Dec 2, 2022 04:31 AM
(This post was last modified: Dec 2, 2022 04:36 AM by C C.)
https://www.scientificamerican.com/artic...come-from/
EXCERPT: . . . But despite appearances, electrons don’t spin. [...] Yet spin is deeply important. If electrons didn’t seem to spin, your chair would collapse down to a minuscule fraction of its size. You’d collapse too—and that would be the least of your problems.
Without spin, the entire periodic table of elements would come crashing down, and all of chemistry would go with it. In fact, there wouldn’t be any molecules at all. So spin isn’t just one of the best tricks that electrons pull; it’s also one of their most crucial. And like any good magician, electrons haven’t told anyone how the trick is done. But now, a new account of spin may be on the horizon, one which pulls back the curtain and shows how the magic works...
[...] 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. “You’re introduced to it, and you think, ‘Well, that’s strange. They act like they spin but they don’t really spin? Okay. I guess I can learn to work with that.’ But it’s odd.”
Recently, though, Sebens had an idea. “Within quantum mechanics, it seems like the electron is not rotating,” he says. But, he adds, “quantum mechanics is not our best theory of nature. Quantum field theory is a deeper and more accurate theory.”
[...] Quantum field theory handles this phenomenon by describing particles as arising out of fields that pervade all of spacetime, even empty space. These fields allow particles to appear and disappear, all in accordance with both the strict dictates of Einstein’s special relativity and the probabilistic laws of the quantum world.
And it’s these fields, according to Sebens, that may contain the solution to the puzzle of spin. “The electron is ordinarily thought of as a particle,” he says. “But in quantum field theory, for every particle, there’s a way of thinking about it as a field.” In particular, the electron can be thought of as an excitation in a quantum field known as the Dirac field, and this field may be what carries the spin of the electron. “There’s a real rotation of energy and charge in the Dirac field,” Sebens says. If this is where the angular momentum resides, the problem of an electron spinning faster than the speed of light vanishes; the region of the field carrying an electron’s spin is far larger than the purportedly pointlike electron itself. So according to Sebens, in a way, Pauli and Lorentz were half-right: there isn’t a spinning particle. There’s a spinning field, and that field is what gives rise to particles.... (MORE - missing details)
EXCERPT: . . . But despite appearances, electrons don’t spin. [...] Yet spin is deeply important. If electrons didn’t seem to spin, your chair would collapse down to a minuscule fraction of its size. You’d collapse too—and that would be the least of your problems.
Without spin, the entire periodic table of elements would come crashing down, and all of chemistry would go with it. In fact, there wouldn’t be any molecules at all. So spin isn’t just one of the best tricks that electrons pull; it’s also one of their most crucial. And like any good magician, electrons haven’t told anyone how the trick is done. But now, a new account of spin may be on the horizon, one which pulls back the curtain and shows how the magic works...
[...] 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. “You’re introduced to it, and you think, ‘Well, that’s strange. They act like they spin but they don’t really spin? Okay. I guess I can learn to work with that.’ But it’s odd.”
Recently, though, Sebens had an idea. “Within quantum mechanics, it seems like the electron is not rotating,” he says. But, he adds, “quantum mechanics is not our best theory of nature. Quantum field theory is a deeper and more accurate theory.”
[...] Quantum field theory handles this phenomenon by describing particles as arising out of fields that pervade all of spacetime, even empty space. These fields allow particles to appear and disappear, all in accordance with both the strict dictates of Einstein’s special relativity and the probabilistic laws of the quantum world.
And it’s these fields, according to Sebens, that may contain the solution to the puzzle of spin. “The electron is ordinarily thought of as a particle,” he says. “But in quantum field theory, for every particle, there’s a way of thinking about it as a field.” In particular, the electron can be thought of as an excitation in a quantum field known as the Dirac field, and this field may be what carries the spin of the electron. “There’s a real rotation of energy and charge in the Dirac field,” Sebens says. If this is where the angular momentum resides, the problem of an electron spinning faster than the speed of light vanishes; the region of the field carrying an electron’s spin is far larger than the purportedly pointlike electron itself. So according to Sebens, in a way, Pauli and Lorentz were half-right: there isn’t a spinning particle. There’s a spinning field, and that field is what gives rise to particles.... (MORE - missing details)
