Sophia Collins, the organizer of I’m A Scientist, recently posted a blog on one of the questions we faced, which provoked a lot of discussion at the time: “how do magnets attract and repel?” (posted by lucasjacobs) . This is a perfectly reasonable question, but it turns out to be difficult to answer. You can read my answer here (comments are very welcome – I don’t think I’ve had any comments on this blog yet, so perhaps they don’t work you can see they work, below – thanks Adam). Sophia’s blog was pretty accurate – in essence we all struggled to answer the question, and after some discussion (e.g., on twitter and with colleagues) we realised that it was not just us, but that magnetism was indeed very hard to explain properly without jargon.
However, Sophia did say this (referring to me):
“Now these scientists include a man who spends many of his days working with an fMRI scanner, containing a magnet so powerful that you have to remove any ferrous object from your person before entering the room. But still, magnetism turned out to be one of those things that he learned about years ago, and sort of assumed he understood.”
Now this is not quite true. The true part is the embarrassing fact that I don’t understand magnetism, the false part is that I had assumed I understood – in fact I was very much aware of, and troubled by, the gap in my understanding. I dropped Physics after my O-level, so perhaps it wasn’t to surprising that I had struggled. But it was also a challenge to the other scientists in my group, all of whom, I believe, have Physics PhDs. I use magnetic resonance imaging (MRI) in my research, I teach MRI at postgraduate level, and I am therefore very interested in magnets and how they work. Over the years I’ve questioned many physicists about magnetism (often to the point of irritation). Although they can generally describe many magnetic phenomena I’ve often come away with the impression that there is a “gap” in the explanation.
In trying to understand this I turned first of all to Richard Feynman who as well as having a hand in the theories that most accurately describe magnetism, was also a great communicator. Feynman’s book “QED: the strange theory of light and matter” brilliantly explains a range of electrical and optical phenomena for a lay audience, avoiding classical physics and using only a (non-mathematical but accurate) description of quantum mechanics. Unfortunately, the QED book doesn’t say much about magnetism.
Here is a clip of Feynman trying to answer a layman’s question about magnetism:
I think the reason he struggles is because he recognizes how difficult the question is, and doesn’t want to fob the interviewer off with an incomplete or misleading answer. Feynman thought a lot about the nature of science and explanation, and he explicitly understood that renaming or describing a phenomenon did not constitute any kind of explanation. When asked to give a talk to a group of science teachers on the subject “What is Science?” he stressed this. I strongly recommend reading the whole talk, but I quote a relevant passage which shows how deeply ingrained this principle was in his psyche – he had learned the lesson from his father, as a child during a trip to the Catskill mountains:
“… this boy said to me, ‘See that bird standing on the stump there? What’s the name of it?’
I said, ‘I haven’t got the slightest idea.’
He said, ‘It’s a brown-throated thrush. Your father doesn’t teach you much about science.’
To return to magnets, I never did hear a clear explanation of how magnets attract and repel one another. For me, a clear explanation would have to be consistent with other mechanistic explanations of electrical and optical phenomena. In his lecture on the topic, Feynman is emphatic that although carefully selected magnetic phenomena can be explained in classical terms, these examples are misleading, in that the intuitions that flow from them are wrong.
I can see that Maxwell’s field equations which describe electrical and magnetic fields in space and time are incredibly useful, and sufficient for many applications of magnetism – talk about fields and lines of force doesn’t really constitute an explanation. Although these concepts go far beyond merely “naming” or even describing magnetism, they don’t really explain what it going on. It is my understanding that, ideas like “fields” and “force” are nowadays thought to summarize more fundamental processes, similar to those covered in QED. From reading this and other books I’ve learned that I have to accept that there are some mechanisms in nature that cannot be understood in terms of the phenomena we encounter in everyday experience. But my understanding is that the mechanism of magnetism is well explained by current theories. It’s just that so far, no one has been able to explain it to me. Doubtless, some of the problems are at my end, but I wonder if there is any physicist out there who is willing to take this challenge seriously and try to explain how magnetism works in a self consistent way without using jargon – Feynman’s QED book suggests that this is not impossible.
The best explanations I have heard so far relate to the virtual exchange of photons (magnons?), and this is the answer I tried to give on the I’m A Scientist website. But, there is something very odd about these virtual particles, in that they clearly influence other magnets and electrons in nearby wires etc. but they do not show up in other ways (for example as light). And the magnetism will only work if they are exchanged very precisely with one another (in time and space) as if each magnet somehow knows where the other one is! Or perhaps I have misunderstood something – after all I only have O-level Physics, and perhaps it is presumptuous to even hope for an explanation I can understand. Feynman was a true genius, and perhaps I have fallen victim to the spell of his charisma; he made me think I could hope to understand some of this stuff, and I am not giving up yet.