moving frames of reference! That is a violation of Galilean relativity!

This can only work if there is some very special observing velocity at which everything works out, and a rule that says that observers at other velocities need to compensate for their velocity relative to the special one. But if that is the case, then we should be measuring different values when the Earth is moving in the same direction as this special velocity, compared to six months later when it is moving in the opposite direction. Which we probably would have noticed by now.

So, assuming Newtonian physics, which none of the actual physicists working on this are doing of course, it appears that a propellantless rocket either violates conservation of energy, or requires one frame of reference to be special. That's a very extraordinary claim. Now if someone can explain to me how dr. White sidesteps this issue (in the simplest terms possible) I'd be much obliged :).
« Last Edit: 05/03/2015 07:31 AM by Lourens »

Offline RotoSequence

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #304 on: 05/03/2015 07:31 AM »
What kind of damage would a special, or preferred frame of reference do to our understanding of the cosmos?
« Last Edit: 05/03/2015 08:17 AM by RotoSequence »

Offline CW

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #305 on: 05/03/2015 07:55 AM »
One might argue that there can't be a true inertial frame, because there is no truly field-free volume of space anywhere in the universe. Also, NASA's Marc G. Millis pointed out (sorry, no link right now) that something like inertial frames may exist, but that the origin of inertial frames remains an unknown till today.

On a side note, in case the refined EM-drive experiments unequivocally demonstrate a thrust generation, it would not demonstrate that the laws of physics are 'broken' by such a device. It would rather demonstrate that our current understanding of the physical world, as we perceive it, is 'broken'.
There is Zero chance to 'violate' anything in physics itself.. because that, which works, works. And that, which doesn't work, doesn't work. Maybe some physicists would feel 'violated' by a working EM-drive or Q-thruster.. who knows :P .

Good luck to Eagleworks (and of course Roger Shawyer).
« Last Edit: 05/03/2015 11:13 AM by CW »
Reality is weirder than fiction

Offline Dmytry

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #306 on: 05/03/2015 12:27 PM »
If the forces were in nanonewton range for very high electric fields in the drive, maybe it would be just our understanding that's broken. But when you have some momentum in the double digit percentage of the total momentum being carried by the EM radiation in the cavity, that's like our communication and radar equipment that would be broken, probably our microwave ovens even, to speak nothing of more sensitive devices. You can't get such momentum to the cavity walls through microwaves without changing how microwaves are!

Everyone's so into talking about the "laws" they forget about actual observations and applications of said laws in practice, in related situations.

There's experiments dating back up to 115 years measuring the momentum that electromagnetic waves impact upon a metal surface. Notably, even the very first experiment had accuracy and repeatability far higher than "yep, looks like there may be a force".

Granted, a lot of it is not in a cavity, but that's some literal magical thinking - an individual piece of copper, an individual electron, those things don't know if they're part of cavity any more than particles of paint would know they're a part of some magical summoning pentacle. This has to be explainable in terms of elementary interactions, which we tested down to parts per trillion, tested especially well for anything involving electromagnetic waves in particular.
« Last Edit: 05/03/2015 12:36 PM by Dmytry »

Offline ppnl

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #307 on: 05/03/2015 02:58 PM »
What kind of damage would a special, or preferred frame of reference do to our understanding of the cosmos?

Very, very, bad not good. Because we live on the surface of a very massive body we humans instinctively think in terms of an absolute frame of reference. Even Galilean relativity is counter intuitive to us. But much of modern science depends on squeezing out that bias. Special relativity for example took Galilean relativity seriously and extended it in a new domain. 

Could Galilean relativity and ultimately special relativity be wrong? Sure, I mean it is profoundly unlikely but I'm willing to consider it. But here is the problem, Shawyer has never shown the first clue that he understands that he is violating Galilean relativity. And when it comes down to it that would be the most important part of his discovery. Launching a few satellites cheaply is small potatoes compared to what may be possible with a deeper understanding of fundamental physics. And if Shawyer's work is valid it will change fundamental physics beyond all recognition. 

Offline RonM

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #308 on: 05/03/2015 03:24 PM »
And now we have a pretty good video, objective  (even including Sean Carroll from CalTech, and Alcubierre stating that he thinks his warp-drive concept is not practically feasible for centuries) about the NSF article on the EM Drive !


There is some hope for the media, as these guys got this "right", fair and balanced, respecting science and yet keeping up some hope and they put the video together in a short amount of time

I went to check local headlines this morning on, the Atlanta Journal and Constitution newspaper website, and the article and video was posted there this morning. Three hours after it was posted it is listed as number one on their most read article list.

Offline Stormbringer

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #309 on: 05/03/2015 03:35 PM »
What kind of damage would a special, or preferred frame of reference do to our understanding of the cosmos?
It would most probably slightly modify current theories. Special frames of reference are possible. At least according to new cosmological and astronomical data analysis of such things as WMAP and Plank observatory data. And there are always theories that invoke them despite the disrepute. There appears to be a preferred alignment of things in the universe like the rotational plane of the galaxies. and this evokes such things at the universe was spinning since it's inception and or dark flow and things like that. These things do lead to the dreaded preferred reference frame. If these observations prove true...

The world as we know it will not end. Theory will adjust to take it into account. It will be a special case and thus be considered as part of the trans-relativity regime. Newton was not destroyed by Einstein. We still use it. Relativity will not be destroyed by something that goes beyond it.
When antigravity is outlawed only outlaws will have antigravity.

Offline vide

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #310 on: 05/03/2015 04:47 PM »
In order for White's proposed explanation to make any sense at all, you need to assume 3 things:

(1) momentum can be stored and propagated through virtual particle pairs that are created in the vacuum fluctuations of free space.  Call this the QVP.  Obviously this is White's controversial claim, but let's entertain the idea.

(2) storing momentum int the QVP must be "difficult".  If it were easy, then momentum would be lost into the QVP all the time, from all different types of interactions, and we wouldn't observe conservation of momentum in general.  For some reason, we must accept that the situation of standing waves in a specially shaped resonant cavity is a special situation that does enable momentum transfer into the QVP.
If electromagnetic waves transfer a fraction of their own momentum to QVP that is a perturbation of the propagation of electromagnetic waves. There may be a very small experimental bound on that in resonant cavities.

Offline Mulletron

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Re: FEATURE ARTICLE: Evaluating NASA's Futuristic EM Drive
« Reply #311 on: 05/03/2015 05:09 PM »
I want to openly acknowledge @TheTraveller who dropped in on the main thread to help out.

He offered fresh insight and stimulated discussion leading to progress being made today. He identified problems and offered solutions.

That kind of can do attitude is exactly what we need around here. I know an expert problem solver when I see one. Hats off to you! Hope you're here to stay.

Others dropping by should follow his example.
« Last Edit: 05/03/2015 05:32 PM by Mulletron »
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