Friday, November 25, 2022

Electrons Are Spinning

Scientific American reports:
Quantum Particles Aren’t Spinning. So Where Does Their Spin Come From?

A new proposal seeks to solve the paradox of quantum spin ...

But despite appearances, electrons don’t spin. They can’t spin; proving that it’s impossible for electrons to be spinning is a standard homework problem in any introductory quantum physics course. If electrons actually spun fast enough to account for all of the spinlike behavior they display, their surfaces would be moving much faster than the speed of light (if they even have surfaces at all). Even more surprising is that for nearly a century, this seeming contradiction has just been written off by most physicists as yet another strange feature of the quantum world, nothing to lose sleep over.

No, this is wrong. Electrons do spin. You only get that paradox if you assume that electrons are very tiny spheres or point particles, but quantum mechanics teaches that electron are non-classical entities with wave-like properties.

The article goes on to give the history of quantum spin, and how crucial it is for understanding chemistry and many other things.

But all of these fabulous discoveries, applications, and explanations still leave Goudsmit and Uhlenbeck’s question on the table: what is spin? If electrons must have spin, but can’t be spinning, then where does that angular momentum come from? The standard answer is that this momentum is simply inherent to subatomic particles, and doesn’t correspond to any macroscopic notion of spinning.

Yet this answer is not satisfying to everyone. “I never loved the account of spin that you got in a quantum mechanics class,” says Charles Sebens, a philosopher of physics at the California Institute of Technology.

No, this is silly. The QM textbooks teach that position, momentum, energy, angular momentum, and spin are observables that correspond to the classical variables, but cannot be taken literally about electrons as point particles, as the uncertainty principle prevents such a literal treatment. There is not really any difference between spin and the other variables in this respect.

I previously posted Electrons do spin.

Peter Woit explains:

Despite what Sebens and Carroll claim, it has nothing to do with quantum field theory. The spin phenomenon is already there in the single particle theory, with the free QFT just providing a consistent multi-particle theory. In addition, while relativity and four-dimensional space-time geometry introduce new aspects to the spin phenomenon, it’s already there in the non-relativistic theory with its three-dimensional spatial geometry.
Asking whether electrons really spin is a like asking whether they orbit the nucleus of an atom. A century ago, physicists tried to model an atom as classical electron orbits, and figured out that it doesn't work. You need a quantum model. But it is still correct to say that the electrons orbit the nucleus.


  1. Oh dear dark gods of entropy and anti-chance, why anyone thinks you can have a diagrammatic point carry a force or carry mass and take themselves seriously is beyond the pale. Without actual physical extension, you simply can't do physics, which requires movement and something capable of doing those movements. I'd also ask the dirty question: If your model of electrons aren't spinning, what EXACTLY is it that describes their charge? Magic? Unicorn farts? Statistics? A simple + or - symbol (circa Benjamin Franklin) floating in a platonic void of vacuous incuriousity of what makes the silly things go? Because someone said so once upon a time and you believed them and just stopped asking?

    Atoms are not structured like damn Rutherford Monkeybread with electrons orbiting like cute little Sputniks in various ringed levels, not even remotely. Nor do electrons have magical sticky super glue powers that hold atoms together and hold up one corner of the accounting for the standard model's teetering coffee table. Heuristical accounting is not valid mechanical structure, it's just a black box model that evades structure. Atoms MUST require a great deal of external energy to move and spin at the speeds they do, else they would be very quickly consuming their own mass in some unknown manner to produce the energy to allow them to move as they do.

    Consider asking yourself: what exactly does make the things go? Until you know that piece of the puzzle, the rest is just crusty layered heuristic bullshit and posturing stacked on top of really creaky theory based on dead models.

    Present mainstream physics basically treats atoms like cars that can drive around forever without an internal structure or source of fuel that would make said movement possible...and then flounders around wondering the merits of sticking their heads into a black hole so they can publish something and be cited.

  2. Dear Roger,

    I wish Dr. Peter Woit would let my comments in.

    In that case, I would have, what I believe to be, a good thought to share --- not just with him but also with his readership.

    His is a good post for a blog, but, no, even while pointing out how simple it all *ought* to be, the post just plain *refuses* to be simple enough.

    And that's where my comment would've come in.

    Anyway, every one to his own free choices [so long as they don't do any bodily harm].