Causality: take another look
John Polasek
to determine whether time precedence is required and I think you will
find that it does not.
Take a careful look at something far far simpler, Newton's law of
acceleration.
F= mA
Which is the cause and which is the effect?
The quick answer is that F is the cause. It certainly seems to be if I
am doing the pushing.
But, observe that it is impossible for me to exert force, no matter
how much I try, without the inertia of m being present, and not
without the acceleration to create the equal and opposite retarding
force.
The force and the acceleration are simultaneous; no force without the
acceleration and none of it can happen without the agency of the mass
which is a transformer of acceleration into force.
The mass being common to F and A assures simultaneity because it feels
the force and the acceleration together.
Cause need not precede effect, nor do you need equations that are
cluttered up with time delay to prove it unless there's a very good
specific reason. Certainly if B always follows A in time you can
assert A as a cause but it would be only with extreme reluctance that
anyone should undertake to write complicated equations and try to
extract some fundamental new truth from it.
The important point that has been missed is that when we relate 2
different dynamic variables such as force and acceleration, without
exception there must be a zero rank or second-rank tensor to relate
the two variables, in this case the inertia of the mass m, which acts
as a pivot or converter between the two. This has been missing in all
this debate about E and B.
We could make it complicated like Jefimenko's equations by pointing
out that both the pusher and the mass being m pushed deflect
initially through their Young's modulus' so that the force builds up
gradually but It is only obfuscating and merely adds bulk.
All of this debate relating E and B has been with absolutely no
regard for permittivity & permeability that act as the attributes of
the objects being affected. Instead of
curl E = -dB/dt use
curl E = -mu*dH/dt
I can control dH/dt which, *acting through mu* makes curl E. Without
mu as an intermediate intervening medium in which E and B are
immersed, you are just pushing letters around.
As an aside, Poynting's vector requires E and H not E and B.
All those charges and currents you are concerned with were left back
at the antenna and of course there is a time delay X/c. But you can't
have charges and currents in the far field, for one reason because
you have already stated in the past that you do not believe Maxwell's
displacement current.
I hope you are not thinking that the light waves in the far field are
still answering to the charges back at the antenna. No they're doing
what distributed capacitance and inductance do, which Maxwell
describes.
Cause and effect cannot be deduced from just an equation. Cause and
effect are very important conceptually when you are surveying a
phenomenon and getting ready to write an equation describing it.
I was going to make this short and punchy, but now I see it's too late
:>)
John Polasek
Benj
> There is another, easier way to test for the principle of causality,
> to determine whether time precedence is required and I think you will
> find that it does not.
> Take a careful look at something far far simpler, Newton's law of
> acceleration.
> F= mA
> Which is the cause and which is the effect?
> The quick answer is that F is the cause. It certainly seems to be if I
> am doing the pushing.
> But, observe that it is impossible for me to exert force, no matter
> how much I try, without the inertia of m being present, and not
> without the acceleration to create the equal and opposite retarding
> force.
> The force and the acceleration are simultaneous; no force without the
> acceleration and none of it can happen without the agency of the mass
> which is a transformer of acceleration into force.
>
> The mass being common to F and A assures simultaneity because it feels
> the force and the acceleration together.
>
The example of F = mA is interesting. For one thing because F and A
are simultaneous and we have postulated that simultaneous events
cannot be causal of each other. So how can this be? Well, first of all
let us remember that in physics we must be talking about REAL events
not "mathematical events''.
So if we apply a force can we measure something real? Sure, how about
the displacement of a particle? Apply an E field to an electron and
you can measure a displacement as a function of X and t. Does a delta
X occur simultaneous with the application of the force (qE)? No it
does not. A particle cannot instantaneously move from a force unless
the applied force is a delta function which we have already discussed
as non-physical. What about the first derivative of X with respect to
time? No it can't change instantaneously either! But what about the
SECOND derivative? That can and DOES change instantaneously to match
the force as seen in the equation F=mA! So the claim is now made that
F causes A and yet are simultaneous hence causal things CAN occur
simultaneously! (No claim is made for A preceding F, however)
But my point would be, is mathematics more real than reality? Is a
second derivative are real honest to God physical quantity or is it a
"mathematical" event. I suggest that it is not physical. It is a
mathematical event. And as we all know mathematics need obey no rules
except self-consistency. I'm assuming E and B (or D and H in free
space) are both different and REAL quantities representing actually
physical characteristics of space. Hence simultaneous actions violate
causality.
That' s my story and I'm sticking to it!
John Polasek
wrote:
Why shouldn't A precede F? If the mass is moving toward me and I put
out my hand to slow it down and stop it, then A is causing F. It's a
completely conservative situation where the mass can change instantly
from acting as a sink to becoming a source.
