Better write it as exp(iwt+ip(t)). The energy density is then constant.
AFAIK, all existing pnenomenology agrees with instantaneous gravitational force. There's no need to change the existing mathematical apparatus. Only the physical interpretation is modified.

Elsewhere on this BB I proposed a simple and cheap experiment to directly measure the speed of gravity. I believe that scheme is not unique in simplicity. What truly amazes me is that nobody even cares to measure the speed of gravitational force, as if the question were of zero importance.

<font size=-1>[ This Message was edited by: AgoraBasta on 2002-10-02 07:02 ]</font>

[quote]
On 2002-10-02 07:01, AgoraBasta wrote:
I'm surprised. I would have thought that you, of all people, would. [img]/phpBB/images/smiles/icon_smile.gif[/img]

Seriously, tests of the general relativity sort have been next to zero importance for over fifty years, I'm not sure why you'd expect that to change.

You're talking about this experiment, right?

Quite right. I've proposed to modify the Walker-Dual scheme to coaxial dipole config and use exceptionally effective signal pickup in the quartz oscillators. Speed of gravity could be measured in a simple desktop experiment.

Since the speed of light depends on the medium, I wonder if the speed of gravity likewise depends on the medium. Would gravity propagate faster in a vacuum than on the desktop?

I'd like to find out about many other things related to propagation of gravity... [img]/phpBB/images/smiles/icon_frown.gif[/img]

Better not. A time domain signal better not have an imaginary component, i.e. it must be completely real. If you wish to work in the frequency domain, that's fine. But you will have to use delta functions. [img]/phpBB/images/smiles/icon_smile.gif[/img]


<font size=-1>[ This Message was edited by: Wiley on 2002-10-02 13:40 ]</font>

If you want it quite real, you have to imagine two real components ping-ponging the energy while carrying it, like E&B are. The outcome is the same, though. Otherwise you have no travelling wave and no energy transport.

I really don't care if you use frequency or time domain, just as long as you use the correct form. I do recommend the time domain for phase modulation since the math is easier. All time domain responses are completely real; imaginary components are artifacts of the Fourier transform (frequency domain representation) which represent the phase advance or delay at a particlular frequency. The expression exp(i*w*t - i*p(t)) is not correct for the time domain nor the frequency domain.

No, you don't. Scalar waves are perfectly capable of carrying a signal. In fact I've phase modulated scalar waves many times.

I do agree that you will get the same result regardless of whether you use the time or frequency domain.

Ah, so we agree that phase modulation transfers energy.

<font size=-1>[ This Message was edited by: Wiley on 2002-10-02 17:40 ]</font>

Any wave requires exchange between two or more kinds of energy. A longitudinal pressure wave is perfectly scalar, yet there's an exchange between potential energy of compression and kinetic energy of the medium. So full energy flux is not phase-dependent in absence of dissipation.
If you keep amplitude constant - yes, energy flux is modulated slightly. But you always can modulate phase and amplitude jointly so that energy flux is constant. Have an example - modulation of EM-wave by longitudinal deformation of a waveguide.

This is true.
This is false. The total energy is phase independent if the phase is constant. This is not true for a phase modulation scheme.

Communication requires energy transfer.

This is true so far as no measurement has successfully determined the speed of gravity. Hopefully this will soon change.
This is a contradiction. The best mathematical apparatus says the speed of gravity is the speed of light (at least in the weak field limit). The interpretation of "instantaneous gravitation force" is incorrect for GR.


<font size=-1>[ This Message was edited by: Wiley on 2002-10-03 16:15 ]</font>

Wiley,

Existing theories require that no energy travels through real space ftl. Momentum can travel ftl (virtual photons). Teleportation/tunneling is possible. Macroscopic quantum systems can transfer information instantly if, and only if, your definition of information allows it. If you manage to build a very long quantum system, you may then send some limited info instantly, but then you wait for the system to regain coherence in no less than light-time. If you have an unlimited number of modes to decohere, you may transmit as much info as you wish while you wait for the used modes to re-cohere. Like I said - all depends on the definition of information.
Are you ready to declare gravity a non-quantum phenomenon?

Communication by a real wave requires energy transfer. Yet it doesn't necessarily require modulation of pre-existing flux of energy.

Gravity in this universe is connected with the mass-energy, so something about the gravity is omnipresent and immutable just as much as mass-energy is conserved. In some way, every piece of mass (every quantum particle) is omnipresent through its inherited gravity. I don't see why should two or more omnipresent entities require time to start interacting, while I do understand why it may take time to finalize the "transaction" in the inertial medium...
So my idea is that all interactions start as instantaneous, and only appear retarded because of interference of medium.

Don't try to build a strawman.

My claims have not changed. They are

• TVF is wrong about distuingishing the speed of gravitational potential and gravitational force in GR. They are intimately linked and travel at the same speed.
• The speed of gravity and the speed of information in (the weak field limit of) GR is the speed of light.

<font size=-1>[ This Message was edited by: Wiley on 2002-10-03 19:19 ]</font>

TVF is still in the process of arguing, here are his own words - In our interpretation of GR, both forces and information can be transmitted much faster than light. In the customary interpretation, neither is possible. The new technical paper, “Experimental Repeal of the Speed Limit for Gravitational, Electrodynamic, and Quantum Field Interactions”, by T. Van Flandern and J.P. Vigier, in Foundations of Physics v. 32(#7), pp. 1031-1068 (2002), deals with precisely this issue, and argues for the new interpretation.
As I pointed out to you, force and potential are very weakly connected and need not have the same speed.

No they are very much related. Your "force-pulses" are horrendously non-physical. In a homogeneous environment, the force field must be continuous; where do the magical force pulses come from?

Give me one physical example of where force is not equal to the gradient of the potential.

My force-pulses are a proof of non-unique correspondence between force and potential. Hence, your "force-potential" argument is mathematically impotent.
Potential is "non-physical", it's mathematical. Force is physical. Physically, potential is built out of force; mathematically - it's the other way around. It's possible to introduce potential for a force field while totally neglecting the physical nature of the force carrier and of the medium. This is exactly what is done in GR, but it still works. All the confirming experiments were done for very long distances and time intervals. It's not impossible that shorter time/distance experiments would produce some "internal structure" of the force that is otherwise averaged out.

This is quite untrue. I can use potential theory to solve the problem. From the potential obtain the force. And by uniqueness theorem, that solution is the only solution.
I suggest you look up the Aharonov-Bohm effect.

Regardless, you have not given me the example I asked for. Give me one physical example where force is not the gradient of potential.

Alright already even. You both seem somewhat entrenched, so let me lossen up the dirt a bit.

First, Agora; Wiley is correct in that Aharonov-Bohm shows potential to be 'physically' observable.
Nevertheless, Wiley, by invoking A-B effect are you not, therefore, required to admit a force arising outside of the field and thus agreeing with Agora on the possibility of a non-unique force arising from potential?
G^2



<font size=-1>[ This Message was edited by: Gsquare on 2002-10-04 23:10 ]</font>

I would suggest that quantum effects have non-unique explanations. The particle wave function, in the forbidden area containing B-field in that scheme, is not zero but rather is an evanescent wave; moreover, particle's own fields do affect the border conditions of that forbidden area. You may also check this link, that deals exactly with Aharonov/Bohm and related effects.
Furthermore, the Aharonov/Bohm effect is basically the same thing that works in every e