Electron Spin: Does an Electron Really Spin?
The Historical Assumption About Electron Spin
Electron spin” implies that an electron really spins. Well, does it? Let us go back in time to answer that question. Scientists (e.g., James Clerk Maxwell, Henry Rowland) in the latter part of the 19th century knew that if they physically spun a charged ball, their action would create a magnetic field. Two young scientists (George Uhlenbeck and Samuel Goudsmit) in the first quarter of the 20th century discovered that even if an electron were stationary, it would still have a magnetic dipole moment. Therefore, they assumed that an electron must be spinning, and they named the property “spin.”
One of them (George Uhlenbeck) shared that assumption with a renowned scientist (Hendrik Lorentz). That scientist assumed that an electron was a classical particle, and he calculated that an electron would need to spin faster than the speed of light—a physical impossibility—to produce its measured magnetic dipole moment. So does an electron really spin?
What Electron Spin Actually Means
The answer is no, an electron does not spin. (Neither is it a classical particle.) Therefore, the name “spin” for the property that causes an electron’s magnetic dipole moment is a misnomer. Today when scientists talk about an electron’s spin, they are talking about its spin angular momentum. It is what gives an electron its magnetic dipole moment. An electron does not have to spin physically to have spin angular momentum: It just has it.
An Everyday Analogy for Electron Spin
Think of electric charge. An electron has a negative electric charge even though nothing inside it is doing the charging. Electric charge is an intrinsic (i.e., built-in) property of an electron. Well, so is its spin angular momentum: An electron has spin angular momentum without any literal rotation.
A Historical Label, Not Literal Rotation
An electron does not spin like a tiny ball or top. Today when scientists talk about an electron’s spin, they are talking about its spin angular momentum. “Spin” is simply a historical label for a quantum property that every electron has.
