This week the ever-inquisitive Gary Matthews pointed me to a 2008 article for Discover Magazine by Bruno Maddox, claiming that physicists cannot explain how magnetism works, and that they are in denial about it. I encourage you to read the article. Maddox is wrong—dead wrong—but his argument displays a number of common misconceptions about science. And I’d like to address some of them. The most important misconceptions Maddox displays are that of first cause, of classical intuition, and of distrust of the abstract. Let’s get started.
(DISCLAIMER: The opinions in this article are my own. I will be describing very little real science here… just philosophy.)
The Misconception of First Cause
Early in his article, claims that nobody can explain how a magnet works and that nobody seems to be particularly bothered by this.
For one thing, as far as I can tell, nobody knows how a magnet can move a piece of metal without touching it.
And for another—more astonishing still, perhaps—nobody seems to care.
I want to talk about the notion of “touch” later. But for now let’s focus on the other part of that quote—that nobody seems to care. What Maddox is getting at, I think, is that science can never answer why something happens… at a fundamental level, it can only offer descriptions and make predictions. It can only tell you how something happens.
A Hypothetical Conversation
Let’s imagine, for a moment, a hypothetical conversation between Maddox and a physicist. If he asks about magnets… the physicist will say something like “oh the electromagnetic force is caused by the magnetic field.”
“Okay, so what causes the magnetic field?” Maddox might ask. And to this a physicist might say “Well, the magnetic field is really a relativistic echo of this more fundamental thing, the electromagnetic field tensor. A magnetic field is created by moving charge… but that motion depends on your point of view. The field tensor is invariant.”
Maddox might push further. “What causes that?” And a physicist might tell him that it’s a low-energy limit of the electroweak force.
Maddox, getting really aggravated now, might push again. “But what causes that?” And the physicist, depending on her leanings on quantum gravity, would give him an unworried shrug. “We don’t know. It just is.”
What’s Wrong With Maddox’s Question
Do you see the problem? It’s the same problem as in theology. If you ascribe cause to something, then you must ask what causes the cause. One (very theological) answer is that God is infinite and can get around these petty problems like cause and effect.
But science has a better answer: we don’t know! And moreover, we cannot know! At a fundamental level, science is based on observations of the world around us. We are limited by what those observations can tell us. These observations can tell us a lot. They can tell us what happens—to bars of iron can be made to pull at each other. They can tell us how it happens—the bars attract if they are oriented in a particular way, otherwise they repel. And, with a bit of cleverness, they can give us the tools to make predictions—an electric current will attract an iron bar.
But observations, at some level, will fail to explain something. And that’s perfectly okay. In fact, it’s better than okay. It’s a good thing to know your limits! And this is a fundamental limit. The success of science is built on knowing that whatever Nature does must be the truth, no matter how counter-intuitive.
I believe Maddox knows this. He certainly lampshades it when he comments that
But as far as I can tell—and isn’t the point of science that all its bigger propositions come accompanied by this noble caveat?—[Steven Weinberg] really can’t [explain how magnets work].
But Maddox sees this as a reason to distrust science and it is not. It is science’s greatest strength.
(I don’t mean to imply that science has no explanatory power. It tells us that magnetism in a bar magnet is caused by either atomic spin or electron spin, for example… which is very powerful. But at some point, the chain of causes stops and you can go no further.)
The Misconception of Classical Intuition
Let’s reflect on that for a moment. Whatever Nature does must be truth, no matter how counter-intuitive. This is the second misconception Maddox displays. Maddox finds it unsettling that we cannot explain “how a magnet can move a piece of metal without touching it.”
But… what does it mean to touch? Let’s think about the subatomic realm, the world of quantum mechanics. In the world of atoms and electrons, “touch” is a fuzzy concept. For one thing, there is no such thing as a “particle.” Protons, electrons, neutrons, and even atoms and molecules, are not localized balls, like we’re used to in our world. They’re waves of probability, distributed throughout space. What this means to us in the world of trains and aeroplanes is not totally clear. But it is the nature of Nature. So particles them, aren’t really particles.
