Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B

Some basic epistemological and pedagogical
questions concerning electromagnetism
Juan Roederer
Geophysical Institute
Emeritus Professor of Physics

Electromagnetism occupies a special situation in physics: it has survived nearly intact all great scientific revolutions — the theory of special relativity (Maxwell's equations are intrinsically Lorentz-invariant, and classical mechanics had to submit gracefully to electro–magne–tism), general relativity (in conformity with the principle of equivalence, in a gravita–tional field a light beam is bent if c·g = 0 and its frequency, i.e., the energy hv of the photons, changes if c||g — the only difference being that gEinstein = 2gNewton for photons), and quantum mechanics (Planck's constant drops out of Heisenberg's uncertainty relation when applied to photons, there is no classical-quantum transition in the spatial domain, and individual photons do exactly what electromagnetic waves do — such as taking two paths at the same time in some optical devices). In what must have been some mysterious presage of future developments, Ludwig Boltzmann once borrowed from Goethe's Faust to portray Maxwell's equations: "War es ein Gott der diese Zeichen schrieb?š I will discuss some questions that are important for a better understanding of electromagnetism, but rarely are addressed in text books:

  1. B vs H: which of the two magnetic vectors is more "physical"?
  2. In a plasma, which is primordial: the magnetic field or the currents?
  3. Field lines: mental artifacts or physical entities?
Friday, 26 January 2007
Globe Room, Elvey Building
3:45 PM