What! Really? Electromagnetism is a Relativistic Phenomenon!

By Max Maxfield |

According to this video, electromagnetism is a relativistic phenomenon. Were you already familiar with this concept, or is it as much a surprise to you as it is to Max?


As a young lad, I played with conventional magnets. The fact that some materials were magnetic and others weren’t -- along with the fact that some materials could be used to form permanent magnets -- didn’t really surprise me; I just took it that this was the way things were.

Come to think of it, I still don’t really understand what magnetism is at its most fundamental level, but I'll worry about that when I have some spare time.

As a grew older, I started to learn about electromagnetic fields and effects. Just to make sure we're all tap-dancing to the same set of drums, let's briefly remind ourselves that a difference in electrical potential across two ends of a conducting wire causes current to flow, and current flowing through a wire causes an electromagnetic field to be generated around that wire.

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Current flowing through a wire generates an electromagnetic field (Source: Max Maxfield)

Correspondingly, if a piece of wire is moved through an externally generated electromagnetic field, it cuts the lines of electromagnetic flux, resulting in an electrical potential being generated across the two ends of the wire.

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A conductor moving through an electromagnetic field generates an electrical potential (Source: Max Maxfield)

We sometimes make use of components called inductors, which may be formed by winding a wire into a coil around a rod of iron or some other ferromagnetic material (the wire will be coated by a layer of insulating material to prevent coil windings forming electrical connections with each other or with the rod). When a current is passed through the coil, the result is an intense electromagnetic field.

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A simple inductor (Source: Max Maxfield)

Once again, I just accepted all of this as being just the way things were. Until now, I've never really stopped to think about how all of this comes to be at the most fundamental levels.

I'm sure you are familiar with some of the surprises that were revealed by Einstein's theories of relativity, such as the fact that space and time are "entwined" in a spacetime continuum, and that the faster you go (with reference to someone or something else), the less time passes for you (again, with reference to someone else).

This leads to relativistic phenomena that form the heart of many science fiction stories, such as Time for the Stars by Robert Heinlein. This tale features two identical brothers: Pat, who stays at home on Earth, and Tom, who travels to the stars on a spaceship that approaches the speed of light. When Tom returns, he's still a young lad, while Pat has grown into a crusty old man.

The reason I mention this here is that I just saw this video, which made me gasp in astonishment.


According to this video, electromagnetism is a relativistic phenomenon. Well, color me dumbfounded and call me a banana (thereby providing the opening to link to my banana slicer column). I had no idea about any of this. Were you already familiar with this concept, or is it as much a surprise to you as it is to me?

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  • by  Vincent van Beveren (edited)
    Does this mean that 'normal' and electro-magnetism are two different things? Hmm...
  • by  Max Maxfield (edited)
    @Vincent van Beveren: "Does this mean that 'normal' and electro-magnetism are two different things?..." I have no idea. I think they have to be different manifestations of the same underlying phenomena, but I wouldn't bet my life savings on it LOL I really wish I understood this stuff more.
  • by  Vincent van Beveren (edited)
    Yeah, I work in a physics institute, and even I am continuously flabbergasted. :-)
  • by  Max Maxfield (edited)
    @Vincent: "...I work in a physics institute, and even I am continuously flabbergasted..." I also still don't understand how mirrors work -- that is, how you see an image reflected in a mirror -- I wrote a column on this ages ago: http://www.eetimes.com/author.asp?section_id=36&doc_id=1284548 Following that column, I read Feynman's QED book, and I still don't have a clue (said Max, sadly)
  • by  PeterTraneus Anderson

    Get a copy of "Einstein's Miraculous Year", edited by John Stachel, Priceton University Press, 1998, which contains translations of Albert Einstein's PhD dissertation and of four papers Einstein published in 1905. Einstein was excellent at explaining things; if you know algebra and basic calculus, you can read his papers.

    In Paper 3, "On the Electrodynamics of Moving Bodies", Einstein derives special relativity from Newton's mechanics and Maxwell's electromagnetics, so obviously electromagnetics is relativistic.

    In Paper 4, "Does the Inertia of a Body Depend on Its Energy Content?", Einstein derives E=mc^2.

    In Paper 2, "On the Motion of Small Particles Suspended in Liquids at Rest Required by the Molecular-Kinetic theory of Heat", Einstein showed that observations of the random Brownian motions of small particles in a liquid could be used to determine Avogadro's number. Paper 1 is Einstein's PhD dissertation, and covers the same material as Paper2.

    In Paper 5, "On a Heuristic Point of View Concerning the Production and Transformation of Light", Einstein used the observed photoelectric effect to show that light is quantized. This is what his 1921 Nobel Prize is for, not for relativity: Quantum mechanics was still radical, while relativity was obvious.

    • by  Max Maxfield

      @Traneus Rex: "...Get a copy of "Einstein's Miraculous Year'..."

      I have to say that I think Einstein was just showing off publishing all four papers in the same year LOL

      Did you ever read Einstein: His Life and Universe by Walter Isaacson? If not, I very much recommend it.

  • by  Max Maxfield

    @Traneus Rex: "...Get a copy of "Einstein's Miraculous Year'..."

    I have to say that I think Einstein was just showing off publishing all four papers in the same year LOL

    Did you ever read Einstein: His Life and Universe by Walter Isaacson? If not, I very much recommend it.

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