Sunday, 27 April 2014

There is no electromagnetic field - get over it!

A quick Sunday post on something I've written a little about before. But first, a quote
"Give me a child until he is seven, and I will give you the man"
This, of course, has a religious origin, but it applies in many human endeavours.  Including science.

I've taught at a university level for more than a decade, and I've noticed something slightly odd. Namely students coming into university seemed to have some particular fixed notions which you have to work hard at to shift.

There are a number of examples of this, including things like the conservation of energy, which was drilled into them at school but when you tell students that energy is generally not conserved in Einstein's theory of relativity, they initially stare in disbelief.

And when it comes to quantum mechanics, they seem to think that electrons are really little hard balls that sometimes behave as a wave, whereas photons are really waves that sometimes act as particles. Really they need to think of electrons and photons as the same kind of quantum wavy thingies.

The other is electric and magnetic fields, blue and red lines that snake through space. Uncovering the existence and influence of the electromagnetic field has taken centuries, and disparate lines of evidence were pulled together by James Clark Maxwell who gave us a famous set of equations (strangely known as Maxwell's equations). They look like this;

Now, I know a few people at maths-o-phobic, but all this says is "tell me where the charges are and how they are moving, and then you can calculate the electric and magnetic fields" (it's actually a little more complicated than that, but it's a good approximation).
Back to students, who learn about electric and magnetic fields at school. They may have seen Maxwell's equations. These red and blue lines really snake through space. They are there. They are real.

But they are not.

When quantum mechanics was developed through the twentieth century, how particles interacted through the electromagnetic force was one of the big questions. And it was the  great Richard Feynman who is the person most associated with working this out.

I strongly urge you to read his own words that led him to find the solution, but what he had to do is get rid of the electromagnetic field as we understand it from Maxwell's equations! Instead, charged particles interact through the exchange of individual photons, and we get the famous Feynman diagrams.
But these photons are only emitted and received when particles interact, and so if we have a lone electron sitting there, it doesn't fire out photons all over the place, hoping another electron comes along and it can interact. A lone electron is not surrounded by a Maxwell electric field. It's not there. No electric field. No magnetic field either.

The actual picture is (of course) a little more complex than this, but it takes students a bit of time to banish the picture that space is filled with red and blue field lines.

And, in truth, that's one of the greatest things that happens in science, when you have to throw out a picture that you thought was the "reality" of the universe, and realise that you were wrong. And on that note, here's a Sunday thought: think about what you currently think about the actual workings of the universe - there's a good chance your probably wrong.

2 comments:

  1. Cool, but how do magnets work ;)

    Inspiring post. As always.

    ReplyDelete