11 nov 2015
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6:43 PM (1 hour ago)
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All, I Made some changes
based upon Forrest's comments. I added David Walton as a signatory in
anticipation of his approval. Here is the revised version. I would like to get
more signatures on this, so please sign on.
Dear Sir,
We think that the paper
“An apparent Paradox: Catt's anomaly” by Massimiliano
Pieraccini and Stefano Selleri, that appeared in the November 2013 issue of Physics
Education, contains serious flaws that need to be corrected, and that it
should not be considered an adequate guide or suitable advice for physics
teachers. Our reasons for concluding this are: 1. It misrepresents the Catt
Question as an apparent paradox; 2. It misrepresents the fundamental issues
behind the Catt Question by not properly explaining the essential issues of the
question; 3. The answer that is proposed it not sufficiently demonstrated in
the mathematics using Maxwell's equations; 4. It fails to properly present a
solution which is based upon the principles of physics being taught to students
at the elementary level; 5.The theoretical claims made regarding the nature of
electricity and magnetism are incompatible with the principles laid down to
students in elementary classes. This last point is the most important since
students are not properly prepared for the new paradigm presented in the paper.
This new paradigm is also incompatible with the currently accepted physics
paradigms that are taught to students.
Regarding point 1. Catt doesn't say there is an anomaly,
he merely asks a question regarding a problem, so Catt's Question is
misrepresented in the title. The authors incorrectly say that “Catt’s
anomaly is a sort of ‘thought experiment’ (a gedankenexperiment)
where electrons seem to travel at the speed of light....” First, the question
is not a thought experiment. It is a question asked within the context of an
example problem. Second, the question makes no claim that electrons travel at
the speed of light, which is impossible, it merely asks how does the charge
travel along with the leading edge of the step when the step is moving forward
at the speed of light, and asks how does the charge arrive
at the bottom wire filling up the space required. The question has to do
with where the charge on the bottom wire of Figure 1 of the paper “comes from”
or how it gets there if the leading edge of the propagating step of energy
shown in the figure is moving at the speed of light.The
alleged answer to Catt's question is that there is actually no paradox or
anomaly. Catt never claimed there was a paradox or anomaly, he merely asked a
question. The answer is to provide a solution for the proposed problem. There
is a lot of information regarding the correct formulation of the question at Ivor Catt's website: http://www.ivorcatt.co.uk/iop.htm
Regarding point 2. In the paper, the solution to the Catt Question was to say
that the electrons follow the field, and so are not the source of the electric
and magnetic fields. The essence of the Catt Question was that; Catt wanted to
know how was it possible for the charge on the bottom wire to fill up the
required space, within the currently accepted physics paradigm as being taught
to science students. The question was formulated with an answer expected to be
compliant with this constraint, otherwise the physics experts would have to
admit that this was impossible, and so a new physics paradigm was required to
be taught. The solution proposed in the subject paper was that the
electrons are not the sources of the fields and so in doing that, the velocity
of the electrons can be much less than the velocity of light. But that solution
is a contradiction of currently accepted physical thought that the charges are
the sources of the fields. In order to adhere to the currently accepted
electron physics paradigm, the solution to the Catt Question has to demonstrate
mathematically that the electric and magnetic fields can move at the velocity
of light, when the sources of the fields, the electrons, do not. There was no
such demonstration provided that conclusively proved this requirement.
Regarding points 3 and 4. The answer proposed by the Italians implies that the currently
accepted physics paradigm is incorrect. They propose that it is possible for a
large number of electrons moving at low velocities to fill up the space created
in the wire, although the wave front is advancing at the speed of light. They
say, “Although each single electron is not able to travel at the speed of
light, a great number of slow electrons are able to produce a current as fast
as an electromagnetic wave travelling at the speed of light in the conductor.” The
justification for this assertion is an analogy where a large number of
electrons are put in motion as when in a marathon the runners all hear the
starting gun at the same time. This concept is beyond the ability of students
to comprehend, because students are taught that it is the steady current of
electricity in the wires that creates the electric and magnetic fields, while
in the explanation given, it is the fields of the wave that produces the charge
and current. The paper gives no physical or mathematical explanation for how
this occurs. There is no electric field in the wires in the direction of charge
flow shown in Figure 2 that can produce a current in the required direction,
and the electric field shown is perpendicular to the wires and external to
them, so it is not possible to understand how the charge flow is induced by the
TEM wave shown in Figure 2. Finally, there is no mathematics derived from
Maxwell's Equations that demonstrates the model as proposed in the paper.
Regarding point 5. In elementary physics classes, students are taught that the
magnetic field is created by a steady state current of electrons in the wires.
In advanced electricity and magnetism courses, students are taught how to
derive the fields using Maxwell's equations from the charge and current as
sources, if it is assumed that the charge and current exist in an already
established steady state. The Catt Question asks how this steady state
condition comes into being, and so it is a much more sophisticated question
than is appreciated by the authors. They answer that the charge and current is
produced by the action of the propagating wave, but they provide no physical
basis for this hypothesis that is understandable within the currently
established teaching concepts of electricity and magnetism.
In conclusion. The Catt Question asks a question about how the steady state electric and magnetic fields come to be established, and does not present an anomaly or paradox to be answered. When it is assumed the steady state is established, then the usual models of electricity and magnetism as taught to students can be used. However, the Catt Question deals with a question regarding how the steady state fields come into being. The answer proposed in the subject paper is beyond the ability of students to comprehend, and has not been properly answered by experts who disagree regarding its solution. This can be verified at the Ivor Catt website:http://www.ivorcatt.co.uk/iop.htm
, where the conflicting proposed solutions are documented.Harry H. Ricker
III, BSEE and MSEE