In reply to Abd ul-Rahman Lomax's message of Sat, 07 Nov 2009 13:56:54 -0500:
Hi,
[snip]
First, let me state for the record that I have serious doubts that this device
works, however I'm trying to keep an open mind, and envisage a way in which it
*might* work. The reason for this is their claim to have measured 16 mN of force
and calculated 16.6 mN. That's awfully close for pure coincidence.
>>I think the original author's intent was this (though I didn't study
>>it properly
>>and may have completely misunderstood):-
>>
>>The drive consumes energy at a constant rate, because we supply energy at a
>>constant rate.
>
>Who (and where) is "we"? I hate to be a stickler, but it's important
>here to become very precise. Where is the energy coming from? It
>makes a difference. It looks to me like the emdrive trick is a result
>of mixing frames of reference.
I assumed that the energy would eventually be carried on board, but that
obviously wasn't the case during their experiments.
>
>> Part of that energy goes into heating the device, and part goes
>>into propelling the vehicle.
>
>Heat is the kinetic energy of individual particles or photons.
>Kinetic energy requires a frame of reference. What's the frame? If it
>is the "craft," which is where the energy conversion is taking place,
>and there is no interaction ("reactionless") or emission of energy
>(the same)
> then there is no kinetic energy at all, unless it is
>entirely internal, i.e., heat or rotary inertia or oscillatory
>inertia, or other contained forms of kinetic energy. Inside the "black box."
Heat is obviously internal, however that's only the waste, not the main
component. If this thing works at all, then I see it working as follows:
Ask yourself the question "How does a photon propagate?". It clearly moves
through space, apparently continually "pushing off" (reacting) against space
time (the vacuum/aether if you prefer) itself, just as in the case of a wave in
water, the molecules react against one another.
Now suppose that this device makes use of that reaction force between the photon
and the vacuum (virtual particles from the vacuum, if that's your thing), to
"get a grip" on the vacuum. Though this "grip" may be tiny, they amplify it by
using resonance, i.e. some part of it is multiplied by the number of times that
the energy bounces back and forth before being lost as heat. Momentum is
conserved, because it is shared with the vacuum, essentially with the whole
universe (and maybe more, depending on your definition of universe).
>
>It's a bit depressing to see the arguments defending the emdrive.
In my previous post I wasn't really trying to defend it, just trying to explain
what I thought Shawyer was saying.
This post OTOH is more of a defense. BTW last time that this device was a topic
of conversation on Vortex I was on the side of the prosecution. I can see both
reasons why it may work, and reasons why it might be unlikely to. The real proof
of the pudding is in the eating. IOW all our arguments are pretty much
irrelevant. It either works in practice or it doesn't.
Put the thing in a weightless environment (preferably in a vacuum), fire it up
under it's own power, and see what happens.
>I've said, if someone has developed a method of reactionless force,
>which is what the emdrive claim is, boiled down, and has demonstrated
>it, there would be enormous implications to basic physics, and,
>indeed, conservation of momentum is violated.
It's only "reactionless" in the sense that there is no reaction mass. That
doesn't necessarily mean that it isn't pushing/pulling against "something".
>Just take two
>snapshots: the situation before the emdrive is turned on, and the
>situation after it is turned off. Conservation of momentum is with
>respect to a particular non-accelerated frame of reference, and with
>respect to any contained system, any "black box" that is not
>absorbing or radiating anything, or where the radiation is balanced.
>Soppose we arrange the emdrive and power source a faraday cage inside
>a sphere, such that the temperature of the sphere is uniform (done
>with heat-sinking and radiation inside the sphere), and the sphere is
>of uniform material. Likewise the environment is arranged to be
>uniform in radiation pressure against all sides of the emdrive sphere.
>
>This is all done in free fall in deep space, so that gravitational
>fields are uniform. So the emdrive-sphere starts in the center of our
>experimental space, no connections or contacts or interactions between them.
>
>In our frame of reference, the experimental space, the net momentum
>of the emdrive sphere begins at zero. The emdrive has a timer which
>turns it on for a period then shuts it off, and the internal
>components settle to zero motion (except for heat). What is the net
>momentum of the emdrive sphere? If it is not still zero, then
>conservation of momentum has been violated.
See above.
>
>Yet Shawyer claims that conservation of momentum is not violated. He
>is obviously contradicting his claim of acceleration!
No, see above.
>
>> If we assume that the energy that goes into
>>propelling the vehicle is converted into kinetic energy (of the vehicle), then
>>the *power* required is the time differential of kinetic energy i.e.
>>d(1/2*m*v^2)/dt. This is d(1/2*m*v^2)/dv * dv/dt, i.e. m*v*a (where a =
>>acceleration).
>
>If we assume that pigs are fishes, then we can all breathe water.
...only if we are pigs. ;^)
>
>Kinetic energy of the vehicle exists in our ("stationary") frame of
>reference. If the vehicle accumulates kinetic energy in our frame,
>then, sure, this energy must have come from some source, presumably
>the power source inside the emdrive system.
I believe that is what the inventor is claiming.
>
>Now, imagine a larger black box, it encloses our frame which encloses
>the emdrive system. Call our frame the "room," perhaps it's a space
>station experimental lab. And there is a hole in the wall of our lab.
>And the emdrive shoots out that hole. What happens to the lab? Does
>the lab move in the opposite direction?
