lemur Posted February 10, 2011 Share Posted February 10, 2011 Since changes in a gravity field supposedly move at the speed of light, I am wondering if the same is true for changes in a (static) magnetic field (e.g. a bar magnet). First, do such magnetic fields change/ripple under any circumstances and, if so, so the "ripples" move at C. If so, are these "ripples" EM waves or something else? If not, why don't/wouldn't magnetic fields change/ripple in the sense that gravity fields are supposed to be able to? Link to comment Share on other sites More sharing options...
davey2222 Posted February 10, 2011 Share Posted February 10, 2011 I think if you move the bar magnet back and forth you are making changes in the magnetic field at an arbitrary fixed point. According to theory EM waves are created. Link to comment Share on other sites More sharing options...
Schrödinger's hat Posted March 4, 2011 Share Posted March 4, 2011 Most changes in an electric or magnetic field will cause an em wave which carries energy away. All changes will propagate at C, regardless of whether they cause a ripple which moves away from the object, carrying energy with it. If you have a charged particle moving at constant speed, or constant acceleration (or a magnet -- not 100% sure about accelerating magnets, can't see any logical reason why not. Moving ones are def. the same), it won't create a travelling wave, but if it changes acceleration, it will. These waves are more easily produced than gravity waves, and much easier to detect. Link to comment Share on other sites More sharing options...
lemur Posted March 4, 2011 Author Share Posted March 4, 2011 Most changes in an electric or magnetic field will cause an em wave which carries energy away. Shouldn't there be some threshold of energy for a "ripple" to result in an EM wave? Or would the threshold for resulting in the EM wave be the same as the threshold of energy needed to generate the ripple in the first place. Another way to look at this is whether a magnetic or electric field has the capacity to contain "ripples" without that energy "spilling" out as EM radiation. Link to comment Share on other sites More sharing options...
DrRocket Posted March 5, 2011 Share Posted March 5, 2011 Since changes in a gravity field supposedly move at the speed of light, I am wondering if the same is true for changes in a (static) magnetic field (e.g. a bar magnet). First, do such magnetic fields change/ripple under any circumstances and, if so, so the "ripples" move at C. If so, are these "ripples" EM waves or something else? If not, why don't/wouldn't magnetic fields change/ripple in the sense that gravity fields are supposed to be able to? Shouldn't there be some threshold of energy for a "ripple" to result in an EM wave? Or would the threshold for resulting in the EM wave be the same as the threshold of energy needed to generate the ripple in the first place. Another way to look at this is whether a magnetic or electric field has the capacity to contain "ripples" without that energy "spilling" out as EM radiation. From your question it is fair to stick to classical electrodynamics. There is no such thing as "changes" to a static field, electric or magnetic. If the field varies in time (i.e. if it changes) it is not static. Any time varying electromagnetic field creates a propagating electromagnetic wave, and the speed is c. Note, this is a propagating electromagnetic wave, not a propagating electric wave or a propagating magnetic wave -- both come with the package. There is no classic limit on the frequency of an electromagnetic wave. Quantum mechanical systems, depending on the specific system, may have limits related to the discrete spectrum of the Hamiltonian. Link to comment Share on other sites More sharing options...
lemur Posted March 5, 2011 Author Share Posted March 5, 2011 From your question it is fair to stick to classical electrodynamics. There is no such thing as "changes" to a static field, electric or magnetic. If the field varies in time (i.e. if it changes) it is not static. Any time varying electromagnetic field creates a propagating electromagnetic wave, and the speed is c. Note, this is a propagating electromagnetic wave, not a propagating electric wave or a propagating magnetic wave -- both come with the package. There is no classic limit on the frequency of an electromagnetic wave. Quantum mechanical systems, depending on the specific system, may have limits related to the discrete spectrum of the Hamiltonian. I'm not sure what the OP meant by "rippling" but it makes me wonder whether two repellant bar-magnets squeezing tightly against each other doesn't change the shape of the field. The two magnets only make contact via their mutual repulsion, so something has to transfer the force through the fields to the magnets themselves. So that leads to the question of whether the fields are perfectly inelastic or if they flex, bend, ripple, etc. Too bad they're not made of light so you could just blow smoke through them to see what they're doing. Link to comment Share on other sites More sharing options...
DrRocket Posted March 5, 2011 Share Posted March 5, 2011 I'm not sure what the OP meant by "rippling" but it makes me wonder..... ????? Did you not make the OP ? Link to comment Share on other sites More sharing options...
lemur Posted March 5, 2011 Author Share Posted March 5, 2011 (edited) ????? Did you not make the OP ? lol. I thought it seemed like a thread I had started. Sorry to laugh - it's all I can do considering the embarrassment. And here I was thinking I wasn't a crackpot because someone else was entertaining a similar notion. Edited March 5, 2011 by lemur Link to comment Share on other sites More sharing options...
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