Does magnetic propagation follow the speed of light? E.g. if you had some magnet of incredible strength and attached an iron wire that is one light year long to it, would the other end of the iron wire begin to show a magnetic field in a year, or could it possibly be faster than a year?
In your example, the relevant speed isn't the speed of propagation of disturbances in the magnetic field, but rather the speed of the alignment of iron atoms.
You are really asking "Does magnetization of a wire/metal propagate at the speed of light?"
The answer is no; it propagates at the speed at which each individual iron atom can align its polarity.
If you are asking, "Do changes in the magnetic field propagate at the speed of light?"
The answer is yes; if a giant, huge, powerful magnet appeared one light year away out of nowhere, then it would take exactly one year for magnets on Earth to feel its pull (however small it may be). That is, it would take one year for the "magnetic force" to reach the Earth.
It cannot be faster than a year, because electro-magnetic waves propagate with the speed of light. The magnetization of the wire will take longer, because it depends on the reaction of the iron atoms to the external magnetic field (they align according to the external field).
As a rule of thumb, one can say that "if it is possible to notify a friend far away with this" then we are talking about the transmission of information, and that can be done with light speed at most according to special relativity.
In your case you could set of an alarm clock on the other end of the wire once the magnetic field reaches the end :-)
My brother and I have made some experiments a number of years ago using a CB radio and a 50 MHZ oscilloscope. When the regular CB antenna was replaced by a single loop coil of approximately 6 inches in diameter with a capacitor shunted across the ends forming a parallel LC resonant circuit tuned to 27 MHZ, the signal from this antenna was infinitely faster than the speed of a regular radio signal.
When the regular radio antenna was replaced by an antenna which only sent out a signal of what one might call electrostatic nature, we got the same results.
These experiments lead us to believe that magnetic fields and electrical fields when acting alone propagate infinitely faster than the speed of light.
Some of our experiments are described at the following website. (The wave patterns are actual oscilloscope printouts): http://www.tuks.nl/pdf/Reference_Material/Fast_Light/Erdmann%20-%20Faster%20than%20Light,%20the%20Revolutionary%20Radio%20Antenna%20that%20Conquers%20Space.pdf
However, see http://arxiv.org/abs/1211.2913 "Such an odd behavior can be found also in electromagnetism, when one computes the propagation of the electric fields generated by a set of uniformly moving charges. As a matter of fact the Li\'enard-Weichert retarded potential leads to a formula indistinguishable from the one obtained assuming that the electric field propagates with infinite velocity. Feyman explanation for this apparent paradox was based on the fact that uniform motions last indefinitely.
To verify such an explanation, we performed an experiment to measure the time/space evolution of the electric field generated by an uniformly moving electron beam. The results we obtain on such a finite lifetime kinematical state seem compatible with an electric field rigidly carried by the beam itself. "
if the speed of the coulomb force could be > c then what of magnetism?
protected by Qmechanic♦ Jun 15 at 6:14
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