For another thing, when we “touch” a table, there’s a lot of empty space between the atoms in our hands and the atoms in the table! What’s really happening is that the atoms in our hands are repelling the atoms in the table… for a variety of reasons, including the electromagnetic force and the Pauli exclusion principle. There’s none of the “touching” Maddox seeks at all! Maddox is disturbed by the idea that we appeal to “spooky action at a distance,” but a more interesting question is are there any forces that aren’t, fundamentally, this sort of spooky action at a distance.
(As a historical note, Einstein described quantum mechanics as “spooky action at a distance” because he was disturbed by the fact that quantum entanglement seemed to violate causality. We know now that it does not violate causality and Einstein was worried for nothing. But the electromagnetic force never bothered Einstein.)
Maddox is falling prey to the fallacy of classical intuition. He believes that because he experiences the world in a particular way, the world must be that particular way. But Nature is not so gentle! We evolved to perceive the world in a way that benefits us evolutionarily… not in the way it really is! Again, the great strength of science as a methodology is that it overcomes this classical intuition and allows us to glimpse the world as it really is. (Or at least, closer to how it really is.)
A Fallacious Distrust of the Abstract
Finally, Maddox says that
When you get right down to it, the mystery of magnets interacting with each other at a distance has been explained in terms of virtual photons, incredibly small and unapologetically imaginary particles interacting with each other at a distance. As far as I can tell, these virtual particles are composed entirely of math and exist solely to fill otherwise embarrassing gaps in physics, such as the attraction and repulsion between magnets.
Well, Maddox is right about one thing. Virtual particles are unapologetically imaginary. This is a complaint that I, and many other scientists, share with Maddox. But this isn’t a problem with the science. It’s a problem with lazy science communication.
As I described above, the notion of a particle is deeply misguiding. A particle is a “human-scale” approximation of the true nature of reality, which is made up fields and waves. Really, force isn’t carried by virtual particles. It’s carried by fields, which interact with each other via waves that travel at speeds no greater than the speed of light. And it just so happens that these waves look like particles to us if we squint. But this doesn’t work all the time. Sometimes the notion of a single particle simply doesn’t make sense.
But, even in the realm of subatomic physics, the idea of a particle is very powerful. It provides intuition and a surprisingly robust computational tool. This is why, historically, high-energy physics has been misleadingly called “particle physics.” (And for those in the know, how the terrible name “second quantization” came to be.) And the notion of a virtual particle, an imaginary particle associated with the excitation of a quantum field, even more powerful.
So… if it makes good predictions…. is a virtual particle really imaginary? Or is it a valid way of interpreting the fundamental nature of reality?
The answer is that, despite my distaste for virtual particles… they’re often exactly as good of a description as waves—better, because they’re easy to work with. It’s true that the description fails sometimes, but so what?
(For experts, I’m discussing the occupation-number formalism of quantum field theory, vs. other formalisms. In particular, the occupation number formalism fails when a vacuum cannot be uniquely defined… a la Unruh effect or curved spacetime.)
This is why Maddox is wrong to distrust virtual particles. Maddox’s distrust seems to stem from the fact that virtual particles are purely mathematical and that there is a more general way to describe quantum fields. But he should not distrust this mathematical abstraction. It is the tool we use to make predictions.
Moreover, it’s the only tool we have. Scientists are not explaining why phenomena occur. Really what scientists do is build Lego models of the universe, simulacra that behave like the universe and allow us to make predictions. Equations and mathematical abstraction are the Lego blocks of our models. And the particle picture of quantum field theory is a very good model indeed.
Maddox’s post is quite old… seven years old by now. I am not the first scientist to refute him. In particular, I’d like to recommend this blog post by Sabine Hossenfelder, which is, as usual, excellent.