What is Light? What are Radio Waves?

  • A talk given at a Santa Fe Science Cafe, 2013 Jan. 16
  • Abstract of the talk
  • Video of the talk
  • Interview on KSFR radio (15 minutes; choose the 3rd audio option)

The great discovery by Maxwell about 150 years ago of the real nature of light stands as one of the greatest discoveries in all of human history. The goal of this talk was to share with people what light really is, because its nature is not widely understood. I also wanted to demistify “electromagnetic radiation” and “electric fields”, terms that for many people are rather scary due to a lack of understanding of what the terms really mean.

Technical comment for physicists: As a result of preparing and giving this talk, I had a minor insight about the physics of light. A colleague has argued that magnetic fields are merely electric fields seen from a different reference frame. I’ve argued that this isn’t the whole story. I offer several examples that show that magnetic fields are not simply relativistic manifestations of electric fields.

(1) All experiments on electrons to date are consistent with them being true point particles, with zero radius, yet they have a magnetic moment even when at rest. There is no reference frame moving with constant velocity in which the magnetic field of the electron vanishes.

(2) Light consists of electric and magnetic fields that are perpendicular to each other, propagating at the speed of light. There is no physically realizable reference frame in which it is possible to transform away the magnetic field.

(3) Here is my minor recent insight: In the classical wave picture, light is produced by accelerated charges. Because the velocity is constantly changing, there is no constant-velocity reference frame in which the charge is at rest, and in which the magnetic field of the charge vanishes.

Bruce Sherwood

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