Gravitational Engineering - What We Can Do Now

My major concern is radiation pressure creating false readings. I would be happy with attempts at isolating the system. Also mounting the entire experiment on springs or rubber mounts might be prudent.
- MV

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My impression is that they intend to use the contraction and expansion of the crystal as motion; which it is but it is extremely samll and the small signal; plus 1/r^2 applied to the movement is going to have an exceptionally weak influence.

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Yes Mac. I'm glad you said that. It's obvious. They forget gravity force applies at the center of mass and depends only on mass and distance. It don't matter if mass contracts or expands, the force remains the same. Even if contraction/expansion occues in a given direction and center of mass changes, we are talking here of extemely small deviations and signals much below the usual noise level.

The usual reaction of those who cannot accept critisism is to accuse the other party of misunderstanding and of a mallicious intent.

<b>Dream on AB</b> but remember there are very competent individuals reading your posts who can judge for themselves the quality of all statements made, including yours and mine. I was going to help make this experiment realistic and feasible but now I won't.

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[Mark]
...They forget gravity force applies at the center of mass and depends only on mass and distance. It do<img src=icon_emptyset.gif border=0 align=middle>n't matter if mass contracts or expands, the force remains the same.
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Not true. But as distance from the (combined) mass increases the force variations become rapidly smaller.

This is a good (well, so-so) case of a pessimist making sense. A mass expanding and contracting will, logically, produce smaller variations in its gravitational acceleration field than a mass that moves all parts of itself in the same direction at the same time (like a guitar string). And, logically again, those variations should drop off faster with distance than the variations from the guitar string.

This is what I was getting at earlier when I said I have a concern about using crystals for our resonant masses. And it is a larger concern for the <b>transmitter</b> than for the receiver.

I've been doing some off-line research to see if I can confirm my suspicions (I have), and I've contacted a crystal manufacturer to see if they can make affordable custom crystals that vibrate like guitar strings rather than like two masses on a spring. I'll keep you posted.

But for our first cheapo attempt we just might be able make any old crystal do the job. If it is really cheap, and fast to do, there isn't much to loose even if it fails. Besides, failure is as much a state of mind as it is an event. If MV's first try doesn't give us incontestable results, do we declare it a failure and give up?

And, the much higher frequency of a typical crystal (100 to 200 KHZ compared to the 40 Hz frequency of the rods in the Walker-Dual experiment) should make it a LOT easier to recognize the small timming differences we are looking for.



Note to MV -
Seriously consider building a parallel "control channel" that uses light as the signal medium.

1) Mount a light bulb (or LED) next to transmitter crystal and drive it the with (a signal derived from) the signal used to drive the crystal.

2) Mount a photo detector next to the receiver crystal and monitor it with one of the scope channels.

You should always be able to look at the drive signal and the photo detector signal and see a delay of about 1 nanoSec for each 30 cm of separation from the transmitter. This will give you a basic reality check on your experimental setup and technique.

In fact, building this control channel first might be a good way to get started.

Regards,
LB

Mark, I dont understand why you support the idea that a cheap system will not work. I agree with you that as you increase the precision you increase the $$; however, I think some important experimental factors such as the control idea listed are important. Can you continue to participate in this objective as the onboard critic without the criticism being taken as personal?

To all: Can you accept this criticism as an objective assessment without emotion? I can... Lets play well together


As an aside, performing science in Russia is challenging, I have been impressed in the past by the frugality of the russians. This doesnt mean that they are cheap or substandard, in contrast, they have solved and tested difficult problems in thrifty manners before. The simplicity of this project is sexy because I think SOME results will be given.

To all: I do not think our setup will give an excellent concrete answer... however it will provide some insight into technical problems that will have to be solved. Hey this is how the TV got made, tinkering is a kick...

-MV

mv,

The center of mass aspect of gravity is why I suggested attaching the crystal at one end and modulating a larger mass. That produces a center of mass change. But their response is it can't be done.

I for one think it will be necessary for any chance of seeing the displacement. Distortions of a crystal can induce COM change but not by much and not necessarialy.

Failure I don't thnk would be a cause to throw in the towel but assess the results and try to determine what is missing in the setup.

Because our testing is still ongoing I can't say as much at this point as I would like. But I can tell you this, as we anticipated, our test results are confirming that COM is not the only consideration.

Hopefully before this project reaches to far into hardware I will be able to shed some additional light on the subject.

<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>[mark] Let me ask you something AB: you want to measure SOG, right? When you have to crystals of constant mass separated by a constant distance the gravity force is constant, isn't it? By exciting the crystals you are not changing the gravity force but only the frequency of oscillation. Gravity force signal cannot be modulated that way. The only way to modulate the signal is by having one of the crystals move around.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>
Like I said, you've got it all absolutely wrong.
Field of dipole made of two masses on a spring along the dipole axis is g = G*m*(1/(r+d/2)^2 + 1/(r-d/2)^2), where r is the distance from the dipole's centre and d is the separation. For r>>d that expression turns into g ~= 2*G*m/r^2 + G*m*d^2/r^4, the variable component here is G*m*d^2/r^4. If we manage to fix one of the ends still, then we get the variable component as G*m*d/r^3. Now each of our xtals comprises a dipole that can oscillate by contracting/expanding when voltage is applied. The receiver dipole couples to variable field component with force 12*G*m^2*d^2*A/r^5 or 6*G*m^2*d*A/r^4 in those two cases respectively (A is the xmtr oscillation amplitude). Here we need to plug the voltage to amplitude and force to voltage conversion coeff's that are characteristic to our xtals, and then we get the sensitivity of our setup for non-periodic excitation. For the periodic signal at resonance freq that would be the Q times higher.
That would be it, more or less...