Let me interpret your "the speed of e&m forcé" as "the speed of propagation of the e&m field".  And the latter, I understand, is equal to c, not infinite.

Simon,

Thank you for your comment.

First, please reference the "speed of gravity" in WIKI. In it the speed of the static field is stated.

Second, please reference the REFERENCES [1-3] listed here. Smirnov-Rueda team claimed that they measured that the speed of the bound electromagnetic field is limit but is larger than the speed of light.

Cornwall,

I think you are right. In the beginning, it need be revised as:

In the “speed of gravity” in WIKI, it is stated that the speed of the static/interactive field…

But, it is clear, there is no experimental evidence and an accepted conclusion for the speed of the electromagnetic force (or static/interactive field). Or, the Smirnov-Rueda team listed in the Reference [1-3] cannot be published.

In the beginning, the state:"In the current physics, it is believed" was revised as

"In the “speed of gravity” in WIKI, it is stated"

The full text of Wikipedia concerning ``infinitely rapid propagation of static fields'': as you will appreciate, they say nothing of the sort. Best wishes!

``The consequence of this is that static fields (either electric or gravitational) always point directly to the actual position of the bodies that they are connected to, without any delay that is due to any "signal" traveling (or propagating) from the charge, over a distance to an observer. This remains true if the charged bodies and their observers are made to "move" (or not), by simply changing reference frames. This fact sometimes causes confusion about the "speed" of such static fields, which sometimes appear to change infinitely quickly when the changes in the field are mere artifacts of the motion of the observer, or of observation.

In such cases, nothing actually changes infinitely quickly, save the point of view of an observer of the field. For example, when an observer begins to move with respect to a static field that already extends over light years, it appears as though "immediately" the entire field, along with its source, has begun moving at the speed of the observer. This, of course, includes the extended parts of the field. However, this "change" in the apparent behavior of the field source, along with its distant field, does not represent any sort of propagation that is faster than light.''

Leyvraz,

Thank you for your comment.

This question was revised. The content involved with the instantaneous speed was deleted.

Excellent! I have started to look at the papers you cite. They are interesting, but I still need to convince myself that there is no contradiction with other well known results. It should be said that Maxwell's equations certainly predict that the propagation speed of the electromagnetic field (it does not matter whether bound or radiative) is c. Thus the papers, if correct, observe a contradiction to Maxwell's equations for a system in which classical Electrodynamics is expected to hold with a high degree of accuracy. This is worrisome at best.

Leyvraz,

 There is no experimental evidence for the speed of electromagnetic force. And, Smirnov-Rueda team only measured the speed of the electromagnetic field. It is certain, the speed of electromagnetic force is a fundamental constant for physics. We need such a constant. If we measure this constant first, we shall contribute a fundamental constant for physics. I very hope to measure it. Are you interested in it?

In addition, the speed of the interacting electromagnetic field also can be measured with this method. We can know whether the two speeds are equal to each other.

Yin> is no experimental evidence for the speed of electromagnetic force

The validity of the Maxwell equations is tested in innumerable ways. And it is a consequence of Maxwells's equations that the "electromagnetic force" travels at exactly the speed of light in vacuum. Which, by the way, would not be exactly true if we lived in a world of two or four space dimensions (where the speed of light would only be an upper limit).

It can be practical to separate the electromagnetic fields around a radiating system into near-fields and radiation fields. This separation is non-relativistic, and leads as an artifact to the result that the two components individually seems to transmit signals faster than the speed of light. However, the sum of faster-than-light signals from the two components cancels exactly.

Olaussen,

Maybe, a lot of physicists think as you. But, many of physicists do not think so. It is clear, if everyone agreed that the speed of the electromagnetic force has been experimentally known, Smirnov-Rueda team’s work could not be published.

Yin> be published.

Experimental work, if done seriously, should always be published. I guess the editors of the respective journals used that principle, detecting no obvious flaws.

But I think there are problems with the experiment. Most other physicists must think the same, otherwise the results would have been discussed all over the place. Because violation of Maxwell's equations for electromagnetism is much more dramatic than faster-than-light neutrinos.

I looked through the Europhysics Letters paper. The authors do not claim that they have been able to transmit signals faster than the speed of light, which is impossible according to equation (1) in their paper, or that they have measured anything in violation of that equation. From a fundamental point of view these are the important aspects.

Practically, the possibility of communicating via near-field effects appears to be an important feature of modern mobile phones (but not faster than the speed of light). 

Olaussen,

However, their result is radically different from the general view of point.

Dear Yin,

Yes, their result is indeed very different, in particular since they do seem to claim faster-than-light transmission of near fields. The issue is that this contradicts Maxwell's equations. Thus equation (7) of the first reference you give (J. Apll. Phys 101) is, according to the authors, something that does not require theoretical explanation. Indeed, it has none and is in contradiction to everything that is known. This leads us to worry, as to whether there is a mistake in the experiment or whether the authors have not overestimated their accuracy. I do not know where the problem is, but I would assume that the errors are underestimated by the authors. Thus on Fig. 6 of that reference, one would like to see errror bars in the experimental data. The v=c curve only deviates from the experiment when both numbers are close to zero. Finally, the ``bound field'' is not a physical object: it is the result of a subtraction of the radiating field, which is a theoretical construct, and the experimentally measured field. This has two consequences: first, the physical significance of the result is somewhat unclear. Second, once the signal becomes small, we cannot be sure whether the separation was cleanly made in the experiment. Thus, in the small signal region, which is precisely where the ``new'' effects are found, we are exposed to problems due to large cancellations, and thus large error bars. I thus cannot find in the article you quote, the kind of extreme high precision and simple layout that I would expect from any experiment claiming to invalidate a theory as well established as Maxwell's equations.

