Do electrons spin?
- kieronconway
- Oct 7, 2025
- 5 min read
Updated: 1 day ago
© 2025 Kieron Conway - All rights reserved.
If you think of an electron as a tiny snooker ball, then of course it spins, right? An electron creates a tiny magnetic field and this can be measured for real. So, if its magnetic field is real - it must spin to create the field, just like spinning neutron stars, only on a much smaller scale!
Of course electrons spin!
Oh No They Don't!
The experiment that proved that an electron has a tiny magnetic field is the Stern-Gerlach experiment (you can read all about it using Google). A beam of electrons fired horizontally into a strong, vertically-aligned magnetic-field, showed something weird. The expected, classical result was that electrons would be deflected up or down and every angle in between, depending on how the tilt of their spin axes were aligned to the vertical field. That's if they really do spin like a tiny snooker ball!
But the electrons came out of the field only deflected UP or DOWN and nothing in between!
So, what's going on?
The best theory that we have to explain electrons (and all fundamental particles) and their behaviour is quantum field theory (QFT), where an electron is an energy excitation in the electron field that pervades all of space. Fields are nothing new: well over a hundred year ago the Victorians recognised that light waves travelled as oscillations in the electromagnetic field that extends throughout all of space.
One of the reasons that QFT is so successful is that it describes all particle and light interactions as interactions between excitations in different fields where energy can be exchanged easily. QFT brings order to what at first sight appears to be chaotic behaviour down at the scale of the atom and below.
Does an Excitation in the Electron Field Spin?
No – not in the everyday sense!
Field excitations do not spin, instead, the term “spin” is used to describe an intrinsic property of a quantum excitation related to the symmetries of space, rather than anything to do with mechanical rotation. It's therefore a somewhat esoteric definition of spin. The point is that the maths used to describe QFT spin looks remarkably like the maths used to describe angular momentum, but it's just a quantum property associated with symmetry rather than something whirling round and round! This similarity in the maths encouraged physicists to borrow the term “spin”, but it's never been about physical rotation.
Two Families of Particles
Quantum field theory groups particles into two families according to their value of spin:
Fermions (like electrons, protons, neutrons, quarks and some atoms) always have half-integer spin values: 1/2, 3/2, 5/2, and so on.
Bosons (like photons, gluons, and some atoms) always have integer spin values: 0, 1, 2, and so on.
For a given particle, the spin magnitude is fixed (for electrons it’s always 1/2). What can change is the projection of that spin along a chosen axis, producing SPIN-UP or SPIN-DOWN orientations.
In composite particles (like nuclei), higher spin states often correspond to excited, unstable configurations, which typically decay into lower-energy states.
Here Comes the Really Odd Bit
If something spins in the normal sense, when it completes a full turn, it ends up looking the same as it did before the start of the spin and this can be said of bosons. But fermions have 1/2 integer spins and they need two full turns to regain their original state!
This strange behaviour lies at the heart of quantum mechanics.
Quantum spin explains why matter is stable
Quantum particles are defined by wave functions. Wave functions are solutions to quantum wave equations (like Schrödinger’s or Dirac’s), which can be used to determine how quantum particles evolve over time. Bosons have perfectly symmetric wave functions and fermions have asymmetric wave functions. The symmetry of the wave functions dictates how particles co-exist in space.
Bosons, with symmetric wave functions (LHS of diagram below) can co-exist, without limitation in the same quantum state. So, you can have huge numbers of bosons all in the same quantum state defined by a single wave function and that's what Bose-Einstein condensates are all about. If a boson's wave function is turned once, it looks the same as it was before the rotation started.
Fermions, with asymmetric wave functions (RHS of diagram below) must all exist in different quantum states. This asymmetric wave function has to be turned twice to regain the same state it had before the spin began. Imagine picking up the asymmetric wave form by its Y axis and turning it once, it looks different. Turn it once more and the original shape is regained.
The shape of the electron's wave function shows that two electrons can co-exist in the same spatial distribution, provided that they have slightly different spin orientations, one SPIN-UP and one SPIN-DOWN, as this constitutes two different quantum states.
This is why electrons in atoms must fill different orbitals or, if they share the same orbital, they must have opposite spin orientations (SPIN-UP and SPIN-DOWN).
Without Pauli Exclusion imposed on electrons and without the two spin orientations, atoms as we know them could not exist.
Wrapping it All Up
Electrons don't spin like tiny snooker balls.
Electrons are considered to be energy excitations in the electron field of space.
Electrons have a measurable, but tiny magnetic field.
The electron's magnetic field can only be orientated in an UP position or a DOWN position in the measurement axis.
Quantum spin is an intrinsic symmetry property, not a physical rotation.
All electrons must exist in different quantum states (Pauli Exclusion).
Two electrons can exist in the same spacial extent (e.g., atomic orbital) as long as one has an UP-SPIN and the other a DOWN-SPIN.
Without Pauli Exclusion and the quantum-spin orientation of electrons, atoms would not exist as we know them.
Final Thought: Atoms as Fermions or Bosons
What about spin and whole atoms?
This depends on the total number of protons, electrons and neutrons (all of which are fermions) that exist in an atom. If the total number is odd, the atom is a fermion; if the total number is even, the atom is a boson.
In a neutrally charged atom, the number of protons is always the same as the number of electrons which yields an even number. So, it's the number of neutrons in an atom that dictates whether an atom is a boson or fermion, although this can be made more complex as there can be spin coupling in a nucleus.
Nevertheless, odd or even neutron populations is a reasonable rule of thumb to determine whether an atoms is a boson or a fermion.
Conclusion
Electrons might not spin in a mechanical sense, but their intrinsic spin property is why the periodic table is the way it is. If this were not the case, the universe would be very different.
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