sci.physics.electromag

On Mar 8, 7:00 pm, "Timo A. Nieminen" wrote:

> Define "causal".

A "causal" form of an equation is when one side of the equation is the
CAUSE of the other side. Maxwells equations are usually written so
that one side is merely equal to the other side but not the cause of
it.

> The usual form of the Maxwell equations takes retardation into account.
> This is one of the big mathematical advantages of a field theory - you
> only need the present-time charge and current distributions, the field has
> all the information we need about past charge and current.

No they don't. They are not causal so they don't take it into account.
They can of course be rewritten in causal form which does take it into
account. So (we've argued this here before) the problem above is your
term "usual form". Maxwell's equations are however causal in essence
and can be rewritten in that form. I guess I don't know what "your"
"usual form" is. I'm just going by textbooks and things like that.

> There is no "usual argument" for extracting a wave equation from the
> Maxwell equations, it's a mathematical derivation, based on the
> mathematics alone. No argument that E creates H or vice versa is needed.
> That some people might use such language to explain the derivation in no
> way makes the derivation invalid or dependent on such assumptions.

Maybe I have no data to back up my statement of "usual arguments" or
on just how many derivations of the wave equation are done a certain
way. I do know that what I said is true sometimes and what you say is
true sometimes as well. AS to percentages, I'll just have to back off
and say I have no data.

> The usual form of the Maxwell equations (the Hertz-Heaviside equations) is
> equivalent to electrodynamics done using potentials only, in the Lorenz
> gauge, which explicitly takes retardation into account. Thus,
> Maxwell-Hertz-Heaviside takes retardation into account, even if not
> obviously.

Yes, this is true. I just said above that Maxwell's equations are in
essence causal. We established that here in a previous thread .

> No. I call religion religion. You appeared to be denying the reality
> fields, as a matter of dogma, without any justification.

Define religion. I DO deny the reality of fields. but it's not dogma.
it's definition. You please explain to me just what give fields
"reality". What particles are they composed of? What energy is their
essence? There is none. They are mathematical constructions! They
only have reality in the brain of a mathematician! The fact that this
mathematical model happens to give results that are in reasonable
agreement with what is measured in the terms of energies, forces,
currents and velocities of real particles does not somehow impart
"reality" to your model. Useful yes. Reasonable answers (we can't be
sure they are "correct"), yes. reality? I don't think you can prove
that.

> You attack supposedly-dogmatic belief in the existence of fields as
> "religious". You attack the agnostic statement that we don't know whether
> fields are really "real" as "religious". Would you attack your own dogma
> as "religious"?

Whoa! Is this a cheap debating trick? This is sort of getting to be
about semantics. If you wish to define a 'field" as the observed
forces and actions of charges moving and static then everything you
say is correct. However that is NOT my definition. I say that the
charges and the forces are observed reality. Field theory is a model
IMPOSED upon that reality. To me this isn't dogma it's logic.

> You also mis-characterise Fred's claims. (Again, what's with the cheap
> debating tricks?) I didn't see any claims that Maxwell's equations are
> absolutely true in ALL cases and never fail, though I did see an
> acknowledgment that Maxwellian fields are a classical average of quantum
> behaviour.

What is this a cheap debating trick? How about this quote:

"Sorry, Maxwell Equations with its fields TOTALLY describe that
phenomenon. Anyone that can prove otherwise has a free trip to
Stockholm. ;-) "

Does that word "TOTALLY" not say it all? He leaves NO room for ANY
exceptions. Please do your research before spouting off.

> A physicist's statement that a "theory is true" is very different from a
> mathematician's statement that a "theorem has been proven". Both will use
> "true", "proof" and "correct" in ways that significantly differ from the
> everyday English usage.

Absolutely! Now we are getting somewhere! You are starting to
acknowledge the difference between a mathematical model and the
underlying reality which the model is (hopefully) reflecting. Proving
a theorem (as I have stated repeatedly here) has NOTHING to do with
"reality". It only has to do with self-consistency within whatever
mathematical system the mathematician has proposed!

> If you want to discuss physics (or the history of physics, or the
> philosophy of physics), do so. If all you want to do is make unsupported
> dogmatic statements, attack your respondants, raise strawmen, and practice
> your usual cheap debating tricks, then there isn't much point in replying
> to you.

Same goes for you, I'd say.

> What does need to be brought is exactly what is meant by "exist". It is
> absolutely certain that electromagnetic fields exist in the sense in which
> they are needed in order to be used in the Maxwell equations - D and H are
> functions of space and time related to charge and current densities by the
> Maxwell source equations, and E and B are functions of space and time
> giving the force that would be exerted on an idealised test
> charge/current. But this is existence in a mathematical sense, not a
> physical sense.

NO! NO! NO! GET THIS STRAIGHT! Is is NOT "absolutely certain that
electromagnetic fields exist"! What exists are are distributions of
electromagnetic FORCES AND ENERGIES which appear to follow the rules
of field theory to a degree! Just tell us WHY it is so hard for
people here to get this simple concept. Is physics today THAT screwed
up?

It seems to me that you are using a different definition of "field"
from me. Apparently you (and Fred) define a "field" as any physical
phenomena that more or less seems to follow the rules of "field
theory". My definition of a "field" is that mathematical construct
generated by field theory.

However, you are correct that if we wish to pursue this discussion, an
agreed upon defintion of "reality" or "real" ad well as "field" is
essential. I presume a key question in your mind would be "is
mathematics real?" I was trying to avoid going there. But it
certainly IS clear that mathematics is not forces and energies in
space (unless you count those inside the brain).

> Which is why I think conservation laws are very important here. If the
> fields possess energy, momentum, or angular momentum (or other fields
> possess charge, mass, or whatever), then one can say they are physically
> real. The current situation is ambiguous.

Yes it is ambiguous. What exactly does it mean when we say a "field
has momentum or energy"? WHAT has moment. WHAT has energy? Maxwell
noted that energy can be transmitted in only TWO ways. One is through
the transfer of mass (kinetic) and the other is in the transmission of
waves in a medium. In a so-called "field" there is no mass. But lo
and behold, modern physics says there is no medium either!!! Whoa! So
what happens is just what people here have been doing. They assign a
reality to the MATH as IF it were somehow "real". I'm sorry, but this
is hand-waving and no explanation of anything!

> Do you realise that this is, in essence, merely your strawman?

Do you realize that this is just your cheap debating trick to wiggle
out of my point?

> Roundness/flatness of the earth is easily determined, with science even,
> and was well-known to the ancient Egyptians, Greeks, and Chinese (and
> likely others).

Not relevant. The issue is how PEOPLE viewed the situation, not what
SOME people knew.

> Anyway, the point is that physics _can't_ be dogmatic, at least for now.
> You complain that physics is too dogmatic, and now you complain that it
> isn't dogmatic enough, that it doesn't proclaim truth?

My point is you are correct. Physics _can't_ be dogmatic for now. And
my complaint is that FAR too many physicists ARE too dogmatic. I have
not said it isn't dogmatic enough. Nice tap dance but not fast
enough.

You want to see dogmatic? Just merely SUGGEST that there is no such
thing as the "big bang"! BWAHAHAHAhaha!