4.5.3 A Synopsis
The Tripartite Model of How Electromagnetism Works
After the second world war, President Truman sought the counsel of J. Robert Oppenheimer, Director of the Manhattan Project which built and delivered the first atomic bombs. “I have blood on my hands,” Oppenheimer is said to have told the man who made the decision to drop the atomic bombs on Hiroshima and Nagasaki. Infuriated, Truman called Oppenheimer a “cry-baby scientist” and said, “I don't ever want to see that son of a b_ in this office ever again.” link
The high stakes world of leadership and politics demands we balance an openness to alternative perspectives with a decisive clarity and relentless focus on practical outcomes. In physics as well, we must simultaneously be receptive to a wide range of potential models but be ready to select the appropriate model and drive it home to a correct understanding of our problem.
I have come to accept a tripartite model of how electromagnetism works: charges and currents, electric and magnetic fields, and finally energy.
Each side of the triangle captures essential features of electromagnetic behavior. Fields – electric and magnetic – act upon charges and currents, respectively. In the language of physics, fields exert forces that tell the charges and currents how to move. Electric fields push or pull charges; magnetic fields push or pull currents or moving charges. At the same time, charges and currents tell fields what to do. The Weber action-at-a-distance model eliminates the field middleman and provides mathematical descriptions of charge and current interactions directly.
The energy is localized according to the field intensity, and the paths or trajectories of the energy flow are governed and guided by the fields.
Energy does work on charges and currents, and charges and currents store potential and kinetic energy in their immediately adjacent fields. Further, there is some indication that mass itself may be electromagnetic in nature [[i]]. In a sense, matter may be thought of as “frozen light,” explained quantum physicist David Bohm (1917–1992) [[ii]].
The tripartite model of electromagnetism may seem a bit out of place given this book’s thesis on the duality of fields and energy. The focus of this book is on the interplay of fields and energy – just the one side of the triangle – because that side remains poorly understood in contemporary thinking. How can we expect to understand electromagnetism if we fail to understand how fields guide and store energy? An understanding of fields and energy is a necessary prerequisite to understanding the role of charges and currents.
This is far from an exhaustive list of potential models. For instance, there are those who will argue that “the Lagrangian,” or “the action” are primary quantities, and in fact, we will see in Chapter 6 that the Lagrangian has a part to play in the overall scheme of things. To be clear, all these models have their places. In all likelihood, they are merely superficial manifestations of more fundamental layers of reality about which we remain ignorant.
In 1881, Oliver Lodge (1851–1940) noted: “Now then we will first ask, ‘What is Electricity?’ And the simple answer must be, ‘We don’t know’” [[iii]]. More than a century of progress has made our ignorance more layered, but we honestly have no better answer today. A wise thinker will follow Newton’s excellent example and “frame no hypotheses” to the exclusion of the others, absent convincing evidence. And as we have seen, even a physically misleading mathematical model that we know does not correspond to the facts of reality may nevertheless be helpful in solving certain kinds of problems. We do know one thing for certain, though. The more models in your toolbox, the better able you are to understand and solve a wider range of problems.
There is one final piece of the puzzle we have yet to consider, however. All the examples thus far involving action at a distance, operated at relatively short distances – distances not much greater than the dimensions of the systems interacting. As we saw back in chapter three, it is possible to have electric fields which are not connected to charges – electric fields which form closed loops and propagate away from a source at the speed of light, carrying electromagnetic energy to arbitrarily great distances. The next part of our story considers the discovery of this behavior and what are the implications for how electromagnetism works.
Next time: 4.6 Hertz & Radiation Fields: The Discovery of Electromagnetic Waves
Full Table of Contents [click here]
Chapter 4 Electromagnetism Comes of Age
4.5 An Introduction to Electromagnetic Models
4.5.1 Potentials and Actions at a Distance
4.5.2 Jefimenko & Lorentz
4.5.3 A Synthesis
4.6 Hertz & Radiation Fields
4.7 How Does Radiation Work?
4.8 Summary & Conclusions
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References
[[i]] Dirac, P. A. M. (1938). Classical Theory of Radiating Electrons. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 167(929), 148–169. doi:10.1098/rspa.1938.0124
[[ii]] Weber, Renée, Dialogues with scientists and sages : the search for unity, London: Routledge & Kegan Paul, 1986, p. 45. Quoting David Bohm:
“So matter, as it were, is condensed or frozen light. Light is not merely electromagnetic waves but in a sense other kinds of waves that go at that speed. Therefore all matter is a condensation of light into patterns moving back and forth at average speeds which are less than the speed of light. Even Einstein had some hint of that idea. You could say that when we come to light we are coming to the fundamental activity in which existence has its ground, or at least coming close to it.”
[[iii]] Lodge, Oliver, “The relation between electricity and light,” Nature, vol. pp. 302-304, January 27, 1881.
Your table of contents reads "4.5.3 A Synthesis" whereas the chapter heading here reads "A Synopsis"
Feynman: "We will now describe the lightning. Again, we don’t understand exactly how it works"
He says this much more eloquently and with humility elsewhere in the lectures. I could not find it...