Sheeeeesh, where did you guys learn classical electrodynamics from? Maxwell's equations describe the whole enchilada of classical EM. Much more than just EM radiation. Check back in the thread; Tom started the belittle crap first. And his first statements were totally wrong. Without charged matter, there is no classical EM. And also nothing to even start EM radiation. J = rho = 0 is a man-made abstract approximation where you are far from the sources.
Well, someone has to make sure the newbies don't get false information that seems to propagate greatly on the unmoderated groups. There are different techniques for encouraging discussion on different groups. You responded, didn't you?
Why am I getting the feeling that is a "loaded" question? :-) In the classical sense or quantum sense? Well, we are talking about classical EM and charge density so matter in that sense is a tangible object. For the second question; unique compared to what?
It really didn't matter, classical or QM. Matter is a collection of charged entities, namely quarks... As for tangible, yes to us. However, tangible is an unscientific and vague terminology. All charges have an E & B field, right? If that field moves wrt any others would there not be induced feedback both the others charges fields around it? Micro eddy-currents???
Properties Fred, what physical property is unique to matter? Photons have momentum & energy. Fields have these too. What measurable property is unique to matter?
I don't understand what you're saying here. Take a region of space where j =3D rho =3D 0 and E and B satisfy Maxwell's equations at each point within that region. There is no abstract approximation as far as i can see.
Newbies learn from discussion, rather than people using the force of their personality to silence people.
Hi Benj, My chapter and verse line was only meant as a thank you for giving the volume and page number. (Sorry if it was taken otherwise.)
And yeah the theorists love to write everything in terms of potentials. (Which I find confusing sometimes.) In the lab I find I'm always trying to determine the fields.. which gives the forces or torques on things.
Fields and potentials are both descriptions of nature invented by humans. Feynman is also famous for describing nature in terms of the paths. The least action principle. If you are smart (which I'm not) you can show that all three descriptions give the same answer.
Thanks again for giving the reference... and quote,
George H.
PS Bill Gates has purchased the rights to the Messenger series of lectures that Fenyman gave at Cornell in '64. Google "Messenger series" +Feynman and you'll find it... unfortunately you have to down load yet another video player.. But it's worth it.
I am not a "turn the other check" kind of person. You slap me; you are going to get slapped back for sure. :-)
Yep, and Mr. Tom Old is still taking his wrong stance.
In classical EM some source (J or rho) had to start the EM radiation in the first place. Correct? That means that for all EM radiation, there is a J and/or a rho source. It might be an abstract approximation, but it can also be a very accurate one if you are very far from the source(s). Theoretically, the field of rho extends to infinity in classical EM. So rho can't be absolutely zero at any distance. For sure can be very close to zero though. This is really just common sense here.
Wasn't trying to silence anyone. These are unmoderated groups; anyone can say anything they want at any time. Let me tell you a little story here. I learned quite a bit of physics on these groups from one of the best physicists to ever participate on these groups. The late Franz Heymann, RIP. Franz used to ridicule the heck out of me almost on a daily basis. Of course, I deserved most of it. But it also got me to study hard to see if what he was saying was right or if he was just "yankin' my chain". :-) I even hired a particle physicist (Dr. Andy Inopin) to tutor me and eventually got a much better and more thorough understanding of modern physics. We ended up collaborating on a paper for an idea that I had. And now I understand where Franz was coming from. So the moral of this story is that there ARE different techniques and we must experiment with them to see how they work.
Do the experiment Benj. Setup a charge density so that you can measure the field E. Now, how do we go about setting up something so that we have rho? Have you lost your common sense all of a sudden? ;-)
These are leading questions, sure :) I am trying to get you to think, simplification, which leads to some rather surprising places/results. At least I thought so.
Localized, yes, this is where QM comes in. You said mass, that is normally synonymous with the term matter. I think you'll find inertia is the only property unique to matter. I wanted to lead here, however, if you can think of anything else, I'd love to know. If matter is all 'localized' charged fields moving them wrt to the underlying background ;; and/or other such should cause the dynamic EM effects, call this a counter EMF feedback that should resist any changes from any established equilibrium.
I call it a mistake! Objects are neither hard nor rigid, They just appear that way to you. You can't even touch one, they are mostly empty space with "subatomic objects" (whatever they are) suspended in fields. Tis you who have lost your common sense. You tell me exactly what charge is and I'll tell you how to create a charge density without any matter. You assumption that "charge" (whatever that is) can only form a distribution in matter is based soley upon the fact that charge sometimes DOES form a distribution in matter. However, I know of no basis upon which you can make the leap that charge REQUIRES matter to form a distribution. Is a whirlpool in the bathtub water an object? I suppose it is. But does it consist of water? Only with a lot of hand waving.
IANAQE ("I am not a quantum expert"), but I think you're getting some place with that last line.
Might that also be the distinction between a particle and a (pure) wave?
That is, all quantum entities (which is to say, _all_ entities, period) exhibit both wave and particle properties and behavior. Ergo, there is not such thing as a "pure" particle -- but entities with rest mass are a bit more particle-like than entities w/o rest mass.
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