In anticipation of the eventual re-awakening of this thread (it seems that "Mozina
vs The World" is its sole reason for existence) I would like to address one of the key problems I see: There is a great deal of discussion that hinges on semantics and the sloppy use of language, rather than a properly precise discussion of the scientific aspects. Science requires a precise use of language. We have to understand that colloquial language has to give way to precise scientific language when the circumstances require it. So, here I want to present proper, authoritative scientific definitions
for key elements of the discussion. In this case I want to make sure that, before we proceed, we have proper definitions in hand for "field lines" and "flux tubes", the key elements of the magnetic fields involved in plasma physics.
I have highlighted
what I think are the key points, but I have tried to cite enough language to provide proper context, as well as to avoid insufficiently brief descriptions. Any other emphasis besides the highlight is carried over from the original text. I encourage the reader to pay attention to the full text of the quotes, and to refer directly to the original sources, which I have linked to as best I can, wherever possible.
Lines of Force Defined
From 26 January 2010
Originally Posted by Tim Thompson
From 20 November 2011
Originally Posted by Tim Thompson
This definition from Lorrain & Corson is quite the same as Maxwell's and is the standard definition for field lines in general; not just electric and magnetic fields, but for any classical field, that is how "field lines" are defined. For example, we find this definition in another, older, standard textbook:
Originally Posted by Smythe, 1950
This definition comes from Static and Dynamic Electricity
, William R. Smythe, McGraw-Hill 1950, 2nd edition (1st 1939), section 1.08 "Lines of Force" on page 7. As before, note that this definition is general despite the specific reference to an electric field. Just replace electric field with magnetic field and the definition is precisely the same, and is in fact so for any classical field.
Flux Tubes defined
Originally Posted by Deiter Biskamp, 1993
The definition quote above is from the book Nonlinear Magnetohydrodynamics
by Deiter Biskamp (Max Planck Institute for Plasma Physics); Cambridge University Press 1993. His reference to equation 2.11 is just Faraday's Law after replacing E
Biskamp Equation 2.11:
All magnetic fields are originally generated by electric currents. However, while the current flows in a confined volume, the consequent magnetic field will fill a vastly larger volume than the current. Hence it is possible to measure an active and time variable magnetic field in a vacuum far removed from the current that generated it. This is a point which seems to be overlooked to me so I want to make sure the point is made explicitly somewhere. Furthermore, magnetic fields and plasmas commonly couple together, so that the plasma will carry the "frozen in" magnetic field with it. So a plasma can be magnetized by a magnetic field that is not generated by that plasma, but by another completely independent plasma far away. As an example, the solar wind carries the solar magnetic field along with it. The magnetic field was originally generated in the sun, but is carried to the outermost reaches of the solar system by the solar wind, which can deform that magnetic field, but has nothing to do with the generation of that magnetic field. Likewise, magnetic fields generated deep inside the sun will pass through the photosphere of the sun and couple with it, despite not being formed in the photosphere by the plasma it is coupled to. So it is important to understand that we can have a magnetic field in a plasma, but not assign the task of generating that magnetic field to that particular plasma.
Also note that, as defined, both field lines and flux tubes are strictly mathematical objects, not physical objects. There are, of course, physical manifestations that go along with the mathematical theory. The mathematics becomes in essence a second language, far more efficient than our own human languages, used to describe the physics. The language of mathematics is far more precise than any human language, and it is truly universal across humanity; everyone has the same understanding of an equation, regardless of the human language they use to discuss that equation. In my short preface I spoke of the "semantics and the sloppy use of language". This thread is replete with attempts to replace mathematical and physical rigor with colloquial English and that is a serious mistake, which we should make an effort to repudiate in the future, for this or any other thread.