- Three Words That Could Overthrow Physics: “What Is Magnetism?”
The standard model still doesn't describe magnets' spooky action at a distance.
"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."
Bizarre, I thought. What exactly does he mean with 'knowing'? Is this a philosophical question? I looked Maddox up on Wikipedia, and learned he is 'best known for his satirical magazine essays'. So then maybe it's a joke, I wondered? Maddox continues that in the further pursuit of the topic he then read the 'Mathematics of Classical and Quantum Physics', from which he likely learned the term 'action at a distance', and that "virtual particles are composed entirely of math and exist solely to fill otherwise embarrassing gaps in physics". He eventually summarizes
"What I have learned, in other words, after 71 days of strenuous research, is that I and my fellow Dummies no longer have a seat, if we ever did, at the dinner table of science. If we’re going to find any satisfaction in this gloomy vale of misery and mystery, we’re going to have to take matters into our own hands and start again, from first principles."I've honestly tried to figure out what he meant to say, but I just can't make sense out of it. You're all welcome to start again, and from first principles. But I think this article sheds a rather odd light on the status of theoretical physics. So here are some comments:
1. Electro and Magnetic
We have experimentally extremely well confirmed theories that allow us to describe electromagnetism to high precision, in the classical as well as in the quantum regime. Maybe that's not satisfactory for everybody. But at least I think the explanation that the electromagnetic interaction is mediated by something called the electromagnetic field is very satisfactory. After all, we are surrounded by electromagnetic waves all the time, and we use them quite efficiently to carry phone calls from here to there, or to maneuver satellites in outer space. To calculate the interaction between two macroscopic objects like a fridge magnet and the fridge, at least I wouldn't use perturbation theory of quantum electrodynamics, but good old Maxwell's equations.
"Electronics for Dummies" maybe isn't exactly the right book to read if you want to understand how electromagnetism works and how to understand the field concept. Since Maddox is concerned with magnets let me point out an often occurring linguistic barrier: Electrodynamics is the theory of the electric and magnetic interaction, as it turns out both are just aspects of the the same field, and parts of the same theory.
To use a well known example, consider two resting electrons. You'd describe their field by the Coulomb interaction without magnetic component. Yet when you move relative to them, you'd assign to them a magnetic field since moving charges cause magnetic fields. This is no disagreement, it just means that under a transformation from one restframe to another the field components transform into each other. It was indeed this feature of Maxwell's equations that lead Einstein to his theory of Special Relativity ("Zur Elektrodynamik bewegter Körper", Annalen der Physik, 17 (1905), p .891–921).
I didn't read "Electronics for Dummies", but browsing the index on Amazon it seems to contain what you'd think, namely what a transistor is and how you outfit your electronic bench. To understand the basics of theoretical physics I would maybe recommend instead
- Evolution of Physics
By Albert Einstein and Leopold Infeld
2. The Standard Model
The interaction between a fridge magnet and the fridge is a macroscopic phenomenon that involves a lot of atomic and condensed matter physics. Ferromagnetism is an interesting emergent feature, and there are probably still aspects that are not fully understood. The Standard Model of particle physics describes the fundamental interactions between elementary particles. Complaining it doesn't describe your fridge magnet is completely inappropriate as said fridge magnet is hardly an elementary particle. You could as well say neuroscience doesn't describe the results of election polls.
See also my earlier posts on Models and Theories and Emergence and Reductionism.
3. Action at a Distance
Quantum mechanics has a spooky 'action at a distance', but of a completely different nature than the force between two magnets. In quantum mechanics there is no field that mediates it (at least nobody has ever measured one). Maybe even more importantly, this is an instantaneous 'action': the wave-function collapses non-locally. Very unappealing. That's why it's spooky (still). This well known problem of quantum mechanics however does not appear in classical electrodynamics, it comes in through the quantum mechanical measurement process.
Maxwell's theory that describes electric and magnetic interaction is local. Interactions between charges are mediated by the fields. The interaction needs to propagate, it doesn't happen instantaneously. The same is true for General Relativity. Yes, Newton called it a great absurdity that "one body may act upon another at a distance through a vacuum without the mediation of anything else, by and through which their action and force may be conveyed from one to another". But this is because in Newtonian gravity interactions were instantaneous. If you'd change the earth's mass, the moon would immediately know about it. It took Einstein to remove this great absurdity, and he taught us that gravity is mediated by spacetime itself. It propagates locally, there is no spooky action on a distance.
To get a grip on Quantum Electrodynamics I'd recommend
- QED: The Strange Theory of Light and Matter
By Richard P. Feynman
4. Virtual Particles
And yes, virtual particles are mathematical constructs that appear within the perturbation series and are handy devices in Feynman diagrams. The use of this mathematical tool however has proved to be correct to high precision. The effects of the presence of these virtual contributions have been measured, the best known examples are probably the Lamb-shift or the Casimir Effect.
It is a general problem which I encountered myself that popular science books use pictures, metaphors or generalized concepts to describe theories, and then the reader gets stuck with possibly inappropriate impressions that wouldn't occur if one had a derivation and thus a possibility to understand the limitations of these verbal explanations. One can e.g. derive the interaction energy between two pointlike sources as being the Fourier transformation of the propagator, the propagator being what describes also the virtual particle exchange in Feynman diagrams. This interaction energy for the photon propagator is just the Coulomb potential as you'd expect. (If the exchange particle is massive, you get a Yukawa potential). How seriously one should take the picture with the virtual particle is a different question though. The interaction between the fridge and the magnet is hardly a scattering process with asymptotically free in- and outgoing states.
I too like to ponder questions like what actually 'is' a particle, much like one can wonder what actually 'is' space-time. However, I admittedly fail to see what the point is of this rambling about "embarrassing gaps in physics" besides expressing the author's confusion about the books he read.
For an introduction into quantum field theory I recommend
(You can download the first chapter which explains very nicely the relations betwen particles, fields, and forces here.)
If you’re going to find "any satisfaction in this gloomy vale of misery and mystery", you’re going to have to take matters into your own hands and read the right books before abandoning the Standard Model.
PS: My husband lets me know he finds my writing very polite, and wants me to refer you to the Dunning-Kruger effect.
TAGS: ELECTRODYNAMICS, PHYSICS, MAGNETISM, VIRTUAL PARTICLES, ACTION AT A DISTANCE, STANDARD MODEL