>But my point would be, is mathematics more real than reality? Is a
>second derivative are real honest to God physical quantity or is it a
>"mathematical" event. I suggest that it is not physical. It is a
>mathematical event. And as we all know mathematics need obey no rules
>except self-consistency. I'm assuming E and B (or D and H in free
>space)
No, it's E. and H. in free space. D and B are the products created
there by virtue of eps0 and mu0.
>are both different and REAL quantities representing actually
>physical characteristics of space. Hence simultaneous actions violate
>causality.
If I have the need to show a relationship between two dynamic
variables A and B then I require a common intermediary at least in the
form of a "coupling constant" to make the equation homogeneous. The
simultaneity inheres in the object in the middle being common to both.
>That' s my story and I'm sticking to it!
John Polasek
Szczepan Bialek
"John Polasek" <jpol...@cfl.rr.com>
news:7juq66586bf6umj35...@4ax.com...
> There is another, easier way to test for the principle of causality,
> to determine whether time precedence is required and I think you will
> find that it does not.
> Take a careful look at something far far simpler, Newton's law of
> acceleration.
> F= mA
> Which is the cause and which is the effect?
> The quick answer is that F is the cause. It certainly seems to be if I
> am doing the pushing.
The F and A are in the same direction.
The problem with EM is in the directions of the cause and effect.
"We have as yet given no answers to the questions, " How are these vortices
set in rotation?"
The question is from:
http://en.wikisource.org/wiki/On_Physical_Lines_of_Force
Next Maxwell wrote:
"We have, in fact, now come to inquire into the physical con- nexion of
these vortices with electric currents, while we are still in doubt as to the
nature of electricity, whether it is one sub- stance, two substances, or not
a substance at all, or in what way it differs from matter, and how it is
connected with it. "
Maxwell-Heaviside space is like the dielectric. Now we know that it is like
Sorin wrote: "high conductive medium at a very low density of matter ".
In such situations is EM fundamental?
S*
> :>)
> John Polasek
>
>
p.ki...@ic.ac.uk
> Take a careful look at something far far simpler, Newton's law of
> acceleration.
> F= mA
> Which is the cause and which is the effect?
> The quick answer is that F is the cause. It certainly seems to be if I
> am doing the pushing.
> But, observe that it is impossible for me to exert force, no matter
> how much I try, without the inertia of m being present, and not
> without the acceleration to create the equal and opposite retarding
> force.
> The force and the acceleration are simultaneous; no force without the
> acceleration and none of it can happen without the agency of the mass
> which is a transformer of acceleration into force.
Following my usual KK-based arguments:
F = mA ---> (d/dt) v = F/m = A
or (d^2/dt^2) d = F/m = A
So whilst force and acceleration are not causes of each other;
it is clear that you can say that both the velocity v and distance
travelled d are caused by the force (or acceleration, according to
preference).
[...]
> As an aside, Poynting's vector requires E and H not E and B.
I can (and have: http://arxiv.org/abs/0908.1721) defined perfectly
good EM continuity equations with Poynting-like flux vectors
ExH, ExB, DxH, DxB; although actually the enthusiast might
construct nine (because you might at P and M to the mix).
I'm not going to claim that all these forms are equally useful,
but we can say that ExH is nice because it is continuous for
propagation across interfaces,
whereas ExB is nice because the material response can be included
solely in terms of electric charge.
> [...]
> Cause and effect cannot be deduced from just an equation. Cause and
> effect are very important conceptually when you are surveying a
> phenomenon and getting ready to write an equation describing it.
But if you have a model described using an equation, you can demand
it responds in a manner compatible with causality; hence the
Kramers Kronig relations.
--
---------------------------------+---------------------------------
Dr. Paul Kinsler
Blackett Laboratory (Photonics) (ph) +44-20-759-47734 (fax) 47714
Imperial College London, Dr.Paul...@physics.org
SW7 2AZ, United Kingdom. http://www.qols.ph.ic.ac.uk/~kinsle/
John Polasek
>John Polasek <jpol...@cfl.rr.com> wrote:
>> Take a careful look at something far far simpler, Newton's law of
>> acceleration.
>> F= mA
>> Which is the cause and which is the effect?
>> The quick answer is that F is the cause. It certainly seems to be if I
>> am doing the pushing.
>> But, observe that it is impossible for me to exert force, no matter
>> how much I try, without the inertia of m being present, and not
>> without the acceleration to create the equal and opposite retarding
>> force.
>> The force and the acceleration are simultaneous; no force without the
>> acceleration and none of it can happen without the agency of the mass
>> which is a transformer of acceleration into force.
>
>Following my usual KK-based arguments:
>
>F = mA ---> (d/dt) v
Strictly speaking, you need v as a function of time before you can
take its derivative.
>= F/m = A
> or (d^2/dt^2) d = F/m = A
>
>So whilst force and acceleration are not causes of each other;
Don't forget, neither can exist without the existence of m. This
inescapable triumverate alone insures simultaneity.
As to choosing cause and effect, the causative component might be one
that gives up energy.
