"Timo A. Nieminen" <timo@[EMAIL PROTECTED]
> wrote in message
news:Pine.WNT.4.64.0806240535450.1160@[EMAIL PROTECTED]
> On Mon, 23 Jun 2008, Bill Miller wrote:
>
>>
>> "Timo A. Nieminen" <timo@[EMAIL PROTECTED]
> wrote in message
>> news:Pine.WNT.4.64.0806221102300.656@[EMAIL PROTECTED]
>>> On Sat, 21 Jun 2008, Bill Miller wrote:
<snip>
>> Correct. And as long as the interaction is of a contact nature, then
>> eveything is OK. But when there is a delay between the action and the
>> reaction, then *for that delay period* momentum is not conserved. But
we
>> know that momentum MUST be conserved, so we must look at Newton with an
>> eye
>> to modifying it to deal with what amounts to a time dependency.
>>
>> This is not a new idea. We have long recognized, for EM that
electrostaic
>> representations break down when time dependency is present.
>>
>> Heaviside suggested this in 1893 but never took it all the way to its
>> logical conclusion.
>
> Heaviside's Maxwellian gravitation? There is no modification of Newton's
> laws of motion in it. Newton's law of universal gravitation, describing
> gravitational forces as interactions between distant bodies, is replaced
> by a field theory, wherein all interactions are local - body interacts
> with local field, not body with distant body.
You must be looking at a different copy of Heaviside's 1893 article. In
it,
he clearly (to me at least) understood concepts of time-dependancy, the
gravitational equivalent of the Poynting Vector (that he claimed partial
credit for) and others. I agree that he did NOT deal with retardation.
Neither did/does Maxwell!
This "action at a distance" has always been an Achilles Heel.
It is resolved, I believe by understanding and applying Causality. We need
to understand that if two events occur at the same time, neither can cause
the other. Instead, at least one must be caused by some other (hidden)
event.
Recognition of this simple concept would, as one example, have stopped
generations of instructors from teaching their students that E causes H
and
H causes E. It would have also stopped generations of mathematical
physicists from publi****ng articles in peer-reviewed publications that
"proved" that E causes H or vice versa. And it would have stopped
generations of experimental physicists from spending countless hours and
dollars in building apparatus to measure the non-existent H between the
plates of capacitors.
If I have understood your position on this, Timo, it is that the teaching
of
this is expeditious & that once one gets to the PG leve, the "true facts"
are revealed and everything is fine.
That leaves hordes of non PG students still believing this rubbish. And it
begs the question of why, in UG cl*****, the instructors don't say
*something* about how theses two parameters don't cause each other, but
that
they always appear simultaneously. I suspect its because the instructors
don't know it!
Is there a single UG EM textbook that correctly categorizes the
relation****p
between E and H? Even ONE?
<Bill takes a deep breath, steps down from the soap box, and shuffles away
from the small crowd of mostly disinterested onlookers. A nondescript
brown
dog sniffs the box suspiciously, turns sidewise and lifts its leg.>
>Newton 1 and 2 are pretty much just definititions of inertial motion and
>force, while Newton 3 is (as above) conservation of momentum. How can
these
>be modified sensibly?
I'd say that looking at Causality and incor****ating what we learn into new
expressions that include factors tor time variation of position and for
timevariation of mass would get the job done. Naturally, any such
additions
must obey conservation of momentum AND must reduce to the original form
when
time dependancy is absent.
>>> Yes, if we consider two m***** as above (or two electric charges) to
be
>>> interacting with each other, we have exactly the problem you point
out.
>>>
>>> Does this mean Newton 3 is wrong? Does this mean momentum is not
>>> conserved? I would say that it means that we simply don't have a
>>> situation
>>> where there are two objects interacting at a distance, but two objects
>>> each interacting with a field. Perhaps the interaction really is as
>>> described by field theory, a local interaction between field and body,
>>> and
>>> we should throw away the classical mechanics idea of interaction at a
>>> distance rather than Newton 3.
>> That's one way of dealing with it. I believe that a better way would be
>> to
>> recognize that Newton's work is not applicable to time dependency.
That's
>> no
>> different, conceptually, from Maxwell's expansion of Ampere's Law to
>> include
>> The rate of Change Of E field in order to deal with magnetic fields in
a
>> time-dependent environment.
>
> I think it is different conceptually. One is a conservation law, and the
> other describes a limited set of experimental observations.
It is true that gravity is a whole bunch of orders of magnitude more
difficult to deal with experimentally than EM. Building planetary objects,
setting them rotating, and zapping them past one another is way beyond our
experimental capability.
BUT, we have a handy set of "toys" in our own night sky. And there we have
an interesting set of pre-made experiments already in process. Like,
maybe,
does our model explain why the rotational speed of the Sun at the equator
is
different from the speed at the poles? Or does it provide some insights
into
Mercury's (supposedly) residual precession? Does it sup****t or deny the
existence of black holes? Does it provide some insight into the "missing
mass of the universe" question? What might it say about gravitational
waves?
Does it provide a definitive explanation of the process wherein potential
energy is converted into kinetic energy by a falling body? Does it explain
why EM beams are deflected by gravity?
But that's a lotta work. Doing it wrong is a lot easier!
Cheers, Bill
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