Best wishes,

Francois

Dear Leyvraz,

Thank you for your serious comments.

I think a point of view by the Smirnov-Rueda team is useful: the experiments that were very difficult to perform before 1900 have been neglected by physicists. Some of the important results need be known from these experiments. For example, the speed of the Coulomb force is such a result. Now, these difficult experiments become easy. It is time to perform some of them.

Best wishes.

Yin

Dear Yin

OK. But you should not think that the experiment you have in mind to determine the speed of the Coulomb force is easy. Two difficulties: one, to move one of the charges by a significant amount in less than a nanosecond. Two: detecting a movement caused by a force which is not huge, over a time of nanoseconds. Remember that a force of 1 N acting on one kg for 1 ns causes a displacement of 5 times 10^{-19} meters.

Best wishes,

Francois

Dear Leyvraz,

Thank you for your comments.

I think, some of the difficulties were considered in the design. First, the motion of two magnetisms is observed. Therefore, many of the disturbing factors can be cancelled. For example, if a time T0 is needed to make the magnetisms have a velocity v, this T0 is same for both the magnetisms.  Thus, T0 need not be measured. Second, the gravity can be used. As the M1 and M2 are suspended by the magnetic force of M3, the gravity can make M1 and M2 moved very quickly.

Best wishes.

Yin

Yin,  you may be interested to learn about yet another experiment that demonstrates superluminal effects with electric fields of fast moving charges:

R. de Sangro, G. Finocchiaro, P. Patteri, M. Piccolo and G. Pizzella, "Measuring propagation speed of Coulomb fields", Eur. Phys. J. C, 75 (2015), 137. arXiv:1211.2913v2

Dear Eugene,

Thank you for your message.

Best wishes.

Yin

I still think you should work out hte details of your design, in an approximate way. The following questions are important: if you want to cut off the current in a magnet, for example, what is the characteristic time for the current to decay? It may well be milliseconds, and this is a serious problem, since th epropagation times you aim to measure, being I assume, some meters, at the speed of light, would be tens of nanoseconds. The other problem is the motion induced in the magnets. You say gravity will make the magnets move ``very quickly''. But you have to consider your timescales: you want to see whether something has moved over a time of tens of nanoseconds. Over such short times, the position changes caused by an acceleration like gravity are very small and presumably undetectable. Do try to work numbers, however approximate.

Best wishes,

Francois

Dear Francois,

Thank you for your questions.

I attached a pdf file entitled “Design to measure the speed of the electromagnetic field/force” here. Some of your questions may be answered.

Best wishes.

Yin

Dear Yin,

I still think you should be *much* more specific: what will you measure with your high-speed camera? I do not think you will measure a time so much as the displacement of your magnets. How large is that displacement? Do you think you can measure it? In other terms: what displacement must be measured to distinguish the kind of Deltat T that you would be led to expect?

Best wishes,

Francois

Dear Francois,

Thank you for your questions.

In Fig.1, if the speed of electromagnetic field/force is v, a time T1 is needed for the electromagnetic field/force propagating from M3 to M1, T1=L1/v. For the same reason, T2= L2/v. ∆T= T1- T2.

As the fields of them are vanished at the same time, assuming that M1 starts to be fallen by the gravity at time t1, M2 shall start to be fallen at the time t1-∆T. At time t2, the speed of M1 accelerated by the gravity is vM1=g∆t. And, the speed of M2 shall be vM2=g(∆t-∆T). ∆t=t2-t1. Therefore, vM2- vM1=g∆T. As vM1 and vM2 are observed, ∆T shall be observed. ∆t can be offset, it need not be considered. In the second case, ∆T can be observed with the same way.

If the time on the level of 10-12 seconds can be measured with the high speed camera, vM1 and vM2 can be easily measured as they can be observed by the eyes of human. But, I have not had any practice about the high speed camera. So, I need coworker who is familiar with this camera.

Best wishes.

Yin

First of all, a camera does not directly measure velocity, but positions. So M_2 has fallen for a time Delta T when M_1 is still not moving. By how much will M_2 have moved when M_1 just starts to move. The answer is g(Delta T)^2/2. For Delta T sim 1 m/v is roughly 1 ns, we have a motion of roughly a millionth part of an angstrom.

Another approach goes as follows: estimate the minimum distance which the camera can reasonably measure. Since it is an optical camera, it cannot be much less than the wavelength, which is roughly 1/2 micron. So how long do you have to wait until M_1 and M_2 both have moved by this length? Roughly this should be of the order of milliseconds. But if you see nothing happen until a few milliseconds, how can you guess up to nanoseconds, which started first?

Best wishes,

Francois

Dear Francois,

Thank you for your questions.

I am very sorry I am not familiar with using the high speed camera. But, I think that the camera can directly measure velocity. It is usually said that this camera can be used to measure the time on some of the level of time, and “Recent advances include the use of High Harmonic Generation to capture images of molecular dynamics down to the scale of the attosecond (10−18 s).” please see:

http://en.wikipedia.org/wiki/High-speed_photography

Best wishes.

Yin