No/yes, because the reaction is shared with the vacuum itself, not just with the
lab. IOW the lab does move, but only in as much as the universe as a whole
moves, which is to say immeasurably small. Though I guess this does raise the
issue of the speed with which the reaction force can be transmitted through the
fabric of spacetime.
>Regardless of internal
>mechanism, in the larger frame, we have a object, the lab, which has
>ejected a bit of mass.
No, the lab didn't "eject" the "bit of mass" i.e. there was no force acting
purely between object and lab as there would have been had there been e.g. an
explosive release of compressed gas between the two.
Every force has two ends. In this case one end is connected to the object,
however the other end is connected to the fabric of spacetime itself, not to any
particular object.
>From normal physics, looking at this from the
>larger frame, there is now kinetic energy in the emdrive system, is
>there kinetic energy in the lab system?
No-ish. See above.
>
>Conservation of momentum would say, yes, and they balance. Net
>momentum is zero. However, if the emdrive is reactionless, there is
>no kinetic energy imparted to the lab system. So there is net kinetic
>energy. No recoil. No equal and opposite reaction.
See above.
>
>>Now since the power input is constant, m*v*a should also be constant, which
>>means that as velocity increases, "a" decreases (assuming constant mass).
>
>In F = ma, there is an assumed frame of reference. And it is assumed
>that a force is acting on more than one body, there is no such thing
>as a reactionless force in Newtonian mechanics, nor in any mechanics
>as far as I know. "Force" means one body or system acting upon
>another."
In this case I thinks it's more a matter of a force between an object and
literally *everything* else. Consider two hockey pucks on the ice. One of them
could move by pushing off against the other (which is essentially the only way
we know), or one could hammer a nail into the ice, and push off against that
(while the other complains bitterly about breaking the rules ;^). If this device
works at all, then I suspect it is by hammering a nail (or at least a small
tack) into the ice.
>A system can't push itself, and, to my knowledge, no
>exception is known at any scale. He's claiming an exception, based on
>some very shaky math and a very shaky experiment, with very little
>detail provided and, given the length of time involved, very little
>publication and no independent confirmation of even his small
>reported effect. And the experimenter is a microwave engineer who
>would not necessarily have any expertise in or experience with
>calculating radiation pressure.
All good reasons why this may not work.
>
>Consider this: in the waveguide, microwave energy is being reflected
>back and forth. There will be pressure against the walls of the
>guide, all the walls. normally, the pressure inside a cavity will be
>equal, unless there is an outside force acting (such as gravity,
>which would increase the pressure at the bottom and decrease it at
>the top, generating a force equal to that of gravity on the contents.)
>
>He claims that the pressure on the sides of the waveguide or cavity
>can be neglected.
This bothers me too, and was actually the basis of my previous objections, and
I'm afraid I don't really understand his explanation of why this is not a valid
objection, though I get the sense that it has to do with the change in
refractive index due to the introduction of a dielectric into part of the
device, which apparently removes the symmetry.
>Now, look at a photon, and let's suppose Q is
>infinite, the walls of the cavity are perfect reflectors. Now
>consider a microwave photon, it has momentum. It is reflected from
>the side, a glancing blow (i.e., low-angle reflection). This will
>create a force on the side. If the side is oriented in the direction
>of the photons, this pressure would be minimal, but that would imply
>that the cavity is the same size at both ends (assuming the ends are
>parallel planes).
That was my argument exactly, last time around.
>Shawyer seems to assume constant radiation pressure
>per unit area, but neglects the sides, so, of course, he ends up with
>a net force in the direction of the larger area. In fact, if somehow
>"friction" with the sides were avoided, if the waves or photons could
>be conducted with no pressure on the sides, the pressure per unit
>area on the smaller end cap would increase. Such that there is no net force.
>
>More likely, there is some of both effects taking place; there is
>pressure on the sides, and so there is a force acting on the sides
>that partially balances out the force acting on the large top endcap,
>and there is increase of pressure on the smaller endcap; my guess is
>that the latter could be a small effect. If I imagine water waves,
>focusing the wave on a small area could increase the pressure, indeed.
>
>There are many possible explanations for some force to be detected in
>Shawyer's demonstrated; any time you have a large mass and lots of
>power, relatively subtle effects that might ordinarily be disregarded
>or considered negligilbe, can be seen if you start to make very
>subtle measurements. Dean drive. The effect of vibration on
>scales.... Heat and effects on air....
...more good reasons.
>
>
>>If "a" decreases with velocity, then so does the thrust. Note that
>>relativity is
>>not taken into account here. All of this is true even at low speeds.
>>
>>Essentially all they are saying is that at constant power input, the
>>incremental
>>change in velocity decreases as you go faster.
>
>Now look at it from the emdrive system. There is no "velocity." While
>the emdrive is on, if it's working, there is acceleration,
>experienced as equivalent to gravity, right? An accelerometer will
>measure this acceleration. Because there is no interaction between
>the emdrive system and the outside frame of reference, and because we
>can see the outside frame accelerating, we know the relationship
>between the acceleration we experience and the apparent motion of the
>external world.
>
>But, with the emdrive operating, does the acceleration we experience
>(which is precisely equivalent to the "force" acting on our emdrive
>system) decline with velocity? If so, we now have a means of
>detecting absolute motion.
You mean this doesn't happen when you drive a car? Isn't it harder to accelerate
from 50 to 60 than from 10 to 20? If not then please explain where I screwed up.
(Ignore the fact that friction increases with velocity).
[snip]
Regards,
Robin van Spaandonk
http://rvanspaa.freehostia.com/Project.html