If I thrust my hand forward with the object, F and A are simultaneous
and F would be the energy donor. If I see the object approaching with
an inappropriate velocity, I can use my hand to bring it to a halt, in
which case the acceleration is the cause, by giving up energy.
>it is clear that you can say that both the velocity v and distance
>travelled d are caused by the force (or acceleration, according to
>preference).
>
>
>[...]
>> As an aside, Poynting's vector requires E and H not E and B.
>
>I can (and have: http://arxiv.org/abs/0908.1721) defined perfectly
> good EM continuity equations with Poynting-like flux vectors
> ExH, ExB, DxH, DxB; although actually the enthusiast might
> construct nine (because you might at P and M to the mix).
>I'm not going to claim that all these forms are equally useful,
> but we can say that ExH is nice because it is continuous for
> propagation across interfaces,
> whereas ExB is nice because the material response can be included
> solely in terms of electric charge.
I would differ with you because only with ExH are the units equal to
real power density
E(V/m)xH(amp turns/m) = watts/m^2 (1)
I perused your scholarly paper and notice that you do not make use of
units. Similarly, you regard bound charges as purely fictional and in
a pure vacuum they are.
But there is the seriously regarded quantum vacuum where several
investigators are examining permittivity and permeability in order to
deduce its physical properties.
John Polasek
>John Polasek <jpol...@cfl.rr.com> wrote:
>> Take a careful look at something far far simpler, Newton's law of
>> acceleration.
>> F= mA
>> Which is the cause and which is the effect?
>> The quick answer is that F is the cause. It certainly seems to be if I
>> am doing the pushing.
>> But, observe that it is impossible for me to exert force, no matter
>> how much I try, without the inertia of m being present, and not
>> without the acceleration to create the equal and opposite retarding
>> force.
>> The force and the acceleration are simultaneous; no force without the
>> acceleration and none of it can happen without the agency of the mass
>> which is a transformer of acceleration into force.
>
>Following my usual KK-based arguments:
sorry-but not acquainted with KK
>F = mA ---> (d/dt) v = F/m = A
> or (d^2/dt^2) d = F/m = A
That is mathematics but to take the derivative requires v as a
function of time.
>So whilst force and acceleration are not causes of each other;
>it is clear that you can say that both the velocity v and distance
>travelled d are caused by the force (or acceleration, according to
>preference).
Another way of looking at it is whether the mass is a source or sink
of energy. Pushed, it's a sink (F=cause); stopping it, it's a source
(A=cause). This might imply that cause requires time precedence but we
know that F and A are simultaneous.
>
>[...]
>> As an aside, Poynting's vector requires E and H not E and B.
>
>I can (and have: http://arxiv.org/abs/0908.1721) defined perfectly
> good EM continuity equations with Poynting-like flux vectors
> ExH, ExB, DxH, DxB; although actually the enthusiast might
> construct nine (because you might at P and M to the mix).
>I'm not going to claim that all these forms are equally useful,
> but we can say that ExH is nice because it is continuous for
> propagation across interfaces,
> whereas ExB is nice because the material response can be included
> solely in terms of electric charge.
I just viewed your estimable paper and am impressed. But I notice that
nowhere were units used. I think to get real physics done you must be
dealing with attributes of objects or fields with specific attributes.
of course this requires extra diligence.
In quantum mechanics they talk of the quantum vacuum and in the paper
to hand, "the quantum vacuum at the foundations of classical
electrodynamics" http://arxiv.org/abs/1005.0131 they are looking to
quantify their vacuum through permittivity and permeability. *
On the other hand you chose to characterize the idea of bound charges
in a vacuum as purely fictional, but such charges are the entire
substance of quantum vacuum. Maxwells equation works in a vacuum:
div D = rho
but it can't happen without electron positron pairs waiting to be
polarized as they would in a quantum vacuum. So space really does act
as if it had more substance then you give it credit for.
We get a nice result as power density using ExH
P= E(V/m)*H(amp-turn/m) = watts/m^2 = VI/m^2 (1)
If I try your DxH it means multiplying the equation by eps0
P? = P*coul/volt-meter = (V*I/m^2) x (coul/V-m) = ampere coul/m^3
It's hard to put a construction on that result. I would say that DxH
is an invalid combination.
Eq. 1 is fine as it stands, and you obtain your second choice, ExB, by
multiplying (1) by mu, but the result is bound to be intractable.
* incidentally I have derived every property of the quantum vacuum and
am preparing a paper. In their paper they deplore the desultory
acquiescence of permittivity and even the D field in the usual
electrodynamics; it's interesting reading.
>> [...]
>> Cause and effect cannot be deduced from just an equation. Cause and
>> effect are very important conceptually when you are surveying a
>> phenomenon and getting ready to write an equation describing it.
>
>But if you have a model described using an equation, you can demand
> it responds in a manner compatible with causality; hence the
> Kramers Kronig relations.
John Polasek